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Cheap LiFePO4 BMS?


jetzi

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1 hour ago, ivan&alice said:

Hang on, something doesn't make sense.

 

Why does the alternator output 14.4V to a LA battery but 13.4V to a Li battery?

 

Isn't it simply that Li can take more current than the alternator is giving so it dragged the voltage down, whereas with LA the battery is limiting the current and so the alternator is regulating itself down to 14.4V? In fact, doesn't anything less than 14.4V mean that the alternator is working flat-out?

 

Doesn't this mean then that there must be something else in my system - a bit of thin wire, or component - that is somehow preventing the alternator from running at full strength? Either that or - as Nick suggested - there's something wrong with my alternator?

Maybe its the difference in sizes of the 2 battery banks?

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4 hours ago, TheBiscuits said:

 

That's an excellent argument for an A2B controller or a controllable regulator for Lead Acid batteries, never mind LiFePOs

Yes. Had you asked me a year ago I would have said such controllers were of little use, but I now think differently! Of course whether it is good for LA batteries or alternators to ram current in at 14.4v is another matter...

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3 hours ago, ivan&alice said:

 In fact, doesn't anything less than 14.4V mean that the alternator is working flat-out?

No, the basic analogue regulators fitted to these sorts of alternators have very soft regulation. If you remember I said that the field current was proportional to the difference between nominal regulated voltage and actual voltage and in order to get maximum field current /maximum output, the voltage needs to be pulled well below the regulated voltage. I’m not sure by exactly what and of course it depends on the specific alternator, but I think we are talking about something near 1v.

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6 hours ago, ivan&alice said:

The voltage sits at around 14.4V / 14.5V if it's only connected to my LA. If it's connected to my Li's the voltage sits at around 13.4 - 13.5, slowly rising and if it ever got to 13.8V I shut it off (manually right now - because I don't have an alternator controller - but so far I haven't taken it above 13.7V when charging via alternator - if any one cell got above 3.6V then my emergency BMS should kick in, which implies a battery voltage of 14.4V but in reality is closer to 14.0 since my cells aren't that well balanced).

 

Note that these voltages are taken at the load side of the system, but there isn't that much in it compared to the voltages at the alternator.

So the regulated voltage is 14.4, and at 13.4v it is only putting put 30A. Something wrong there I suspect. I know you say the actual alternator voltage isn’t that much higher, but you haven’t quantified that! I think you should check the voltage at the batteries and the voltage at the alternator when the latter is putting in the 30A. Don’t forget that voltage can be dropped both in the positive and negative wires - people tend to forget about the possibility of high resistance in the negative. So you should put your meter probes on the battery positive and negative, and then on the alternator positive and negative (or casing). If the alternator really is only producing 30A at 13.4v and decent rpm then it is either a very small alternator, or something is wrong with it.

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40 minutes ago, nicknorman said:

No, the basic analogue regulators fitted to these sorts of alternators have very soft regulation. If you remember I said that the field current was proportional to the difference between nominal regulated voltage and actual voltage and in order to get maximum field current /maximum output, the voltage needs to be pulled well below the regulated voltage.

I'm not thinking of the regulation but just the fact that a circuit under load will drop the voltage down. Why does a LA battery happily have its voltage raised all the way up to the 14.4V regulation but the Li battery does not? My understanding of electricity is that it's because in the case of the LA, the current is being limited by the battery (the load). In the case of the Li, the current is being limited by the alternator's capacity (the source).

 

So kind of like if you pinch the end of a hosepipe, you'll get less water but it's because the load is not accepting it - the pressure will remain high inside the hosepipe. Whereas, if you turn the tap down, then you'll get less water but it's because the source is not pushing as hard - the pressure in the hosepipe is less. I don't know if that's a fair analogy. But this is the explanation that makes sense to me on why 14.4V on the LA, and then 13.4V as soon as I connect the Li.

 

41 minutes ago, nicknorman said:

I know you say the actual alternator voltage isn’t that much higher, but you haven’t quantified that! I think you should check the voltage at the batteries and the voltage at the alternator when the latter is putting in the 30A

You're right and I will double check this tomorrow, but I recall it being roughly the same. I might be remembering wrong.

 

42 minutes ago, nicknorman said:

Don’t forget that voltage can be dropped both in the positive and negative wires - people tend to forget about the possibility of high resistance in the negative.

Now this is an explanation I can get behind. The negative wires flow through to the engine block and I haven't changed these out. I think they're probably very thin - though they must be sufficient for the starter motor current. I think the bracket/bolts holding the alternator to the engine are also painted and not very conductive? I will try wiring a thick cable directly from the alternator casing to the negative of my Lis tomorrow and see what it does.

 

Thanks kindly for the pointers!

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21 hours ago, ivan&alice said:

Do you mean to say that you just leave it on all the time? Or that you manually turn it on before charging (say, half an hour before a cruise or sunrise?)

We just turn them on before charging with the alternator. Even when below zero C, as a domestic supply they perform quite adequately whilst discharging.

From memory the solar controller is configured not to charge below zero C.

A few years back, the recommended charge cut off temperature was zero C but that has been revised upward to 5 C more recently.

If I remember correctly the winter of 2017/2018 dropped into sub zero temperatures for several weeks. At that time we didn't have any heaters, insulated enclosures or even temperature sensors. I'm sure we would have charged with the alternator whilst below zero C at some point.

By contrast, last winter there was barely a frost so the heaters didn't get much (if any) use.

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9 hours ago, ivan&alice said:

I'm not thinking of the regulation but just the fact that a circuit under load will drop the voltage down. Why does a LA battery happily have its voltage raised all the way up to the 14.4V regulation but the Li battery does not? My understanding of electricity is that it's because in the case of the LA, the current is being limited by the battery (the load). In the case of the Li, the current is being limited by the alternator's capacity (the source).

Sounds right to me.

You should be getting more than 30A - not sure what your alternator rating is. As with most things in the automotive world, the specifications are usually overstated. We have a 100A iskra (though some sources rate it as 90A) It only gives this current when stone cold, soon dropping down to about 80A as it warms up. This current is RPM dependant, so it is possible to compensate for the drop-off, to some extent, by increasing the revs.

Failed diodes can also cause a drop off in available current. As most alternators usually have at least 3 phases, with a rectifier consisting of at least 6 diodes, a loss of a single diode does not necessarily cause a complete failure. Photo shows iskra diode pack where a pair of diodes presumably went short circuit for a while, caused some melting of the plastic, before blowing open circuit. In this case the current reduced to around 60-80A, and was more RPM dependant. A curious configuration of diodes in this rectifier - it has 8 ;)

20171028_142921_iskra.jpg

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3 hours ago, Craig Shelley said:

Sounds right to me.

You should be getting more than 30A - not sure what your alternator rating is. As with most things in the automotive world, the specifications are usually overstated. We have a 100A iskra (though some sources rate it as 90A) It only gives this current when stone cold, soon dropping down to about 80A as it warms up. This current is RPM dependant, so it is possible to compensate for the drop-off, to some extent, by increasing the revs.

Failed diodes can also cause a drop off in available current. As most alternators usually have at least 3 phases, with a rectifier consisting of at least 6 diodes, a loss of a single diode does not necessarily cause a complete failure. Photo shows iskra diode pack where a pair of diodes presumably went short circuit for a while, caused some melting of the plastic, before blowing open circuit. In this case the current reduced to around 60-80A, and was more RPM dependant. A curious configuration of diodes in this rectifier - it has 8 ;)

 

I think it must have 9, maybe one vaporised! Our Iskra certainly does. 6 big fat ones to bridge rectify the 3 phase and 3 small ones for the field current. The bigger Iskra ones like ours have zener diodes, which means they go into reverse conduction with a voltage transient such as load disconnect, thus limiting the value of the spike and hopefully protecting the alternator. So in theory I should be able to disconnect the batteries from the alternator whilst it is charging, but I don’t plan to test that!

Edited by nicknorman
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The voltage at the alternator is 14.4V, and the voltage from alternator body to Li pos is abour 14.3. So I believe Nick was right and the low amps are almost certainly due to volt drop and almost certainly due to the negative cable being too thin.

 

I am debating whether to upgrade it though, because I think this thin negative cable is the only thing saving my alternator from overheating. I do have 70mm cable so I think I should make up a cable and see what the effect is, watching the alternator temperature and current. I anticipate that I'll see 50A+ and a very hot alternator, but I believe the voltage at the battery should remain around 13.7V while charging because more than that would imply that the battery is full.

 

Will test this setup (and my understanding of electrickery) out tomorrow.

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In another thread on 12V batteries, Tony B asked about a graph I had produced - which involved a typical days cruise charging Lithiums. I thought it useful to pop it on this thread for any peeps who are confused by the various voltages quoted in charging Li's. The graph is attached below.

 

This was from back in August when we were still getting to grips with charging on the new boat. The graph gives quite a bit of info re charging of Lithium batteries.

The initial peak at 9.20 and the 'ragged decay' for the first 10 mins was the engine being turned on and then me faffing around with the BtoBs. Cant exactly remember what was going on! I think one of the BtB's (we are using 2 *60A ones in parallel) was only set at half power hence the 60A current (should have been 80A ish). By 9.30 I had sorted it and the current went up to 85A. The batteries were about 190Ahrs down on full capacity from the other graphs in the system. We motored for around 2 and a bit hours but just after 10.00 I noticed the current had dropped to 40A so checked the BtoB's and noticed one had gone into float - hence the 40A current. More faffing reseting the BtoB to a better custom programme and off it went again back up to the 'full' charge amps delivered by the BtoBs. At 11.45 we finished our cruise and turned off the engine. The voltage had only just got to 13.7V and this is around 75% SoC at the 60A charging rate. We had put in around 150Ahrs during the cruise in the 2 and a bit hours. Batteries very happy sitting at 75%. This is typical of our battery usage now with us being around -200Ahrs overnight and getting back to -50Ahrs at the end of each day. The batteries seldom get over 80% full as we tend to just do 2-3 hours a day.

 

Now the point of this post. Li's are very different in their variation of voltage during charge. For LAs at 70% charge, you turn the engine on and you will get nearly 14.0V out of the alternator which will then increase to say 14.2V and stay there forever as the regulator goes out of the bulk phase. Li's however show a much lower voltage at the battery terminals and in my case around the 13.3V point on intial charge (estimate SoC around 50%). This voltage then increases with time and then in this case we stopped charging at 13.7V as we finished the days cruise. One big thing to notice though is the dip at 10.00 when the BtoB needed reseting. Notice the voltage dropped by 0.1V when the current dropped from 80A to 40A. This is typical of what we see now that we are able to control the current used to charge the Li's. On our old boat we only really had the ablilty to charge at 30-40A so never understood the effect on charge current on voltage observed. With this new boat, we can control the charging current in approx 20A increments up from 20A to around 100A. Now, 0.1V in voltage on the battery terminals might not seem a lot but at the 13.6V level, it represents around 60-80Ahrs (ie the current put back in the batteries whilst waiting for the voltage to rise from 13.61 to 13.71 has been measured at 60-80Ahrs on a number of occasions).

It is therefore critical if you are trying to gauge how full you are by voltage that you understand the effect of current. This has made it a lot more complicated for me trying to operate 2 BtoB's in parallel as if they are both on and working nicely, I get 80-90A out and I can monitor the voltage nicely and set them to go to float at my prescribed voltage which will be near my target 80% SoC. However, if one of the BtoB's decides to go to float 'cause its having a bad day, the charge current drops to half, the voltage drops by 0.1V and the voltage target means a higher state of charge. MP has always said that termination has to be done on voltage and current.

What does it mean in practice? Usually the BtoBs play ball and go to float around the 80% but I do have the auto isolation set at 13.9V which will stop overcharging.

Everyone needs to look at their own voltages to understand the termination limits. I'm not convinced 2 BtoB's are such a good idea. Nick's alternator regulator is a better idea if you are willing to do surgery on your alternator. The AtoB I had on my old boat was a far simpler.

 

 

Screen Shot 2020-08-11 at 13.19.48.png

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Good post Bob, I do my charging by solar and what I have noticed that even at at big amps70 + the voltage only goes up by .1- .2 volts if I turn off charging it almost instantly drops totally different to LAs, it's the same with my drive bank which is much larger bank it has to be the lack of resistance in comparison to LAs that are causing Ivan's low voltage readings?

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We're starting to get some interesting data from the new monitoring system. There are a few interruptions on these graphs where we disconnected cables to tidy up the installation, paint the boxes etc...

 

The temperature graph shows some of the batteries leading/lagging, i guess due to differences in the physical locations of the enclosures.

Interestingly, the effect of internal heating due to charging can be seen quite clearly. Engine was run on the 4th and 6th Nov. My understanding is that the linear(ish) portion of the heating is caused by resistive/chemical heating of/within the battery (temperature probe is attached to the battery terminals). The gradual ramp-up thereafter, I believe, is cause by the higher ambient temperature in the engine compartment. The gradient change on the temperature graph when the charging was switched on/off on the 6th Nov is quite noticeable.

1225568202_Screenshotfrom2020-11-0810-38-58.png.c324a7afe66cca38b451ee20b978f06e.png

 

It gets even more interesting to see what the individual cell voltages are doing. The graph "Cell Balance - Battery A" shows that during discharge, cells A3 and A4 have a slightly higher voltage than A1 and A2, but intriguingly the roles reverse when the batteries are being charged. I can only guess that this is because cell A1, and to a lesser extent A2, have a higher internal resistance than A3 and A4. Packs B and C exhibit similar variation but with different cells appearing to be more dominant. These traces agree with the spot measurements I have carried out manually over the past few years. Note: the voltage ripple is caused by the fridge compressor cutting in/out.

1387521137_Screenshotfrom2020-11-0810-40-16.png.722ee80b2cebaba3de754ce351bf4ef2.png

 

There's still more work to do on the graphing/dashboard side of things and the current shunts still need to be wired up. I'm hoping to eventually have it controlling stuff rather than just gathering data.

Over the next week or so the data might begin to look a little cleaner with fewer interruptions. I'm sure, as always, there'll be something new to learn.

Screenshot from 2020-11-08 10-37-59.png

Screenshot from 2020-11-08 10-37-33.png

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47 minutes ago, Craig Shelley said:

 

It gets even more interesting to see what the individual cell voltages are doing. The graph "Cell Balance - Battery A" shows that during discharge, cells A3 and A4 have a slightly higher voltage than A1 and A2, but intriguingly the roles reverse when the batteries are being charged. I can only guess that this is because cell A1, and to a lesser extent A2, have a higher internal resistance than A3 and A4. Packs B and C exhibit similar variation but with different cells appearing to be more dominant. These traces agree with the spot measurements I have carried out manually over the past few years. Note: the voltage ripple is caused by the fridge compressor cutting in/out.

1387521137_Screenshotfrom2020-11-0810-40-16.png.722ee80b2cebaba3de754ce351bf4ef2.png

 

There's still more work to do on the graphing/dashboard side of things and the current shunts still need to be wired up. I'm hoping to eventually have it controlling stuff rather than just gathering data.

Over the next week or so the data might begin to look a little cleaner with fewer interruptions. I'm sure, as always, there'll be something new to learn.

 

It is interesting to see specific data. Very useful to post. Keep em coming.

I find that there is significant heating on charging. The graphs I posted in the previous post didnt have a temperature line but the temp went up from 23 °C to 30°C on that charge cycle (its far less in winter!).

The cell voltage variation is very similar to ours with. You get a bigger delta when charging. Where you in the voltage knee when you got your 40mV delta on the 6th?

 

I'm not sure I like your 12 cell voltage dials on the dashboard! I would prefer the graph with cell voltages so you can see the variation with time. That is the missing bit from my data storage, I cant record the cell voltage data on the victron system....only the full bank voltage.

I dont think you said why you have 12 cells rather than only 3? Its far less complicated with 3!

 

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Attached a 70mm cable from the negative of my Li battery (via my BMV712 shunt) directly to the casing of the alternator. Gave my engine some throttle and started her up.

 

The current climbed quickly from 50A to a maximum of 81.8A (!) and it was running around 3 minutes. So - clearly - the negative connection was the limiting factor with my curent. Nick - I owe you beer.
 

I measured the alternator temperature with my infrared gun, and I could feel the heat almost immediately. The most I saw was 85 degrees, but it's difficult to get a reading on the internals and so it might have been much higher. When I saw a puff of smoke out of the alternator I turned the engine off and terminated the experiment! The alternator is pretty dirty inside, so I think the smoke was probably from some old soot or rubber dust. After disconnecting the thick cable it went back to charging at 30A.

 

So - at least I know that the alternator is putting out decent current if I'll let it, but I'm not really sure what to do now. I can't let it put out 80A because it will melt in ten minutes flat.

 

Perhaps I just need to use an intermediate-sized cable. Or insert a resistor in series? Or perhaps I should create a cooling system, and make sure I have a spare alternator to hand?

 

What we all really need - actually - is the ability to programme our alternators to put out less current. I probably need to stop looking for a shortcut.

 

 

MaximumCurrent.jpg.959acfb3c3ba640b3c43c52a7d39568e.jpg

1 hour ago, Craig Shelley said:

The graph "Cell Balance - Battery A" shows that during discharge, cells A3 and A4 have a slightly higher voltage than A1 and A2, but intriguingly the roles reverse when the batteries are being charged. I can only guess that this is because cell A1, and to a lesser extent A2, have a higher internal resistance than A3 and A4.

Wouldn't this be the case if Cells A3 and A4 have slightly lower capacity? That is, they will reach full first and reach empty first?

 

 

1 hour ago, Dr Bob said:

I'm not sure I like your 12 cell voltage dials on the dashboard! I would prefer the graph with cell voltages so you can see the variation with time. That is the missing bit from my data storage, I cant record the cell voltage data on the victron system....only the full bank voltage.

I dont think you said why you have 12 cells rather than only 3? Its far less complicated with 3!

Logging of the individual cell voltages is IMO the most important bit of data to be logged - unfortunately the whole bank doesn't really give you any useful information except at the very top and only if you are sure that your batteries are perfectly balanced. I have started baby steps towards creating an Arduino based monitor for my cells which I want to log every say second or whatever. Right now I'm not even logging the data from my Victron kit though apparently that can be done with Pi running a Victron Venus OS.

 

I think you mean 4 cells not 3 since LiFePO needs 4 cells to produce a 12ish volt battery? I believe Craig said that he uses 4s3p (i.e. 12 cells of 1 unit / 3 batteries rather than 3p4s i.e. 4 cells of 3 units / 1 battery) for two reasons - one pragmatic, because of how the wiring worked out, and the other because he wanted to be able to monitor the health of each individual physical cell unit. That was something I'd considered originally as well for the same reason but I was convinced against it because a) of the complexity and b) because having 3 cell units (4 in my case) in parallel to make a cell is more robust and stronger cell units will protect the weaker ones. I am still not sure if that reasoning was solid, I do love that Craig can identify individual physical cell units that may get sick and need replacing.

 

Eventually what I'd love to get is a CSV file dumped out every week (say) that logs individual cell voltages, cell temperature, alternator temperature, alternator RPM, current, and whatever else I can think of. But unfortunately it's a luxury rather low down on my list of boat jobs to do.

Edited by ivan&alice
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28 minutes ago, ivan&alice said:

I think you mean 4 cells not 3 since LiFePO needs 4 cells to produce a 12ish volt battery?

Yes, a typo. I meant 4 cells.

3p4s is far less complex and the 3 in parallel will all have the same voltage so less to go wrong in balancing. I guess it is possible that one individual cell of a 3p could go bad but that would soon show up as the capacity of that big cell (3p) would go down so the cell voltage deltas would show up big time at high and low SoCs. My cell 1 (comprising 3 individual 160Ahr cells) is the first to get into the high voltage knee and also into the bottom voltage knee so the 3 paralleled cells must have a lower capacity than the other seriesed cells but it doesnt bother me a bit as the delta cell Vs are never more than 50mV in the range of charge I use ie  20% to 100%. I think I would notice quickly if this changed due to an individual cell going wrong. What I find interesting is that in the 31 months I have had my system wired up, the voltage, current, charge and discharge values have not changed at all and I can still plot my daily data directly onto the graphs I produced back in early 2018 and they fit the lines perfectly. Can you imagine doing that with lead acids? The thundersky cells are very stable!

Having 12 cells vs 4 would require 12 fuses rather than 4 and loads more wiring!!!!!!!!

 

46 minutes ago, ivan&alice said:

Logging of the individual cell voltages is IMO the most important bit of data to be logged - unfortunately the whole bank doesn't really give you any useful information except at the very top and only if you are sure that your batteries are perfectly balanced.

I am not really sure I agree. In my first 6 months I logged a lot of data - all bank voltage and current via the victron portal (on the Rasp Pi) and the cell voltage on paper (on charging).

Now, 2 1/2 years on, there is no need. Ok I have the victron portal data to hand, but the only use for the data is to post on here!!! I monitor the delta cell voltages and if anything 'different' shows up then I get the paper log out and refer to that.......but it never does. The total bank voltage and current is the only thing you really need to look at. For the first  6months I was really interested in following the data but now I just dont bother. A quick glance at the meters once a day and that is it.

It was similar with my Tesla. For the first two months, I followed the power usage on TeslaFi (you have to pay for that!) every day (few hours). I never look at it now. It just works.

Monitoring data on Lithiums is important in the first few months to understand what you have but then once tuned....it is just plug and play. Very very little to do!

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13 minutes ago, Dr Bob said:

I'm not sure I like your 12 cell voltage dials on the dashboard! I would prefer the graph with cell voltages so you can see the variation with time. That is the missing bit from my data storage, I cant record the cell voltage data on the victron system....only the full bank voltage.

I dont think you said why you have 12 cells rather than only 3? Its far less complicated with 3!

LOL the back bedroom already looks like a time machine from the '80s. The main interface to this is currently via smartphone/tablet, it's still undecided if we'll ever install a fixed display. The representation is a little experimental to see what works best. My father prefers to interpret an analogue dial over reading digital display. He finds the existing 7seg readouts need a lot more mental effort to understand.

 

As for the 12 rather than 3 (I'm assuming you mean 4). Some of the decision is a little historical in how the battery packs have been assembled and installed. We've ended up inheriting some of the layout limitations from the original lead acid batteries. With hindsight we would have been far better off to have had a fresh start, and possibly install them into a more convenient location, but at the time we didn't have the tools or knowledge of how to make up the cable assemblies. We were very fortunate that Jeremy Bloomfield had offered to assemble a cable set with Anderson connectors to enable us to retrofit it into the existing connection points. Also at the time, it was my father's first year onboard, and the boat hadn't exactly been problem free.

 

I've deliberated over adding the remaining links to the battery pack as only have 4 cells to monitor is far simpler, but it would now be a bit messy as there would need to three cables interlinking between the enclosures. Then there'd be the question of what fuses to install and to devise a means of disconnection to enable enclosures to be removed. The other thing which crossed my mind was regarding the fault tolerance of the pack. In the unlikely scenario that one cell began to break down, and I must stress that I don't know what the common failure modes of these cells are so this is speculative, but if there were some form of "non-catastrophic" membrane failure of one of the cells, I theorised that there might be a better chance of not damaging the other cells if the inter-connections weren't fitted. i.e. no cells directly in parallel with each other. Also with the cells separated, it might give some insight into how each cell is performing individually, and how they are contributing to the overall pack. There's still a lot we don't know about how these batteries perform in this application, and I certainly don't mind sharing what we learn as the project evolves.

 

So the reason is partly historical, partly theoretical and partly educational.

SevernSegPhoto.jpg

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1 hour ago, Dr Bob said:

In my first 6 months I logged a lot of data - all bank voltage and current via the victron portal (on the Rasp Pi) and the cell voltage on paper (on charging).

Now, 2 1/2 years on, there is no need. Ok I have the victron portal data to hand, but the only use for the data is to post on here!!! I monitor the delta cell voltages and if anything 'different' shows up then I get the paper log out and refer to that.......but it never does. The total bank voltage and current is the only thing you really need to look at. For the first  6months I was really interested in following the data but now I just dont bother. A quick glance at the meters once a day and that is it.

It was similar with my Tesla. For the first two months, I followed the power usage on TeslaFi (you have to pay for that!) every day (few hours). I never look at it now. It just works.

Monitoring data on Lithiums is important in the first few months to understand what you have but then once tuned....it is just plug and play. Very very little to do!

 

My system is still maintaining a complete log on five minute time points, and that information was really useful during the development phase. The log doesn't just include battery parameters, but also the state of the BMS. You can look and see when charge termination happened, and what conditions caused the BMS to do it, and the internal state of the SoC estimator algorithm. I consider the development stage more or less complete now, and like Dr Bob I rarely look at the logs except to do some sanity checking once on a while. The percentage state of charge display in the engine room is all that's needed day-to-day.

 

MP.

 

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3 hours ago, ivan&alice said:

Attached a 70mm cable from the negative of my Li battery (via my BMV712 shunt) directly to the casing of the alternator. Gave my engine some throttle and started her up.

 

The current climbed quickly from 50A to a maximum of 81.8A (!) and it was running around 3 minutes. So - clearly - the negative connection was the limiting factor with my curent. Nick - I owe you beer.
 

I measured the alternator temperature with my infrared gun, and I could feel the heat almost immediately. The most I saw was 85 degrees, but it's difficult to get a reading on the internals and so it might have been much higher. When I saw a puff of smoke out of the alternator I turned the engine off and terminated the experiment! The alternator is pretty dirty inside, so I think the smoke was probably from some old soot or rubber dust. After disconnecting the thick cable it went back to charging at 30A.

 

So - at least I know that the alternator is putting out decent current if I'll let it, but I'm not really sure what to do now. I can't let it put out 80A because it will melt in ten minutes flat.

 

Perhaps I just need to use an intermediate-sized cable. Or insert a resistor in series? Or perhaps I should create a cooling system, and make sure I have a spare alternator to hand?

 

What we all really need - actually - is the ability to programme our alternators to put out less current. I probably need to stop looking for a shortcut.

 

Jolly good. I think an “intermediate sized” negative cable would be the simplest answer - having a bit of resistance in the circuit, but not too much!

 

Although I have never tried it I think an alternator could easily be modified to reduce the maximum output by reducing the maximum field current. In the case of our Iskra the field resistance is about 3.5 ohms, meaning that when the regulator is hard on (14v across it to give maximum field current) it is taking a bit over 4 amps. Adding say a 1.8 ohm resistor into the field circuit would reduce the maximum possible field current to about 2.6A which would reduce the maximum output to around 2/3rds. Of course it would have to be a chunky resistor as it would dissipate over 12 watts.

 

In my case the field current limit can be set to 2A maximum by software, (so no extra heat dissipation)  thus reducing the output to around 85A (175A alternator) and keeping it nice and cool. This of course being the right way to do it!?
 

Oh and edited to add that somewhere you are dropping perhaps a volt at 30A in the negative circuit, that is 30 watts so something must be getting hot!

Edited by nicknorman
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2 hours ago, Dr Bob said:

Yes, a typo. I meant 4 cells.

3p4s is far less complex and the 3 in parallel will all have the same voltage so less to go wrong in balancing. I guess it is possible that one individual cell of a 3p could go bad but that would soon show up as the capacity of that big cell (3p) would go down so the cell voltage deltas would show up big time at high and low SoCs. My cell 1 (comprising 3 individual 160Ahr cells) is the first to get into the high voltage knee and also into the bottom voltage knee so the 3 paralleled cells must have a lower capacity than the other seriesed cells but it doesnt bother me a bit as the delta cell Vs are never more than 50mV in the range of charge I use ie  20% to 100%. I think I would notice quickly if this changed due to an individual cell going wrong. What I find interesting is that in the 31 months I have had my system wired up, the voltage, current, charge and discharge values have not changed at all and I can still plot my daily data directly onto the graphs I produced back in early 2018 and they fit the lines perfectly. Can you imagine doing that with lead acids? The thundersky cells are very stable!

Having 12 cells vs 4 would require 12 fuses rather than 4 and loads more wiring!!!!!!!!

 

I am not really sure I agree. In my first 6 months I logged a lot of data - all bank voltage and current via the victron portal (on the Rasp Pi) and the cell voltage on paper (on charging).

Now, 2 1/2 years on, there is no need. Ok I have the victron portal data to hand, but the only use for the data is to post on here!!! I monitor the delta cell voltages and if anything 'different' shows up then I get the paper log out and refer to that.......but it never does. The total bank voltage and current is the only thing you really need to look at. For the first  6months I was really interested in following the data but now I just dont bother. A quick glance at the meters once a day and that is it.

It was similar with my Tesla. For the first two months, I followed the power usage on TeslaFi (you have to pay for that!) every day (few hours). I never look at it now. It just works.

Monitoring data on Lithiums is important in the first few months to understand what you have but then once tuned....it is just plug and play. Very very little to do!

Exactly the same as myself at first puter out and plugged in and then I realised what was the point? they were always ok so I couldnt be bothered anymore. When I fitted the batteries to the truck I checked it a couple of times as they were working way harder than on the boat same thing always ok so I gave up

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2 hours ago, Dr Bob said:

Yes, a typo. I meant 4 cells.

3p4s is far less complex and the 3 in parallel will all have the same voltage so less to go wrong in balancing. I guess it is possible that one individual cell of a 3p could go bad but that would soon show up as the capacity of that big cell (3p) would go down so the cell voltage deltas would show up big time at high and low SoCs. My cell 1 (comprising 3 individual 160Ahr cells) is the first to get into the high voltage knee and also into the bottom voltage knee so the 3 paralleled cells must have a lower capacity than the other seriesed cells but it doesnt bother me a bit as the delta cell Vs are never more than 50mV in the range of charge I use ie  20% to 100%. I think I would notice quickly if this changed due to an individual cell going wrong. What I find interesting is that in the 31 months I have had my system wired up, the voltage, current, charge and discharge values have not changed at all and I can still plot my daily data directly onto the graphs I produced back in early 2018 and they fit the lines perfectly. Can you imagine doing that with lead acids? The thundersky cells are very stable!

Having 12 cells vs 4 would require 12 fuses rather than 4 and loads more wiring!!!!!!!!

 

I am not really sure I agree. In my first 6 months I logged a lot of data - all bank voltage and current via the victron portal (on the Rasp Pi) and the cell voltage on paper (on charging).

Now, 2 1/2 years on, there is no need. Ok I have the victron portal data to hand, but the only use for the data is to post on here!!! I monitor the delta cell voltages and if anything 'different' shows up then I get the paper log out and refer to that.......but it never does. The total bank voltage and current is the only thing you really need to look at. For the first  6months I was really interested in following the data but now I just dont bother. A quick glance at the meters once a day and that is it.

It was similar with my Tesla. For the first two months, I followed the power usage on TeslaFi (you have to pay for that!) every day (few hours). I never look at it now. It just works.

Monitoring data on Lithiums is important in the first few months to understand what you have but then once tuned....it is just plug and play. Very very little to do!

Do you find that the BMV stays reasonably in SoC sync during the periods when you don’t charge to 100%?

Edited by nicknorman
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1 hour ago, nicknorman said:

Jolly good. I think an “intermediate sized” negative cable would be the simplest answer - having a bit of resistance in the circuit, but not too much!

 

Although I have never tried it I think an alternator could easily be modified to reduce the maximum output by reducing the maximum field current. In the case of our Iskra the field resistance is about 3.5 ohms, meaning that when the regulator is hard on (14v across it to give maximum field current) it is taking a bit over 4 amps. Adding say a 1.8 ohm resistor into the field circuit would reduce the maximum possible field current to about 2.6A which would reduce the maximum output to around 2/3rds. Of course it would have to be a chunky resistor as it would dissipate over 12 watts.

 

In my case the field current limit can be set to 2A maximum by software, (so no extra heat dissipation)  thus reducing the output to around 85A (175A alternator) and keeping it nice and cool. This of course being the right way to do it!?
 

Oh and edited to add that somewhere you are dropping perhaps a volt at 30A in the negative circuit, that is 30 watts so something must be getting hot!

Added in a length of 25mm cable (so now, this original negative cable plus this extra 25mm one) and ran the engine for about 15mins now.

 

It seemed to bring the current down to 50A at idle, which sounds about ideal! but the outside casing of the alternator got up to 85 degrees and I managed to measure about 110 degrees through the grille which seems worryingly hot. Again, I turned it off aftrer 15 or so mins of running when I noticed faint smoke and a faint burning smell. Also with throttle the alternator was producing 60-65A, so while cruising I'd probably want to disconnect this cable and slow charge.

 

I think the next step is probably to try some fans and ducting to cool the alternator, if I can output 50A consistently I will be more than chuffed with that.

 

What I will also do is try to buy a spare alternator. I'm much more inclined to experiment in the knowledge that I have a backup. If the alternator dies on me out here in the middle of nowhere and in winter with no solar, that will be rather an emergency.

 

And yes the 25mm cable became only just noticeably warm. I'm not sure which of the original cabling was getting warm but somewhere something is, you're right.

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3 minutes ago, ivan&alice said:

Added in a length of 25mm cable (so now, this original negative cable plus this extra 25mm one) and ran the engine for about 15mins now.

 

It seemed to bring the current down to 50A at idle, which sounds about ideal! but the outside casing of the alternator got up to 85 degrees and I managed to measure about 110 degrees through the grille which seems worryingly hot. Again, I turned it off aftrer 15 or so mins of running when I noticed faint smoke and a faint burning smell. Also with throttle the alternator was producing 60-65A, so while cruising I'd probably want to disconnect this cable and slow charge.

 

I think the next step is probably to try some fans and ducting to cool the alternator, if I can output 50A consistently I will be more than chuffed with that.

 

What I will also do is try to buy a spare alternator. I'm much more inclined to experiment in the knowledge that I have a backup. If the alternator dies on me out here in the middle of nowhere and in winter with no solar, that will be rather an emergency.

 

And yes the 25mm cable became only just noticeably warm. I'm not sure which of the original cabling was getting warm but somewhere something is, you're right.

bilge fans are very cheap Ivan, Bob fitted one to his last boat, I have 2 on my boat one for the motor and one for the speed controller they eep both items cooler

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24 minutes ago, ivan&alice said:

Added in a length of 25mm cable (so now, this original negative cable plus this extra 25mm one) and ran the engine for about 15mins now.

 

It seemed to bring the current down to 50A at idle, which sounds about ideal! but the outside casing of the alternator got up to 85 degrees and I managed to measure about 110 degrees through the grille which seems worryingly hot. Again, I turned it off aftrer 15 or so mins of running when I noticed faint smoke and a faint burning smell. Also with throttle the alternator was producing 60-65A, so while cruising I'd probably want to disconnect this cable and slow charge.

 

I think the next step is probably to try some fans and ducting to cool the alternator, if I can output 50A consistently I will be more than chuffed with that.

 

What I will also do is try to buy a spare alternator. I'm much more inclined to experiment in the knowledge that I have a backup. If the alternator dies on me out here in the middle of nowhere and in winter with no solar, that will be rather an emergency.

 

And yes the 25mm cable became only just noticeably warm. I'm not sure which of the original cabling was getting warm but somewhere something is, you're right.

I think your 85 and 110 degrees are probably OK. Alternators do run very hot. I’ve set my temperature limit to 90C, but if you look at the spec sheet for my alternator it says the maximum ambient temperature is 110C. That is AMBIENT temperature, not the temperature of the alternator, which presumably could be a lot more!

 

Remember that the engine rpm relates to alternator fan rpm which relates to the cooling airflow. Running the engine at idle is going to result in maximum field current, thus maximum heat generated by that, and minimum airflow. I wouldn’t be surprised if the alternator ran cooler at cruising rpm and 65A, than it would at idle and 50A.

 

Obviously, having a spare alternator is a good idea if there is only one on the engine.

Edited by nicknorman
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20 minutes ago, ivan&alice said:

Added in a length of 25mm cable (so now, this original negative cable plus this extra 25mm one) and ran the engine for about 15mins now.

 

It seemed to bring the current down to 50A at idle, which sounds about ideal! but the outside casing of the alternator got up to 85 degrees and I managed to measure about 110 degrees through the grille which seems worryingly hot. Again, I turned it off aftrer 15 or so mins of running when I noticed faint smoke and a faint burning smell. Also with throttle the alternator was producing 60-65A, so while cruising I'd probably want to disconnect this cable and slow charge.

 

I think the next step is probably to try some fans and ducting to cool the alternator, if I can output 50A consistently I will be more than chuffed with that.

 

What I will also do is try to buy a spare alternator. I'm much more inclined to experiment in the knowledge that I have a backup. If the alternator dies on me out here in the middle of nowhere and in winter with no solar, that will be rather an emergency.

 

And yes the 25mm cable became only just noticeably warm. I'm not sure which of the original cabling was getting warm but somewhere something is, you're right.

What is your alternator? I have no problems running my 70A A127 flat out for hours (which produces around 60A). That is in a large well ventilated engine room, not under deck boards, but you experience seems to be smoke after a short time, rather then from high ambient temps.

 

MP.

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