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Cheap LiFePO4 BMS?


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55 minutes ago, nicknorman said:

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.

I would have been tempted to leave it for a full hour if it wasn't for the puff of smoke. The alternator is absolutely filthy inside, diesel soot from an old exhaust leak, which probably doesn't help with the cooling and might just be the source of the smoke. Interesting point that it might run hotter at idle. I assumed the opposite so I put it into idle to test it.

 

Yes agreed, I think I may get 2 spares and try surgery on the one at my leisure. With a spare I'm alright with pushing this one a bit and seeing what happens.

 

30 minutes ago, MoominPapa said:

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.

I wish I knew. It doesn't really have any identifying marks or labels on it. I don't actually know that it is a 70A, in fact now that I've seen it produce around 85A I'm not sure that it could be.

 

Is A127 the name of the form factor? I would like to buy a spare but I'm not sure how to tell what I need nor whether it's right- or left-hand.

 

There are some 75A A127 alternators for sale dirt cheap (50 quid) on eBay - https://www.ebay.co.uk/itm/LUCAS-A127-TYPE-ALTERNATOR-RIGHT-HAND-RH-12V-75AMP/324193342893

 

I've posted some pics of it before on this forum so here they are again. The belt drives the pulley clockwise if you face the pulley (looking astern). The writing on the regulator reads

 

07-032
YY13454 14V

 

There's also an embossed number on the casing which is 4135.

 

 

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4 hours ago, nicknorman said:

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

It's not bad. I never look at SoC but just follow Ahr in/out (from which SoC is derived) and voltage. I find that the Ahrs out is pretty accurate for a few weeks and we usually do a longer cruise at least every 2 weeks so it syncs to around 90% SoC ie the Ahrs are set to zero when the B2Bs go to float. The actual battery state is then what the BMV is showing in Ahrs out minus around 40Ahrs extra. In reality I just look at the voltage and can easily compute in my head how full we are or how low it is (if I look at the current chage or draw first!).

I do a full charge every 3 months when we get into a marina.

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12 minutes ago, Dr Bob said:

It's not bad. I never look at SoC but just follow Ahr in/out (from which SoC is derived) and voltage. I find that the Ahrs out is pretty accurate for a few weeks and we usually do a longer cruise at least every 2 weeks so it syncs to around 90% SoC ie the Ahrs are set to zero when the B2Bs go to float. The actual battery state is then what the BMV is showing in Ahrs out minus around 40Ahrs extra. In reality I just look at the voltage and can easily compute in my head how full we are or how low it is (if I look at the current chage or draw first!).

I do a full charge every 3 months when we get into a marina.

I just look at the volts, I always have the fan on the composting toilet running so its normally very stable. The great thing about these batteries is how fast they recover from a hard drain on them. 

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The pictures are not an A 127.  They may be an A127i  which has an internal fan and more output than a plain vanilla A127.

 

With luck Sir Nibble will be around and tell us what it is.

 

The left hand right hand bit is explained on the ecus direct website.

N

 

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16 minutes ago, Col_T said:

Apologies for another basic question. 

 

Volt drop can occur in both +veg and -ve cables. Presumable current will be the same in both cables, regardless of size and any volt drop?

Yes, provided there is not also a negative path through the metal of the hull, the engine and the alternator frame.  In that event slightly less current will flow in the negative cable than the positive one.

Not enough to be worth worrying about though.

N

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53 minutes ago, Col_T said:

Apologies for another basic question. 

 

Volt drop can occur in both +veg and -ve cables. Presumable current will be the same in both cables, regardless of size and any volt drop?

Yes. Current is preserved around a circuit. Kirchov’s first law.

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35 minutes ago, BEngo said:

Yes, provided there is not also a negative path through the metal of the hull, the engine and the alternator frame.  In that event slightly less current will flow in the negative cable than the positive one.

Not enough to be worth worrying about though.

N

The current sharing between any alternative hull return paths and the intended one will of course depend on the relative resistances. With the hull having a pretty large effective CSA even though it is steel not copper, then I suggest it could be quite a big current, which is why the hull should only be connected to negative at one point, which is probably the engine.

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Just to round this off, I have found a combination of cable length and thickness that gives a consistent output of 50-52A and an alternator temperature of 60 degrees on the casing, 80 degrees if I shine through the grilles. I can also disconnect this cable if I'm about to go on a long cruise or if the ambient temperature is higher than normal (it's around 11 degrees at the moment). I'm calling this good enough for the next couple of months, in the meantime I'm going to try to buy 2 replacement alternators, one to try my hand at field current surgery and one for a spare in case I burn out my current one. I'll contact Beta Marine to find out what specs of alternator I need for my old Beta 38. 

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Finally got around to sitting in front of my computer and writing some code for the home made BMS which I’ve attached to the CALB cells. Well, just one set of cells ie 200Ah which is plenty for the moment. Firstly, pleased to see that the voltages of the 4 cells are within 2mV of each other as supplied from China.

 

Secondly, wow the internal resistance is so low! Adding my power supply to charge at 5A (which ok is not much in the context of 200Ah) only increases the cell voltage by about 3mV. Amazing! I will have to be careful to ensure clean contacts etc for the interconnects, otherwise there is a good chance that the interconnect resistance will be more than the cell resistance!

 

And also wrote the code to operate the Tyco BDS-A battery disconnect relay, which as we know needs a pulse of around 75mS to operate. It takes about 3A and having a longer pulse or worse, somehow leaving the 12v applied, will no doubt melt the coil in short order. So it’s important to have a robust pulse generator.
 

I know that MP created some dedicated hardware for it but for me it was just 7 lines of code. And 4 of them were to turn off low and high priority interrupts (to ensure the processor wasn’t distracted doing something else) and turn them on again afterwards. Then just 3 lines of code, 1) turn on the MOSFET, 2) wait 75 mS, 3) turn off the MOSFET. Easy Peasy!

 

Does demonstrate the advantages of using relatively low tech like a PIC or Arduino whereby being in total control of the processor, vs say a Raspberry Pi with a huge linux operating system whereby you don’t really know what the processor is doing half the time.

Edited by nicknorman
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43 minutes ago, nicknorman said:

Does demonstrate the advantages of using relatively low tech like a PIC or Arduino whereby being in total control of the processor, vs say a Raspberry Pi with a huge linux operating system whereby you don’t really know what the processor is doing half the time.

I dont know what the processor on my rasp pi is doing any of the time.😄

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34 minutes ago, blackrose said:

To what extent is partial charging relevant to LiFePO4 batteries as it supposedly is for mobile phone batteries?

 

https://www.androidauthority.com/maximize-battery-life-882395/

 

Just wondered and I can't possibly read 67 pages of posts to see if it's already on here...

Mine never charge to 100%, they wander between 13.1 and 13.9 volts. I would think that they are 10 years old now with 3 years ish in my ownership. I don't expect to replace them ever as I am 62, and don't work them hard at all

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42 minutes ago, blackrose said:

To what extent is partial charging relevant to LiFePO4 batteries as it supposedly is for mobile phone batteries?

 

https://www.androidauthority.com/maximize-battery-life-882395/

 

Just wondered and I can't possibly read 67 pages of posts to see if it's already on here...

 

LiFePO4 doesn't mind partial charging. In fact you would do better to not fully charge. None of us fully charge our batteries, except briefly getting to 100% to top balance - and then immediately discharging them.

 

The important things are to not overcharge, not overdischarge, and not charge batteries near freezing.

 

The different lithium technologies are very different so you can't really extrapolate from mobile phone batteries which don't use LiFePO4. But I note that the article you linked also mentions that the "memory effect" or recommendation to fully charge is no longer relevant to modern mobile phone batteries.

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I've bought the bits (Raspberry Pi 2 and 3x hellishly expensive VE Direct to USB cables) to set up a Pi Venus system to monitor my Victron equipment.

 

I do want to monitor the individual cells as well, and my plan up to now is to use my Arduino and some cloud function to aggregate all the data into one place.

 

However to avoid having to run both the pi and the Arduino, and also because I feel much more confident with a pi than an arduino, I'm thinking of connecting 4 voltage meters to the pi as well to monitor the cells. Here's one article that shows how to connect analogue voltage meters to the pi. I still have to look into whether or not the pi will be able to run both the Venus stuff and a job that would log the other voltages (every second or whatever).

 

@Dr Bob I know that you are running the venus software on a pi, I wondered if you know off hand whether it would be feasible to use the pi for monitoring additional things simultaneously?

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2 minutes ago, ivan&alice said:

I've bought the bits (Raspberry Pi 2 and 3x hellishly expensive VE Direct to USB cables) to set up a Pi Venus system to monitor my Victron equipment.

 

I do want to monitor the individual cells as well, and my plan up to now is to use my Arduino and some cloud function to aggregate all the data into one place.

 

However to avoid having to run both the pi and the Arduino, and also because I feel much more confident with a pi than an arduino, I'm thinking of connecting 4 voltage meters to the pi as well to monitor the cells. Here's one article that shows how to connect analogue voltage meters to the pi. I still have to look into whether or not the pi will be able to run both the Venus stuff and a job that would log the other voltages (every second or whatever).

 

@Dr Bob I know that you are running the venus software on a pi, I wondered if you know off hand whether it would be feasible to use the pi for monitoring additional things simultaneously?

Is this a boat you have or are you on the ISS?

 

Just asking.

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9 hours ago, ivan&alice said:

I've bought the bits (Raspberry Pi 2 and 3x hellishly expensive VE Direct to USB cables) to set up a Pi Venus system to monitor my Victron equipment.

 

I do want to monitor the individual cells as well, and my plan up to now is to use my Arduino and some cloud function to aggregate all the data into one place.

 

However to avoid having to run both the pi and the Arduino, and also because I feel much more confident with a pi than an arduino, I'm thinking of connecting 4 voltage meters to the pi as well to monitor the cells. Here's one article that shows how to connect analogue voltage meters to the pi. I still have to look into whether or not the pi will be able to run both the Venus stuff and a job that would log the other voltages (every second or whatever).

 

@Dr Bob I know that you are running the venus software on a pi, I wondered if you know off hand whether it would be feasible to use the pi for monitoring additional things simultaneously?

I don't know enough about Pi's. I would also have liked to record cell voltages but couldn't see how to do it. The Venus software is just plug and play and sends all the data from the BMV to the Victron server automatically. Not a clue how you can 'break into' the programming to ask it to monitor more. I am useless at programming Pi's so would struggle just to connect to the cell voltages on the rasparian system!

Let me know if you find a way to do it. It would be interesting, but with 2 years experience now, it is not needed.I use the Pi access to the BMV as my main way of monitoring the power, especially when we leave the boat.

Edited by Dr Bob
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On 10/09/2020 at 07:58, Murflynn said:

that is 60% useful capacity ...........................   so there is not really a huge advantage in that respect over LA's that are used between 50% and 100%.

 

apart from the weight issue, I am again beginning to lose confidence in the alleged benefits of Lifepo4.

If I still had the boat I would be seriously looking at LiFePo4 batteries. Actual to be more specific I would be looking far deeper into the charge control. Lead acids also have voltage constraints and the charging system AND user training in the main have conspired to produce a simple system. Try charging any lead acid at 15 volts for months on end, specially if you do not top them up or regularly discharge to 11 volts and see how long they last and how reliable they are.

 

Once you  get the maximum and minimum  states of charge control sorted (so just like lead acids in resect of control limits but not the same values) you are left with cell balancing and as Dr B and Peterboat have confirmed its not really an issue if you set very conservative maximum and minimum charge values. Even if you must wring the maximum capacity out of lithiums, as said, there are automatic cell balancing solutions available. to a degree I would suggest this "extra" protection is analogous to the gizmos that are added to LA charging systems to allegedly get them fully charged fatser.

 

The major advantage as I see it is that lithiums will be very happy to take the maximum charge you can throw at them as long as the charge control systems allows them to. Suddenly your 90 amp alternator becomes a true 90 amp alternator rather than perhaps a 20 to 30 amp alternator taken over the  charging to full period for lead acids. This is arguably no advantage while you are on a shoreline but its a distinct advantage when out cruising or  when relying upon solar. The disadvantage as I see it is simply the cost and the danger that taking the cheaper route with second hand batteries MIGHT leave you with very expensive duff cells.

 

Again, as I understand it at present , the majority of today's solar controllers might not be a very good match for lithiums in that they may drop to a float voltage too early and thus minimise the advantage lithiums have for fast charging but I think that is solvable with expensive controllers.

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3 minutes ago, Tony Brooks said:

If I still had the boat I would be seriously looking at LiFePo4 batteries. Actual to be more specific I would be looking far deeper into the charge control. Lead acids also have voltage constraints and the charging system AND user training in the main have conspired to produce a simple system. Try charging any lead acid at 15 volts for months on end, specially if you do not top them up or regularly discharge to 11 volts and see how long they last and how reliable they are.

 

Once you  get the maximum and minimum  states of charge control sorted (so just like lead acids in resect of control limits but not the same values) you are left with cell balancing and as Dr B and Peterboat have confirmed its not really an issue if you set very conservative maximum and minimum charge values. Even if you must wring the maximum capacity out of lithiums, as said, there are automatic cell balancing solutions available. to a degree I would suggest this "extra" protection is analogous to the gizmos that are added to LA charging systems to allegedly get them fully charged fatser.

 

The major advantage as I see it is that lithiums will be very happy to take the maximum charge you can throw at them as long as the charge control systems allows them to. Suddenly your 90 amp alternator becomes a true 90 amp alternator rather than perhaps a 20 to 30 amp alternator taken over the  charging to full period for lead acids. This is arguably no advantage while you are on a shoreline but its a distinct advantage when out cruising or  when relying upon solar. The disadvantage as I see it is simply the cost and the danger that taking the cheaper route with second hand batteries MIGHT leave you with very expensive duff cells.

 

Again, as I understand it at present , the majority of today's solar controllers might not be a very good match for lithiums in that they may drop to a float voltage too early and thus minimise the advantage lithiums have for fast charging but I think that is solvable with expensive controllers.

You are right Tony. Y mate a Tony has just bought 3 valence batteries he has a Stirling advanced alternator to batteries charger so its been set to 14 volts bulk 13 .8 float I would think it will reduce daily engine running to 1 hour! A big reduction in the 3 hours currently 

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21 minutes ago, peterboat said:

You are right Tony. Y mate a Tony has just bought 3 valence batteries he has a Stirling advanced alternator to batteries charger so its been set to 14 volts bulk 13 .8 float I would think it will reduce daily engine running to 1 hour! A big reduction in the 3 hours currently 

And I don't see how 3 hours  charging LAs will get them to anything like fully charges so your mate is courting premature loss of capacity by sulphation. That's another advantage for lithiums because they don't but I suspect there is a process that gradually reduces their remaining life and/or capacity but not anything like sulphation and the low cyclic life of LAs.

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I started playing with one set of my CALB 200Ah cells (because experimenting with all 600Ah was going to take too long off the boat with only a 20A charger!). I top balanced them which didn’t require much, seemed pretty good as shipped. It is amazing how they just sit at 3.2 or 3.3something volts and then suddenly it’s 3.5 then 3.6 even though I was only charging at 5A with bench power supply by then. So all balanced at 3.6v, less than 1Ah to be moved around, and now I’m discharging via a BMV 712 to check capacity. Slow going as I can only drain 8A, but so far I’ve got to 60% and the cell voltages are within 3mV of each other. Yes that’s 0.003v. Which is pretty amazing. Also the difference between open circuit voltage and draining at 8A is about 3mV per cell. They really are a different beast!

 

I can sort of see now that routine cell balancing probably won’t be necessary even if the SoC is taken quite high.

Edited by nicknorman
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8 minutes ago, nicknorman said:

I started playing with one set of my CALB 200Ah cells (because experimenting with all 600Ah was going to take too long off the boat with only a 20A charger!). I top balanced them which didn’t require much, seemed pretty good as shipped. It is amazing how they just sit at 3.2 or 3.3something volts and then suddenly it’s 3.5 then 3.6 even though I was only charging at 5A with bench power supply by then. So all balanced at 3.6v, less than 1Ah to be moved around, and now I’m discharging via a BMV 712 to check capacity. Slow going as I can only drain 8A, but so far I’ve got to 60% and the cell voltages are within 3mV of each other. Yes that’s 0.003v. Which is pretty amazing. Also the difference between open circuit voltage and draining at 8A is about 3mV per cell. They really are a different beast!

 

 

Now you can see why I like them so much! The voltage drop under load is very consistent and once you get used to them you can pretty easily 'guess' the rested voltage at your normal discharge rates.

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52 minutes ago, nicknorman said:

I started playing with one set of my CALB 200Ah cells (because experimenting with all 600Ah was going to take too long off the boat with only a 20A charger!). I top balanced them which didn’t require much, seemed pretty good as shipped. It is amazing how they just sit at 3.2 or 3.3something volts and then suddenly it’s 3.5 then 3.6 even though I was only charging at 5A with bench power supply by then. So all balanced at 3.6v, less than 1Ah to be moved around, and now I’m discharging via a BMV 712 to check capacity. Slow going as I can only drain 8A, but so far I’ve got to 60% and the cell voltages are within 3mV of each other. Yes that’s 0.003v. Which is pretty amazing. Also the difference between open circuit voltage and draining at 8A is about 3mV per cell. They really are a different beast!

 

I can sort of see now that routine cell balancing probably won’t be necessary even if the SoC is taken quite high.

Same as Bob says they really are a revelation I have not had the puter on mine in way over a year, I have checked the van ones which work harder than the boat but again well balanced 

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