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Cheap LiFePO4 BMS?


jetzi

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1 hour ago, MoominPapa said:

On a completed system, I might agree, but on mine, as I was doing software development as I went along, it's been quite useful. The other reason for doing using it is the failsafe is powered direct from the Li batteries, and thus remains powered when the microcontroller is powered off. A simple switch in the microcontroller power line thus becomes a reliable way to remotely isolate the batteries: turn off the controller and 2 seconds later a minimal piece of hardware opens the contactor next to the batteries under the bed.

The datasheet implies that there is magnetic blowout, and the specs for large-current opening are only valid in one direction. If you can decipher from the datasheet which direction it is, I'd be interested, it wasn't clear to me. As this application needs to break normally modest currents in both directions, I didn't worry.

 

MP.

 

If you need to break high two-way currents would not the simple solution be to have two relays in series, back-to-back in opposite directions with the operating coils in parallel?  That way one blowout will always be the right way round.  Not cost free and another two connectikns for volt drop. Failure modes might be interesting, but for a fallback system how many levels of failure does the system need to cope with?

 

N

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5 minutes ago, MoominPapa said:

<Consults BMS code>

 

I have two low voltage cutoffs. The first is the per-cell one, which is the last-ditch. Less than 2.9 volts on any cell for more than 5 seconds and it triggers,

 

The second is the "your battery is discharged and is you don't stop, it will get cut-off" alarm. The voltage on that is higher, because it's mainly meant to warn that the voltage has dropped enough that significant discharge of the parallel LA is happening. That trips is the battery voltage drops below 12.52 - (I/128) for more than three minutes.

 

I can't claim the factors and delays  were arrived at by careful experiment and theorising, they are numbers which seemed sensible after staring at read-outs and seem to work, so are a reasonable starting point. 

 

TL;DR for a 480Ah bank, reduce the threshold by about .75v for every 100A of discharge.

 

MP.

 

Yes I had intended to have a buzzer / aural alarm for “approaching disconnect” to give some reaction time before an actual disconnect.

Thanks, so if 480AH gives 0.75v per 100A (this presumably is the battery voltage reduction, not the cell voltage reduction) then that gives a r of about 7.5 mOhm, or capacity /64,000. 1/4 that per cell.

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1 hour ago, nicknorman said:

Right next question, if there is to be a low voltage disconnect I think it needs to take into account battery discharge current.

16 minutes ago, MoominPapa said:

 

 

I have two low voltage cutoffs. The first is the per-cell one, which is the last-ditch. Less than 2.9 volts on any cell for more than 5 seconds and it triggers,

 

 

Nick,

remember that if your bank is top balanced which is likely, there will be more of an inbalance at the bottom so if the cells are not well matched this could be a significant inbalance. Under normal operation this is fine and not a problem. Its only an issue when your SoC drops and you get one cell to the bottom knee ahead of the rest. So as MP says, you need a cell level disconnect. Mine is set at 2.8V (but that is what the BMM8 sets it to). Not my choice.

Edited by Dr Bob
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Just now, BEngo said:

If you need to break high two-way currents would not the simple solution be to have two relays in series, back-to-back in opposite directions with the operating coils in parallel?  That way one blowout will always be the right way round.  Not cost free and another two connectikns for volt drop. Failure modes might be interesting, but for a fallback system how many levels of failure does the system need to cope with?

 

N

I think bearing in mind the relay only operates following some other failure, or when irresponsibly discharging the batteries to “flat”, it should hardly ever, if ever, operate in anger. And if it does operate it will be unlikely to be at high current (provided battery internal resistance is taken into account). So I think the accumulation of some damage caused during a very few activations outside the spec, is unlikely to be a problem in reality.

1 minute ago, Dr Bob said:

Nick,

remember that if your bank is top balanced which is likely, there will be more of an inbalance at the bottom so if the cells are not well matched this could be a significant inbalance. Under normal operation this is fine and not a problem. Its only an issue was your SoC drops and you get one cell to the bottom knee ahead of the rest. So as MP says, you need a cell level disconnect. Mine is set at 2.8V (but that is what the BMM8 sets it to. Not my choice.

Definitely. This will be top and bottom disconnects at cell level.

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21 hours ago, Dr Bob said:

I will post details of the tyco relay tomorrow unless someone has the details to hand.

 

For them happy with 100A domestic draw, never mind the £70 Tycho relay, here is a bistable latching relay switching 100A for just a tenner:

 

https://www.ev-power.eu/Battery-Management/DC-Power-Latching-Relay-100A-Coil-12V.html?cur=1&listtype=search&searchparam=relay

 

 

And a LOAD of other interesting lithium stuff on that site. 

 

 

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3 hours ago, nicknorman said:

Ok thanks. Datasheet bottom right of first page has a + and - annotation, so A is - and B is +

 

I must say with RS selling this at £60 including vat, zero power consumption in either state,  it seems a no-brainer to use it. Has adequate current capability for me ie 260A at 25C. And it should in theory never need to operate!

 

Except...

 

Right next question, if there is to be a low voltage disconnect I think it needs to take into account battery discharge current. I know that Li has much lower internal resistance than LA but at say 200A discharge on a 400AH battery there must be a fair bit of voltage droop. Obviously one doesn’t want the low voltage protection to trip the batteries just because I put the 2kw electric kettle on with 40% SoC remaining. So could it be expected that there is a fairly consistent voltage drop for a given high current as a proportion of total capacity. Ie an effective internal resistance that is a function of battery capacity that could be modelled in, so that the low voltage cutoff would be x volts + (I x r) where I and r are the instantaneous discharge current and notional battery internal resistance? Does r vary a lot with either temperature or SoC?

 

So many questions!

Nick on a simpler voltage based system like mine, if my washer/dishwasher/electric kettle goes on it will knock down the meter from say 13.3 volts to 13.1 volts, as soon as the demand goes it will go back up to 13.2 volts. This was when I had 4 x 138 ah batteries,  now I have 6 it will recover back to 13.3 volts. It doesn't seem to matter how discharged they are it point 2 of a volt down,  and then back up, they really can hand out amps without the associated voltage drop

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1 hour ago, peterboat said:

Nick on a simpler voltage based system like mine, if my washer/dishwasher/electric kettle goes on it will knock down the meter from say 13.3 volts to 13.1 volts, as soon as the demand goes it will go back up to 13.2 volts. This was when I had 4 x 138 ah batteries,  now I have 6 it will recover back to 13.3 volts. It doesn't seem to matter how discharged they are it point 2 of a volt down,  and then back up, they really can hand out amps without the associated voltage drop

Ok thanks. We are probably into territory where it is the interconnects resistance that is as significant as the actual cell voltage drop, so of course it will depend on where exactly the voltage is measured.

2 hours ago, Mike the Boilerman said:

 

For them happy with 100A domestic draw, never mind the £70 Tycho relay, here is a bistable latching relay switching 100A for just a tenner:

 

https://www.ev-power.eu/Battery-Management/DC-Power-Latching-Relay-100A-Coil-12V.html?cur=1&listtype=search&searchparam=relay

 

 

And a LOAD of other interesting lithium stuff on that site. 

 

 

Of course if you have a proper boat, the alternator is way more than 100A!

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Anyone considering building their own BMS should look at devices like the TI BQ79606A:

 

http://www.ti.com/product/BQ79606A-Q1

 

Accurate voltage and temperature measurement for multiple cells (6 per chip, stackable), includes 150mA load-balancing MOSFETs. Cost is around £5.

 

Plenty of other similar devices from companies like Intersil, all targeted at the huge BEV market -- which means boats get to use them "for free" ?

Edited by IanD
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1 hour ago, IanD said:

Anyone considering building their own BMS should look at devices like the TI BQ79606A:

 

http://www.ti.com/product/BQ79606A-Q1

 

Accurate voltage and temperature measurement for multiple cells (6 per chip, stackable), includes 150mA load-balancing MOSFETs. Cost is around £5.

Definitely worth a look - quite similar to the AD chip I mentioned earlier, but newer. However it isn’t stocked by RS or Farnell yet, I can’t immediately find a retailer selling just the chip (as opposed to the evaluation board). But maybe by the time I get around to it, it will be readily available.

 

Its a pity they both only do 6 cells - anyone with a 24v system would need to stack, which adds significant complexity.

Edited by nicknorman
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1 hour ago, nicknorman said:

Definitely worth a look - quite similar to the AD chip I mentioned earlier, but newer. However it isn’t stocked by RS or Farnell yet, I can’t immediately find a retailer selling just the chip (as opposed to the evaluation board). But maybe by the time I get around to it, it will be readily available.

 

Its a pity they both only do 6 cells - anyone with a 24v system would need to stack, which adds significant complexity.

There are others which do up to 12 cells in one chip, try Intersil.

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On 17/11/2019 at 16:50, Dr Bob said:

See response above on shutting off the charger. Yes you do then need to think about how you isolate your Li's from the LAs and I am not sure what the optimum is as I have not thought it through. (Acute brain drop occurs if you try and think too much!) Maybe Richard can explain his proposed system? -it sounds like worth trying but there is a lot of detail to iron out.

Collected my batteries today, but I'm flying by the seat of my pants here, so just have an idea in my head that I hope will work.

 

In principle, I have an alternator that will put out about 35A, so if I set my charger to draw no more than 30A from the inverter, the alternator should be able to keep up with the inverter, and the LAs shouldn't be depleted to any degree. Bear in mind, I don't do much cruising, and charge mostly with a genny via the Sterling charger, so charging by alternator is not a big requirement for me. It may be be that I never use this facility, preferring to charge the LAs with the alternator.r

 

In isolating the Li's from the LA's.... I plan to have them completely separate, with a surface mounted battery isolator type switch enabling me to choose which supplies the domestic services at any one time. I am looking at a "1-2-both-off" type switch, but would prefer a "change over" switch which has "1-2-off", and no "both", options. The changeover switches I have found seem to have limits of 20A or so, which might be enough, but I think I prefer something with a capacity of 100A, (not sure why?).

 

When you talk about isolating the LI's from the LA's, surely they must always be isolated as the voltages of separate banks will not be the same, such that there would be a flow from one to the other  - I'm not sure if this matters, or is desirable, or not?

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8 hours ago, Richard10002 said:

Collected my batteries today, but I'm flying by the seat of my pants here, so just have an idea in my head that I hope will work.

 

In principle, I have an alternator that will put out about 35A, so if I set my charger to draw no more than 30A from the inverter, the alternator should be able to keep up with the inverter, and the LAs shouldn't be depleted to any degree. Bear in mind, I don't do much cruising, and charge mostly with a genny via the Sterling charger, so charging by alternator is not a big requirement for me. It may be be that I never use this facility, preferring to charge the LAs with the alternator.r

 

In isolating the Li's from the LA's.... I plan to have them completely separate, with a surface mounted battery isolator type switch enabling me to choose which supplies the domestic services at any one time. I am looking at a "1-2-both-off" type switch, but would prefer a "change over" switch which has "1-2-off", and no "both", options. The changeover switches I have found seem to have limits of 20A or so, which might be enough, but I think I prefer something with a capacity of 100A, (not sure why?).

 

When you talk about isolating the LI's from the LA's, surely they must always be isolated as the voltages of separate banks will not be the same, such that there would be a flow from one to the other  - I'm not sure if this matters, or is desirable, or not?

Im confused by what your proposing but is it: separate LA and Li banks. LA charged from alternator, inverter fed from LA batteries, used to run a charger to charge the Li. If so, sounds fairly odd, rather inefficient and means you can’t run the inverter from the Li. But I suppose it does solve the problem of connecting an alternator directly to the Li.

 

Anyway, having LA and Li batteries connected in parallel does work. This is what several members on here do. If the LA batteries are fully charged they can be held up at say 13.6v by the Li, without taking any significant current. The Li batteries will supply power demands from the boat until they get quite low, at which point yes maybe the LAs will start to deliver current too - maybe around 12.8v or so.

Edited by nicknorman
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12 hours ago, Richard10002 said:

Collected my batteries today, but I'm flying by the seat of my pants here, so just have an idea in my head that I hope will work.

 

In principle, I have an alternator that will put out about 35A, so if I set my charger to draw no more than 30A from the inverter, the alternator should be able to keep up with the inverter, and the LAs shouldn't be depleted to any degree. Bear in mind, I don't do much cruising, and charge mostly with a genny via the Sterling charger, so charging by alternator is not a big requirement for me. It may be be that I never use this facility, preferring to charge the LAs with the alternator.r

 

In isolating the Li's from the LA's.... I plan to have them completely separate, with a surface mounted battery isolator type switch enabling me to choose which supplies the domestic services at any one time. I am looking at a "1-2-both-off" type switch, but would prefer a "change over" switch which has "1-2-off", and no "both", options. The changeover switches I have found seem to have limits of 20A or so, which might be enough, but I think I prefer something with a capacity of 100A, (not sure why?).

 

When you talk about isolating the LI's from the LA's, surely they must always be isolated as the voltages of separate banks will not be the same, such that there would be a flow from one to the other  - I'm not sure if this matters, or is desirable, or not?

It does complicate things with your alternator/inverter/charger/Li charging.

If I was doing it, I would try to get it so the Li's were paralleled with the LA's and connected together for normal use ie discharge and charging via the genny to charger to circuit. So in normal use, the charger can back off when the Li's get full....unlikely in winter.....and the Li's always above 12.8V so the LA's never discharge. So in the circuit you need a shunt on the -ve cable from the Li's (to measure A, Ahr and voltage in the Li's) and on the +ve from the Li's you need a fuse and then your auto disconnect switch. What switch are you using? The BEP or the Tyco. I have also added a belt and braces approach and put a manual battery isolation switch on the LA side of my BEP switch.

Now the issue comes if you want to use the alternator. In the above config, you could run it but you might not have enough control over the alternator output ie too much current..or being able to terminate the charge if the Li's get full.....again unlikely in winter. It would be worth having this config available to try as in winter you will only run your engine a bit and never likely to get full or overstress the alternator as the ambient is cold. You can 'learn' the system doing this. If you go on a long cruise then just isolate the Li's after an hour or two. You may find this works fine for the next 3-4 months and then you can think of improving it. Maybe an alternator option will pop up in that time.

Now, you could do the above with a slight mod to allow the alternator/inverter/charger/Li charging thing. Disconnect the charger 12V+ wire from where it connects into the current LA system and reconect to the terminal on the manual disconnect switch on the Li side. The charger is therefore feeding in between the manual switch and the auto switch. If you therefore wanted to charge this way rather than direct from the alternator, you just isolate the manual switch but your boat services will be drawing from the LA's only.....but your change over switch is going to have the same issue (I think) in isolating the Li's from the domestics.

If you then want to charge just the LA's to fill them back up, you reconnect the LAs via the manual switch and trigger the auto disconnect to isolat the Li.

Watch how discharged the LAs get in this system...if you are significantly discharged ie <70% then you will have to recharge at a decent voltage ie>14V.  If you are only discharging by 5% or maybe 10% then the <14V regime of the Li system is likely ok....it is for me.

Let us know how big your LA bank is, how big is you Li bank and what modules you are using for measuring voltage, A, Ahrs, cell voltage and how are you going to disconnect on high/low voltage, high/ low temperature and high/low cell voltage.

 

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On 19/11/2019 at 09:17, nicknorman said:

Im confused by what your proposing but is it: separate LA and Li banks. LA charged from alternator, inverter fed from LA batteries, used to run a charger to charge the Li. If so, sounds fairly odd, rather inefficient and means you can’t run the inverter from the Li. But I suppose it does solve the problem of connecting an alternator directly to the Li.

 

Anyway, having LA and Li batteries connected in parallel does work. This is what several members on here do. If the LA batteries are fully charged they can be held up at say 13.6v by the Li, without taking any significant current. The Li batteries will supply power demands from the boat until they get quite low, at which point yes maybe the LAs will start to deliver current too - maybe around 12.8v or so.

You're confused!!! :)

I think "flying by the seat of my pants" tells you where I am :) and your input is welcomed.

 

On the alternator thing, I saw you guys talking about a special gizmo to keep the alternator safe, and merely came up with a way of taking it out of the equation...... in my system, with my cruising profile. I agree on the inefficiency, and not being able to run the inverter from the Li's..... but this is early days, with baby steps. As a matter of interest, I watch a boaters video last night where his solution to the alternator issue was to use a B to B gizmo from starter battery to Li's.... I think it's been mentioned here.... possibly limiting if the gizmo has a 60A limit, and the alternator can give out much more.

 

On the isolated/parallel thing... if I have a 1-2-both switch in the positive lines of both banks, to the domestic switch board, I think selecting "both" would parallel the banks, so I would have the flexibility to be isolated or parallel.

 

I may be wrong but, in my system, I like the idea of being able to charge the LA's at a higher voltage than the Li's. Given that, in the early days, the Li's wont be connected to the inverter, there is a strong chance that the LA's will be well below fully charged from time to time.

 

If what I do works in the first instance, I can modify things as I go along and get more comfortable with how things work.

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1 hour ago, Richard10002 said:

You're confused!!! :)

I think "flying by the seat of my pants" tells you where I am :) and your input is welcomed.

 

On the alternator thing, I saw you guys talking about a special gizmo to keep the alternator safe, and merely came up with a way of taking it out of the equation...... in my system, with my cruising profile. I agree on the inefficiency, and not being able to run the inverter from the Li's..... but this is early days, with baby steps. As a matter of interest, I watch a boaters video last night where his solution to the alternator issue was to use a B to B gizmo from starter battery to Li's.... I think it's been mentioned here.... possibly limiting if the gizmo has a 60A limit, and the alternator can give out much more.

 

On the isolated/parallel thing... if I have a 1-2-both switch in the positive lines of both banks, to the domestic switch board, I think selecting "both" would parallel the banks, so I would have the flexibility to be isolated or parallel.

 

I may be wrong but, in my system, I like the idea of being able to charge the LA's at a higher voltage than the Li's. Given that, in the early days, the Li's wont be connected to the inverter, there is a strong chance that the LA's will be well below fully charged from time to time.

 

If what I do works in the first instance, I can modify things as I go along and get more comfortable with how things work.

Richard it's winter put them into parallel and try them,  you charge by genie mostly so all will be ok.  Observe volts I am sure you won't get into beyond 13.9 territory, if you go for a cruise do the same. 

Now in the meantime something will know doubt be designed that will sort out future problems 

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1 hour ago, peterboat said:

Richard it's winter put them into parallel and try them,  you charge by genie mostly so all will be ok.  Observe volts I am sure you won't get into beyond 13.9 territory, if you go for a cruise do the same. 

Now in the meantime something will know doubt be designed that will sort out future problems 

 

Surely if you have a genie, you make one of your three wishes to always have fully charged batteries? ??

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On 20/11/2019 at 14:53, peterboat said:

Richard it's winter put them into parallel and try them,  you charge by genie mostly so all will be ok.  Observe volts I am sure you won't get into beyond 13.9 territory, if you go for a cruise do the same. 

Now in the meantime something will know doubt be designed that will sort out future problems 

I'm currently waiting for some cable, terminal rings, and bus bars to arrive, after which I'll start putting things together.

 

However... there is some conflicting information here, where your attitude is the gung ho, "what can go wrong one", and Dr. Bobs who seems to have several gizmos in the chain, just in case one gizmo fails. That sounds quite rude, but it's not meant to be. There is a lot to be said for either approach, and I'd guess I'm going to end up somewhere in the middle :) I still have some answers/comments about my plans, which will be better made to Dr. Bobs post somewhere above.

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1 minute ago, Richard10002 said:

I'm currently waiting for some cable, terminal rings, and bus bars to arrive, after which I'll start putting things together.

 

However... there is some conflicting information here, where your attitude is the gung ho, "what can go wrong one", and Dr. Bobs who seems to have several gizmos in the chain, just in case one gizmo fails. That sounds quite rude, but it's not meant to be. There is a lot to be said for either approach, and I'd guess I'm going to end up somewhere in the middle :) I still have some answers/comments about my plans, which will be better made to Dr. Bobs post somewhere above.

Richard its winter and cruising for you is more than likely short, plus generator charging via your inverter/charger is controlled so it should be safe for the winter months, honestly I don't want you to destroy your batteries but for the next few months I suspect long alternator charging is out 

/

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4 minutes ago, peterboat said:

Richard its winter and cruising for you is more than likely short, plus generator charging via your inverter/charger is controlled so it should be safe for the winter months, honestly I don't want you to destroy your batteries but for the next few months I suspect long alternator charging is out 

/

Agreed.... that's why I'm going to end up somewhere in between :)

 

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On 19/11/2019 at 14:19, Dr Bob said:

It does complicate things with your alternator/inverter/charger/Li charging.

If I was doing it, I would try to get it so the Li's were paralleled with the LA's and connected together for normal use ie discharge and charging via the genny to charger to circuit. So in normal use, the charger can back off when the Li's get full....unlikely in winter.....and the Li's always above 12.8V so the LA's never discharge. So in the circuit you need a shunt on the -ve cable from the Li's (to measure A, Ahr and voltage in the Li's) and on the +ve from the Li's you need a fuse and then your auto disconnect switch. What switch are you using? The BEP or the Tyco. I have also added a belt and braces approach and put a manual battery isolation switch on the LA side of my BEP switch.

Now the issue comes if you want to use the alternator. In the above config, you could run it but you might not have enough control over the alternator output ie too much current..or being able to terminate the charge if the Li's get full.....again unlikely in winter. It would be worth having this config available to try as in winter you will only run your engine a bit and never likely to get full or overstress the alternator as the ambient is cold. You can 'learn' the system doing this. If you go on a long cruise then just isolate the Li's after an hour or two. You may find this works fine for the next 3-4 months and then you can think of improving it. Maybe an alternator option will pop up in that time.

Now, you could do the above with a slight mod to allow the alternator/inverter/charger/Li charging thing. Disconnect the charger 12V+ wire from where it connects into the current LA system and reconect to the terminal on the manual disconnect switch on the Li side. The charger is therefore feeding in between the manual switch and the auto switch. If you therefore wanted to charge this way rather than direct from the alternator, you just isolate the manual switch but your boat services will be drawing from the LA's only.....but your change over switch is going to have the same issue (I think) in isolating the Li's from the domestics.

If you then want to charge just the LA's to fill them back up, you reconnect the LAs via the manual switch and trigger the auto disconnect to isolat the Li.

Watch how discharged the LAs get in this system...if you are significantly discharged ie <70% then you will have to recharge at a decent voltage ie>14V.  If you are only discharging by 5% or maybe 10% then the <14V regime of the Li system is likely ok....it is for me.

Let us know how big your LA bank is, how big is you Li bank and what modules you are using for measuring voltage, A, Ahrs, cell voltage and how are you going to disconnect on high/low voltage, high/ low temperature and high/low cell voltage.

 

LA Bank is probably somewhere between 150Ah and 200Ah. Li bank is 4 x 130Ah = 420Ah. I'm going to keep them separate in the short term, but will have the "Off-1-2-Both" switch, so will be able to parallel them at a flick, (I think :) ) 

 

I'll probably end up with a Victron BMV 712 for monitoring but, for now, I've ordered one of these - a bit like the gizmo that Will Prowse uses, and which looks quite handy for not much money:

 

https://www.amazon.co.uk/gp/product/B07KW2GMS1/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1

 

These batteries are 12V units, so no direct access to cells and cell level info. (However, I should soon be able to connect them to some software on a laptop which will give a variety of cell level info, including voltage, temp., cycles, balancing and stuff). As such, there is no facility to shut things down in over/under temp and voltage circumstances, (although I think the internal BMS shuts down if over/under voltage.... and maybe over/under temp. If not, there is a flashing light on top of the batteries which flashes red if something isn't right).

 

Like Peter says, high voltage, at battery level, shouldn't be an issue as the charger will limit this. I may fit a Victron Battery Protector in the output cables to monitor for under voltage situations. In addition, low temperature shouldn't be an issue as I just wont charge if there is a chance that it is below say 5C., (unlikely as they will be inside the living accommodation, and it is rare that I have needed to charge as soon as I get on board a cold boat). Having said that, I may fit some kind of temperature monitor like this:

 

https://www.amazon.co.uk/Inkbird-All-Purpose-Temperature-Thermocouple-Calibration/dp/B008KVGWT4/ref=pd_ybh_a_28?_encoding=UTF8&psc=1&refRID=ARYJG3TV0B28HBFRV105

 

It only handles up to 10A, so may need to use it to activate a relay or two, to shut down the circuit if the temp is too high or too low, or I might find a gizmo that will handle the likely Amps that might be drawn, (probably only 20A or so for the domestic circuits, but could be up to 200A if I get the inverter connected to the Li's). It wouldn't do any harm for me to have to fit a relay or two as i have been aware of them for almost half a century, but never really understood how they work. Not sure where the sensor would be best placed with 4 batteries. (Apparently each battery has 6 temperature sensors internally, maybe nearer to the top of the cells than the bottom).

 

Those are my thoughts/plans for now but, given that I will be watching them like a hawk in the early days, I might just charge them up individually to similar voltages, connect them together, and give it a go. 

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4 minutes ago, Richard10002 said:

LA Bank is probably somewhere between 150Ah and 200Ah. Li bank is 4 x 130Ah = 420Ah. I'm going to keep them separate in the short term, but will have the "Off-1-2-Both" switch, so will be able to parallel them at a flick, (I think :) ) 

 

I'll probably end up with a Victron BMV 712 for monitoring but, for now, I've ordered one of these - a bit like the gizmo that Will Prowse uses, and which looks quite handy for not much money:

 

https://www.amazon.co.uk/gp/product/B07KW2GMS1/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1

 

These batteries are 12V units, so no direct access to cells and cell level info. (However, I should soon be able to connect them to some software on a laptop which will give a variety of cell level info, including voltage, temp., cycles, balancing and stuff). As such, there is no facility to shut things down in over/under temp and voltage circumstances, (although I think the internal BMS shuts down if over/under voltage.... and maybe over/under temp. If not, there is a flashing light on top of the batteries which flashes red if something isn't right).

 

Like Peter says, high voltage, at battery level, shouldn't be an issue as the charger will limit this. I may fit a Victron Battery Protector in the output cables to monitor for under voltage situations. In addition, low temperature shouldn't be an issue as I just wont charge if there is a chance that it is below say 5C., (unlikely as they will be inside the living accommodation, and it is rare that I have needed to charge as soon as I get on board a cold boat). Having said that, I may fit some kind of temperature monitor like this:

 

https://www.amazon.co.uk/Inkbird-All-Purpose-Temperature-Thermocouple-Calibration/dp/B008KVGWT4/ref=pd_ybh_a_28?_encoding=UTF8&psc=1&refRID=ARYJG3TV0B28HBFRV105

 

It only handles up to 10A, so may need to use it to activate a relay or two, to shut down the circuit if the temp is too high or too low, or I might find a gizmo that will handle the likely Amps that might be drawn, (probably only 20A or so for the domestic circuits, but could be up to 200A if I get the inverter connected to the Li's). It wouldn't do any harm for me to have to fit a relay or two as i have been aware of them for almost half a century, but never really understood how they work. Not sure where the sensor would be best placed with 4 batteries. (Apparently each battery has 6 temperature sensors internally, maybe nearer to the top of the cells than the bottom).

 

Those are my thoughts/plans for now but, given that I will be watching them like a hawk in the early days, I might just charge them up individually to similar voltages, connect them together, and give it a go. 

I have something similar to your top link for my drive batteries works ok Richard 

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12 hours ago, Richard10002 said:

LA Bank is probably somewhere between 150Ah and 200Ah. Li bank is 4 x 130Ah = 420Ah. I'm going to keep them separate in the short term, but will have the "Off-1-2-Both" switch, so will be able to parallel them at a flick, (I think :) ) 

 

I'll probably end up with a Victron BMV 712 for monitoring but, for now, I've ordered one of these - a bit like the gizmo that Will Prowse uses, and which looks quite handy for not much money:

 

https://www.amazon.co.uk/gp/product/B07KW2GMS1/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1

 

These batteries are 12V units, so no direct access to cells and cell level info. (However, I should soon be able to connect them to some software on a laptop which will give a variety of cell level info, including voltage, temp., cycles, balancing and stuff). As such, there is no facility to shut things down in over/under temp and voltage circumstances, (although I think the internal BMS shuts down if over/under voltage.... and maybe over/under temp. If not, there is a flashing light on top of the batteries which flashes red if something isn't right).

 

Like Peter says, high voltage, at battery level, shouldn't be an issue as the charger will limit this. I may fit a Victron Battery Protector in the output cables to monitor for under voltage situations. In addition, low temperature shouldn't be an issue as I just wont charge if there is a chance that it is below say 5C., (unlikely as they will be inside the living accommodation, and it is rare that I have needed to charge as soon as I get on board a cold boat). Having said that, I may fit some kind of temperature monitor like this:

 

https://www.amazon.co.uk/Inkbird-All-Purpose-Temperature-Thermocouple-Calibration/dp/B008KVGWT4/ref=pd_ybh_a_28?_encoding=UTF8&psc=1&refRID=ARYJG3TV0B28HBFRV105

 

It only handles up to 10A, so may need to use it to activate a relay or two, to shut down the circuit if the temp is too high or too low, or I might find a gizmo that will handle the likely Amps that might be drawn, (probably only 20A or so for the domestic circuits, but could be up to 200A if I get the inverter connected to the Li's). It wouldn't do any harm for me to have to fit a relay or two as i have been aware of them for almost half a century, but never really understood how they work. Not sure where the sensor would be best placed with 4 batteries. (Apparently each battery has 6 temperature sensors internally, maybe nearer to the top of the cells than the bottom).

 

Those are my thoughts/plans for now but, given that I will be watching them like a hawk in the early days, I might just charge them up individually to similar voltages, connect them together, and give it a go. 

Richard,

That all sounds good. I think you are going to enjoy your new batteries. Peter is right that in the winter, you are not likely to have any problems. If you are using say 100Ahr per 24 hours then you will cycle your batteries between – 250hrs and -150hrs with the charger each day so never getting near the top or bottom voltage limits. You will soon forget about looking at them and just run the genny for a few hours a day. By the time it warms up again you will have a far better understanding of what to do for YOUR system ….as you are breaking new ground with these type of cells rather than the bare cells.

A few points I would think about.

If you are charging via the genny, you will be OK with your battery charger unless something goes wrong with it. That is why I would put an auto disconnect on it. If you get the BMV 712 that has the relay that can disconnect the BEP switch on high/low voltage and temperatures (or get the tyco switch – with some sort of activation circuit ie MP's). You will always be on the boat when charging so maybe instead of an auto-disconnect you could have an alarm to warn you. The BMV 712 does have an alarm but the old firmware had this alarm set at 4Khz so most peeps couldnt hear it. The new firmware sorts this problem. There are some cheap boards from Amazon for £10 that sound an alarm if over say 13.9V (user configurable). In your case at least put an audible warning system in place in case the charger goes bad and tries to stick 20V or something into the Li's. I went for the belt and braces approach of the auto disconnect to protect my £1000 of batteries.

With the drop in 12V cells, you dont need to worry about cell in-balance – hence monitoring cell voltages - as the internal BMS will do that but have a think about what happens if one 12V unit has an issue...ie an in-balance. The internal BMS will isolate it leaving the other 3 in parallel. Could this cause a cascade type shut down? That is breaking new ground. Peter's system never gets to full charge with high Amps. Yours might.

When you get them in place, I would charge them up to full with say a 40A charge current and watch the voltage....and write it down along with the A and Ahrs used. Watch for the current dropping to say 20A and note the voltage. You are now fully charged and your charger should be stopping. As you dont want to charge to 100% each time – better to go to 80%- next time drop the voltage by 0.1V and see how charged you are by looking at Ahrs used. Your charger should then be stopping the charge before you get to problems. I know MP will come back about target voltages but at these low charging currents 30-40A, you should be around the 13.9 or 14.0V at termination. At higher currents then that voltage will be more. You need to scope it out for your system. When you do this for the first few time, dont take your eyes off the meters as the voltage can rise very fast and you cant see the cell voltages for all the cells.

When you have found out the voltages you need, make sure your charger shuts off when you get to wotever voltage  you choose then you can forget about them!

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