Monitoring lithium batteries

[PMB]

2 minutes ago, Robbo said:

If your needs are no more than 200amp (like a 2kw inverter) and have a 100amp or less alternator the Victron BMS12/200 seems to be the good option as the batteries are directly connected through this.   The other BMS is more of a remote controller that tells chargers and loads to turn off.   For a alternator this would be connected to the starter batteries and the BMS controls the split charge relay.

We're a bit over that. It'll be the 3kw inverter as the 2kw one is right on the limit for washing machine. And the domestic alt is (will be when the engine arrives) a 175a

[MtB]

I deeply dislike this term “BMS”.

 

An external bms can not possibly know what each individual cell is doing, so we have to have the internal bms inside the battery apparently. This is a different thing from the external bms now being talked about that contols the charge source. 

 

So the term bms is being used for at least two different things. 

[Robbo]

33 minutes ago, PMB said:

We're a bit over that. It'll be the 3kw inverter as the 2kw one is right on the limit for washing machine. And the domestic alt is (will be when the engine arrives) a 175a

I think Jono has a similar config, he has used the VE Bus BMS to be the controller, this can connect to the 12/200 BMS to control the alternator (the 12/200 doesn’t do the BMS bit then).   Jono has it limited to 200amp, although i thought it could only do 100amp.   This would be a question for Victron.

link; https://www.victronenergy.com/upload/documents/VE.Bus-BMS-to-BMS-12-1200-alternator-control-cable-EN.pdf

29 minutes ago, Mike the Boilerman said:

I deeply dislike this term “BMS”.

 

An external bms can not possibly know what each individual cell is doing, so we have to have the internal bms inside the battery apparently. This is a different thing from the external bms now being talked about that contols the charge source. 

 

So the term bms is being used for at least two different things. 

External BMS’s like the ones from Victron are connected to the batteries so they know what each individual cell is doing in the battery bank, all the batteries  are connected via another cable that goes in series between all the batteries for communicating with the BMS.

Edited August 18, 2018 by Robbo

[smileypete]

Maybe have a couple of 12V FLA batts for 12V pumps, lights; then a 24V lithium pack that runs the big inverter. Charge it with boost converters set to lithium voltages, use a low voltage disconnect and the inverter remote to protect from over discharge.

 

OK you lose some efficiency but all the charging sources can be fairly conventional. Could even use the lithiums to give the FLAs a full charge when they need it, running the 12V while doing so. And if the lithiums run out of power unexpectedly you still have 12V for basic service.

 

ETA: Would also need a 12V split charge relay so the lithium charging doesn't flatten the FLAs, but that's no biggie.

Edited August 18, 2018 by smileypete

[Dr Bob]

33 minutes ago, Mike the Boilerman said:

I deeply dislike this term “BMS”.

 

An external bms can not possibly know what each individual cell is doing, so we have to have the internal bms inside the battery apparently. This is a different thing from the external bms now being talked about that contols the charge source. 

 

So the term bms is being used for at least two different things. 

I agree with you Mike.

If you do a diy job using second hand batteries then you will end up with 2 different BMSs. One 'battery level' one controling the individual cells and one controlling the charge devices. If you buy a turnkey system from victron etc, you may end up with one BMS which does both and you may not have a clue what is going on and how to control it. I think I prefer the former!

[MtB]

4 minutes ago, Dr Bob said:

I agree with you Mike.

If you do a diy job using second hand batteries then you will end up with 2 different BMSs. One 'battery level' one controling the individual cells and one controlling the charge devices. If you buy a turnkey system from victron etc, you may end up with one BMS which does both and you may not have a clue what is going on and how to control it. I think I prefer the former!

 

Yes the former is my preference too. The problem here is there are no sellers of bare cells here in the uk afaik. So proprietary ‘fully managed’ systems seem to be the only option here in the uk. 

 

 

[Dr Bob]

30 minutes ago, smileypete said:

Maybe have a couple of 12V FLA batts for 12V pumps, lights; then a 24V lithium pack that runs the big inverter. Charge it with boost converters set to lithium voltages, use a low voltage disconnect and the inverter remote to protect from over discharge.

 

OK you lose some efficiency but all the charging sources can be fairly conventional. Could even use the lithiums to give the FLAs a full charge when they need it, running the 12V while doing so. And if the lithiums run out of power unexpectedly you still have 12V for basic service.

 

....but that seems to defeat the object of having to charge for hours and hours. You need to keep you FLA's at 100% every few days otherwise they will sulphate so you need 3 or 4 hours of engine running etc in winter.

The beauty of the lithiums is you only run your engine for an hour a day in summer (plus solar) and maybe 2 hours a day in winter with a 90A alternator and a 120Ahr usage overnight. I would be happy to manually switch my alternator supply to a 'dump' or off after an hour, set my solar to 13.8V and then rely on an emergency over or under voltage to disconnect etc.

[Detling]

47 minutes ago, Dr Bob said:

If you buy a turnkey system from victron etc, you may end up with one BMS which does both

Nope Victron have an internal battery BMS that balances cells as well as emergency cutoff. they also have the bank BMS which does the same emergency cutoffs and seems to like limiting the charge current, the 12/200 BMS  spec says it limits the alternator to 80% of its 'fuse' value the biggest 'fuse' on their spec is 100 amp so that is 80 amp max charge from your alternator, not much good if you have a 175Amp alternator and a big bank. 

[mrsmelly]

23 minutes ago, Dr Bob said:

....but that seems to defeat the object of having to charge for hours and hours. You need to keep you FLA's at 100% every few days otherwise they will sulphate so you need 3 or 4 hours of engine running etc in winter.

The beauty of the lithiums is you only run your engine for an hour a day in summer (plus solar) and maybe 2 hours a day in winter with a 90A alternator and a 120Ahr usage overnight. I would be happy to manually switch my alternator supply to a 'dump' or off after an hour, set my solar to 13.8V and then rely on an emergency over or under voltage to disconnect etc.

During this one hour a day engine running in the summer how far do you travel? One hour a day is less than we do as continuous cruisers, what is this a boating forum or an off grid living forum? Surely you are not suggesting people leave their boat in one place? ?

[TheBiscuits]

47 minutes ago, Detling said:

[...] so that is 80 amp max charge from your alternator, not much good if you have a 175Amp alternator and a big bank. 

Technically true, but it will keep pushing in those 80A until the LFP batteries are "full" in a couple of hours rather than put in 160A at the start and then rapidly tail downwards to finish at around 4A after 10 hours.

[WotEver]

27 minutes ago, TheBiscuits said:

Technically true, but it will keep pushing in those 80A until the LFP batteries are "full" in a couple of hours rather than put in 160A at the start and then rapidly tail downwards to finish at around 4A after 10 hours.

And of course it also means that the alternator is running well within its capacity. One of the worries written here in other threads is how long a 60A alternator would last, pushing 60A continuously for a couple or three hours. 

[Dr Bob]

30 minutes ago, WotEver said:

And of course it also means that the alternator is running well within its capacity. One of the worries written here in other threads is how long a 60A alternator would last, pushing 60A continuously for a couple or three hours. 

......or even continuously for an hour.

[TheBiscuits]

5 hours ago, Mike the Boilerman said:

I deeply dislike this term “BMS”.

 

An external bms can not possibly know what each individual cell is doing, so we have to have the internal bms inside the battery apparently. This is a different thing from the external bms now being talked about that contols the charge source. 

 

So the term bms is being used for at least two different things. 

Yep.  Battery Management System.  Or Bleedin' Magic Smoke when they go wrong!

 

This might help:

 

http://liionbms.com/php/about_bms.php

 

or play with the cell balancing:

 

http://liionbms.com/balance/

[cuthound]

23 hours ago, Mike the Boilerman said:

I deeply dislike this term “BMS”.

 

An external bms can not possibly know what each individual cell is doing, so we have to have the internal bms inside the battery apparently. This is a different thing from the external bms now being talked about that contols the charge source. 

 

So the term bms is being used for at least two different things. 

 

Because of the industry I worked in, to me  "BMS" means Building Management System. This term has been in use for over 40 years.

 

The thing looking after the battery was a "battery monitor" or "battery controller" ?

Edited August 19, 2018 by cuthound
Clarity

[peterboat]

Well I can tell you that a BM2 does calibrate itself to Lifepo4 batteries, Monday night a solar panel went faulty and took my bank down to 9.4 volts yesterday I sussed out the problem [capacitor] and all was well in the charging dept. The bank still isnt fully charged and the BM2 shows that so just maybe you need a disastrous failure to make things work ? As we speak 13 volts showing 27 amps going in washing machine on and still a long way to go before fully charged!!

[WotEver]

34 minutes ago, peterboat said:

Monday night a solar panel went faulty and took my bank down to 9.4 volts yesterday

Why didn’t the BMS disconnect on low voltage?

[rusty69]

Just now, WotEver said:

Why didn’t the BMS disconnect on low voltage?

Why did the BMS cross the road?.............. 

 

 

 

 

Cos he was connected to the battery chicken! 

[peterboat]

32 minutes ago, WotEver said:

Why didn’t the BMS disconnect on low voltage?

Because it hadnt got low enough to do damage? I will have to plug in and see what the batteries say but busy with other stuff at the moment like painting the roof before fastening the new panels down forgot to say batteries at 13.2 volts and 50 amps going in

[Dr Bob]

10 hours ago, peterboat said:

Because it hadnt got low enough to do damage? I will have to plug in and see what the batteries say but busy with other stuff at the moment like painting the roof before fastening the new panels down forgot to say batteries at 13.2 volts and 50 amps going in

Is it possible the low voltage response is only to disconnect any load on the battery and leave in place any charge source which is needed on deep discharge. A charge device may not be thought of as a load so not disconnected. That then is a worry.

[MtB]

15 minutes ago, Dr Bob said:

Is it possible the low voltage response is only to disconnect any load on the battery and leave in place any charge source which is needed on deep discharge. A charge device may not be thought of as a load so not disconnected. That then is a worry.

 

I believe Peter's batteries only have internal voltage management so the only thing it can do is disconnect the terminals, or not. 

 

How it copes with cell balancing of the several hundred tiny cells in each battery remains a mystery. I suspect it doesn't even bother to try. 

 

 

[peterboat]

56 minutes ago, Mike the Boilerman said:

 

I believe Peter's batteries only have internal voltage management so the only thing it can do is disconnect the terminals, or not. 

 

How it copes with cell balancing of the several hundred tiny cells in each battery remains a mystery. I suspect it doesn't even bother to try. 

 

 

It does Mike because when I plugged in the cells were balanced, or is it a case that the batteries just balance when they charge?

The voltage cant have been critical because the LEDS were still flashing green if its critical they flash red and go on red permanent

[MtB]

6 minutes ago, peterboat said:

It does Mike because when I plugged in the cells were balanced, or is it a case that the batteries just balance when they charge?

The voltage cant have been critical because the LEDS were still flashing green if its critical they flash red and go on red permanent

 

How many cells in each of your batteries?

[peterboat]

1 hour ago, Mike the Boilerman said:

 

How many cells in each of your batteries?

400

[MtB]

6 hours ago, peterboat said:

400

 

I thought it was something like that.

 

Do the internal electronics maintain balance of all 400 cells or were they just balanced at manufacture, and as they drift out of balance are individual cells getting too high or too low allowed to fail and just drop out of use?

 

I suspect the Victron batteries have just four large cells inside so monitoring balance is both far easier and far more important. 

[Robbo]

48 minutes ago, Mike the Boilerman said:

 

I suspect the Victron batteries have just four large cells inside so monitoring balance is both far easier and far more important. 

Confirmed, the 12v ones have 4 cells.