Battery charge - how are you measuring your lithiums?

[Johny London]

Trying to fill in another piece of the jigsaw puzzle that is lithiums. I figure for now I could rig some up to just charge off the victron/genny and  solar, both of which I believe have suitable controller options. But I'm not sure about how to meter the charge? I think amp counting but would appreciate a nudge in the right direction (or preferably, a series of massive great sign posts!). 

ta

[Mike Hurley]

Watch journey with jono on youtube, he explains his install in great detail.

[Johny London]

Already have, still puzzled. Would like to know what several lithium users on here have?

 

Edited November 23, 2018 by Johny London

[Robbo]

Why not just use a amp counter battery monitor like the BMV?   If your going Victron that seems to be the obvious choice.

[Johny London]

To expand on that, I know he has Victron BMV meters, but I'm not sure if they just count amps or if the newest ones have something else - think I read that they automatically re calibrate themselves when they sense 100% charge? But if I was using the 20-80% regime not sure that would apply? Just confused ..

[TheBiscuits]

Set the counter so it thinks you have 80% of your actual capacity... 

[MtB]

Johny, broadly speaking there are two types of LiFeP04 batteries you can choose. A proprietary system with electronics built into the battery to carry out all management functions e.g. Victron, Valence, RELiON. Or you can buy bare cells and design your own management. Which are you planning to go? I think only with the bare cells is your question relevant. With built in management you use the software and/or instrumentation supplied by the manufacturer to find out the SoC. 

 

This may be wrong in detail but it is my broad understanding. 

[Tom and Bex]

I use a Victron BMV-701 to monitor state of charge on our 320ah lithium bank. There is a section on I think the Victron site about the settings to use for lithium. We also use an ISDT bc-8s battery checker to monitor individual cell voltages with alarms set for over voltage, under voltage, and cell difference. 

 

We generally charge for a couple hours every 2 days or so. Difficult to know accuracy of the BMV, but seems to produce quite consistent results. We generally aim to stop charging when the split charge relay cuts out (controlled by alternator controller and programmed to turn off at end of bulk charging). This consistently seems to be around the 80% mark on the BMV with amps having dropped to 60-65ish. 

 

Our plan is to charge to 100% to synchronise the BMV every 4-6 weeks or so, probably when going for a pump out. Lowest the batteries have been so far is 9% and. When out cruising they hit 100%, then alternator controller goes into float and they settle at high 90's% by end of day.

 

Best thing I've done to the boat is fit lithium batteries. Only been 2-3 months so far, but saved a lot in fuel and engine hours already. Initially we monitored them quite closely, but now just use as much power as we want when we want, and charge as and when we feel like it. Just have occasional glance at SOC on BMV to check all is in order. 

[MtB]

33 minutes ago, Tom and Bex said:

I use a Victron BMV-701 to monitor state of charge on our 320ah lithium bank. There is a section on I think the Victron site about the settings to use for lithium. We also use an ISDT bc-8s battery checker to monitor individual cell voltages with alarms set for over voltage, under voltage, and cell difference. 

 

We generally charge for a couple hours every 2 days or so. Difficult to know accuracy of the BMV, but seems to produce quite consistent results. We generally aim to stop charging when the split charge relay cuts out (controlled by alternator controller and programmed to turn off at end of bulk charging). This consistently seems to be around the 80% mark on the BMV with amps having dropped to 60-65ish. 

 

Our plan is to charge to 100% to synchronise the BMV every 4-6 weeks or so, probably when going for a pump out. Lowest the batteries have been so far is 9% and. When out cruising they hit 100%, then alternator controller goes into float and they settle at high 90's% by end of day.

 

Best thing I've done to the boat is fit lithium batteries. Only been 2-3 months so far, but saved a lot in fuel and engine hours already. Initially we monitored them quite closely, but now just use as much power as we want when we want, and charge as and when we feel like it. Just have occasional glance at SOC on BMV to check all is in order. 

 

T & B,

 

What lithiums do you have please? Bare cells or a proprietary system? I've an idea you mentioned buying Victron. 

 

If Victron, the 100% you see is quite likely to be 80% or so at the bare cell level I'd guess, from what I've gleaned about the dangers of truly charging to 101%. The software is bound to keep a bit of headroom concealed from you. 

 

And float charging them is guaranteed to kill them from what I've read. They simply don't need it so again, the software will probably be giving you the illusion. 

[Tom and Bex]

Bare cells. 2nd hand 160ah Thundersky cells to be exact. Only Victron item I've purchased is the BMV monitor. 

 

Generally charged from alternator controlled with arduino alternator controller. Charged at 14.0V until amps drop to 12A (4% battery capacity). This is taken as my 100% charge. 

 

100% charge is ok, it's over voltage and holding at high charge that kills cells. That can happen quickly at the end of charge. Float mode on the alternator aims to keep amps flow into battery at 0A (with a max voltage of 13 point something). This generally lets them discharge to mid 90's% before amps stabilise at 0.

[MtB]

Ok thanks!

 

Do you have any under/over voltage protection or do you manage them totally manually? 

 

I'm tempted to buy some bare cells and just monitor them myself and bugger all the pishing about with automated BMS etc. 

 

[Tom and Bex]

I do have a simple BMS that provides high and low voltage cut based on individual cell voltages. Bought from Australia as was the easiest and simplest I could find for the price. 

 

I'm sure a basic alarm such the ISDT device above would be fine for users such as yourself who know their usage pattern and are prepared to monitor the batteries themselves. My primary concern was what would happen if we were away for several days with the fridge on. That's my primary reason for the BMS I chose. 

[MtB]

3 minutes ago, Tom and Bex said:

My primary concern was what would happen if we were away for several days with the fridge on.

 

Damn, this is EXACTLY what do, having a selection of hulls on which to sleep! 

[Tom and Bex]

I got the feeling most people switch everything off when leaving the boat - we tend to just leave it all switched on, as we would in a house.....

[MtB]

1 minute ago, Tom and Bex said:

I got the feeling most people switch everything off when leaving the boat - we tend to just leave it all switched on, as we would in a house.....

 

Me too, and in summer I let the solar take the strain. In winter I start the Whispergen remotely every day or two.

[Tom and Bex]

But your batteries never get to 100% in winter............

 

Get yourself some lithiums - you know you want to?

[MtB]

3 minutes ago, Tom and Bex said:

But your batteries never get to 100% in winter............

 

Get yourself some lithiums - you know you want to?

 

I do! 

 

The hard bit is deciding which ones. 

 

I might just try a pair of lead carbon batts first though.... If I can get to the bottom of whether they really need charging to 100% periodically, or not. And how to desulphate them if/when necessary. These seem to be the hard questions no-one addresses. 

[Tom and Bex]

I think lithiums are becoming a more proven technology than lead carbon, particularly for off grid use. 

 

One of the biggest hurdles to overcome I think is how to successfully/safely manage alternator charging. I've used a separate arduino based alternator regulator, but it does require modification to existing regulator. I'd be interested to hear how other lithium users have managed this.

[Johny London]

Tom and Brex - your set up sounds like heaven!!! A couple of hours charge every two days? Just marvellous.

So, I just need an alternator charge controller, a BMV meter, and another thing that keeps an eye on the cells themselves? Maybe a low voltage cutoff.

 

Yes, for cost reasons I want to go for "bare cells" or at least those ones Peterboat has, (Valence) which actually I believe do some internal balancing on their own.

I'm thinking of this initially: To create a second battery bank (the lithiums) and use genny/inverter charger, and the solar to charge them, just to prove the technology. I can add in the alternator charge later on, and in the meantime that would be feeding the old L/A's - as a back up and of course it is winter so at least a safety net. Plus wont have to worry about the alternator not having a load. I can always hook back up to the LA's if it all goes Pete Tong. Of course that means more new cabling and isolator/fuses/bank switch etc so a bit more cost. And I know I need to keep the two things separate because of different settings for the charging gear.

It all seems like trying to get the fog to clear so I can go ahead. I don't want to fritz the lithiums on day 1 but they do look like the answer.

 

Jonos system - despite having Victrons he's made an incredibly elaborate system with lots and lots of failsafes built in - I don't think it is just a standard Victron setup, it goes way beyond. He had to come up with the circuit diagram with the aid of another chap - if it was purely an off the shelf Victron set up I think they would have the circuit diagram on their website with a list of parts and (although at quite a cost) you could just follow that no questions asked.

 

I think I'm going to get a couple of those lithiums, start building the system and take it a step at a time, carry on using the LA's till I feel ready. 

[WotEver]

8 minutes ago, Johny London said:

I think I'm going to get a couple of those lithiums...

Think carefully about where you’ll locate them too. Jono got all excited this week because Victron issued a software update to cut the batteries off if the temp dropped below 5C. 

[MtB]

23 minutes ago, Johny London said:

I think I'm going to get a couple of those lithiums, start building the system and take it a step at a time, carry on using the LA's till I feel ready. 

 

The factors to consider are:

 

1) They can only take a tiny charge current when around 0C or lower. You will wreck them if you charge at normal current when they are cold.

 

2) If you run them down too flat you risk wrecking them. You may get way with it, you may not.

 

3) If you charge them to 100% this is fine. Charge to 101% and you will wreck them. This is why peeps talk about only charging to 80%. To swerve this risk.

 

4) If they get hot (over 50C) they will probably be killed. Not sure why they would get that hot though.

 

5) If you install automatic disconnection to prevent overcharging, disconnection of the alternator whilst charging will wreck it.

 

 

So as long as you can mitigate these risks you'll be fine. Bear in mind it only takes one oversight though. This is why proprietary systems are so complex and expensive - the cells inside need protecting from the idiot users who aren't interested in the five points above and expect them to behave just like LA batts.

[Detling]

I have heard of underfloor heating mats as used in bathrooms being modified to fit around and under the cells thermostat controlled to keep them just over 5 degrees. They use their own power to do this so you need to make sure you have enough to avoid overcharge. But for systems charged daily works fine.

[Tom and Bex]

14 hours ago, Johny London said:

Tom and Brex - your set up sounds like heaven!!! A couple of hours charge every two days? Just marvellous.

That was the main motivation. No running the engine/generator for 8hrs putting in single figure amps into the batteries!

 

14 hours ago, Johny London said:

So, I just need an alternator charge controller, a BMV meter, and another thing that keeps an eye on the cells themselves? Maybe a low voltage cutoff.

Yes - although alternator controller needs to be fully programmable and to replace existing regulator functions. Ours has connections to the BMV shunt so can be programmed to change charge settings based on amps flowing into battery instead of pure voltage. Low voltage cut is strongly advised - can be based on pack voltage, but to gain max usable capacity a cell voltage cut is recommended. High voltage can be taken care of with alarm, generally you would be present during charging (solar excepted but with conservative values should be fine).

 

14 hours ago, Johny London said:

Yes, for cost reasons I want to go for "bare cells" 

That's why I went for (2nd hand) bare cells. My total setup cost just over £1k including additional wiring improvements. 

 

14 hours ago, Johny London said:

I'm thinking of this initially: To create a second battery bank (the lithiums) and use genny/inverter charger, and the solar to charge them, just to prove the technology.

I did consider paralleling the lithiums with the lead acid initially, but the cost savings weren't that great in the end. As to charging with generator, we can only charge at 30A with genny compared to over 100A via alternators so negating one of the big advantage of lithiums to accept high charge rates. 

 

14 hours ago, Johny London said:

Jonos system - despite having Victrons he's made an incredibly elaborate system with lots and lots of failsafes built in - I don't think it is just a standard Victron setup, it goes way beyond.

I did look at his system, but it was way to expensive for me to consider so I designed my own to be as simple but safe as possible within a tight budget. This was after many hours reading articles and discussions online and coming to my own conclusions as to risk vs benefit of the different options.

 

14 hours ago, Johny London said:

I think I'm going to get a couple of those lithiums, start building the system and take it a step at a time

I was pushed into action by the need to replace our 12 month old cheapo batteries that were down to considerably less than half original capacity!

 

14 hours ago, WotEver said:

Think carefully about where you’ll locate them too. Jono got all excited this week because Victron issued a software update to cut the batteries off if the temp dropped below 5C.

That's why after careful consideration I decided to locate ours inside just next to the rear steps. Our alternator controller takes care of not charging them below freezing, but can't imagine many scenarios where they will get that cold inside the cabin. Hopefully if it's that cold and we're away the solar output will be quite low.

 

13 hours ago, Mike the Boilerman said:

2) If you run them down too flat you risk wrecking them. You may get way with it, you may not.

Solved with a low voltage cut, particularly if based on cell voltages. Need to be careful nothing bypasses it though - this includes battery monitoring! 

 

13 hours ago, Mike the Boilerman said:

3) If you charge them to 100% this is fine. Charge to 101% and you will wreck them. This is why peeps talk about only charging to 80%. To swerve this risk

It's not quite as simple as that, it comes down to how you determine 100% again! As there is no need to ever charge to 100% then why bother? Our setup is arranged to take 100% as being  tail current of 4% @ 14.0v but think that's pushing it a bit really and thinking of changing it to 8%. If you look at the charge curves you can see how little capacity you put in at the end of charge as the current tails off and voltage rises rapidly. Some people charge to a set voltage such as 14.0v and then stop. My experience seems to show that takes you up to 80-85% which might be enough and certainly gives a big safety margin. 

 

It's important to remember not to let any individual cell go higher than 3.6-3.7v during normal charging, and avoid holding them at that level. Whilst on the subject of charging, it's worth mentioning temperature compensation. This should be disabled on all charging sources. It's not needed and risks cells going over voltage in cold weather - almost the opposite of what you want. 

13 hours ago, Mike the Boilerman said:

5) If you install automatic disconnection to prevent overcharging, disconnection of the alternator whilst charging will wreck it.

Unless you have alternator connected to start battery and combine them for charging. Alternative is to cut charging by cutting the power to external regulator if used or ?field wire if internal reg, but this requires modification of alternator. One of our alternators is modified to use external reg and the other charges the start battery and is combined with the lithiums until they hit the absorption voltage of 14.0v.

 

13 hours ago, Mike the Boilerman said:

So as long as you can mitigate these risks you'll be fine. Bear in mind it only takes one oversight though.

That's what I hope our system is designed to do. Having lived with it for a couple months or so now, I'd be fairly confident to do away with some of my safeguards and rely on low voltage cut off based on pack voltage only, and alarms for the rest. If you don't mind losing a bit of useable capacity, then just have a high voltage cut set to 14.0v, charge to there and stop. That avoids the need for alternator and other charge controllers. 

 

Having said that, I'm very happy with our setup, the performance of it,  and the peace of mind it gives. 

[Sea Dog]

This ^^^^ is really quite interesting. It also appears to herald the move to lithium out of the fantasy world into the real world in terms of cost.  Good work.