Monitoring lithium batteries

[mrsmelly]

1 hour ago, nicknorman said:

However, let’s not forget the £5000 per year you spend on candles!

And that's were the joke is. We live aboard full time winter, summer no matter and with the tried and tested cheap and safe fla way never ever have a problem running everything we need and never get even close to running out of power and err don't even have candles on board.  Just because lion batteries cost eighty billion pounds doesn't mean they are a better solution it simply means they are massively more expensive way of approaching the same solution.

[nbfiresprite]

2 minutes ago, mrsmelly said:

And that's were the joke is. We live aboard full time winter, summer no matter and with the tried and tested cheap and safe fla way never ever have a problem running everything we need and never get even close to running out of power and err don't even have candles on board.  Just because lion batteries cost eighty billion pounds doesn't mean they are a better solution it simply means they are massively more expensive way of approaching the same solution.

He too poor for candles, He has to make do with making his own 'Rush Dips' from the left over used grease from the stern gland and the dried pith of rush plants.

[Robbo]

8 minutes ago, mrsmelly said:

Just because lion batteries cost eighty billion pounds doesn't mean they are a better solution

But they are a better solution and work out cheaper long term.   Why would anyone want LA if you have to replace them every other year and run your engine hours on end to charge them when there is no need?

[peterboat]

14 minutes ago, mrsmelly said:

And that's were the joke is. We live aboard full time winter, summer no matter and with the tried and tested cheap and safe fla way never ever have a problem running everything we need and never get even close to running out of power and err don't even have candles on board.  Just because lion batteries cost eighty billion pounds doesn't mean they are a better solution it simply means they are massively more expensive way of approaching the same solution.

Sorry Tim I paid £320 each for mine with very few cycles on them they are awesome LAs are not even in the same league and they are light so no ruptures when lugging them about.

[mrsmelly]

1 minute ago, Robbo said:

But they are a better solution and work out cheaper long term.   Why would anyone want LA if you have to replace them every other year and run your engine hours on end to charge them when there is no need?

Well for a start it means committing for a long time to one boat and one boat doesn't suit all so personally I change mine when needed and having a large investment in batteries isn't what I would like. We cruise daily so have no need of expensive fast charging solutions and will be plugged in this winter on virtually free mains electricity. I simply don't think we are anywhere near the stage yet that lion are simply plug and play like fla but of course one day maybe. If the boat is seldom cruised and definitely never being sold or swopped and never on an umbilical they may seem to some a good idea but I will wait till the technology is sound.

4 minutes ago, peterboat said:

Sorry Tim I paid £320 each for mine with very few cycles on them they are awesome LAs are not even in the same league and they are light so no ruptures when lugging them about.

Blimey Peter why lug them about? Mine are moved to the boat and fitted and left till removal, hardly onerous innitt. You will tell me to buy an eco fan next ?

[Robbo]

18 minutes ago, mrsmelly said:

Well for a start it means committing for a long time to one boat and one boat doesn't suit all so personally I change mine when needed and having a large investment in batteries isn't what I would like. We cruise daily so have no need of expensive fast charging solutions and will be plugged in this winter on virtually free mains electricity. I simply don't think we are anywhere near the stage yet that lion are simply plug and play like fla but of course one day maybe. If the boat is seldom cruised and definitely never being sold or swopped and never on an umbilical they may seem to some a good idea but I will wait till the technology is sound.

As said many times LiFePO4 is really for boats that are off grid in winter, in other circumstances you are not going to get the benefits from them as you should put the money into solar first.     Wiring and installing isn't that much of a pain, if you can wire a shunt, you can wire for LiFePO4's - or even go for the drop in replacement ones with built in BMS like from the likes of Relion.    You can move them from one boat to another if you so wish like you could do with a solar system or generator.    The technology is sound already.     The only real argument against them is that the up front cost us prohibitive to a good many of us.

Edited August 8, 2018 by Robbo

[Dr Bob]

3 hours ago, Mike the Boilerman said:

 

 

Dr Bob has raised a question with this thread that has troubled me too with lithiums.

 

GIven they accept (effectively) unlimited current during charging, and it is critically important to stop charging before they get to 100%, how is the state of charge determined during charging?

 

Peterboat is the only only so far to give an answer, which to summarise is "don't worry about it, the BMS handles all that". Now that just doesn't cut it for me. Dunno about Dr Bob!

 

So the question I have, and perhaps Dr Bob too, is "how does the BMS know the SoC during charging"? I think the only way for it to know is to count the AH out and back in repeatedly from a known starting SoC. 

 

3 hours ago, Mike the Boilerman said:

 

So the charge voltage rises proportionally with SoC regardless of charge current? 

 

 

 

ISTR the internal resistance of a lithium is discountably small so the corollary to this must be that during discharge, the terminal voltage does not change with load either, so SoC during discharge is really easy for the BMS to know too. Yes?

Yes, that is my question as I wanted to understand how you know when to stop charging. From what Peter and wotever have said, yes, you track the increasing voltage at the lithium battery and stop when it gets to 13.8V (or whatever voltage says 80% full).

........but is that right? Peter, you say your solar charges at 13.8V and drops to 13.6 on float.....but if its charging at 13.8V, why doesnt it just turn off as that is your 'trigger' voltage? Similarly, an alternator is going to be putting in 14.4v (or whatever you set it at) so shirley the battery is not showing an increasing voltage with charge time but is showing the voltage that the charge device is giving it. What am I doing wrong?

[Detling]

I believe that the only sure way to get SOC is amp counting. Lithium is almost perfect for this, take 100 amps out and you only need to put 100.2 back unlike LA where you need to put back between 115 and 130 amps depending on type and age etc. With lithium the amp hour counter is your friend but does need to be correctly set up. Most of the ones today have various tweeks to allow for peukerts effect and the need to put in more than you take out. This is useless for lithium. A very basic amp hour meter is what you need no clever stuff. Once a month or so you need to carefully charge to a high level and than zero the amphour counter to allow for the small differences in charge that have built up over a few thousand amps in and out.

Voltage alone can be dangerous as prolonged tiny charge rates can and have damaged batteries, solar/mains float are the usual problem. When you get to your 90% plus you need to disconnect the charger and not leave it on float. (Long term storage should be below 80% anyway).

As you see they are very different to LA and just fitting them is only the start you have to relearn battery managment from the ground up. 

[MtB]

1 hour ago, Detling said:

Voltage alone can be dangerous as prolonged tiny charge rates can and have damaged batteries, solar/mains float are the usual problem. When you get to your 90% plus you need to disconnect the charger and not leave it on float.

 

This still troubles me. Peter charges at 13.8v  until 80% he says.  Peter, how do you know when 80% has been reached? 

 

But in particular, when Peter drops back to 13.6v ‘float’, surely the charge current will fall to zero as terminal voltage remains at 13.8. 

[peterboat]

3 hours ago, Dr Bob said:

 

Yes, that is my question as I wanted to understand how you know when to stop charging. From what Peter and wotever have said, yes, you track the increasing voltage at the lithium battery and stop when it gets to 13.8V (or whatever voltage says 80% full).

........but is that right? Peter, you say your solar charges at 13.8V and drops to 13.6 on float.....but if its charging at 13.8V, why doesnt it just turn off as that is your 'trigger' voltage? Similarly, an alternator is going to be putting in 14.4v (or whatever you set it at) so shirley the battery is not showing an increasing voltage with charge time but is showing the voltage that the charge device is giving it. What am I doing wrong?

 

2 hours ago, Detling said:

I believe that the only sure way to get SOC is amp counting. Lithium is almost perfect for this, take 100 amps out and you only need to put 100.2 back unlike LA where you need to put back between 115 and 130 amps depending on type and age etc. With lithium the amp hour counter is your friend but does need to be correctly set up. Most of the ones today have various tweeks to allow for peukerts effect and the need to put in more than you take out. This is useless for lithium. A very basic amp hour meter is what you need no clever stuff. Once a month or so you need to carefully charge to a high level and than zero the amphour counter to allow for the small differences in charge that have built up over a few thousand amps in and out.

Voltage alone can be dangerous as prolonged tiny charge rates can and have damaged batteries, solar/mains float are the usual problem. When you get to your 90% plus you need to disconnect the charger and not leave it on float. (Long term storage should be below 80% anyway).

As you see they are very different to LA and just fitting them is only the start you have to relearn battery managment from the ground up. 

 

31 minutes ago, Mike the Boilerman said:

 

This still troubles me. Peter charges at 13.8v  until 80% he says.  Peter, how do you know when 80% has been reached? 

 

But in particular, when Peter drops back to 13.6v ‘float’, surely the charge current will fall to zero as terminal voltage remains at 13.8. 

Right I will say it again as know one is reading it I have no alternator I charge purely of solar my controller is the best that money can buy [midnite] it charges at 13.8 volts for 50 mins then goes down to 13.6 volts float when batteries are fully charged it turns off! In the event it fails I have a an over voltage disconnect, remember I am getting ready to dump my dirty diesel and fit an electric motor, so I am seeing if solar on its own can do the job [it can] I know people think its difficult but it isnt voltage is how my BMS determines how full they are by voltage not amps

[cuthound]

10 minutes ago, peterboat said:

 

 

Right I will say it again as know one is reading it I have no alternator I charge purely of solar my controller is the best that money can buy [midnite] it charges at 13.8 volts for 50 mins then goes down to 13.6 volts float when batteries are fully charged it turns off! In the event it fails I have a an over voltage disconnect, remember I am getting ready to dump my dirty diesel and fit an electric motor, so I am seeing if solar on its own can do the job [it can] I know people think its difficult but it isnt voltage is how my BMS determines how full they are by voltage not amps

 

Out of interest how are you going to charge from solar in the winter, or is your solar array large enough to provide sufficient charge current even in the depths of winter?

[peterboat]

3 minutes ago, cuthound said:

 

Out of interest how are you going to charge from solar in the winter, or is your solar array large enough to provide sufficient charge current even in the depths of winter?

Over 2 KW about to be fitted but I do have a brand new 24 volt Whispergen ready to be fitted as well

[cuthound]

3 minutes ago, peterboat said:

Over 2 KW about to be fitted but I do have a brand new 24 volt Whispergen ready to be fitted as well

 

You shouldn't have any charging or heating problems in mid-winter then ?

[Dr Bob]

49 minutes ago, peterboat said:

 

 

Right I will say it again as know one is reading it I have no alternator I charge purely of solar my controller is the best that money can buy [midnite] it charges at 13.8 volts for 50 mins then goes down to 13.6 volts float when batteries are fully charged it turns off!.....................I know people think its difficult but it isnt voltage is how my BMS determines how full they are by voltage not amps

Peter, I am a bit confused. Yes I saw you didnt have an alternator. What I am not understanding is what 'voltage' is the BMS determining full. When your solar comes on, the voltage is 13.8v and it holds at that until full....then goes to 13.6V as a float. OK. I understand. .....but how does the solar know it is full and time to switch .....or is it the BMS that measures a voltage and then tells the solar controller to go to float. If it is the BMS, how is it getting the voltage because surely the voltage on the battery terminals is 13.8V all the time?

The same would then be true of an alternator or a land line battery charger.

[MtB]

42 minutes ago, Dr Bob said:

Peter, I am a bit confused. Yes I saw you didnt have an alternator. What I am not understanding is what 'voltage' is the BMS determining full. When your solar comes on, the voltage is 13.8v and it holds at that until full....then goes to 13.6V as a float.

 

Peter keeps subtly changing the story! 

 

In post 35 above he says the Outback solar controller charges for 50 minutes at 13.8v then reduces to 13.6v. This strikes me as wholly unsatisfactory. 

 

I suspect what actually happens is because the lithiums will soak up as much current as any charger can deliver, the charge voltage remains lower than 13.8v but climbs slowly as SoC rises. Then when the Outback finally reaches 13.8v it steps back to 13.6v. Perhaps this happens to take 50 minutes this time of year.

 

It ought really to turn OFF once 13.8v is reached (assuming 13.8v does actually correspond to 80% - but I've seen no evidence this is the case so far). 

 

 

 

Edited August 8, 2018 by Mike the Boilerman
Add a bit.

[MtB]

On 07/08/2018 at 14:31, Dr Bob said:

Daft question coming!

I've been reading all the threads on LiFePo batteries so reasonably up to speed on the technology.....but I have a question.

One of the benefits claimed is that the voltage of the lithiums doesnt vary "much" with SoC....but then here's me thinking you can still monitor SoC by looking at the 'at rest' voltage and I guess the 'smart' chargers like my victron IP22 Blue smart (when in lithium mode) are monitoring voltage when charging and deciding to switch off when a certain voltage is reached. Is the variation of lithium voltage vs SoC big enough for charge to be monitored and turned off at say 80% full.

 

Desperately trying to keep the thread on topic while people swerve it off at tangents all over the place, Dr Bob have you read the following blog?

 

https://marinehowto.com/lifepo4-batteries-on-boats/

 

This a yank with the most grating of posting styles, but having chugged through the whole blog I have to say he addresses almost all of the questions I have ever thought of about lithiums, along with a whole load of questions I hadn't thought of. ISTR last time I read it he went in to charge monitoring quite deeply but I've forgotten what he said. He NEVER says 'leave it to the BMS' in fact quite the opposite. He just doesn't trust them - with clearly stated reasons. 

 

I must read it again myself! 

[Detling]

Lithium do NOT have a float mode.  The do suggest a low constant current for the final topping off charge. Lowering the volts may help but monitoring volts and current is the only way to safely reach high SOC. You can go for many cycles between 30% and 80% without going higher if you have a good system. But every so often the BMS needs to balance the cells and the only way is either to charge to 100% or a very deep discharge(bottom balancing) which is as rare as hens teeth. The hybrid buses I know about run 30% to 70% many times a day, they stop the engine charge at 70% to allow for regenerative braking to go above. But once a month they undergo a 100% charge carefully monitored to allow the cells to be balanced, usually they are all within a few % of each other. If not they are swapped out.

 

 

[MtB]

Little snippet of wisdom from the link I posted:

 

Wallet Burns:

Since opening this article to the public I have now had what I consider a rather insane number of *LFP owners contact me who have ruined LiFePo4 batteries (not all marine based). In almost all of these cases of destroyed LiFePO4 batteries the resounding tone I hear come through is;

“People on the internet made it sound easy.“

[Dr Bob]

2 hours ago, Mike the Boilerman said:

 

Desperately trying to keep the thread on topic while people swerve it off at tangents all over the place, Dr Bob have you read the following blog?

 

https://marinehowto.com/lifepo4-batteries-on-boats/

 

This a yank with the most grating of posting styles, but having chugged through the whole blog I have to say he addresses almost all of the questions I have ever thought of about lithiums, along with a whole load of questions I hadn't thought of. ISTR last time I read it he went in to charge monitoring quite deeply but I've forgotten what he said. He NEVER says 'leave it to the BMS' in fact quite the opposite. He just doesn't trust them - with clearly stated reasons. 

 

I must read it again myself! 

Right, that's my bed time reading for tonight! Thanks for the link.

[rusty69]

1 minute ago, Dr Bob said:

Right, that's my bed time reading for tonight! Thanks for the link.

You read it first time round iirc

[Dr Bob]

2 minutes ago, rusty69 said:

You read it first time round iirc

The link!!!! Eeeeeeeeeeeeeeeeeeeejut!.......or have I read it already?

[rusty69]

7 minutes ago, Dr Bob said:

The link!!!! Eeeeeeeeeeeeeeeeeeeejut!.......or have I read it already?

Jeez Dr Bob, you read 1/2 the linked article last time it was posted in March. Maybe you just need to read the other half.  p9, post #203

 

 

Edited August 8, 2018 by rusty69

[MtB]

27 minutes ago, Dr Bob said:

The link!!!! Eeeeeeeeeeeeeeeeeeeejut!.......or have I read it already?

 

You can't have done or you would recognise the style grinding your gears....

[WotEver]

4 hours ago, Mike the Boilerman said:

It ought really to turn OFF once 13.8v is reached (assuming 13.8v does actually correspond to 80% - but I've seen no evidence this is the case so far). 

13.8V is 3.45V/cell. 14.0V is 3.5V/cell.

 

100% SoC is 3.6V/cell.

The minimum cut-off voltage is 2.8V/cell.

 

So there is a range of 0.8V from 0% to 100%.

 

80% of 0.8V is 0.64V. 2.8V + 0.64V = 3.44V.

90% of 0.8V is 0.72V. 2.8V + 0.72V = 3.52V

 

So... 13.8V (3.45V/cell) is nearasdammit 80%. 14V is nearasdammit 90%. 

 

Sufficient evidence?

 

Tony. 

[TheBiscuits]

5 minutes ago, WotEver said:

13.8V is 3.45V/cell. 14.0V is 3.5V/cell.

 

100% SoC is 3.6V/cell.

The minimum cut-off voltage is 2.8V/cell.

 

So there is a range of 0.8V from 0% to 100%.

 

80% of 0.8V is 0.64V. 2.8V + 0.64V = 3.44V.

90% of 0.8V is 0.72V. 2.8V + 0.72V = 3.52V

 

So... 13.8V (3.45V/cell) is nearasdammit 80%. 14V is nearasdammit 90%. 

 

Sufficient evidence?

 

Tony. 

Only if you believe your voltmeter calibration is accurate enough.