Another Lithium battery thread

[MoominPapa]

47 minutes ago, tree monkey said:

You could make some pocket money installing these

I have looked at the wiring of many boats, and run away screaming.

 

MP.

[Dr Bob]

35 minutes ago, tree monkey said:

You could make some pocket money installing these

They do sound really good ......which is why I am fitting them.....but they do need a lot of looking after. Mine are under the bed so each night I can read them a bed time story and tuck them up. They do need that. Peeps should not underestimate the level of knowledge needed to care for them. MP, T&B and Peterboat are experts on this type of electronics and know what they are doing. I'm initially going to run them in parallel with my lead acids so will just isolate them every time we leave the boat and maybe not even use them with the alternator in the first 1-6 months (the solar can charge them) until I know how they charge with all my different charge sources. One screw up and you could kill them. If you want an idiot proof system with little operator input then maybe these are not the answer, or you can pay Victron £6K for a system. I dont think these are for everybody.

[WotEver]

1 minute ago, MoominPapa said:

I have looked at the wiring of many boats, and run away screaming.

Me too. Guy says “Could you quickly sort out...”. I reply “Nope”. 

[tree monkey]

11 minutes ago, MoominPapa said:

I have looked at the wiring of many boats, and run away screaming.

 

12 minutes ago, Dr Bob said:

They do sound really good ......which is why I am fitting them.....but they do need a lot of looking after. Mine are under the bed so each night I can read them a bed time story and tuck them up. They do need that. Peeps should not underestimate the level of knowledge needed to care for them. MP, T&B and Peterboat are experts on this type of electronics and know what they are doing. I'm initially going to run them in parallel with my lead acids so will just isolate them every time we leave the boat and maybe not even use them with the alternator in the first 1-6 months (the solar can charge them) until I know how they charge with all my different charge sources. One screw up and you could kill them. If you want an idiot proof system with little operator input then maybe these are not the answer, or you can pay Victron £6K for a system. I dont think these are for everybody.

 

I was being slightly flippant tbh, I really struggle following these threads but am learning bits all the time, what I do know is lead acids and a simple bog standard system suits me for the time being.

 

[MoominPapa]

4 hours ago, MoominPapa said:

I have looked at the wiring of many boats, and run away screaming.

 

MP.

I should perhaps confess that the wiring on this boat is no better than it ought to be, but the difference is that I have the wiring diagram for most of it in my head (that's the only place it exists). On Other People's Boats I don't have that advantage.

 

Last year I offered to take a look at a boat which wasn't charging. It turns out that it had been built as a diesel/electric hybrid, though the electric motor had been removed. As the legacy of that, it had a 48v battery bank, charged by two 24v isolated-return alternators in series. with the centre point connected to the centre point of the bank. At first I couldn't understand why some of the batteries measured 13.8v and some measured 11.5v. I got as far as working out that the all four 12v  batteries were in series and that one alternator was not charging and then I had to politely admit defeat.

 

MP.

[Tom and Bex]

13 hours ago, sirweste said:

well lads, that was quite a read. Impressive work from the sounds of it. Having mortally wounded my 6 T-105s within 3.5 years and the cost of like for like replacement looking like ~ £900, lithium is a definite consideration. Especially as I'm a CC so never-ever have shoreline.

 

Cheers to all the contributors for an excellent on topic thread.

 

Now I need to try and make sense of it all and draft up a circuit diagram & shopping list 

Happy to comment on ideas you come up with either here or via pm. We live off grid and have to say I think the lithiums offer us a better return on investment than solar (although both together are excellent combo for off grid liveaboard). Saved a fortune in diesel over this winter, down from average of 4hrs per day to average of about an hour. 

 

5 hours ago, Dr Bob said:

They do sound really good ......which is why I am fitting them.....but they do need a lot of looking after. Mine are under the bed so each night I can read them a bed time story and tuck them up. They do need that. Peeps should not underestimate the level of knowledge needed to care for them. MP, T&B and Peterboat are experts on this type of electronics and know what they are doing.  

 

One screw up and you could kill them. If you want an idiot proof system with little operator input then maybe these are not the answer, or you can pay Victron £6K for a system. I dont think these are for everybody.

I'd hardly call myself any sort of expert! Just trying to share the knowledge I've gained over the past year or so of my research and experience. 

 

If installed correctly with the correct settings etc, they should be maintenance free - just use them and charge them as and when you want with no real worries about how they're treated - that's certainly how we use ours. There's no way my wife would put up with constant monitoring and looking after batteries - she just wants to use them!

 

Quite agree they are not for everybody, not yet anyway. I don't think they are as fragile as some seem to think. I seem to remember @peterboat has taken his quite low with no I'll effects. I would like to think our system has been designed to be idiot proof. The BMS will protect from over discharge if we ignore the monitor and alarms, and over discharge would be just as likely with lead acid. All our charging sources are set not to overcharge, and again, the BMS would protect the cells if the chargers developed a fault.

 

I think if properly installed and set up they are at least as safe as lead acid, if not safer, and less likely to be damaged. I agree it does require some basic knowledge and careful system design to achieve this though, and if you don't feel confident then you have the option of the £6k Victron system!

 

5 hours ago, WotEver said:

Me too. Guy says “Could you quickly sort out...”. I reply “Nope”. 

I've been roped into doing repairs for a couple of our neighbours recently. It's much more difficult and time consuming when faced with fault finding an unfamiliar boat, with no wiring diagram and seemingly illogical wiring colours that change half way along the loom! Both boats had a broken wire in the engine to control panel loom (along with several other faults). 

 

1 hour ago, MoominPapa said:

I should perhaps confess that the wiring on this boat is no better than it ought to be, but the difference is that I have the wiring diagram for most of it in my head (that's the only place it exists). On Other People's Boats I don't have that advantage.

 

MP.

Same here! It's amazing the difference it makes having the wiring diagram in your head! Really should get some of it onto paper at some point though - no doubt in a few years I'll start forgetting bits of it. 

 

Tom

[frahkn]

6 hours ago, Dr Bob said:

They do sound really good ......which is why I am fitting them.....but they do need a lot of looking after. Mine are under the bed so each night I can read them a bed time story and tuck them up. They do need that. Peeps should not underestimate the level of knowledge needed to care for them. MP, T&B and Peterboat are experts on this type of electronics and know what they are doing. I'm initially going to run them in parallel with my lead acids so will just isolate them every time we leave the boat and maybe not even use them with the alternator in the first 1-6 months (the solar can charge them) until I know how they charge with all my different charge sources. One screw up and you could kill them. If you want an idiot proof system with little operator input then maybe these are not the answer, or you can pay Victron £6K for a system. I dont think these are for everybody.

 

Given your somewhat on/off relationship with the gods of electricity, would it not be better to leave the care issues in the hands of Mrs Bob? If you must be adventurous perhaps a tea towel would be appropriate?

[rawsondsr]

7 hours ago, Dr Bob said:

One screw up and you could kill them

What kills lifepo4s?

[Dr Bob]

7 hours ago, frahkn said:

 

Given your somewhat on/off relationship with the gods of electricity, would it not be better to leave the care issues in the hands of Mrs Bob? If you must be adventurous perhaps a tea towel would be appropriate?

Now please don't take the Michael please Frahkn. Living on the bleeding edge can be a challenge! ?

I've got the tea towel at the ready when I start the install this weekend.

I've got one for the duck as well.?

[Dr Bob]

7 hours ago, rawsondsr said:

What kills lifepo4s?

Overcharging, undercharging, charging at low temps, mechanical damage.......

The individual cells cannot be charged over 3.8V (may get away with a smidgeon more...maybe 4.0v). So maybe you charge your 12v bank to 14.4v but what if the cells are out of balance and one gets to 4v while the rest of the bank is 3.50v? You have to be careful when you get near 100% SoC that you don't kill cells. Cell balancing becomes an issue but shouldn't be needed more than once every few years if you steer clear of 100% SoC. Some writers however do suggest getting up to 100% every 8-12weeks as they claim a memory effect!!!

Similarly at the bottom end there is a lower cell voltage which will kill a cell so no full discharge, so again unbalanced cells will be an issue. Normally run them with a SoC range of 20-80% to keep totally safe. You can push them more but maybe that will reduce total cycles.

Charging more than 0.1C at less than zero deg C will kill them. It's not clear how this varies manufacturer to manufacturer but a one off event can be fatal. At the other end thermal run away would not be good.

Mechanical damage leading to buckled plates, internal shorts etc is an issue. I am happy with them on my NB but no way would I consider using them on a light weight modern lumpy water boat. Strapping them together to avoid swelling is needed.

 

eta. That's a top level summary. Lots more detail on storage SoC etc, low temp performance etc

 

Edited February 28, 2019 by Dr Bob

[Detling]

11 hours ago, rawsondsr said:

What kills lifepo4s?

Major difference is Lead Acid is if you overcharge, or run them flat, you can with care get some useful life out of them ie you have damaged but not killed totally, Lifepo4's just die no second chances.

[Dr Bob]

Guys,

Just about to start plumbing in the new batteries and finishing a risk reveiw.

One thing that came up in the risk review is how to deal with low voltage. Now I have two levels of audible alarms and two auto disconnect measures but the issue is what voltages to set them at. I had originally thought to put the low voltage audio alarms around 13.0V and 13.1V and maybe overall voltage cut off at 12.8V and then set up the minimum cell voltage alarms at 3.0V and 2.9V with the Aussie BMS unit disconnecting at 2.6V (IIRC).

Problem is, what happens when I put the Nespresso machine on? With the lead acids currently in the morning, the voltage is normally at 12.4-12.5V and putting the nespresso machine on for its 60secs or so, the voltage drops to circa 11.4V lowest as it is drawing 150A (ish) from the 660Ahr bank. I know the lithiums will be much much more stable but how do you think the 480Ahr bank will drop in voltage. I would really like to avoid the alarms going off when using the nespresso.

Is @MoominPapa @Tom and Bexor @peterboat (or anyone else with Lithium's) about who can guesstimate what voltage drop I am likely to get, so I can set my low level alarms?

[peterboat]

1 minute ago, Dr Bob said:

Guys,

Just about to start plumbing in the new batteries and finishing a risk reveiw.

One thing that came up in the risk review is how to deal with low voltage. Now I have two levels of audible alarms and two auto disconnect measures but the issue is what voltages to set them at. I had originally thought to put the low voltage audio alarms around 13.0V and 13.1V and maybe overall voltage cut off at 12.8V and then set up the minimum cell voltage alarms at 3.0V and 2.9V with the Aussie BMS unit disconnecting at 2.6V (IIRC).

Problem is, what happens when I put the Nespresso machine on? With the lead acids currently in the morning, the voltage is normally at 12.4-12.5V and putting the nespresso machine on for its 60secs or so, the voltage drops to circa 11.4V lowest as it is drawing 150A (ish) from the 660Ahr bank. I know the lithiums will be much much more stable but how do you think the 480Ahr bank will drop in voltage. I would really like to avoid the alarms going off when using the nespresso.

Is @MoominPapa @Tom and Bexor @peterboat (or anyone else with Lithium's) about who can guesstimate what voltage drop I am likely to get, so I can set my low level alarms?

Bob 20% of full is what I would consider the low disconnect about 12 volts is safe and wont do any damage, alarm at say 12,3, so you know you have a problem. The lithiums really can hold up when you are drawing heavy amps, when my dishwasher was on this morning the bank only went down to 13.1 volts and then went back up to 13.4 as soon as the heat cycle finished

[MoominPapa]

Agree with @peterboat Your audible alarms at 13v are too high. I'm seeing resting voltages dropping to 12.9 on a 2/3rds discharged bank, and heavy load voltages going lower.

 

I have a bit of a delicate balance to strike here, since my start battery is in parallel with the lithiums. If I go too low (ie below about 12.7v) then I'll be taking charge from the starter LA battery and risk not being able to start the engine. On the other hand, the only thing my BMS can do at the bottom end is to sound an alarm and disconnect the lithiums, at which point the loads are 100% on the start battery and it will go flat anyway. I think the solution is to have two alarm levels. A disconnect to protect the lithiums at 12v or 3v per cell, and a warning beep once the voltage gets to 12.6 or 12.7 to tell me that I'm starting to eat my start battery charge. In practise, I'll know that, because I follow the state of the batteries closely, but one day I might not be there, so making the system civilian-proof would be good.

 

MP.

 

 

 

 

[Dr Bob]

1 hour ago, peterboat said:

Bob 20% of full is what I would consider the low disconnect about 12 volts is safe and wont do any damage, alarm at say 12,3, so you know you have a problem. The lithiums really can hold up when you are drawing heavy amps, when my dishwasher was on this morning the bank only went down to 13.1 volts and then went back up to 13.4 as soon as the heat cycle finished

Thanks Peter, I will use those figures until I get to grips with the way the voltages go. Good to hear the voltage drop is not too much.

 

1 hour ago, MoominPapa said:

Agree with @peterboat Your audible alarms at 13v are too high. I'm seeing resting voltages dropping to 12.9 on a 2/3rds discharged bank, and heavy load voltages going lower.

 

I have a bit of a delicate balance to strike here, since my start battery is in parallel with the lithiums. If I go too low (ie below about 12.7v) then I'll be taking charge from the starter LA battery and risk not being able to start the engine. On the other hand, the only thing my BMS can do at the bottom end is to sound an alarm and disconnect the lithiums, at which point the loads are 100% on the start battery and it will go flat anyway. I think the solution is to have two alarm levels. A disconnect to protect the lithiums at 12v or 3v per cell, and a warning beep once the voltage gets to 12.6 or 12.7 to tell me that I'm starting to eat my start battery charge. In practise, I'll know that, because I follow the state of the batteries closely, but one day I might not be there, so making the system civilian-proof would be good.

 

Thanks MP. I am leaving my 600 Ahr lead acid in to start with so will not have that issue - so I cant see mine getting down to the numbers Peter quoted but I will start with those values. If you are down to 12.9v on 33% Soc and that drops a bit more with a heavy load then that argues for Peters numbers as well.

Thanks to you both.

[Dr Bob]

Update on progress.

Started the Lithium install today.

12 * 160Ahr Thundersky 2nd hand cells in a 3 Parallel 4 Series arrangement. Constrained via Jeremy's metal straps and now the wooden box built in under the bed (easier to read them bedtime stories). As MP said early, the top of the cells is very exposed so covered with a 6mm perspex sheet, screwed down.

I've only wired in the BMV 712 shunt so far and temporarily connected the meter so I can monitor volts/amps.

Tomorrows job is to connect through to Lead acid circuit via the motorised switch and manual switch on the positive side, plus if time get the cell monitoring volt meter attached.

 

[MoominPapa]

1 hour ago, Dr Bob said:

Update on progress.

Started the Lithium install today.

12 * 160Ahr Thundersky 2nd hand cells in a 3 Parallel 4 Series arrangement. Constrained via Jeremy's metal straps and now the wooden box built in under the bed (easier to read them bedtime stories). As MP said early, the top of the cells is very exposed so covered with a 6mm perspex sheet, screwed down.

I've only wired in the BMV 712 shunt so far and temporarily connected the meter so I can monitor volts/amps.

Tomorrows job is to connect through to Lead acid circuit via the motorised switch and manual switch on the positive side, plus if time get the cell monitoring volt meter attached.

 

Point of order, Dr Bob. The jumper between the two 6v blocks should be at the other ends of the run of three terminals, for cell balance reasons. At the moment the cell with the jumper is also the cell that's connected to the next cell in series on the other side, whilst the parallel cell at the other end has the resistance of four extra straps. That will affect the current distribution between the parallel cells.

 

Does  the power wire to the shunt have a fuse in it?

 

MP.

 

[Dr Bob]

17 minutes ago, MoominPapa said:

Point of order, Dr Bob. The jumper between the two 6v blocks should be at the other ends of the run of three terminals, for cell balance reasons. At the moment the cell with the jumper is also the cell that's connected to the next cell in series on the other side, whilst the parallel cell at the other end has the resistance of four extra straps. That will affect the current distribution between the parallel cells.

 

Does  the power wire to the shunt have a fuse in it?

 

MP.

 

Ok. 

So you are saying move the connecting wire two cells to the right (both ends of it)?

I can see what you are saying. I did it this way as Jeremy had it connected this way and told me to do it this way. You can just see the white cross he made. 

I will change it over tomorrow.

Yes the BMV positive feed to the shunt has a fuse in the line- there are 2 wires to the shunt, one for the temp probe and one for the power. All set up now and alarmed. I will have to think about additional temp monitoring wires but not seen anything suitable at the moment. I need to find somewhere to mount the BMV meter and drill a big hole. Also need to tidy up the positive supply wires.

Thanks for spotting it.

 

[MoominPapa]

3 minutes ago, Dr Bob said:

Ok. 

So you are saying move the connecting wire two cells to the right (both ends of it)?

I can see what you are saying. I did it this way as Jeremy had it connected this way and told me to do it this way. You can just see the white cross he made. 

I will change it over tomorrow.

Yes the BMV positive feed to the shunt has a fuse in the line- there are 2 wires to the shunt, one for the temp probe and one for the power. All set up now and alarmed. I will have to think about additional temp monitoring wires but not seen anything suitable at the moment. I need to find somewhere to mount the BMV meter and drill a big hole. Also need to tidy up the positive supply wires.

Thanks for spotting it.

 

Yes, two cells to the right. If you rotate one of your blocks of cells by 180 degrees, you can avoid the jumper cable crossing or getting near to any other terminals. I chose to orientate mine with the external connections and the jumper connections on the "inside", but you could do it just as well with them on the outside. Check back in this thread for photos. I think it's potentially important to have the wiring maintain the cell balance in the 3P blocks. The principle is exactly the same as when connecting 12v batteries in parallel and was thoroughly worked out on the forum in the days of Gibbo.

 

MP

 

[WotEver]

10 hours ago, MoominPapa said:

The principle is exactly the same as when connecting 12v batteries in parallel and was thoroughly worked out on the forum in the days of Gibbo.

http://www.smartgauge.co.uk/batt_con.html

[Dr Bob]

The continuing stoooooory of a quack who's gone boldly where no man has gone before - apart from Peter, Tom and MP, etc.

An update on progress and some intial thoughts. I know this has drifted a bit from the intial intention of the thread.....but I started it so......! This maybe useful for anyone following on behind and I know I will get a steer if the experts think I am doing it wrong.

Just to recap, I have put in a 'simple' system with the Li's piggy backing on my 660Ahrs of existing (good condition 2 year old cheapie LA's). Installation so far has been straightforward as all I am doing is adding extra wires and stuff to my existing battery system. I am not replacing anything and one switch turns it back to what it was (except changing the settings on all the charge devices but lets come to that next week). Over the weekend, I boxed in the batteries and yesterday got the +ve and -ve links in between the two banks, the positive line having a fuse, a motorised switch and a manual switch. It took about 4M of 50mm cable to reach the LA shunt and the Invertor 12v +ve connection. Maybe that will give a bit of a voltage drop but that is positive as it means less voltage charge. (Overcharging is my main 'worry').

So last night once the solar had given up, I turned off the shore power, turned the inverter on and turned the Li's on. Total bank voltage at 13.24V. Turned all the TV gubbins on an -10A out. Voltage dropped about 0.1V. I will keep an eye on the difference between loaded voltage and at rest. I read them a bedtime story, ' Where the wild things are' and then went to bed. This morning they were at around 13.13V with 5A out with 90Ahrs total out - so I have managed to get them to lower than 80% SoC. I wont know the full state of charge 'till I charge them back to full. The duck liked the story too. I have got the 'The tiger who came to tea' tonight. The interesting bit was Mrs Bobs 2 cups of Nespresso coffee this morning. 100A (ish) out and the voltage droped to 12.75V on the Li's. That helps me understand my lower voltage level. Thinking about it, once the voltage gets down to 12.7V, the LA bank will start delivering power, which in this case of 100A discharge for 60 secs it did. The LA bank is 660Ahrs so that will tend to stabilise the voltage drop, so maybe if the LA bank is always full, I will not see voltages lower than 12.7V unless they are also depleted. Once the nespresso was turned off, the lithium bank had 10A going into the LA bank which decayed over 10 mins to zero as the Li's replaced the charge that the LA's had lost ( I ran the nespresso 3 times in total).

This morning I disconnected the bank and went back onto the LA's with shore power on - to use the immersion. Job today is to wire in the cell monitoring/alarm device so I can easily see the cell voltages.

First impression from last night is great. We always see the LED cabin lights changing when the toilet is flushed (with the vacuum pump and water pump activated). No trace of that last night. Looks like the electrics are far happier sitting at a stable 13.2V rather than the 12.5V we normally see in the evenings.

I'm happier now I have the Li's lower than 80% SoC.

[MoominPapa]

We're hanging out in the Leicester Line, taking it slow and easy. 

 

The last time our batteries were at 100% SOC was just as we arrived into Market Harborough, a week ago. Since then they've been moving between 80Ah down and 250Ah down. Doing that to LA batteries is Not Good (though we did used to do it, which is one reason why we broke them regularly). The Lithiums are happy to be treated like that, and working well.

 

MP.

 

ETA. the lowest they've ever gone is 320Ah down (on 480Ah bank.) I'm keen to explore the lower reaches of SOC, but need a convenient time, when it will be easy to recharge once we hit the "this far but no farther" point.

Edited March 5, 2019 by MoominPapa

[Dr Bob]

On 05/03/2019 at 14:38, MoominPapa said:

The last time our batteries were at 100% SOC was just as we arrived into Market Harborough, a week ago. Since then they've been moving between 80Ah down and 250Ah down. Doing that to LA batteries is Not Good (though we did used to do it, which is one reason why we broke them regularly). The Lithiums are happy to be treated like that, and working well.

 

MP.

 

ETA. the lowest they've ever gone is 320Ah down (on 480Ah bank.) I'm keen to explore the lower reaches of SOC, but need a convenient time, when it will be easy to recharge once we hit the "this far but no farther" point.

Thanks MP.

I've now got most of the wiring done - everything except wiring the auto disconnect - the job for tomorrow. Over the past 2 nights I discharged down to around 230Ahrs out so SoC about 50%. Today I charged them up at 60-80A in 2 hours with the victron combi - they just gobble up the power - and then changed to the IP22 for 90 mins and watched the charge current drop from 30A to 12A - at which point the overall voltage was 14.06V, so I turned the charger off.

The individual cells at the end were c1 3.501V, c2 3.551V, c3 3.518V and c4 3.491V

Cell 2 looked like it was on a mission to win. A little bit of cell balancing needed then. C1 had been the laggard before and during the charging but C4 fell back quite quickly at the end. Not sure how normal that is?

A question then, to balance the cells I have two routes. First, put a known load across one cell for a specific time. I have a 10A load (at 3.3V). It looks like I only need to take 1Ahr out of the high cell as that is the Ahrs per cell put in in the time period between the time the high cell got to a set voltage and the time the median cells got to that voltage. Is that logic correct? Does around 1Ahr sound about right?

The other route is let the cell monitoring meter do it - it claims it can balance but cant see how that works as the laggard cell at the end of charge was not the lowest at the start of the charge. MP, I know you used a self balancing function, did you do it during a discharge or charge cycle?

[MoominPapa]

2 hours ago, Dr Bob said:

Thanks MP.

I've now got most of the wiring done - everything except wiring the auto disconnect - the job for tomorrow. Over the past 2 nights I discharged down to around 230Ahrs out so SoC about 50%. Today I charged them up at 60-80A in 2 hours with the victron combi - they just gobble up the power - and then changed to the IP22 for 90 mins and watched the charge current drop from 30A to 12A - at which point the overall voltage was 14.06V, so I turned the charger off.

The individual cells at the end were c1 3.501V, c2 3.551V, c3 3.518V and c4 3.491V

Cell 2 looked like it was on a mission to win. A little bit of cell balancing needed then. C1 had been the laggard before and during the charging but C4 fell back quite quickly at the end. Not sure how normal that is?

A question then, to balance the cells I have two routes. First, put a known load across one cell for a specific time. I have a 10A load (at 3.3V). It looks like I only need to take 1Ahr out of the high cell as that is the Ahrs per cell put in in the time period between the time the high cell got to a set voltage and the time the median cells got to that voltage. Is that logic correct? Does around 1Ahr sound about right?

The other route is let the cell monitoring meter do it - it claims it can balance but cant see how that works as the laggard cell at the end of charge was not the lowest at the start of the charge. MP, I know you used a self balancing function, did you do it during a discharge or charge cycle?

 

Based on what you said, 1Ah  is believe-able. They are clearly pretty well balanced.

 

As for automatic balancing, I have implemented that during charging, but I'm not sure how effective it is - as you say the imbalance really only becomes obvious at the end of the charge cycle. Auto balancing during discharge is dangerous. You can end up doing the battery equivalent of salami-slicing the legs off a table whilst trying to stop it wobbling. I only have manual balancing during discharge.

 

My cells seem to be subtly different from each other One is always the first to start to rise as charging terminates, another always lags in cell voltage during charging  (but not discharge), and a third sags more under heavy discharge than the others. I have no idea what that means, if anything.

 

Interesting that you got the current down to 12A. I'm seeing the same end voltage but terminating at C/20, ie 24A. Maybe I should keep going a little and see how fast the current drops.

 

MP.

 

[Dr Bob]

1 hour ago, MoominPapa said:

 

Based on what you said, 1Ah  is believe-able. They are clearly pretty well balanced.

 

 

 

My cells seem to be subtly different from each other One is always the first to start to rise as charging terminates, another always lags in cell voltage during charging  (but not discharge), and a third sags more under heavy discharge than the others. I have no idea what that means, if anything.

 

 

Interesting that you got the current down to 12A. I'm seeing the same end voltage but terminating at C/20, ie 24A. Maybe I should keep going a little and see how fast the current drops.

 

MP.

 

Do you think they are well balanced? I was worrried one shot off too quickly. If I stop charging at 13.8-9v then they do look ok.

 

Just from the one charge cycle, I can see my 4 cells are different. They behave very differently if under charge or not, i.e. their rate of change is different. I think I will give them names. I read them " the hungry caterpillar" tonight. The duck went looking for one.

 

Yes, I was surprised the Amps dropped that fast, it was using the Victron IP22 30A charger, yet 3.55v seems quite low for 100% charge. I'll try to take 1Ahr out of cell 2 in the morning and then recharge to see if I can balance a bit better then try and run for 3-4 days at 30-80% SoC. 

Ive set the solar up for absorption at 13.9v with a float of 13.2v (can't turn it off) and that seemed fine today. The victron IP22 was in lithium mode and was merrily still in absorption when I turned it off. I must get the disconnect to work tomorrow.

Thanks for the help MP.

 

 

eta... just re-read your post and 3 of your cells sound exactly like mine! Maybe this is a new hobby....classifying LiFePo4 cells.

Edited March 6, 2019 by Dr Bob