Cheap LiFePO4 BMS?

[George and Dragon]

On 05/11/2019 at 02:00, Tom and Bex said:

We've managed over 12 months and not managed to kill our lithiums yet! Our last set of LA's were down to under 50% capacity after just 12 months. 

 

Sorry for coming to this thread very late (this is page 16 of 58) so there are doubtless responses to this that might tell me more, but how do you kill lithiums other than by charging them below 0 degrees C?

[WotEver]

6 minutes ago, George and Dragon said:

how do you kill lithiums other than by charging them below 0 degrees C?

By discharging them too low or by overcharging them. 

You only have to do either of those once. 

[peterboat]

7 hours ago, magnetman said:

I am specifically looking to make myself a portable mains energy storage package. 

 

I won't need it in summer, can just use it as an extra power pack for my electric canoe and recharge on solar, but for winter when I am unwilling to run the engine solely to generate power it makes sense to import the stored mains electric and use it over the weekend that I am on the boat. 

 

The RC hobby chargers seem to have programmable limits on voltage so I think I would trust it not to over charge. And i'd be on top of the thing when discharging anyway so can do manual management and like I said the mppt  LVC via a relay and solenoid would probably sort the low voltage problem fairly reliably. 

 

And I'm not buying used batteries. 

 

It's an unusual way to do if but I reckon it'll work. 

 

 

 

 

 

 

 

Fit a battery balance board or buy a valance battery otherwise irs bound to go wrong 

9 minutes ago, WotEver said:

By discharging them too low or by overcharging them. 

You only have to do either of those once. 

When I purchased my valence 36 volt batteries some were flat as pancakes! All bar 3 charged up okay so I have to say that while some might be rubbish some aren't 

[nicknorman]

29 minutes ago, George and Dragon said:

Sorry for coming to this thread very late (this is page 16 of 58) so there are doubtless responses to this that might tell me more, but how do you kill lithiums other than by charging them below 0 degrees C?

Yes over charging or over discharging, but that is on a per cell basis, not necessarily the whole battery (comprising 4 cells in series). Unlike lead acid, when a Li cell is full it doesn’t want to pass any more current, instead it’s voltage rises and it gets damaged. So if the maximum cell voltage is say 3.65, 4 such cells in series = 14.6v. So you have a 14.6v charger, what could possibly go wrong?

 

Well if the cells aren’t in exactly the same state of charge with exactly the same capacity, it’s quite likely that say 3 cells will still be charging at say 3.4v, whilst one cell has reached full and wants no more. So its voltage jumps up to make the difference (this is called moving up the “knee”)  ie its voltage is now 14.6 - (3.4v x 3) = 4.4v. You have just killed it!

 

The same kind of thing applies if you over discharge, one cell will plummet and be damaged even though the overall battery voltage isn’t too low.

 

This is why either you, or a BMS, has to monitor individual cell voltages and disconnect the charge or discharge before any one cell reaches a critically high or low voltage.

[Dr Bob]

1 hour ago, nicknorman said:

Yes over charging or over discharging, but that is on a per cell basis, not necessarily the whole battery (comprising 4 cells in series). Unlike lead acid, when a Li cell is full it doesn’t want to pass any more current, instead it’s voltage rises and it gets damaged. So if the maximum cell voltage is say 3.65, 4 such cells in series = 14.6v. So you have a 14.6v charger, what could possibly go wrong?

 

Well if the cells aren’t in exactly the same state of charge with exactly the same capacity, it’s quite likely that say 3 cells will still be charging at say 3.4v, whilst one cell has reached full and wants no more. So its voltage jumps up to make the difference (this is called moving up the “knee”)  ie its voltage is now 14.6 - (3.4v x 3) = 4.4v. You have just killed it!

 

The same kind of thing applies if you over discharge, one cell will plummet and be damaged even though the overall battery voltage isn’t too low.

 

This is why either you, or a BMS, has to monitor individual cell voltages and disconnect the charge or discharge before any one cell reaches a critically high or low voltage.

So keep them between 20% charged and 80% charged and you will all have a happy life. Siiimple.

[peterboat]

20 minutes ago, Dr Bob said:

So keep them between 20% charged and 80% charged and you will all have a happy life. Siiimple.

Wot like wot we dus? The problem then is Bob that for Andrew it means his 40 ah battery is 20 odd ah ruining his plan! I honestly think that the idea is a waste of time and money 

[Murflynn]

9 hours ago, Dr Bob said:

So keep them between 20% charged and 80% charged and you will all have a happy life. Siiimple.

that is 60% useful capacity ...........................   so there is not really a huge advantage in that respect over LA's that are used between 50% and 100%.

 

apart from the weight issue, I am again beginning to lose confidence in the alleged benefits of Lifepo4.

[magnetman]

12 minutes ago, Murflynn said:

that is 60% useful capacity ...........................   so there is not really a huge advantage in that respect over LA's that are used between 50% and 100%.

 

apart from the weight issue, I am again beginning to lose confidence in the alleged benefits of Lifepo4.

For your boat you may as well stick with lead acid. Weight isn't really that important and I don't think the charging points on the River will allow a rapid recharge anyway which is one of the key advantages of lithium batteries. 

 

So if weight is of no concern and charging power is limited then just use AGM batteries. 

 

 

 

 

[Dr Bob]

13 minutes ago, Murflynn said:

that is 60% useful capacity ...........................   so there is not really a huge advantage in that respect over LA's that are used between 50% and 100%.

 

apart from the weight issue, I am again beginning to lose confidence in the alleged benefits of Lifepo4.

I don't see the weight or capacity as things to get excited about.

The two benefits that make them essential for me are

- never having to try to get them full again and

- they take all the power you throw at them until  nearly full ......

which means in our case reducing engine hours by 50% to charge.

Once you get into your routine they are fit and forget.

[BEngo]

Even that  10% extra is worth having.  It means the difference between 240 Ah and 200 Ah useable in a typical 400 Ah set up. That is a 20% increase in useable. And Don't forget cycle life.  Better than even traction LA batteries so through life cost lowered.

 

N

[Dr Bob]

1 minute ago, BEngo said:

Even that  10% extra is worth having.  It means the difference between 240 Ah and 200 Ah useable in a typical 400 Ah set up. That is a 20% increase in useable. And Don't forget cycle life.  Better than even traction LA batteries so through life cost lowered.

 

N

Cycle life is all tied up in the cost benefit so may not be that attractive or at this point in time a believable benefit. Not having to faff around replacing batteries is a good benefit though.

One useful benefit is that your electrics are operating at 12.8 to 13.4 volts all of the time...rather than down at the 12.0-12.3V range which you get with LAs under load. Water pumps, ebersparkythingies, etc work much better at 13V.....but I just see this a nice to have.

[magnetman]

Interesting on the GWL power website (Czech) they have some monolithic LFP blocks which they claim do not require balancing . 

 

https://shop.gwl.eu/LiFeYPO4-batteries-12V-1-1/Lithium-Battery-12V-90Ah-WB-LP12V90AH.html

and a bit of discussion where they admit that some users have had the top off. 

 

 https://gwl-power.tumblr.com/post/2173754848/faq-12v-monolithic-batteries-balancing-and

[peterboat]

42 minutes ago, magnetman said:

Interesting on the GWL power website (Czech) they have some monolithic LFP blocks which they claim do not require balancing . 

 

https://shop.gwl.eu/LiFeYPO4-batteries-12V-1-1/Lithium-Battery-12V-90Ah-WB-LP12V90AH.html

 

and a bit of discussion where they admit that some users have had the top off. 

 

 https://gwl-power.tumblr.com/post/2173754848/faq-12v-monolithic-batteries-balancing-and

Andrew buy a valance battery from James I will have a word with him if you want?

[nicknorman]

1 hour ago, Murflynn said:

that is 60% useful capacity ...........................   so there is not really a huge advantage in that respect over LA's that are used between 50% and 100%.

 

apart from the weight issue, I am again beginning to lose confidence in the alleged benefits of Lifepo4.

I think this 20-80% thing is in danger of becoming the standard, which is a shame because it wastes 40%. The main reason for the 20-80% thing is because people have cobbled together systems that aren’t really doing the job properly or efficiently. I appreciate that is isn’t easy to do it properly but surely in the not too distant future someone will come up with a robust system that allows fully capacity to be used. Well I certainly will, but not commercially.

[Murflynn]

1 hour ago, BEngo said:

Even that  10% extra is worth having.  It means the difference between 240 Ah and 200 Ah useable in a typical 400 Ah set up. That is a 20% increase in useable. And Don't forget cycle life.  Better than even traction LA batteries so through life cost lowered.

 

N

even I can do the maths, thank you.

 

just sayin' that in my case (not living aboard, trailable cruiser used for several short trips every year charging at hook-up points every night) the lithium solution does not really stack up.  My LA's typically last 4 years, using the cheapest batteries I can find, and cost about £300 to replace. 

 

Magnetman's advice (he knows my  boat) seems to be the realistic viewpoint.   Yes, I would like my boat to weigh 100kg less when launching and retrieving, but apart from that it just isn't worth the hassle.

[peterboat]

4 minutes ago, nicknorman said:

I think this 20-80% thing is in danger of becoming the standard, which is a shame because it wastes 40%. The main reason for the 20-80% thing is because people have cobbled together systems that aren’t really doing the job properly or efficiently. I appreciate that is isn’t easy to do it properly but surely in the not too distant future someone will come up with a robust system that allows fully capacity to be used. Well I certainly will, but not commercially.

I hate to say this Nick but car makers use 20 to 80% as well, Nissan leafs are an example why, short battery life due to charging to 100%! Vauxhall Amperas have a usable 16kwh pack but only use 11kwh if my memory is correct, Tesla you have to press a button to charge beyond 80% and do it to often and your warranty is compromised.  

[peterboat]

17 minutes ago, Murflynn said:

even I can do the maths, thank you.

 

just sayin' that in my case (not living aboard, trailable cruiser used for several short trips every year charging at hook-up points every night) the lithium solution does not really stack up.  My LA's typically last 4 years, using the cheapest batteries I can find, and cost about £300 to replace. 

 

Magnetman's advice (he knows my  boat) seems to be the realistic viewpoint.   Yes, I would like my boat to weigh 100kg less when launching and retrieving, but apart from that it just isn't worth the hassle.

From my experience I would not be able to make my boat work for me using my old LA traction batteries, charging is to slow using solar.  Also the weight issue and maintenance are rubbish, LAs are pointless given their limitations  for my sort of usage 

[magnetman]

What did you say your cruise wattage was 3.2kw or something? 

 

 

[MoominPapa]

38 minutes ago, nicknorman said:

I think this 20-80% thing is in danger of becoming the standard, which is a shame because it wastes 40%. The main reason for the 20-80% thing is because people have cobbled together systems that aren’t really doing the job properly or efficiently. I appreciate that is isn’t easy to do it properly but surely in the not too distant future someone will come up with a robust system that allows fully capacity to be used. Well I certainly will, but not commercially.

Agreed. Given how expensive capacity is in LiFePO4, it's crazy to waste it or over-buy by using a non-optimal control system.

 

MP.

 

ETA, also in practice to use all the capacity of a bank, you need accurate metering. You can't wait 'till tomorrow to charge when the batteries are down to 30% unless you can be sure that the 30% number is accurate, and the lights are not going to go off in the middle of the evening.

Edited September 10, 2020 by MoominPapa

[magnetman]

24 minutes ago, Murflynn said:

even I can do the maths, thank you.

 

just sayin' that in my case (not living aboard, trailable cruiser used for several short trips every year charging at hook-up points every night) the lithium solution does not really stack up.  

Out of interest do you know what rating the EA charging points have at the moment? I've got a feeling it's a 6a thing but could well be more. 

 

It would make a difference to the viability of larger electric boats with lithium batteries / fast charge availability. 

[peterboat]

8 minutes ago, magnetman said:

What did you say your cruise wattage was 3.2kw or something? 

 

 

3.3 Kw so I have 10 hours of cruising, but sun shining increases it or in some cases covers it

[Dr Bob]

34 minutes ago, nicknorman said:

I think this 20-80% thing is in danger of becoming the standard, which is a shame because it wastes 40%. The main reason for the 20-80% thing is because people have cobbled together systems that aren’t really doing the job properly or efficiently. I appreciate that is isn’t easy to do it properly but surely in the not too distant future someone will come up with a robust system that allows fully capacity to be used. Well I certainly will, but not commercially.

 

24 minutes ago, peterboat said:

I hate to say this Nick but car makers use 20 to 80% as well, Nissan leafs are an example why, short battery life due to charging to 100%! Vauxhall Amperas have a usable 16kwh pack but only use 11kwh if my memory is correct, Tesla you have to press a button to charge beyond 80% and do it to often and your warranty is compromised.  

Yes, my Tesla does have dire warnings about charging to 100% all the time and the sophisticated charging regimes it allows keeps charging rate low once over 80%. For example, when I turn up at a motorway service charger with 20% SoC, the charger whacks the power in at 140KW but by the time its up to 80% that is reduced to 50KW. The Li bank is 10 times the size of the one on my boat and to warrant the batteries for 8 years (assuming 20% loss of capacity in that time) you need to follow the instructions.

For a narrowboat the power duty is soooooo... much lower so I suppose you can take it up to 100% a lot more often but we dont really know what the lifetime will be for doing this every 'cycle'. My guess is that they will last 10 years wotever we do but there is more to go wrong by taking them up to 100% and safety is a big issue for me.

Nick is right about our cobbled together systems and Cars can do it to 100% because they have idiot proof systems that are well beyond the most of us, but I would prefer to play the safety card and keep below 80%.

[peterboat]

1 minute ago, Dr Bob said:

 

Yes, my Tesla does have dire warnings about charging to 100% all the time and the sophisticated charging regimes it allows keeps charging rate low once over 80%. For example, when I turn up at a motorway service charger with 20% SoC, the charger whacks the power in at 140KW but by the time its up to 80% that is reduced to 50KW. The Li bank is 10 times the size of the one on my boat and to warrant the batteries for 8 years (assuming 20% loss of capacity in that time) you need to follow the instructions.

For a narrowboat the power duty is soooooo... much lower so I suppose you can take it up to 100% a lot more often but we dont really know what the lifetime will be for doing this every 'cycle'. My guess is that they will last 10 years wotever we do but there is more to go wrong by taking them up to 100% and safety is a big issue for me.

Nick is right about our cobbled together systems and Cars can do it to 100% because they have idiot proof systems that are well beyond the most of us, but I would prefer to play the safety card and keep below 80%.

I don't think any of the car makers charge to 100% on a regular basis after the leaf issues of course the real issue was was passive heating and cooling, the new SUV has gone for a much more sophisticated system.  For us boat users their is no need to stress our batteries its pointless and as you have said possibly unsafe. My new car batteries will be charged to the same routine for the same reason 

[nicknorman]

41 minutes ago, peterboat said:

I hate to say this Nick but car makers use 20 to 80% as well, Nissan leafs are an example why, short battery life due to charging to 100%! Vauxhall Amperas have a usable 16kwh pack but only use 11kwh if my memory is correct, Tesla you have to press a button to charge beyond 80% and do it to often and your warranty is compromised.  

Yes I know, but the usage pattern is much harsher and any slight loss of ability to deliver high currents is untenable.

 

I am sure that charging to 100% does reduce life. But when that life is so long, does it matter? And does cost of the life reduction exceed the cost of the additional 40% of capacity that one has to purchase in order to only use the 20-80% regime? I don’t think we know.
 

In my case I will be charging to 80% when planning to cruise the next day, and to 100% when not planning to cruise the next day. And 50% when leaving the boat. The occasional charge to 100% is necessary for top balancing and to reset the Ah counter.

[magnetman]

30 minutes ago, peterboat said:

3.3 Kw so I have 10 hours of cruising, but sun shining increases it or in some cases covers it

You've got 33kwh of battery? That's impressive !! You could set yourself up as a charging station for small boats