An affordable way to fit Lithium Batteries?

[MoominPapa]

1 minute ago, nicknorman said:

So you would select 80% or whatever if it was just an overnight stop, and 100% if the intention was to tie up for a few days.

That's exactly how it works. Having more options than 100% and 80% seemed like needless over-complication.

 

MP.

 

[nicknorman]

7 minutes ago, MoominPapa said:

That's exactly how it works. Having more options than 100% and 80% seemed like needless over-complication.

 

MP.

 

Yes just a switch would do it in terms of HMI.

[Dr Bob]

3 hours ago, nicknorman said:

I just bought a small 7.5AH 12v (nominal) LiFePO4 battery for a glider. The low voltage disconnect is 10v, the recommended charge voltage is 14.4v and it claims more than 3000 full depth cycle life. I therefore wonder if all this fuss about keeping between 20% and 80% SoC is actually that important. No doubt it will give better cycle life but when the worst case cycle life is already 3000, how much does it matter?

I guess the 14.4v is to get up to full charge quickly. I think you are right that they will still last long enough for us if charged to 100% all the time but aiming for 80% is more about avoiding overcharging......i.e. not having to think about them. In the winter I will probably spend more time thinking about power and get them up to 100% more often.....

The 80% 'limit' for me is more about 'fit and forget'. It seems to be working!

Best of luck with the glider system!

[WotEver]

Haven’t I read somewhere that charging to 100% increases the odds of imbalance?

[Alfabiker]

Just coming back to my original post for a moment, I don't have a separate alternator controller, but my alternator (70A on a Beta 38) does produce 14.4 volts anyway, I wasn't really concerned that I wouldn't manage to charge an LI battery sufficiently.  It was rather that the low resistance of an Li battery might cause the charging current to rise too much and overheat the controller (I assume that the resistance does rise as charge increases though?)

 

But again, there don't seem to be any caveats about this in relation to "drop-in" LI batteries so what is the story here?

[Alfabiker]

sorry I meant "overheat the alternator" of course!

[peterboat]

16 hours ago, nicknorman said:

I just bought a small 7.5AH 12v (nominal) LiFePO4 battery for a glider. The low voltage disconnect is 10v, the recommended charge voltage is 14.4v and it claims more than 3000 full depth cycle life. I therefore wonder if all this fuss about keeping between 20% and 80% SoC is actually that important. No doubt it will give better cycle life but when the worst case cycle life is already 3000, how much does it matter?

The batteries I have just collected were in some cases down to 2.7 volts and some nearly fully charged  [36 volt batteries] they have all charged back up, and the BMSs reset, how this low voltage and full charges over their previous lives have affected their life only time will tell? However when I charged them up I managed to put over 32 KWHs into them in total  [new they are nearly 1.2 KWHs per battery]

[peterboat]

1 hour ago, Alfabiker said:

Just coming back to my original post for a moment, I don't have a separate alternator controller, but my alternator (70A on a Beta 38) does produce 14.4 volts anyway, I wasn't really concerned that I wouldn't manage to charge an LI battery sufficiently.  It was rather that the low resistance of an Li battery might cause the charging current to rise too much and overheat the controller (I assume that the resistance does rise as charge increases though?)

 

But again, there don't seem to be any caveats about this in relation to "drop-in" LI batteries so what is the story here?

In my case they charge with full amps until full [13.9volts] then drop into absorb at a very low amps then float at 13.7 volts, I only have solar and the whispergen to charge both banks [I have a leisure to drive battery charger 24 volts to 80 volts]

[peterboat]

15 hours ago, MoominPapa said:

That's exactly how it works. Having more options than 100% and 80% seemed like needless over-complication.

 

MP.

 

 

13 hours ago, Dr Bob said:

I guess the 14.4v is to get up to full charge quickly. I think you are right that they will still last long enough for us if charged to 100% all the time but aiming for 80% is more about avoiding overcharging......i.e. not having to think about them. In the winter I will probably spend more time thinking about power and get them up to 100% more often.....

The 80% 'limit' for me is more about 'fit and forget'. It seems to be working!

Best of luck with the glider system!

 

1 hour ago, WotEver said:

Haven’t I read somewhere that charging to 100% increases the odds of imbalance?

I am staying at 80% regardless it really does avoid imbalance and my system is really easy to check with the laptop, however I havent been bothering as the system stays good at the 80% capacity, as Tony says 100% can cause issues

[Dr Bob]

5 hours ago, WotEver said:

Haven’t I read somewhere that charging to 100% increases the odds of imbalance?

....ah yes. That was the other reason I keep below 80%.  ?

If you are going up to 100% you do need to watch the individual cell voltages.

[nicknorman]

9 hours ago, WotEver said:

Haven’t I read somewhere that charging to 100% increases the odds of imbalance?

I don’t think it increases the chance of imbalance but it does mean that imbalance becomes a potentially critical issue. But then a decent BMS should go some way to helping maintain balance, and ultimately isolating the battery before critical overcharging of a cell occurs.

[Dr Bob]

2 hours ago, nicknorman said:

I don’t think it increases the chance of imbalance but it does mean that imbalance becomes a potentially critical issue. But then a decent BMS should go some way to helping maintain balance, and ultimately isolating the battery before critical overcharging of a cell occurs.

The snag is that you dont see the imbalance at the lower state of charge. On mine it only shows up when I take it over 95% SoC....which I do every few months to reset the AmpHr counter and to stop the mythical memory effect. Charging to 100% shows up an inbalance if it is present. I am not sure there is enough info on the web to explain why inbalances occur in the real world.

[MoominPapa]

10 hours ago, Dr Bob said:

The snag is that you dont see the imbalance at the lower state of charge. On mine it only shows up when I take it over 95% SoC....which I do every few months to reset the AmpHr counter and to stop the mythical memory effect. Charging to 100% shows up an inbalance if it is present. I am not sure there is enough info on the web to explain why inbalances occur in the real world.

Real-world imbalances are just down to the fact that the cells are not completely identical, I think. I tend to side with Nick on this one: restricting maximum charge doesn't make much difference to the rate imbalance builds up, but it does avoid its consequence: over-voltage of one cell at full charge (or under-voltage is discharge.) the problem is that the imbalance happens at both ends: restricting the range to 20% to 80% means you're only using just over half of the battery you paid for.

 

MP.

  

[Dr Bob]

5 hours ago, MoominPapa said:

Real-world imbalances are just down to the fact that the cells are not completely identical, I think. I tend to side with Nick on this one: restricting maximum charge doesn't make much difference to the rate imbalance builds up, but it does avoid its consequence: over-voltage of one cell at full charge (or under-voltage is discharge.) the problem is that the imbalance happens at both ends: restricting the range to 20% to 80% means you're only using just over half of the battery you paid for.

 

MP.

  

Yep agreed. I successfully rebalanced mine a few months back as they were a bit out (one cell up by 60Ahrs) the first time in 3 months I took them back to 100%. Took em back to 100% this week and they are balanced fine. Typically <10mV delta top to bottom regardless of charge or draw now I'm below 90% again.

 

I've been doing a bit of reading on the memory effect and wonder if this could also be a reason for an individual cell to stop taking charge so throwing out the balance. Couple of links below. The cruiser forum one is 470 pages long and has spawned a 'memory effect' thread in the last year.......cant find it again at the moment. Seems like a couple of guys on the cruiser forum are seeing something that could be a memory effect but the data is all over the place and that forum is as bad as this one for trying to get to the bottom of something . The last 5 pages of the Crusier forum thread have a link somewhere.

 

http://www.cruisersforum.com/forums/f166/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069.html

https://phys.org/news/2013-04-memory-effect-lithium-ion-batteries.html

 

 

[MoominPapa]

39 minutes ago, Dr Bob said:

Yep agreed. I successfully rebalanced mine a few months back as they were a bit out (one cell up by 60Ahrs) the first time in 3 months I took them back to 100%. Took em back to 100% this week and they are balanced fine. Typically <10mV delta top to bottom regardless of charge or draw now I'm below 90% again.

 

I've been doing a bit of reading on the memory effect and wonder if this could also be a reason for an individual cell to stop taking charge so throwing out the balance. Couple of links below. The cruiser forum one is 470 pages long and has spawned a 'memory effect' thread in the last year.......cant find it again at the moment. Seems like a couple of guys on the cruiser forum are seeing something that could be a memory effect but the data is all over the place and that forum is as bad as this one for trying to get to the bottom of something . The last 5 pages of the Crusier forum thread have a link somewhere.

 

http://www.cruisersforum.com/forums/f166/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069.html

https://phys.org/news/2013-04-memory-effect-lithium-ion-batteries.html

 

 

My superficial understanding of this "memory effect" is that it's an interaction with the charging algorithm. Lithium ions which are deep within the electrodes (massive oversimplification) need more voltage to move them. If you stop charge a lowish voltage, the deeply-buried lithium never gets shifted, and a little more gets buried on each charge, so the true state of charge when the cut-off voltage is reached is slightly smaller each cycle. Getting cells up to 3.50v is enough to avoid the problem by getting to the deeply-buried ions, which is why I do that.

 

Reference:

 

https://makermax.ca/2019/08/lithium-battery-memory-effect/

 

MP.

 

 

[Dr Bob]

6 minutes ago, MoominPapa said:

My superficial understanding of this "memory effect" is that it's an interaction with the charging algorithm. Lithium ions which are deep within the electrodes (massive oversimplification) need more voltage to move them. If you stop charge a lowish voltage, the deeply-buried lithium never gets shifted, and a little more gets buried on each charge, so the true state of charge when the cut-off voltage is reached is slightly smaller each cycle. Getting cells up to 3.50v is enough to avoid the problem by getting to the deeply-buried ions, which is why I do that.

 

Reference:

 

https://makermax.ca/2019/08/lithium-battery-memory-effect/

 

MP.

 

 

Yes, that's pretty much the same as other papers on it. These all show the voltage of a single cell. I wonder if you can get this effect on one or two of a 4 cell system (ie a 12V bank) but not in the other two. If you charge to say 80% SoC on each cycle, is it possible that the lowest of the 4 cells (by voltage) sees more of a memory effect so increasing the inbalance. As cycles go by, this effect could then change the Ahrs going into each cell and you get a big inbalance next time you take the whole bank up to 100%. I reckon in the first 3 months of running mine, I did 80 or so partial cycles up to 80% ish.

Its not an issue for me....just interested to understand what can affect the cells. As you say, pushing them all to 3.5V sorts it out.....which I need to do to re-sync the BMV monitor.

[peterboat]

I think I am in Teslas and GMs corner on this, they only charge to 80% and get best life out of their batteries, other car makers are experiencing battery degradation because they do charge to 100%, so I will follow the leaders in this, and worry about a memory effect if it happens. 

For me with my large banks and large solar array I dont suppose losing some power matters because it never happens, I have never taken the batteries down to 20% because it just doesnt happen, I think Bob has commented in the past that doesnt get low either?

 

[Dr Bob]

50 minutes ago, peterboat said:

I think I am in Teslas and GMs corner on this, they only charge to 80% and get best life out of their batteries, other car makers are experiencing battery degradation because they do charge to 100%, so I will follow the leaders in this, and worry about a memory effect if it happens. 

For me with my large banks and large solar array I dont suppose losing some power matters because it never happens, I have never taken the batteries down to 20% because it just doesnt happen, I think Bob has commented in the past that doesnt get low either?

 

I've not been below 12.7V so prolly 30-35% SoC. I don't trust the amp hr counter when it is that low.

......but then again we are always on the move every other day so it never gets lower.

[MoominPapa]

1 hour ago, peterboat said:

I think I am in Teslas and GMs corner on this, they only charge to 80% and get best life out of their batteries, other car makers are experiencing battery degradation because they do charge to 100%, so I will follow the leaders in this, and worry about a memory effect if it happens. 

The only EV I have any experience of is the Nissan LEAF, and that has to be told to charge to 100% for times when maximum range is required. It defaults to a lower maximum charge.

 

MP.

 

[cuthound]

15 hours ago, MoominPapa said:

The only EV I have any experience of is the Nissan LEAF, and that has to be told to charge to 100% for times when maximum range is required. It defaults to a lower maximum charge.

 

MP.

 

 

Same as Kia, Hyundai and Tesla EV's then.

[rusty69]

On 28/09/2019 at 21:39, MoominPapa said:

Maybe I need a spare boat to do R&D with!

You can use ours if you like MP!

[MoominPapa]

2 hours ago, rusty69 said:

You can use ours if you like MP!

Only if you bring it up to the top of the T&M, where I am now.

 

MP.

 

[peterboat]

On 30/09/2019 at 23:39, MoominPapa said:

The only EV I have any experience of is the Nissan LEAF, and that has to be told to charge to 100% for times when maximum range is required. It defaults to a lower maximum charge.

 

MP.

 

I have checked the 30 kg model charges to 30kwh but only has a usable 28kwh I think the 24kwh model is similar.  Later models have had software updates to maybe limit charging, I know the Ampera has a 16kwh battery but charges to a lot less than that which is why they recently sold their spares as battery failure is extremely rare 

[Tom and Bex]

We often charge to 95% and sometimes to 100%. Only time will tell how damaging this is, but from what I've read, it's the holding batteries at 100% that I'd the problem, not charging them to that and using them straight away. And of course the balancing issue, but if carefully top balanced they should stay that way (or use a cell balancing system - either stand alone or built into bms. 

 

When the solar really starts to drop off, I might do a full discharge test to see if there is any change to capacity from last year.(Our 100% is based on charging at 14.0v until tail current drops to 5% of bank capacity as programmed in our alternator controller).

 

Finally this bms caught my attention in an email the other day. Looks simple to install, and reasonably priced for the functions it offers. Can also control bi-stable relays or conventional replays directly with no additional circuitry which is what brought my eye to it. Seems to have all the controls you'd need (except cell balancing if you want that).

[Dr Bob]

32 minutes ago, Tom and Bex said:

 

Finally this bms caught my attention in an email the other day. Looks simple to install, and reasonably priced for the functions it offers. Can also control bi-stable relays or conventional replays directly with no additional circuitry which is what brought my eye to it. Seems to have all the controls you'd need (except cell balancing if you want that).

The bms looks interesting.

In my set up, I bought the Aussie cell monitoring for around £80 and the BEP motorised switch for £150 .........and then used my BMV battery monitor to activate the auto disconnect. This unit however as you say can activate bi-stable relays so that means for less than £200 you can autodisconnect at individual cell voltages. The aussie unit only disconnects on very high or very low voltages. Buy a relay from a car breakers yard and for £150, you have the basis for a workable BMS. For another £20 you can have a 4 cell voltage monitor display as well.