LiFePO4 issue?

[GeoffL]

Hmmm, don't think that'll happen Geoff.
They suggest charge voltages of 14.6V so the BMS over voltage threshold MUST be higher and is probably considerably higher than this (3.65v / cell) and therefore alternator charging at 14.4 volts won't trigger cut off unless one cell is massively out of whack with the others.
Good luck with the Festival BTW, it looks great

According to the 'net, cell voltage at 100% SOC is 3.65V while charging and drops to 3.40V after resting. So, for a 4-cell battery (which is what I have), that's 14.6V and 13.6V respectively. Thus, unless the cells are perfectly balanced, an over-voltage condition in one cell seems possible. For example, if three cells were 0.1V lower than the fourth, 14.6V would be split 3.725V for the highest voltage cell and 3.625 for the other three. As you can see from the screenshots I uploaded, the differential is over 0.1V at 100% SOC although it's less than 0.005V at 80% SOC. Hence the cells don't appear to need to be massively out of whack. A 0.1V differential would be enough to trigger an over-voltage condition at just 14.3V...

Thanks re. the festival: I got press-ganged into a shanty band a couple of months ago and I'm still busking for a lot of their repertoire; so that good luck might be needed :vbg:

 

[merl]

Yep, I get where you're coming from, I guess it'll ultimately depend on exactly what the BMSs cell overvoltage is set at. I'd anticipate this will be significantly higher than the upper limit of recommended charge voltage?
The other thing is that IF the BMS does trip off when does it re-connect again?? And what happens when it does? Without detailed info it's all a bit finger in the air Geoff but personally I think you'll be fine, LFP seems to be very tolerant and not fussy at all. Discharge below 2.3 v/ cell excepted.

 

[Chasn]

Geoff. Depending on which BMS was used in your battery the balance current that's drawn from the strongest cell can often be tiny, it therefore takes ages to drag that cell down to a similar level to the lowest cell in the pack, this problem is often exaserbated by the fact that a lot of BMSs only provide cell balancing while the battery is actually being charged or even worse being charged above a set current. (maybe this is the 10A figure that you mentioned?)
Take a look at the BMS settings and see if there's a 'balance' setting page where you can set the charge current when balancing commences and set this as low as possible, ideally there'll be an option to make balancing happen continuously or ALWAYS, so the cells will balance constantly.

Do not do this. Setting the balancing at below 3.45v/cell (13.8v battery voltage) will upset balancing. I have three 30kwh packs balanced with 2A and it works just fine after an initial top balance. The expert on all things LFP batteries is Andy in Australia (see the Off-grid Garage YouTube videos). With such a flat charge curve you only know which are the strong and the weak cells once you are higher than the plateau voltage.Balancing below 3.45v/cell will make this worse.

 

[merl]

Do not do this. Setting the balancing at below 3.45v/cell (13.8v battery voltage) will upset balancing. I have three 30kwh packs balanced with 2A and it works just fine after an initial top balance. The expert on all things LFP batteries is Andy in Australia (see the Off-grid Garage YouTube videos). With such a flat charge curve you only know which are the strong and the weak cells once you are higher than the plateau voltage.Balancing below 3.45v/cell will make this worse.

Hmm, can't agree there and neither does Andy. He himself recommends setting the balance to 'always'

 

[GeoffL]

Do not do this. Setting the balancing at below 3.45v/cell (13.8v battery voltage) will upset balancing. I have three 30kwh packs balanced with 2A and it works just fine after an initial top balance. The expert on all things LFP batteries is Andy in Australia (see the Off-grid Garage YouTube videos). With such a flat charge curve you only know which are the strong and the weak cells once you are higher than the plateau voltage.Balancing below 3.45v/cell will make this worse.

Thanks for the pointer to Andy's channel. However, in my case this is moot since the BT app supplied only lets me monitor what's going on and I have no way of adjusting any settings. As others have mentioned or at least implied, if I set my SCC up for fixed time absorption at 14.2V or more, my LFP battery should receive an adequate charge each day without needing me to continue to intervene!

 

[wildebus]

Thanks for the pointer to Andy's channel. However, in my case this is moot since the BT app supplied only lets me monitor what's going on and I have no way of adjusting any settings. As others have mentioned or at least implied, if I set my SCC up for fixed time absorption at 14.2V or more, my LFP battery should receive an adequate charge each day without needing me to continue to intervene!

The reason why the app won't let you adjust anything is quite simple really.... more people f*** up their self-built/white-box lithium batteries by messing with the settings then ever make them better! So the more professional/dedicated battery suppliers usually lock down the configuration options. When I install Lithiums, I MUCH prefer to use batteries that are not configurable as that way I know they will carry on working after installation and not get "optimized".
I have never once had the need to do ANY balancing of my Lithiums as they were built correctly in the factory and configured prior to shipment to the distributor.
I wonder how all those people with the 'dumb' Lithiums without Bluetooth BMSes every managed to use them successfully!


PS. Good luck with Andys channel I know people like to watch him but he does my head in Can't manage more than 5 minutes

 

[mariesnowgoose]

 

[GeoffL]

The reason why the app won't let you adjust anything is quite simple really.... more people f*** up their self-built/white-box lithium batteries by messing with the settings then ever make them better! So the more professional/dedicated battery suppliers usually lock down the configuration options. When I install Lithiums, I MUCH prefer to use batteries that are not configurable as that way I know they will carry on working after installation and not get "optimized".
I have never once had the need to do ANY balancing of my Lithiums as they were built correctly in the factory and configured prior to shipment to the distributor.
I wonder how all those people with the 'dumb' Lithiums without Bluetooth BMSes every managed to use them successfully!

I now know what you mean. If I'd gone with my first choice (Fogstar Drift), I'd have had a JBD/Overkill BMS and a BT app that would let me configure it (soz: f*** it up) trying to correct what turned out to be a simple misunderstanding. Nice to know that you never had the need to rebalance any of your batteries, particularly since two of them are the same model as the one I've fitted! I'll hold off buying that expensive Victron IP65/10A until (if ever) rebalancing is needed!

PS. Good luck with Andys channel I know people like to watch him but he does my head in Can't manage more than 5 minutes

if you can't manage more than 5 minutes, how am I supposed to cope :vbg: That said, I've still got to get my head around your words of wisdom re hybrid systems!

 

[GeoffL]

Now I've a little experience of my current setup, this post is a bit of a footnote. The first thing of note is that I probably need to swap the Autotrail-fitted Sargent mains charger for something that is LFP-specific. I looked at Victron's IP65 series, but those seem to have the same 'adaptive absorption' that's caused me issues with the SmartSolar SCC. I spent last weekend on EHU for the first time and the voltage differential between the highest and lowest got close to 0.2V, with cell 4 having the highest voltage and the battery only charging to just over 80% before the BMS shut off charging with yet another COV event. I turned off the mains charger on Saturday so that charge would come only from the solar system until the van was driven. We left Clyro at about midday, at which point the battery was back up to about 86% SOC and in 'standby' mode after yet another COV event. We spent the night at a park up near Launceston before taking the van back home yesterday (Monday) to unload and then take the van back to storage. By the time we got back to storage, that battery was back in 'standby' mode but with 100% SOC. We didn't get any of those shenanigans while at the Falmouth festival -- but then we didn't have EHU and so were purely relying on solar to recharge the battery for the five days we were at that campsite. Being able to achieve 100% SOC again now that I've switched off the mains charger suggests the need to replace it...

 

[colinm]

sounds like you have the same problem 'robinhood' on oal had, he dropped in a lithium keeping his ebl and a couple of times it shutdown, his answer was to disable the internal charger on the ebl and fit a Victron lithium charger.

 

[merl]

Geoff, I'm wondering if you're getting duff info from the BMS WRT those percentage capacities of around 80%, do you have any cell voltages readings/screenshots of voltages from that point in time? There's always going to be differences in cells making up a pack but 20% imbalance is massive, maybe the BMS is using voltage readings to give you a percentage value and the BMS is simply rubbish at doing this?
If that's not the case then from what you're saying it appears that cell 4 is still attaining a higher voltage than the other 3 cells, this could be caused by either cell 4 being of lower overall capacity OR the cell is actually OK and the pack simply needs rebalancing.
Personally I'd disconnect the LFP from the LA and then discharge the LFP until it disconnects due to Low voltage cut off and then check the individual cell voltages again, if cell 4 is now sitting at a lower voltage than the other 3 then you've got a faulty cell with low capacity. Hopefully cell 4 is sitting at a higher voltage than the rest indicating it's a balance issue which you should be able to rectify.

 

[GeoffL]

Geoff, I'm wondering if you're getting duff info from the BMS WRT those percentage capacities of around 80%, do you have any cell voltages readings/screenshots of voltages from that point in time? There's always going to be differences in cells making up a pack but 20% imbalance is massive, maybe the BMS is using voltage readings to give you a percentage value and the BMS is simply rubbish at doing this?
If that's not the case then from what you're saying it appears that cell 4 is still attaining a higher voltage than the other 3 cells, this could be caused by either cell 4 being of lower overall capacity OR the cell is actually OK and the pack simply needs rebalancing.
Personally I'd disconnect the LFP from the LA and then discharge the LFP until it disconnects due to Low voltage cut off and then check the individual cell voltages again, if cell 4 is now sitting at a lower voltage than the other 3 then you've got a faulty cell with low capacity. Hopefully cell 4 is sitting at a higher voltage than the rest indicating it's a balance issue which you should be able to rectify.

Thanks. I suspect that you've misinterpreted what I wrote. It isn't a differential of 0.2, but 0.2V. So (made up figures as the van's stored over half an hour from home), cell 4 might be at 3.560V while the lowest cell might be at 3.360V. The highest cell voltage will have caused the BMS to shut off charging even though the other cells are not fully charged, resulting in (say) as overall 80% SOC.
FWIW, I'm beginning to suspect that cell balancing occurs when there is no charge available (i.e. from the SCC, mains charger or alternator) and so the normal practice of keeping the mains charger continuously on might have prevented the BMS from rebalancing the cells. At least, the cell voltages had a differential of around 0.1V with 100% SOC by the time I got the van back to storage yesterday. I think I'll hold off buying. that Victron IP65 charger for now and see if I can get by with switching the Sargent mains charger on only when the solar system can't cope as that will test my hypothesis re. cell balancing and, if my hypothesis is correct, I'd have to do the same thing with the Victron charger anyway!
Thanks again

 

[merl]

Thanks. I suspect that you've misinterpreted what I wrote. It isn't a differential of 0.2, but 0.2V.

Not quite sure what you mean by the above but I was using the 80% charged /20% remaining from your post where you said

... and the battery only charging to just over 80% before the BMS shut off charging

As I mentioned previously I think you should first establish if you've got a bad cell or an unbalanced pack by doing a deep discharge to zero% cut off level because if you've got a bad cell you'll never attain close to 100% capacity or a balanced pack. If you've got a correctly calibrated shunt fitted to the van then that will tell you a lot too if you do a zero to full charge/discharge, as I mentioned previously, what you're BMS is reporting could be misinformation and ultimately you may be faffing and worrying over nothing.