Weird charging behaviour from pair of Renogy LifePo4

[StevieRuss]

I recently fitted two 100ah Renogy LifePo4 batteries to our van which replaces two ageing 120ah AGMs. I also fitted a Victron 100/30 which is supplied by three 120watt Renogy solar panels on the roof. There is also a 30amp DC charger running from the alternator.

So, both batteries charged to nearly 100% as reported by the iPhone app via bluetooth. After the first week, I noticed that only one of the batteries was discharging with the other supplying the full load. On checking the cell voltages the battery that was not discharging had the cells at these voltages

cell 1 - 3.4v
cell 2 - 3.4v
cell 3 - 3.5v
cell 4 - 3.4v

The batteries do self balance and the battery that was actually doing all the work had cells that were all at 3.3v. I kept my eye on it for a few days and the pattern formed that battery one (with the varying cell voltages) would fully charge to mostly 100% and the second battery to around 99.1% at which stage any load required (fridge on all the time and a lot of charging with USB and the inverter) would come from the second battery with the balanced cells. When that battery got to around 85-90% the main battery had tended to balance its cells and started to join in supplying the load.

Another point to add is that when the following morning came and the solar panels started to function again that the most depleted battery was helping itself to a lot more of the current and would charge up again. That battery always seems to have balanced cells and the other not until it had time to settle itself.

I'm not sure what to think now. The batteries were bought last year and were in storage in their new boxes for around 8 months though that had gone in to their deep sleep mode and were around 55% when they were started up. I'm not sure if this is something that may sort itself out. It was fine for the first week with even discharging and balanced cells but now this. I'm not sure if charging them up with the plug in charger (also a Victron 30amp charger) that is fitted to the van may help. All the wiring was done by me with 16mm cable in most places and all the cables for charging are the same length and fused.

Many thanks in advance for any insights

 

[Shimmy]

It sounds like you might have a cabling issue. Are your batteries wired diagonally, or do the loads connect to one battery that is paralleled with the other?

 

[DIYrich]

Battery activation switch?

 

[StevieRuss]

It sounds like you might have a cabling issue. Are your batteries wired diagonally, or do the loads connect to one battery that is paralleled with the other?

They attach to one battery and then parallel to the other. My brains says this is the wrong way but I read (somewhere) that Renogy recommend doing it that way. It's not a terrible issue changing it if you think it would actually help.

 

[StevieRuss]

Battery activation switch?

They both charge and discharge so the battery is actually functional. The activation switch on the Bluetooth ones is actually via them receiving a current whereas their other ones (with the ethernet connection to link them together) uses a switch on the end of a little ethernet cable to activate them. In turn they go in to a shelf mode when they are unused for 24hrs (I think).

 

[littleharbor2]

They attach to one battery and then parallel to the other. My brains says this is the wrong way but I read (somewhere) that Renogy recommend doing it that way. It's not a terrible issue changing it if you think it would actually help.

Diagonal is better. Keep the loads and charging cables together so you are only using two terminals. Better yet is the use of bus bars. They make connecting/disconnecting much simpler. You can add new loads and/or batteries easily

 

[StevieRuss]

Diagonal is better. Keep the loads and charging cables together so you are only using two terminals. Better yet is the use of bus bars. They make connecting/disconnecting much simpler. You can add new loads and/or batteries easily

I was going to do buss bars when I was originally going to fit a Victron shunt but these bluetooth batteries with an app have made that somewhat redundant for my purposes. I may though take the plunge and just rewire it though they are under the passenger seat of the van and a bit fiddly to work on so i've tried to keep it simple. Maybe i'll draw it all up again and give it a go, obviously if diagonally wiring sorts this issue out.

 

[mikefitz]

I don't think it's a battery wiring issue.
I suspect one of your batteries is entering protection mode due to high cell volts and disabling the discharge path.
After a time, the cell volts will fall below the release voltage, and discharge will resume.
It's probable your charge voltage is too high.
Lowering the charge volts to 14.0 volts or even lower to 13.8 will still achieve almost full charge. To some extent the reported SOC by the Renogy app may be inaccurate. Provided the battery volts, rested, exceed 13.4 volts, consider the batteries charged.

What are the charge profiles for the solar and dc to dc charger?

Mike

 

[StevieRuss]

I don't think it's a battery wiring issue.
I suspect one of your batteries is entering protection mode due to high cell volts and disabling the discharge path.
After a time, the cell volts will fall below the release voltage, and discharge will resume.
It's probable your charge voltage is too high.
Lowering the charge volts to 14.0 volts or even lower to 13.8 will still achieve almost full charge. To some extent the reported SOC by the Renogy app may be inaccurate. Provided the battery volts, rested, exceed 13.4 volts, consider the batteries charged.

What are the charge profiles for the solar and dc to dc charger?

Mike

I just run the standard LifePO4 preset on the Victron units. I think they’re 14.2 but I can go into expert mode and run 14v to see if that helps though. Good call. I had considered doing that to be honest. It does feel that the second battery is stopping to balance its cells to be honest and then coming out to play when they are. When it starts to discharge I check the cell voltage and they’re all running at 3.3v at that point.

Is it worth charging them separately then linking them back up? As I said it was fine for a week and then this started happening. The second battery’s SOC never makes it past 99.1% according to itself where as the one that goes out of balance always reaches 100% every time.

 

[mikefitz]

Charging separately is perhaps not worth the effort, but would prove that one battery BMS was shutting down the charge path.
Renogy reports SOC related to voltage levels it considers to be 'full' or 'empty' and computes from that. I would regard 99% as full for practical purposes. Renogy voltage readings to one decimal place perhaps mask the true situation
Victron default charge voltages 14.2 charge, 2 hours absorption, 13.5 volts float, try 14.0 volts, hopefully over a few weeks the balance near full charge will improve.

 

[StevieRuss]

Charging separately is perhaps not worth the effort, but would prove that one battery BMS was shutting down the charge path.
Renogy reports SOC related to voltage levels it considers to be 'full' or 'empty' and computes from that. I would regard 99% as full for practical purposes. Renogy voltage readings to one decimal place perhaps mask the true situation
Victron default charge voltages 14.2 charge, 2 hours absorption, 13.5 volts float, try 14.0 volts, hopefully over a few weeks the balance near full charge will improve.

I’ll give that a shot. Many thanks for your and everyone else’s contributions. Always much appreciated. ?

 

[Renogy Solar]

The battery cell voltage error within 0.2V is normal, it does not affect the use, please feel free to use

 

[740GLE]

200mv normal?

My the standards have dropped!!!

So if a delta of .2mv is acceptable, you’d need a charge voltage of no higher than 14v for a worse case scenario.

 

[740GLE]

I don't think it's a battery wiring issue.
I suspect one of your batteries is entering protection mode due to high cell volts and disabling the discharge path.

You just contracted yourself, the wiring can definitely cause one battery to receive more of the charge than another. Knowing this is also a mobile set up that always adds a layer of “make it work” not make it right.

Sure, I agree proper wiring may not solve an issue with a slightly off battery bank, but having the proper wiring and current sharing most certainly won’t hurt the situation.

 

[MisterSandals]

They attach to one battery and then parallel to the other.

Is the battery that appears to be doing all the work the “one battery”?

Happen to have a pic of this wiring?

If I were a betting kind of guy, my money would be that this is most if not all of your problem as described.

 

[mikefitz]

With a low charge current, less than 30 amps, 16mm2 cable and two 100Ah batteries installed next to one another, the wiring should have minimal effect on charging. ( assuming no issues with cable termination lugs and adequate torque on battery post fixings )
Renogy admit that the BMS computed values reported via the app may not be accurate. Independent monitoring with a DC clamp meter may provide useful information.
The key Information given, was, the battery with the high cell was not discharging at all, whilst the battery with lower cell volts was supplying all the load current, even with inadequate wiring, if both batteries were active, current flow from both would have been seen, even if the currents were not equal.
Renogy batteries will shutdown for seemingly bizarre reasons .

Mike

 

[Shimmy]

With a low charge current, less than 30 amps, 16mm2 cable and two 100Ah batteries installed next to one another, the wiring should have minimal effect on charging.

Yes and no. You can see it easily enough with a multimeter though; measure the voltage delta on the positive side between the cable lug from the inverter (not the battery post), and the battery post of the far battery while charging. Repeat on the negative side and add the two values together. Under 10mV total is negligible, but it isn't that hard to get up to 100mV if there is a wiring problem and they aren't wired diagonally.

 

[740GLE]

Or just measure the current on one battery and the other, unless they are 100% identical, one battery will be charged faster than the other.

Even if you measure 14.5a and 15.5a, that will cause a big enough imbalance after enough time/cycles.

And we all know nothing is 100% perfect (unless we’re talking about my wife).

 

[Decto]

I have exactly the same issues with Renogy batteries, however I have the 170Ah without the BMS so it is difficult to see what is happening at a cell level. The batteries will disconnect at anywhere from 14V to 14.4V (measured at the terminals) and go into high protection, I assume an individual cell is reaching cut off and so disconnecting the pack.

Deep cycling does fix it for a while, but it then comes back with shallow cycling (solar top up)

Still haven't solved it after a few months, however after sticking a 300Ah Fogstar battery in parrallel the issues with my inverter failing for low voltage at switch on have gone away. (The fogstar and cabling can provide 100% of inveter load).

Once a high load is applied and the battery voltage drops, the Renogy batteries will kick in.
I do then have an issue with the Renogy pushing some charge back into the Fogstar once the load is removed, but so far this hasn't exceeded 20A.

Unfortunately I can't refund as Renogy support through Amazon UK is totally useless and just deny anything other than charge to 14.4V

My next step will be to see if I can open the battery without destroying it and replace the BMS, or if not at least add some sort of monitoring / bleed so I can balance the cells periodically.

My original thread here.

Renogy - odd parallel behavior

Hi all, Joined today so I could view some of the images, so really didn't expect to be posting a question this soon. I have setup a solar shed as a project to get some experience over the next 12 months or so before commiting to a full house solar + battery install. Bought this setup about 6...

diysolarforum.com

 

[RCinFLA]

Any BMS cell voltage readout that only shows single decimal point digit is next to useless.

Any BMS with cell voltage reading accuracy of +/- 0.2v is useless.