Has anyone been able to get REC to fully charge a battery?

[MurphyGuy]

This is interesting. Not sure how this affects anything.

In the REC Manual, it lists an ADC reference voltage under command REFC? (see photo)

The spec is supposed to be 5.000v +/- 0.003 (Read Only) but mine is 4.992

I'm wondering if the fact that it is 8mV off the mark has anything to do with the fact that my highest cell settles at about 8mV below the End of Charge setting. Maybe just a coincidence .

 

[MurphyGuy]

I only use the REC shunt.

Another possibility is that your cells diverge too much when they reach their balance point - and the REC reduces current to prevent overheating.

My cells are quite old, and when i haven’t seen 100% SOC for a while they will take a few days before the balancing algorithm returns to 100%.

As you can see from my screenshots, they are still a bit imbalanced but still get to high 90’s before SI frequency shift.

As Hedges points out, my experience is only with SI8.0H. As far as i’m aware the REC is the same, i use the REC SI BMS. I keep forgetting that the US Sunny Island is different, i have no experience there i’m sorry.

If you type in REFC? to your communicate box, what does your reference voltage return as?

 

[toms]

If you type in REFC? to your communicate box, what does your reference voltage return as?

I’ll let you know tomorrow. (i don’t have a PC permanently connected)

 

[bdserv]

I did set my END OF CHARGE to 4.16 once, then waited until all cells were over 4.1, then reset the END OF CHARGE to 4.1 while it was charging. It immediately stopped charging and reset the counters to 100%.

Failing discovery of a setup or firmware solution I would automate this sequence using something like an attiny85 or esp8266. Would be simple enough to monitor the REC for cell voltages and charge cycle status via the serial port or wifi, and make the setting adjustments when appropriate.

 

[Goboatingnow]

No luck. REC emailed me an updated firmware version that behaves differently but still won't allow a full charge in a reasonable amount of time.

And now they won't return emails. I take this as a warning that they know there's a problem with certain applications.

What's different with the new firmware you ask? Well, instead of starting to taper the current when the first cell hits the Balance Voltage Start setting, it doesn't start tapering the current until the first cell hits the End Of Charge setting, which is FAR better. All cells must reach the End Of Charge setting for the coulomb and SOC counters to re-calibrate, which never happens.

So now, instead of my pack (highest cell) getting to within 50 to 70 mV of being fully charged, the highest cell reaches full charge. But by the time the lowest cell has gotten to within 15mV of a full charge, the current has tapered down to just 1 or 2 amps.

At just 1 or 2 amps of charging, it would take about 12 hours to move the lowest cell the remaining 15mV, and by that time, the sun will have gone down long ago.

The guy over at OGSS did his best to help, but I don't think he is privy to the proprietary algorithm that REC uses so his assistance is limited to what is in the user manual. I haven't even bought anything from OGSS and he was trying to solve my problem, so that's a big thumbs up for them.

I'm beginning to think that the REC BMS is really for charging applications that have an unlimited 24 hour energy supply, and not really designed to get off-grid batteries charged up quick enough to keep up with the sun. If I were to leave the system plugged into the grid charging, I'm confident it would eventually get to a full charge, but it will never happen using off-grid solar.

A bit disappointed in that regard, but the reality is that in the bigger picture, it's not a show stopper problem. The battery pack will still charge, REC is still going to keep it from going kaboom, and I can always reset the SOC counter manually if needed. I just need to open the user interface, type in a bit of code, and tell it what SOC it should be at.

Interesting I’m building my own bms this winter so this is all interesting info