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

[toms]

Yeah, I think I was being too conservative with my numbers. I switched back over to the off-grid system for tonight to let the pack drain down to 3.7-ish. Then I'll fire up the solar again in the morning and it will charge at 100+ amps. Lets see if it will race up to the 4.1 (End of Charging) setting and then disable the charge. I expect it will taper off some, but that (1.1 amps x number of devices) would take forever to move a 480ah pack.

Baxter kind of opened my eyes as to how I should interpret the balance settings.

I think you’ll be surprised. I have installed a REC on a 600ah pack and it’s doing fine.

The current needs to taper when balancing, it doesn’t take much to reach 55°C then it cuts charging.

If your cells need more balancing, install cooling (a fan) on the REC module.

 

[MurphyGuy]

I think you’ll be surprised. I have installed a REC on a 600ah pack and it’s doing fine.

The current needs to taper when balancing, it doesn’t take much to reach 55°C then it cuts charging.

If your cells need more balancing, install cooling (a fan) on the REC module.

Doesn't seem to be working.

No cell has gone over 4.055 when charging at high amps, and the BMS is already ramping down at 61.60hz. It is only allowing 40% of the available solar power to charge the battery.

Per the instructions:
When any cell reaches the voltage interval between Balance Voltages Start and Balance Voltage End, the charging current starts to ramp down to 1.1 A x Number of Devices until the last cell rises to the End of Charge Voltage

But that's NOT what's happening. It is ramping down as soon as it gets within 100 mV of the END OF CHARGING setting. No cell has reached the 4.1 volt (Balance Voltage Start) setting, or has come closer than 4.055. I know because I'm sitting here staring at it.

As I'm typing this, it has now increased to 61.65hz, charging amps reduced to 19.5 amps, highest cell at 4.032
UPDATE: Now at 61.69hz with the highest cell still at 4.032.

The BMS is not waiting to reach BALANCE VOLTAGE START to begin its ramping down of the charge current. And I can predict, by past behavior, that by the time the first cells reaches 4.08 volts, the frequency will be up in the 61.90hz range, and it will only allow 3 to 5 amps of charge. By the time the highest cell reaches 4.1 volts, which it probably never will, the sun will be going down.

And this all assumes house loads stay steady. If someone turns on a vacuum cleaner or something, it will get even worse and possibly even go backwards.

I'm going to let it continue and see what happens, but it seem to be behaving exactly the same as yesterday. Gets within 100mv of Balance Voltage Start, then starts ramping down the current. It almost seems to follow the Inverse Square Law where twice as close = four times the attenuation.

Currently at 61.76 hz and trickling 9.07 amps into the battery with the highest cell being 4.032 volts. At that rate, the highest cell will never get to 4.1 before the sun goes down, and the lowest cell will be 10 to 15mV behind that one. My SOC and Coulomb counters will never reset.

 

[Baxter2120]

I am using REC-BMS together with Victron DVCC and can definitly confirm that it only starts to ramp down the charge current when the first cell hits the end of charge voltage.

Are you sure that the BMS tells the chargers to reduce the charge current and there is no internal charge control of your inverter/chargers active?

Can you see what the REC-BMS is communicating to the SMA SI Master via CAN?

 

[MurphyGuy]

Here's an update:

I am using REC-BMS together with Victron DVCC and can definitly confirm that it only starts to ramp down the charge current when the first cell hits the end of charge voltage.

Are you sure that the BMS tells the chargers to reduce the charge current and there is no internal charge control of your inverter/chargers active?

The Sunny Island's have no problem pumping 120 amps into the battery. I have the max amps set at 120 within the Sunny Islands.

Can you see what the REC-BMS is communicating to the SMA SI Master via CAN?

Can I see it? How would I do that?

The only thing I've done is to communicate with the BMS to verify it reports back the correct settings. For a while, I thought maybe the changes I was making in the user interface software were not being recorded to the BMS, but when using the Communicate function and having to type in the codes MAXC? SISN? etc, it returns all the correct values.

I have a 2nd brand new never used REC BMS unit here.. Going to plug it in an see what happens tomorrow.

And here we are where it always ends up.. It will sit like this for the rest of the day.

 

[Baxter2120]

Just to be sure, have you established the CAN communication between the REC-BMS any our SMA?

 

[Baxter2120]

I found the following section in this document https://us.v-cdn.net/6034073/uploads/CCWTW0ZAVBMU/sma-can-protocol.pdf


Battery charging current limitation: This is solely the limit for the charging current sent to Sunny Island. It is not to be understood as a set-point as the available charging current is calculated by other algorithm and not to be set by the battery. Please note that the actual charging current is not constant but changes according to the algorithm. This value is the allowed, typical or rated charging current value for the whole battery pack. It is just the limit which must not be exceeded during charging. Please note that the battery system should fit the technical requirements of Sunny Island (see Section 10 "Technical data SI6.0H-11", page 35).


Sounds like the SMA SI is not reacting on the reduced charge current limits provided by the REC-BMS (only the maximum charge current) an has its own algorithm? But I am not an SMA user, maybe someone else with more SMA experience can comment on that?

 

[MurphyGuy]

Just to be sure, have you established the CAN communication between the REC-BMS any our SMA?

View attachment 109867

Yes. The BMS is controlling the Sunny Islands.

 

[MurphyGuy]

I found the following section in this document https://us.v-cdn.net/6034073/uploads/CCWTW0ZAVBMU/sma-can-protocol.pdf


Battery charging current limitation: This is solely the limit for the charging current sent to Sunny Island. It is not to be understood as a set-point as the available charging current is calculated by other algorithm and not to be set by the battery. Please note that the actual charging current is not constant but changes according to the algorithm. This value is the allowed, typical or rated charging current value for the whole battery pack. It is just the limit which must not be exceeded during charging. Please note that the battery system should fit the technical requirements of Sunny Island (see Section 10 "Technical data SI6.0H-11", page 35).


Sounds like the SMA SI is not reacting on the reduced charge current limits provided by the REC-BMS (only the maximum charge current) an has its own algorithm? But I am not an SMA user, maybe someone else with more SMA experience can comment on that?

The Sunny Islands will pump up to 120 amps into the battery when allowed. We have enough solar for far more than that, and I set the limit within the Sunny Islands at 120 amps myself.

When the battery is 100 mV below the "Balance Voltage Start" setting, the Sunny Islands will be pumping full power (Up to 120 amps) into the battery and the system will be at 60hz.

As soon as the battery is within 100 mV of the "Balance Voltage Start" setting, it will start to ramp down. When it gets within 50 mV, it ramps down to just a few amps.

Changing the Balance Voltage Start setting does in fact change the point at which the BMS starts to ramp down the current.

 

[Baxter2120]

The Sunny Islands will pump up to 120 amps into the battery when allowed. We have enough solar for far more than that, and I set the limit within the Sunny Islands at 120 amps myself.

When the battery is 100 mV below the "Balance Voltage Start" setting, the Sunny Islands will be pumping full power (Up to 120 amps) into the battery and the system will be at 60hz.

As soon as the battery is within 100 mV of the "Balance Voltage Start" setting, it will start to ramp down. When it gets within 50 mV, it ramps down to just a few amps.

Changing the Balance Voltage Start setting does in fact change the point at which the BMS starts to ramp down the current.

I do not think that the BMS is ramping down anything (or the SI is reacting on that), pls see the quoted section and the linked document.

Pls check the charging setting in your SI. It is not a BMS issue.

 

[MurphyGuy]

I do not think that the BMS is ramping down anything (or the SI is reacting on that), pls see the quoted section and the linked document.

Pls check the charging setting in your SI. It is not a BMS issue.

I'm a bit confused at what you're trying to get at. The only battery relevant settings in the Sunny Islands, when a BMS is connected and the Sunny Islands are the Sunny Islands are in BMS mode, is the maximum allowed charging current (mine set at 120 amps), and the minimum SOC allowed before SI shuts down on its own.

The BMS tells the Sunny Islands how much current to send into the battery and the Sunny Islands comply. If the BMS says go ahead and send the maximum, then the Sunny Islands will limit the current to the 120 amps I set as the maximum charging current.

As I understand it, the BMS tells the Sunny Island how much juice to allow, the Sunny Islands then adjust grid frequency to cause the SunnyBOY inverters to slow down.

Am I missing something?

 

[Baxter2120]

I'm a bit confused at what you're trying to get at. The only battery relevant settings in the Sunny Islands, when a BMS is connected and the Sunny Islands are the Sunny Islands are in BMS mode, is the maximum allowed charging current (mine set at 120 amps), and the minimum SOC allowed before SI shuts down on its own.

The BMS tells the Sunny Islands how much current to send into the battery and the Sunny Islands comply. If the BMS says go ahead and send the maximum, then the Sunny Islands will limit the current to the 120 amps I set as the maximum charging current.

As I understand it, the BMS tells the Sunny Island how much juice to allow, the Sunny Islands then adjust grid frequency to cause the SunnyBOY inverters to slow down.

Am I missing something?

Yes, the BMS tells the SI only the allowed maximum.

But at the end of the charge curve the SI switches from constant current ( 120amps in your case) to constant voltage, and the SI is ramping down the charge current and not the BMS (the BMS is just sending/updating the maximum charge current). Ramping down the current starts sooner if you reduce the charge voltage.

The default charging voltage of the SI is 54V (can be overwritten by the BMS) BUT not more then 63V


If the REC is updating the maximum charge current during the charge process or not is unkown (at least for me).

So we do not know if the REC-BMS is sending a charge current limit which is to low (unlikely based on your description but still possible) or the SI is reducing the charge current to early/fast.

 

[MurphyGuy]

Yes, the BMS tells the SI only the allowed maximum.

But at the end of the charge curve the SI switches from constant current ( 120amps in your case) to constant voltage, and the SI is ramping down the charge current and not the BMS (the BMS is just sending/updating the maximum charge current). Ramping down the current starts sooner if you reduce the charge voltage.

The default charging voltage of the SI is 54V (can be overwritten by the BMS) BUT not more then 63V

View attachment 109876
If the REC is updating the maximum charge current during the charge process or not is unkown (at least for me).

So we do not know if the REC-BMS is sending a charge current limit which is to low (unlikely based on your description but still possible) or the SI is reducing the charge current to early/fast.

From the REC BMS manual:
The communication between the REC BMS and the SMA Sunny Island charger is established through the CAN bus. All the parameters that control the charging/discharging behavior are calculated by the BMS and transmitted to the Sunny Island unit in every measurement cycle.

It is the BMS that is the problem, or one of my settings. I have an idea and will come back tomorrow with an update. Going to replace the BMS with a spare unused unit and see if it behaves the same way.

 

[Baxter2120]

From the REC BMS manual:
The communication between the REC BMS and the SMA Sunny Island charger is established through the CAN bus. All the parameters that control the charging/discharging behavior are calculated by the BMS and transmitted to the Sunny Island unit in every measurement cycle.

It is the BMS that is the problem, or one of my settings. I have an idea and will come back tomorrow with an update. Going to replace the BMS with a spare unused unit and see if it behaves the same way.

The BMS can not control the charger, no BMS can do that.

BMS is just sending the limits, within the charger works on its own.

You have to check which limit the BMS is sending to the charger and when (and you have to know how to do that in a SMA system because you are operating it).

For the time being, the SI part is a black box to us, you are only assuming that the BMS is sending wrong values without knowing it.

 

[toms]

All the systems i have set up use the Sunny Island in AC coupled setup.

I agree that the REC is what should be telling the Sunny Island to lift frequency to taper charge current.

Not sure why it’s commanding that before it should though - i’m curious to see how this turns out, sorry i can’t help you more.

 

[Maitake]

I just wanted to say, that is a beautiful battery build, I'll be using that as a guide for positive and negative busses in my build. (more pics please)
Obviously you know what you are doing, but is there a chance the B- connection for the BMS is on the wrong side of the shunt?
I haven't puzzled it all the way through, but this could possibly create a 50mv problem, which is on the order of what you are seeing.

 

[MurphyGuy]

All the systems i have set up use the Sunny Island in AC coupled setup.

I agree that the REC is what should be telling the Sunny Island to lift frequency to taper charge current.

Not sure why it’s commanding that before it should though - i’m curious to see how this turns out, sorry i can’t help you more.

Here we are with a brand new REC BMS I had as a spare.
END OF CHARGING 4.1
BALANCE VOLTAGE START 4.1

As soon as the first cell crossed 4.000 volts, the 60hz started creeping up. When the first cell got to around 4.020, it was already starting to throttle at 61.10hz.

I am currently at 61.70hz and the highest cell is at 4.026 volts. This BRAND NEW unit is behaving exactly like the other one.

It takes a lot of energy to move a 480ah battery pack from 4.026 to 4.1 volts, and with the BMS only allowing a few amps to trickle in, it will never get there before the sun goes down.

I can not imagine this being a problem with the Sunny Islands as I have not messed with any settings inside them other than setting the required stuff.

 

[MurphyGuy]

I just wanted to say, that is a beautiful battery build, I'll be using that as a guide for positive and negative busses in my build. (more pics please)
Obviously you know what you are doing, but is there a chance the B- connection for the BMS is on the wrong side of the shunt?
I haven't puzzled it all the way through, but this could possibly create a 50mv problem, which is on the order of what you are seeing.

Thank you!
Unfortunately, it looks like my beautiful battery is using a faulty BMS or has some other issue. Some more pics for you.

 

[MurphyGuy]

I just wanted to say, that is a beautiful battery build, I'll be using that as a guide for positive and negative busses in my build. (more pics please)
Obviously you know what you are doing, but is there a chance the B- connection for the BMS is on the wrong side of the shunt?
I haven't puzzled it all the way through, but this could possibly create a 50mv problem, which is on the order of what you are seeing.

Thank you for the suggestion, I just checked it.
I don't think it matters which way the actual physical shunt is pointing, but the B+ wire from the BMS is on the side that comes from the pack's Neg terminal.
Double checking the REC BMS manual, I DO have it correct.

 

[MurphyGuy]

Never going to reach full charge. Actually going backwards a bit.

Beginning to think these Sunny Islands won't reach a full charge when Off-Grid. I think I'm going to try discharging a bit, then using the Sunny Islands in Grid Charge mode to see what happens.

 

[MurphyGuy]

UPDATE:
Been stuck at around 4.025 volts for about an hour now and the BMS won't allow more than 3 to 5 amps charge.

I raised the Balance Voltage Start and Balance Voltage End settings up and there was no effect.

After another 10 minutes, I raised the End Of Charging setting from 4.1 to 4.15 and it took off at 71 Amps charging! WOW!

But I'm going to bet that in 20 minutes when the highest cell reaches 4.1 volts, it is going to exhibit the same behavior.

The problem seems to be that the BMS is not behaving as the manual claims. When it gets to within 70mv of the END OF CHARGE setting, it ramps down to ridiculously low charge rates.