Back to basics: Force battery charging

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Don58
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My RE system: Radian system. GS8048A Inverter, GSLC, 2x FM80. Battery = 48VDC 700Ah Iron Edison LiFePo4 (lithium iron phosphate).

Back to basics: Force battery charging

Post by Don58 »

A scenario comes to mind and I'd like to understand it better. Might be I just don't grasp everything in the manuals.

My understanding is that upon power on, the system assumes our LiFePO4 battery's state of charge (SOC) is 100% and does no charging right off. When it sees the battery voltage has dropped a bit, it starts the charger (if it has power available), continues on monitoring voltages, and in time the Radian system is synced up to accurately know the SOC of the battery, and charges it or not as appropriate. Roughly correct so far?

My question is, what happens in the scenario when the battery, upon power up, is nearly completely discharged, or it has no load, and in either case will not discharge any further. Suppose, in other words, the battery needs charging upon system power-up before there has been any further battery discharge. Are there any settings or tricks to get the system to charge a battery that it assumes (incorrectly) is at 100%?

This isn't a concern in any standard scenario, except perhaps if the newly installed battery is fully discharged, but I need to figure it out anyway. Thank you.
raysun
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Re: Back to basics: Force battery charging

Post by raysun »

There's a lot more to the charging logic than described in the OP.

However, when a system with an FNDC is powered on, the assumption is the battery is at 100% SoC.

The inverter chargers may or may not activate, depending on several factors:
• An AC source with sufficient current capacity to support charging.
• Charger mode is not OFF.
• Charging status is flagged to start (or complete) a charge cycle.

The latter is the complex logic alluded to above. Its described in the inverter manuals so I won't try to duplicate it here.

The wisest approach, when installing a new battery and bringing the system up is to manually start a charge cycle using an AC source (Grid or Gen) that will establish a full state of charge.

If the battery is fully depleted, the voltage may be (and should be) below the Low Battery Cut Off setting. This would preclude the inverter from starting. External charging may be required. Alternately, lowering LBCO before installing a depleted battery, and charging immediately with the inverter charger may allow the system to eventually reach a normal operating state.
Don58
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My RE system: Radian system. GS8048A Inverter, GSLC, 2x FM80. Battery = 48VDC 700Ah Iron Edison LiFePo4 (lithium iron phosphate).

Re: Back to basics: Force battery charging

Post by Don58 »

Thank you. But I haven't got there yet.

The situation is simply that I want to charge the battery when the system is first connected and turned on and is not under load. This is because in our implementation, depletion under load and then power off and disconnection are normal usage. Later a good 240VAC is connected, at which point we need recharging without a load being applied.

This means I want to charge the battery even though the Radian thinks it is at 100% SOC. The battery voltage will be lower than the Absorb and Float settings, but of course nowhere near as low as LBCO. I have experimented with setting Re-Bulk to a value above the battery but still below Absorb, but when I press Start Bulk it still doesn't start the charger.

"Charging status is flagged to start (or complete) a charge cycle."

Something in the logic that I don't see is preventing this.

Seems to me that in a newly installed system the same situation applies. Except, maybe a new system doesn't start the charger until the battery, presumably received with some charge on it, has been further discharged so that the system thinks it's sufficiently below 100%. If this is so, it's what I need to get around. In my recharging scenario, I cannot also put a load on the system AC output. (Hmm. If it's truly absolutely necessary, I jut thought of a way. But I hate inelegant solutions.)

Note that a system configuration for normal operation and a configuration for this charging scenario can be different. Reprogramming for different scenarios is an option.

Thank you for any further insight.
raysun
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Re: Back to basics: Force battery charging

Post by raysun »

How is it being determined that the system thinks the battery is at 100% SoC? Is there a FLEXNet DC battery monitor in the system?

With Grid, or Generator input, manually starting a Bulk Charge cycle should do just that, without regard for SoC.

What is Absorb Time, and Float Time set on the FM80s and the Radians?

How are the Absorb and Float voltages set on the FM80s and the Radians?
Don58
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My RE system: Radian system. GS8048A Inverter, GSLC, 2x FM80. Battery = 48VDC 700Ah Iron Edison LiFePo4 (lithium iron phosphate).

Re: Back to basics: Force battery charging

Post by Don58 »

Yes, there is a FLEXnet DC in the system. My observation is that SoC is always reported as 100% upon power up.

Please note, our usage model includes complete disconnection and power down and then reconnection and power up regularly, at which time the battery needs charging whether or not the system thinks it's at 100%.

I'm encouraged that you say a Bulk Charge should start without regard to SoC.

Absorb and Float times are set to 0.5 hr each. I've experimented with those a little to no effect.

Absorb and Float voltages are set according to the battery specs, 55.2V and 53.6V resp. Battery is 48V 700Ah, reading at 53.5V by the Inverter and 52.7V with a voltmeter. I calibrated that once but cannot now because I can't seem to get the charger OR the inverter going. Doesn't matter anyway as I'm not concerned with accuracy now, just function.

I've adjusted Absorb, Float, Re-Float, and Re-Bulk voltages up and down to see if I can learn what difference they make, but in no case did anything different happen. The system might say Bulk Charge is on, but there is no current flow. I may not have been quite systematic enough about these adjustments, but it seems to me that if Absorb and/or Float are above the perceived battery level, something should happen.

Thanks for all your input.
raysun
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Re: Back to basics: Force battery charging

Post by raysun »

Don58 wrote: Thu Dec 03, 2020 10:31 am Yes, there is a FLEXnet DC in the system. My observation is that SoC is always reported as 100% upon power up.

Please note, our usage model includes complete disconnection and power down and then reconnection and power up regularly, at which time the battery needs charging whether or not the system thinks it's at 100%.

I'm encouraged that you say a Bulk Charge should start without regard to SoC.

Absorb and Float times are set to 0.5 hr each. I've experimented with those a little to no effect.

Absorb and Float voltages are set according to the battery specs, 55.2V and 53.6V resp. Battery is 48V 700Ah, reading at 53.5V by the Inverter and 52.7V with a voltmeter. I calibrated that once but cannot now because I can't seem to get the charger OR the inverter going. Doesn't matter anyway as I'm not concerned with accuracy now, just function.

I've adjusted Absorb, Float, Re-Float, and Re-Bulk voltages up and down to see if I can learn what difference they make, but in no case did anything different happen. The system might say Bulk Charge is on, but there is no current flow. I may not have been quite systematic enough about these adjustments, but it seems to me that if Absorb and/or Float are above the perceived battery level, something should happen.

Thanks for all your input.
The FNDC will default to 100% SoC on power up. It has no way to determine the true SoC until the battery is fully charged.

If there is AC IN to the Radian of proper quality that it is accepted, and of proper amperage to service (whatever) loads, and charging demands concurrently, then the inverter automatically switches to charger mode.

Whether charging takes place is dependent on multiple factors:
• The battery must have sufficient minimum voltage (42V I believe.)
• Charger must be assigned non-zero amperage from the AC IN feed.
• Charger mode must be set to ON.
• AC IN must be set to the proper source (Grid or Gen).
• A charge cycle may need to be started manually.

That the inverter/charger seems to not be responding to AC IN at all seems suspicious if an incorrect configuration, setting, or the unit being damaged.

Make sure AC voltage is present at the proper AC IN terminals.

Review the AC Current Limit settings for the AC source and charger.

Check the event log of any errors.

Check the Mate is indicating AC IN is being accepted.
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Re: Back to basics: Force battery charging

Post by sodamo »

You can unplug the FNDC from Hub then plug back in when fully charged. Disconnected, your system will still see voltage but not SOC.
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solarpv123
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Re: Back to basics: Force battery charging

Post by solarpv123 »

It is my understanding that for Lithium batteries the SOC is not accurate.
Previously, it was stated that to properly set the SOC you must unplug the communication cable from the hub to the fndc.
This is correct - BUT this resets SOC to 100%. Therefore you need to make sure the batteries are actually at 100% capacity.
raysun
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Re: Back to basics: Force battery charging

Post by raysun »

solarpv123 wrote: Sat Dec 05, 2020 11:45 am It is my understanding that for Lithium batteries the SOC is not accurate.
Previously, it was stated that to properly set the SOC you must unplug the communication cable from the hub to the fndc.
This is correct - BUT this resets SOC to 100%. Therefore you need to make sure the batteries are actually at 100% capacity.
That is not entirely true. I have a lithium battery which is generally cycled daily. At the end of the charge cycle, the difference between the FNDC reporting 100% SoC and the battery reaching programmed charge termination is 3AH for a 450AH battery, or roughly 0.7%, well within acceptable measurement error for this type of meter.

Assuming the FNDC didn't sync daily, and the measurement errors were cumulative, after a week, the error might be in the 4.9% range. Not great, but not bad for this type of metering, easily resolvable by simply charging the battery to 100% SoC and permitting the FNDC to sync.
Don58
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My RE system: Radian system. GS8048A Inverter, GSLC, 2x FM80. Battery = 48VDC 700Ah Iron Edison LiFePo4 (lithium iron phosphate).

Re: Back to basics: Force battery charging

Post by Don58 »

I'm getting the idea that my problem with charging the battery was not related to the system thinking the battery is at 100%. I should be able to get the charger going (at high current) no matter what SOC the FNDC etc thinks it's at.

Is this correct?

Charging should (as is typically the case) be predicated by voltage, and where the battery voltage sits with regard to settings for Float, Absorb, etc. I played with those a bit and got nowhere, and have to conclude that the fact my GS8048A is damaged on the AC output side is preventing charging operations. Not sure how they're linked, but until that's resolved I probably can't expect the charger side to do everything right. I'm pursuing an RMA. Hope to find out what, if anything, we did to it.
raysun
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Outback IBR3 battery enclosure
Suniva 330 watt panels (12 - 6 strings of 2 in series)
Hyundai 355 watt panels (6 - 3 strings of 2 in series)
Honda EU7000is gas fuel generator

Re: Back to basics: Force battery charging

Post by raysun »

Don58 wrote: Mon Dec 14, 2020 3:19 pm I'm getting the idea that my problem with charging the battery was not related to the system thinking the battery is at 100%. I should be able to get the charger going (at high current) no matter what SOC the FNDC etc thinks it's at.

Is this correct?

Charging should (as is typically the case) be predicated by voltage, and where the battery voltage sits with regard to settings for Float, Absorb, etc. I played with those a bit and got nowhere, and have to conclude that the fact my GS8048A is damaged on the AC output side is preventing charging operations. Not sure how they're linked, but until that's resolved I probably can't expect the charger side to do everything right. I'm pursuing an RMA. Hope to find out what, if anything, we did to it.
Yes, the SoC calculation by the FNDC are status rather than control, unless Auto Charge Termination Control is enabled.

If the inverter isn't working (no AC OUT) then the charger may be impacted as the two functions share circuitry. (The charger is basically the inverter running in reverse).

Is the generator rated for 50A AC continuous output from the outlet that's feeding the AC IN to the inverter? The generator setting on AC IN and CURRENT LIMIT should match the generator's rated output. Otherwise the inverter may try to draw too much current from the generator under heavy load conditions, causing the generator to be overloaded.
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