Smart Solar Chargers overcharging

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tarmacshredder asked Apr 19, '22

Smart Solar Chargers overcharging

I am hoping for advice on how to resolve over charging in my off grid eco home system. Although I have not posted before I have done lots of research on the forum and Victron website but not sure why I am having trouble stopping the charge controllers charging when they have reach absorption and then floating. My setup consists of currently 3kw of solar (to be increased to 10.5KW when I get the other panels mounted) >2x 250/100 smart solar ve can charge controllers (linked by can but only using one currently) Victron Venus GX, BMV 700, 10KVA Quattro (old firmware), 4x BMW I3 lithium 120amp 48V batteries in parallel and a 7.5KW backup generator. I have the charge controllers set to absorption for minimum time at 49.2V and originally had the float voltage at the same but recently changed to 49V to try and stop the charge controllers overshooting (has made no difference). I have my max battery voltage set below the max for the batteries so there is room for error but they are regularly charging to 49.5-49.6V and the charge controllers are still putting in more wattage than is being consumed even when floating. They do level out at this sort of voltage but its not whats set. I do have a SimpBMS battery management which is currently switched off as after a reset of the Venus GX to get the WIFI to reconnect it displayed the batteries were at 120V which is obviously incorrect. >The system has been running for nearly 2 years, last summer I had some issues of it over charging but not to the extent it is already doing this year. I am nervous about connecting the additional panels at the moment incase it increases the overcharge problem. I am also looking to set up load diversion to use excess PV for heating hot water through 2-3 elements in a 300+ litre thermal store. I would be keen to hear of other peoples experience in doing this in an off-grid setup, I am thinking of using a controller to output a 0-10v output to control a PWM controller outputting 0-230V connected to the heating elements in the thermal store. Appreciate any help and advice.

overvoltage

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Alexandra ♦ commented · Apr 19, 2022 at 06:46 PM

@Tarmacshredder

What was reading 120v on the batteries?

Mppt Charge controllers? Bmv? Or something else?

It will probably be qorth updating firmware on the entire system. Resetting up and seeing if that sorts out the issue. I have seen half updated components behave weirdly with each other

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snoobler commented · Apr 19, 2022 at 07:37 PM

What are the 13 cells' voltages at peak absorption just prior to float?

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Answer 1 · 2022-04-19T20:03:03Z

tarmacshredder answered · Apr 19, 2022 at 08:03 PM

The 120v was displayed on the SimpBMS battery management, but only after the Venus GX's power supply which it shares was disconnected and reconnected to reset the WiFi, True voltage of batteries was just under 48v from memory.

I have just done a firmware update on the charge controllers approx 2 weeks ago and checked the Venus but it was current. After the update the charge controllers output changed to 0 watts output as batteries were fully charged but the following day was back to normal overcharging. The inverter is the older chip set so can not be updated.

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Answer 2 · 2022-04-19T21:10:59Z

snoobler answered · Apr 19, 2022 at 09:10 PM

Voltage of the battery is irrelevant. Your battery is comprised of 13 cells in series.

What are the 13 cells' voltages at peak absorption just prior to float?

If you are operating the battery without a functional BMS, there's a good possibility that you're in the process of destroying or have destroyed the battery especially given the behavior described.

Operating a Lithium battery without a functional BMS is the #1 best way to destroy your investment with a potential catastrophic outcome including fire.

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Answer 3 · 2022-04-20T09:57:17Z

tarmacshredder answered · Apr 20, 2022 at 09:57 AM

Thanks @snoobler for you help.

The BMW i3 batteries have 12 cells in series with a max voltage of approx 4.15v x12 =49.8v

The cells on all 4 packs have a max cell voltage of 3999mv and min of 3937mv a variance of 62mv. Before connecting the SimpBMS battery management this was less than 30mv, the battery management acts as a master and uses the original BMW slave battery monitors on each pack to monitor cell voltage, temperature and to balance. This balancing feature pulled down one cell and has resulted in the wider cell voltage margin than the packs had for over a year running without it. Today I have switched it on to read the cell values and it is showing a voltage of 191v. I just do not trust it to manage the batteries. As there are only 12 cells in series in each pack it's not like a Tesla pack with hundreds of cells.

The Victron Smart Solar chargers only see voltage they don't see individual cell values so when they hit 49.2v they should switch off and maintain at 49v that's what the settings are for but they are not doing that and I carnt workout why.

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snoobler commented · Apr 20, 2022 at 02:07 PM

the sum of those voltages are less than the total by at least 1V, so I assume you're not reporting the cell voltages when the MPPT is running at 49.XV+. Again, what are the voltages of the cells at absorption.

If your BMS is reporting an incorrect total voltage, are you certain it's functioning properly? Will it protect the cells? If not, you should replace it.

Do you have temperature compensation enabled?

Do you have ESS enabled? It's my understanding that ESS settings will override MPPT settings.

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tarmacshredder commented · Apr 20, 2022 at 04:52 PM

Thank you @snoobler for your reply.

I am unable to see what the voltage of the cells is at absorption as we have past that point today. At float the VRM is showing a voltage of 49.22v and the cell voltages are 4051mv lowest 4119mv highest. The Solar chargers are showing a voltage of 49.44v and the bmv 49.33v.

As I have previously stated the SimpBMS battery management is switched off. 1) it is displaying the battery voltage as 191v which automatically flags a system over voltage, 2) when it tried to balance the cells it created the imbalance of previously 18-30mv now around 60mv. A suggestion to an alternative BMS that can be used with the i3 battery packs would be greatly received.

I am not sure why the temperature compensation is required as the cells remain at a pretty much constant temperature and I am not sure it is compatible with the earlier firmware on the quattro inverter.

As far as I am aware the ESS Victron system is only suitable for grid tried setups and the ESS manual states

When not to use ESS

Off-grid systems - either with or without generator.

When I originally looked at building the setup it was my understanding from what I read that the Victron GX would control the system but it doesn't in an off-grid setup. It was always my intention to have the battery management balancing and controlling the charge of the batteries, but after literally hundreds of hours with the developer of the battery management I can not get it to work as I intended.

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snoobler tarmacshredder commented · Apr 20, 2022 at 05:04 PM

Wanted to see that cells weren't pushing past 4.20V.

Get another SimpBMS?

Not sure it will work, but they're pretty flexible with active balancing - JK BMS - one per battery. Will require that you directly connect sense harness to cells.

A LiPo battery without a BMS is a ticking time bomb. This is not something you should continue.

Temperature compensation should not be used with Lithium. Did you confirm it isn't active?

Agree, ESS should not be used. Confirming it's not.

Recommend you give yourself more headroom until you get a BMS on your system. Adjust absorption to 48.6 and float to 48.0V.

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Answer 4 · 2022-05-06T10:33:02Z

tarmacshredder answered · May 06, 2022 at 10:33 AM

Just a quick update as I have managed to get the charge controllers back to doing what they used to before this glitch which had appeared this year.

Thanks to both the info @Alexandra and @snoobler gave has got it back up and running properly.

I had carried out a firmware update at the start of my troubleshooting and although the Venus automatically updates the 2 charge controllers don't. So I updated the one that is being used and then updated the second. It said update successful and closed the Bluetooth connection as usual. However I have subsequently gone into the second charge controller and it said it required an update to latest version which is the one I had installed. So I again did the update, logged out and back in and it is now running the latest version same as other charge controller. However some of the settings had changed so absorption time was 15mins, which wasn't correct and the temperature compensation was switched on which it shouldn't have been. So I changed these settings to 0 mins absorption and temp compensation off and touch wood since they have been behaving them selves.

As I have discovered previously though, changing one thing always has a knock on effect, the VRM portal flow chart no longer shows the tag next to the charge controllers to say if they are bulk, absorption or floating which is a pain and not sure how to resolve that.

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klim8skeptic ♦ commented · May 06, 2022 at 10:47 AM

VRM portal flow chart no longer shows the tag next to the charge controllers to say if they are bulk, absorption or floating which is a pain and not sure how to resolve that.

This has been a topic lately.

Perhaps you could check your mppt's status via remote console?

Or even look at the mppt's led status?

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