MPPT works with 3S2P panels but not 4S1P, 4S2P, or 5S1P even though I'm under the voltage rating?

[BlackSquirrel]

This is a strange one for you all. My basic project is that I have an already existing and functional home-made UPS and I thought it would be cool to add a solar charge controller to it for some additional capability.

I'm honestly not even sure which part of my setup is the source of my problem. Maybe (hopefully) I'm just missing something obvious. Like the title says, I have a setup that works with 3 panels in series, but not 4 or 5. But in the 4 or 5 panel case I'm still below the solar voltage rating of my MPPT. Here's the system info:

• 48 V lithium iron phosphate battery pack, home-made using individual 200 Ah cells. It is a 16S1P configuration. I have a Daly BMS that is functioning just fine. All cells were top-balanced and during the testing described below it was at about 70% charge with a maximum cell-to-cell voltage difference of about 0.03 V. This battery and BMS are known to be functional, they are currently use it as an UPS.
• The inverter charger is a SunGold unit. It is not relevant to the testing below as it was powered off and disconnected during all testing to help isolate the problem. The only important information is that I can and do charge the battery pack with it at around 15 amps, which is how I know the battery pack works and stays in balance. Per the battery specs I could charge with more amps but I choose not to.
• I have 12 identical 12 V portable solar panels. They are nominal 100 Watt panels, and have a Voc of around 22.1 V, which was confirmed on all panels with a volt meter in full sun with MC4 connectors disconnected. These are also all confirmed to be functional, I have used them before and they all generate their approximate nameplate capacity of 100 W in full sun.
• I have a Victron SmartSolar MPPT Ve.Can 150/85 charge controller. I suspect this is the source of the strange behavior.
• I have all appropriate safety protections in play, my wires are sized appropriately, OCPD on battery pack, etc.

So here's the behavior I'm seeing: The MPPT seems to output very low charge power on solar (4-5 W) if my solar voltage is too high. But all my testing has stayed within the solar voltage spec of 150 V. And I know it's not a power problem because I can run panels in a 3S2P, 3S3P, or even a 3S4P configuration and everything works great! All results below are from a cloudy day, so I was especially not stressing any components.

My testing:

• 3S1P works fine. 60.96 V of solar. 300 W maximum power, actually receiving 153 W due to clouds. Screenshot below.
• 4S1P doesn't work. 91.99 V of solar. 5 W of charge power. I left it for over 30 minutes and it definitely included moments of full sun. Screenshot below.
• 4S2P doesn't work. 93.31 V of solar. 2 W of charge power. Also left for ~30 minutes to definitely include moments of full sun. Screenshot below.
• 5S1P doesn't work. 113.41 V of solar. 4 W of charge power. Also left for ~30 minutes including moments of full sun. Screenshot below.
• 3S2P works fine. 63.78 V of solar. 314 W actual power from nominal 600 W of panels (again, cloudy day). Screenshot below.
• 3S3P works fine. 65.32 V of solar. 559 W of actual power from nominal 900 W of panels. Screenshot below.
• 3S4P works fine. Forgot to screenshot this one but I measured roughly 65V solar and it charged at around 950 W of power for over 10 minutes, fluctuating with clouds.

I confirmed charge current with a clamp meter for all tests. BMS agreed with the charge current reported by Victron and measured with my clamp meter. Victron firmware is up to date. I'll also add that the whole time neither the Victron MPPT nor the Daly BMS threw any kind of error code.

Any thoughts? I should have no problem doing 5 panels in series, it's over 30 V below the rating of the controller. And I'm well under-using the MPPT device, it's rated for thousands of watts more than I'm pushing with it.

Screenshots:
3S in 1P, 2P, and 3P in cloudy conditions:


4S1P 4S2P:

5S1P:

Victron battery settings:

 

[Rocketman]

You’ve got me at a loss…

Do you have a breaker or switch between the panels and the mppt( to turn off the sun)? And between the mppt and battery. Have you tried “turning it off and on again”?

A couple of times (two or three over years), my Victron mppt 100/50 got stuck as it was looking for the mppt point. The solution was to turn off the sun, turn off the mppt (to the battery), wait 30 seconds… turn the mppt back on, and turn the sun back on. (I don’t know which steps were absolutely needed- that’s just my process). Then it worked just fine. As I recall - this would only happen with cloudy-ish skies.

Good luck!

You may also want to forward this email to your Victron dealer.

 

[BlackSquirrel]

You’ve got me at a loss…

Do you have a breaker or switch between the panels and the mppt( to turn off the sun)? And between the mppt and battery. Have you tried “turning it off and on again”?

A couple of times (two or three over years), my Victron mppt 100/50 got stuck as it was looking for the mppt point. The solution was to turn off the sun, turn off the mppt (to the battery), wait 30 seconds… turn the mppt back on, and turn the sun back on. (I don’t know which steps were absolutely needed- that’s just my process). Then it worked just fine. As I recall - this would only happen with cloudy-ish skies.

Good luck!

You may also want to forward this email to your Victron dealer.

It's a good thought, but indeed I did try exactly that, and saw the same behavior on different days in different weather conditions. I didn't get screenshots but I repeated this test a couple of weeks ago in full sunlight. I was hoping it wasn't a faulty Victron unit but I can't imagine what else it would be at this point.

 

[sunshine_eggo]

+1 to @Rocketman

Sounds like a bum controller to me.

My 250/100 and the prior 150/100 were always bulletproof, but I've only every used them in 2S2P or 3S3P configurations (47Voc panels). It has always behaved as expected.

Contact your dealer for replacement. If they don't agree to replace, you can submit a ticket through Victron.

https://professional.victronenergy.com/support/

 

[Warpspeed]

Agree, something is definitely not right with that controller.

 

[StuartV]

Could it be too many Amps? with the 4+S config?

 

[BlackSquirrel]

For any and all people of the future who stumble upon this thread with a similar problem: it turned out to be a faulty charge controller. I put in a warranty request, sent the unit back to the distributor, and they tested it and found it to be faulty. The sent me a replacement MPPT that works perfectly fine.

Thanks for the input everyone!