Issue with MPT-7210A

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rokempes

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Jun 20, 2021
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Hello,

I’m trying to charge my 10kwh li-ion battery pack (18s) using 2 x 340w solar panels connected in paralel. Panel voltage is 35.5v. I’m using MPT 7210A as a charge controller, battery charge cut-off set to 73.4 volts. I can’t figure out why doesn’t go over 96watts. I’ve tested with a dc-dc 1200w step up converter and I get about 500watts, but with mpt 7210 cannot go over 96watts. I’ve put a step up between the battery and mpt, set the output to 60 volts instead of 73, and I get about 400watts, but when connected directly to the battery pack, it seems to stop at 96w. Also, panel voltage doesn’t go under 36.7v. Any idea how to solve this?
 

OffGridInTheCity

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These have a 10a 'max' on the output side (if memory serves) rather than watts. So 10a * 50v = 500w - maybe you're running into this.
 

rokempes

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These have a 10a 'max' on the output side (if memory serves). It's not about input - but output/charging max. 10a * 50v = 500w - maybe you're running into this.
On the display it says 1.25A, 72.5v. 500w should be great… but I’m getting less than 100w. Now is raining, I get 87w, but in full sun, I only get 96w from 2 340w panels.
 

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OffGridInTheCity

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Ah - I misunderstood. Its true that there's a 10a limit on output but its the input side that you're having trouble with.
OK - the unit does not like to 'step down' its a 'boost' unit that can take 12v input and boost to 24v or 48v type of thing. I've never seen it used with other than 12v panels (for example).

Maybe the voltage of your 340w panels is too high for this unit and it can't process it effectively. Other's may comment. You may need to get a different charge controller that is suited to your panel input.

Do you have the 2x panels wired in parallel?

You can certainly get a lot more power (regardless) by getting a charge controller than can handle your panels. If this is of interest - we can suggest a few.
 

rokempes

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Ah - I misunderstood. Its true that there's a 10a limit on output but its the input side that you're having trouble with.
OK - the unit does not like to 'step down' its a 'boost' unit that can take 12v input and boost to 24v or 48v type of thing. I've never seen it used with other than 12v panels (for example).

Maybe the voltage of your 340w panels is too high for this unit and it can't process it effectively. Other's may comment. You may need to get a different charge controller that is suited to your panel input.

Do you have the 2x panels wired in parallel?

You can certainly get a lot more power (regardless) by getting a charge controller than can handle your panels. If this is of interest - we can suggest a few.
Thank you! Of course I’m interested in any controller capable of 73v output. This is the only one I’ve found. Most controllers work up to 48v.

And yes, my panels are wired in parallel.
 

OffGridInTheCity

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Thank you! Of course I’m interested in any controller capable of 73v output. This is the only one I’ve found. Most controllers work up to 48v.

And yes, my panels are wired in parallel.
So you want 72v nominal.
Here's one that seems legit - https://makeskyblue.com/products/72v-50a-mppt-solar-charge-controller-for-3600w-pv-solar-panels - with
System voltage automatic recognition72V (DC60V~DC90V)

Midnite Classic 200&250 also can do 72v nominal - http://www.midnitesolar.com/pdfs/Classic-Lite-SL-Chart.pdf - but these are $700 range.

The consideration for the above (which is why you probably chose MPT-7210a) is that the PV input (to a charge controller) needs to be higher than the battery voltage (coming out of a charge controller). Even if you put your panels in series - you're only going to have a 70v Vmp.
----------------------
I just looked up the specs of the MPT-7210a here ... https://zhcsolar.com/product/mpt-7210a-mppt-controller-48v-60v-72v-boost/
Notice that max input voltage is "Voltage: DC 12-60V"... so your panels (in parallel) should not be too high.

I have a DIY solar generator where I use 2 x 100w Renogys -> MPT-7210a and it works to a 24v battery. I've gotten 150watts (75% of panels) So the unit 'can work'... .

Sorry to not be of more help except to perhaps ask the obvious questions in an effort to move the conversation forward:
- Maybe try 1 300w panel (reduce incoming amps) and see if it make any difference....
- Can you add a 3rd panel - for 105v Vmp? to get in range of the MakeSkyBlue charge controller?
- Can you do other than 72v battery?
 
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rokempes

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I cannot add a third panel. There is no room. This set-up is on an electric sailboat, using a 72v, 9kw BLDC motor, so modifying the battery set-up is not an option. I’ve tried with only one panel, I get the same 96w. I’ve also tried to add 2 3mm wires in paralel from the junction, didn’t help either. It seems something like a bug in the controllers software. It just stops at 96w. Tomorrow I will change the input capacitors and try with the panels in series (72v as input for the mpt).

I’m considering buying another unit - maybe I got a faulty one. Also, I’ve used some plastic spray on the board (for humidity protection). Maybe that broke something, but the spray is specially designed for PCB.
 

OffGridInTheCity

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I cannot add a third panel. There is no room. This set-up is on an electric sailboat, using a 72v, 9kw BLDC motor, so modifying the battery set-up is not an option. I’ve tried with only one panel, I get the same 96w. I’ve also tried to add 2 3mm wires in paralel from the junction, didn’t help either. It seems something like a bug in the controllers software. It just stops at 96w. Tomorrow I will change the input capacitors and try with the panels in series (72v as input for the mpt).

I’m considering buying another unit - maybe I got a faulty one. Also, I’ve used some plastic spray on the board (for humidity protection). Maybe that broke something, but the spray is specially designed for PCB.
For discussion...
You can parallel the output of MPT-7210a That's why I asked about maybe 1 panel? and do 1 MPT-7210a per panel and get up to 200w. Maybe even get smaller panels and have 3 or 4 100w panels and find a combination of panels + paralled MPT-7210a that get you up to the watts you are OK with.

Crazier - go with a conventional charge controller-> smaller battery (12, 24, 48v) -> Inverter -> 72v charger. Even if you loose 15% in the process you should be able to get say 600w (from panels) - 15% = 510w total. The intermediate battery need not be that large.

Would be interested if you find time to post your future results.

*I agree - maybe this specific unit is 'bad' as well - they are not know as top tier pieces of equipment :)
 
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jdeadman

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The top number on the 7210 you need to set to your panels MPPT point. I found for my 21V oc (open circuit) they got the most power at 14V that was going to a 7s Li-ion pack with a max V of 29V But I was only ever able to see 50% of my Panels rated capacity. But Play with the Panel Voltage number to see if you get it to work better. Also check your max voltage on the controller to make sure it's working. I would also test each panel by getting a clamp DC meter and shorting the panel and test the current then open the panel (open circuit) and test the voltage, that will give you the Max panel Wattage (VxI) and you can make sure both panels are working. If you get a different Voltage OC then I would take 70% of that number for your MPPT voltage.
 

ajw22

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to add to jdeadman:
Glancing over the manual, it seems this charging unit (I've never used it) needs several parameters set in advance to work properly. Primarily the ideal PV panel voltage "Vmp" (35.12V in your case) and maximum charging current the battery can take.
Looking at your posted pic#1, the current PV panel voltage shows 32.55V, which is a fair bit lower than the ideal setting, so might suggest the settings are not correct.
If you're getting a fairly constant max of 1.25A, then maybe the current limit is set to that?

https://www.yampe.com/images/pdf/2907.pdf ; page 5
 

rokempes

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to add to jdeadman:
Glancing over the manual, it seems this charging unit (I've never used it) needs several parameters set in advance to work properly. Primarily the ideal PV panel voltage "Vmp" (35.12V in your case) and maximum charging current the battery can take.
Looking at your posted pic#1, the current PV panel voltage shows 32.55V, which is a fair bit lower than the ideal setting, so might suggest the settings are not correct.
If you're getting a fairly constant max of 1.25A, then maybe the current limit is set to that?

https://www.yampe.com/images/pdf/2907.pdf ; page 5
I’ve tried everything, setting voltage from 33v to 45v, still 96w. Indeed, when I took the pictures it was cloudy.

Today I’ve added a 1200w boost converter before the MPT unit. Set the output to 60v and I got 350watts. It seems that the problem is linked to the panel voltage/battery voltage. Orderer another unit today, still thinking the unit is faulty.
When I get 96w on a sunny day, the panel voltage is 36-37volts. Voltage on the mpt was set to 35v.
Introducing a boost converter before the MPT seems to increase the maximum power 3.5 times. It seems that this unit has some problems boosting 35v to 73v.
Will test in the next days another unit.
 

daromer

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It have a max current. It wont go above that on input limiting max output power.
 

ajw22

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italianuser

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Just supposing: the difference in voltage between panels and batteries is too high. As a test I'd try charging a 24V battery (or two 12V batteries in parallel series). I'd bet a coffee it will give you full output. So... If I won a coffee by now LOL I would continue the test with a 36V battery to see the outcome... :giggle:

[EDIT: series]
 
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rokempes

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Ok, after testing it seems that MPT 7210A has some problems with stepping up 35v. I’ve replaced the 2 input capacitors with the 100v ones (instead of 63). Added a step up with output voltage of 64 volts before the MPT unit, set output to 73v and now I get 400w. It seems that on high voltage set-up this unit has some issues. I don’t know if is related to the input voltage or the output voltage. Now is cloudy, I will add some pictures as soon as it clears up. In theory, it should be able to deliver 500w out of 680w maximum. (0.8 x 680 x 0.95 x 0.95).

I want to document this for others with similar set up.
 

italianuser

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Ok, after testing it seems that MPT 7210A has some problems with stepping up 35v. I’ve replaced the 2 input capacitors with the 100v ones (instead of 63). Added a step up with output voltage of 64 volts before the MPT unit, set output to 73v and now I get 400w. It seems that on high voltage set-up this unit has some issues. I don’t know if is related to the input voltage or the output voltage. Now is cloudy, I will add some pictures as soon as it clears up. In theory, it should be able to deliver 500w out of 680w maximum. (0.8 x 680 x 0.95 x 0.95).

I want to document this for others with similar set up.
Very good, you found the correct fix (y)I think it could be a problem on "high voltage differences" instead of "high voltage".
I was wondering if reviews online ever noticed this problem...
 

rokempes

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Ok, so now is 9:30AM, sunny day. I get 275w from 680w (2 x 340) panels, which is great! I’ve added a picture with the 1200w step up that I used which has a nice feature - low input voltage cut off. I’ve set it to 34volts (panel is 35.5). When it hits 34v on the input, it connects the input with the output (same voltage). When this happens the boost function is managed by the MPT controller.
 

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