MPT-7210A Questions

rev0

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Hi All,

I've been charging my 48V 1.3kWH pack from a 160W panel in my patio, using an MPT-7210A. I followed some Youtube videos on how to set it up, get it to auto-charge, etc. but I've discovered some odd things about it so far and I can't tell whether I have a defective unit or whether this is "normal".

First, I can't set the fan speed to anything besides 100% power otherwise the output gets unregulated and the screen flickers. I've made a video which I shared with the seller, who is asking me now how much it will cost me to "repair at a shop" so they can give me a partial refund. Otherwise they seem clueless about this issue:

Second, it does not seem able to charge constantly/consistently. Most I've seen it put out is 107W into the batteries, which is fine for me, but after 30s(?) of running at ~100W, it then shuts off the output, "rests" for a while, then slowly ramps power back up to ~100W. Is this a setting issue, is it overheating, is this just normal? This may be why I'm only getting ~110WH on a sunny day even though I should have at least 2 hours of direct sunlight.

Any comments from others who have used this cheapo controller would be helpful, as I'm still just starting out/learning about solar charge controllers.
 

Korishan

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Sounds to me like something is getting hot inside and thermally shutting down. Watching the video, it looks like it's possibly the power regulator is causing an issue with the screen. Or an incorrectly sized capacitor and it's constantly getting drained/recharged, causing the flickering.

Other than that, I'm not sure. :s
 

floydR

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In parts 3 and 4 he talks about replacing the capacitors both smd and the lager ones on the board.
Mikes DIY Powerwall Update 31 MPT-7210A MPPT Solar Charge Controller Testing Part1/4
later floyd
 

rev0

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Thanks, I'll check those out. Looks like he replaced the fan also in a later video.
 

daromer

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Hmm first one seem to be an error. The 2nd can also be related to the set tracking point. What voltage are your panels and what tracking point have you set?
 

rev0

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Still can't figure out the fan issue; tried adding a bigger capacitor in parallel with the fan output but it didn't change anything. Instead I switched to a larger, quieter, and as it turns out twice as power efficient (~82mA vs ~160mA) 80mm fan and 3D printed an adapter for it. At least this way it's quieter and using less power at 100% setting:


image_hdudok.jpgimage_kntuab.jpg


image_gbwtkc.jpg

image_kikuqy.jpg


File is here if anyone else wants to do this mod, it's not very good for airflow since it's offset and very shallow of an adapter, but it's probably still about the same airflow as the original 40mm fan:https://www.thingiverse.com/thing:2771460

Otherwise, I did the 100nF -> 10nF mod for C22,23,24 as Mike did in his Youtube videos, might help a little, not yet sure. I'll add a pair of 2200uF 50V capacitors on the input from the solar panel also which may help a bit with quick voltage drops like a plane/bird flying by.

I'll also be adding in an ESP8266 (D1 Mini) and current/voltage logger from here:https://secondlifestorage.com/t-Adding-Logging-to-MiBoxer-C2-4000 also.


daromer said:
Hmm first one seem to be an error. The 2nd can also be related to the set tracking point. What voltage are your panels and what tracking point have you set?

Tracking point is set to 35.1V, panel is a 160W Pmax panel at 35.1V Vmp and 44.2V Voc.
 

rev0

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Here's some scribbles about the circuit diagram ifanyone is interested, I only bothered with the main power path so I can add a loggerand some bits trying to figure out what was wrong with the fan:


image_argfbz.jpg


The shunt before the battery outputis approximately 10mOhms, whichgave me 9.64mV/A at 2A load.
 

rev0

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Well, got back from vacation and found out I had reversed the polarity of the panel like a dummy, so I only have one day of solar so far. Today it didn't seem to record any data even though it got lots of sun, probably because the MPT-7210A is in a metal cabinet (outdoors)with poor Wi-Fi, even though it's only about 10' away from the access point (indoors). Here's the log it recorded from the bench test charging a battery, then the solar panel voltage log from yesterday:


image_mygyub.jpg


image_wfxkmb.jpg
 

thanar

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I also got an MPT-7210A unit and have been running onto the same issue with strange battery voltage reading when the fan setting is anything below max. I also thought of adding a capacitor in parallel, since the fan also does a voltage regulation sound when not at max setting, but since you already tried it, I won't be. Have you found any solution on running the fan at a lower setting?
The other issue you're facing I believe is normal for MPPT units.
 

rev0

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I never discovered why this was happening. Seems to be a design issue. I ended up just using a lower speed 80mm fan.
 

thanar

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I added 3mm spacers between the fan and the aluminum case, the noise is much milder now
 

thanar

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Ok, I have another question:
What if you connect a BMS-equipped battery on the MPT and for some reason there's an imbalance in the pack and the BMS kicks in and cuts the power to the battery, as it should do. Wouldn't that harm the MPT, given the requirement to connect the battery BEFORE connecting the solar? That way, when the BMS reconnects the battery, it's gonna be like you're connecting the battery AFTER the solar source.
Thoughts?
 

Korishan

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just have a capacitor between the MPT and bms. That way the MPT will always sense the proper voltage. When the bms kicks back in, the cap will discharge into the battery and the MPT will sense the correct the voltages of the string.

That's my view on it, though. I'm sure others more qualified can supply a more accurate and robust answer. But I just happen to be awake atm :p
 

rev0

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thanar said:
Ok, I have another question:
What if you connect a BMS-equipped battery on the MPT and for some reason there's an imbalance in the pack and the BMS kicks in and cuts the power to the battery, as it should do. Wouldn't that harm the MPT, given the requirement to connect the battery BEFORE connecting the solar? That way, when the BMS reconnects the battery, it's gonna be like you're connecting the battery AFTER the solar source.
Thoughts?

Not quite sure how this could cause any damage. I have my battery disconnected for long periods of time with solar still connected. The MPT just thinks the battery is full since it goes to CV mode with no current output.
 

thanar

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There's no problem with having no battery connected. You just should not (I don't know why, it just says so in the chenglish manual) connect the battery while the solar is connected. Thing is, if a BMS has cut off power to the battery, and it so happens that it resets and connects the battery at some point, that would be like connecting the battery to the MPT while the solar input is already live.
 

rev0

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It may put extra stress on the DC-DC converter since connecting a lower voltage load suddenly would dump a bunch of current, first from the output capacitors, then presumably from the DC-DC converter until it takes time to regulate back down near the battery voltage. That said, if the BMS is cutting power to the battery it is probably because it has already hit max voltage and is disconnecting to give time to balance. At least that's how my BMS is configured, I'll let you know if I have any problems in about a week when my ~1.8kWH pack is charged (from my 100W panel) :p
 

Korishan

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It's also possible that the "first" power on should be with battery connected first, then solar. This might be due to the characteristics of the way the unit pre-initializes itself. Once it has done this the first time, all re-connections afterwards might not matter. So as long as the time between full power disconnect isn't too long (for the capacitors and such to discharge).
At least, this is a theory.
 
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