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MPT-7210A Questions
#11
(02-13-2018, 03:23 PM)gpn Wrote: What are you using for a data logger?

It's an ESP8266 + ADS1115 and custom board, there's more detail here: https://secondlifestorage.com/t-Adding-L...er-C2-4000
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#12
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.
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#13
I never discovered why this was happening. Seems to be a design issue. I ended up just using a lower speed 80mm fan.
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#14
I added 3mm spacers between the fan and the aluminum case, the noise is much milder now
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#15
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?
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#16
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 Tongue
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#17
(03-04-2018, 01:47 PM)thanar Wrote: 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.
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#18
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.
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#19
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) Tongue
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#20
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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