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685eric asked

MPPT 100/50 Charge Controller Reading Wrong Voltage


I am having an issue with my MPPT 100/50 charge controller reading the wrong voltage, which in turn does not fully charge my battery bank. The charge controller is networked with a SmartBMV battery monitor. The charger controller receives battery voltage and temperature from the battery monitor through VE smart networking.
For example, my battery monitor is reading 26.45v. This is the correct reading, verified by a volt meter and consistent with the state of charge. When I log into the charge controller, the voltage is reading 27.26v. This is WAY high!! This stops my batteries from fully charging. If I sit there in the app and watch the battery voltage for a while, it will sometime dip down to ~26.8v and then jump right back to ~27.2v. When this happens, EVERYTHING is off. No charging or discharging. Battery monitor voltage does not move and stays right around 26.45v.

I thought maybe the battery monitor was sending the charge controller the wrong voltage, so I removed the VE smart networking between the two devices. So now the charge controller is reading the voltage for itself. The charge controller was still reading around 27.2v. Nothing changed. Reconnected the network, charge controller was receiving the correct battery temperature, but the voltage was again high, around 27.2v. Do I have a bad charge controller? It is less than a year old. I am not a novice at this as I have an undergrad in mechanical engineering and a master’s in industrial engineering. My day job is mostly electrical engineering. This issue is starting to drive me nuts. Am I missing something? Is this a known issue? Firmware on both devices are up to date. Battery monitor v4.03, charge controller v1.46.

MPPT ControllersBMV Battery Monitor
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4 Answers
685eric avatar image
685eric answered ·

After reading a lot of questions on here, I think it is a connection issues. I think the wire I have is thick strand wire. I will get some new wire and see what happens.

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zali avatar image zali commented ·

Tell me more on this, I'm having the same issue...I'm using what I feel is 6 gauge fine stranded wire to go about 25ft from my charge controller to me battery bank (in RV) and once the solar gets around 250+ watts coming in, the charge controller starts climbing on battery voltage right up to the absorption setting while the battery monitor stays constant at a good voltage. What kind of wire did you use? I am noticing that when the charger is at a higher input watt that the positive lead going to my batter does get a bit warm to the touch. Did you notice the same issue?

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danmannale avatar image
danmannale answered ·

Hi @685eric

Did you find out what it was? I am having a very similar problem..Seem like the voltage reading is calibrated wrong on my (new) device...

Best regards,

Daniel



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zali avatar image
zali answered ·

Wanted to post this here so others with this same issue can be aware. I have a 100/50 charger controller & 4 x battle Born 12V batteries. I'm using 6AWG stranded wire from the controller to the batteries and in the middle put a 50 amp fuse...well turns out the fuse block was creating some kind of voltage blockage and that was my problem. I have since taken the fuse block out of the mix and all is working as it should...granted I still need to put a fuse block in, but this time I'll get a much better one. I read another post talking about testing the voltage at every junction point from the charge controller to the batteries...yup that did the trick. If others are having this issue, start with the wires from the controller to the batteries and go from there.

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mitchporter answered ·

Just wanted to say thanks to the peeps for posting this. After replacing the blade fuse on my MPPT 75/15 I noticed the app wasn't accurately reporting the battery voltage by saying it was higher than it actually was, in line with the symptoms mentioned in here. This thread made me stop and think I may not need to disconnect it and take it back to the retailer, but the problem might actually be caused by the fuse. The moral of my experience is don't buy replacement fuses from the dollar shop! They may look like the real deal, but God knows what they're made of! (btw SCA fuses work fine).

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