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Wiebe Ruiter avatar image

How to correct or repair a BlueSolar MPPT 150|35 that is reading battery voltage wrong

I have a working installation of a BlueSolar 150|35, v1.16, connected to 2 parallel series of 3 250W/24V panels. The battery bank consists of 5 pairs of 2 batteries, each battery a 110VA 12V stationary battery. The system has been working for almost 2 years without any problem. Four days ago, this changed:

- the system did not have power anymore to run a water pump

- because the battery voltage was too low, about 22.5 Volts

- the MPPT was stuck in 'float' mode really early in the day and because of this, never charged to batteries

Yesterday I managed to (re)connect the MPPT to a Linux machine using the VeDirect RS232 connector. Connecting using minicom, baudrate 19200 and 8bits, I got data frames from the MPPT, below a copy of one of them:

PID 0xA04B
FW 116
SER# HQ1746JGWU1
V 27320
I 300
VPV 101460
PPV 9
CS 5
ERR 0
H19 159940
H20 36
H21 723
H22 23
H23 400
HSDS 314

This tells me, that the MPPT thinks that the battery voltage is 27320 volts. One minute after seeing this, I measured the battery voltage using a multimeter. Battery voltage is 23,3 volts on the multimeter. The MPPT software seems to stay in float, because of the high voltage it measures.

What are my options ?

- is there a way to re-calibrate the voltage measurement of the batteries ?

- is it safe to re-configure the treshold voltage, set it to a higher value, like 30 or 32V, in the hope that it will go to float when the battery actually has 27 or 28 Volts ?


MPPT - Solar Charge Controllervoltagemppt chargingbattery system voltage
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3 Answers
Matthias Lange - DE avatar image
Matthias Lange - DE answered ·

Did you check the fuses between MPPT and battery?

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Gave my comments as separate answers, please excuse me for that. See my other answer.

I did check the wiring and switches, but I can not identify any problems. All switches / elements seem OK. However, when I measured the voltage on the battery terminal of the MPPT, it is 27,2 V just like the data link tells me. All battery pairs have 23,2 V.

The voltage drop must be caused by the wiring. Which is a really good thing, because I should be able to fix it without buying/replacing anything difficult. I live in an area of Brazil, where anything that comes by mail;takes a month or more, even more so with the current situation. I still do not understand how that can change overnight, but:

Your answer put me on the right track. Thank you very much! Have a good eastern weekend.

Wiebe Ruiter avatar image
Wiebe Ruiter answered ·

Sorry, just a detail I got wrong in the answer: the switches per battery pair are rated 50A, not 40A as shown in the photo.

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Wiebe Ruiter avatar image
Wiebe Ruiter answered ·


I have this kind of switch between each pair of the batteries and the connection to the MPPT. Earlier on I had one circuit breaker for the whole battery bank, but I installed them for each battery pair last november, in order to make maintenance on the batteries easier. This was the last time I did maintenance on the system. All cables are 6mm copper cables.

All switches are on, no 'ugly' connections or burn marks, no corrosion visible, no warmth beyond the normal temparature here (+/- 30 degrees), everything firmly connected. Yes, these switches are made for 220V, but they are rated 40A.

The highest current I have in my historic data, going back to 2018, was 17A battery current as measured by the MPPT.

What should I look for ? I understand that you want me to check, if this voltage drop can be caused wiring.. is that correct ? It happened overnight, there was no gradual thing here. I will check everything again.



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I'm not an electrician but I don't think you should be using AC breakers on DC circuits. I've done some reading on this particular topic and although some people do it, it's not advised. Here's some great explanations on why:

https://www.quora.com/Why-we-cant-use-AC-circuit-breaker-for-DC

I noticed on one of your other comments that your voltage readings are different on the MPPT terminals and different on the battery terminals and you suspect there might be an issue with the cable - if you were carrying more current than the cable was capable of and the AC breaker didn't trip then you might have damaged the cable through persistent heat damage and this might be the reason why?

Yes, it was exactly this. After checking all switches, I thought all was fine. However, when I measured voltage drop from component to component it was the cable from the MPPT to the first contact, before going to the batteries. The contact was corroded and caused resistancea and yes, definately a lot of heat. The switches did not trip because it the corroded point was before this point, it was the point where I had the main switch originally.

Using AC switchers is indeed hardly ideal, but I am living in an area (north of brazil) where it is really hard to find the right components. I read in the article you mentioned: 'Typically a 110V AC breaker will only be rated for 30V DC, and it will still suffer more erosion and have a shorter life.'. I have 220V switches and I am using them for 24V (max 27,5) and highest historic battery current of 17A. However, I really do not like the erosion and shorter life part, so will look for better components again.

The MPPT is working fine again after switching out the cable and the connector, however, I am definately looking for better components to reduce or eliminate the corrosion.