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enya avatar image

BlueSolar MPPT 75/50 & External Voltage and Temp sensor to optimise charging

Hi team,

Seeking optimal setup for solar charging and ensuring live Volt and Temp values are used during charge cycle.

I understand the BlueSolar will use internal temp sense for baseline just prior to start of day charging. Can the MPPT use the temperature sensor on the 702 for live input during charge cycle to compensate from temperature.

Additionally can the MPPT source voltage at SHUNT on 702 to more actual gauge the votage level at the battery specifically rather that at the MPPT. (I have noted a differance from what the MPPT show as voltage vs what the 702 shows as voltage at the battery by 0.5VDC. The distance between MPPT and SHUNT/Temp Sensor is cable length POS of 5-6 meters plus return of same distanace for NEG. Cable gauge is 70mm2, so I don't believe differance is due to voltage drop over cable length?)

There are 2 x MPPTs and 2 x 702 are connected to VenusGX. I am currently running 702 with temp sensor, but in future would like to move to midpoint monitoring on 702 and use alternative battery temp sensor conneced to VenusGX for use by the MPPTs

Thank you.


MPPT - Solar Charge ControllerTemperature Sensortemperature compensation
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Voltage differances.pdf

See attached VRM portal view of differing Volt between MPPT and BMV

2 Answers
JohnC avatar image
JohnC answered ·

Hi @Enya

Re the differing V's. If the BMV was supplied with a 100mA fuse, replace it with a 1A fuse. T1AL250V for reference (mightn't be a Victron p/n).

This issue has cropped up before, and that seems to be always the recommendation. Too much resistance in the small fuse?


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Hi @JohnC,

Thank you for the advice. I reviewed the fuse and yes it is a 500mA. I was just about to go and get the small 1A fuse as you suggested , when I thought to do a little more investigation. I measured with my Multimeter (MM) the actual volts at the same place as the sensor and also at the Battery terminals output of the MPPTs. Both are reading sight discrepancies. What I believe is causing the discrepancy is 3 fold.

First there is what you have suggested wrt fuse. I measured at the same battery terminal that the sensor is on and got the following results.

BMV702 display reports 12.61V

VictronConnect reports 12,61V

MM at same terminal is 12.56

A delta of 0.05V

Second is within the MMPT. Using Victron Connect to display.

MPPT voltage 12.63

MM at the MPPT Output terminals 12.57

A delta of 0.06

Third

The difference between MM at MPPT output and MM at Battery Terminal.

MM at the MPPT Output terminals 12.57

MM at same terminal is 12.56

Delta of 0.01 ( assumed due to cable length)

I think I will do the following.

A replace fuse as you suggest.

B redo testing with MM on battery terminal vs BMV702 display and VictronConnect

C All going good with the fuse fix, Introduce Distrubuted Voltage and Current Control (DVCC) with Shared Voltage Sense (SVS) and Shared Temperature Sense (STS) as suggested by Klim8skeptic for the introduction of midpoint monitoring via the BMV702 optional function and additional cabling.

Regards

klim8skeptic avatar image
klim8skeptic answered ·

Hi Enya,

" in future would like to move to midpoint monitoring on 702 and use alternative battery temp sensor conneced to VenusGX for use by the MPPTs"

This is how my system is setup and working.

DVCC, SVS, STS, SCS all work well.

The only thing that is not working is synchronized charging for the bluesolar mppts.

Don't buy anymore BT dongles, put that money towards a Venus and cables.

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Good Morning @klim8skeptic,

I did sum reading wrt to DVCC. I had not been following the develop of this function since first discussing it with Victron some 2 years ago. Good to see that it came to fruition. Tell me what temp sensor did you use into the GX? ASS000001000

Regards

Hi Enya,

Not sure of Pn, but I used this.

Further reading.