Solar Victron Question

[nixfwc]

I have 260 watts of solar coming through a Victron MPPT controller to feed two 6 volt Costco batteries on my 2014 Alaskan CO. I have the Victron bluetooth feed going to the Victon app on my phone from my controller and also have a Bogart meter. The Victron voltage reading, taken from the blue tooth app on my phone, always shows about a half a volt more charge on the battery side than my Bogart shows. Bogart reads directly from the battery.I imagine the Victron is measuring at the terminal on the controller that lead to the battery. I have also checked the readings at the battery with my Fluke meter and they are the same as the Bogart readings. I would think the Victron and Bogart would have the same battery voltage readings. Is it possible I have a half a volt voltage drop from the battery to the charge controller? It is about a six foot 10 gauge wire.I don't understand why this difference. I sure would like to get that missing half volt. Or am I missing something here? Thanks for the help and I hope everyone is well.

 

[rando]

12 feet of 10Awg wire has a resistance of about 0.012ohms. At 20A (the most you would get with your solar system) this would be 0.25V drop. Chances are you are seeing this drop coupled with a less than perfect connection somewhere along the way. What does your Fluke say at the battery terminals of your charge controller?

 

[Vic Harder]

also try moving the test points that the Bogart is connected to to match the Victron, and see if they now agree. I can't imagine that they'd be different if connected to the same points.

 

[nixfwc]

Ok took measurements. Fluke and Bogart same battery voltage readings. Solar system on float, 2 amp input,28 watts according to victron blue tooth iPhone reading. At victron MPPT battery +, fluke reads 14.08 v, victron says 14.02 v. Bogart and Fluke both read 13.7 v at battery. Checked both at battery terminal and through chassis ground. Checked victron Sol+ for the hell of it; victron says 19.46, Fluke reads 19.06 v. About .38 v difference between Victron battery reading and reading at battery, so maybe there is not a problem; when it is on bulk charge I think it is closer to .5 volts difference though.
I have 2 solar panels, 100 and a 160 watt. 100 watt is moveable for when I am shaded. the panels feed through Victron 100/20 MPPT Smart regulator to two costco 6 v FLA batteries. And there is a Blue Sea VCR between the chassis batteries and the house batteries connected through a 10 gauge wire.
My compressor 12v fridge draws in the range of 2 amps when it is running ( about 4 amps on start up) and I am about to add a POC for night time use, as I loose O2 at night. It draws about 4 amps. I want my batteries to keep up with this load at least until I can get a Battle Born lithium battery. Costco batteries new last year.

 

[rando]

Sounds like both the Victron and Bogart are pretty much spot on, and you have a wiring issue between the the Victron and the battery. Either need to figure out what is up with the wiring, move the Victron closer to the battery or add the smart sense:
https://shop.pkys.com/Victron-Energy-SBS050100200-Bluetooth-Smart-Battery-Sense_p_7663.html
to measure the battery voltage at the battery terminals.

 

[nixfwc]

After futsing around tightening connections, checking cables and such I have been able to get the voltage difference down to 1 volt plus or minus a few 10ths. I am going to leave it there for now. Just checked my amp draw with ridge running and POC running and it looks like the draw is going to be about 4 amps. Hopefully that will leave me with sufficient charge. Fridge won't run all night so perhaps a 28 to 30 amp draw for the night. I need that Battle Born battery but can't afford it just yet. I hear also from Will Prouse and others that lithium batteries are going to come down in cost later this year.