Electrical BMS and Battery Upgrade .... Quandry

Of course I forgot you had split it all up ..............

I'm probably wrong but I think if you have 2 separate strings in series but joined together individually at the controller then its series connected in parallel so the controller would only see the prime voltage being 44v or whatever ,2 x the VMP of one string on the controller screen not 4 x VMP .......... all your panels would have to be connected in series and run to the controller for you to see a higher voltage ...... So a NEG of one string connected to POS of the other string with the other Neg and Pos connected to the controller ....... then again if all wired together and just a shi*ty day,shadow could have knocked out a set or they are only making 11 volts each ...

In vans I can't see a need for series, van cable length is not really an issue, higher volts means less amps which means less charge capability and when I have tested mine the voltage drop is bugga all, even with the 8B&G 10m and 5m extenstion cables run out but the amps produced by the lower voltage is greater by far than with higher volts and AMPs are what gives the battery its grunt ......................


So all in all everything good, should have stayed out there I think with this weather......

All you need to do is set up some Andersons near the controller so you can arrange the input to the controller to one string of panels in series and problem solved when you want to plug in some portables, I have mine set up so I can shut down the roof and just run the portable if need be ...

Your right about the MPPT unit deciding how much power it wants at the time, running the battery down and plugging the fridge into the van power showed me how my set up worked, the MPPT drew enough to cover what the fridge was taking from the battery plus a little bit for charging, when I fired up TV, radio and STB to draw another 4a it just cranked up a bit more to cover it, I was expecting to see massive power drawn from solar but no just enough to cover needs ... did work out that if I ran out of gas one morning I would have a few hours to chase up more and the fridge would be okay to run off van for as long as the sun shone.... cheaper than running the genny for sure.

If I had matching panels on my roof I would do some trials on series/parallel but with 2 x 110w @ VMP 17.6v/VOC 21v panels and a 200w panel @VMP 18v/VOC 22V I know it would be no good, so parallel is the go and with a max of about 23w from them combined in parallel its cool... I thought the 200w job being 13 yrs old and was about done but last meter I put on it was still throwing near specs so getting a roof of identical panels is not planned now, paraellel shunts plenty of ampss so would probaby stay that way even with identical panels ...

Hitting the road said:

Thanks Boots, Drover...I had considered setting the system up so that I can run roof, portable, or both...but hardly worth it really. I can unplug the roof panels at the MPPT if I want to use just the portable, or the roof set just by not putting out the portable set up. And..after some extra research found out why as you both wrote I am seeing the outputs I am.
Happy enough though...

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Yep, if it works then why stuff around anymore ..................... took a couple for years for me to redesign my circuit panel, new circuit breakers and stuff , it was the new air compressor that brought it on as it blew everything, mongrel thing wanted more juice than I had allowed for, so now the pump will melt before my board sparks up ..................... though now having the ability to just flick a switch and shut down the roof panels does make it easier for maintenance or breakdowns to disconnect without shorting something out and battery disconnect just takes a micro second .......................

Good to hear you went away and didn't break anything ...................