Series/parallel wiring idea?

They have to be inline, just like in the diagram.

John

My bus is entirely 12V for both house and chassis. Yes, I know all about the reasons to have 24V instead of 12V, but the extra complexity of mixing two voltages in a bus is not worth it for me, so 12V it is! I would like to keep all four positive terminals in line and all four negatives in line. There are actually two separate slide-out battery trays next to each other, each tray holding four batteries side-by-side as in the diagram, and I want to have both trays' positives all next to each other, i.e. in the center, to minimize any chance of them getting too close to the outer edges of the trays and touching something. This means that one set of four batteries would be a mirror-image of the other set, with all eight positive terminals grouped together in the middle. Does that make sense?

If I can take each tray's feeds off batteries 2 and 3 it will reduce the length of cables needed when the trays are fully extended out.

Space is always at a premium in a bus or RV, so I want to make everything as compact as possible while still keeping full accessibility. When the trays are fully extended I can easily reach the innermost batteries to check their SG or tighten connections.

All the series/parallel wiring diagrams I've found show their feeds coming off the ends, but maybe that's because nobody else has any need to do otherwise!

Thanks, John

vtmaps wrote: »

Yes, that will work. That doesn't solve your main battery issue which is that you have 4 parallel batteries. That is a recipe for a short lived and troublesome battery bank.

--vtMaps

No, I have only two paralleled pairs of batteries per tray. Remember that each tray of four batteries is fed by its own separate charge controller (which is in turn fed by its own separate array of four solar panels) - in effect I have two independent house battery systems. Because the two arrays of solar panels will be producing slightly different power levels for three quarters of the year, each array needs its own charge controller - MPPT controllers get confused if their panels are producing different amounts of power (where would the Maximum Power Point be?).

All my panels are hinged to a central walkway on the roof. They can either lay down against the roof at 21 degrees down, or they can be raised to horizontal (not that I would do that very often), or they can be raised to 21 degrees up, 33 degrees up or 45 degrees up. In summer one side of panels would be down against the roof and the opposite side would be raised up 21 degrees, in spring or fall I could raise the opposite side to 33 degrees, and in winter that side would be fully raised to 45 degrees. This way half the panels will be facing the sun as best as possible, and the other half will be at the 21 degrees summer angle all year long. Got it?! That's why each array of four panels needs its own CC. If I need separate CCs, I might as well have separate battery banks. This way I have complete redundancy - if one CC or one bank of batteries fails, I'll still have at least 50% of my power capacity. I could also change out each bank of batteries at different times, or even use different types of batteries altogether if I had no choice. And in case you're wondering, I can have each battery bank isolated from the other by means of 250A Schottky diodes that will electrically separate them, or if needed I can bypass the diodes and combine the two banks into effectively one large single bank

It sounds more complicated than it really is!

I got all eight panels man-handled up onto the roof and have secured them inside each support frame, so now I've got power flowing down to the CCs' circuit breakers. Tonight I'll make the 4/0 feed cables, then I'll have solar-powered AC power for the first time in the bus. Yeah! I'm excited.

John

westbranch wrote: »

John, I am confused , is your bank to be 2 trays with 4 batteries each in 12 volt or 24 volt config... reason I ask is the diagram you posted is for 24 volt.. and you keep on talking about needing JUST 12V.?

http://www.electricfence-online.co.uk/ishop/images/1047/Serial_ParallelBatteries.jpg

Each tray of four 6V batteries will produce about 450Ah at 12V. The two trays will be effectively paralleled together to provide 12V at about 900Ah to the inverter and DC load center. Because each tray of batteries is separately charged by its own CC, I don't regard the eight batteries as being 2-series 4-parallel, but instead they are two separate banks that are each 2-series 2-parallel. I hope that's more than a semantic distinction!

Sorry if that drawing was misleading - it was the only depiction of four series and parallel batteries in a side-by-side configuration that I could find on the internet. See, nothing's simple!

So, tonight I'll be making lots of 4/0 feeder and interconnection cables, not only for the house feeds to the two Blue Sea 6006 switches, but I also have separate feeds to a separate pair of Blue Sea 9001 and 9002 switches for taking the house batteries' power to the bus's starter motor. This way I can start the engine off the house batteries in an emergency, or at least boost the two Group 31 start batteries if I need more Reserve Capacity - it takes a lot of power to turn over a big diesel engine in cold weather. I replaced my two 8D starting batteries with Group 31s because the 8Ds are too damn heavy, but there may be times I need some help from the house batteries. This is why it's important to keep the house battery cables as short as possible - there's going to be a lot of cables in a relatively small space, and I don't want then tangling and getting caught on things when I pull the trays out.

John.