fulltiming electric plans for off grid use

[Coolasluck]

Well-Known Member
I have been considering running two banks of batteries in my coach,one for 12 volt,and one for 24 volt.
I have an eberspacher that runs off 24volt a pure sine wave inverter that is 24 volts a compressor fridge that is 12/24 volt and will be fitting the webasto diesel heater setup at 24 volt.

The 12 volt side of things will be water pump currant one is 12 volt ,spark generator for the hob and some gauge readers for the lpg and the freshwater tank.Also the lights will be 12 volt as is the toilet electrics.I will also be fitting some 12 volt cigarette sockets in the bedroom and in the bench seating,these will act to keep 12 volt devices on charge as well as using some fans for cooling in hot climes.
My aim is to have 5 solor panels possibly 120 ,100 or 80 watters.
I was thinking of having 2 to charge the 12 volt system which will be 2 lead acid normal car batteries,these can also act as spare batteries for the engine and will serve both domestic and emergency starter issues,

The 24 volt side of things is mainly going to be used for heating the water and running the compresser fridge.In winter obviously the heating will be on also using more power unless of course i am in sunny spain for this setup i am thinking of using the 3 solor panels for charging plus a durite 24 volt b 2 b charger.
Obviously i am trying to be geared up for being offsite and avoiding those lovely campsites.I will be using 2 x 220 amp batteries for the 24 volt setup.

Interested on opinions please.

 

[sparrks]

I would just have one big 24v battery bank to supply the "heavy" needs and split the Battery bank with 2 12v tap offs with the load split evenly over the 2 12v banks - you're only talking about pump, spark generator and a few low wattage LED lights.

 

[richardstubbs]

Hello, I'm new ;-) Ten years' experience in off-grid solar power (developing countries mostly) though, so I hope I can help. Hope a month after the post isn't too late.

Sparks is right; it's much more efficient to use a single large 24 Volt battery; you can use all the power however you like then, and less will go to waste.

I'd strongly advise against splitting the 12 Volt load over the two halves though, sorry. Why? Because you then have two earths at different potentials - if at some point in the future the two circuits become connected together (maybe by someone else even) then you will be putting a dead short across a 220 Ah battery at worst, and 24 volts on your 12 Volt circuit at best. It will definitely work that way, and if it's fused properly then maybe it'll be OK, and you may well never have a problem, but it's not good practice and should really be avoided if possible.

The right way is to connect the 12 Volt loads across the 0-12V half of the battery, and use a battery equaliser to even the charge across the 24V pack. I don't think I'm allowed to post links, but if you Google for "battery equaliser" you'll find a few. It's a switch-mode converter that charges the lower 12V half from the upper one as it discharges. Will cost a bit more, but not as much as a separate 12V pack I suspect and it's the right way to do it. You need to look for one that's designed for renewable energy applications - you don't want it to use much power itself!

Also, don't be tempted to use car batteries as deep-cycle batteries. When I was new to the solar business I thought that was all nonsense so I tried it - they last about 5-10 deep discharge cycles, so don't waste your money. Look for leisure or deep-cycle batteries which have a cold cranking amps rating on them instead. Lots do - they're used in boats and have to start a big diesel. It'll work out much cheaper in the long run.

Hope this is some help,
Richard.

 

[geebus]

Why not get a 24v - 12v transformer?

Everything I've read suggests it's a bad idea to draw from half of a battery bank, though the equaliser would help.

My lorry (as I got it) has 4 I think - for the lighting, pump and a few other bits. Not sure how much energy I'm losing, but you'll lose some whatever.
I'll probably slowly replace some bits with 24v or items that do both - such as led lights that can handle either, so if I do end up getting a 'complete set' I can get swap over to 24v for that circuit.
A lot of cig-lighter chargers can run off 24v, but do check first, of course.
I plan to wire in a couple of dual 24v USB sockets with switches directly, so phone et can be charged without faff.

If you've got the space, I'd look at bigger solar panels - ones that are rates for 24v and tend to be 200w (maybe a little lower) and above seen to be a fair bit cheaper.
I paid £95 (overstock) for my 230w poly. When I get some cash, I want to get 4x290w mono from bimble solar, which are £166 each + £39 shipping for the lot.

 

[FULL TIMER]

I would also stick with the one 24v bank with the B2B charger and ideally a mains 24v charger for when hook up is available, I more or less have this set up in mine using one of the excellent Sterling Power chargers. For your 12v needs get a 24v - 12v dropper I normally use Durite ones and just feed a separate fuse block from this for the 12v stuff, I always tend to think that simpler equals less hassle,