Hi guys, I had an idea I wanted to bounce around a little, and maybe get help improving on, and thought it could be of help to some people too perhaps.
A bit of background, my partner and I have bought a Mercedes Vito panel van to convert into a campervan. We've already used an older converted Vito, so we know the size etc is good for what we need. We have a decent amount of DIY skill between us, and a decent education in electronics and electricals. 'How hard can this be?!'
As usual, the thing that seems to be taking the most time in consideration and planning is the electricals. We want to have electric hook-up and a leisure battery. We want the leisure battery to be able to charge from:
1. The starter battery (via a voltage sensitive relay)
2. Hook-up
3. Solar panel
While a Zig and such like will cope with the first 2, it's not easy to see how to make it work with a solar panel, and the whole thing relies on remembering to flip switches. If you don't manually switch everything just so, it's possible to trigger the mouldy milk or non-starting van syndromes. I'm not a fan of either of these, and I'm forgetful, so a different solution was considered.
Step 1 - Not a zig
This part is simple, if not using some sort of Zig we need instead a charger, 12v fuse box and a voltage sensitive relay (VSR).
Step 2 - What runs what
- Lighting, fridge (we have a super little 12v compressor fridge which uses 0.26kw over 24 hours - around 22 amps), water pump and some 12v sockets all run from the 12v fuse box, which will be powered by the Leisure battery.
- 240v sockets will run from a hook-up. We thought about getting an inverter so we could potentially run these sockets from the battery when not hooked up, but we have gas for the kettle and 12v sockets for phone charging so there's not really any need.
- Power for the charger is a more difficult one, traditionally a charger has a single 240v input, but we have a 240v hook-up, 14v-ish alternator and 10-18v Solar panel. So we put on our deerstalkers and investigated some possible solutions.
Step 3 - Charging stuff
So the first proper hurdle is deciding on the charger and how to supply power to it. First thing we decided was we want a decent charger of the intelligent (PWM) charging type. We discovered you can get DC to DC chargers, or you can get some clever charge controllers and they are quite forgiving on the input voltage, which would mean that the Solar panel, Van battery and output from a transformer (connected to the hook-up) would be all around the same voltage. Lovely.
Next up, we considered connecting all of the Live wires and sticking that to the charge controller input, but decided that was asking for trouble. We thought about a manual switch, but again that'll be forgotten on a regular basis and mouldy milk syndrome is bound to occur. We looked for something that would add up the inputs and create a stable output instead, but the only thing we could find that resembled this was a dual input charger which has just 2 inputs and cost a couple of hundred quid. The only thing we can think of here is a set of relays that only allows one flow of power out of 3.
So, since only one power supply will be used in the charger, there has to be a set of rules to determine which. The order of preference for the power supply is
1. Hook-up
2. Starter battery
3. Solar panel
Since relays are switched by active/inactive circuits, if we get relays that are closed (circuit is complete) unless another circuit is active, we can do this:
- Solar panel has 2 relays between it and the charge controller, both closed (so that the power from the solar panel gets to the charger) unless there is power in either the Hook-up or Starter battery circuits.
- Starter battery circuit has a single relay that will pull open and cut off the circuit if there is power in the hook-up circuit
- Hook-up circuit has no relays, if the van is hooked up, the power in the circuit will pull open the switches in the starter battery and Solar panel circuits.
So, that's a summary and pretty pictures of what we plan to do. As we progress with the project we'll write up some blog post style stuff for the conversions section of the site. A few questions for anyone that has any input:
A) Will the van battery produce too much power (amps) for the charge controller to cope with? I was assuming the charge controller will draw what it needs, but is it possible that there will there be a surge when the van starts that might cause damage?
B) Any suggestions on alternatives to get the 3x power inputs to charge the battery?
C) Is there a fool proof way to wire up a zig to avoid human forgetfulness ruining a holiday?
Please feel free to poke holes in all of this, and point out problems, alternatives and improvements. We've not started wiring it up except for the hook-up point and the 240v fuses and sockets, so finding the problems now would be the best time :)
