Solar Cell Installation

[Mark Elvin]

Can somebody sanity check this for me? I'm convinced I'm OK, but before committing I'd like a second set of eyes in case I can't see the wood for the trees.

I'm popping a 100w 12v cell on the roof, through to a 30A controller.

I calculate the output current of the controller to be 8.33A @ 12v (100w/12v)

So I'm OK the use a wire rated at 25A, Ref 25 here - http://www.vehicle-wiring-products.eu/V ... inwall.php , or am I missing something obvious.

I'm going to pop the V- from the 30A controller to a good earth point on the body too, any reason I should go back to the leisure battery terminal instead? After all, they are all connected through the batetry earth.

[Mini Men]

I have done similar, 65W panel at present but upgrading to 100W with 30W solar controler. However I did connect both +/- of the contoller outputs direct to the battery terminals. However the load neg is connected to the chassis so I only had to run a single cable for the load + to the rear. I used a 4mm here but I had it spare.

Fused all the + close to the terminal at 30A

The output from the controller can be more more than the 8A as it can draw from the battery up to 30A but depends on what you are running from the connecting to the contoller load terminal.

[Mark Elvin]

We have nothing connected to the controller output currently (no pun intended), but thinking about it we could power the fridge & USB charging points from it, but that still only equates to 9.1A. Even if I added a couple of meters of white led strip lighting we are looking at at most 10A so should be OK on that front I guess.

[Dodgey]

The wire from the 100w panel to the solar charger should be 17.5Amp or above. It won't put out more that 5.5 amps, but the higher the cable rating, the more efficient it is at carrying the current and maintaining the voltage. The calculations on 17.5amp 2mm sq cable over 4 metres at 16volts is around a 2.5% loss. Using 4mm sq cable the loss is 1.75 %, so for much chunkier cable there is hardly anything in it. Longer cable runs are a different matter.

Your earths should all go to chassis as that is the thickest "cable" you can imagine! - so you should get the best earth possible. I often run separate earth cables to batteries just so it's easier to isolate problems.

The cable from the solar charger to the battery depends on one of two cases:

1- Just going to use the solar charger as a charger - then 17.5 amp 2mm sq cable is fine again.
2- Going to plug things into the load port of the solar charger? particularly a fridge? Then run nice thick cable back to the battery. Something like 4.5mm sq or larger. Say, up to 6mm sq.

The reason for (2) is that if you hook heavy loads up to the solar regulator, then you need decent cable to support those loads back to the battery. The reason having a fridge dictates a much thicker cable is that compressor fridges use a lot more than their rated 4 amps each time the compressor starts (the fridge starts humming when the thermostat kicks in every few minutes) - if you use a thin cable, it restricts current flow, and the fridge, on compressor startup, does not get the power it needs, and sees this as an indication that your battery is low, and then goes into low battery mode, and just sits there with the cooling fan running, but no refrigeration. In real terms this means your fridge will shut down much earlier than it should do.

I've tested it, and on small cables the fridge might cut off after 1 day, but with thick cable, 2 days. It can make that much difference.

p.s. you will never get 8.3 amps out op a 100w panel. You need to do your calcs at the panel's rated open voltage which will be more like 18 volts which will be 100/18 = 5.55 amps. Expect around 5 amps. 5.5 in nice bright light with the panel pointing at the sun.

[Mark Elvin]

I think for peace of mind I'll run a dedicated 6mm cable from the battery to the solar controller.

[Dodgey]

Indeed. If you do it now, you'll never have to upgrade the cable in the future!

[Dodgey]

small update - I saw a 100W panel I installed today put out 6 amps in good sun.

[mikexgough]

Just got back from a 9 day off grid trip in France/Low Countries.... solar (one of dodgey's kits) worked brilliant.... compressor fridge was working harder than in the UK in 30c temps.... one morning I checked the coolant...as you do... and the LB was already charged fully and the SB was being charged..... at 10:30 a.m...

[dave_aber]

I have a 100W panel on the roof, connected through a 30A controller to my rear fusebox (in the conversion wardrobe).

My LB is up the front and connected back to the rear fusebox by heavy cable (60A IIRC).

From this fusebox, I have cables as heavy as I could fit (These may be 60A cables also, might be 32A) down to the fridge compressor which is above the wheelarch, about 1m away from the fusebox.

I am getting the "fan running, no compressor" symptom. on the fridge whilst camping off grid.

When I am driving about, and leave the fridge on, it seems to always be cold (freezer shelf frozen)

When it failed the other day, I checked the L/B (10am, sunny) - way up over 12v, so the solar is doing its job.

So, I began to suspect that the compressor was parking in a 'sticky' position when stopping. Gave it a shake or 2, and it started running OK.

A couple of hours later, back to the fan running on its own again.

So, it could be voltage drop on startup (but it's been OK for 3 years on this wiring), or it could be getting old / reluctant to start, and the vibration of driving around might be giving it just the nudge it needs.

When I get back from my current work trip away, I plan to get the connections apart just in case there is any corrosion or similar nasties. I am also considering fitting a small 12v cell next to the fridge to prop up the power on startup, one of the wee ones in the portable starter packs should do it.

Any thoughts from those in the know?

DA

(Vitrifrigo C42L fridge with an external Danfoss BD35 compressor)

[g8dhe]

I would think the start current is most likely with a cleaning of the motor needed - will be very interested as we have the same fridge!

[dave_aber]

A cleaning of the motor itself will be tricky - it's in the welded-shut black pot.

Will investigate the connections & terminals and let you know.

DA

[Dodgey]

It sounds to me like your battery might be dying.

Driving - you get full alternator power - circa 90-100amps!. Fridge runs.

On solar parked up - if the battery can't handle any real load, then the solar will run the fridge when it's producing over 4 amps, BUT.... your fridge needs a lot more than that to start the compressor. So you might have the fridge compressor trying to start up, demanding loads of amps for a brief moment, which should be the job of your battery, but your battery can't deliver, and the solar can't deliver the start-up amps, so it won't start up.

In good sun, fire up the engine, wait for the fridge to fire up, open the fridge door (to keep it running) then switch off the engine. If I'm right, the fridge will run and run, UNTIL.... you turn the thermostat down/close the door, then it won't restart, or it will, only once or twice.

Or... check your earths too.

[dave_aber]

Sounds like a good call.

I've not noticed the battery showing any signs of failing, but with the solar connected all of the time, it is being kept topped up so the voltage at least always shows good - perhaps it can't handle load any more.

I'll get it on a load tester, it is ~4 years old, so although I'd have expected more life it may be dying.

[Dodgey]

Well, you never know. Duff batteries will frequently show full voltage when you charge them.