My P38 needs to spend some time parked up, and will likely only get driven once a week or so (unless we actually get some snow down this way for a change...) over the next few months. It has a good battery, and I haven't had any drain issues that I'm aware of. It does have a tracker fitted that draws a tiny bit of power however. It may be that it gets left quite a while, and I don't really want to risk the battery draining. Last time it did (before the new battery, admittedly) I was on holiday, and it went nuts, and burnt out the front door latch motors.

I have no access to mains power, or I'd just connect it up to a CTek charger, leaving me thinking about solar panels. I will be putting a cover over the car to keep it clean, so I was thinking about a panel of some size with magnetic feet lobbed on the roof on top of the cover, cable fed in under the tailgate and eventually plugged into the rear 12v socket (mine is switched, so it can be always on direct 12v).

Looking on eBay, I have many options. I presume I'd want something between 10-25w, and if I'm at the higher end, a charge controller would be a good idea.

Has anyone played with such setups? OB, I recall seeing you say somewhere you have something setup on your motorhome?

My mate in France has a 10W one attached to the battery on his boat which can get left for up to a couple of months in winter. He's never had any problems firing up the 5.2 litre V8.

This:
http://www.maplin.co.uk/p/30w-solar-panel-n97df
and this:
http://www.maplin.co.uk/p/12v-30a-solar-charge-regulator-n28kr
are the closest "modern" equivalents I can find to the 5 year old (and still going strong) system I have.
Not sure about weatherproofing though. On mine it's inside the sunroof.

Hmm I'm sure I replied, maybe I forgot....

I'm tempted to try a 10w one without a controller to start with, bearing in mind how much daylight we actually get, and for how long...

It's a shame the P38 sunroof has that ceramic/etched sun shade in the glass, or that would be a nice spot for a solar panel inside (if it weren't being covered, anyway).

The little unregulated one's are OK for short term use (wouldn't leave one on for months). There's a small risk of overcooking your battery, but only if you left it in the desert for ages with it on full output. They're reputed to be weatherproof too so could sit outside a cover.
I'm sure enough light gets through sunroof glass, even with the etching, to keep a small panel happy. After all, quiescent current drain is only 20mA so there's only the chemical discharge thing going on.

Supposedly had a regulator with a couple of very big panels on the roof of my dad's motorhome but still cooked the batteries. Little panel probably OK without a regulator but could check and adjust charging current - With battery fully charged, connect panel in broad sunlight and check charge current, if too high wire some resistance in series such as e.g. a brake bulb? Quiescent drain will depend on the size of the battery?

Simon

Nope. Quiescent drain is what's drawn by the car once it's sleeping (alarms, clocks, ICE etc)
Chemical drain is the natural loss of charge when battery is sitting. Temps and environment affect this.

Lpgc wrote:

Quiescent drain will depend on the size of the battery?

I can agree, although would regard chemical drain also as quiescent drain which will be related to battery size..
I wonder how the 20mA vehicle electrical drain compares to the chemical drain - Suppose we left a 100AmpHr battery stood in the garage without a charge... 8760 hours in a year but how much of that 100AmpHr capacity would remain after a year.. If it was down to 50% capacity it would have lost 50AmpHrs and chemical drain would have been nearly 6mA - would seem this would have to be a pretty decent battery.
Down by 50AmpHrs after 3 months then chemical drain would have been around 12mA... How much of a battery's charge could we expect to remain after a year? Probably a bit difficult to apply real world figures, especially if battery isn't as new, but chemical drain would seem enough to affect the charging figures aimed for, especially as solar panel won't be charging at night - E.g. with 20ma vehicle drain, 10ma chemical drain, solar panel only charging at night, battery charge efficiency never 100%, even 40ma from panel during the day might not be enough for the battery to have as much charge on return as it had when it was left.

Simon

We're getting technical, excellent :)

My quiescent draw is going to be a little higher than most I'd imagine - the tracker draws 27ma while sat there with a data connection open, spiking very briefly every 60 seconds to transmit.

Because they're relatively cheap, I'm going to start with a 10w panel on the roof and keep a close eye on the state of the battery and charge current for a while and go from there.

It's fascinating once you get in to the maths Simon.
Chuck in a few freezing nights then see how that battery holds up!

Hehe, well, could get anoraky and deeper into it I suppose but I'll refrain! As a kid I made a lead acid battery, flashing from the roof of a building that was to be knocked down and talked grandma into buying some sulphuric acid from a hardware store (I kid you not!) and it worked, plenty holes in my bedroom carpet and stuff though. Dad once accused me of smoking when he saw my yellow fingers but was fine with the fact the yellow stuff was result of purposefully blowing up a big capacitor in a biscuit tin using AC power.

Simon

Just because I am new to the forum and figure you guys should know: If a RR with a "new" battery is parked- say- for a month- should the battery be drained? I am concerned with the BECM needing to be re-programmed after all of the nightmare I went through a few months ago. Anyone?

In a nutshell, probably will be drained.
You shouldn't have to have BECM re-programmed just 'cos your battery goes flat though. I seem to remember from "the other site" that you've had key and fob issues that Marty sorted for you, so hopefully the worst you'll have to deal with is re-syncing your fobs.
I know your car's still laid up with overheating issues, but it's never too late to put a battery maintainer on it if you can.

mymysteri wrote:

Just because I am new to the forum and figure you guys should know: If a RR with a "new" battery is parked- say- for a month- should the battery be drained? I am concerned with the BECM needing to be re-programmed after all of the nightmare I went through a few months ago. Anyone?

mymysteri wrote:

Just because I am new to the forum and figure you guys should know: If a RR with a "new" battery is parked- say- for a month- should the battery be drained? I am concerned with the BECM needing to be re-programmed after all of the nightmare I went through a few months ago. Anyone?

In your position I'd loosen off the battery terminals, lock unlock the car and unhook the battery within 20 secs (I think it is?) of the unlock. That way the BECM won't go into lockout mode, you can store the battery somewhere safe and hook it up to a charger after you remove it and before you put it back. That way your Range Rover is locked, pretty well immobilised and your battery is safe from harm.

Of course, if you try that with mine it does the full screaming siren thing, but that's just The Duchess and her paranoia :)

My SE is left with the battery disconnected. I lock it with the bonnet open, disconnect the negative lead and close the bonnet. When I want to start it for shunting around purposes, I unlock the drivers door with the key, open the bonnet, reconnect the battery (which causes the drivers door to lock again so don't leave the key in the car), unlock again so all doors unlock and I can then start it. Some have said that it's better to disconnect the battery while it's unlocked and if you do need to lock it, then do it manually with the sill buttons before locking the drivers door with the key. Whichever way you do it the car is locked and the battery won't go flat no matter how long you leave it (as long as it is a decent battery that doesn't go flat because it feels like it).

A 10w panel appeared today. I've just tried it in the shed (given its dark, naturally) and under an LED floodlight above my desk, its managing a short circuit current of a whopping 3ma. I hope it manages a bit more outside in daylight... will take it to work with a meter and find out tomorrow.

Well then, I think this plan is a bit of a non-starter.

Tested the current produced by the 10w panel today in typical British winter conditions - overcast but fairly bright. 14ma.

At that rate, I'd need to fill the windscreen with solar panels to have any hope of putting a bit of charge into the battery during a short winter day.

Something's not quite right there. If my schoolboy physics is correct W=IxV so 10w/12v should deliver 0.8A. Now I know there are efficiency losses but that's a hell of a way off spec!

Using this one as an example http://www.ringautomotive.com/uk/products/Cars/Battery+Care/Solar+Power+Battery+Maintainer/RSP600 which is a 6watt, they state 343mA output. Multiply that up to 10watt gives 605mA

Yes, I agree - I think you just need a few more panels....
(although the ones you have are rated @ full sunlight)

Here is some handy data on the topic though:-

https://www.batterystuff.com/kb/articles/solar-articles/solar-info.html