Solar powered trickle charger for 997.2

[uyurday]

Hi everyone,

Interested in getting a solar powered trickle charger for a 997.2. Battery is pretty new and won't need the charger to charge up from flat, just want to use when I'm away for a couple of weeks, to make sure battery stays topped up. To preempt any questions, unfortunately I don't have the facility to use mains power, so solar powered trickle chargers are my only option. And I realize we don't get much sun in this country

From what I've read on various forums, the cigarette lighter socket on the 997's is live even when the engine is switched off. It seems like a lot of the models out there have some sort of mechanism to protect against reverse charging as well, although some of the comments on e-commerce sites are mixed on this (few comments suggesting they used a certain model and the battery was flat the next morning).

My questions are:
1) is this a good idea? or am I introducing other risks of damage while I'm away? I'm also thinking of getting a jumpstart booster pack in case I come back to a flat battery, but I'd rather not just rely on that and actually keep battery charged up so as to maximize its life
2) what size (how many watts) would I need? there are 1.5w, 1.8w, 4w, 5w, 7w, 15w options but this needs to be balanced by size of panels and what can reasonably fit on the front or rear dashboard. The general view online seems to be that 4-5watts would be enough but again some dissenting views also...
3) what model would you recommend? Maplin has various sizes, Amazon has Visua brand chargers, other brands I've seen are NOCO, Sunforce. There is also one that AA sells but it uses the EOBD socket, which I've been advised against tampering with. Here are a couple of the ones I've found:
https://www.amazon.co.uk/SOLAR-POWER-BATTERY-TRICKLE-CHARGER/dp/B002V9JEF0/ref=cm_cr_othr_d_product_top?ie=UTF8
http://www.maplin.co.uk/p/solar-powered-12v-24w-battery-trickle-charger-n59fu
https://www.amazon.co.uk/NOCO-BLSOLAR2-Solar-Battery-Charger/dp/B00B7GC50Y
4) do I need a charge controller? again, mixed feedback on this online. Some say must have, some say only for above certain watts, suggesting for a 4W charger you wouldn't need one
5) is the built-in diode to prevent reverse charging enough?

Thanks in advance!
Utku

 

[angusc]

Interesting topic and I will be watching for some good informative replies. I used a 5w solar panel on my Cayenne as I leave that in a car park for months on end. Should be no problem charging through the cigarette lighter socket as I do that on my Carrera 997.1 that's in the garage. Porsche sell the trickle charger for that very purpose.

But I think you need more than 5W. More like 15-25w I don't think the cheap solar chargers put out what they say. I also did some internet reading and basically a controller is required for the larger panels I was considering spending around £70 on a set up but the panel and controller are not so portable and a convenient to use.

It would be great to hear from someone else that has experience in setting up a larger solar panel system, maybe someone who also does some camping.....

 

[uyurday]

Thanks Angus
Yes, if you go for 15-25w, sounds like you definitely need a controller. I wonder if that size is necessary though just to top up the battery. I suspect the longest my car will be parked and undriven is 2 weeks. I guess a fair question is, do I even need to worry about trickle charging if the longest the car will sit is 2 weeks...

 

[tscaptain]

I had a solar panel/charge controller set up 8 years ago when my garage then didn't have power. If you read through this thread
https://www.porscheclubgb.com/forum/tm.aspx?m=422766&high=solar+panel
there might be some info of interest.

It certainly seemed to work ok although the panel I had was mounted on the garage on not sat on the dash.

 

[angusc]

If you leave your car for no more than two weeks......I would just buy a new battery and not worry about the solar charger. I put one new battery on my Carrera and two on the Cayenne as it has a back-up battery and have always had good starting when I'm around and using the cars. Longer than three weeks and you probably need to think about a trickle charger.

 

[uyurday]

thanks ts... I had seen that thread, but thought since it was from 2009, maybe I should see what the latest thoughts were...

angus, agreed... I do have a new Bosch S4 battery in, so hopefully 2 weeks won't completely drain it...

 

[angusc]

Nice review and write up captain!

Unfortunately the link is dead and the company seems to have changed website address or dropped off the mortal coil......off to do some googling.

 

[Lancerlot]

Charging rate is normally measured in amps. The charging rate shouldn't exceed the fuse rating of the circuit. So if it's a 10amp fused circuit, it will take a 5-7amp charge with enough to spare.
However, 15 watts doesn't seem very much for charging. It's only 1amp, OK for a trickle charge but not something to leave connected for an indefinite period.
If you are intending leaving it connected for sometime, you really need a smart charger that continuously monitors battery condition and switches into standby at the appropriate time.
Regards,
Clive