solar battery charger-any experience?

[shogun]

I am restoring my E32 750iL Highline. Old battery I will replace this weekend. Engine is presently on running on weekend for a short time while I do the repairs. That means that the new battery will loose power again at this period of repair, and also later, cause I will use that car only for special occassions, weekends etc.
Anyone tried one of these solar battery chargers? Is that any good to
-keep the battery charged and charge it a little bit
-should have a protection to not overcharge the battery

But so far I found only systems with 120-170 mA output.
Like these samples here
http://cgi.ebay.com/SOLAR-PANEL-12-V...QQcmdZViewItem
http://cgi.ebay.com/SOLAR-CAR-BATTER...QQcmdZViewItem
Car is parked outside, so the solar panel should fit into the window of the car.
Difficult to get a normal battery charger installed there connected to the normal power line.

Thanks for the input.

[Hector]

solar charger should work ok.

Here's an example:

An 12 V 80 Ah battery has a power rate= 960 Wh.

Self Discharge of a new battery/month = 2 to 3% (it's higher for older batteries due to internal resistance and such)

Power rate loss in a month = 28.8 Wh @ 3%

Per day, power rate loss is roughly = 1 Wh

The solar charger will operate 5 to 8 hours/day depending shading conditions...

Time needed to overcome self discharge = 1 Wh/1.5 W = 0.67 hr

So if you use your 1.5 W solar charger for more than 0.67 hr/day you should be fine to beat self discharge, and charge your battery.

All this is based on a new battery of 80 Ah and 3% self discharge/month. Can't recall what the battery rating is for the e34. Also, the 1.5 W peak power from the charger is for sunlight hitting the cell at normal incidence. Any off-angle sunlight and placing the charger behind glass will make the charger operate less efficiently.

If you want to make sure you're generating decent charge, then hook up 2 of these chargers in parallel.

[Steven G]

Hi,
I bought 4 VW solar battery chargers on ebay and they seem to work fine. You won't charge the battery with it but you will maintain the charge with it. One thing I've found out is that the 2 chargers I bought the first time, when used on a sunny day the voltage reaches 19 volts or more, but the other 2 I bought (later production dates) never go over 13 volts and these have a small circuit board in the plug (I think it protects from overcharging it).
Steven G.

[shogun]

Thanks,
especially to Hector for the calculation. So far was installed a 12V 85 Ah battery under the rear seat, it will now be replaced by a 12V 100Ah.
In addition I have one in the trunk - standard on the Highline because of the cooler box and extra aircon for rear etc.- which is 12 V 30Ah.

So both I have to charge basically to keep them alive.

That is a good hint, that the solar charger does not work so well when installed behind the window glass, like the ones for VW are on offer. So maybe better I get a weatherproof version like this one I found in the U.K. ?
http://cgi.ebay.com/1-8W-Weatherproo...QQcmdZViewItem
If someone knows a source and has a link for a good one, please let me know.
Thanks

[Hector]

I believe this one is coverglassed. Give them a call. Actually, all PV products that operate in the field should be protected from the elements.

http://www.global-merchants.com/home/hppanel.htm

Thanks,
especially to Hector for the calculation. So far was installed a 12V 85 Ah battery under the rear seat, it will now be replaced by a 12V 100Ah.
In addition I have one in the trunk - standard on the Highline because of the cooler box and extra aircon for rear etc.- which is 12 V 30Ah.

So both I have to charge basically to keep them alive.

That is a good hint, that the solar charger does not work so well when installed behind the window glass, like the ones for VW are on offer. So maybe better I get a weatherproof version like this one I found in the U.K. ?
http://cgi.ebay.com/1-8W-Weatherproo...QQcmdZViewItem
If someone knows a source and has a link for a good one, please let me know.
Thanks