Hi

I don't use my 928 S4 that much, so every time i'm ready for a trip, the battery is flat
So i have been thinking about installing a battery cutoff switch, have any of you guys done that ? Pictures would be great.

I'm also thinking about a battery maintainer, what should i go for ?

Regards

Mads

 

There are many previous posts about these items - do a search - see the current one too on battery disconnects...

Alan

 

Mads, you don't even have to search... there is a current thread on the front page regarding battery disconnects, called "If you have one of these battery disconnects, remove it"

Click and read - there are several recommendations for good disconnects, and one strong recommendation against a bad one!

 

I will answer the battey maintainer question. VW/Audi, in it's infinite wisdom began offering these tricle chargers with new cars back in the late '80s. There are literally hundreds of them avail every week on ebay in the US. Either find one that will ship to you, or locate one in the Norse lands. Get the kind that has the lighter adapter end and plug it in to your car. Aim the solar charger at the sun, and you should be okay.

The best answer of course, is to locate your parasitic current draw and eliminate it. It takes time, and a good DC ammeter and the wiring diagrams.

http://cgi.ebay.com/ebaymotors/Genui...QQcmdZViewItem

 

Doc - check the wiring diagrams - this just won't work...

Unfortunately it may seem to be working (charge light etc) - because there is a lot of other X-bus stuff attached there...

Alan

 

Bummer, it works good on RVs and my old Lambo. I guess the lighter isn't hot with the key off. Well, it could be spliced into the 30 buss somewhere, but that's a bit more work.

Sorry.

 

For a plug in 110v maintainer the Schumacher ones work fine - I have one.

As above - you need to wire a plug in of some kind to the battery terminals. Or you can permanantly install it in the car - then you only have to plug the car in to 110V...

Unfortunately in a 928 there isn't much room near the battery... if you are in a place where the sun shines - the solar cell ones are a nice idea instead or as well...

Alan

 

Is is on some model year 928s.

 

I don't think so.... which year are you thinking of?

It certainly is not on a GTS...

Alan

 

Sorry for not doing a search first
Sounds like it's the tickel charger i should go for, it's proberbly not to smart to reset the ECU alle the time.

Mads

 

Yes if its parked a lot (presumably garaged) a trickle charger is best - I'm sure there are 240v equivalents at similarly reasonable prices - maybe even the same brands are available.

Alan

 

On a GTS, no. I know that at least some '88, and I believe some '87, yes. There may be other years as well, and it may not be consistent in the single model years where it does occur, but there were definitely some built with the lighter socket constantly hot.

 

Larry

Not according to the wiring diagrams... and I do trust them on this one.

Its always possible someone screwed with any particular car of course.... for whatever reason...

I seriously doubt Porsche ever built it that way - they chose to use the X-Bus deliberately - starting '79 all the way to '95.

I think it was a good choice to make too (less risk of running the battery down inadvertently).

Alan

 

Alan, can you explain your rationale for why a trickle charger in the lighter socket will not work?

My '89 GT lighter socket is always on - I have to unplug the V1 from the socket even after shutting off the car. Is it supposed to go dead after a period of time? And even if the lighter socket is always live, is there a wiring reason why a trickle charger would not work? What about attaching it to the jump points in the engine bay? Should that work?

I just ordered a 5.5W (~0.5 Amp) solar charger for extended periods of storage. It comes with both battery clamps and a lighter socket adapter, so I can still use it either way, but the lighter socket would probably more convenient.

I guess the way to test it would be to disconnect the battery, plug the charger into the lighter socket, and test for voltage at the ends of the battery cables.

 

Using the underhood attachments works fine on my '88 for a trickle charger. As far as I know an '88 or '87 that has a hot lighter with the key off has been "adjusted" after market.
If your lighter is hot with the key off, then a trickle charger to the lighter should work fine.
If your V1 is alive with the key off then that's the only test you need.