Thanks Charley - exactly right on all counts.

 

Alan
I work away from home for up to 2 months at a time so I use a battery maintainer. I have one called an 'Optimate'. Made in Belgium IIRC, it's one of the best tools I've ever bought. It has an output of about 600mA and alternately charges, then stops and measures the rate of decay of the battery voltage, then charges again as required. In the 5 years I've been using it my car has never failed to start regardless of how long it's been standing idle. The only drawback is that the battery water level seems to fall. Once I had to add over 100ml. There's no sign of a leak so I assume it boils off. Do you have this problem when using your maintainer and is it normal?

Colin. 89GT.

 

Colin - not that I know of - electrolyte loss seems about normal - which is to say I do lose some very slowly. Maybe in the typical 2 year life of a battery here I might top it up once and it probably takes <50ml across all cells.

Bear in mind its very hot here and very low humidity too.

Alan

 

LOL as opposed it running down in the manner Porsche intended.

 

I did have some parasitic issues when i got the car - they were pretty much all stupid PO stunts. I have since left my car for up to 6 weeks with no measures taken and have it start right up ... I think that's acceptable and probably what Porsche intended.

I know many people have issues - I put a lot of it down to previous poor (...bizarre even!) maintenance and odd aftermarket stuff mostly...

Seems like many 928's went through a period of a second (or third...) owner who bought the car cheap and was also too cheap to maintain it properly... quite wierd butchery often ensued - a big shame for many cars. For the typical domestic shop in the 80's/90's or a home mechanic these cars electrical systems were indeed like rocket science...

Alan

 

Thanks for your responses, guys!

As for live lighter sockets, I am actually surprised to hear that some model years are switched off - I thought more or less all German cars have live lighters (and used to have live radios). My dad's 1980 VW Dasher had a live radio and a live lighter socket, as did my wife's 1998 Passat (by then they switched the radio). Her 2005 Audi A3 has TWO live lighter sockets (they really, really should have switched one of them).

My preference is of course for a switched socket, and I may end up rewiring it like that so I don't have to unplug the V1 every time I shut off the engine.

 

Any 928 with an always live cigar lighter socket has been "adjusted".

 

Definitely not, at least not "adjusted" in the sense that it occurred after the cars left the assembly line. The topic has come up before, either here or on the mailing list. There absolutely were some 928s that came from the factory with the cigarette lighter always hot, regardless of what's shown in the wiring diagrams. There's a reason that Porsche released corrections to the wiring diagrams. Because of errors or inaccuracies as compared to actual wiring as produced. With the number of changes and variations that occurred with different things on these cars during their production, during even the same model year, there's no way I'd consider any of the wiring diagrams absolutely accurate for all cars as they were produced by Porsche.

 

I talked to a friend of mine, who has a company that sells UPS (powersupply). He says that it's very important that a maintainer does not deliver more than 13,7 V, if it charges with more than 13,7 V it will use up the battery acid.

Mads

 

So Larry you've said this before.

I agree there are some individual errors in the wiring diagrams. There are also change-over issues where minor changes noted for one model year actually start earlier or later than you would expect based on model year change-over dates - presumably a component stocking issue. Porsche also occaionally uses heavier gauge wiring than is indicated.

Other than those issues I have rarely found any other changes and the wiring diagrams (although quite hard to interpret) are actually amazingly accurate w.r.t. build details. I have spent a lot of time on the wiring diagrams of these cars and have a pretty good understanding of these issues.

They do include more information than most alterative types (quite effectively obfuscated in some instances).

Did they start building cars with quite different configurations than the diagrams say for any model year?

Well it wouldn't fit into any of these common error types - it would just sound a lot like sloppy engineering.

So did it happen... I suppose its possible (special orders? sloppyness?) but I still have major doubts.

It is of course quite easy to change this over at any time - there are other live battery power sources in the console. A good test for this on those that are live would be to see if the Cigar lighter fuse still controls the lighter? for that it would require that the CE panel be wired differently... not likely in an after market modified car.

BTW If you plug a trickle charger in to your lighter socket and the charge light comes on it means nothing... The only test is if equipment plugged in continues to operate with the key out.

Lets hear reports from follks with always live cigar lighters - ideally who have had them since new?

Alan

 

GAZ - maybe you can test your socket and fusing as in the above post...

For the radios - Porsche always had a switched supply for them on the 928. There is a special (R) output from the ignition switch just for this (R: radio). Note that this is unfused all the way from the battery when switched on - it presumes the fuse in on the radio. This is not really a smart choice IMO... its a place you pretty much know will be messed with in the cars life!

In later models (85+ for all, earlier for amp equipped cars) unswitched supplies were also added for the radio (fused on CE panel - via the amplifier/"booster" connection/fuse if there is one). Newer head units typically use both supplies and will turn off/on with the switched supply - yet can still be turned on manually with the key out using the unswtched supply (most have a timeout for this mode).

Alan

 

This is MUCH too simple a statement to make. There are a lot of electrical variables involved it this. If you check the open circuit voltage of any charging system for a vehicle they all put out more than 13.7V. It must be a regulated output that adjusts with the current demand.

If you use a small garage charger, it will likely not have the regulator circuit installed, and this will boil off the electrolyte given time. They should not be used as a maintainer, only a short term charger. I would councel agains using one of the big, air-cooled battery chargers on any modern car because of the current and voltage available. This is particularly important on the 928.

Most of the small systems are called 'maintainer' or 'float charger'. These type are designed to be left connected permanently while the car is not run. They still put out more than 13.7V open circuit, but will regulate, and shut off once the battery is fully charged. This is true of the VW/Audi solar chargers too. They will not overcharge the battery, and will not damage the battery in normal use.

 

The popular Schumacher 1.5a maintainer switches on at voltages between 11 and 13, off when voltage reaches 14. In my normal maintainer service on the 928, the battery "leaks down" to 13, charger comes on. Voltage -slowly- works its way up to 14, when charging stops. Simple, and the 'on' part of the duty cycle isn't long enough to boil off electrolyte.

 

Guess I'll be the first one. The '88 that I have has an always live lighter socket. The fuse that's indicated as being the cigarette lighter fuse in the wiring diagrams, and on the factory fuse/relay chart that comes with the car, is the one that does actually control the lighter socket. All wiring and connections from the lighter to the fuse panel is 100% factory stock looking. I've had the fuse panel out and all wiring and connections on the back of it were 100% factory stock looking as well. What I mean by the wiring and connections being stock looking is that the wire gauge and color are exactly the same as stock, and that any terminals are exactly the same type and are are crimped in exactly the same way as stock, and even have the same coloration from age as the others in the area.

In the past decade or so, I've come across a few other 928s with an always live socket. I'd say I've looked through more than my share of 928 wiring, and removed fuse panels more times than I want to remember during the course of troubleshooting and making modifications, but never specifically looked at the lighter wiring on any of those other cars to try to establish whether it was all a factory looking configuration or not.

Either that or sloppy assembly or manufacturing. I know some of you remember those "green wires" for the ignitions on the earlier cars that were manufactured with the incorrect polarity. To me, sloppy engineering would be more like those unfused power lines running around the car that have been mentioned.

 

'88 S4 and '93 GTS, live with ignition only.