[winstonbike]

Anything special I need to do? I assume not, just want to make sure I don't do something stupid.

Thanks

[Vicegrip]

Red + Black - For the most part the simple 912 point and coil ignition and generator with mechanical regulator are robust. There is little risk of damage to the system during a normal jump start. Good thing too I have killed the battery in mine about 10 times.

[RoninLB]

there is always a possibility of alternator damage from jump starting. The safest would be to disconnect the weak battery and let the jumper car charge the weak one.

[Vicegrip]

True, does that hold true for a genorator as well?

Overall the best way to jump is one of the $50 rechargable portable jump start packs. Some will allow you to hook them up and trickle charge for 10 min or so and then you can crank. All will jump without sending an overcurent into the cars system.

[RoninLB]

Originally Posted by Kurt Mickelwait

True, does that hold true for a genorator as well?

It's the diodes that blow. Alternators have AC that uses diodes to chop 1/2 the wave. If I have to jump I'll attach my car first to the cables then attach to the donor car. If a spark happens it's at the donor. A voltage spike is ng. I haven't read about the details in years. I'm sure hard info is available somewhere. And a jumped car will see an alternator putting out mucho amps. Mucho amps = heated alternator.

[Vicegrip]

This one got me to thinking.

True about the mucho amps during recharge but this holds true with a low battery situation or not regardless of jump start or not. The alt or gen will, under regulation, restore the charge to the battery using as full a load as is posable given the RPM. An example would be a push start or even a so low it just barely cranked over start. There will be max load from a low charge start on a cold rainy night. Recharging while running the lights, blower and wipers. Add the AC clutch for late cars that use AC to help with defrost. while the alt is fully loaded the car is moving the air over is cool and the temp rise on the core will remain in check. A hot summer night and the car sitting while the bat recharges might run the core temp well over what would be seen otherwise.

Recharge cycle duration is the difference. That is to say how long the alt or gen is running at full cap to restore the charge.

There was a situation at a track this year where a late model 911 had a battery momentarily installed reverse polarity. This "Let The Smoke Out" of many electrical components on the car and knocked it dead. This same thing on a 912 with stock electrics might have done little if corrected quickly.

[OldTee]

I'm confused. I thought it was a 69 912. Didn't they have generators. If so the system is tough as nails. Kinda like a oversexed VW. Kick the thing in the a$$, drop it down a cliff and it will sing for you. A alternator needs some battery voltage to excite the primary. A generator will produce voltage with just rotation, but for best results have a working battery.

[RoninLB]

ok..

some alt and regulators are more prone to heat damage than others. Generally 210deg should be ok for our 911 alt, although some track guys complain about the internal regulated alt. So I guess it's all an educated guess what you can get away with.

hard info: When a good car battery is used to jump a dead battery and the dead battery car starts the voltage will spike in the good battery car when the cables are removed and may kill the transistorized regulator, at least. This can be avoided by turning on all accessories and lights in the car that's doing the jump.

[Vicegrip]

Good thinking and very true on the donor car. I was only thinking of the 67 912.

John you are right a 67 912 has the small diameter generator and it is bullet proof but the jump car might not be.

Best $50 bucks I have spent in a while was one of the rechargeable jump start kits. It even has a small compressor for topping off tires. The jump start kits remove the risk of jump-starting. Just remember to recharge it every 3 months or so.

[OldTee]

You are correct about those 'Jump Start" aux batteries. I have one and am dying to try it some day. I hadn't thought about donar car damage and you well may be right. These new cars have a lot of electronics in them and diodes like to pop with reverse current. Always remember to remove the ground cable first, preferably from the sick car.