MainePorsche

All excellent pieces of information. To avoid the first instance, a heavily discharged battery should always be disconnected before receiving a charge, right?
I also heard that the positive post terminal in the engine bay should never be used as a connection point to jump start a 928. In fact, jump starting a 928 should be avoided if time allows for properly charging the battery. Is that true?


Yes to both... :-)
__________________
John '86 Euro S2 16v
SharkTuned LH & EZ-F
www.jdsporsche.com

Quote:
Originally Posted by John Speake
Things that can shorten the life of an LH are using a normal 5A battery charger on a well discharged battery without first disconnecting the LH ECU 35way connector.

The resulting big current surge can kill the LH. So the object is to minimise such surges if possible. Also old spark leads that arc to the engine castings are known to be high risk.

Similarly high voltage "boost" starting packs can deliver substantially more than the recommended 16v maximum.

My rebuilds offer much better transient protection that the original tile.


Here's my question.
In reading JPTL's thread on fuel delivery issue, I came across the two above posts regarding battery charging an the possibility of providing to much amperage to the LH, and damaging it. Though the original design provided for easy charging through the jump post (as it is called), should charging (not trickle - jump starting) take place as John suggests ?
His experience, and wisdom, is always respected.
What say the Wise ones ?

Tom in Austin

Good post. I have jumped my car once using the post for + and a crossmember bolt for ground. Fortunately that's the only jump start it's ever needed.

For charging I disconnect the ground strap and put the clamps directly onto the battery terminals. Theory being nothing can hurt the electronics if there's not a ground path back to the battery. Hope that's correct.

MainePorsche

Yes Tom, logically that is the way to do it.
I've heard in discussions here the contrary in that it makes no difference, and was not problematic.
I'd lean towards John as this offers ultimate controller protection, but I just bring this up for discussion.
Knowledge is good.

jpitman2

For jump starting there are going to be times when only the jump post is accessible - who has leads long enough to get to the battery when the rear end is up against a wall/fence in a car park, or a single car garage? Do you need to fit a spike suppressor into the line from the jump post?
jp 83 Euro S AT 56k

MainePorsche

Spike suppressor... interesting.
Wonder what Alan thinks of this ?
Was thinking about fabricating a large gauge kind of pigtail to the battery, giving access to a direct battery charge. Is easy to disconnect ground sttap in order to isolate. Would of course keep them capped.

Speedtoys

Deleted...gah.

dr bob

So...

Look to what the source is and assess the ability to create a voltage spike that makes it to the LH or other intelligent but fragile electronics piece. A battery and alternator in another car is limited to fourteen point something volts by its own voltage regulator and the impedance of that car's battery. Risk for jump-starting is very small.

The poorly-named "jump-start" post is connected to the starter and ultimately the battery via the relatively small power cable in the front of engine harness to the alternator. From the alternator, the wiring is marginal at best for real jump-starting until it actually gets to the starter. So using the "jump-start" terminal to try and start the car is probably not a Good Idea. It's OK to use that point for battery boosting, so long as the voltage is held to less than maybe fifteen volts, better if a little lower.

Old-school "battery chargers" are typically higher-voltage transformers, a diode pack, and a thermal circuit breaker. The actual charging current is a function of battery terminal voltage, and whatever voltage the transformer can generate less the voltage drop through the diodes. Since olks who 'buy' a, say ten-amp charger expect it to supply current at ten amps, the available voltage will be high enough to do that even when the battery terminals are at 14.5 volts already. Leave that kind of charger connected for too long, and eventually the terminal voltage will rise to close to whatever the transformer can put out, again minus the voltage drop through its diodes. Could easily be sixteen volts or more, too much for the LH controller to see reliably.

"Smart" chargers and maintainers charge at max capacity but typically the rate is tapered off as terminal voltage passes fourteen or so. So less chance of boiling the battery electrolyte, or damaging sensitive electronics.

Charging the beatery while it's in the battery well -- The battery sits in a tightly-enclosed space. High-current charging typically causes outgassing of hydrogen and oxygen into that space, plus it sometimes causes acid vapor carryover. The hydrogen and oxygen together spell explosion if there's any ignition source available. You've probably read one or two references to using the vapor/vent hose connection on the battery to route the outgassing and acid carrover out of the compartment. There are other reasons why you probably want to charge with the lid open or better, with the battery out of the car. One is that you can check the electrolyte levels before you charge. You probably stand a better chance of getting cables connected right, keeping in mind that getting them reversed can easily cause an internal explosion in the battery case. That can be really messy, in my experience.


So... smart charger OK with battery in the well and connected. Battery boosting from another car using the jump post is OK, provided the jumper cables are the typical 10ga and the 928 battery isn't really low or dead. For a real jump start, you really want to put he posive clamp directly on the battery positive terminal. the negative jumper-cable clamp needs to go to something grounded but not within line-of-site of the battery itself. Then the negaive clamp is the last connection made, and the first disconnection as soon as the engine starts.


In my soft in-the-car toolbag is a set of mini jumper cables made from heavy-gauge speaker wire and some battery charger clamps. I figure that the 10ga wire and the small clamps will limit current to something short of car wiring meltdown levels if I ever need them, even if they are used at the "jump post" under the hood. Similarly, if used to help another owner, they will protect my car's wiring the same way.

I made the cable set after a long-ago Sharktoberfest fun-ride left another owner stranded on PCH after a gathering and form-up stop. He was at the rear of the line of cars as we rolled up, and had his parking lights on for safety. Tired battery and half an hour of parking lights turned into no-start and a call to AAA for a jump. Should that happen again, I'll be ready with my mighty booster cables.


Oh, charging a dead battery or storing the car for winter? Remove the battery to a safe place, where it won't freeze and can be safely connected to the smart charger/maintainer for what it needs.

MainePorsche

Thanks Bob. On duty and responding on my new smart a$$ phone.

jpitman2

Bob, sounds like you are saying a cheap charger is more likely to damage a car than a jump start? You can get surge protectors that mount permanently across the battery poles, as well as built into jumper leads. I have no time for the cheap jumper leads - despite having fat looking leads, they usually only have 1/8" copper cores, and their clamps are ally anodised to look like copper. I made mine out of 70 sq mm welding cable which is fine stranded and very flexible, and the clamps will give provide very good wrist exercise while fitting.
jp 83 Euro S AT 56k CIS - no ecu to blow!

dr bob

Cheap chargers have no voltage limiting, and generally if left to themselves will overcharge, boil out electrolyte and ultimately ffer to high a voltage to the system.

The battery is a fabulous spike suppressor. Almost anything you add will pale in comparison. Spikes happen when some low-impedance inductive device has a field collapse and discharges back into the system. Unfortunately the battery is at the other end of a string of conductors when you try to jump-start from the jump-start jump post. If you must use the jump post and a donor vehicle, let the donor vehicle charge your battery for a bit rather than just clamping on and hitting the key.

Alan

I think the best advice on charging is to get a high quality modern charger, ancient beasts most likely don't control voltage well - overvoltage is what kills sensitive electronics. Long term over current while charging tends to cause battery damage.

This advice applies to battery maintainers too - the best modern ones are truly suitable for permanent connection through the winter, while the worst old ones will harm the battery if left connected for too long, because they never turn off.

If you do need to use a med-high current or older style charger and have no other options then disconnect the battery from the vehicle (e.g. remove ground strap) and its best to remove the battery from the vehicle, and monitor it closely - charge until restored but not for too long.

If the battery is just low on charge (still can crank slowly and voltage is >11.75v) starting with booster cables from another car's battery or battery pack connected via the front post is unlikely to do any damage IMO as long as the other car isn't running - just use it's battery - not it's alternator (because alternator voltages on another car may be too high and particularly will likely spike up when the starter stops operation). Plug in (to operate, not just to charge) starter packs are generally just a bad idea - and fairly rare - similar reasons to fear them from a voltage control perspective. Battery at rest voltages below 11.75v suggest the battery is severely depleted and may overload the alternator (recharge it off the car), ths may be true even up to 12v. Voltages below 11v suggest the battery is actually damaged and it may be dangerous for the electronics to run with it in this condition (poor alternator voltage control) and it will likely fail to start the vehicle every time now.

After starting always monitor the voltage when you disconnect the additional battery - if voltage rises or is unstable - shutdown immediately and get a new battery. Best to just check battery voltage before you try to jump start to see if the battery is low on charge or damaged.

Now it's almost certain that the car will start more easily if you can connect directly to the battery at the back anyway - so that would be preferred whenever its possible.

So Bottom line is buy only good quality modern chargers that are well rated for lead acid charging modes, there have been some good threads on this recently, disconnect the battery when doing anything but a true maintainer mode. Connecting a quality maintainer to the front post is fine.

Alan

John Speake

Just as important a over voltage is a big current surge when trying to charge a well discharged battery with a battery charger or slave battery.

So just disconnect the LH ECU 35way connector, if you using the "jump start" terminal. With a slave car just connect it to the 928 and leave it for a while so it will put some charge into the battery. The car will then probably start after getting some charge back into the battery.

Or connect a charger and charge in the normal way. Then disconnect the slave, reconnect the LH and the car will probably start...

MainePorsche

The Wise have spoken...

Thanks for your input on this discussion.

Alan

A large current surge from a battery doesn't worry me one bit - just so long as the source and destination are just batteries or primarily resistive loads. If the source is an alternator I'd be more worried. It is really only voltage that kills sensitive electronics, current surges involving inductive elements can certainly induce high voltages under some conditions - but its still just that voltage that actually kills circuits that are just sitting in parallel to the current source & sink.

Alan