Jump Starts

[Chook]

I can use Jump Leads to start a dead battery in my H3 but a couple of times now I have tried to jump lead start others with no success. Wonder if it is just the way the Auto Electrician has wired up my extra battery or part of the voltage controlled alternator computer thingy (yes that's the technical term LOL JKS). Last time I tried we used a voltage meter to try work out what was happening and the voltage hardly went above 12 (and dropped just under when I connected jump leads to the other vehicle with the dead battery even with my engine running). Revving my engine made no difference as the voltage stayed around 12v due to the alternator voltage control (where normal alternators go higher as you rev the engine). Has anyone else jump started another vehicle with your H3 ???? Is it the Alternator voltage control that is the problem ???? Any other hints/tips ???? Do I need to go back to my Auto Electrician ????

 

[SuperBuickGuy]

You should have 13.8v while the motor is idling.... if not, it's probably time for a new alternator

 

[Chook]

That is what I am used to but my 2008 h3 seems to have a special alternator and voltage regulating circuit. My auto electrician says it is likely there to improve fuel economy's her the alternator only produces when it is needed. Because of the alternator & voltage reg he couldn't install a regular dual battery but instead an odysee racing battery for emergency starts. I am wondering if that is the reason why I can't jump others as the emergency battery charges first. Before I go back to the auto electrician thought I would ask if this is a 2008 or newer issue with the new alternator etc.

 

[Happy Hummer]

Use a jump box it is so much cheaper and easier.Chris

 

[f5moab]

You should have 13.8v while the motor is idling.... if not, it's probably time for a new alternator

Maybe, maybe not depends on the duty cycle command from the computer. Actually after initial startup and for the first 30 seconds of idle, you should have 14.5 volts. After the initial 30 seconds the system goes into power management system that is a direct control from the ECM (or PCM depending on model year) to the internal generator regulator, from information monitored by the BCM (more complicated than that, but why get too involved. There is a fail safe that if the internal regulator loses contact with the ECM/PCM for a set time, it will default to 13.8 volts. So, depending on ambient temps, battery voltage prior to startup, AC on, lights On, etc., the output can vary quite a bit.

This is the same system that makes the lights dim at night with a full load and the brake area applied, the same system that might drop the generator output to around 12 volts while cruising on the hwy during the daytime, etc. It is a system to allow the generator to output only what is really required and it will (hopefully) increase fuel mileage and the life of the generator.

I'm not too sure about the original question. But if the OP is saying he cannot jump start another vehicle with his H3, something is wrong. Just the battery alone, if in good condition, should be able to jump another vehicle (just like a jump box). Only reason I could see this happening is if the battery in the H3 is shot and there is a shorted cell. But a shorted cell should also mean the H3 won't start either. However if the BCM thinks something is wrong with a battery, it can signal the ECM/PCM to drop the generator's duty cycle to around 20 percent, or 11.8-12.XX volts.

 

[Chook]

Thanks F5 the batteries are good just the voltage never went higher than 12.8v while I was checking it with the meter. (Not enough volts to start my friends diesel when cold) but it seems I will need to take my H3 back to the auto electrician to get it sorted but my belief is the BCM & Alternator are the reason.