Outer Limits 4x4 Board

Hi Guys,

I have problems with alternator dying since I connected additional battery to the main car's battery. No isolators were used of any kind just 35mm copper cable to connect the main and axillary battery.

1. Installed a dual battery and connected it in parallel with the main car’s battery. That worked fine for a week or so and after that the car’s alternator stoped charging. The local auto-electric said that the coils had burnt for some reason.
2. To replace the original alternator, I bought an after market alternator and fit it to the car. Again the dual battery was still connected to the car. This second alternator worked fine for several days and then it started malfunctioning as well, but this time the aftermarket alternator was producing too much voltage, which at some point burned some fuses and damaged some components in the car.
3. Again I took the car to the local auto-electric and he repaired car’s original alternator, fit it to the car and replaced burnt fuses, so most of the things work now (At this point we also disconnected the dual battery from the car). The only thing that doesn’t work at the moment is the “central locking”, “rear-wiper”, ”interior-lighting”, “clock” and there could be few other things that I didn’t notice. The auto-electric believes that “body control ECU” is the problem but he can’t know for sure.

Did anyone had a similar experience and do you believe the alternator problems are related to the second battery being installed?

BTW: local auto-electric claims the dual battery setup should not matter.

Cheers,

Slobo

It's unlikely to be related to the dual battery system, but I wouldn't say impossible.

If the alternator hasn't been well designed it's possible that standard load plus charging two batteries means it's putting out more current for longer than the manufacturers intended, which is causing overheating in your vehicle. Highly unlikely, but not impossible.

The over-voltage was probably a voltage sensing problem - some Pajeros are know to do this if the Hazard light fuse blows. The regulator is trying to maintain a particular voltage - if it doesn't see that voltage, it will ramp up the alternator output until it sees it. If it can't see the voltage because of a fault (such as a broken connection) then the alternator will run at max output - which is typically WAAAAY too high for modern electronics to handle.

Come to think of it, both problems could be the same root cause - alternator not seeing sense voltage, so it's been running at max. First alternator (possibly old and tired?) overheated before the voltage took anything out, second alternator blew things.

So both faults could've been inadvertantly caused by the dual battery install, but the auto-sparky should've fixed the voltage sensing problem by now. If that's what it was.

Install a voltmeter, and watch it.

I think Scott's onto something.

There may be a smallish wire from the alternator that connects to the battery along side the heavy main one. This smaller wire is there to sense the actual voltage at the battery rather than just assume the voltage is the same as what the alternator is putting out. If that wire has a poor contact (or no contact) with the battery it will register with the alternator's regulator as needing a bit more "kick" from the alternator causing the alternator to output more voltage.

Things to do:

Measure battery voltage with vehicle off and left for 1-2hrs (baseline)

Measure battery voltage immediately after starting, both at the battery and at the big alternator post using the batt -ve/earth and then again using the chassis and then engine earth. (looking for correct voltage output with no voltage differences between the readings)

Check all earth leads (the battery is usually earthed via tha chassis and the alternator is earthed via the engine). Corrosion is a biatch... Quick fix to test the earths is to use a jumper leads from the batt -ve to both chassis and the engine.

Thanks for the feedback guys,

I left the car with auto-sparky so I can't measure the voltages or inspect the tiny voltage sensing wire. but will do that once I get the car back.

1. I don't understand the way that tiny voltage sensing wire works. I assume it is connected to the positive battery terminal, which is also the case with main alternator wire, so both of them would have the same voltage. Can you please explain?

2. Now that you explained how voltage sensing stuff works there is something I didn't mention. When we were fitting the main wire to the second aftermarket alternator the wrench touched the earth and main alternator fuse (140A) was blown straight away. As we didn't have proper replacement we jammed a bit of 6mm wire until Toyota ordered fuse for me. Unfortunately the havoc happened before I got the fuse. One thing I noticed is that insulation on 6mm wire has melted.

slobo wrote:Thanks for the feedback guys,

I left the car with auto-sparky so I can't measure the voltages or inspect the tiny voltage sensing wire. but will do that once I get the car back.

1. I don't understand the way that tiny voltage sensing wire works. I assume it is connected to the positive battery terminal, which is also the case with main alternator wire, so both of them would have the same voltage. Can you please explain?

2. Now that you explained how voltage sensing stuff works there is something I didn't mention. When we were fitting the main wire to the second aftermarket alternator the wrench touched the earth and main alternator fuse (140A) was blown straight away. As we didn't have proper replacement we jammed a bit of 6mm wire until Toyota ordered fuse for me. Unfortunately the havoc happened before I got the fuse. One thing I noticed is that insulation on 6mm wire has melted.

1. To explain, when the battery is under heavy load (driving lights, winching, high power inverter, etc) there will be a voltage drop caused by heavy current flow along the alternator charging wire as the alternator tries to share some of the load with the battery. This means the voltage at the alternator post is going to be higher than at the battery itself which is no way to charge a battery as the alternator thinks it is charged (using the heavy cable alone). That sense wire independently measures the voltage at the battery and allows the alternator to compensate for the voltage lost along the length of the heavy alternator cable under heavy load. Now if that sensing wire is a bit corroded it wouldnt see the correct voltage either, and the alternator would try to up the voltage to compensate even further giving the original symptoms you described.

2. I don't think the fuse blowing would be much to worry about, but a trip to the wreckers will get you a fuse in good nick to use in the meantime. As you noted, insulated wire is only going to end up with a fire from molten plastic and is not going to blow at the required time to save your loom. Pull it/replace it with the real thing (Bursons/Repco/other second tier supplier?)

Thanks mate, very helpful

BTW, I am looking to get dual battery system installed not sure if Sure Power sold by ARB is a good option or there are better ones. I don't like TJM one as most of the stuff these days is made in China.