Offroad-Express

Hey guys. I disconnected both batteries today to do some work on the truck. I have noticed that since reconnecting, they don't appear to be charging as the voltmeter has slowly dropped, and it is getting harder to start.

Have read on here through the search function that sometimes the regulator can get a spike and fry itself. Is this likely to be my problem? If so, how do you go about disconnecting/reconnecting batteries without frying it each time?

Many thanks

Hi are you sure you hooked all the battery cables back up? you may have missed the alternator.

does the voltage ingrease when you start it or is it 12V and below?

Start simple the regulator needs quite a sustained spike to kill it and if you disconnected the batteries you can weld etc.

Worth checking all the big fuses in the engine bay, start simple and work up from there.

If they check out okay then it's time for some diagnostics using a multimeter. If you don't have one get a cheap as multimeter from Dickies and check the output of the alternator then work through the dual battery system to find out where you are losing your power.

Matt.

Went through the haynes manual today for testing the alternator and regulator. Both checked out fine. Correct resistances/voltages etc. The starter solenoid is a little sticky, so will replace that anyway. Checked all battery leads again, and found one of the negatives a little loose. So will see tomorrow if tightening this has fixed anything.

When the truck is running, the in-cab voltmeter is right up at 18 volts, however when you turn the key to acc to glow the plugs, the volts are hovering around 9. I am thinking maybe the neg lead on the starboard batt being a little loose may have been interrupting the charge coming from the alternator. We'll see tomorrow.

Thanks for your suggestions so far. Thats whats so good about having these forums.

18 volts is far too high, does sound like your ground problem is the cause.

If the alternator can't tell the charge of the batteries then it will attempt to keep charging them. Some alternator's have a separate sensor wire for determining the charge level.

I wouldn't be too worried by 9 volts whilst the glow plugs are working as long as the voltage returns after the timer stops.

18 volts though will kill your batteries if it's actually getting to the batteries. It will boil them and destroy them.

Matt.

I don't think my alternator has a sense wire, but I will double check. I was thinking the 18V reading was because the batteries were sucking up a lot of charge, due to being flatter than normal. Prior to all this crap happening, the meter would sit around the 12 to 14 mark, and only increase after starting, before returning to the 12 - 14 mark.

When they charge they receive amps not volts so as the load on your system increases whilst the truck is running the voltage should stay constant but the alternator will output more amps to compensate.

If the truck isn't running the volts will decrease though.

If it goes above about 15 you can start to have problems. Some newer systems are getting towards 16 volts but the older gear should really never see more than about 14.8.

Matt.

if its runnin at 18 volts the voltage regulator is stuffed in the alt

If the batteries are not connected properly ie the alternator is running unconnected then it can go that high.

Running the alternator not connected though will most likely kill the regulator....

Matt.

The regulator checked out OK as per the manual, but I have replaced it anyway, and all is good now. Thanks for the help guys.