Over-Charging with Auxillary

[yakumo]

Hi guys,
I have another question for you all, I have a dual battery set up in my GQ which was installed when I purchased her, just with no second battery installed.
I put another battery in and I didn't notice anything strange for some time,
My old man used my car and left the ignition on for some time (burning out the points) she ran fine for a couple of hours after before backfiring and not leaving much left of my exhaust. (I was just about to leave on a trip and it was night time, a mate even pulled a sicky to get an extra day in) I've replaced the points but she keeps burning them out, Not long after I realised that my voltometer read 20V and after checking with a multimeter realised it was true.
I've since turned the aux battery off (its an idiot switch) and she's now charging up to a much healthier 14V MAX. Any idea's on why, and what I can do to use my AUX battery again?

[the evil twin]

Holy Cow... thats an odd problem.

It almost sounds as if the Aux is wired in series giving you a 24 volt system but it cant be... it would fry half the wiring.

Is the Aux in good nick or a dodgy one that was lying around.

Have a real good look at wiring for the Aux battery checking for dirty termianls etc and how it is earthed.

With the engine off, Aux isolated and using your multimeter check the voltages from the Battery positive to engine block (not battery negative) of both batteries.

[patch697]

When I started reading this my mind went straight to a screwed regulator (Hitachi alternators have a habit of doing this) but when I read it all came good with the second battery disabled that ruled that out.

What your describing doesn't sound right & I'd like to know

A:if you had those readings over both your batteries or just the auxiliary?

B: do you know what the setup is ie: make & model

C: can you post up some pics of the setup so we know what we are dealing with in order to be advise you.

[yakumo]

I will get that during the day, Basically the negatives from both batteries are to the block, and the positive is joined between the batteries with a switch isolator, the dash read 20V and I checked it at the starter (factory) battery with the multimeter to get the reading of 20V

[the evil twin]

Yeah, I thought similar Patch...
there is def something oddball wrong eh, but what...

[the ferret]

Both batteries should be the same size, and if one is smaller or one is half dead, it will tell the alternator to keep charging the good battery, it's a wonder the good battery hasn't boiled dry.
Cheers, the ferret.

[yakumo]

Ah, the batteries are different sizes, however they both have enough guts to crank the car over by themselves no problems.

[the evil twin]

Ah, the batteries are different sizes, however they both have enough guts to crank the car over by themselves no problems.

Size doesn't matter unless your car is a female :)

OK... Uummm... how do you know that? Did you disconnect the main and try with the Isolator switch made or did you try the Aux in place of the Main?

The reason I ask is that the Alternator is sensing off the Main battery and it is exceptionally odd to have 20 volts in circuit with both batts and 14 with only teh main

[yakumo]

Main disconnected and switch on

[the evil twin]

Thinking about this further something doesn't make sense... correct me if this timeline is wrong but from teh thread...
Car didn't have 2nd battery when bought...
2nd battery fitted "for some time" with no probs...
Ign left on and points burnt out...
Replaced points and after a few hours backfired and burns out points ever since...
Noticed Voltmeter at 20 Volts and confirmed until 2nd battery disconnected...

Is the car on LPG? (maybe the backfiring is unrelated or simply a points symptom)

When you parallel the batteries does the Voltage immediately rise to 20 Volts?

If only one battery is in circuit (either one) I assume the charging voltage is normal?

[yakumo]

After the ignition was left on it ran fine for some several hours after, when it backfired (yes on lpg, caused by poor spark because of the points, I have new plugs and leads, done timing ect, and it started backfiring on petty aswell) Im an LPG mechanic so I know what caused that. when you start the car its relatively right (13-14v) its after driving for a few minutes it gradually rises, normally around 16, however longer drives tend to see it reaching 20V. when theres one battery it charges correctly, yes.

[yakumo]

The Backfire was caused by the points, however after I replaced them, it doesnt take long for it to start playing up again, I could only guess the points continually burnt out due to the high voltage, however I'm putting an electronic ignition (pertronix) when it arrives (hopefully by friday).

[patch697]

Ok.... For starters the voltage needs to be checked at the alternator then at both batteries & while its running at idle & at around 2000rpm with a meter. (don't go off the gauge there not accurate)

If you could do this & post up the results that would be great.

Secondly.... when you say isolator, can you describe what it is? ie: just a manual switch that allows to switch between your 2x batts or run them both at the same time or something that controls itself?

As for your points, Patrols have a bad habit of frying them, around every 5 to 10,000k's "GQ especially". It's coursed by pore earth & signal decay over the distance between the distributor & the coil.

When the points were changed, did the condenser get replaced as well? If not this is could be the course of your pore spark issue. GQ's ate also quite sensitive to dwell angles when on LPG. Between 38 to 40 is the optimum rather than the 36 thats recommended by the manual.

The pertronix unit your about to fit is only a points replacement unit & I'd be getting this voltage problem sorted before installing it cos if this is the reason your points are frying, I suspect it will fry the pertronix control unit & this will stop you dead in your tracks.

It may also pay to have a read of this thread. Even with your pertronix unit you will still need this mod.

http://www.nissanpatrol.com.au/forums/showthread.php?299-Information-on-TB42s-extended-rotor-button

[Yendor]

I would check the alternator voltage sense circuit.

It's the small white wire that connects to the alternator via the 2 pin plug.

It should have battery voltage at all times, the alternator senses this voltage to maintain the correct charge rate, if there is a fault in this connection it can cause the alternator to overcharge.

The small white wire connects to the larger white wire about 6 inch in the harness from the alternator, I have seen a few where this connection fails.

If this is the problem the best way to fix it is to run a wire from the positive of the cranking battery via a fuse and connect it to the small white wire at the alternator.

I cant explain why it seems it is only overcharging with the second battery connected, I don't see how a battery alone could cause this, I guess if you have another battery you could try putting this in.

[albi]

when you replaced the points ,did you replace the condensor?????

[yakumo]

Hey guys, no I didn't replace the condensor, :S, strangely the problem seems to have fixed itself, this concerns me a little.