strange gremlin, any help would be appreciated

[Tiny]

I have a tb42 mav, pretty much stock, althoug it does have a dual battery set up on it, was on when I bought it, second battery was dodgy, never changed it and had never caused problem, but it could be that

it is a runabout....expensive one I must say, but it gets used to tow the car trailer from time to time and get a run into work when its raining or to cold for the bike. it has sat for long periods due to long mining rosters

during that time I found the battery was draining, so would take the lead off. then it wasn't charging properly and found a loose earth strap so I pulled all the straps and leads off, cleaned, refitted and sprayed with the anti corrosion terminal spray but by that time the battery was pretty farked so I replaces with an n85 I think, big fucker anyway.

went fine for ages, but then after I quit the mining job I needed to use it more often and found the battery was draining again so I replaced the terminals that were looking a touch average and put an isolater on the positive, full cut off, all the accessories etc go to the isolater and then one lead to the battery.

now if I charge the battery and isolate it it stays charged, battery is good, no dropped cells etc. there is still a drain somewhere, but with the isolator that is not much of a problem, but it has developed another problem, alternator has charge, but it doesn't seem to be charging through to the batttery. The batery light stays on dimply as does the handbrake light "the one with the ! in a circle in brackets" driving in daylight with no lights etc on there seems to be enough chrge getting through to keep the battery toped up, but in the morning with lights on and heater on the battery light and handbrake light are way brighter and there is not enough charge to maintain the battery and it slowly drains

anyone got any idea?

[-Scott-]

My first step would be to confirm that you don't have a high-resistance connection anywhere; that the voltage regulator is seeing battery voltage, and not some lower voltage caused by voltage drop across a connection.

Try to measure voltage across each joint that you can access - that is, multimeter probe either side of the joint (to measure the drop across the joint) - not just -ve probe on -ve terminal, and random probing with the +ve probe.

If there's nothing evident there, then I'd start to suspect the alternator and/or regulator. It sounds to me like there's insufficient field current; most likely causes would be brushes or regulator.

[Tiny]

My first step would be to confirm that you don't have a high-resistance connection anywhere; that the voltage regulator is seeing battery voltage, and not some lower voltage caused by voltage drop across a connection.

Try to measure voltage across each joint that you can access - that is, multimeter probe either side of the joint (to measure the drop across the joint) - not just -ve probe on -ve terminal, and random probing with the +ve probe.

If there's nothing evident there, then I'd start to suspect the alternator and/or regulator. It sounds to me like there's insufficient field current; most likely causes would be brushes or regulator.

hmm, so the alternator may be charging, but insufficient amps? is that how it would work? charge at 14.8 volts or whatever but bugger all amps?

[-Scott-]

hmm, so the alternator may be charging, but insufficient amps? is that how it would work? charge at 14.8 volts or whatever but bugger all amps?

Something like that, yes.

The regulator adjusts the output by adjusting the "field" current; as load increases the field current is increased to allow the alternator to produce more power. If the field current is limited for some reason then the alternator can only produce a limited amount of power - so it's OK when there's little electrical load, but struggles at higher loads.

[pongo]

yep, alt/reg on the way out.

Get a new or rebuilt one and all will be sweet

[chimpboy]

hmm, so the alternator may be charging, but insufficient amps? is that how it would work? charge at 14.8 volts or whatever but bugger all amps?

Something like that, yes.

The regulator adjusts the output by adjusting the "field" current; as load increases the field current is increased to allow the alternator to produce more power. If the field current is limited for some reason then the alternator can only produce a limited amount of power - so it's OK when there's little electrical load, but struggles at higher loads.

If the alternator isn't coping wouldn't you end up seeing lower voltage anyway?

[-Scott-]

If the alternator isn't coping wouldn't you end up seeing lower voltage anyway?

Yes. But is it "not coping" because it is simply too small, or is it "not coping" because it's faulty?

From Tiny's description, that "lights and heater" in the morning are enough to cause it to struggle, I doubt that the problem is simply an undersized alternator. It doesn't sound like he has a large load on it - unless there's an issue with his second battery, causing most of the alternator output to go there?

[Tiny]

If the alternator isn't coping wouldn't you end up seeing lower voltage anyway?

Yes. But is it "not coping" because it is simply too small, or is it "not coping" because it's faulty?

From Tiny's description, that "lights and heater" in the morning are enough to cause it to struggle, I doubt that the problem is simply an undersized alternator. It doesn't sound like he has a large load on it - unless there's an issue with his second battery, causing most of the alternator output to go there?

maybe thats worth ding as wel, replace the second battery or disconnect the solanoid and see what happens