Theory on battery charging issues

[Nefarious]

Got back from my Edinburgh-London-Edinburgh trip on Friday, and while the car was mostly faultless, it did refuse to start (dead battery) once I'd arrived it London. Not much grief, as I just popped it on trickle charge overnight, but it got me thinking about why I (and, seemingly, lots of you) have this issue. My battery was brand new (Optima), and the alternator seemed to be getting a decent idle charge to the battery, so why shouldn't it charge?

My theory is this: In the Tuscan racers, the alternator wheel size is set up for the engine to be spinning at or near redline most of the time. In a road car, a long journey where you don't get much above 3k rpm (e.g. an hour and a half crawl round the M25), it's not spinning the alternator fast enough to produce a big enough voltage difference for a decent charge. Swap the alternator wheel for a smaller one?

[julian64]

If you connect the diagnostic to your car you will likely see that at idle 1000 or below the battery is not holding its own with lights and aircon etc.

On my car the revs needed to service and charge the battery with full electrical drain is 1200. but anything over that and the car has no problem.

I would probably suggest you drive for a while with the diagnostics connected to look at the charge, because with that story you certainly have a problem.

[Nefarious]

It's certainly an odd one. After the car wouldn't start (not even with the help of a power pack), I jump started and then went for a 2 hour drive at night (mixed urban and dual carriageway) - the battery was completely dead before I started and there was no dimming of the headlights or other electrical wierdness, which implies to me that the alternator is doing its job fine.
I've got a gold plated audio spec item to replace the big fuse (contacts were filthy and the fuse itself was bent and slightly corroded), and had no issues on the way home, so we'll see how it runs.
I'm also going to be replacing quite a lot of the cabling (esp. the high gauge stuff) as part of my new owner list, so if it's still playing silly buggers after that, then I'll dig out the diag gear...

Edited by Nefarious on Wednesday 10th October 08:27

[SimonSparrow]

julian64 said:

If you connect the diagnostic to your car you will likely see that at idle 1000 or below the battery is not holding its own with lights and aircon etc.

On my car the revs needed to service and charge the battery with full electrical drain is 1200. but anything over that and the car has no problem.

I would probably suggest you drive for a while with the diagnostics connected to look at the charge, because with that story you certainly have a problem.

I've seen that with mine too. At idle power is leaving the battery, its only above tickover that its putting anything back in. So driving in London traffic with lights and cooling fans on it quite hard on the battery.

[thegreengoblet]

A few months back, I had a period of time where my interior lights were always on. I didn't notice until late one night when I had to go outside and my interior was lit up! Played about with the light switches and the door switches and they eventually went out. Don't know how much drain they place on the battery, but nevertheless still a drain. They've been ok since. Very strange.

[touching cloth]

I am just back from Germany where I had a few probs with electrics and charge, all pretty similar. Various issues raised themselves all symptomatic of the obvious big fuse failure (bouncy and finally non existant revcounter being the main one on mine) so the fuse was changed, indeed it fell to pieces on removal so was probably due. However symptoms pretty much continued unabated, alternator was pinpointed as maybe being on last legs, although was still kicking out voltage when measured. However, finally the cabling was inspected closer and it was this that was the problem... the connections onto the fuse were in a bad way, but also the cable itself is brittle and clearly old, neither of which help it cleanly transfer the full charge from the alt. Luckily simply getting rid of the grud around the fuse connections cleared up my probs enough to get me homw, but I will still take the advice of the Dulford chaps who did that fix, and change to fresh cabling as well at the earliest opportunity. The funny thing is, it is amazing even with that part down, how much loss must have been happening and getting worse over a period of time; things like slow windows which I have been noticing for a few months (and was putting down to window motors) have all suddenly disappeared and where I used to always have a little bounce in the revcounter especially so at higher revs, even this has now disappeared.

The alternator is I think a land rover item, so IMO should really be able to do the job (maybe not quite at idle but like Julian says 1200 sounds fine - running even a dosile cruise should be giving enough revs to do what it needs to). You have probably, like me, got rid of a huge part of your probs by overhauling the fuse and the connections, but again I think you are wise to look at refreshing the cabling as well.

[Steve_T]

IIRC it's a 140 Amp Landrover alternator. Should be more than enough. Perhaps we should do a group buy on an appropriate reel of cable?

[alinton]

I really hate to invoke 'The Big Fuse' as its often erroneously blamed for all manner of things, from doors not opening through headlamps flashing to the seat being uncomfortable.

But what you've described is a classic case of the connections to the fuse being dirty or corroded.

The fuse is between the alternator and the battery, so if its connections go high resistance the battery won't be charged. You'll jump start the car fine, and if you charge the battery it will charge fine and the car will start.

But go on a long drive, and when you get there and park, the car won't start next time.

Been there.

Either the alternator is jiggered, or, more likely, the connections around the 100A fuse aren't good.

My guess is that by replacing the fuse - and, I assume, tightening/replacing the fuseholder - you'll have fixed the problem.

Andy.

[SimonSparrow]

You can check the voltage at the battery and then compare it to the output voltage from the alternator and see if there is a difference. If there is, then the big fuse or cabling needs looking at. If the voltage is the same, then its either ok, or if low voltage, then your problems could be elsewhere.

My alternator was still within range, but at the lower end of it at 13v. It was replaced last service and now reads 14+v at the battery when the revs are raised.

[alinton]

True, _except_, if the fuse is showing resistance, the voltage may look ok at the battery when not much current is being drawn.

But when the battery is attempting to draw higher current, like when its trying to charge from the alternator, the voltage drop across a faulty fuseholder will be higher.

So the voltage comparison method is not always conclusive with this fault.

A.

[Nefarious]

Tried to start the car last night (having put it away on Friday night after the London-Edinburgh run), and it was completely dead. And that's after cleaning up the fuse and its connectors back in London.

It's a little worrying that it won't even start off a jump pack (although I guess they don't put out the required CCAs). Even a jump off a diesel engined Nissan Patrol was hard work and only just managed to turn the engine.

As I mentioned before, I'm changing all the cabling anyway, for peace of mind (especially given all the talk of fires recently), and I've got an audio ASL fuse to replace the existing big fuse. I guess these jobs will have to be brought up the priority list...

Oh and cabling is cheap - I'm planning to use high-gauge welding wire.

Edited by Nefarious on Wednesday 10th October 08:29

[Woody]

Nefarious said:

Oh and cabling is cheap - I'm planning to use high-gauge welding wire.

Wouldn't have thought that was the best way.

You'll want something insulated and stranded - solid will be no good due to the heat and vibration etc.

To be honest a decent quality cable shouldn't be too expensive anyway.

Chris

[thegreengoblet]

I've been contemplating covering my wires with heat shielding - you know the type that has a fur one side and a reflective side on the other. Could help to prolong the life especially in that engine bay.

[dilbert]

Starter motor?

[Nefarious]

Considered the possibility of it being the starter motor, given the difficulty starting, even with a jump, but there don't seem to be any other start motor symptoms. Maybe a bad connection to the starter motor, or just a bad earth (which would affect both charging and starter motor operation).

Woody - the stuff I've got in mind is insulated and stranded (like the cable for a ground clamp on a MIG welder), just a bit meatier than the standard battery cable you usually get.

Edited by Nefarious on Wednesday 10th October 13:07

[TimJM]

touching cloth said:

all symptomatic of the obvious big fuse failure (bouncy and finally non existant revcounter being the main one on mine)

My revcounter is bouncy - I just thought this was the norm for a TVR. I don't have any other issues - does this mean the big fuse could be on the way out?

[Fusion-Ed]

you want to sort the wiring sooner rather than later. A few really deep discharges will really damage the battery even an Optmia.

[touching cloth]

TimJM said:

touching cloth said:

all symptomatic of the obvious big fuse failure (bouncy and finally non existant revcounter being the main one on mine)

My revcounter is bouncy - I just thought this was the norm for a TVR. I don't have any other issues - does this mean the big fuse could be on the way out?

Depends, as I say mine has gone through various periods of bounciness and different extremes - a little at the higher end always seemed to be there and I too put it down as a "they all do that sir"; however when the big fuse is close to going I have also found that it tallies with a rev counter that swings like a metronome on pretty much anything bar the steadiest of throttles. As it is now (post the terminal cleanup but still on old cables), I am getting very little if any bounce at all at any revs. You could well have a fuse past its best if you are getting an increasing amount, or if it is a more a gentle swaying around and about the real reading, then you could also just have gradually deteriorating connections/cabling, a quick overhaul of these areas might well limit or stop it all together, or I guess it could also just be something else.

[Woody]

Nefarious said:

Woody - the stuff I've got in mind is insulated and stranded (like the cable for a ground clamp on a MIG welder), just a bit meatier than the standard battery cable you usually get.

Ah now I see - sorry, with the term 'welding wire' I was thinking of heavy guage wire for welding. Not the earth cables.

Chris

[V8Cerbera]

touching cloth said:

TimJM said:

touching cloth said:

all symptomatic of the obvious big fuse failure (bouncy and finally non existant revcounter being the main one on mine)

My revcounter is bouncy - I just thought this was the norm for a TVR. I don't have any other issues - does this mean the big fuse could be on the way out?

Depends, as I say mine has gone through various periods of bounciness and different extremes - a little at the higher end always seemed to be there and I too put it down as a "they all do that sir"; however when the big fuse is close to going I have also found that it tallies with a rev counter that swings like a metronome on pretty much anything bar the steadiest of throttles. As it is now (post the terminal cleanup but still on old cables), I am getting very little if any bounce at all at any revs. You could well have a fuse past its best if you are getting an increasing amount, or if it is a more a gentle swaying around and about the real reading, then you could also just have gradually deteriorating connections/cabling, a quick overhaul of these areas might well limit or stop it all together, or I guess it could also just be something else.

Mine bounces at idle. Hold any revs ya like and it's fine, totally stable but idle it bounces around from 800 to 400 to 600 to 500 to 800 to 0 to 200 to 0 again back to 800....

This pretty much ceases once the car has warmed up a bit