Charging light slow to go out

sdibbers

Well-Known Member
#1
I managed to get a good strong charge from the AC11 alternator after replacing the dodgy wiring found in the depths of the engine bay. When running the voltage runs between 13.5 and 14.2v. However, when I start the car if its been sitting for a week in the garage I notice it takes a while for the charging light to go out. Sometimes up to a minute. The charge is still happening ok. I have a solid state replacement for the warning light relay that's known to be a problem. Should I suspect the alternator needs help or the control box on the inner wing?

PS this is a 1969 2000TC ex AC NADA car if that helps.

Thanks in advance,

Steven
 

ghce

Well-Known Member
#3
The likely problem is that the low voltage of the battery is pulling the alternator output low resulting in the slow light.

Whats of more concern is that your charge voltage is too low, 14.2 Volts is a little on the low side, really you want to be seeing 14.5 up to 15.0 V and at 13.5 I would be doing furthur investigation as that really wont be providing any charge at all.

One thing you could try is having your DVM ( Digital Volt Meter) measuring directly off the back of the alternator to check you haven't got any wiring problems / losses, if you are still seeing low volts you will need to check out the regulator box or the rectifier stack.


Graeme
 

sdibbers

Well-Known Member
#4
@gche Good info, the battery is certainly marginal at the moment with sub zero temps and not much driving due to salt everywhere. I’ll charge the battery and try next weekend. TBH the battery is about 5 years old and I know modern batteries don’t last that long.

On the loss side I’m pretty confident now that all’s good on the wiring side. I repaired and cleaned/replaced all suspect wiring and connections recently as charging had failed down to bad in loom repairs from previous mechanics.
 
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sdibbers

Well-Known Member
#6
The likely problem is that the low voltage of the battery is pulling the alternator output low resulting in the slow light.

Whats of more concern is that your charge voltage is too low, 14.2 Volts is a little on the low side, really you want to be seeing 14.5 up to 15.0 V and at 13.5 I would be doing furthur investigation as that really wont be providing any charge at all.

One thing you could try is having your DVM ( Digital Volt Meter) measuring directly off the back of the alternator to check you haven't got any wiring problems / losses, if you are still seeing low volts you will need to check out the regulator box or the rectifier stack.


Graeme
Rechecked this weekend, charge at idle is 14.2v so I think all is good there. I charged the battery on Friday and sure enough it barely turned the car over on the Saturday. Pretty sure its seen its last at 6 years of age. I guess that's normal with modern batteries.
 

ghce

Well-Known Member
#7
Rechecked this weekend, charge at idle is 14.2v so I think all is good there. I charged the battery on Friday and sure enough it barely turned the car over on the Saturday. Pretty sure its seen its last at 6 years of age. I guess that's normal with modern batteries.
Battery Technology has improved so much in the last 20 years that while an old tech battery only had a warranty for a year but lasted 8 years on average the new modern high tech battery has a 2 year warranty and only lasts 26 months before it fails.

But back to your battery did you check the leakage current from your battery? The clock can cause issues with high current drain as can other faulty wiring. Though to be honest 6 years sounds like a likely reason for failure.

Graeme
 

sdibbers

Well-Known Member
#8
I did put an ammeter between the + terminal and lead. Very little draw (less than 10 mA) so I don’t think it’s parasitic loss.

I’m leaning towards the battery. It’s six years old, only has 575 cold cranking amps and slows down quickly during turning over the engine when cold. Even after a full charge from a charger. Doesn’t seem to have an issue with charging any more.
 
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ghce

Well-Known Member
#9
I did put an ammeter between the + terminal and lead. Very little draw (less than 10 mA) so I don’t think it’s parasitic loss.

I’m leaning towards the battery. It’s six years old, only has 575 cold cranking amps and slows down quickly during turning over the engine when cold. Even after a full charge from a charger. Doesn’t seem to have an issue with charging any more.
some things can be done to improve old batteries, the main culprits are self discharge due to crud build up at the bottom of the plates, flushing out the electrolyte on a fully charged battery and replacing the battery acid with new acid of the correct specific gravity can improve things theoretically but I can't say I have had too much success with this approach.

Another thing ( which I have never tried) is an additive which supposedly reduces or removes the battery plate sulphation.

One method I have had success with on old batteries is to trickle charge them at 14.4 volts ( all the time you aren't driving it) eventually (months later) the batteries internal resistance will drop and your cranking current will be improved.

Probably if you employed all 3 methods you could gain another year out of it but for all the hassle a new battery is far easier.

Graeme
 

sdibbers

Well-Known Member
#10
The hassle plus the hassle of disposing of the old acid make a new one the way forward. The existing battery has a quite low cca already from new.
 

colnerov

Well-Known Member
#11
some things can be done to improve old batteries, the main culprits are self discharge due to crud build up at the bottom of the plates, flushing out the electrolyte on a fully charged battery and replacing the battery acid with new acid of the correct specific gravity can improve things theoretically but I can't say I have had too much success with this approach.

Another thing ( which I have never tried) is an additive which supposedly reduces or removes the battery plate sulphation.

One method I have had success with on old batteries is to trickle charge them at 14.4 volts ( all the time you aren't driving it) eventually (months later) the batteries internal resistance will drop and your cranking current will be improved.

Probably if you employed all 3 methods you could gain another year out of it but for all the hassle a new battery is far easier.

Graeme
Hi, When I worked for the bus company the electrician could be seen sometimes washing batteries out to re-acid them. I'm not sure of his success rate but he wouldn't have been doing it if it didn't work.

We used to use the tablets at my mates garage usually when there were a number of batteries pulled out of cars being broken. they had been sitting around flat for a while so there was not much to lose given their price. Success rate was 75% I suppose. The product over here was 'bat-aid' made by Granville, a tube of 12 tablets, enough for a battery, is £4 even today so not expensive.

Colin
 

cobraboy

Well-Known Member
#12
On another car I have a mediocre quality Unipart battery bought in 2008, I wrote the date on it. This battery has always been connected to a C-TEK conditioner in the garage and it is still very good.
I guess the cost of the conditioner - about 40 quid, has paid off on that one.
 

sdibbers

Well-Known Member
#13
Good to know on keeping the batteries going. I think I will sort out a battery tender for the new battery. The correct size (24) battery is meant to be 700 CCA, the one fitted is undersized has the terminals too close to the hold down clamp for comfort and is only rated at 550 CCA. I doubt it was fit for purpose when fitted and is dying an early death partly because of that.
 
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