Battery not charging.

[GreyPrimer72]

Hello All,

I am having a few problems with my battery not charging very well. I have checked the fan belt and it has the correct tension. If I take the battery out, and charge it with a charger, it will work for a about 15 starts before it is drained again. I think the battery is ok (the charger I am using has a built in tester that says it is ok)

I have measured the voltage from the across the 2 terminals on the Dynamo and am getting about 5 volts while the engine is running. (Shouldn’t this be 12v?)

Could anybody give me any tips or tests to diagnose the problem?

Thanks
Graham

 

[Araon]

Ah well think you've just bdiagnosed the fault there.... there should be around 13v when charging of the dyno....

 

[Justin & Muttley]

As Araon says - it should be much higher...

check this out:

http://www.nls.net/mp/volks/htm/gen.htm

 

[GreyPrimer72]

THanks!

 

[currylager]

Check the condition of the dynamo brushes and the integrity of all the control box/dynamo connections before getting too technical :wink:

 

[Clarkson46]

You're confusing yourself. If I understand you correctly, you have measured the voltage between the 2 terminals on the dynamo, that could be any voltage. What you need to do is measure the voltage between the battery positive terminal and chassis with the engine running at say 1500 rpm. You should find, if all is well, around 14 volts or a little higher. The problem with poor charging may not be your dynamo, the regulator can also cause problems.

Have a look at this website it may help.

http://www.nls.net/mp/volks/htm/gen.htm

 

[Justin & Muttley]

...
Have a look at this website it may help.

http://www.nls.net/mp/volks/htm/gen.htm

That looks suspiciously like the link I posted up there ^^^

 

[58herbie]

it's all well and good checking to see if you have your voltage, but you also need to check to see if you have your charging current too, for this you need a needle type ampmeter (not digital) to check see what amps are being put into battery. you are best taking to an auto electrician if you do not have this type of ampmeter and get them to do this test..

if you do let me know and i can give you step by step instructions of how to do it..

Jon.

 

[Clarkson46]

If you have 14.4 volts at the battery positive then you have charging current, Ohm's law says so. Don't get bound up in ammeters they really don't tell you very much unless you understand what the readings actually mean.

 

[58herbie]

If you have 14.4 volts at the battery positive then you have charging current, Ohm's law says so. Don't get bound up in ammeters they really don't tell you very much unless you understand what the readings actually mean.

well being a auto sparky for a living i do..

right to test
1) disconnect wire from regulator B+ (becareful not to ground) connect voltmeter + lead to here and - lead to mounting screw of regulator.
start engine increase revs to 2000 you should get a reading between 13.5 to 14.5 volts.

(when engine is turned off voltmeter reading should drop from 12v to 0v just before engine stops completly this shows regulator points are not sticking)

2) next test the genny, remove terminal D+ (again becareful not to ground) you will need a test wire of about 4mm diam here due to current load. and run test no longer than 10-15 sec's . connect voltmeter + to D+ and meter - D- which is the screw terminal on the genny case.. readings @approx 1500rpm genny should give 12v and @ 3000rpm you shoild get 36v..
if you get these readings the trouble is with the regulator.

which is where the test with the ampmeter comes in....................................

3) remove terminal D+ again on gennerator connect meter + to this and meter - to the wire going to regulator(the one you have just removed). basically so the meter is in lline.
Start the engine and reduce revs until meter needle goes in negative (discharge) range/readings.Stop the engine, The meter needle should jump back to Zero before the engine has stopped completly.If the meter does not jump back when engine is completly stopped, regulator is defective. Discharge current readings for generators between 1968 and 1972 are between 2.0 amps and 11.5 amps...

i could go deeper into generators and regulators on bench testing, stripping and repairing but it might bore you....

8) 8) 8)

 

[Mike F]

Electrically I am a muppet - best say that first!

I have a similar problem but have an alternator. I have tried putting the probes of my multimeter across the two contacts on the alternator and got -0.004 whatevers (volts I guess?).

Or should I have the positive probe on the contact connecting to the battery and the other on an earth?

 

[58herbie]

you can either measure at the battery as the other wire at the alternator is the warning light not an earth, or you measure at the alternator and put the meter neg wire to battery neg..and meter poss to D+ (thick red wire) on Alternator.

Jon

 

[Mike F]

Thanks - just done that and it's reading 13.8 (volts presumably) which is guess is OK.

At least I can rule out the alternator now, cheers dude!

 

[58herbie]

Mike,

Does your van seem alright on short journeys, but no charge on long journey's, does warning light come on and then go out, does it stay out if you put lights, wipers, radio etc (not indicators) on and leave van on idle..

does battery lose charge after standing a while??

jon

 

[Mike F]

I've not got the confidence in the van to try driving it too much at the moment!

The starter seems to struggle though the engine starts OK. The red light goes out as normal. When I drove it maybe two miles the other day it really struggled to restart when I got home. A few weeks ago I drove 5 miles and it sounded like the battery was flat (new last Dec). I was on a hill so jumped it.

There doesn't seem to be any short circuits having tested as in John Muir. I have cleaned the contacts on the starter as well by the way.

One possible cause may be a split wire on the headlights which needs sorting - but am pretty sure it is not shorting there.

Does anything stand out?

Cheers!

 

[58herbie]

nothing really, jumps out. what make of Battery. might be worth taking to an auto electrician and getting a drop test done on the battery to check its holding the charge, also get them to check the alternator charge to both volts and amps...

also if they have a miditronics tester get them to do a starter crank test..

jon