Battery running down...

Discuss Electrical problems here.
Forum rules
By using this site, you agree to our rules. Please see: Terms of Use
Post Reply
TimM
Minor Friendly
Posts: 43
Joined: Fri May 21, 2010 7:14 pm
MMOC Member: No

Battery running down...

Post by TimM »

Hi,

I have noticed that after charging up my battery and then driving about it eventually leads to having insufficient power to start the car. The car is a 1961 positive earthed model, completely as standard with no modern electronics. It is fitted with a dynamo and voltage regulator. The red light goes out when it is driven, so indicates that the dynamo is working OK. There is no battery drain.

I am wondering if the battery needs to be replaced with something that can lose some juice before it cannot turn over the engine.

Any ideas happily taken!
User avatar
geoberni
Minor Legend
Posts: 3561
Joined: Fri Aug 04, 2017 11:19 am
Location: North Leicestershire
MMOC Member: Yes

Re: Battery running down...

Post by geoberni »

I would not rely on the little Red Light alone, if the symptoms are indicating otherwise.

The lamp is telling you that the Dynamo is outputting the right voltage.
Basically when the voltage output of the generator is lower than the voltage of the battery, the light will be on.
The current path is from the battery through the light, through the generator to ground then back to the other side of the battery. In effect, the battery is "charging" the generator.
When the voltage output of the generator rises to the level of the battery, the light goes out.

But you've got the battery running out of 'ommpf' whist driving around.
It might be that the Dynamo is not outputting enough current to charge the battery, or the battery is so worn out it's not accepting it.
It could be worn out brushes on the dynamo, or it could the battery sulphated up with age.
One of the reasons I have an ammeter fitted, so I can see when the battery is charging.

Do you have a multimeter?
If you do, is it rated for 10Amps (that's the most common Amperage rating)?
Basil the 1955 series II

Image
oliver90owner
Minor Legend
Posts: 1653
Joined: Thu May 12, 2016 6:33 am
MMOC Member: No

Re: Battery running down...

Post by oliver90owner »

That ‘there is no battery drain’ might indicate you have checked for zero current between one battery terminal and its normal connector?

Presumably, once charged, the battery maintains its proper voltage and will start the car easily, say, a week later?

As previously, the ‘ignition light being extinguished’ is nothing more than that the dynamo is developing some voltage.

Is the fan/dynamo drive belt in good condition and tensioned correctly?

What type of battery is fitted?

It would appear that the battery is simply not being adequately charged. That could be connections, voltage control, dynamo or drive belt - even a battery with low electrolyte level.
simmitc
Moderator
Moderator
Posts: 4718
Joined: Thu Apr 15, 2004 9:43 am
Location: Essex
MMOC Member: Yes

Re: Battery running down...

Post by simmitc »

In addition to the above:
Are you certain that the red light is connected to the charging? The reason for asking is that over the years with different owners, the lights can get swapped round and the red could be oil pressure which would behave as you describe :-?
The voltage regulator could be at fault.
Do you have a multimeter? We need to check where the problem lies, rather than just changing bits on the chance that they might cure the problem.

Two checks to run immediately:
Fully charge the battery, disconnect it from the car and leave to stand for a day. What voltage is shown across the terminals?
With the battery fitted, switch on the headlamps and try to start the car. Can the battery start the car, how dim do the lights go?
Rev the engine, do the headlights get significantly brighter?
Leave the fully charged battery on the car for a day and then check the voltage across the terminals.
TimM
Minor Friendly
Posts: 43
Joined: Fri May 21, 2010 7:14 pm
MMOC Member: No

Re: Battery running down...

Post by TimM »

Thanks guys! I have a meter so will start checks today. :)
TimM
Minor Friendly
Posts: 43
Joined: Fri May 21, 2010 7:14 pm
MMOC Member: No

Re: Battery running down...

Post by TimM »

simmitc wrote: Fri Mar 04, 2022 4:18 pm In addition to the above:
Are you certain that the red light is connected to the charging? The reason for asking is that over the years with different owners, the lights can get swapped round and the red could be oil pressure which would behave as you describe :-?
The voltage regulator could be at fault.
Do you have a multimeter? We need to check where the problem lies, rather than just changing bits on the chance that they might cure the problem.

Two checks to run immediately:
Fully charge the battery, disconnect it from the car and leave to stand for a day. What voltage is shown across the terminals?
With the battery fitted, switch on the headlamps and try to start the car. Can the battery start the car, how dim do the lights go?
Rev the engine, do the headlights get significantly brighter?
Leave the fully charged battery on the car for a day and then check the voltage across the terminals.
OK so the battery shows about 13V charge all day when not connected. It will turn over the car and start it with the lights on. No dimming or brightening when I rev the engine and after being connected for a day remains at 13V.
simmitc
Moderator
Moderator
Posts: 4718
Joined: Thu Apr 15, 2004 9:43 am
Location: Essex
MMOC Member: Yes

Re: Battery running down...

Post by simmitc »

On the plus side, the battery sounds OK, and you have confirmed (as you originally wrote) that there is no drain or short on the car. On the downside, there is no charge flowing into the wiring, so it's probably a dynamo issue.

Check fan belt tension and that neither wire has come loose from the rear of the dynamo. You could try re-polarising the dynamo.
Disconnect both wires from the rear of the dynamo. Connect one end of a spare piece of wire the the F (small) terminal. Flash (briefly touch) the other end to the non-earthed terminal of the battery. Expect a spark. Repeat, remove the spare wire and reconnect both "proper" wires. Retest to see if the lights get brighter when you rev the engine.

For more in-depth testing, see https://www.autoprotips.com/testing-a-d ... ng-output/
TimM
Minor Friendly
Posts: 43
Joined: Fri May 21, 2010 7:14 pm
MMOC Member: No

Re: Battery running down...

Post by TimM »

Thank you. I have tried cleaning the dynamo leads etc and will next take it out and see what sort it is and either replace it or see if can be fixed. :)
kennatt
Minor Legend
Posts: 2625
Joined: Fri Feb 02, 2007 9:11 pm
MMOC Member: No

Re: Battery running down...

Post by kennatt »

see here https://www.howacarworks.com/illustrati ... amo-cables https://www.matchlessclueless.com/elect ... e%20dynamo% Swap voltmeter for millimetre and check vehicle neg or pos earth.
User avatar
geoberni
Minor Legend
Posts: 3561
Joined: Fri Aug 04, 2017 11:19 am
Location: North Leicestershire
MMOC Member: Yes

Re: Battery running down...

Post by geoberni »

Battery certainly seems OK. It might be the Regulator, but before testing that, which can get a little fiddly, I'd take a look at the dynamo brushes, probably a good change they have worn away.
Basil the 1955 series II

Image
oliver90owner
Minor Legend
Posts: 1653
Joined: Thu May 12, 2016 6:33 am
MMOC Member: No

Re: Battery running down...

Post by oliver90owner »

Dynamo basic operation is easily checked. It should operate as a motor when connected directly to a battery. If the dynamo ‘motors’, then it is likely the voltage control box which is causing your troubles - all other things checking out.

This is not a definitive test for a good working dynamo, but is often a good indicator. If it won’t motor, it definitely needs attention.
myoldjalopy
Minor Legend
Posts: 2516
Joined: Tue Jan 29, 2013 10:32 pm
Location: Kernow
MMOC Member: Yes

Re: Battery running down...

Post by myoldjalopy »

You can do this rough and ready test with the dynamo still in the car. Just loosen the dynamo enough to remove the fan belt, remove the cover of the control box and press down the cut-out contact (the one on the right hand side as you face the car...do not press the regulator contact). A good dynamo will then run briskly as a motor. Make sure the cut-out disconnects again after this test. If it won't run, or runs sluggishly or erratically, the dynamo is faulty.
TimM
Minor Friendly
Posts: 43
Joined: Fri May 21, 2010 7:14 pm
MMOC Member: No

Re: Battery running down...

Post by TimM »

Thank you so much everybody!

Well, I have put in a new dynamo, checked the fuel lines, pump etc. and all seem fine. Now, the car turns over but doesn't fire up! I had to take off the ignition coil and refit on the new dynamo so wonder if that could be the issue. There is a lead with a spade connector on it that it just flapping about and not attached to anything, so this looks wrong to me.

Any more ideas?? :o
simmitc
Moderator
Moderator
Posts: 4718
Joined: Thu Apr 15, 2004 9:43 am
Location: Essex
MMOC Member: Yes

Re: Battery running down...

Post by simmitc »

What colour is the wire?

You should have a white wire going to the -ve terminal on the coil and a white with black tracer to the other +ve terminal. The other end of the white/black wire should go to the terminal on the side of the distributor body. (based on the +ve earth).
TimM
Minor Friendly
Posts: 43
Joined: Fri May 21, 2010 7:14 pm
MMOC Member: No

Re: Battery running down...

Post by TimM »

Aah! I see that now... it worked! Thank you again :D
User avatar
geoberni
Minor Legend
Posts: 3561
Joined: Fri Aug 04, 2017 11:19 am
Location: North Leicestershire
MMOC Member: Yes

Re: Battery running down...

Post by geoberni »

So hopefully this has sorted out the battery charging issue.
Perhaps look at servicing the old dynamo sometime, if you didn't purchase an 'exchange' item.
Basil the 1955 series II

Image
TimM
Minor Friendly
Posts: 43
Joined: Fri May 21, 2010 7:14 pm
MMOC Member: No

Re: Battery running down...

Post by TimM »

Indeed. I am also going to check the voltage regulator too. Thank you :)
Post Reply