Dynamo testing

[welshrat]

My battery is not charging and I have an ignition light that remains on, its probably gonna be the dynamo but was wondering if anyone new how I can confirm this without taking it off. I have a pretty good multi meter but never really learned how to use it, auto electrics have always confused me.

[Trickydicky]

The quickest way to test it is to measure the battery voltage while revving the engine slightly, it should measure 13.5v to 14.5v. But as the ignition light is on it would seem the Dynamo is not charging. It could simply be the brushes that have worn down and they are easy and cheap to replace.
Another way to test the Dynamo is to remove the cables from it and with your meter set on the volts dc range connect the red probe to the terminal which had the heaviest cable connected and the black probe to earth, start the engine and Rev to 1500rpm and if the Dynamo is working you should read 1.5v to 3v.

[bmcecosse]

Been covered many times..... Remove wires and fan belt. Join the two terminals with a cable and connect to the. Non earth battery term. It should run as a motor.

[kennatt]

turn meter to 20V put positive to positive earth to earth on battery,start and see what shows,if ok look for 13.8/14 volts.

[Trickydicky]

If you need to replace the brushes, here is a link to buy a repair kit for the C40 dynamo. http://www.jcrsupplies.co.uk/products/D ... PARTS.html
It contains all you need to overhaul a dynamo.

[welshrat]

Thank you for the information, quick fix in the end just one of the brushes stuck in its gage. I have posted my concerns on here in the past about my battery boiling after going out for a run, after sorting the dynamo my meter is reading 18+ volts when revving the engine. Is this correct could it be the cause of battery hiss?

[panky]

What's it showing at the battery?

[bmcecosse]

That's WAY too high and may explode the battery and will certainly blow your bulbs..... As above - is it connected to the battery ???

[welshrat]

Conected to battery and this is where readings taken from. What controls the amount of volts being fed back to the battery? Also eplains why all the bulbs at rear blew recently!

[meh]

I hope you carry a fire extinguisher

[welshrat]

I do as it happens, so any ideas on what the problem is, pretty sure its a standard dynamo however may have changed the pully in the distant past, also needed to swap the control box some time ago. Just checked when I flagged up my concerns about the battery, it was June 2011, to be fair BMC suggested it might be volts too high.

[bmcecosse]

The adjustment is on the smaller bobbin - read up how to adjust in section N 9 of the workshop manual ! Aim for 13.8 volts with engine revving.

[welshrat]

Will do some studying. Could it be battery related as recently charged it up over-night and battery was again bubbling and hissing the following morning?

[bmcecosse]

No - the dynamo is overcharging! The battery may of course now be ruined by the crazy high voltage - and consequent overcharging.....

[welshrat]

Sorry for being rather slow on this one but motor electrics and I have always had a difficult relationship, my mother also said that I was special!
So swapped the control box today and readings on my muti meter are the same. Switching to 20 volts, attaching red lead to positive on battery, black lead to negative on battery, engine off reading about 12, engine ticking over is 13-4, revving takes the reading steadily up to 18-19. Could it be amps that I am reading, amp meter inside the car go up to 30 (I think) and appear to match reading on muti meter.
Is it possible that my dynamo is the faulty item and providing too many volts?

[bmcecosse]

Can't see that - unless it's a 24 volt dynamo ???? Is that possible ??? Can you try another battery - if the cells are shorted - maybe allowing the volts to rise crazily....

[welshrat]

will try a different battery as you suggest and see if it makes any difference.

[bmcecosse]

Has that dynamo 'always' been on the car ?

[welshrat]

No but it is a Minor or mini dynamo, have had several kicking about since the Romans were in town (Caerleon people will understand this).

[bmcecosse]

Try another - I think it must be a 24 volt dynamo....., or in some way it has failed internally to produce very high volts.. I really can't see it being the battery.