Dynamo charging rate

[jagnut66]

Hi,
I just tested a friends car with my digital meter, as he was concerned that his dynamo wasn't charging properly, I then looked up what it should be reading to confirm my thoughts, this is what I found, via an online Google search:

Anything between 13.5 volts to 14.5 volts tells you the alternator/dynamo is charging around the correct parameters. Anything lower than 13.5 volts shows it is not putting out enough power to charge the battery efficiently and electronic items on the vehicle may behave erratically.3 Dec 2014

Before I suggest he forks out for a replacement, I just wanted to run this by you folks on here, as my alternator charged car charges at this and I wanted to be sure Google has it's facts right for the dynamo.
His battery shows 12.85 volts when the car is switched off but this seems to drop when the engine is running (lights etc. off).
He wants to stick with a dynamo for now and his car is mostly original, so a good working dynamo is what he's aiming for.
Many thanks,
Mike.

[svenedin]

I’m no expert on this at all but there are three basic things to check. Whether the dynamo is working properly, whether the control box is working (whether the dynamo is actually charging the battery) and the condition of the battery. The RB106 is often overlooked and is a bit cruel to the battery so batteries don’t last as long as they do on a modern car. Very simple checks: charging light on speedo. Normal for it to flicker on tickover but go out with a little bit of throttle. Turn on the headlights at idle and you can hear the extra dynamo load on the engine, again a little throttle and the headlights brighten. The (genuine) Lucas C40 is a very good dynamo if looked after. Trouble is people are not prepared to spend proper money on having them professionally overhauled and buy nasty pattern part copies and then say dynamos are rubbish. Well yes the cheap ones are indeed rubbish. I have two dynamos. Rebuilt one always in stock on my shelf.

[JOWETTJAVELIN]

Wants the commutator cleaning first and brushes checked before adjusting the reg. And a drop of oil in the end bearing.

[geoberni]

The Control box consists of 2 Coils, the Regulator on the Left, the Cut Out on the Right.
The Cut Out disconnects the battery from the system until the engine is spinning the dynamo fast enough, to stop the battery motoring the dynamo. That coil operates at about 12.7-13.3v.
The Regulator coil is set to control dynamo output at about 15-16 volts, which is a bit high by modern standards.
So there are those that advocate having it set a little lower, around 14-15 v.

Don't go blaming the Dynamo when it might be the RB106 that needs cleaning/adjusting.

[jagnut66]

Don't go blaming the Dynamo

I'm not blaming anything at present Berni, simply seeking information.
I watched a video on U-tube that goes over what you mentioned above and covers the two adjustment screws on top. So, with my meter as a guide, I am thinking of adjusting his charge output up and then seeing if it remains constant or drops off again. However I can't imagine that someone would turn the charge output down as low as it is, so maybe it will turn out to be the control box that needs changing. Time (and testing) will tell.
Best wishes,
Mike.

[geoberni]

Don't go blaming the Dynamo

I'm not blaming anything at present Berni, simply seeking information.
I watched a video on U-tube that goes over what you mentioned above and covers the two adjustment screws on top. So, with my meter as a guide, I am thinking of adjusting his charge output up and then seeing if it remains constant or drops off again. However I can't imagine that someone would turn the charge output down as low as it is, so maybe it will turn out to be the control box that needs changing. Time (and testing) will tell.
Best wishes,
Mike.

Mike
I wasn't saying you specifically were 'blaming the dynamo', I was indicating that is where many will head off to.
It may simply be the Regulator needs a good clean of the contact surfaces and resetting. If it's not been maintained, then 'pitting' of the contact surfaces over the years can lead to material transferring from one contact to the other, altering the gap.
I'd always look to restoring the old one if practicable before replacing..