Is 15.8 volts too high?

[Huntsman]

Morris charging sat 15.8 volts, that too high?

New control box and new dynamo. I think there's an adjustment in the control box, need to check the manual.

[Allan L]

My handy reference (Newnes Motor Repair) says that the open-circuit voltage for a CVC regulator should be 14.9-15.5 v .
That is at 20ºC and for each 10º above 20º subtract 0.2v and for each 10º below add 0.2º
Generator should be run at 3000 r.p.m.
I'd say that unless the temperature was quite high 15.8v is o.k.

Edited by Allan L on Saturday 1st April 14:24

[Sparky137]

Huntsman said:

Morris charging sat 15.8 volts, that too high?

New control box and new dynamo. I think there's an adjustment in the control box, need to check the manual.

Modern car batteries will boil up at that voltage. Their maximum long term charge voltage is 13.8 Volts with a short term charge of 14.4V being alright.

http://www.operatingtech.com/lib/pdf/A%20Guide%20t...

[HustleRussell]

Too many volts

[Allan L]

The OP didn't say if it was an open circuit voltage reading, but as that is the only voltage you can measure when setting up Lucas control boxes, I think we can take it as that.
A normal lead-acid battery has an open-circuit voltage around 2.2v per cell.
When connected to a battery the measurable dynamo output voltage is lower and depends, in part, on the charge state of said battery.

The file in the link is irrelevant as it does not deal with vehicle electrical systems but with uninstalled battery charging

[Huntsman]

Allan L said:

The OP didn't say if it was an open circuit voltage reading, but as that is the only voltage you can measure when setting up Lucas control boxes, I think we can take it as that.
A normal lead-acid battery has an open-circuit voltage around 2.2v per cell.
When connected to a battery the measurable dynamo output voltage is lower and depends, in part, on the charge state of said battery.

The file in the link is irrelevant as it does not deal with vehicle electrical systems but with uninstalled battery charging

I had a digital volt meter across the battery posts while the car is running, revved up to maybe 1500 or 2000rpm and the meter read 15.8.

[Allan L]

Huntsman said:

I had a digital volt meter across the battery posts while the car is running, revved up to maybe 1500 or 2000rpm and the meter read 15.8.

I'm no electrical engineer but I would expect that the state (and type) of the battery affects the voltage you measure where you measured it.
Measuring Open circuit means your reading is not influenced by the battery, so my suggestion is that you measure the Open Circuit voltage and compare that with what I quoted!

[Huntsman]

Just to close out.

When I went to investigate, I double cleaned the points in the regulator box, cleaned a few wires, and the bd thing wasn't charging at all!

I tested the dynamo by linking the terminals and providing power, it motored round, I read that if a dynamo motors then its fine. I took this to mean the regulator was faulty.

I did the only thing a competent old car mechanic can do in such circumstances....bought an alternator conversion kit...