Dynamo question

[David Stepney]

My RP is fitted with the later 35M instrument but still charging through an early (CF1?) cutout with no internal resistors. Half charge is achieved with a separate  2 ohm power resistor under the dash.

Om winter charge, the dynamo is just about getting into its stride at about 30mph (about 2000 rpm) and gets to full output at about 35. At this point my ammeter is reading about 10 amps, but, as Rekkers has pointed out above, it shows a slight discharge with the headlamps on. I suspect that my ammeter is a bit vague and, whilst it tells me whether the dynamo is charging or not, I wouldn't place too much reliance on the figures it shows.

I think that a more accurate way of determining safe charging rate is to measure the voltage at the battery. My dynamo gives 6.7 volts at 'max chat' which is about what I would expect.

[Bob Culver]

Hi Howard
Are you operating as 12v? The cut in voltage can be measured; covered recently.

Hi Others
The original headlamps were only 18w each and dyn just exceeded balance. Near all now have larger bulbs so easy to overtax dyn..
Sealed Ca batteries are not supposed to exceed 7.3 volts so unregulated charging is now more of a  of a challenge than ever. Unfortunately available cheap indicators are for 12v. Analogue meters can be set up with a zener diode to amplify the scale but I found driving a Seven could never take eyse off the road long enough to read! Many run a low charge and rely on a smart home charger, if you can find a 6v one.... The dyn charge voltage rises as the battery becomes charged, rapidly after7v.

[Howard Wright]

Hi Bob

No 6 volt!

Cheers

Howard

[Ivor Hawkins]

Hi Howard,

I assume you mean you a running on six volts, I’ve ditched the 12 volts and running on six again and the car (and myself) are much happier!

I’m not knocking you 12 volt chaps by the way, it’s just my system is much happier with the original set up.

[Ray White]

David. For what it's worth, my 1930 Swallow saloon is just like that.  I much prefer the later dynamo and I had the CF1 rebuilt. I also have a half charge resistor hidden from view.  No complaints from me.

[Terry McGrath]

Had my dyno rebuilt 4 years ago but thought that 1 or 2 amp charge insufficient so moved the 3rd brush to produce 10 amps. Too lazy to bother reducing this to 6 or 7 amps, it threw its solder yesterday after a long fast run and stopped charging. Expensive mistake and lesson learnt.

[Denis Sweeney]

Terry, that’s an interesting comment, some weeks back I posted a thread on the fact that a wire from a brush to the D terminal had mysteriously “broken” and the dynamo naturally stopped charging, this, with help from friends on here, was repaired and all was good again.
But was the fact I had been running at 10 to 12 amps the cause of the failed wire??
Anyway now down to about 6 amps.