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Dynamator output

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RadfordJim
Posts: 97
Joined: Tue Feb 16, 2016 10:19 am
Location: Coventry

Dynamator output

Post by RadfordJim »

I've just replaced the battery on my SP and checked the voltage across the terminals with an accurate multifunction tester, which indicated 12.8V dc.
With the engine running I checked again and my tester shows 12.9V ac with a frequency of 34.5 Hz at 650 rpm tickover.
When I increase engine speed the voltage increases slightly but Hz goes up almost in proportion. I would have thought the Dynamator should give a pure DC output like a standard alternator, as confirmed on my daily driver.
Any thoughts would welcome.
Jim in Coventry - Home of the Daimler

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Vortex O'Plinth
Posts: 928
Joined: Fri Feb 12, 2016 8:15 pm
Location: Gloucestershire

Re: Dynamator output

Post by Vortex O'Plinth »

Perhaps you have a diode down?
Nick

"Don't bother with the Air & Space Museum - there's nothing to see.......".

Ian Slade
Posts: 531
Joined: Sat Feb 13, 2016 9:54 am
Location: Scotland

Re: Dynamator output

Post by Ian Slade »

Nick, there ain't any diodes in a dynamo :lol: :shock:
Owner since the 70's, Genghis is slightly to my left.

bobtills
Posts: 20
Joined: Wed Sep 25, 2019 6:05 pm
Location: North Wales

Re: Dynamator output

Post by bobtills »

You've got your meter set to AC? The squiggly line, instead of the straight line?

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Vortex O'Plinth
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Joined: Fri Feb 12, 2016 8:15 pm
Location: Gloucestershire

Re: Dynamator output

Post by Vortex O'Plinth »

Ian Slade wrote:
Tue May 19, 2020 3:31 pm
Nick, there ain't any diodes in a dynamo :lol: :shock:
That's true Ian, but Jim is running a Dynamator i.e. an alternator disguised as a dynamo, and alternators do have diodes.
Nick

"Don't bother with the Air & Space Museum - there's nothing to see.......".

Ian Slade
Posts: 531
Joined: Sat Feb 13, 2016 9:54 am
Location: Scotland

Re: Dynamator output

Post by Ian Slade »

Whoops sorry Nick, read it as a dynamo :lol:
If that is the reading from a multi meter then that is the RMS value the AC component is higher, about 18v and could well cook the battery if left too long or even melt wiring insulation
Owner since the 70's, Genghis is slightly to my left.

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RadfordJim
Posts: 97
Joined: Tue Feb 16, 2016 10:19 am
Location: Coventry

Re: Dynamator output

Post by RadfordJim »

Many thanks for the replies gentlemen, a faulty diode does seem most likely, thank you Nick. I posted in case anyone has experienced similar or measured the output of a Dynamator.
I suspect it's been like it for a long time as it's probably the reason for any LED that I fit flickering dimly when switched off. I couldn't say as I've never checked the voltage before. The output can't be a pure sine wave otherwise the battery wouldn't charge at all!

I'm thinking a 50A bridge rectifier (£3 fleabay) across the output might work. My local alternator repairer won't even look at it. He said he can't get spares so suggested I get a new one!

For info, my multifunction meter just has one V setting and differentiates between ac and dc automatically, ranging from 10 to 600 volts. It shows 2 parallel lines for dc and the squigly sine wave for ac, along with the frequency. It's cleverer than me!
Jim in Coventry - Home of the Daimler

classiclife
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Joined: Wed Sep 05, 2018 9:55 am
Location: Ridgewood - East Sussex
Contact:

Re: Dynamator output

Post by classiclife »

Hello Jim,

Paul Baker who owns Smart Power may well be worth contacting. I had an original Lucas 11AC built from scratch and he did a superb job. He has extensive knowledge along with a second to none spares access.

He is based in Barby near Rugby, CV23.

Regards.

Richard.

https://www.smartpowerclassicandvintage.co.uk/
1968 Daimler V8-250 Saloon
DLOC East Sussex Area Representative.

Southern Classics Society Events Co-ordinator.
www.southernclassics.org.uk

Brian-H
Posts: 87
Joined: Fri Aug 09, 2019 6:04 pm
Location: Loughborough

Re: Dynamator output

Post by Brian-H »

It depends on the exact waveform as to what the meter is reading when it displays the "~"

i.e. the waveform could be anything, not just sine, nor offset sine (on top of DC).

But ether way, as said, it won't be doing a battery any good if it's able to push several amps at its peak voltage (whatever that is)

If you have access to an oscilloscope and capture (or photograph) the waveform, then it might be possible to come up with a solution "external" to the "generator".

Ozzsp250
Posts: 217
Joined: Tue Feb 16, 2016 12:35 am
Location: Arizona, USA

Re: Dynamator output

Post by Ozzsp250 »

I changed to a Dynamator and had one fail the diode assembly and there were no spares diode assemblies available. I purchased a replacement and it constantly supplies (outputs) 14.2 - 14.3 volts from just above idle. The first dynamator failure also destroyed my electronic ignition module. I think quality may be an issue as they appear a cheaply made product.

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