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MG Midget and Sprite Technical - dynamo

I have an AH Sprite Frogeye, 1275 cc engine and the dynamo of the previous engine. I find the capacity of the dynamo too small and the battery runs empty after a long drive in the night if I also have additional equipment like navigation lights, compass etc switched on. I want to replace the dynamo by a more modern alternator. Anything I have to watch? Especially how to deal with the rev counter? It is now mechanically driven by the dynamo. How to convert to an electronic rev counter? Where can I get a rev counter with the same look as the old one?
Negative is already to earth in my car.
J.W. Vlaanderen

It sounds as though the dynamo isn't actually charging properly, rather than the 'capacity of the dynamo too small'.

It could be a fault with the regulator, or it may need adjusting.

Have you checked the charging voltage?
Dave O'Neill2

I changed a MkIV to alternator recently and it is pretty straight forward. THere are several links to sorting the wiring as the control box is done away with. You should also run some additional wires in parallel with the existing ones as they have the potential to carry more current than is usual with a dynamo.
Can't help with the mechanical rev counter as this wasn't an issue on my car. There must be lots of advice on that one around..... someone will post very soon Im sure.
GraemeW (Kent!)

Heres a diagram to convert to an alternator:

http://mgaguru.com/mgtech/electric/ac101.htm

Tach conversions are done here in the states.

http://nisonger.com/

There must be someone closer to you J.W.

Hope this helps! :-)
Steven Devine

Dave, I do some rally driving and need therfor more light. Also additional instruments are necessary. That's why I run short of power.

Steven, Thank you for your information. I'll check if there is some one closer to do the modification. Anyhow, if there isn't I have an adress to go to.
J.W. Vlaanderen

I do have a text in Dutch how to convert. You can see it on the site of the AHOCN (austin healey ownersclub Nederland) if cant get acces: give me your mail adress

flipatbruhlpuntNederland

Flip Brühl

If, when converting to alternator, you retain the regulator consider placing wires that join the terminals beneath the unit. This then leaves a useful storage area in the cap of the regulator for instance I keep a spare set of spark plugs in my regulator. Equally it could be a receptical for any small items.
Alan
www.masckent.org
Alan Anstead

Yup. You could keep a rubber in there. You never know when you're gonna get lucky. ;).
Lawrence Slater

Lawrence,
Ha ha ha.... Yes a very convenient storage compartment. After she pops your hood you will have to get out and pop your hood. Redundant systems?
Steven Devine

For the Rev Counter conversion try JDO Instruments.
John Ostick in Yorkshire
mrm goslin

Michael, I contacted JDO. For 130 GBP they convert my mech rev counter into an electronic one.
J.W. Vlaanderen

Im glad Mike goslin piped in. Looks like he was a good source for a closer place... Goodluck with your project J.W.! :-)
Steven Devine

Adrie Rijstenbrij Badhoevedorp modified the rev counter, it is his profession.
Flip Brühl

I think the early Lucas C40 is good for 22 amps so this should equate to a load of approx 250 watts.
Check the total wattage of your lights etc and if its more than this, then you're right, you need an alternator.
If not, maybe a good overhaul with new brushes would help?
M J Chapman

The frogeye uses a C39 dynamo which has a lower output, about 19amps, I believe
Bob Beaumont

This thread was discussed between 24/11/2013 and 28/11/2013

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