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Dynamo and starter - PB

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Tim Sharp

United Kingdom
305 Posts

Posted - 04/01/2017 : 09:53:35

Chris and JA

Thanks for those thoughts. The idea of just getting a 6v (which seems more available) and leaving it running without load had crossed my mind yesterday. When I used to race F1 stock-cars we never fitted an alternator as it only caused a load and did nothing to contribute to the battery over such short races. I have been coming to the idea of fitting a dynamo but not wiring it up and ensuring that it has good bearings and spins with as little friction as possible. I was umming over gutting the windings completely and leaving a bare shaft but can see where JA is coming from over the damping effect. Possibly I can remove the brushes and any other drag inducing items but keep the windings in place. I know I will not get any weight saving but if I want to save the few pounds I can loose it from me instead!

It would be interesting to work out the battery usage over say a 20 min race to see the effect on a battery not receiving any charge from a dynamo. I always carry a spare fully charged battery in the tow car anyway so as long as I can do a couple of starts and 20 min of running with no charging I see no problem.

Great ideas guys, thanks again.

Regards

Tim Sharp
PB0685 - Nuneaton

Ian Bowers

United Kingdom
948 Posts

Posted - 04/01/2017 : 10:12:01

This may help decide whether you battery can cope with a couple of starts and running for an hour or so:

"A standard small car battery is about 45 amp/hours. That means that it will supply 2.5 amps for 20 hours. A battery should not be discharged at a higher current draw, or asked to deliver more amps than its amp/hour rating divided by 10 in order to get maximum capacity out of it."

When running with a duff dynamo my ammeter was showing around 4amp drain, so there should be plenty of go in the battery to meet your needs and still not wreck the battery.

Ian Bowers
OD 6791
J3 3772

Westbury

United Kingdom
2060 Posts

Posted - 04/01/2017 : 10:51:52

A magneto would help also!

Chris

Oz34

United Kingdom
2583 Posts

Posted - 04/01/2017 : 11:53:21

Plus starting with the handle. You could then remove the not inconsiderable weight of the starter! Plus of course the even greater weight of the battery if you use a mag.
Dave

Edited by - Oz34 on 04/01/2017 11:54:27

Bruce Sutherland

United Kingdom
1581 Posts

Posted - 04/01/2017 : 15:40:51

Tim,
Another alternative to consider - a VW Beetle early air-cooled 12V Bosch dynamo converted as described by Bob Lockley - ref: http://www.triple-mregister.org/uploads/retro/MMM%20Gereator%20Rebuild.pdf .

You'll need the the input and output bevel gears to go with the above, but you get substantially more amps than the original Rotax/Lucas units.

I have a full set of engineering drawings developed from Bob Lockley's sketches, - can make copies available.

PS. make sure you get the older shorter version of the Bosch dynamo - 30A not 38A.

Bruce. (PB0564)

NeilS

United Kingdom
199 Posts

Posted - 04/01/2017 : 16:28:34

For a sprint and hillclimb car a dynamo is not necessary. Ignition uses 4A (on 12V) . I spent most of my life running Sports prototype racing cars and we did anything up to a 2 hour race with no dynamo or alternator right up until electronic fuel injection arrived! we did use a jump battery in the pits to start though. Even so for the average of about 4 minutes track time per day on a hilclimb there is no issue.

Plenty of MMM cars ran with just a plain shaft inside the dynamo case to reduce inertia.

However I believe that Peter at Classic Dynamo and Regulator Conversions has just unearthed a stash of DDS and Rotax dynamos for MMM cars

Neil