how to limit a DC generator ?

I've got a plan to exchange the AC windings in a small 600w petrol generator for a 12 v DC dynamo, as used to be used in cars, before alternators , so i will have a battery charger for my boat.

However i want to have a way to control the maximum amp out put of the generator, so that i can tune it to the engine power, i expect the full output will be too much load for the engine.The engine is a fixed speed @ 3000 rpm.

Any sugestions ?

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"They" stopped using "generators" on cars and switched over the "alternators" for a good reason.

However, you still might be able to find a "voltage" regulator at any place that handles automobile parts.

When the voltage regular fails on a dynamo system, the generator overheats. The "hot part" in a dynamo is inside and can't be cooled. A dynamo regulator usually has a current sensing coil. An alternator regular just has the voltage control. In either case they control the output by controlling the current if the "field" winding. The relay (in a relay system) often "vibrates" on and off. It works.

If your problem is that the dynamo draws more shaft power than your engine can comfortable supply, the solution is to change the pulley size and slow down the dynamo.

Reply to
John Gilmer

assuming the existing generator is functioning and outputs sufficient power, is an appropriate voltage and frequency... why not just get a battery charger and run it? let say you decide on a peak load of 300W divide by

13.8 volts to get 21 amps. they would let you run a couple of typical 10A chargers and you would get the benefit of whatever regulation and 'smart' features that are built in to the charger.
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Farmers sometimes would use a rheostat and just turn a knob to adjust the voltage. They used these on irrigation power units with alternators. These engines would run hundreds of hours in the summer and would ruin batteries due to overcharging. Some alternators must've had defective voltage regulators.


Reply to
Dean Hoffman

You may well find that changing the windings for DC 12volts and changing the slipring commutator for a segmented arrangement for DC will be too much. or even if you use an AC arrangement and diodes the rewinding will be quite a task.

Much easier as someone else suggested, just get an inverter and a mains battery charger.

A lot of small petrol generators already come with a DC output (not yours I guess).

Reply to
John G

Depends upon the dynamo

Lucas type C40 is very common (but you can check the body - its stamped there)

The closed bracket type was normally used for agri/marine and had a regulator called an RB108

The type of regulator for 12v car systems for this type of dynamo (with open bracket - ventilation) is called an RB340

(All Lucas part numbers- although there were many spurious manufacturers)

3000 rpm should be fine for this dynamo - if there is no loading apart from charging your batteries - although it might be an idea to assess exactly what the loading will deep are the batteries cycled -

The closed type is regulated at a lower setpoint to prevent oveheating

If this isnt the case I'm sure I can find a solution given the dynamo type

There are a few different configuarions


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battery chargers have built in resistance to prevent explosions when the cables or battery become shorted, there are not any other significant losses in a charger.

the current will depend on the battery parameters and state of charge.

any charging method that does not incorporate current limiting will be quite dangerous.

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Most of these charges will have high leakage step down transformers rather than resistive loading. The inductance is before the rectifiers.


-- Fermez le Bush--about two years to go.

Reply to
Salmon Egg

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