Use of Generators with Speed Controllers

Sometimes we are asked about whether a battery can be kept charged up by a small motor generator set while the vehicle is running. Indeed, we have also been asked whether a controller can be operated from a generator without any battery.

This page discusses these points.

Contents, this page

• Generator charging in use
• Overvoltage levels
• Generator with no battery
• Advice on batteries and generators
• Other relevant pages

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Generator charging in use

Generally this is no problem to the controller, however it may not be ideal for the batteries.

A generator will normally be set to keep the batteries fully charged. So the controller, when it goes into regenerative braking, has to dump the braking energy into already fully charged batteries! It can do this – but only by overcharging the batteries, for short periods this should not be a problem, just be aware of the issue.

Overvoltage levels

Also be aware of the overvoltage level of the controller. If the overcharged battery voltage hits this, regenerative braking will cease.

A better solution

Instead of the generator keeping the batteries fully charged, it could be adjusted to keep them perhaps 80% charged, so there is adequate spare capacity for regenerative braking.

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Generator with no battery

Although not ideal, we have tested this arrangement fitted to the Scamp model locos, although the waveforms are pretty messy, it actually works quite smoothly.