Micro-generators to charge batteries

[fluffc]

Hi all,

Just pondering.

Since running a conventional generator (even a 500W one) to charge batteries 'wastes' lots of fuel, has anyone tried to make a micro-generator system specfically for charging batteries.

I am thinking here of a very small engine - eg as used in model aeroplanes, and a small alternator.

Anyone come across these, or got any thoughts?

Or am I barking up the wrong tree, and in fact using a 500W generator to charge a battery is quite energy-efficient?

??

 

[simonfraser]

was thinking along the same lines, small wind generator perhaps too

i only need 7A per weekend, solar works but takes up a lot of space

 

[JREdginton]

Mmm, interesting thought. Can't say I've come across one but!!! I did stumble across a model diesel/electric locomotive model some time ago that used a small IC engine to run an alternator to drive the locos electric motor. Will try and dig up a link for you.

 

[fluffc]

Hi John,

That sounds quite interesting - let us know when you have the link /forums/images/graemlins/smile.gif

 

[JREdginton]

Here ya go ... http://pilgrimlocomotiveworks.co.uk/

Not the link I found first time round but may be of interest?

 

[William_H]

I would suggest that the most efficient set up would be a small petrol motor like a lawn mower engine coupled to a reasonably large automotive alternator. Instead of having a regulator just connect the field directly to tyhe 12 volt system. Or if you want to be carefull fit a variable resistor or even design a constant current regulator.
The alternator will try to produce as many volts hence as much current into the batteries as the alternaor can produce as limited by its internal resistance or more likely limited by the power of the engine.
You may need to tweek the alternator speed to match the engine max power speed and the field current to get the most current into the batteries.
This whole device should give a lot of current and so require a fairly short running time. You will need an amp meter to fine tune to amx efficiency.

Now back to the 250 volt generator. The way to sqeeze the full power out of the generator is to run the 240 volts into a large transformer to give about 18 volts AC. Ideally you will have a transformer where you can adjust the taps to give a variety of fine adjustment to the output volts. This connects to a bridge rectifier of high current rating ie 40 amp. Use an ampmeter again to adjust for max current into the batteries.
You will find if the secondary voltage is too low then there will not be enough voltage to push large currents into the battery. If the secondary is too high then the high current will be limited by the transformer resistance and again output current will not be optimum. All this while ensuring that the generator can cope with the load. At least you will be sure all your petrol is turning into the max possible amps into battery.
Or buy a big crude style battery charger to run off the generator.
Avoid the regulated automatic types. You just want continuous grunt.
As for smaller demands I find the sollar panel the best. I lash it to the boom cover when I am away from the boat and unplug and remove before sailing. olewill

 

[sarabande]

I have got a couple of micro generators at home somewhere. They are 12v and were part of the Civil Defence kit, used for local radio stations.

I'll get hold of one from the attic at the weekend and put up a photo next week.

 

[AngusMcDoon]

I would have thought an even smaller engine than that for battery charging. Chainsaw/strimmer engines seem to be the smallest I've seen, apart from model engines of course.

Model engines are smaller, but often require exotic fuels to run on.