Micro Generator - Measuring Amps

Drascomber

Drascomber

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The "Winter amusement kit" is slowly progressing.

I now have the generator side of things (permanent magnet motor) set up on the bench and producing 18V at what seems to be an acceptable but yet to be measured rpm.

The next issue is to find out if it produces the 5 Amps or so that I seek.

Presumably I first have to regulate it down to the 14.5 Volts or so needed for Battery charging - possibly with something like this Solar panel regulator and then connect it to a battery with the ammeter in series.

Is this the way?
Do I have to find a flat or dead battery in order to find out what the max output is?
 
That regulator should do it.

Just one other thing. If your project gets going you will have to work out some method of dumping the extra energy if the unit is generating more than you need. I suspect that the regulator is a linear device and will get very hot if the input starts to exceed its ratings.
 
Presumably your generator is producing DC, so you won't be needing a rectifier?

But yes, you'll need a regulator, and the one you mention looks like it will do the job. Maplin sell a similar product for £12.99, but it can only handle 5A.

What are you using to drive your generator? I'm thinking of building a wind powered generator because I reckon I can build for a lot less than the cost something like a Rutland.
 
Something like that will probably do. It does not say on what principle it works though. It wont regulate the output from a permanent magnet generator but it will regulate the feed going to the battery by virtue of being a shunt regulator or by some electronic jiggery-pokery such as "pulse width modulation".

A regulator for a wind turbine might be more appropriate.

You will need the reverse feed protection mentioned or the battery will simply drive your generator as a motor. A diode is all that is required for that.

Rather than try it out on a battery with unknown charging characteristics I would first try it on a variable resistive load. A number of 12 volt bulbs perhaps and monitor both volts and amps. Find out just what is is capable of. I'd do that before spashing out on a regulator.

Also look at the regulator(s) Maplin offer (maybe the same) and those for Rutland wind generators.
 
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I suspect that the regulator is a linear device and will get very hot if the input starts to exceed its ratings.

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But that's why it has a specified maximum current rating.

The simplest solution would be an 8A fuse. Perhaps an 8A trip would be more practical. The maximum current ratings of these regulators (I'd have thought) would be specified over a period of time; for example 8A for 10 seconds, because the limiting factor will be the capability of the device to dissipate heat. And if we're talking about a wind powered device, high current might be expected in bursts, rather than continuously. So it might need a more complex solution than a fuse or a trip. The other factor to consider would be the voltage capability of the device; too high a voltage and the semiconductor would just break down.
 
Info
The service power source will be a miniature 4 stroke internal combustion engine. The experimental power source is a mains electric motor. The motor being used as generator is DC so no rectifier needed.

There is a lot of stuff on the web about making your own wind generator - mainly for homes on hills. However, weight is an issue for a boat wind generator on a pole and getting similar performance to a Rutland will not be easy. Still it will be a lot more fun.
 
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I would first try it on a variable resistive load. A number of 12 volt bulbs perhaps and monitor both volts and amps.

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I guess if I put them in series the 18V won't blow them..
I wonder how many I have in stock . . . .
 
I would just shove the 18volts onto a battery on the bench. It won't stay at 18volts and may not drive anything into the battery. Better to try this before more expenditure.
What are you turning it with? and will the final power source have the same torque?
 
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A number of 12 volt bulbs perhaps

[/ QUOTE ] Perhaps a better idea would be to wind a resistance with some nichrome wire

18swg nichrome has a resistance of 0.92 ohms/metre. (see table in Kaye and Laby online for other sizes)

Maybe you could use the wire from an old electric fire element but you would have to be careful about it getting seriously hot.
 
As already stated connect it straight to a 12v battery via an ampmeter.
The current going into the battery will pull the output voltage down to that of the battery on charge. The internal resistance of the motor will cause the voltage to fall to a degree determined by the current which is determined by the battery voltage.

A better test would be to connect a 2.2 ohm resistor rated at 60 watts. This can be 6 x 12 ohm 10 watt resistors in parallel or any other combination to give 2.2 ohs with a total 60 watts dissipation capability. As already suggested 60 watts of 12v light globes will also do however lamp resistance varies according to temperature so at lower powers may confuse the results.

I think in practice you should try the battery first. This will give you a ball park idea of what the motor will produce. The output very much depending on motor speed and internal resistance.
You can not however do anything without a suitable amp meter.

Try a .1 ohm wire wound resistor which will give a volt drop when in a circuit of .1 volt per amp which can be measured on a Digital volt multimeter. Just remember that the .1 ohm will reduce the current because of the resistance.

It is certainly too early to go buy a regulator. My guess is that for a large battery a regulator will not be necessary because you will be unable to overcharge the battery. However decide when you get it all up and running. good luck olewill
 
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