Using a DC Motor dynamo (generator) to power bs1

Blake

Does anyone have any experience powering a Basic Stamp 1 (or 2) from a dynamo. I am spinning a DC motor and my meter reads a voltage of about 20 volts. I send this through a 12 volt voltage regulator and onto a BS1 and circuit. Any advice on the matter or know anywhere specific to look for information?


Thanks,
Blake

Bruce Bates

Blake -

If this were a real world application, such as having a bicycle tire driving the dynamo, here is what I'd do. I'd use rechargable NiCad batteries to power the PBASIC Stamp. Then I'd use the dynamo to re-charge the batteries. This way, if you're standing still at a stop light, the micro-controller board will still be powered. The battery depletion from that wait will soon be replenished as you begin moving again, when the dynamo recharges the batteries.

Just be careful to put some sort of limiting system on the charging circuit so the batteries don't become overcharged. Another benefit to a system like this is that the PBASIC Stamp will never see the inconsistant voltage which varies as much as the output of the dynamo will. The voltage output of the dynamo will often vary with speed.

The last benefit of this system is that the amperage capacity of the batteries, and not the amperage capacity of the dynamo, is the limiting ampacity of the entire system. Thus, a small dynamo could power a system which provides more short term amperage than the dynamo is instaneously able to produce.

Regards,

Bruce Bates

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Veni, Vidi, Velcro! - I came, I saw, I stuck around!

Blake

I agree with you about using batteries. I did this with a solar powered basic stamp project. However, in this real world application, I want function to cease on the basic stamp when the dynamo stops turning. No work = no treat. One main question I have is do I need to necessarily "condition" the dynamo output other than using a standard voltage regulator. I have been thus far unable to find an answer to this on google.

Thanks,
Blake

Mike Green

No specific experience, but you have a small generator. The output of the dynamo will be very noisy and the voltage will vary widely depending on its speed. The voltage regulator will help, but needs a large filter capacitor on its input. I suggest something like 470uF or 1000uF with a voltage rating of 35V. Also use a smaller capacitor between 0.1uF - 0.47uF rated at 50V across the larger one.

If you use a diode in series between the dynamo and the input filter capacitor, it will prevent the capacitor from discharging through the dynamo when it slows down. This will allow the capacitor to power your BS1 for a while after the dynamo slows down.

Bruce Bates

Blake -

In addition to Mike's fine advice, here's what actually going to happen, so we'll let you be the judge. The PBASIC Stamp will go into RESET mode as soon as the voltage drops below the "brown-out" point. This is NOT when the dynamo stops producing power, but when the voltage drops below something like 4.5 VDC (check this voltage for accuracy).

Once in RESET mode, it will remain in RESET mode unless or until the voltage is increased to a proper operational voltage, or when the voltage drops dead altogether. In either case, of being in RESET, or the voltage completely dying, the Stamp will no longer function at that point. When the Stamp begins operation again, it will start at the beginning of the program once again.

Regards,

Bruce Bates

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Veni, Vidi, Velcro! - I came, I saw, I stuck around!

Blake

Is this what you mean? I am unsure about the placement of the second capacitor.


Thanks,
Blake

Mike Green

That's it!

Note that 0.47uF capacitors usually are not polarized. You should also have a capacitor across the output of the regulator. Check the datasheet for the device for the recommended value. The diode should be a 50V unit at least.

Blake

cool, i happened to have a 50v diode and a 50v 1000uF cap in stock and hooked it up, works pretty good. I'll get the other caps tomorrow.