Using brushless motor as a dynamo generator?

[Smoker]

Is it possible to charge let's say a 12V battery or use a 12v capacitor and directly connect an invertor for 120vac?

 

[knightmb]

Is it possible to charge let's say a 12V battery or use a 12v capacitor and directly connect an invertor for 120vac?

Technically, sure.

My electric lawnmower uses a big 12 volt battery with a 1500 inverter to power it at 120VAC. So substitute the battery with a generator (or hub motor) and the same concept should work, but I don't know if a brushless motor that powers our e-bikes makes the best generator or not. When making 120 VAC, it takes some serious amps at 12 volts, probably more than the brushless motor will be able to generate safely.

 

[fechter]

As knightmb pointed out, you'd have to use a hubmotor with enough amp rating to run the inverter. If you're using a brushless motor, you'd also need a a 3 phase rectifier with the same rating.

The output voltage of the generator (alternator in this case) varies with rpm, so you'd need to keep the rpm fairly constant.

This is basically how the newer Yamaha and Honda generators work. Brushless alternator to dc, then a dc to ac inverter. This provides a very stable output.

 

[Smoker]

How about a brushed ebike hub motor? could I connect directly to a 12v battery and charge it? how would I keep it from spinning with 12v hooked up?


Electric lawn mower sounds cool. I have some 1/2hp 120vac motors lying around. Would these be good canidates for an electric push lawnmower? How did you get the blade on the output shaft?

Thanks

 

[billvon]

>How about a brushed ebike hub motor? could I connect directly to a 12v battery and charge it?

Yes.

>how would I keep it from spinning with 12v hooked up?

You wouldn't. If it spins slower than base speed it takes power. If it spins faster than base speed it becomes a generator. Arrange gearing so you can spin it faster than base speed.

>I have some 1/2hp 120vac motors lying around. Would these be good
>canidates for an electric push lawnmower? How did you get the blade on
>the output shaft?

Electric lawnmowers are pretty cheap! You can get one for around $100 on ebay. I would think you'd have to do a bit of (easy) machining, drilling and tapping to get an adapter for the blade - but 1/2 hp sounds a bit low for a mower.

 

[knightmb]

Electric lawn mower sounds cool. I have some 1/2hp 120vac motors lying around. Would these be good canidates for an electric push lawnmower? How did you get the blade on the output shaft?
Thanks

It might work, but it's cheaper to buy the corded electric mower and put a portable power source on it. Mine is the 12 amp model (1440 watts), it has a 12 volt AGM 33AH battery with the 12 volt to 120 volt AC inverter in a basket.

It can cut grass for an hour before the inverter shutdowns (goes off at 10.5 volts, one day I'm going to hack that to 10 volts so that it runs longer). I had a 6.5 HP mower before, self propelled and everything. It was a heavy beast, but cut ok. The electric mower though, even with that heavy SLA is still lighter by far compared to the gas mower. I sold the gas mower and made back all the money I spent putting the electric mower together and then some left over. So far, the electric mower has gone through this year with ease. Cheap electric power, no stall in high grass, quiet enough to cut grass and carry the phone around with me. It's about as loud as a dust buster. Always turns heads with the neighbors, it's light enough for me to push around with one hand up and down hills

The good thing, it has two extra outlets, I plug my electric weed eater in to it and weed eat the yard on purely electric also. Since it's on wheels, I need only run it to the front yard or back yard where I do this. I have plenty of long 100 foot outdoor power cables for the weed eater, so it's easy.

But... if I had some of those NiMH, I could put together a 33AH pack easily, so it would be even lighter, would probably run a little longer as well. Charging would be fun though.

 

[xyster]

>How about a brushed ebike hub motor? could I connect directly to a 12v battery and charge it?

Yes.

>how would I keep it from spinning with 12v hooked up?

You wouldn't. If it spins slower than base speed it takes power. If it spins faster than base speed it becomes a generator. Arrange gearing so you can spin it faster than base speed.

How about using a diode so the battery can be recharged by the motor, but not spin the motor?

 

[fechter]

>how would I keep it from spinning with 12v hooked up?



How about using a diode so the battery can be recharged by the motor, but not spin the motor?

Right. That's what I did on my hydroelectric generator. I used a brushed motor and a single Schottkey diode to prevent discharging through the motor. That works fine.