13-08-2015, 01:31 PM
I was recently given a 3.6V rechargeable dremel.
This is hideously under-powered and the cells are past their best as well. I tried it connected to an old motor-bike battery and it then had plenty of torque, as well as being far too fast.
I've now made one of these PWM controllers for it but for all that it worked first try it is not behaving as expected and I'm wondering if this is because I used an IRF640 FET. My other deviation was to use a 100kΩ pot with a 100kΩ fixed resistor across it.
I hadn't got a powerful enough 12V transformer so used a 12V SMPSU which I thought was rated at 4A.
On testing I found the the speed varied but the torque was low on any setting.
Checking revealed that the SMPSU is actually rated at 2A so I tried it on the battery and found the effect was just the same.
I doubt that the pot will be the problem as the output voltage varies as expected; it seems as though the current is somehow being limited.
My question is: is the incorrect FET likely to be causing the problem or should I be looking elsewhere? It's far from urgent and I can get an IRL530N when I next order some bits from somewhere.
Cheers
Joe
This is hideously under-powered and the cells are past their best as well. I tried it connected to an old motor-bike battery and it then had plenty of torque, as well as being far too fast.
I've now made one of these PWM controllers for it but for all that it worked first try it is not behaving as expected and I'm wondering if this is because I used an IRF640 FET. My other deviation was to use a 100kΩ pot with a 100kΩ fixed resistor across it.
I hadn't got a powerful enough 12V transformer so used a 12V SMPSU which I thought was rated at 4A.
On testing I found the the speed varied but the torque was low on any setting.
Checking revealed that the SMPSU is actually rated at 2A so I tried it on the battery and found the effect was just the same.
I doubt that the pot will be the problem as the output voltage varies as expected; it seems as though the current is somehow being limited.
My question is: is the incorrect FET likely to be causing the problem or should I be looking elsewhere? It's far from urgent and I can get an IRL530N when I next order some bits from somewhere.
Cheers
Joe
