holy crap! whats the voltage rating on your fets? that waveform has some nasty voltage spikes! if you dont have input capacitors(source to v+) than thats why. if you do have the bank of electrolytic cap equalling <10mOhm and 50 ripple amps .. then you must decrease distance from: drain to diode; input caps to source; and input caps + to diode + . reducing these three lengths to <1/2" will greatly reduce needed gate R and will be able to run massive amps with cool fet.
Very cool. It's great to see someone doing it, not just talking about it. Looks like you're using N-channel FETs and switching to ground. It's also interesting to notice the little "bounce" in the waveform when the motor speed is trying to adjust. Are you using snubbers? I know that one of the possible problems is trying to switch too fast and having the FET slam on when you don't want it to. So many questions...What's your target current rating?
Some of you have asked for schematic, here is an layout of how it could be done
img189.imageshack.us/img189/6785/pwmstyring.png
NOTE: this is only a draft, that might need some tweaks for your circuit.
depending on the mosfet you use and the frequency this circuit is useful up to around 60-80Ah of short peaks (limited because of heat dissipation)..
There is a lot of ways to do this, and this is just an idea and it might be a good idea to add a mosfet driver after the opamp.
sponkii 11 months ago
@sponkii you have to add ht tp (remove) :// in fornt of the link for it to work
sponkii 11 months ago
@sponkii
ht (remove) tp://img189.imageshack.us/img189/6785/pwmstyring.png
this link should work
sponkii 11 months ago
Hi Sponkii,
It is a nice PWM... liked the video, ok can u plz give the circuit diagrams also....
thankx dude.
chaolo1 2 years ago
holy crap! whats the voltage rating on your fets? that waveform has some nasty voltage spikes! if you dont have input capacitors(source to v+) than thats why. if you do have the bank of electrolytic cap equalling <10mOhm and 50 ripple amps .. then you must decrease distance from: drain to diode; input caps to source; and input caps + to diode + . reducing these three lengths to <1/2" will greatly reduce needed gate R and will be able to run massive amps with cool fet.
causalitist 3 years ago
Cant remember but is is 60v or so..
i know that I has big spikes, there are caps and diode, the distance between diode and mosfet could be shorten..
but there is no problem with hot mosfets,
but i have also made another and smaller board, which runs a lot better, at a little higher freq... but not fiddling with that project right now..
at the time a D-class amplifier is more fun :D..
sponkii 3 years ago
Would you please post the schematic for your 160ah pulse width modulator?
leslaw9999 3 years ago
Would you please post the schematic for your 160ah pulse width modulator?
atomicprism 3 years ago
Yes.. i'll se if i can find it..
it is based on a LM324 and a MOSFET driver
sponkii 3 years ago
where'd you get the motor and the oldschool (cheap, i assume) scope?
oehrlein49 3 years ago
Yep a old scope. but fine.
I got it from a friend of my father.
the motor is from a circulation pump from a bus.
actually, there is a lot of good stuff on buses, manly the big ones for long traveling.
sponkii 3 years ago
The random flickering noice on the scope is because of the motor brushes are poor quality..
sponkii 4 years ago
Very cool. It's great to see someone doing it, not just talking about it. Looks like you're using N-channel FETs and switching to ground. It's also interesting to notice the little "bounce" in the waveform when the motor speed is trying to adjust. Are you using snubbers? I know that one of the possible problems is trying to switch too fast and having the FET slam on when you don't want it to. So many questions...What's your target current rating?
wires99 4 years ago
yes i'm using N-channel Power FETs..
the little bounce is from the motor because of self induction. i dont know the right term but "roll off"...
dont know what a snubber is. but just a regular FET-Driver and 4powerfets.
the PWM is made by a LM324..
the maximum constant current is 160Ah(when fully open), in pulse is a bit more.
this motor uses about 100Ah at 24v when blocked.. and 20-50Ah under regular usage..
sponkii 4 years ago