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90vdc pwm controller

Posted: Wed Jul 19, 2006 7:07 pm
by icestorm
I recently tore apart an old treadmill to extract its motor and speed control circuts. I orginally planned to just reuse its existing circut but have now decided to upgrade my project to have computer control capibility. Does anyone know where I can either A) purchase a pwm 90v dc speed control circut or B) find a schematic to build one myself. I've searched a bit through the forums but havn't had a whole lot of luck. There is a lot here that covers dc motors and pwm but nothing that seems to talk about that high of a voltage. Any help would be great.


Posted: Wed Jul 19, 2006 7:22 pm
by Bob Scott

Could you supply some more information please? I am surprised that it is DC not AC.
How did you determine that the treadmill has a 90V dc motor?
Does the treadmill use a transformer and rectifier to generate 90V?
How much current is the motor rated for? Horsepower will do also.
How much current does it A) use while it is running? B) use while it is starting up or laboring?

Just about any PWM circuit operating at lower voltage can drive an output transistor(s) to run your DC motor in one firection only.


Posted: Wed Jul 19, 2006 7:31 pm
by icestorm
On the motor was a sticker that gave more information about the motor. It listed it as a 90v dc motor rated for treadmill duty. It is a 1 hp motor. There wasn't really any more info. on the motor itself. As far as the current circut goes I can't really tell you a whole lot about it. I've built other circuts in the past but have not dealt much with motor circuts and typically just use prebuilt power supplys. I know that there is a transformer in the current circut but don't know what I would be looking for as far as if there is a rectifier or not.

Posted: Wed Jul 19, 2006 7:54 pm
by icestorm
I wanted to add that the intended project will probabbly never touch the speed or length of duration that it was orginnaly designed for. It will probabbly be being used at 5min to half an hour intervals and run at a very low to medium rpm.

Posted: Wed Jul 19, 2006 8:06 pm
by Chris Smith
Try "Woods", they may give you the needed schematics?

Industrial controlls.

I have repaired many of these units, and they work well, are simple, and you can copy them very easily.

Posted: Wed Jul 19, 2006 8:15 pm
by icestorm
what is Woods. I'm guessing its a website that I dont know about yet. I have not been a forum member very long and have only recently in the last month or so seen the nuts and volts magazine that led me here. Again thanks for all the help.

Posted: Wed Jul 19, 2006 8:45 pm

Posted: Wed Jul 19, 2006 9:10 pm
by Chris Smith
"Woods Controllers". [old company]

They make all the assembly line motor controllers, DC, pulse etc. for assembly line control.

Try "Woods DC Controllers" as there is a long list of things?

Posted: Thu Jul 20, 2006 6:25 am
by haklesup
Elaborating on Bobs commnet about boosting a lower voltage PWM. Take this very simple circuit for example

Your objective would be to replace the transistor with one rated for the voltage and current you require. Its not that simple though since the gate voltage will need to be a lot more than 12V to turn that thing off so you'll need an intermediate level shifting circuit to boost the gate voltage to as close to 90V as possible. I'm thinking a bipolar transistor or just skip the FET in favor of a bipolar in the first place.

BTW, search on "90V motor speed controller" and you'll find both projects and products. Here's a winner on price and spec. ... tem=KIT_67

Posted: Thu Jul 20, 2006 3:25 pm
by jwax
Are there two wires from that motor or four?
If four, two would be field, two for armature.
Controlling the field current controls your motor- way less current than the armature will draw.
I've used a small wirewound pot from the armature leads (90 VDC), and fed a few hundred milliamps into the field for a speed control.

Posted: Thu Jul 20, 2006 5:37 pm
by josmith
For what it's worth unfiltered DC rectified directly from 110volt single phase current is often called "90 Volts DC" I always thought of it as a misnomer.

Posted: Thu Jul 20, 2006 5:45 pm
by Bob Scott
Look up this location suggested by Chris:

Be careful if you are thinking of building your own controller if you are not very familiar with electronics. If you intend to run this motor from rectified AC mains and do not use some type of power transformer or other isolation you could:

1) Trip a circuit breaker or blow a fuse
2) Fry the controlling computer
3) electrocute yourself
4) Any combination of the above

Good Luck,

Bob :cool:

Posted: Fri Jul 21, 2006 1:42 am
by MrAl
Hi there,

I dont understand. A 90v controller is just a higher voltage one
that would use higher voltage transistors, maybe in a bridge
configuration. What is the mystery here, or did i misunderstand
the question?

As others have said however, this kind of voltage is dangerous for
many reasons. If you dont have much experience you should
probably get someone else to build you one or buy one already
Not only can you get a dangerous shock, but high voltages like
that often cause very high currents which are both untimely and
unexpected. These high currents combined with the high voltages
cause parts to explode, sending pieces out in all directions.
Safety glasses are a must. The pieces can also be very hot!
Be very, very, careful.

One time i was troubleshooting a low voltage power supply that
plugged directly into the wall. Internally, the power supply
used an on line technique to reduce the voltage. What happened
was i had the board on the white counter top, and a resistor
fried when i plugged it in. The resistor got hot so fast i didnt have
time to shut down or whatever so the spew from the resistor
made a permanant mark on the nice white counter.
Never again he he.

Oh yeah, when i turned it on i was back about 6 feet away from
the board, because i have learned when you turn something
like that on for the first time you should stay as far away from
it as possible until you establish its stability.
Now i have also learned not to do stuff like that on the nice
white counter top ha ha.

Posted: Fri Jul 21, 2006 2:16 am
by dyarker
It isn't the 90V itself Bob is worried about, but that the source might not be isolated from the 120VAC mains.


Posted: Fri Jul 21, 2006 8:46 am
by haklesup
Then either use an isolation transformer or use a GFCI to plug it in. Also incorporate a fuse or circuit breaker just a little bigger than you need for power.

An isolation xfmr will limit the total current available to damage you or the circuit in the event of a fault. You're going to need something like a 12V transformer to make voltage for the ICs so just get another and turn it backwards and connect it to the first xfmr (secondary to secondary) Both need to have sufficient current to source the motor or you will starve it for power.

The GFCI will trip if current flows out of your circuit into something like you or an adjascent grounded surface.

and the (properly sized) fuse will prevent components from heating to the point of exploding.

If you leave out all of these "safety components" your design may not be safe.