Complete confusion
I've been given a 24v 100W DC electric motor (as I'm sort of known for messing about with that sort of shit), but generally, if it's outside of a computer I haven't got a clue.
I've also been given a 12v battery to go with it, and when I connect it up, it goes like shit off a shovel.
How can I control it's speed? I know I need a PMW, and I've found a 12v 30A one on ebay, how can I tell if this will be man enough for the job?
(dchurch bah, Fri 28 Jan 2011, 21:17, 24 replies, latest was 15 years ago)

Use the force.

( SteveFrench Cardio is for homo's. do you even lift bro?, Fri 28 Jan 2011, 21:27, Reply)

ribbons and kittins

( Citizen Cavy Admires your passion for conformity, Fri 28 Jan 2011, 21:37, Reply)

flux capacitor? *shrugs*

( girlinthehole, Fri 28 Jan 2011, 21:40, Reply)

Are you planning on getting a milk round
And looking for a way to power your float?
( JeffTheDogFucker Can you dig it?, Fri 28 Jan 2011, 21:53, Reply)

Best Father Ted ever! (imo)

( SteveFrench Cardio is for homo's. do you even lift bro?, Fri 28 Jan 2011, 21:57, Reply)

Pat Mustard.

( JeffTheDogFucker Can you dig it?, Fri 28 Jan 2011, 22:00, Reply)

Right then!
I'm off to bed to watch Father Ted.

And that is NOT and ecumenical matter.
( girlinthehole, Fri 28 Jan 2011, 22:04, Reply)

*Kicks Bishop Blousie up the arse!*

( JeffTheDogFucker Can you dig it?, Fri 28 Jan 2011, 22:11, Reply)

Wire a rheostat (two-pole variable resistor) into the circuit between the supply and the motor.
The speed of the motor depends on how much current passes through.
( The Mock TurtIe ™ --- Thinks you are a cunt, on, Fri 28 Jan 2011, 22:33, Reply)

I
thought that too, but the electro-engineer at work told me that the current the motor would draw at that wattage would melt such a thing in no time and that I'd need a PWM instead.
(dchurch bah, Fri 28 Jan 2011, 22:36, Reply)

Hmm, that looks more complicated.
From a few minutes' googling, it seems like your best bet is to use integrated circuits or rig up a simple pulse train in conjunction with a MOSFET. Or a buy a kit.
( The Mock TurtIe ™ --- Thinks you are a cunt, on, Fri 28 Jan 2011, 23:01, Reply)

The
more I google about it, the more confused I get.
(dchurch bah, Fri 28 Jan 2011, 23:10, Reply)

i reckon...
all you'll need is a heavy enough rheostat.
the 100A rating'll be max so 30A may be enough.
( blaireau69 , the Cumbrian Travis Bickle., Fri 28 Jan 2011, 23:11, Reply)

This will just lead to the installation of an electric fire with a small motor attached.

( Bartleby A dead man on vacation, Fri 28 Jan 2011, 23:15, Reply)

isn't that the idea?

( blaireau69 , the Cumbrian Travis Bickle., Fri 28 Jan 2011, 23:18, Reply)

And empty the battery in no time too.
I thought the idea was to control a motor.
( Bartleby A dead man on vacation, Fri 28 Jan 2011, 23:21, Reply)

sorry, i've been feeling flippant all day.
it's been a cunty week.
( blaireau69 , the Cumbrian Travis Bickle., Fri 28 Jan 2011, 23:35, Reply)

What about putting a big resistor before the rheostat and a power transistor after it?

( The Mock TurtIe ™ --- Thinks you are a cunt, on, Fri 28 Jan 2011, 23:30, Reply)

Yeah, something like that.

( Bartleby A dead man on vacation, Fri 28 Jan 2011, 23:32, Reply)

The motor should only draw about 4A running.
So your 30A controller should be OK. Mount it on a heatsink and keep an eye on the temperature.
( Bartleby A dead man on vacation, Fri 28 Jan 2011, 23:11, Reply)

I'm
told that it would run the motor, but I wouldn't get 100W out of it.

...which, I assume, means that it won't run as fast.

When I connect it to the battery direct the thing pisses round, so it being slower is not a problem.

Am I right in assuming that's what the lower wattage would mean to me?
(dchurch bah, Fri 28 Jan 2011, 23:21, Reply)

What I'm trying to make
is a full sized (maybe a little smaller) train wheel (made of mdf or chipboard), or series of wheels with pushrods, as my youngest daughter asked why the steam train (near our house) had a "metal bit" connecting the wheels, so I explained it, but thought it would be cool to build a model with her over a few weekends that they could control the speed of.

Turns out, it's much harder than I first thought.
(dchurch bah, Fri 28 Jan 2011, 23:23, Reply)

Sounds fun.
The controller is good for about 360W, and should make the motor run down to at least half speed, possibly less, but it depends on the construction of the motor. At lower speeds, the motor may be jerky.

It would be better to let the motor run quite fast and drop the speed by a belt drive on to a large wheel, like a turntable.

Gaz me if you want any more help, its my bed time now.
( Bartleby A dead man on vacation, Fri 28 Jan 2011, 23:30, Reply)

Well....
the motor came from a mobility scooter, so I assume that at low speed is *should* be quite smooth - from what I've seen of those things, they don't accelerate all that fast!

Thanks for the help, for the sake of 20 quid on ebay, I'll take a chance on the controller.
(dchurch bah, Fri 28 Jan 2011, 23:32, Reply)