Okay, so PWM, what an awesome idea for controlling electronic motors. What motors are in our cars, well there are a few but stepper motors don't count. Depending on your mods to the car here is a list of a few; radiator fan(s), blower, windshield, fuel pump, windshield washer pump, water pump.
I know for a fact that PWM is more efficient and better for a motor than a large resistor so why hasn't anybody done this yet? I plan on adding PWM to my radiator fan when I get an electric water pump, both of which will be PWM controlled. In the meantime let's K.I.S.S. and focus on one thing that's always ticked me off... the blower motor. Wouldn't it be nice to be able to have an infinately adjustable speed? I think it would, so I'm planning on starting with that first.
Does anybody have any specs like current draw on the motor? If not I'll get to it Wednesday.
Also, does anybody have links or recommendations for circuit designs? I'm open to just about anything except discouragement. All the kits I've seen are around 5amps max but I think the blower motor will be more than that. The fuel pump is also above the 5amp kit recommendations. BTW, Summit sells a product that does this for the fuel pump but it's expensive. It just comes in a pretty red anodized billet aluminum case .

 

PWM is very useful in controlling small low current solenoids in electronically controlled transmissions, injectors that have relatively low current requirements. As far as the fan motors go even with driving them pulse modulated you still need a decent driver. I built a solid state fan relay some time back that fit into the standard fan relay housing. The problem is the fans at start draw16 amps or more and without adequate heatsinking the device went into thermal runaway. Also, the devices(semiconductors) get pricey when you get into the high current area. Most likely thats why the manufacturers use current methods. There are many simple circuits you can build, but in reality it's probably not worth the effort for high current devices.

 

Yeah, things are looking rather expensive with the high current. I still want to get this blower motor working right because right now it's just pissing me off that I have "might as well be off", "I can hear it but is that all?", "that's better", and "holy cow did somebody just open a can of dry my eyes out?" Something adjustable would be very welcome. For the fuel pump I just want to turn it down at idle so it's not as loud. Also doesn't waste as much current that could otherwise be going to things.
I found a MOSFET 30amp design that's looking promissing. Can't I just double up the power transistors/fets for more current?

 

why not use a petentieometer? it's cheaper

 

Not when it needs to handle the current of a fan motor. Inexpensive potentiometers make nice firecrackers.

 

just a thought, although it will probably work too slow, but maybe use a relay controled by PWM to power the heavy amp stuff.

 

A mechanical relay couldn't switch fast enough, unless maybe it was vacuum sealed. Even still, it would be no time before the contacts were destroyed. A solid state relay is still an expensive proposition.

 

How much current can a controller from an electric RC car handle?
I just thought of it, so I'm sure it won't work.

Does the blower motor have a rating for watts or amps on it?

Be careful to verify that everything is within their rated limits or you can risk a fire- not worth it.

 

thats why i said it was just a thought, people who know me run when i think,.. haha. but some more thinking on my part, i seem to remember caddy uses a variable voltage to the blower control module for the A/C on some of their newer cars, the ones with what they call the pancake blower motor. the module can possibly be picked up for cheap from the wrecking yard.
the PC at work is down right now, so we have no repair manuals, stupid NTLDR missing error. i'll try to remember to check once i get it back up.

 

Nah, that's what fuses are for.

 

I just don't want to get in trouble for suggesting something.

Like using a dimmer switch from a light fixture.

 

That would actually work. Rheostats are nothing more than a very large variable resistor (pot). But like I said earlier, dropping the voltage isn't an option right now. I want to keep the same voltage and PWM it.
I do think there are cars out there that would have these kinds of controllers but I haven't found any yet.
Also, the dimmer on the gauge lights is a Rheostat but for like 1amp. I'll be replacing that too with a PWM circuit. That one would be a lot easier and only like $4 worth of parts.

 

The dimmer switch would work, considering they handle something like 1800 W and the fan motor will blow the fuse before it gets to 780 W. You'd need an old rheostat type though, instead of a new solid-state one.

 

Why wouldn't a solid state one work?
Just curious.

 

The solid state ones use a triac, to so they need AC. Coincidentally, they actually dim by PWM.

 

Sure, you can cascade the drivers, just remember to use a low value resistor from each device output to correct for different device gain characteristics.

 

Have taken a current measurement yet? This says 17A with some mods. I would think that should do it. $19.95 not worth piecing one together at that price.

http://www.circuithut.com/index.php?.../view/full/263

Edit: BTW, PWM is a great way to get more liner dimming of LED back light dashes......

 

Sorry to bring this back from the dead.... My company makes swimming pool salt chlorine generators, and as such the power supplies are PWM (uses a SG2525) and 4 IRFP240's.. Those 4 together handle 250W without getting very warm. Power mosfets are excellent for this type of high current switching. All this relay talk gets me clicky LOL. 20A at 12V should be plenty for the cooling fan, so for $20 or so in parts and a reasonable electronics background you could have a decent PWM controller with a **** and everything.

 

That could work real well for the fan and water pumps. If somebody were to spend the time designing a circuit it might be worth looking into embedding the on/off logic. Tap into the CTS sensor, program the micro onboard... yeah, that would be cool.

I while back I found a golf-cart controller that would work. It cost somewhere around $45 complete. Imagine the amp rating of that controller. All I remember now is that the FOS was 5 meaning it had 5 times the current handling.

 

Why are you going to design, source the parts, and build one? Unless it's for fun, all that work has already been done. The kit price went up $5, still cheaper then $45. And cheaper kit are out there.

 

Here is a link for for one up to 15 amp for $24 shipped.

http://www.bakatronics.com/shop/item...emid=444&catid=