How to controll speed on electric motor...

[k0ua]

That would not work well due to large heat generation when not fully closed. The answer is switching controller like Soundguy suggested.

Well I was thinking he would only need to drop about 4 volts say from 14 to 10 to maybe get the speed he wants.. we need to know the current draw on that motor, but I am thinking only 10 amps or so, so a 4 volt drop at 10 amps that is 40 watts to dissapate in heat.. so a heat sink maybe 6 inches square? Sure not as effecient as a switcher, but maybe doable. But like I said I would probably just buy one too. Just an Idea.

James K0UA

 

[Soundguy]

Well I was thinking he would only need to drop about 4 volts say from 14 to 10 to maybe get the speed he wants.. we need to know the current draw on that motor, but I am thinking only 10 amps or so, so a 4 volt drop at 10 amps that is 40 watts to dissapate in heat.. so a heat sink maybe 6 inches square? Sure not as effecient as a switcher, but maybe doable. But like I said I would probably just buy one too. Just an Idea.

James K0UA

been a while since I worked with old large silicon like that... so I went and grabbed a datasheet... and yeah.. looks like it WOULD work.. but I think I'd still go the PWM route.. me anyway.

soundguy

http://www.datasheetcatalog.org/datasheet/siemens/Q62702-U58.pdf

 

[k0ua]

been a while since I worked with old large silicon like that... so I went and grabbed a datasheet... and yeah.. looks like it WOULD work.. but I think I'd still go the PWM route.. me anyway.

soundguy

http://www.datasheetcatalog.org/datasheet/siemens/Q62702-U58.pdf

I am pretty old and sometimes think about old ways this is how we would have done it. 35 years ago.

James K0UA

 

[k0ua]

In Reality the OP is not going to fab up anything from componets anyway, we just need to help him find a controller that he can hook up easily, hopefully with a good application sheet with drawings. I am sure all this talk of switchers , Pulse Code Modulation, Pass transistors and 3 terminal regulators is making him more uneasy than anything. It is about like when I go delving into hydraulics, totally out of my realm and all the darn different fittings JIC, NPT ORB and on and on.. I studied it today for about 2 hours and did learn a lot, but I had to stop, my head was hurting:laughing::laughing:

James K0UA

 

[BobRip]

In Reality the OP is not going to fab up anything from componets anyway, we just need to help him find a controller that he can hook up easily, hopefully with a good application sheet with drawings. I am sure all this talk of switchers , Pulse Code Modulation, Pass transistors and 3 terminal regulators is making him more uneasy than anything. It is about like when I go delving into hydraulics, totally out of my realm and all the darn different fittings JIC, NPT ORB and on and on.. I studied it today for about 2 hours and did learn a lot, but I had to stop, my head was hurting:laughing::laughing:

James K0UA

Exactly. Be aware that the startup current of this motor is going to be much higher than the run current.
Soundguy, I know you could build this and have it working in a few hours. The OP is a self confessed non electrical person. He would not find it so easy.

 

[sparc]

If this is a small universal motor like a router then why not try a router speed control? They can be found at most woodworking stores, are inexpensive, and work well (for routers).

Woodcraft, Woodworkers Supply, MLCS Woodworking, Rockler are just a few of the places that should have them along with eBay and Amazon.

 

[SPYDERLK]

Exactly. Be aware that the startup current of this motor is going to be much higher than the run current.
Soundguy, I know you could build this and have it working in a few hours. The OP is a self confessed non electrical person. He would not find it so easy.

Yes. With a slowed motor the pulse currents are going to be high. With a 12V motor of any power, such as a good handdrill or larger, probably in the 40A & up range. As the motor takes load the pulses will widen more and more as load increases. Pulses may reach 100%. You dont want to undersize the semiconductor.
larry

 

[Redneck in training]

If it is serial motor then it will run on DC and AC as well. So to limit POWER you need a transformer with several taps for example 8, 10, 12, 14 V. Speed will vary with load.
If you want speed control then you need a speed feedback.

 

[Tags]

Ok, did some homework today. The electric motor draws 43 amps, is continuous duty, is 1/2hp, and is 12volt. Dont know if these details change things or not, but I do know that 43 is ALOT of amps....

 

[BobRip]

If this is a small universal motor like a router then why not try a router speed control? They can be found at most woodworking stores, are inexpensive, and work well (for routers).

Woodcraft, Woodworkers Supply, MLCS Woodworking, Rockler are just a few of the places that should have them along with eBay and Amazon.

These are designed for AC operation. They probably have SCRs which only work on AC unless they have another SCR to turn off the first SCR.

 

[BobRip]

Ok, did some homework today. The electric motor draws 43 amps, is continuous duty, is 1/2hp, and is 12volt. Dont know if these details change things or not, but I do know that 43 is ALOT of amps....

Is that the peak current or continous? That would be about 516 watts ( 12 X 43). That sounds about right for a continous duty current for 1/2 HP motor. The starting currents will be several times ( 3 to 6) higher.

 

[k0ua]

Ok, did some homework today. The electric motor draws 43 amps, is continuous duty, is 1/2hp, and is 12volt. Dont know if these details change things or not, but I do know that 43 is ALOT of amps....

Oh boy.. yes 43 amps is a lot of amps. and nothing I have talked about or shown is going to work for that.. let me look around some.. I was half expecting you to come back and say 4 amps.. Man a 1/2 horse motor to sling some salt? whatever the heck for? and this is wired up with #4 wire? from the battery?.. That is a healthy motor. Do your lights go dim when you turn this thing on? so 43 amps X 13.8 volts (nominal charging system voltage with engine reved up) = 593.4 watts. 1/2 horsepower = 746/2= 373watts/593.4 watts = 62.8 % effecient.. yeah, could be about right. WOW is all I can say.
I am wondering if you can do something mechanical to narrow the "spreader beam" instead of slowing down the motor. How about is it direct drive or chain driven.. change sprocket? Lets think out of the box here. Dropping 4 or so volt (just and estimate) at 43 amps is like 172 watts to dissipate as heat.. Now we are talking big multiple pass transistors and really big heat sink to make a linear pass transistor regulator. This is not a very good approach.. A switcher is going to be the way, but you are not liable to find one on flea bay for $20 bucks like I was headed for. that will handle this much current. Maybe someone else has some better ideas. ?

James K0UA

 

[k0ua]

Yeah Bob's right, I did not even take into account the starting surge currents. that thing looks like a crecent wrench laying across your battery for a few milliseconds until it get's to rolling. Any electronics sure would have a have a big Cap to take those kinds of startup currents.

James K0UA

 

[BobRip]

Yeah Bob's right, I did not even take into account the starting surge currents. that thing looks like a crecent wrench laying across your battery for a few milliseconds until it get's to rolling. Any electronics sure would have a have a big Cap to take those kinds of startup currents.

James K0UA

It would be good to measure the actual motor cuurrent during actual use with material being thrown. The motor is probably not fully loaded. Some clamp on ampmeters can measure DC current. Get this and we can figure some resistor values and power disapation.

 

[Redneck in training]

Yeah Bob's right, I did not even take into account the starting surge currents. that thing looks like a crecent wrench laying across your battery for a few milliseconds until it get's to rolling. Any electronics sure would have a have a big Cap to take those kinds of startup currents.

James K0UA

Starter can take twice as much so I doubt there will be an issue.

 

[Soundguy]

Oh boy.. yes 43 amps is a lot of amps. and nothing I have talked about or shown is going to work for that.. let me look around some.. I was half expecting you to come back and say 4 amps.. Man a 1/2 horse motor to sling some salt? whatever the heck for? and this is wired up with #4 wire? from the battery?.. That is a healthy motor. Do your lights go dim when you turn this thing on? so 43 amps X 13.8 volts (nominal charging system voltage with engine reved up) = 593.4 watts. 1/2 horsepower = 746/2= 373watts/593.4 watts = 62.8 % effecient.. yeah, could be about right. WOW is all I can say.
I am wondering if you can do something mechanical to narrow the "spreader beam" instead of slowing down the motor. How about is it direct drive or chain driven.. change sprocket? Lets think out of the box here. Dropping 4 or so volt (just and estimate) at 43 amps is like 172 watts to dissipate as heat.. Now we are talking big multiple pass transistors and really big heat sink to make a linear pass transistor regulator. This is not a very good approach.. A switcher is going to be the way, but you are not liable to find one on flea bay for $20 bucks like I was headed for. that will handle this much current. Maybe someone else has some better ideas. ?

James K0UA

this is EXACTLY why i suggested a pwm.

again.. I built a motor controller for an electric prototype vehicle that ran similar current using irfz40 mosfets. good handfull of them.. like 20-30$ worth of them. might have been 10-15 of them. been a couple decades..

soundguy

 

[Brad_Blazer]

This looks like what you need for $60.
http://www.sparkfun.com/products/9668

 

[k0ua]

This looks like what you need for $60.
Digital PWM Motor Speed Controller - 50A - SparkFun Electronics

Looks like you found it!

James K0UA

 

[johnrex62]

Sheesh! you guys lost me as soon as you went beyond hook the red wire on the + connector and the black wire on the - connector. :confused2:

 

[Tags]

This looks like what you need for $60.
Digital PWM Motor Speed Controller - 50A - SparkFun Electronics

Thanks alot for all the help fellas! I'm still waiting to check the amp draw upon startup, but is seems like this would do the trick. My hats off to you Brad for locating it!