Rectifier vs Speed controller for DC gearmotor

Thread Starter

Ambean81

Joined Apr 2, 2018
3
I am replacing an old Bodine gearmotor with a newer model that draws more current. The old motor utilized a dart speed controller that is not rated for my new motor’s amperage. My application does not actually require any control of the speed, in fact I would prefer operation of the motor to be on/off only. This being the case, is it possible to use a $5.00 rectifier in place of the speed controller which would cost around $150.00? Would such a configuration also require a capacitor to smooth the current? Any advice would be greatly appreciated, I will post photos of the placard on the motor as well as my old speed controller.B2F30A1C-15F2-4648-A8D5-2390D66E2944.jpeg 31DCF525-DF17-4A8D-8043-37346F8F61FB.jpeg
 

MaxHeadRoom

Joined Jul 18, 2013
28,619
If controlling from rectified AC direct via a bridge, you do not need a Cap, as did not the Dart controller.
That motor is not very high HP anyway.
Max.
 

Thread Starter

Ambean81

Joined Apr 2, 2018
3
Thank you Max for the very prompt reply and the good news. Any chance you or someone else could suggest a suitable rectifier for this situation? My input is 120v..
 

Thread Starter

Ambean81

Joined Apr 2, 2018
3
I ordered the rectifier Max suggested, wired everything up and it’s working perfectly. The only issue I have now is that the motor is turning a little fast for my application, approximately 24 rpm. What would be the simplest way to reduce the speed to approximately 15 rpm?
 

MaxHeadRoom

Joined Jul 18, 2013
28,619
RPM control could be a simple Triac 'Dimmer' style circuit before the bridge.
One of the off the shelf ceiling fan types should work.
Max.
 

MisterBill2

Joined Jan 23, 2018
18,176
Max is right, BUT you may also need to put a diode in series with the motor. I don't recall why, but the one time that I used that kind of speed control I did need to add the diode. But once I added it the thing worked perfectly.
 

falade47

Joined Jan 24, 2017
178
Max is right, BUT you may also need to put a diode in series with the motor. I don't recall why, but the one time that I used that kind of speed control I did need to add the diode. But once I added it the thing worked perfectly.
I might want to make myself think he means a shunt diode
 

MisterBill2

Joined Jan 23, 2018
18,176
Max, I don't recall the reason, but more details here. It was a series universal motor powering a very small hoist, selecting up or down by reversing the field connections. The customer demanded variable speed and so it included a triac speed controller from Graingers. In theory it wold be a perfect setup, but it did nit work right until I added the diode, the only one that I could find in the area, rated about ten amps and 400PIV. Unfortunately that was a long time ago and I don't recall anything else, except that it was getting late in the evening and we were the only ones in the building. But the customer was totally satisfied.
 

MisterBill2

Joined Jan 23, 2018
18,176
Indeed it was, or at least part of the system was. It is at least slightly possible that there was already a diode embedded in the motor. It was a case of adding to an existing system, completing the installation after everybody had gone home, so as to not disrupt their daily routine. It was a university laboratory, to be more specific. An interesting place at the time.
 

MisterBill2

Joined Jan 23, 2018
18,176
It would not really apply to the OP's application though.;)
Max.
The fact that I had to add the diode in a somewhat similar situation was an adequate reason to state that they might possibly also need to do it. The problem at the time was in total defiance of logic, and so it would not be intuitive to consider adding the diode. But that was the solution.
 

Dodgydave

Joined Jun 22, 2012
11,285
I ordered the rectifier Max suggested, wired everything up and it’s working perfectly. The only issue I have now is that the motor is turning a little fast for my application, approximately 24 rpm. What would be the simplest way to reduce the speed to approximately 15 rpm?
If you use an ordinary light dimmer with a Bridge rectifier across the motor, this will alter the speed/voltage.

7902c4caa3b7e1a7e460a4fbab71a828.gif
 

MisterBill2

Joined Jan 23, 2018
18,176
But he is getting a pretty good post count for only being here a short time.
Currently I have had the time to visit this site quite a bit. When business gets busy that may not happen so much. Some questions and problems are interesting, some of them demonstrate how much some folks don't know. And I really am not aware of what the deal is about "post count" . I look through the listings and try to check out the ones with the fewest comments because some of them are really challenging questions, and it is more likely that I can provide answers that may benefit folks.
 
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