Need Help Wiring DC Motor with PWM

[snub]

I found an interesting wiring diagram on the interweb showing how to control a DC motor with a SPDT switch and 2 automotive type relays. The motor is the kind where the direction of rotation is changed by reversing the polarity of the 2 input wires. The way it was wired seemed odd to me, grounding through the switch and power was going to 2 terminals on the relay. Anyways, I hooked it up as per the diagram, and it works just fine.

So then I'm thinking I'd like to hook up a Pulse Width Modulator to control the speed and wondering why I can't use a single PWM straight off the power supply. I didn't think it would work and I was right. It doesn't. At least not how I have it wired. I even tried a second PWM from a different manufacturer and same thing. Motor runs at full speed, won't slow down.

I'm wondering why it doesn't work and if there is another way to wire it. First diagram is the one I found at Burden Supply, the second is how I wired in the PWM.



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[PK]

Basically you need to PWM the power going to the motor, but NOT the power going to the relay coils. So wire both 86 terminals of the relays to the +ve terminal of the battery (and only to the + terminal of the battery).

PK

[snub]

Thanks for the reply PK, but I'm not understanding. Are you saying to supply PWM regulated to the #87 terminals and battery voltage to the #86?

[RobWilson]

like so Snub

As PK mentioned the relay coil will  have some issues being supplied with a PWM supply 


Rob

[snub]

Well, back to the drawing board. I hooked it up as you showed, but still no love. Motor runs at full speed. I tried another PWM with the same result. I even reversed the terminals at 86 and 87 just to be sure.

[PK]

Are you sure that terminals 87 only connect to the PWM output (ie not to the battery) You should be able to measure the DC volts across the motor change as you vary the PWM.

[tom osselton]

I dont know to much about wiring but shouldn't the fuse go directly to the + pulse width  control? The diagram shows it going to both the pw and the relay wouldn't that render the pw useless?

[RobWilson]

Hi snub

Just to clarify make sure the control side of the relays are wired up like so .

[RobWilson]

I dont know to much about wiring but shouldn't the fuse go directly to the + pulse width  control? The diagram shows it going to both the pw and the relay wouldn't that render the pw useless?

The fuse is just  supplying two separate curcuits .

1 . A supply to the PWM controller

2.  A supply to the direction control

In reality  they would  have their own fuse . But they would still be conecting to B+

[John Rudd]

The coil is connected to pins 85 and 86, pin 30 is the common connection for the contacts on pins 87 and 87a.

Just wire up the relay contacts to give a double pole changeover arrangement.
The fwd/rev switch then acts to either energise or de-energise the relays giving the fwd or rev action,is another way of doing it.

[Alan Haisley]

Well, back to the drawing board. I hooked it up as you showed, but still no love. Motor runs at full speed. I tried another PWM with the same result. I even reversed the terminals at 86 and 87 just to be sure.

Where did you get the wiring diagram for the PWM? Have you tried wiring just the power supply, the PWM, and the motor to make sure that you can speed control at all? What does that working diagram look like?


Alan

[seadog]

I've just had a look at the circuit and it occurs to me that you've commoned the battery negative and the motor negative output terminals. Have you metered the these terminals to see if they are electrically common. I've a feeling that they won't be.

[snub]

Thanks for the help guys, I'm still plugging away at it. 'seadog', I think you're on to something with the way I have the negative terminals commoned.

[John Rudd]

Snub,
See the attached sketch....
Hope this is simple enough for you..
I used a simple changeover switch to energise/de-energise the relays for FWD and REV

[snub]

Thanks for the sketch, John Rudd, but schematics are my Achilles heal. If someone out there is bored to tears, maybe they could convert it into a diagram like the one in my first post. Also not sure why you wrote "Rev-Not Used"

[John Rudd]

Snub,
I cant see how to make the drawing any simpler....

The wire connections are all identified by the numbers that appear on the relays....
The "rev-not used" simoly means that the second connection on my switch is not connected to anything.....in reality the relays are either in or off giving fwd or rev.

Might I suggest you get some books on basic electrics and have a read?

I'm always willing to help out, just ask if you're not sure..

[daGrouch]

Separate the BATT- from MOTOR-  ( electronic circuits like to switch or act on the (-) for some reason).
Power the relay coils from BATT+ instead of PWM+.

Yeah, it looks weird at first glance. 
With both relay's OFF both motor leads are connected to PWM- so nothing happens.
With UP relay ON the red motor lead goes PWM+ while black motor wires stays PWM- and motor spins.
With DOWN relay ON red motor wire remains PWM- and black motor wire goes PWM+.



CAUTION: I don't know how the PWM will like having the motor load switched or removed while it's on.

[shipto]

beat me to it daGrouch I just did almost exactly the same drawing 
Although the switch would need to be center off or there would be no stopping the motor from running short of turning power off.

[RobWilson]

Odd , is that not exactly what I had redrawn in post #3   

And clarified in post #7

Rob

[daGrouch]

beat me to it daGrouch I just did almost exactly the same drawing 
Although the switch would need to be center off or there would be no stopping the motor from running short of turning power off.

That's why my post has so many typo's - I was rushing to post before you! 

He showed a SPDT-CO so he had center-off covered.  He doesn't show if or how he want's to switch the PWM so maybe it's a given.  If not then a DPDT-CO could be used instead to power the PWM only when needed provided the PWM retains it's speed setting when powered off.

[daGrouch]

Odd , is that not exactly what I had redrawn in post #3   

And clarified in post #7

Rob

Well, yeah.

Snub requested a drawing in his format to help him visualize it his way and I happened to be bored ATM.  
I could have changed the notation to Latin or Klingon but I didn't want to get yelled at.

[shipto]

Odd , is that not exactly what I had redrawn in post #3   

And clarified in post #7

Rob

So it is I had not looked at yours but I also didnt notice the center off switch on the origional drawing, must be old age 

[RobWilson]

Thanks for the sketch, John Rudd, but schematics are my Achilles heal. If someone out there is bored to tears, maybe they could convert it into a diagram like the one in my first post. Also not sure why you wrote "Rev-Not Used"

And It was my understanding he wanted Mr Rudds wiring diagram redrawn 


Rob 

[RobWilson]

Anyway what I fined odd is that there is no pot shown in the wiring diagram    maybe its a wireless pot 



And a bit more info from the OP  like the make /model of the PWM controller would be a help .

Rob

[John Rudd]

So is this sorted now?
I guess we need sone feedback ?

Rob, could be the pot is an integral part of the speed controller?

[RobWilson]

Aye its a possibility John     I am just used to the wiring on Zapi,Curtis and Sevcon type PWM controllers 

Personally I would hook up the motor direct to the PWM unit bypassing the relays and see if there was then any motor control. If there was motor control then that would rule out a  faulty PWM controller  . Then the fault has to be in the relay wiring . 




Rob

[John Rudd]

Aye its a possibility John 

Personally I would hook up the motor direct to the PWM unit bypassing the relays and see if there was then any motor control. If there was motor control then that would rule out a  faulty PWM controller  . Then the fault has to be in the relay wiring . 




Rob

Absolutely, if ever there's doubt, always go back to basics.....

Anyway I'm off to whittle some metal......

[RobWilson]

And what are you whittling ?  a fan maybe 

I have a choice tonight make a curry or fit my new DRO to mill mmmmmmmmmm.

Just as a side note if there is anyone in the North of England that is in  need of an  electric vehicle tweaked / faults read , (FLT, access equipment , tow tractor,  golf buggy  )  drop me a PM

Just a few of the handheld programmers for electric vehicles  I own and work with daily .




Rob

[John Rudd]

And what are you whittling ?  a fan maybe 

I have a choice tonight make a curry or fit my new DRO to mill mmmmmmmmmm.



Rob

Ummm, fan,yep...needs doing.

Curry or mill?

Gotta be a curry with a few beers....mill can wait..

[snub]

Thanks again for all your help. The PWM is just a generic brand from China, similar to the one in the picture below. I tested it by directly hooking it up to the motor and it works just fine. Like I mentioned, I also tried a second PWM in the first circuit diagram. Both failed to regulate the speed the way I had it wired. I'm guessing that the battery voltage was overriding the modulated voltage. I'm going to rewire it using the newly supplied diagrams and I'll let you know how it turns out.


.

[snub]

We have a winner!!! First diagram I used was the one from daGrouch and it worked perfectly. Motor direction reverses as needed and speed control is perfect. No hiccups whatsoever. And so simple. Lots of smart people on this forum, I'm so glad I joined.

Just for future reference I have included the diagram from daGrouch.




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[shipto]

Out of interest what ampage is the motor your using? Is there a reason for not just doing it with a DPDT-CO switch?

[snub]

I'm using a 5 amp fuse and it's not blowing so something less than 5. The wires from the motor are 18 gauge so I didn't figure it would draw many amps.
The reason for the SPDT switch is because I'm working on a project to use newer style headlight motors on my '66 Corvette that originally came with the old style motors where the case was grounded. I want to use the original switch that was used on these cars.