Connecting a pair of motor controllers.

[Ron LadenParticipant @ronladen17547]

I,m not too bad with electrics but a bit dull when it comes to electronics and would appreciate some advice….is it possible to connect and operate an identical pair of DC motor controllers from one speed potentiometer..?

The controllers come wired with a potentiometer which has 5 cables,  if I wire the two sets of 5 cables to one pot will it work..?

Also the controllers are wired with 3 cables to a double throw reversing switch, again could they both be connected to a single switch..?

I wondered if it would cause problems between the two controllers or not work at all or even cause damage to the controllers.

Thanks

Ron

 

Edited By Ron Laden on 03/06/2019 08:07:19

Edited By Ron Laden on 03/06/2019 08:16:15

Edited By Ron Laden on 03/06/2019 08:17:57

Edited By Ron Laden on 03/06/2019 08:24:07

Edited By Ron Laden on 03/06/2019 08:24:49

[Ron LadenParticipant @ronladen17547]

[Stuart BridgerParticipant @stuartbridger82290]

I'm no motor control expert, but electronic basics would indicate that the two circuits would need to be kept isolated. This is easy though, you just need a Double Pole Double Throw (DPDT) switch and a dual gang potentiometer. The latter being two pots on a common shaft. Both cheap and easy to source.

[Ron LadenParticipant @ronladen17547]

Thanks Stuart, that makes sense.

Ron

[Stuart Smith 5Participant @stuartsmith5]

Ron

Does the potentiometer have a switch? If it has 5 wires it could have 3 for the potentiometer and 2 for a switch.

Another Stuart

[Ron LadenParticipant @ronladen17547]

Posted by Stuart Smith 5 on 03/06/2019 08:50:58:

Ron

Does the potentiometer have a switch? If it has 5 wires it could have 3 for the potentiometer and 2 for a switch.

Another Stuart

Hi Stuart, yes the original pot has a switch so as you suggest the 2 wires must be the switch. I assume you can get dual gang pots which are switched..?

Ron

[Brian OldfordParticipant @brianoldford70365]

Posted by Ron Laden on 03/06/2019 08:58:26:

Hi Stuart, yes the original pot has a switch so as you suggest the 2 wires must be the switch. I assume you can get dual gang pots which are switched..?

Ron

If you need seperate switches and can only find a pot with a single switch you could slave a two pole relay off the switch.

[Brian GParticipant @briang]

If the DPDT switch is used on the output to reverse the motors, to keep the outputs isolated you would need a 4-pole double throw switch on the outputs. Alternatively, if you don't need centre off, you could do the same thing to the output as Brian suggested for the potentiometer switch and use a single pole switch (or one pole of the existing switch) to control a pair of DPDT relays.

Brian (another one)

[Ron LadenParticipant @ronladen17547]

Posted by Brian Oldford on 03/06/2019 09:09:26:

Posted by Ron Laden on 03/06/2019 08:58:26:

Hi Stuart, yes the original pot has a switch so as you suggest the 2 wires must be the switch. I assume you can get dual gang pots which are switched..?

Ron

If you need seperate switches and can only find a pot with a single switch you could slave a two pole relay off the switch.

Thanks Brian,

I will have a search, I would need a 100K dual gang pot with a single switch (switches both pots) will see what I can find.

Ron

[Ron LadenParticipant @ronladen17547]

Posted by Brian G on 03/06/2019 09:29:00:

If the DPDT switch is used on the output to reverse the motors, to keep the outputs isolated you would need a 4-pole double throw switch on the outputs. Alternatively, if you don't need centre off, you could do the same thing to the output as Brian suggested for the potentiometer switch and use a single pole switch (or one pole of the existing switch) to control a pair of DPDT relays.

Brian (another one)

Thanks Brian.

The reversing switch is not on the outputs, its wired into the controller circuitry.

Ron

Edited By Ron Laden on 03/06/2019 09:35:23

[Ron LadenParticipant @ronladen17547]

I just wonder how matched the two sides of a dual gang potentiometer are, percentage wise would they be within 5% of each other when connected to the controllers or better/worse..? I am assuming that two identical controllers would be quite close output wise but if the dual pot adjusting them is well out of balance that could be an issue.

I can live with a motor speed difference from the two controllers of around 5% possibly a bit more but not too much more.

[Robert Atkinson 2Participant @robertatkinson2]

Can you provide details of the controller model?
The more advanced conntrollers actually use a 0-5V (or similar) control voltage which is generated by a potentiometer a 5V supply. If thi is the case you could use a single pot with 3 connections (common, 5V and variable) to one controller and two (common and variable) to the other. If they are cheap ones using a RC circuit then you will need a dual potentiometer. Make sure that it is linear NOT log or "audio" taper. The matching between sections would normally be better than 5%.

https://uk.rs-online.com/web/p/potentiometers/1638384/

Rober G8RPI

[DalboyParticipant @dalboy]

Looking at this from a different point of view will both motors always be running the same rotation if so will one of the controller and potentiometer be able to run both motors. So two motors and only one controller and potentiometer.

I use to wire two motors to one controller in model boats when only had a two channel set

[Brian OldfordParticipant @brianoldford70365]

Posted by Ron Laden on 03/06/2019 18:48:44:

I just wonder how matched the two sides of a dual gang potentiometer are, percentage wise would they be within 5% of each other when connected to the controllers or better/worse..? I am assuming that two identical controllers would be quite close output wise but if the dual pot adjusting them is well out of balance that could be an issue.

I can live with a motor speed difference from the two controllers of around 5% possibly a bit more but not too much more.

If you need better "balance" you might consider using a couple of PWM ports on an Arduino. With care I would think you should be able to get sub 1% balance.and a whole heap more functionality should you need it.

[Ron LadenParticipant @ronladen17547]

The idea of using 2 controllers is for the 5 inch class 22 loco I am designing/building. Its a twin bogie loco and I am using 2 x 24 volt/150 watt motors on each bogie, 4 motors in total. The controllers I am considering are the budget (Chinese) type, they are PWM ctrls rated at 10-55 volt, 40 amp continuous, 60 amp max. I am running one of these ctrls in the 0-4-0 shunter and to date it works very well, 10-15 amp in general running with 28 amp max when working hard.

I am estimating that the class 22 would be in the 20-30 amp region with 45-50 amp max or thereabouts. If the budget controller is as rated (I dont know) then a single ctrl should do the job but it would be near its top end. I thought a pair, one driving each bogie would halve the load and make things easier on the controllers and that is where my thinking came from. I could pay over £200 for a ctrl which would cope easily plus have some loco bells and whistles but if a pair of budget type will do the job at 1/10th the cost then that is an attractive option.

Brian, as I mentioned my electronics understanding is not too good so can you explain an Arduino, I have no idea what that is.

Ron

Edited By Ron Laden on 04/06/2019 08:02:16

[SillyOldDufferModerator @sillyoldduffer]

It might be possible to connect the two together electrically, but as we don't know the controller circuitry doing so is downright risky. I'm with Stuart. Get a dual potentiometer and a DPDT switch. Linking the controls mechanically eliminates any chance of getting into electrical poo, and it's a simple and cheap solution.

I doubt 5% difference on the pots would make much difference to the motors, and it's likely the pots will track closer than 5% anyway. If it's a problem you can buy high-tolerance components but I wouldn't bother unless you hit trouble with ordinary potentiometers like these. Amazon also do DPDT switches. Many, many other suppliers, switched double pots and DPDT are both common as muck electronic parts, and you don't need anything special to work a controller.

Dave

[JourneymanParticipant @journeyman]

I'd go for a bigger controller this is rated at 60A continuous from Amazon.co.uk

Only £25.00 – Might do the job?

John

Edit: forgot the price!

Edited By Journeyman on 04/06/2019 10:26:53

[Brian OldfordParticipant @brianoldford70365]

Now I've looked at those budget controllers I concur with SOD. Without getting them on the bench and having a poke around at the circuitry to find out exactly how the pots are connected into the gubbins it might be better to stick to two pots on a common shaft.

As these controllers are PWM devices I'm sure it could be done in the way I suggested with an Arduino but it would take a little R&D to avoid letting out any of the blue smoke.

[AdrianRParticipant @adrianr18614]

If the controllers are driving separate motors which are effectively mechanically connected via the rails does it matter much if there is a small miss match. It just means one motor will work slightly harder than the other till it reaches full speed.

Dual gang potentiometers are the way to go, if you want to use separate controllers.

If you ever need more controllers you can also get modular potentiometers which can have about 8 on one shaft.

Adrian

[Robert Atkinson 2Participant @robertatkinson2]

Another option, depending on your batteries would be to use 48V and run the motors in series/parallel on one controller. Series the two motors sharing an axle and parallel the two bogies. If you series the bogies then one slipping would "take" all the voltage and you will loose power at the other bogie.

Otherwise I concur, a dual pot is the way to go. If I had a controller to hand I'm sure a simpler control could be worked out, but I don't.

To keep it mechanical you could of course make a throttle lever and gear (ot miniature toothed belt, crank etc) to the two control pots…..

Robert G8RPI.

[Ron LadenParticipant @ronladen17547]

Thanks guys, I agree that the simplest option is a dual gang pot and providing any output difference from the two controllers is reasonably small I cant see there been any problems. I have been searching and found a lot of 100K dual pots but I still havnt found a 100K linear "switched" dual which is what I will need.

Brian, a picture below of the controller should you be interested, it means nothing to me but you no doubt understand it.

[John ShepherdParticipant @johnshepherd38883]

Ron

Have you considered using two single pots and connecting the shafts with gears so that one is connected to the control knob and the other is a slave?

The advantages are:

1. you can make mechanical adjustments to reduce the difference (if any) in the two pots.
2. two single linear pots will be easier to source
3. there are plenty of cheap plastic gears around that will do the job.

John

[John ShepherdParticipant @johnshepherd38883]

Ron Have you considered using two single pots and connecting the shafts with gears so that one is connected to the control knob and the other is a slave? The advantages are: you can make mechanical adjustments to reduce the difference (if any) in the two pots. two single linear pots will be easier to source there are plenty of cheap plastic gears around that will do the job. John

[Neil WyattModerator @neilwyatt]

I would advise a single controller.

In my experience potentiometers can be mismatched at the very bottom of their travel so it's quite likely that one motor will power up before the other.

One motor powered and one stopped is more likely to promote slipping than in two motors already turning. And this right at the times when you need the best control over adhesion.

Using one high-power controller will ensure both motors can balance (if one slips it will generate more back-emf diverting power to the other motor, and if one motor stalls it will 'steal' power from the other – an ideal situation).

Neil

[AdrianRParticipant @adrianr18614]

Ron

Here is a link to 100K linear pots

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