battery loco controller

[duncan webster 1Participant @duncanwebster1]

I started a thread on this some time ago, but I can’t find it, so had to start a new one. I’m hoping the combined wisdom of you lot will help me releasing the expensive magic smoke.

To recap, I’m using 2 ebay motor controllers to power 2 motors on my latest creation. Why? They were cheap. The way you would wire one up is shown below

When I put my multimeter across the pot it reads ~1k at first, but this rapidly climbs to 4K7 and then stays there. I assume this is due to a cap somewhere. Obviously I want to control it using one potentiometer, the forward/off/reverse (pins 10,11, 12) is going to be by 2 pole 3 way rotary switch, so can be kept apart. The switch shown between pins 8&9 is built into the pot, as the motor can be firmly off by putting the the forward/off/reverse to off, so I’m proposing to permanently connect pins 8&9. Pin 5 seems to be connected internally to pin 1. Pin 7 has 5v on it. What I’m not sure about is:

should I connect pins 5 together on the 2 controllers?

Should I connect pins 7 likewise. I’m concerned that if the 5v regulators in the 2 controllers are not exactly matched they could fight each other

 

I’m proposing N/O push button between the +5 and the pot to act as a deadman. Let go and it cuts the power.

[Robert Atkinson 2Participant @robertatkinson2]

Your diagram is correct. They may be a slight mismatch between the outputs but the motors won’t be identical either.
Another option is two potentiometers one for each controller. This can be either a dual gang pot e.g. https://uk.farnell.com/citec-te-connectivity/27esa472mmf50nf/res-4k7-0-4w-1-turn-panel/dp/3399766
Make sure you get a LINEAR pot. Most dual pots are Logarithmic also called “audio taper”.
Or it could be two single pots mechanically ganged together. This can be arranged to allow balancing between the two motor systems. You could allow the body of one pot to be rotaed over a small range if using gears or timing belts to connect them or variable length levers if using a lever system.

Robert.

[duncan webster 1Participant @duncanwebster1]

Thanks, I’ll get the bits ordered.

[Halton TankParticipant @haltontank]

The only that worries about new set is the lack of Dead Man’s Handle or Kill Switch.

It reminded of an incident that happen many years at my club track. An electric loco was pulling a train of driving skate and a passenger car when for some reason the driving skate derailed and loco became uncoupled from the train. Being relieved of load the loco shot off like rocket and dragged the hand controller fro the drivers hand and continued its merry way. Alas it did survived the next corner and being a raised track the result was not pretty.

In your case I would reinstate the switches between pins 8 & 9 on both controllers using a DPST (double pole single throw) push button switch. I would use a switch with a large button or better still use a lever to operate the switch.

 

Regards Luigi

[BazyleParticipant @bazyle]

I may be a good idea to spring load the potentiometer and if children are going to drive sometimes have a hidden switch that cuts down top speed by introducing a resistor in the 5v line to the potentiometer. A 1/4 inch phono jack incorporating a shorting link with chain to driving car is a simple precaution.

[duncan webster 1Participant @duncanwebster1]

I did say I will have a N/O push button in the 5v supply to the pot. This will act as a deadman.

Children will only drive under direct supervision

[duncan webster 1]

On duncan webster 1 Said:

…

Children will only drive under direct supervision

Children of all ages?   I’ve started to enjoy Thomas the Tank Engine again…

😈

 

[duncan webster 1Participant @duncanwebster1]

I never stopped, but not the American version. And have you forgotten Ivor the engine?

[duncan webster 1Participant @duncanwebster1]

Well that didn’t work too well. I used automotive 20A fuses which immediately blew when I connected it up, presumably on inrush current. I then replaced the battery with a transformer rectifier driven from a variac so I could ramp up the volts. The motor at the top in my diagram worked fine, but the one at the bottom just runs full speed. I’m now pondering either getting a twin gang pot, or biting the bullet and buying a 4QD. I must admit the second option is tempting, just wire and go

[Roger BParticipant @rogerb61624]

Have you swaped the two drives to see if you get the same result? A faulty drive is always a posibility.

[John Doe 2Participant @johndoe2]

I don’t know anything about the controllers in question, but you have tapped the slider voltage from the top controller potentiometer to drive the second controller, and you have removed the second controller’s pot completely. The second controller might, however, need to “see” a complete potentiometer connected, without which it might get confused and could be why it is commanding full revs.

You might try putting a 4k7 resistor between pins 5 and 7 in place of the potentiometer track.

If that fails, you will have to use a dual-gang potentiometer – one gang per controller – as I think Robert suggested.

 

 

[duncan webster 1Participant @duncanwebster1]

Relating this story at the ME club yesterday turns out a member has a 4 qd controller surplus to requirements, so it’s 4qd here we come

[duncan webster 1]

On duncan webster 1 Said:

Well that didn’t work too well. I used automotive 20A fuses which immediately blew when I connected it up, presumably on inrush current. I then replaced the battery with a transformer rectifier driven from a variac so I could ramp up the volts. The motor at the top in my diagram worked fine, but the one at the bottom just runs full speed. I’m now pondering either getting a twin gang pot, or biting the bullet and buying a 4QD. I must admit the second option is tempting, just wire and go

As the circuit looks good to me, I suggest something is wrong with the wiring.   A photo would help.

That the second unit runs it’s motor flat out suggests either that it’s being fed 5V from the pot (pin 7) when it should be connected to the wiper (pin 6), OR, that its controller is faulty.

One unlikely possibility is that pin 5 is not ground.  Try connecting both pin 5s together.

For debugging, I’d disconnect the parallel wiring and start by testing the two controllers independently.    Prove both controllers and motors work as singletons.

Then disconnect the pot from controller two, as per diagram, and see if the pot wiper (6), will control both motors.

Why is nothing ever easy?  Should be straightforward!

Dave

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