motors and controller for battery loco

[duncan webster 1Participant @duncanwebster1]

I’m busy making a little battery loco, excuse it’s for the grand children.

I’ve bought 2 off motors 12v 120W claimed efficiency ~70%, so somewhere around 14A full load. I’ve measured the resistance by putting a light bulb in series across a 12v battery and measuring volts/amps with the motor prevented from rotating. !.6A, 0.37V, which I make 0.23 ohms.

I was going to just buy a 4QD controller, but then I found these

which claim to be good for 60A and are very cheap. However, if I was unwise enough to apply for whack to 2 motors in parallel at very low speed I’d have ~50A per motor. First thought is to have 2 controllers, perhaps with a 2 gang pot, but I’d experiment with just connecting one pot to both controllers. This would allow me at some time in the future to play about with automatic slip control

Of course the controllers might be current limited, the blurb says

Input Voltage: DC 10V-55V

Max. Current: 60A

Output Voltage: Linear with load

Continuous Current: 40A

Speed Range: 0% to 100%

Control Frequency: 15KHz

Regulation Method: Potentiometer(linear)

Regulation Type: Regulating Current

Forward & Reverse: Support

Digital Location: 0-100

Suitable for: Brushed DC motor

 

Anyone got any constructive comments

[Robert Atkinson 2Participant @robertatkinson2]

Looking at the photos of the PCBs I doubt the unit has any active current limitin. That said the 0.23 ohms you have measured is very much worst case. You have not included the resistance of the wiring, fuse (you are going to put a fuse in circuit?) or the internal resistance of the battery. Added to this the current will fall as soon as the motor starts to turn. The unit will almost certainly use MOSFETs. These genally have a puls rating at least 5 times their DC rating So may well be OK. That said itwould be safer to use one unit per motor and they are cheap enough.
You could use a single potentiometer for two controllers. Connect all three wires from one controller to the pot (short out the switch wires or use a separate switch, possibly double pole to be safe) and just the black and yellow wires (CCW and wiper connections) of the second controller. You will have to sort out the forward/off/reverse switch as well. It should be possible to use a single pole switch (the original) but I can’t tell without the unit os circuit. Worse case is use a double pole switch.

Robert.

[duncan webster 1Participant @duncanwebster1]

Thanks, I’ll order a couple. As you say it’s worst case as if I were unwise enough to give it full whack from standstill I reckon the wheels would spin, and so very rapidly drop the current.

[BazyleParticipant @bazyle]

I am a little confused by the extra switch – does it have two ranges?

Forward reverse support ?? eh?

But looks a useful unit ie cheap.

[duncan webster 1Participant @duncanwebster1]

Forrards and backards as we’d say on God’s county

[noel shelleyParticipant @noelshelley55608]

With all this rain, Ahead and astern may be more appropriate ? Noel.

[Author]

Posts