DC motor controller

mchammer

Hi ,

Not sure if this is the right spot for this but I'm trying to find a replacement for a 12v dc motor speed controller for a motorised golf trolley. I bought one on ebay, it's a 12v 15a and hooked it up but it only turns the wheels very slowly and the power output in terms of amps is hardly registering at all. I would have thought the controller should be able to output up to 15amps via the potentiometer??
http://www.virtualvillage.com/12v-15a-dc-motor-speed-control-pwm-hho-rc-controller-003601-055.html

They also have a 30amp controller which I might try?? anyone have any ideas?
Thanks
MC

brightspark

can you give more information about the motor?

mchammer

brightspark wrote: »

can you give more information about the motor?

it's a 180watt motor - not sure if its brushed/brushless - you can see what it looks like in the link below

http://golfglider.com/category.php?cat=2

cheers

Bruthal

If it has 2 wires to it then its a brushed motor, a brushless one would have 3 wires into it. Anyway, they would likely use a pulse width modulation controller (pwm) to vary the speed of the motor, which just switches the motor fully on and off rapidly, the on to off ratio gives the speed depending on the potentiometer position.

I would of thought the 15 amp one would of worked alright.

DublinDilbert

180w @ 12v should be about 15A.

Is there a current limit pot or max voltage output pot on the controller?

Are you using the correct input trottle pot? Is it hooked up correctly?

Put an ammeter in series with the motor and volt meter in parallel, that will tell you what's happening...

Bruthal

If it is a pwm controller, could have the input/output mixed up alright. Some photos might help.

mchammer

DublinDilbert wrote: »

180w @ 12v should be about 15A.

Is there a current limit pot or max voltage output pot on the controller?

Are you using the correct input trottle pot? Is it hooked up correctly?

Put an ammeter in series with the motor and volt meter in parallel, that will tell you what's happening...

thanks. the max continuous current is 15a.. had a dc power supply with ammeter and the normal amps consumed by a normal working unit is about 5-7amps and you would be getting good speed at that... no amps really registering with this controller that i can see (its an analogue ammeter)
have tried it with a 10k potentiometer and the 22k it comes with and very slow altogether.... will take a few photos tomorrow and stick them up
cheers

DublinDilbert

Maybe you just got a faulty speed controller?

Are you using this with a battery or off a power supply? Any chances you've got a flat battery??

Bruthal

Neighbour was just showing me his golf trolley an hour ago, wont move at all. Its the motor controller anyway, so i might make a pwm one up for that. Have you any mos-fets dublindilbert:)

mchammer

DublinDilbert wrote: »

Maybe you just got a faulty speed controller?

Are you using this with a battery or off a power supply? Any chances you've got a flat battery??

right... managed to take some photos of the controller.. apologies for the crudeness of the setup.. and the rather untidy workbench!

basically using a 12v transformer and hooking it up to a capacitor and bridge rectifier to make a crude 12v dc power supply.. have an ammeter hooked up so i can see power usage on anything that runs off it..
I have this hooked up to the controller and the output of the controller connected to a 12v coolbox/fridge which runs about 5 amps...

The weird thing is the controller worked perfectly with the coolbox and in using it to dim 12v lightbulbs and that kind of thing... I hooked up a small 12v tyre inflator/compressor thing which normally draws about 5 amps and it worked but not very well kinda the same as the motor in the golf trolley.

I'm thinking that these motors probably require more current at start up and the controller is limiting the start up current too much?? any ideas???

DublinDilbert

mchammer wrote: »

right... managed to take some photos of the controller.. apologies for the crudeness of the setup.. and the rather untidy workbench!

basically using a 12v transformer and hooking it up to a capacitor and bridge rectifier to make a crude 12v dc power supply.. have an ammeter hooked up so i can see power usage on anything that runs off it..
I have this hooked up to the controller and the output of the controller connected to a 12v coolbox/fridge which runs about 5 amps...

The weird thing is the controller worked perfectly with the coolbox and in using it to dim 12v lightbulbs and that kind of thing... I hooked up a small 12v tyre inflator/compressor thing which normally draws about 5 amps and it worked but not very well kinda the same as the motor in the golf trolley.

I'm thinking that these motors probably require more current at start up and the controller is limiting the start up current too much?? any ideas???

It sounds like the controller has a hardware current limit in it of 15A and will not pass anything more than that. Your motor will probably need 40/50A for a split second to get it turning then its current will drop right back. I would imagine if you pop a volt meter across the motor terminals you'll probably have 1V or something tiny on it.

Have you looked inside the controller? it might have a pot to set the h/w current limit for it?

Just one other thing, your ammeter is in series with the supply (Ibat), you probably should also have one in series with the motor too. As your PWM'ing the motor the supply current is not equal to the motor current.

If you assume the controller is 100% efficient Pin = Pout.
Pin = Vbat x Ibat = Pout = Vmotor x Imotor

What I would guess is happening is
Imotor = 15A (current limit)
Say Rmotor = 0.1 Ohms (armature)
=> Vmotor = Imotor x Rmotor = 1.5V

Vbat = 12V

12 x Ibat = 1.5 x 15 = 22.5

Ibat = 22.5/12 = 1.8A

The 1.8A would barely register on the ammeter that your using as it has a max full scale of 30A by the look of it.

mchammer

DublinDilbert wrote: »

It sounds like the controller has a hardware current limit in it of 15A and will not pass anything more than that. Your motor will probably need 40/50A for a split second to get it turning then its current will drop right back. I would imagine if you pop a volt meter across the motor terminals you'll probably have 1V or something tiny on it.

Have you looked inside the controller? it might have a pot to set the h/w current limit for it?

Just one other thing, your ammeter is in series with the supply (Ibat), you probably should also have one in series with the motor too. As your PWM'ing the motor the supply current is not equal to the motor current.

If you assume the controller is 100% efficient Pin = Pout.
Pin = Vbat x Ibat = Pout = Vmotor x Imotor

What I would guess is happening is
Imotor = 15A (current limit)
Say Rmotor = 0.1 Ohms (armature)
=> Vmotor = Imotor x Rmotor = 1.5V

Vbat = 12V

12 x Ibat = 1.5 x 15 = 22.5

Ibat = 22.5/12 = 1.8A

The 1.8A would barely register on the ammeter that your using as it has a max full scale of 30A by the look of it.

Thanks for the explanation starting to make sense of it now

Cheers

DublinDilbert

robbie7730 wrote: »

Neighbour was just showing me his golf trolley an hour ago, wont move at all. Its the motor controller anyway, so i might make a pwm one up for that. Have you any mos-fets dublindilbert:)

How much current are you looking to pass? I'll see what i've got in the lab here. They can always be paralleled up too. The top side fly back diode will need to be fairly chunky too...

Bruthal

DublinDilbert wrote: »

How much current are you looking to pass? I'll see what i've got in the lab here. They can always be paralleled up too. The top side fly back diode will need to be fairly chunky too...

Probably similar to the OP here, but i think the neighbour is going to splash out and get a replacement controller. Will end up being close to €100. Making one would be just as good and cost almost nothing.

mchammer

robbie7730 wrote: »

Probably similar to the OP here, but i think the neighbour is going to splash out and get a replacement controller. Will end up being close to €100. Making one would be just as good and cost almost nothing.

just an update to the above - I ended up hedging my bets and went for the next size controller up i.e 30amp and it has worked nicely. Will have to see how it does on the course over a while but so far so good and a nice smooth start on it. Will take a few pics and post them up later...

http://www.virtualvillage.com/36v-30a-dc-motor-speed-control-pwm-controller-rc-models-003510-003.html

The original controller on the manufacturer website they are looking for €140 and this one cost €20 delivered from ebay...