1. Home
  2. Hobby Electronics Basics
  3. Scale Model electric train - motor control

Scale Model electric train - motor control

My uncle has a 7 1/2" guage train track. He currently has 1 gas and 1 steam engine. We would like to make an electric train that would be very simple and safe to operate, such that an average 10-year-old could manage it.

I am planning to use a 12V car battery/batteries for power, and I have an extra 2000-lb winch motor I can use. I have taken the gearing out of it, so the shaft spins quite fast. I will make a PWM circuit for it, with either a set speed (or a couple of them), and basic on/off and forward/reverse. If it has enough power, I would have a normal throttle for the big kids (adults :) ) to use. The body I am going to use for the train weighs about 150lbs.

I'll use mosfets to link the PWM to the motor, but I'm unsure of a few things:

- How do I measure/calculate how much current my motor will draw, so I can select the proper mosfets?

I have hooked the motor straight to a battery, and if it's not more than the 10A my meter can handle, I'd measure that, but I'm more concerned about surges and variations due to load etc.

- How can I avoid burning the motor out if it stalls (too much weight/ uphill/stuck)

Being a winch motor, I don't know if I have to worry about it. Wouldn't winch motors have that kind of thing built in?

- Is there a problem if the train goes downhill? Will it feed back and melt stuff? If I use a controller with a current feedback/current set- point, will that keep the motor from going too fast?

And, of course, is there anything else I should consider? (Yes, I will be using fuses!)

I have considered buying a prebuilt controller, and I'm quite happy to, so long as I know it will handle the current. It would be fun to make my own though ;)

Reply to
Echinos
Loading thread data ...

Ideally, you would read the nameplate data, but I'm assuming there is no nameplate. I built a drive using HRF3205 MOSFETs with a HIP4081A MOSFET driver. It can handle up to 75A with heat sinks. Your 12VDC winch motor probably has much less current draw than that.

That's right. In my experience, a typical DC motor will only draw 20%

- 40% of its full-load current under no load.

If your motor doesn't already have thermal overload protection, one way is to limit the current to the motor with fuses or a circuit breaker. A better way is to use commercial motor overload protection relays (e.g. Allen-Bradley)

Maybe.

If the torque applied to the motor shaft is great enough, it will become a generator. The generated energy will be fed back to the battery or dissipated as heat in the drive. This can be bad if the voltage gets too high. Dynamic braking resistors are sometimes required to brake the motor in these situations - the motor's energy is dissipated as heat in the DB resistors.

It's a personal choice. Building your own drive can be very frustrating, but ultimately rewarding. It could be cheaper too, depending on how many components you fry :-).

Reply to
bennet

See if you can find specs on the motor. Look for stall current. That would be you minimum specs for controls.

Tom

Reply to
Tom Biasi

Yeah, from what I've seen by poking around with google, I will probably be OK with 20 or 30 amps. The motor should be about 1hp.. I might be able to calculate something using that.

Is there a way to make a controller hold the motor at a certain speed & current, even though it is going downhill?

I'll look into this - if I get ambitious, I might try regen braking too.

Well, the controller itself is not really what I'm trying to save money on, it's more the motor. It seems that this may be made much easier if I were to buy a motor, so I know all the specs etc, but this winch motor seems like it should do the job nicely, if I can get the controller part worked out.

Reply to
Echinos

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.