[Electricboogaloo]

So I'm most of the way done building an electric cart for my kids...and myself really. I used 2 500W 36V DC motors, one on each rear wheel, and some cheap ebay 500w controllers.

The controllers didn't have reverse or electric braking so I got 2 DPDT stomp switches and placed them where the brake would be (both pressed by the same pedal). The speed controllers output runs up to the switches and the NC function send the power to the motor for forward. The NO function flops it to Rev.

This worked fine but the switches are not rated for the current and burn up. So I'm thinking I'll hook the switches up to some relays that can handle the amps.

Now, my actual questions.
1. Is it okay to suddenly switch the direction of power or will this harm the controllers/ motors? I was surprised that when you press the switch, you get pretty good braking at speed and only have to apply (reverse) throttle at very low speed to stop completely.

2. Is there a much better/ simpler way to add e-brakes to a controller that doesn't have them.

Thanks!

 

[MesquiteTim]

Put actual brakes on it and only switch forward to reverse when no current is flowing.

 

[catphish]

1. Is it okay to suddenly switch the direction of power or will this harm the controllers/ motors? I was surprised that when you press the switch, you get pretty good braking at speed and only have to apply (reverse) throttle at very low speed to stop completely.

You need to think about where the energy is actually going. It has to get converted to heat in 1) the motors 2) the wiring or 3) the controller.

You have already discovered what happens when this happens in the switches, and if it happens in the eletronics of the controller, the result will be similarly unpleasant. The motors might be able to dissipate the heat if you just short circuit them with a powerful enough switch, but you need to be very careful not to overheat the windings.

 

[Electricboogaloo]

Thanks for the insight everyone. I do intend to add mechanical brakes but the whole cart is made from scratch so it's a time consuming process. I also would really like to have regenerative brakes but am having a hard time getting info on them.
So, follow up question, Does anyone know where I can get a 36V motor controller with regen braking for Brushed motors? All of the speed controllers I see are either cheap ones like I have or, the ones that have more features are set up to work with brushless motors with Hall sensors. Ideally a 1200W controller with reverse as well.

Thanks again!

 

[brian_]

Does anyone know where I can get a 36V motor controller with regen braking for Brushed motors?

You're not going to find a controller with regenerative braking for a series-wound motor, although in the unlikely case that your motor is shunt wound (separately excited, or SepEx - the Curtis trademarked term) a good controller should have regeneration.

 

[piotrsko]

To do reverse or regen in a series brushed, you need to be able to control the field windings separate fron the comm windings since brushed motors will self feed back and go ballastic on voltages. There were a couple of chinese controllers that advertised regen, but afaik, they didn't work or let the smoke out.

 

[Electricboogaloo]

Thanks for the info everyone. I'll probably try the relays as a temp solution, since the reverse current is only going to the motors (right?) And they don't get very warm at all on my test drives so far. Then I'll see about getting some motorcycle brakes adapted to the driveshafts.

 

[brian_]

To do reverse or regen in a series brushed, you need to be able to control the field windings separate fron the comm windings ...

Right... and if the field and armature currents are different it's not a series motor any more.

 

[piotrsko]

Right... and if the field and armature currents are different it's not a series motor any more.

the field windings size and power capability determine if it is a series wound capable or not, cant use a sepex wired in series for long and develop much power. Besides we're talking switching for regen capability

 

[brian_]

the field windings size and power capability determine if it is a series wound capable or not, cant use a sepex wired in series for long and develop much power. Besides we're talking switching for regen capability

And you can't run the field of a motor designed for series operation at armature voltage, so series and separately excited motors are not really interchangeable - a typical SepEx controller won't have the field current capability to properly operate a motor which is wound for series operation. So we're back to the problem that a series motor isn't suitable for regen with any readily available controller.

Sure, build a Rube Goldberg control system of relays (connecting the field in series with the armature one way for forward, in series with the armature the other way for reverse, and to the field terminals of a SepEx controller for regen) and you can reconfigure the control of the wrong motor to reverse and to regenerate to a limited extent.

 

[MattsAwesomeStuff]

Sure, build a Rube Goldberg control system of relays (connecting the field in series with the armature one way for forward, in series with the armature the other way for reverse, and to the field terminals of a SepEx controller for regen) and you can reconfigure the control of the wrong motor to reverse and to regenerate to a limited extent.

So you're saying there's a chance?

Nothing hokey about using relays to flip forward/reverse, that's how electric forklifts worked for 60 years, works just fine. Abusing a sepex controllers on a series motor masqerading as an only-technically-sepex motor because you actually have independent access to the terminals... mmmmyeah I mean, it's possible and I'd love to see it just because it's entertaining to see something be built the wrong way and brute forced into compliance, and actually observe what you had to settle for for performance... but I dunno that I'd recommend it unless someone enjoys the challenge of it for its own sake.

 

[piotrsko]

I see it as 2 relays and a couple of diodes on some sort of limited system field battery. Might just need one dpdt relay and the backside of dual throttle pot

If you stay below the comm zorch voltage why cant a series motor be run parallel field? Wouldn't be as efficient, low voltage, and suck current like a short......