Electric mobility scooters

I need to control 1 DC brushed motor fwd and rev. Have 24 vdc lead acid battery ( 2 x 12 in series) I have bought controllers that says rated for 25 amps ( joke) I think maybe I can use one of those to control an big IFET . I also looked at a controller called Sabertooh 2x25 , can I strap both out puts to feed 1 motor. I have several scooters that were free, all have controller failure s. No schematics are yet found, thanks ,Daryllynn at kb5zxm @ yahoo or gmail.

You might want to try using an automobile starter motor solnoid they will operate 100s of amps and are controled by a small relay or switch. Most car parts stores have them gust ask for a starter soloind for a 65 Ford Mustang or truck. Golf cars also use them.

Sammy

Daryllynn: I need to control 1 DC brushed motor fwd and rev. Have 24 vdc lead acid battery ( 2 x 12 in series) I have

Be careful with the motor and with the batteries - those motors have immense torque, and if you aren't careful the batteries can become an impromptu welder very easily (no joke).

First - you should measure (or find out) what the maximum (stall) current for the motor is; that will allow you to reliably size the controller you need. You need a controller which can handle at least this amount (ideally, add 5-10 percent extra as a buffer).

Daryllynn: bought controllers that says rated for 25 amps ( joke) I think maybe I can use one of those to control an big IFET .

Those controllers are likely FET based, and probably will handle that amount of current (though only with the proper heat-sinking - if you are talking about the small and cheap chinese controllers - you'll want to validate the heat-sinking used - but if the controller electronics are legit and not cheap knock-offs, it will probably work ok).

I wouldn't try using those controllers to control something bigger - especially not something you have to build yourself. Unless you have a lot of experience, DIY h-bridges (which you'll need if you want fwd/rev control - a single FET won't do it) can quickly turn into money pits...which isn't a big deal if you are willing to sink that kind of money for a learning experience - but if your goal is of a more practical nature, then spend the money for a proper pre-built h-bridge controller.

Daryllynn: I also looked at a controller called Sabertooh 2x25 , can I strap both out puts to feed 1 motor.

AFAIK, you can't bridge/parallel the Sabertooth - but I might be wrong. Download the datasheet, and/or contact the manufacturer:

https://www.dimensionengineering.com/products/sabertooth2x25

It's a FET based bridge - in theory you could parallel it, but it may use a design that precludes this. Still, 25 amps is nothing to sneeze at. Depending on your motor, it might not have a very high stall torque, and this controller would work great (use two motors, then, and have a differential steering system for a robot - or a homebrew segway - if that's your aim).

Daryllynn: I have several scooters that were free, all have controller failure s. No schematics are yet found, thanks

You won't find such schematics. I work with a guy here in Phoenix refurbishing and donating old electric mobility scooters and chairs. We also use leftover parts to build art and robotics projects. I'm pretty familiar around these machines. You aren't going to find schematics for the controllers, because they are all proprietary medical-grade systems; any alteration to such a controller would void the protections the manufacturer has in place as sellers of medical devices. They are designed to be very difficult to use as a custom motor controller, with a variety of in-place fail-safe systems designed to make the system shut down in an error mode for the slightest of issues. The controller PCBs themselves tend to be potted in epoxy or some other conformal coating, making it difficult or impossible to work on or re-use the components of the controller for any other purpose. They are configurable as well - but typically require a special configuration pendant device, which costs a boatload of money (and most only cover a subset of all chair controllers).

That said - it can't hurt to open the controller up and take a peek; you might be surprised at what you do find.

Make sure that you always install a proper slo-blow fuse of the correct maximum total current rating for the system, as close to the positive terminal of the battery as possible. This will help prevent some serious issues as you work on things.

Also - if you plan on using any of these items for a robot base or similar - always work on it (especially during testing and software development) with the wheels off the ground. Failure to do so can result in a heavy, dangerous, and difficult to stop runaway incident occurring. These machines are very heavy, and very unforgiving. They can seriously injure and maim if not treated with respect and understanding. It is also imperative, if you are using this for a robot, that you design into the system at the beginning some method of "emergency stop" - both a physical and a remote system. Ideally, you would have something that could be physically removed (via a highly-visible grab strap) to cut the power from the battery to the robot instantly; the secondary system would be an emergency one-way cut-off button (or a large red button with a separate relay controller to cut the power). Last would be a relay to cut the power controlled via a hand-held remote controller (kinda like a vehicle kill-switch with a key fob controller). All of these devices should "fail safe" - that is, if they fail, they should fail in such a manner as to kill the power to the robot.

All of this should be designed and developed first - before you get the motors rolling and the machine moving, because like all security systems, bandaid patching it in later will lead to a less-than-perfectly-working system. It is one system that you don't want failing at the wrong moment.

Good luck with your project, and I hope this post helps you.

:D

Daryllynn: I need to control 1 DC brushed motor fwd and rev. Have 24 vdc lead acid battery ( 2 x 12 in series) I have bought controllers that says rated for 25 amps ( joke) I think maybe I can use one of those to control an big IFET . I also looked at a controller called Sabertooh 2x25 , can I strap both out puts to feed 1 motor. I have several scooters that were free, all have controller failure s. No schematics are yet found, thanks ,Daryllynn at kb5zxm @ yahoo or gmail.

25A controller will probably fry, such motors are a small fraction of an ohm and can pull 100's of amps in stall.

Something rated for 50A continuous and 100 peak would be better.

However how big is the motor - do you have any information on it? Do you know how to do a four-terminal resistance measurement on the winding.

Roboteq do good controllers I am told. However if you got the motor from a mobility scooter the controller from the scooter is the obvious controller to use.

MarkT: 25A controller will probably fry, such motors are a small fraction of an ohm and can pull 100's of amps in stall.

Not always - I used to think this too, until one of the guys that helps my friend and I (we're a varied at times "team") was using a large Vantec controlled by an Arduino - and was having problems getting it to work (it ended up being an issue with the controller needed a specific PPM pulse-width timing that the Servo library wasn't giving, as seen on a scope - we had to slightly hack the library to get it to work properly). Anyhow, in the course of trying to diagnose that, we thought that the motors might be pulling a ton of current and somehow reseting the Vantec and/or the Arduino.

He went home an measured the stall current, and found it to be really low - well under 10 amps, actually. The running current under a load was an amp or two.

That isn't to say these motors are all like this - in reality, most do have extremely high stall currents, and fairly large loaded running currents.

MarkT: Something rated for 50A continuous and 100 peak would be better.

If it's needed, sure - but if the motor doesn't need it, buying something that large can be an expensive overkill solution.

MarkT: However how big is the motor - do you have any information on it? Do you know how to do a four-terminal resistance measurement on the winding.

Finding information on these motors can be like pulling teeth - you certainly won't get it from the chair manufacturer, mainly for the reasons I already stated. Model numbers printed on them are typically "house numbers" for the chair manufacturer, and can't be generally looked up. That doesn't mean you shouldn't try, as not all chair manufacturers use customized motors.

MarkT: Roboteq do good controllers I am told.

Yes they do; so does Vantec (only the older controllers had the pulse width issue, btw). Either would be a good solution for high-current control of wheelchair gearmotors. Just be prepared to spend a boatload of money for such a solution (esp from Roboteq - they make Vantec look low-cost).

MarkT: However if you got the motor from a mobility scooter the controller from the scooter is the obvious controller to use.

Again - likely not, as I covered before; these controllers have numerous safeguards put into place to keep them, well, safe for their medical purposes. If you don't give them -exactly- the right signals (whatever they are - because the information isn't published) - if they are off by small amounts, or certain checks don't pass - the controller will go into an error mode. I've seen it happen because of dirty carbon brushes on a motor (that was fun to diagnose - talk about an intermittent problem!). Finally, the diagnostics and setup pendants needed to get the most out of the controller (or at times, needed to dial them back a bit!) are expensive when you can find them on the used market (they are only sold new to authorized repair services for the manufacturer - so when they are sold on the secondary market, they can sometimes command several hundred dollars - depending on the model and age).

Mobility scooters have one motor to drive both wheels, its usually pretty chunky (except for the lightweight folding scooters which are underpowerd).

A 10A stall current suggests a working current of 1 to 2A, which isn't enough at 24V for traction I reckon.

You might get a 43A BTS7960B motor controller like below and see if it will adequately control your motor.

http://www.ebay.com/sch/i.html?_from=R40&_sacat=0&LH_BIN=1&_nkw=43A+BTS7960B&_sop=15