replacing 24v motor with 48v motor in existing system

[rsouthgate]

I'm trying to re-purpose a garage door opener to use as a pool cover opener. The device has a 24v DC motor that doesn't seem to be too happy pulling the pool cover (it works but stops randomly - I'm assuming because of over-current protection but no indication is given).

I was thinking of replacing the 24v motor with a 48v DC motor (since these are popular with e-scooters and seem cheap). But I need some advice on how best to do this. The existing motor has a two wire connection on the PCB and an earth connection. I assume the 24V on the two wires reverses to switch between winding and unwinding. On the gearing there is a small PCB with a chip and what I imagine is a magnet connected to the spindle and this plugs back in to the main PCB and tells the whole thing when to start and stop - and it's this gearing and rotary feedback device that I want to retain.

So if I can find a 48v motor that can accept the same gearing mechanism what is the best way to drive it from the +/-24v output? Is there a bi-directional relay for switching 48v from a 24v input? Is it unrealistic to consider stepping up the 24v to 48v given that I'm looking for more power? The whole thing does have a grunty coil transformer for 240vAC -> 24vAC... Not sure what current it would be rated to though... is there a way of finding out?

Is there another way of doing this that I haven't considered?

 

[Bluejets]

Is there another way of doing this that I haven't considered?

Yes.
Leave all existing gear in place and gear down the drive mechanism by 50%.
Much like starting a car in first gear instead of top gear.
I wouldn't imagine high speed would be a factor in covering or uncovering a pool.

 

[crutschow]

As an alternate to a gear mechanism, you might consider a small, cogged timing belt with a 2:1 pulley configuration.

 

[Bluejets]

alternate to a gear mechanism

The ratio reduction I referred to wasn't necessarily "gears" as such.
It is basically a term for ratio reduction.
i.e. gear-up, gear-down, in top gear etc.

 

[Minder]

So if I can find a 48v motor that can accept the same gearing mechanism what is the best way to drive it from the +/-24v output? Is there a bi-directional relay for switching 48v from a 24v input? Is it unrealistic to consider stepping up the 24v to 48v given that I'm looking for more power? The whole thing does have a grunty coil transformer for 240vAC -> 24vAC... Not sure what current it would be rated to though... is there a way of finding out?
Is there another way of doing this that I haven't considered?

Just going from 24v to 48v motor will not guarantee more torque, for a DC motor, torque is directly related to current.
To get an idea of the present motor size, is to check if the transformer has a Va rating on it.

 

[rsouthgate]

To get an idea of the present motor size, is to check if the transformer has a Va rating on it.

I don't see a Va rating but for secondary winding it says 24V AC @ 5.2A continuous, 14A @ 25% duty cycle. So does that mean a VA of 125?

I don't understand the 14A 25% duty cycle though... I guess that means it can peak to 14A but for how long? At its current RPM I'd expect it to run continuously for approx 3 mins to fully retract cover.

Existing 24V motor is marked as ATA #87282 CGMA 18V2 24VDC

 

[rsouthgate]

Gearing does sound like a better solution. And this is probably a mechanics question rather than one for the electronics forum, but this is the existing gearing mechanism. I'm struggling to see how I could further reduce this without moving the motor (which I would prefer to avoid since it would mean reworking the mounting / housing).

The other option i was thinking about was a big torsion spring on the actual roller itself to balance the cover and therefore lessen the required torque of the motor... in much the same way garage roller doors are balanced.

 

[Minder]

Bit of a job to change the gearing, using a higher torque motor may require a larger supply transformer.

 

[crutschow]

I don't understand the 14A 25% duty cycle though... I guess that means it can peak to 14A but for how long? At its current RPM I'd expect it to run continuously for approx 3 mins to fully retract cover.

That duty-cycle is likely for less than 3 minutes of ON time, more like the time it takes for a garage door to operate.

 

[Bluejets]

I'm struggling to see how I could further reduce this without moving the motor

Pulleys and vee belts on the output. Or another gearset.
As you say, this is not a mechanical forum.
Look at what existing pool cover motors might use.