Newbie with 24v motor question

[Newfoundland]

Hi all newbie here.
I have a mobilty scooter that I'm turning into a ride on landrover for my lads. The electrics are knackered but the motor etc is fine if I run a wire straight off the batteries. The problem is the motor runs at full speed like this and is too fast. So can I put a speed controller inbetween the battery and motor without any problems?
Thanks for any advice you have, matt

[Newfoundland]

Anybody?

[piratepaul]

Yes you can.

The easiest way is to use a potentiometer but it is inefficient at low speed.

That is assuming it is a commutator motor, as it works when you wire it to a battery it probably is...it can't be a stepper motor any way.

I work nights and do 50 hours a week just now, I also have a trawler an am expecting storms, don't know when I will be back on here but I will be, time is in short supply.

Tar&stuff.

[piratepaul]

A variable resistor would be better than a pot.
It would be inefficient at low speed because it would dissipate power in the resistor, as resistor resistance is 0 at full throttle it would be efficient at full throttle.

Tar&stuff.

[Pauldf]

I'm pretty sure they usually use some sort of pulse to control the speed. The big disadvantage of using resistors is they will get hot (not the best thing to have with kids) and also use the battery up faster.
You can probably buy a 24v motor controller for not a lot of money.

[Newfoundland]

Thanks for the replies. Yes safety is my main concern. I've tried a speed controller off eBay that had a potentiometer and 3 pole switch for reverse, but I don't think the amp rating was very high. The heat sink got very hot quickly then stopped working all together. I've seen some 24v electric bike controllers for around 20 notes on ebay so I might try one of those. They don't have reverse so could I have a switch after the controller that reverse polarity? Many thanks for your advice so far. Matt

[David]

Hello. Sounds like a fun project for your lads!
Yes, Speed controllers for DC motors use pulse control - the only place I remember seeing restive control was in model locomotives, where the current drain was small.
Batteries can supply surprising amounts of current (because of their low internal resistance), and a very hot heat sink is always a sign of excessive current. You could reverse the motor by having a two pole switch which just transposes the wires, but the switch must be adequately rated (i.e. big enough!) Don't attempt to switch from forward to reverse unless the motor is stopped - interrupting the DC current when it is feeding an inductive load could lead to arcing.

[Newfoundland]

Thanks dave. As it's a 24v motor with two 12v batteries in series what if I just use one battery, would this reduce the output as the scooter was rated at 8mph wich is a bit too quick. I can't test as the original batteries are knackered and need too buy new ones. Thanks matt

[Pauldf]

Reversing a motor will depend on what type of motor it is, if it has a wound rotor and a wound stator then just swopping the supply over doesn't cause it to reverse. You'll need to reverse just the rotor OR the stator windings.

[Newfoundland]

Thanks Paul. I tried swapping the wires around when I wired it straight off the battery and it reversed. Would just using one battery slow it down slightly as it's a bit quick at full speed? Thanks