# 24v motor on 12v battery?



## johnogbirk (Jun 4, 2011)

Hello;
Im trying to make a small garden tractor, and have few ?

If I feed my 24v DC motor with 12v DC, will it turn ½ speed when loaded?
What will 12v in a 24 v motor do to the efficiency at, say, ½ and full load?

When I decide size of fuse, can I simply make a test run and use the temperature of the motor as a guide to the motor being overloaded?

Say, run the motor at ½ my expected load. Check temperature, run again at 3/4 of expected load etc.

Its small, Afikim PR4P16RX ver 3 24v.
I want to run without controller, just on-off... 

Thanks guys, John from Denmark


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## rmay635703 (Oct 23, 2008)

Its hard to answer but generally speaking, yes the motor will turn at roughly half the same speed at the same load.

Effectively you will draw the same or more amps to spin at half the speed, the efficiency is reduced when amp draw is higher. (more amps at lower voltage through the same wire is a bit less efficient)

Other things can go on though, for example spinning at a lower speed may need much less power than spinning at the rated speed so you may end up traveling a bit faster than expected.

My EV running at 72 volts goes about 50mph at 48 volts it goes 38mph which as you can see is not 2/3s the speed.

Amp draw is lower as well.


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## piersdad (Aug 16, 2008)

the motor will need to be able to handle at least 20 amps to drive the tractor and that with out much load
if it is as light as a mobility scooter and say 6 km/h then 15 amps at 12 volts but any heavy load or rough ground and the current will go up
check the amp rating or horsepower or wattage of the motor 12X15 =180 watts =.24 hp
1 hp = 746 watts
at 12 volts 1 hp current would be 62 amps
at 24 volts 1 hp " " " 31 amps


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## johnogbirk (Jun 4, 2011)

Thanks to you both.
The project is slowly starting to run.
I´ve tested with 12 v on the 24v motor, and gear ratio for asphalt.
Now I´m changing sprockets, and going into the garden.

Report soon to come.
Cheers, john


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## elektroboy (Jun 22, 2011)

Hi,
A lot is said already, but here's something to add.
Going 'off-road' will cost a lot more power then on road.
I can't find your motor on the internet.
It is important to stay under the maximum current for this motor.
With just testing on temperature you might be too late.


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## johnogbirk (Jun 4, 2011)

elektroboy said:


> Hi,
> A lot is said already, but here's something to add.
> Going 'off-road' will cost a lot more power then on road.
> I can't find your motor on the internet.
> ...



I thought I would run the motor at ½ the expected load, after ½ an hour check temperature. Will ½ an hour be long enough?

Would I need an amp meter to tell the size of my fuse?
cheers, john, Denmark


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## piersdad (Aug 16, 2008)

1/2 hour would be some indication an amp meter would be the first and best investment but make sure it can register at least 30 amps.
that way once the vehicle is moving you can continuously watch the current and know exactly what the motor is doing


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