36v 800W vs 48 1000W

Electric Motors and Controllers
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cero   10 mW

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36v 800W vs 48 1000W

Post by cero » Aug 19 2013 3:37pm

Can someone explain what is the differnece betwen 36v 800W hub motor and 48v 1000W, you can find both on ebay.
I'm figuring, if I put 48v into 36V 800W motor i get 1000W out of it with same currnet. Heating of motor winding is proportional to current going through motor, but that stays the same because of current limit in controller.
So I'm a little confused why two types of maybe same motor?

chilledoutuk   100 W

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Re: 36v 800W vs 48 1000W

Post by chilledoutuk » Aug 20 2013 10:38am

Most 36v controllers can handle 48v but the LVC will be setup for 36v batteries normally something like 31.5v.

Something to Keep an eye on at least.

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serisman   100 mW

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Re: 36v 800W vs 48 1000W

Post by serisman » Aug 20 2013 11:37am

There *may* be a difference in the winding of the motors that would affect the speed (RPM).
So, if you put 48V into the 36V motor it *might* spin at a higher speed than putting 48V into the 48V motor.

As an example, cell_man offers a direct drive motor with 3-4 different winding options:
http://em3ev.com/store/index.php?route= ... uct_id=111
The listed RPM values are with a 36V input (I think). Each motor would spin a percentage faster with a 48V input.

The winding will determine the speed at a certain voltage. You can (almost) always go to a higher voltage for a faster speed (or a lower voltage for a lower speed).

The wire thickness will determine maximum current which will determine the torque. You usually don't want to increase the current too much (this is how you burn out a motor... the wiring heats up and the insulation melts causing a short circuit).

Wattage is just voltage times current and doesn't mean much by itself (other than a comparison to other motors that are fed similar voltages). For a given motor, you can increase the voltage while keeping the current the same, and the wattage will increase. The heat generated is mostly due to the current NOT the wattage.

So, given the same winding and the same wire thickness a 36V 800W motor is probably the exact same as a 48V 1000W motor. If they have a different winding and/or wire thickness they are different, but either one could be made to go faster by increasing the voltage.

Maybe the seller can provide more information?

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serisman   100 mW

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Re: 36v 800W vs 48 1000W

Post by serisman » Aug 20 2013 11:59am

Here is another example motor from cell_man that has different winding options:
http://em3ev.com/store/index.php?route= ... duct_id=52

So, in this example, the same motor housing can be wound in one of 4 different ways that affect the speed (at a given voltage).
There are 6 turn, 8 turn, 10 turn, and 12 turn options. They are all rated for 25-30 A. This probably means that the wire size is different (i.e. they use a thinner wire to be able to get more turns wound), but because there are more turns available the end result is you can draw around the same current.

A motor wound with 8 turns and fed with 36V (320 RPM) could be marketed as a 36V 800W motor (22.2A).
The same motor could also be marketed as a 48V 1000W motor (20.8A) but would spin faster at ~420 RPM.
Or, a motor marketed as 48V 1000W could actually be wound with 10 turns and fed with 48V (~340 RPM) and would be a similar speed as the 36V 800W motor that was wound with 8 turns and fed with 36V. Feeding this 10 turn motor with 36V would spin slower at 255 RPM and you would still only want to give it around 22.2 A or about 800W.

So, the marketed voltage/wattage of a motor doesn't tell the whole story. You would also want to know the RPM at that voltage/wattage.

cero   10 mW

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Re: 36v 800W vs 48 1000W

Post by cero » Aug 20 2013 1:42pm

serisman we are thinking the same way, except I didn't know that thing about turns. I'm still not convinced that chineese, as simple as they are, are using voltage/ power as a sort of marketing trick.

Btw. In my case, I bought cheap 36V 800W motor and controller set, I tested it (400km) with 62V, worked ok, so now I'm suplying it with 48v lifepo4 set. Compairing to some guy, who has default 48v 1000W power set on his bike, on the road we achived the same top speed. I'm just thinking of some simple motor mod: puting termal switch (120°c) as nearest as possible to motor windings and connecting it betwen hall sensors. In that case i can encrease motor current without worring to melt the motor.

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serisman   100 mW

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Re: 36v 800W vs 48 1000W

Post by serisman » Aug 20 2013 1:53pm

By the way, I think I read in another post that the motor windings won't start to lose their insulation until 250c and that it is safe to run them up to 200c. You might want a thermal switch that is higher than 120c. Do you know how warm/hot the windings get currently?

Out of curiosity why do you want to increase the current?

cero   10 mW

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Re: 36v 800W vs 48 1000W

Post by cero » Aug 20 2013 3:47pm

Yup i know about higher temperature, but thermal switch is not directly in the winding but close, so there is thermal bridge to cross. I want to have higher current to have higher torque, wich might be useful to climb steeper hills.

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