# Can I run a motor at low amps?

I am converting a motorcycle to ev and ran into a problem. The motor I am going to use will pull 160to200 amps but my batteries are lithium 50amps. So pulling 2c ill only have 100 amps. Will this severely lower the motor to a point where i cannot move and get up to speed or should it simply take out on my torque and cause my to accelerate a lot slower? I am trying to decide whether to just buy the 50 amps for now and grab another set to put in parallel later or just spring for the 100 now so that i can reach >50. If it will still reach about the same speed just take longer to get up to that speed I would rather buy the 50 amps and buy a second pack later. I am not sure of any of these things though and would appreciate any help. =]

What sort of motor are you running?
eg. Permanent Magnet brushed DC, series wound DC, shunt wound DC, BLDC, AC

For example, with permanent magnet brushed DC motors, speed is roughly proportional to voltage and torque (therefore acceleration) is roughly proportional to current.

Another example, with series wound DC motors, speed is roughly proportional to voltage and torque (therefore acceleration) is roughly proportional to the [B]square of the current (ie. current x current)[/B].

When you say your motor will pull 160 to 200 amps, is that peak current or continuous current?

First check motor current (continuous and peak current) and voltage rating and type of DC motor. These are required to estimate motor efficiency. To extend the life of the battery pack, do not discharge the batteries more than 80%.

[QUOTE=tyscof;13350]I am converting a motorcycle to ev and ran into a problem. The motor I am going to use will pull 160to200 amps but my batteries are lithium 50amps. So pulling 2c ill only have 100 amps. Will this severely lower the motor to a point where i cannot move and get up to speed or should it simply take out on my torque and cause my to accelerate a lot slower? I am trying to decide whether to just buy the 50 amps for now and grab another set to put in parallel later or just spring for the 100 now so that i can reach >50. If it will still reach about the same speed just take longer to get up to that speed I would rather buy the 50 amps and buy a second pack later. I am not sure of any of these things though and would appreciate any help. =][/QUOTE]

To answer your question. I must assume you mean your pack is a 50ah pack. That 2c is for continuous discharge and your cells will give you depending upon the cells used at least 8c burst for a few seconds. My lithium cells are rated at 1C continuous and have given me 7C with no trouble when asked to do so. They were rated very conservatively. You could get to speed using 100 amps by the way but it would be slow as cold molasses. If you are looking at 100ah Calb Gray cells you would be good to go. The 60ah Gray cells will pump out a serious amount of current with no trouble. They have been tested at 10C with out breaking a sweat. I’d look into those as they are small and would do you well.

Also the higher the voltage of the pack the lower the amperage you need to run. With low volt systems you need to run higher currents and the CALB 60ah Gray cells will do that for you.

Pete

The current you quote is the maximum the motor will draw.
At no load it will pull very little current.
You need some means of limiting the current to what is safe for your battery under all circumstances. ie the motor speed control.
Some motors can be “overloaded” for a short time safely.
Obviously either your motor is unneccesarily big or your battery is too small.
You big problem will be cooling the motor at low speeds, it needs an eternal means of cooling. This is why many EV traction motors are liquid cooled, just like a IC engine

[quote=Harry130747;15940]The current you quote is the maximum the motor will draw.
At no load it will pull very little current.
You need some means of limiting the current to what is safe for your battery under all circumstances. ie the motor speed control.
Some motors can be “overloaded” for a short time safely.
Obviously either your motor is unneccesarily big or your battery is too small.
You big problem will be cooling the motor at low speeds, it needs an external means of cooling. This is why many EV traction motors are liquid cooled, just like a IC engine[/quote]

No-one can day how your bike will perform, there are too many variables.
There are several different sorts of motor and motor speed control.
It also depends on the maximum speed of the motor and the gearing, the weight of the bike and how fat you are