How to compare "power" of motors of different voltages?

Thread Starter

Pdalton

Joined Jul 16, 2016
11
I am trying to determine whether there would be any "power" improvement achieved in a cordless electric trimmer product by simply changing the voltage of the battery.

The trimmer originally was sold using a 3.6v battery. It got many bad reviews for being underpowered. Now, the manufacturer is selling what appears to be the same product, but now running on an 18v battery.

The manufacturer does not identify whether the same motor is being used in both versions of this product nor - for the motor in either version - any specs for hp, watts, amps, etc. Only the difference in battery voltage is stated.

I imagine the higher voltage battery could allow the product to run longer, but I don't know how to determine whether just running the same motor at that higher voltage also increases its power output (hp or torque).

I suspect I haven't been able to provide enough technical information to allow a definitive answer, so I would appreciate knowing what additional information I should try to get by contacting the manufacturer directly, and also how I can use the information to compare the relative power of electric motors using different voltages of battery power.

Thanks
 

crutschow

Joined Mar 14, 2008
34,201
It's undoubtedly not the same motor.
A motor designed for 3.6V will likely burn out if 18V is applied (although it will probably have more power until it burns out :eek:).
Motors are optimized to run at a particular voltage with only a small margin for operation at a higher voltage.

And an 18V battery won't necessarily last longer than a 3.6V battery.
Batteries have a Ah rating with their total energy determined by the Ah times its voltage.
For the same physical size a battery with a higher voltage will have a lower Ah rating (making their total energy more or less equal).
Battery life is determined by the power required by the motor which is volts times current.

The main reason for using a higher battery voltage is that the motor can be made to generate more power for a given size, but that will actually reduce battery life for a given physical size battery, not increase it.
 

Tonyr1084

Joined Sep 24, 2015
7,829
When I was young (a very very long time ago) I had an electric train set. It was powered by a 12 volt transformer, some rectifier and a very large variable resistor. I happened across a 24 volt transformer and hooked that up to the train control and promptly noticed much higher speeds of my train - until it burned out. "(

I concur with Crutschow; a low voltage high amperage battery can have the same power as a high voltage low amperage battery. And we're assuming the physical size is the same. Put it this way: a 2 volt 5 amp hour battery has as much power as a 5 volt 2 amp hour battery. Both batteries have 10 watt hour power. I'm sure I'm mis-using the terms a little bit here, but the intent is to show that 5 X 2 = 2 X 5 = 10.

I doubt the manufacturer wants to give you information on their products. I once called a sprinkler control manufacturer to inquire of a resistor value (the one in my unit burned up and was unreadable). They refused to give me the resistance value and the wattage. Looked like a 2 watt resistor to me, but it was so badly burned there was no hope of deciphering its value. I bought it at a yard sale for a buck, knowing it didn't work.

The guy started trying to tell me about cascading failures, saying that when one component goes down it can drag several others with it. This was the main power resistor through which all power flowed. If it burned out it would simply act like a fuse, shutting power off to the unit. So I told him that what he was telling me was that if I unplug the unit it would die. Or if there was a power failure. He kept trying to BS me until I told him the date code on the board. It was built in September of one year and in May of the next year it was dead. He didn't know I knew more about electronics than he thought I knew. But he told me that I could return the product for a free replacement. That was even better than knowing the stupid resistor value. Apparently someone hooked it up wrong and burned it out. Good news for me.

The point is - manufacturers like to guard their secrets. Makes them feel superior to those who don't "KNOW" anything. You and I, and everyone else here are a little smarter, and know that motors usually have some kind of marking on them that typically leads to information about that product. So if you have numbers on your new motor - we can help you look up the specs on it.
 
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