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### Topic: start-up current vs start-up rms current (Read 632 times)previous topic - next topic

#### lmfao

##### Nov 29, 2019, 09:40 pm
Hi!

it says in the datasheet of my motor that the start-up current is 2.8A (max), and I looked at a driver board that can output max 2.6A(rms). What does rms mean and will the driver board deliver enough current?

thanks for any replies!

#### groundFungus

#1
##### Dec 01, 2019, 12:10 am
Post a data sheet for the motor and a data sheet for the driver.  RMS means Root Mean Square and that term is usually associated with AC voltage and current.  What kind of motor do you have?

#### Paul_KD7HB

#2
##### Dec 01, 2019, 02:16 am
And RMS will give you the equivalent DC continuous current value of your AC sine wave current.

Paul

#### gilshultz

#3
##### Dec 01, 2019, 06:21 am
In time your driver board will fail, keep the load down on the motor until you can get a new driver board. They have a maximum rating for good reasons as they have motor currents.  "RMS" stands for Root Mean Square, and is a way of expressing an AC quantity of voltage or current in terms functionally equivalent to DC. For example, 10 volts AC RMS is the amount of voltage that would produce the same amount of heat dissipation across a resistor of given value as a 10 volt DC power supply.  Try this link for a good explanation. https://www.animations.physics.unsw.edu.au/jw/power.html  This response is to help you get started in solving your problem, not solve it for you.
Good Luck & Have Fun!
Gil

#### MarkT

#4
##### Dec 01, 2019, 11:35 pm
Hi!

it says in the datasheet of my motor that the start-up current is 2.8A (max), and I looked at a driver board that can output max 2.6A(rms). What does rms mean and will the driver board deliver enough current?

thanks for any replies!
The start up (aka "stall") current of a motor depends on the winding resistance and the supply voltage.

Stall current = supply voltage / winding resistance.

You can measure the winding resistance between the terminals with a multimeter.

The driver current value given is presumably a continuous current limit of 2.6Arms, the pulse rating is the thing to look for, that needs to be bigger than the stall current.  The continuous rating should be bigger than the load current of the motor under the conditions you'll be using.

If the motor can be stalled for more than an instant, then the continous rating should cover it.

Also most motors are going to overheat if stalled at full supply voltage for any length of time, since they rely on airflow for cooling.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

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