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### Topic: How to deal with high starting current (Read 335 times)previous topic - next topic

#### xixigogo

##### Jun 12, 2018, 12:07 pmLast Edit: Jun 13, 2018, 03:43 pm by xixigogo
You will need an H bridge controller to be able to run both ways.  The H bridge will need to be able to handle the required continuous current of the motor as well as the brief stall current at startup.
I'm have motor driver IBT_2 which is able to output 43A maximum for a 24V motor with starting current 80A (rated current 20A).

Is this not reasonable ? can you please explain a bit of the relation between motor starting current and the current through the motor driver ?

Thanks a lot!

#### bos1714

Hello there!

When you break it down, a motor is a coil. The equation for a coil is V = L(dI/dt). What this means is that when power is first applied to the coil(we'll say motor for now), a large amount of current is required to start the motor shaft turning. This starting current is also sometimes called the kickstart current, and is several times higher than the normal running current.

Whatever motor-driver or H-Bridge you are using must be able to handle both of these current ratings. Do you know the kickstart and normal running currents for your motor? If not, try to find a datasheet online.
Time line? Time isn't made out of lines. It is made out of circles. That is why clocks are round.

#### xixigogo

Hello there!

When you break it down, a motor is a coil. The equation for a coil is V = L(dI/dt). What this means is that when power is first applied to the coil(we'll say motor for now), a large amount of current is required to start the motor shaft turning. This starting current is also sometimes called the kickstart current, and is several times higher than the normal running current.

Whatever motor-driver or H-Bridge you are using must be able to handle both of these current ratings. Do you know the kickstart and normal running currents for your motor? If not, try to find a datasheet online.
The starting current of my motor is 80A and the rated current is 20A.
Does it mean that I need a motor driver which can handle 80A ?

#### xixigogo

Hello there!

When you break it down, a motor is a coil. The equation for a coil is V = L(dI/dt). What this means is that when power is first applied to the coil(we'll say motor for now), a large amount of current is required to start the motor shaft turning. This starting current is also sometimes called the kickstart current, and is several times higher than the normal running current.

Whatever motor-driver or H-Bridge you are using must be able to handle both of these current ratings. Do you know the kickstart and normal running currents for your motor? If not, try to find a datasheet online.
So I am advised using 2 motor drivers in parallel and adding extra cooling to ensure enough current to support my motor. Does it make sense to you ?

#### bos1714

#4
##### Jun 13, 2018, 06:25 pm
Yes this makes sense. With 80A running through, there's going to be a fair amount of heat, even just for the brief time the 80A is flowing. Even with 20A you are going to need a decent heat sink.
Time line? Time isn't made out of lines. It is made out of circles. That is why clocks are round.

#### morrisonandboyd

#5
##### Jun 13, 2018, 09:08 pm
I would recommend looking up the locked rotor motor current and sizing the drivers and heat sinks accordingly.

I would also add a little head space to that so if you have a locked rotor current of 80 amps, would recommend sizing for 90 - 100 amps. Yes, more expensive now, but you'll thank me later.

H-bridge is separate matter, but IGBT's are cheap...

MB

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