# Controlling a 2.4V motor at 570mA, startup Current?

Hello,

I am trying to control 2 vibrating DC motors,
Operating voltage: 2.4V
Operating current: 570mA

I am having a difficult time finding a motor controller that will output a voltage of 2.4V and be able to supply enough current.

The startup current taken from the datasheet is 3.2A, do I need to have a controller or voltage regulator that can supply above 3.2A?
Or since this is just a spike will it be ok?

Can I control 2 motors in series with a 5V supply, with enough current?

I have looked at these, but unable to find something with enough output current:

https://www.pololu.com/product/2130

https://www.pololu.com/product/2118/specs

Any help greatly appreciated.

So a couple things;

(1) The 2.4V motor with 570mA and 3A startup current…Seems like pretty unusual specs. Do you know where those numbers are coming from? It sounds to me like a very low resistance motor with low inductance and cheapo motors are usually higher resistance and inductance, but I don’t know much about such small motors none of that might apply to tiny motors. Basic question: Is this motor special in some obvious way? What are you using it for.

(2) What do you mean “control two motors in series”? You can drive two motors in series, but you won’t have control over them. If they are the same motor type they won’t drive exactly the same speed, because DC motors tend to vary a little especially cheap ones. moreover, in series as one motor faces resistance they will start drawing different amounts of power from the series connection, and so a change in speed in one motor due to load will affect the other motor.

Honestly I haven’t thought about DC motors in a while and don’t know enough to immediately realize how that affect will work. I am not sure if you have the two motors physically coupled to the same drive if the effect would be beneficial (such that the motors share the load) or if it works in opposite directions so the motors do the same as syncing.

(3) You have a tricky question! 570mA is about 2-3x higher than the easy answer of “just use a discrete NPN/PNP h-bridge!” which can be helpful for these very low voltage loads. But 2.4V is very low for these drivers.

(4) There’s a way to dramatically decrease the startup current by use of a MCU. You can just “ramp” the applied voltage over a few seconds so by adjusting a PWM gradually up. So the motor starts by seeing 1V, pulling X current, then it sees 1.5V, maybe starts moving, pulling Y current, then 2V, but because it starts moving a bit before it sees the full 2.4V, it is actually not going to pull the full startup current at 2.4V, since it has already started generating back EMF and only “sees” a lesser voltage than 2.4V.

(5) some of these drivers can definitively deal with instantaneous spikes greater than their rating. They often have regulation internally for those purposes. But I used the baby orangutan which I think had a spike current in parralel of either 3A and 6A, and then it had internal regulation that kind of works like option (4) in principle. Anyway, if the spike is too fast, the regulation can’t kick in, and you can blow even well protected drivers in that manner. For me the spike was fast because I started using a lower inductance and lower resistance maxxon motor and hadn’t fully investigated the spikes (I used the maxxon motor because I was having trouble with pololu motors on account of them not being intended for as torque-y applications as the 5-10x more expensive maxxon motors.)

Hello.

Tomek hinted at this, but to expand on it further: if you use a motor driver that allows you to adjust the duty cycle of your motor power supply, you can effectively supply a lower voltage to your motor. For example, if you have a 6V battery, you can apply a 40% duty cycle to your motor driver or controller and effectively supply 2.4V to your motor. Motor drivers that can do this usually have a PWM input. In general, we recommend using motor drivers that can continuously handle the maximum amount of current your motor will draw. In your case, I recommend using our MC33926 motor driver.

-Jon