1
$\begingroup$

I have a 18 V rated driver I'm using to drive two 12 V DC gear motors using my Arduino. I bought a new battery pack which is rated 3300 mAh 25C, 11.1V making the total current input 82.5 A. My driver is rated for 7 V min and 18 V max, no current rating is given.

My motors are 12V max current under load is 9.5 A.

So just to be sure, can using this battery destroy my motor driver?

This is the datasheet.

$\endgroup$
  • 1
    $\begingroup$ One number missing is - the maximum current the motors will take when in your application. But I doubt that will be anywhere near enough to damage a 25C battery. You should try to check the maximum current of the driver though. Do you know what chip/transistors it's based on? That might give a clue what the current rating is. $\endgroup$ – Andy Jun 1 '16 at 7:50
  • $\begingroup$ Do you have a datasheet for those motor drivers? $\endgroup$ – Bence Kaulics Jun 1 '16 at 8:14
  • $\begingroup$ @BenceKaulics yes I have, link in the post $\endgroup$ – YaddyVirus Jun 1 '16 at 9:57
  • $\begingroup$ @BendingUnit22 I'm very sorry I was in the process of updating my question when my internet connection was dropped, now that it is back, the question is updated. Apologies... $\endgroup$ – YaddyVirus Jun 1 '16 at 12:22
4
$\begingroup$

You are approaching the problem from wrong side. Current capability of a battery (25C) has nothing to do with that how much current will it actually source. It is the load (motors in that case) what defines the current, not the battery. You could use 10C, 25C, 50C battery, and the current flowing through the motors would be (approximately) the same, as long as it does not exceed the maximum current allowed for the battery (82 Amps in your case)

As a side note - I find it hard to believe, that there is no maximum current defined in the motor driver datasheet. It is the key information. Please post te link to the datasheet, or just a part number.

$\endgroup$
  • $\begingroup$ My motor driver can give output of max 20 amps, that's why I chose it to run those motors as they draw max 9.5 amps under load. Link to the datasheet added. $\endgroup$ – YaddyVirus Jun 1 '16 at 12:31
  • $\begingroup$ Exactly this. @YaddyVirus, try thinking of Ohm's Law as $I=V/R$. Current is always the output, and depends on resistance and voltage. As long as you aren't over-volting the device or shorting the output it should be fine. $\endgroup$ – Chuck Jun 1 '16 at 22:45
  • $\begingroup$ Exactly, and since the motors will not draw more than 9.5 amps at any given time, the max current that flows in the motor driver is 9.5 amps which is much less than the 20 amp output limit, which means the battery is safe to use and will last quite a long time per charge. Thanks! @Chuck $\endgroup$ – YaddyVirus Jun 2 '16 at 5:16
1
$\begingroup$

If I might add to the previous answers: I noticed in the referenced datasheet that the 20A maximum current rating for this driver is limited to less than 10 seconds and the maximum current is further limited to 10A for less than 60 seconds. Maximum continuous current ( >60 sec.) is then given as 5A without heatsinks but with, I'm assuming, decent cooling airflow. I don't see any maximum current ratings with heatsinks but I would guess they would be somewhat better with sufficient cooling air.

Given that the maximum load draw of 9.5A is close to the maximum 10A/10 second rating and almost double the 5A continuous current rating and if in the application that these motors are used they draw that much current for any significant amount of time it could be possible that the controller would be overloaded.

So no, as previously pointed out, your battery will not damage your driver. But your motors, or more specifically your application, might burn up your driver, depending on actual use.

$\endgroup$
  • $\begingroup$ Well I've been using the controller with those motors for quite a while now, and I didn't notice any problem. Yes, airflow is decent, its mounted on an open, flat surface, and that's probably why its stil fine $\endgroup$ – YaddyVirus Jun 2 '16 at 21:16
  • $\begingroup$ Then you're probably OK. I'd keep an eye on the mosfet temps and if they're getting very hot to the touch it would probably help to extend their lifetime by glueing on some heatsinks. $\endgroup$ – wchundak Jun 2 '16 at 21:34
0
$\begingroup$

The Datasheet which you gave on the very first page the current rating of the motor is given that is 20A.

enter image description here

It does not mean that you can run 20A all the time enter image description here

Secondly There will be no problem of current unless there is high load on the motors. I like to tell somethings about battery. What I am trying to say is that when you use a battery of 3300 mAh it means that if you can draw 3300 mA current from that battery this battery will last for an hour. Similarly if you drawing 1650 mA current it will last for 2 hours.

Now about motors drivers, motor drivers may fail due to battery for two reasons

1- When you apply more voltage to motor driver than it mend to withhold.( Which in your case you are aware of and it is not a problem).

2- When you run a motor through driver and the load of the motor has exceeded and is drawing more current. For example when you try to stop a running motor manually then motor will try to draw more current. Now if it happens your motor driver will not blow instantaneously but it will take some time. That is mentioned in the second image.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.