What is going to blow up? - 4 dc motor - Pololu MC33926 - 12v 1900mAh

Hi,

I want to drive 4 dc motor [127rpm, 0.32A (max load), 1.45A (stall)]. Two motors are connected to each channel in Pololu MC33926 which can deliver a continuous 3A per channel.

I have been running the motors using an AC/DC adapter of 12V, 10A.

If I switch the power source to a battery pack of 10 AA, 1.2v, Ni-MH, 1900mAh => 12V, 1900mAh then I might run in the situation where the motors might require more current that what is available and something bad is going to happen but I don't know exactly what it is. I know the driver shield has current protection but I don't really know if this is enough to prevent my battery pack from exploding.

Thanks.

One question is what might blow up the cells immedeately, what might shorten their life. Check the specification of the Ni-MH cells.

The main item you should be looking at is the C rating of the battery.

@TmFKAAWOL
From my old working with chargeble battories the term C10 was used. That was the dischargecurrent, the capacity, 1900mAh, divided by 10. Discharging using that current and cutting off at a descided voltage gave information.
So, I interpret Your previous post like C is 1900mAh.

A modern battery might have 10C (or higher) rating, meaning, in this case, 19 A, but for six minutes.

Thanks … That is the other limit in using battories. I never faced that before. Making a short is probably the best way to blow up cells but making tests for the blow up current would depend of the make of the cell I think. In the end the question about how to get the longest life time of the cells ought to be the most interesting.

These are the batteries I was planning to use: Panasonic eneloop

Good. Follow that line and find the data You're looking for.

In addition to limiting the current to extend battery life, it's also worth noting that the short circuit current of batteries like these can be high enough to cause considerable damage to your circuits such as burning up tracks, melting insulation on wires etc. On unattended operation it could easily cause fires.

It is a good idea to place a traditional fuse with a slightly higher rating than the electronics current limit as close as possible to the battery. You may also consider strapping a thermal fuse to the battery.

Ohhh I forgot to mention that what I am building is a 4WD robot. For now is expected to be an obstacle avoiding vehicle and the plan is to upgrade it to a GPS driven vehicle.
It is not going to be unattended.

JonathanCR:
Ohhh I forgot to mention that what I am building is a 4WD robot. For now is expected to be an obstacle avoiding vehicle and the plan is to upgrade it to a GPS driven vehicle.
It is not going to be unattended.

You can use ultrasonic sensor HC-SR04 for obstacle detection and you can use gps module vk16e, data output in NMEA format.

jackthom41:
You can use ultrasonic sensor HC-SR04 for obstacle detection and you can use gps module vk16e, data output in NMEA format.

Yes, I'll use the ultrasonic sensor for now. But I am a little bit concerned about my power source.
I guess it is going to be a try and see situation. I am not going to run the boot at full speed. I measured the current draw in one channel at 50% speed with two motors and it was 0.20A @ max load and 0.50A @stall so hopefully my battery pack is goin to be enough for a 5 minutes ride.

Check the specificasions regarding how low the voltage that type of cells is allowed to go. F ex. LiPo cells are damaged if they are discharged to deaply. What is valid for Ni-Mhcells I can't tell.

JonathanCR:
Hi,

I want to drive 4 dc motor [127rpm, 0.32A (max load), 1.45A (stall)]. Two motors are connected to each channel in Pololu MC33926 which can deliver a continuous 3A per channel.

I have been running the motors using an AC/DC adapter of 12V, 10A.

If I switch the power source to a battery pack of 10 AA, 1.2v, Ni-MH, 1900mAh => 12V, 1900mAh then I might run in the situation where the motors might require more current that what is available and something bad is going to happen but I don't know exactly what it is. I know the driver shield has current protection but I don't really know if this is enough to prevent my battery pack from exploding.

Thanks.

NiMH won't ever blow up, you are thinking of lithium! Over current will get them very hot, be very inefficient, and might cause them to vent electrolyte and steam. What will happen first though is the voltage dropping and the motors slowing down, which might enable you to prevent damage to the batteries if you take heed.