Hi!
I am building a RC lawnmower. I was stupid, I bought a Sabretooth 2 x 12 dual motor controller and connected it to 2 x wheel chair motors using a 24v Lead acid battery bank and controlling it with a RC transmitter and receiver. All good on bench test but lasted about 5 minutes on the road test before I cooked the motor controller.
I clearly should have bought a 32 amp per channel Sabretooth and I am now going to do that. However, I have been reading that these motors can draw a lot more, especially if they stall. So, even with a 32 amp per channel motor driver I would like to put a fuse in the circuit, so I don’t cook another Sabretooth. The motors are Sunrise Medical SRG0410 24 V, with the brake removed 32/07 whatever that means Part Number 101363. Like many others difficult to find what they are rated in Watts but I understand that is variable and especially in a stall situation they can draw a very high current. The question is will that high current in a stall exceed the 64 amp peak current that the Sabretooth 2 x 32 specs specify?
Has any one cooked a Sabretooth 2x32 using it with wheelchair motors and how did that occur? Can anyone recommend where to insert a fuse in the circuit to protect the motor driver and what would be a sensible size fuse?
Thank you so much in advance for your help!
Hello @MarttheFart and welcome to the RobotShop community,
The Sabertooth has thermal and overcurrent protection, so it is strange that you burned your old driver. You may want to contact Dimension Engineering as the cause might not have been what you think. About the fuse, you can use it on the motor leads, but not on the battery, here’s the information they have provided:
If this is more of a hobby project instead of an industrial product, most people do not use fuses. The Sabertooth has built-in current limiting.
We prefer that you fuse the motors rather than the battery leads, or if for safety reasons you need to fuse the battery that you do it at a much higher current than the motors. The reason is this:
Because Sabertooth is a regenerative driver, it relies on having a battery to put regenerated energy back into when you command a stop (and at other times). If you draw enough power to blow a battery fuse, all of a sudden the Sabertooth has nowhere to put the energy. It will see the fault, though, and try to stop the motor. It doesn’t, however, have anywhere to put the energy (the mechanical energy of the vehicle and the electrical energy carried in the windings and the caps). So blowing a battery fuse will sometimes kill the driver – which we would replace under warranty, but it’s still annoying for all parties.
The better way to do it is to fuse the motor leads. If a motor fuse blows, the motor will freewheel, the Sabertooth will sit there contentedly, and the only thing you will have to replace is the fuse.
I hope that helps!
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That is a great reply, thank you. I had assumed that the Sabretooth 2 x 12 had exceeded its peak current rating 24 amps and that is why it blew. On reflection though another possibility is that it overheated. I mounted it with standoff’s so there was air below it but it was in a closed box. however if it had thermal and overcurrent protection, why did it blow? It would be surprising that it over heated so quickly but it is certainly a possibility. I will buy the Sabretooth 2 x 32 which has a much higher peak current rating 64 amps, so a bigger safety margin. I will also improve the cooling buy putting a computer fan into the box and drilling air intake holes. If I can find a contact I will fly all of this past Dimension Engineering to hear their thoughts. I will leave the fuses out but I don’t want to blow another motor driver.
Many thanks
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