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Drive motors with higher voltage than rating.

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flat_battery
(@flat_battery)
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Joined: 1 year ago
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A question for the forum.
I'm slowly putting together a radio controlled 4wd bot, nothing too ambitious as it's my first.
The motors are 12v gearmotors.
The drivers are BTS7960B, one driver for two left motors one driver for two right motors.

I have a radiolink transmitter R7FG which requires 3v to 12v input
The Arduino Mega requires 7v to 12v (Ideally)
and lipo batteries are either 11.1v or 7.4v

The motors will run at 11.1v but they run better at 12v

My thinking is this.
Connect two 7.4 lipos in series to get 14.8v or thereabouts.
Use a buck converter down to 12v for the radiolink and arduino.

And here's the real question. Given that I'm using PWM to drive the BTS7960B's I think I could use the full 14.8v as battery input if I'm careful and don't run them full cycle 100% / 255.
Perhaps limit it to 82% / 209 which I think is around 12v.

Any thoughts / advice appreciated?

 


   
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Foxy
 Foxy
(@foxy)
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Joined: 2 years ago
Posts: 61
 

If the motors are really dc motors with brushes and commutator they will be pretty tolerant of a minor overvoltage in this range.  (I remember GE mill duty motors routinely operated at double name plate voltage).  So I wouldn't worry much in this case particularly as you intend to limit the average dc to 100% np via pwm.  The BTS7960B is actually the reversing bridge, not the motor and I didn't find a voltage rating for it but I still wouldn't worry much.  

If the motors are actually so-called "brushless dc" or BLDC they are ac motors with a built in inverter and I don't know how they would handle pwm--perhaps someone else has looked into this.


   
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flat_battery
(@flat_battery)
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Joined: 1 year ago
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@foxy Thanks for the reply. The motors are zgb37rrg which are carbon brushed so I think I'm good, just needed a 2nd opinion. (interesting aside regarding the GE motors).

I did an apprenticeship at GEC Rugby UK about 44 years back. It was like something out of a Charles Dickens story with regards to health and safety and the general working conditions. Interesting to watch people assemble motors that had windings bigger than a dodge ram. 🙂

 


   
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Foxy
 Foxy
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@flat_battery   I worked at a GE Canada plant for some years and found working conditions quite good.

I can't help getting a chuckle from the Dronebot's description at one point of dc motors (at least the hobby type) as being small size high speed.  One of my jobs was controls for a couple of 8000 HP 30 rpm motors


   
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