I was wondering if there is any reason I am missing why I couldn’t run the orangutan X2 at 24 volts. I am planning on using it for a large device that is currently set up to run at 24 volts.
I was looking at the data sheet for the VHN2 and it is rated to up to 41V, but it says on your website that above 16V you have experienced shoot thru currents. For what I am planning on using it for shoot thru currents will not matter.
I also examined the schematic for the X2 and it looks like everything except the VHN2 motor supply receives a 5V supply from a LM2937 voltage regulator. I looked up the specs for the voltage regulator and it is rated to 26V. (national.com/ds/LM/LM2937.pdf)
Unfortunately, just about everything is built around the 16V limit. The VNH2 can shut itself off above 16V. The 41V rating means the chip won’t break, but it will not drive the load. For the voltage regulator, there are also power dissipation considerations, and it can get quite hot even at 12V and just powering the board and LCD backlight. Finally, the power switch is also designed for operation to 16V (it’s tested to about 20V).
We have a new motor driver that can work at 24V, so you might be able to use that with a separate logic board running at a lower voltage (such as the X2, though that might be a waste if you have no other use for the built-in motor driver).
Thanks for the reply about running the entire system at 24V
On my previous post I meant VHN3 not VHN2. I got them mixed up.
I was also looking at the schematic and thinking that I might be able to disconnect pins 6,7,12,13 between the top and bottom board. I would then connect the lower board thru an external voltage regulator to 9V and run the top board at 24V. I would use the VHN3 board. What are your thoughts on this? If you don’t think it will work, I will use 2 of the motor controllers you linked in your previous post.
The VNH3 is worse than the VNH2. The VNH3 doesn’t have the voltage cutoff built in, but it has bad shoot-through issues that cause it to destroy itself if you use PWM above 16 or so volts. If you just want full on/full off control or very low-frequency PWM (few hundred Hz, maybe), the VNH3 can be useful at 24V, and then you could do the thing of powering the bottom board separately.
Thanks for the info. Sounds like I will be better off using 2 of the high power motor drivers and a baby orangutan 168. My thoughts right now are to connect the PWM input for one motor driver to PB1(OC1A) and the other to PB2(OC1B). I will then use 2 other digital outputs to control the direction.
On the page for the motor drivers you recommend using something to limit the voltage output from the batteries to 24V. How would you recommend for doing this with a NiMH battery and a 10 amp current? Looking up the specs for NiMH batteries the peak voltage is 29V (batteryspace.com/index.asp?P … ProdID=979), but that is close to the 30V limit.
29V is uncomfortably close to the limit; do the batteries really get that high in normal usage? One thing to look out for is in-system charging, in which case you might see an even higher voltage. If charging involves disconnecting the battery from the motor controllers, you might be able to just let them sit a bit after charging, and they might drop to something closer to 27V.
In general, you can consider using a transient voltage suppressor (TVS), which you can mount close to the motor controllers. You would probably want a 26V unit, which would typically keep you under 30V. However, if your battery stays around 27-29V for a long time even with some load, the TVS might not be able to handle the power that you would be dumping into it.
We’ll also be making a version of the same motor driver board that can handle up to 50V peaks, though the continuous current will be down to around 8A; would that work for you? If so, when do you need the motor drivers?
I do not know if the batteries usually run anywhere near 29 volts. On the website with with the batteries it says that the working voltage is 24V and the max voltage is 29V. I will be disconnecting them to charge them, so the charging voltage is not an issue. I already have the batteries and the motors that I am using, so I can’t change that. This is for a senior design project and we are reusing parts from a previous year.
How soon are you planning on having the 50 V motor controller out? I am hoping to order parts the end of next week, or the week after. I am using one 140 watt motor (about 6 amps) per motor controller, so the board you are working on would work.
We might have something within the next week; it depends on how the production of other scheduled products goes. I’ll let you know how things are going.
