The application is a remote clamshell observatory roof which opens via a pair of 12v gear motors driven by a pair of BTS7960 H-bridges. The BTS7960s are controlled by an Arduino Nano which receives commands from the main observatory computer. Observatory is powered by a 12v 200ah LiFepo4 battery and solar panels. There are times, however, that the roof needs to be opened for maintenance when the computer, Arduino and BTS7960s are not powered on. I plan to do this with a pair of cross wired DPDT center off momentary toggle switches in the circuit between the BTs and the motors.

The question is, when a switch is activated a voltage will be applied to the output terminals of the idle BTS7960. I know that the input terminals are not polarity protected. I am concerned that some other restriction might apply to the output.

 

Hi Glen,
Have you considered using a DC reverse blocking diode in the connection to the BTS960 output?
And adding a high value pull down resistor on the BTS output.
E

 

when a switch is activated a voltage will be applied to the output terminals of the idle BTS7960

why?

i certainly would not want to be on the roof with it even if i have manual control of the motors in my hands when there is a possibility for someone to power up computer and starts sending controls to the same motors. i would want that the alternative control is unplugged and locked out somehow. that is the whole point of SPOC (single point of control) - the safety.

why not give them option to plug the motors into another circuit (one with manual controls) or have a keyswitch to choose which controls are active?

 

Plugging the motors into a different system for manual control will certainly be the safest method. If the manual control must be plugged into a "parking plug position" when not in use, to enable the computer control, it would be very close to idiot proof.
I have worked at a place where Lock-out/Tag-Out was not enough. Remove the 3-phase fuses and wire a short across the load terminals wound up being the solution, in addition to Tag-out. That organization is no longer in existence.

 

I had thought about blocking diodes but the polarity is reversing to open and close the roof.
Getting on the roof is not a risk. The observatory is built on a 4'x4' Northern Tool utility trailer.
MisterBill has the safest method. The motors are connected to the control panel by a single 4 pin jack. However, to reach the connector the roof has to be open. I'm thinking a 4PDT switch next to the manual override switches might be the answer for the two roof motors. .

 

OK, that is a whole lot smaller than the last observatory I have seen. Actually, it would be called a PORTABLE Observatory!
No chance of anybody being "on the roof" and having safety issues arise.
Still, having the manual control as an alternate plug-in will be a simple way to avoid both the voltage on the drivers and the change-over switch wiring effort. Also, probably the very least added expense because of only needing one additional connector.

 

that is so much smaller than i imagined as well. and it looks neat...