DPDT Fail-safe DC motor actuator

Thread Starter

MichaelNicholas

Joined Dec 14, 2018
1
Thanks in advance,
we are designing a roll-off roof moved by a 12 VDC linear actuator. The actuator has its own limit switches, so the roof controller needs only provide +12 volts to open and -12 volts to close. The equivalent of a software controlled DPDT switch is the function. It is in a remote site powered by solar panels/battery system. A separate system (battery) is used to power control functions.

We would like an electrical relay that that applies +12 volts to the actuators when the relay is actuated. This could be set to open the roof. Imagine that when the relay is not activated, a spring forces it to apply -12 volts to the actuator, which closes the roof. A disadvantage in this approach is that the relay has to be energized for the whole time the roof is open. Power is at a premium and would like to avoid as much as possible power to hold the relay in the +12 Volt position. Is there such a device?
 

BBee

Joined Dec 6, 2018
35
Non quite sure of the details of your request, but it is possible to obtain latching relays that, when switched, do stay in the closed / switched position without the coil being energised. I have not used them so cannot go into detail, but they are worth a look.

Tracy
 

MaxHeadRoom

Joined Jul 18, 2013
20,675
These are magnetic latching relays, IOW they have memory, even unpowered, they stay in the same/latest state.
They do need the opposite momentary polarity to switch on as well as off.
Max.
 

MisterBill2

Joined Jan 23, 2018
6,039
It would also work very well to have two relays, possibly interlocked, one to open and one to close, and both relays off once the position has been reached. The really simple approach will be to add a timer to the software set long enough for full opening or closing. In addition this will stop the system and save power if the limit switches fail to switch off. And the two relays can be simple 2-pole normally open contacts, possibly a cost saving.
A second approach will be to use two relays again, one to set the direction and the other to switch on the power to the motor. Once again, a timer to release both relays after the thing has moved. This second approach has the benefit of not being able to short circuit the drive power source if there is a software error. The main down side is needing two outputs instead of one.
 
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