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HOW: Relay reversing polarity?


#1

Hi

I have an actuator that needs 12V in 250 ms to open, and 12V in 250ms to close.

The problem for me: it requires reversed polarity to open.

I have the X1 relay module, and the load module. Any ideas?


#2

The only way I can think of is by using an additional double pole double throw relay to reverse the polarity.


#3

Use 2 double pole changeover relays. This way you guarantee never to short the output together. The X1 is single pole so no use to you.

On the first relay, connect the COMMON pins to your +12V supply (via the second delay) and then the CLOSE and OPEN contacts are wired to the output with cross over link between them this can be your reverse polarity relay. You set this relay for normal pol and switch it for reverse pol.

The second relay is used to switch the +12V ON and OFF.

This also means you only need a single polarity supply. No need for a negative supply input.

Of course, you can also use a transistor or MOSFET to switch the +12V on and off which will switch faster than a relay anyway but you still need 1 changeover relay.

If you need a schematic for this, just let me know and I’ll knock one up for you.


#4

I looked at the schematics for the relay module considering a special design with two relays like you describe. But I am afraid I don’t understand the purpose of all components. If you could quickly draft a circuit I would be very happy.


#5

No worries. This should do you.

The relay on the left can be replaced with the X1 but if you are going to do a custom PCB, you might as well do it all on the one and save all the wiring. :slight_smile:

I’ve used the same 12V to power the relays keeping it simple.

The relays are 2 different types but relay K2 can use the same type as relay K1 and just use the one contact.

Any questions just let me know.


#6

Brilliant stuff, thank you so much Dave… considering a little module for this. Might be on time that I try some module building…

Found this relay on ebay, would that do the job? http://www.ebay.com/itm/390424610961?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649

Thanks again!


#7

It would but you’ll need t be sure and have 5V to switch it. As you are switching +12V I would suggest getting a 12V relay and save having to generate or have 5V to the board. That’s assuming your Gadgeteer does not have 5V available. :slight_smile:


#8

Ok, I am going for coil voltage at 3V (Gadgeteer) and 12V switch, right?

Found this one on mouser: http://dk.mouser.com/ProductDetail/TE-Connectivity/19022B2US/?qs=sGAEpiMZZMtSzCF3XBhmWxSICMMNssF%2bv3cMLRLZ74Q%3D

Would that fit better?


#9

I found this module http://www.ebay.com/itm/Two-DPDT-Signal-Relays-Module-Board-12V-for-8051-PIC-SKU170001/130971304409?rt=nc&_trksid=p2047675.m1851&_trkparms=aid%3D222002%26algo%3DSIC.FIT%26ao%3D1%26asc%3D17214%26meid%3D801055968511169632%26pid%3D100005%26prg%3D8039%26rk%3D3%26rkt%3D4%26sd%3D130690277968%26

Which I think I will be able to wire according to your instructions!


#10

Perfect. It will work ideally and save you on the cost of a custom PCB, assuming you only need to build one or a few.

For a custom board, keep the coil voltage at 12V. The Gadgeteer at 3.3V or 5V will be able to switch the relays because of the transistor drivers.

Oh by the way, if you use my circuit, you can add two 100K resistors, one from each of the transistor base connections to ground and this will prevent the relay switching on during power up if the IO port can provide enough current in the default INPUT state and some form of pullup is enabled. I missed that part out. I knocked it up quickly after you asked and I forgot that the drive input will likely be an INPUT during power up. This has never been an issue for me in the past as I used AVR’s and they are configured very quickly at startup but .NETMF takes a little longer before you application is run.

If you got the eBay board you indicated, then this already has them.