How to find polarity of nonlatching relay?

Thread Starter

geratheg

Joined Jul 11, 2014
107
I have the datasheet for a relay I'm using, and I know what the polarity is.

However, what if the datasheet was not available, I can find out which contacts are supposed to by powered from a supply just by the resistance. But how would be able to find out which way current is supposed to go?

Here is the relay I'm referring to: http://www.futurlec.com/Relays/HFD31-12.shtml
 

Brevor

Joined Apr 9, 2011
297
I can find out which contacts are supposed to by powered from a supply just by the resistance. But how would be able to find out which way current is supposed to go?
Connect it to a DC supply and see which way(s) works.
 

Thread Starter

geratheg

Joined Jul 11, 2014
107
Ok, that's easy. I thought maybe there was a method of doing this with just maybe a multimeter and without a power supply.
 

t_n_k

Joined Mar 6, 2009
5,455
It would be interesting to know for the relay in question if the coil is actually polarized for correct operation. I wouldn't be surprised if the DC could be applied to the coil in either direction without any loss of functionality.
 

Ramussons

Joined May 3, 2013
1,404
Some relays have an In Built Surge Suppressor using a Diode. These relays have a polarity. I have quite a few DPDT 12 Volt relays in TO-18 package that have polarity marked.

Ramesh
 

KMoffett

Joined Dec 19, 2007
2,918
According the the pin-out diagram in your link...if polarity mattered...pin #1 is (+). But that is probably of a consequence only in the single coil, latching versions. Yours can go either way.

Ken
 

Thread Starter

geratheg

Joined Jul 11, 2014
107
According the the pin-out diagram in your link...if polarity mattered...pin #1 is (+). But that is probably of a consequence only in the single coil, latching versions. Yours can go either way.

Ken
Mines is non-latching and polarity does matter. It would make sense for polarity to not matter, hmmm but it does matter for me. Otherwise the switch doesn't switch if I reverse the polarity. It only switches with the correct polarity.
 

MaxHeadRoom

Joined Jul 18, 2013
28,617
What is the exact part No? there are three versions of your relay?
pin 1=+v 10=-v even for the non latching, per the spec sheet.
Max.
 

Alberto

Joined Nov 7, 2008
169
It only switches with the correct polarity.

Then as already mentioned in post #6 your relay has a diode across the coil. So you must respect the polarity.

Alberto
 

MaxHeadRoom

Joined Jul 18, 2013
28,617
It only switches with the correct polarity.

Then as already mentioned in post #6 your relay has a diode across the coil. So you must respect the polarity.

Alberto
The spec shows it is a polarized relay, and no diode is shown in the diagram, just that it will not operate unless correct polarity, if a diode was present, it would most likely have blown open by now if connected wrong.
Max.
 

KMoffett

Joined Dec 19, 2007
2,918
Odd too! On the non-latching and single-coil latching relays they show the coil polarity. But on the two-coil latching they show polarity for the Set coil, but not for the Reset coil.

Ken
 
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