Am I crazy?

[ashart]

I have an old P&B open-frame DPDT relay removed from an Elmac AF-68 power supply.  The relay is a typical type often found in a plastic case bearing an octal plug.

The relay is marked KR-2539.  I have been unable to find an old data sheet.

My problem is that the coil resistance is a mere 30 ohms!  This would dissipate a whopping 4.8 watts on the 12 volt application, which in fact occasionally goes up to nearly 11 watts (!) when the 12-volt source varies.

It would be easy to just throw it out as a bad relay, but astonishingly, there's another relay in the rig with an identical 30 ohm coil.

Thinking that the coil power of such a relay should be a lot closer to 1 watt than 10 watts, I'm confused.  Has anybody got an old P&B catalog or data sheet that could prove to me that I have 2 identically defective relays or whether I should go back to relay school?

Tnx es 73.

al hart
al@w8vr.org

[AB2EZ]

Al

I cannot address your first question.

With regard to the relay:

Are you sure this relay operates with 12VDC rather than 12.6VAC? The relay's coil has significantly more inductive reactance at 60Hz than it has DC resistance.

Stu

[ashart]

Hi Stu, es tnx fer the reply.

I'm pretty sure.  Both relays are in DC circuits, so there's no reason to have an AC relay.  Moreover, the relay has no copper slug (shader ring) around the pole piece that I'm used to seeing on AC relays.  

Every fact contributes to the confusion, not to the solution!

-al hart

[Pete, WA2CWA]

I believe the KRPA series TE/Potter Brumfield relays replaced the much older KR series. Here's the specs for the KRPA:

http://www.te.com/catalog/bin/TE.Connect?S=21425&M=FEAT&P=77712&U=&BML=18110&LG=

Short form version:
see the PDF below

If it's the M-1070 you're using, The two relays have two different part numbers: KR-2634 (RY201) and KR-2539 (RY202). Not sure of the differences (maybe just number of contacts).

[WD5JKO]

I was betting the coil was 6V DC rated. The PDF Pete sent shows a 6V 32 ohm coil at 1.15 watt rating.

So with the Elmac AF68 perhaps the DC supply was configurable for both 6V and 12V automobiles. With 6V the two relays are in parallel and for 12V they are in series? Just guessing I know.

Jim
Wd5JKO

[ashart]

Eureka! You have found it!

Jim's solution of the 6 volt operation must be absolutely correct!  Yes, the power supply does operate from 6 volts, but neither I nor my pal working with me even thought of that issue.

Besides, if P is really equal to v^2 /r, on 6 volts one gets 36 volts / 30 ohms, exactly equal to the 1.2 watts that the current-day catalogs suggest.

Thanks to all, and a cigar to Jim.


73.

-al hart
w8vr