relay wiring for power supply cooling fan

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Forum Name: Relays
Forum Discription: Relay Diagrams, SPDT Relays, SPST Relays, DPDT Relays, Latching Relays, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=133502
Printed Date: July 01, 2025 at 4:00 PM

Topic: relay wiring for power supply cooling fan

Posted By: unlimitedtowing
Subject: relay wiring for power supply cooling fan
Date Posted: February 02, 2013 at 8:48 PM

I just installed two whelen ISP188 power supplies in a custom box with a fan mounted on top for cooling. The issue I am having is when I actIvate my front strobes the signal wire from my relay in turn fires my rear strobes when that switch is off and vice versa. I need a way that will independently turn the cooling fan on when I activate either front or rear without turning both on. Sorry for the long post, any help would greatly be appreciated!

Replies:

Posted By: oldspark
Date Posted: February 02, 2013 at 11:08 PM

Depending on how it's wired, diodes should do it.
EG - if you have a switch operating a relay for each SP188, then a diode from both switched to the fan.
If the fan is under 1A then 1N400x diodes should do (1N4004, 1N4007 etc).

If above 1A, then you could use the 3A rated 1N540x diodes or - else if above 3A - thru the diodes to a fan relay.

Posted By: unlimitedtowing
Date Posted: February 03, 2013 at 9:41 AM

I am using two Dei 610T relays. My current wiring is as follows: (85) Ground (86) wired off of each acc. of front and rear strobe switches (87) Constant 12 Volts (30) To positive wire on external fan. Like I stated earlier when I turn on my front strobes and also turns on the rear strobes because of the way I have the relay wired. If I use the diodes like you stated is my current wiring of the relays ok? Also, where exactly would I place the diodes? I uploaded two pictures, one of the box I made and the second is of the switchs that I'm using to run the two Whelen ISP188 power supplies. The first switch powers on front strobes and the second switch powers on the rear strobes. The other eight switches are for pattern selection.

Posted By: unlimitedtowing
Date Posted: February 03, 2013 at 9:54 AM

Posted By: unlimitedtowing
Date Posted: February 03, 2013 at 9:57 AM

Posted By: unlimitedtowing
Date Posted: February 03, 2013 at 9:59 AM

Couldn't get the pics to load properly, sorry

Posted By: oldspark
Date Posted: February 03, 2013 at 6:25 PM

I think you are suffering the discrimination posted_image

this site has against Junior Members. Alas I'm way too old to remember such details, but as I recall, posting images was part of that. If its a URL, merely paste its text in your reply.
(BTW, that "discrimination" is good wrt spammers etc, but it is a PITA for bonafide users.)

I'm still vague as to your wiring from your verbal.
However, if the relays are switching the strobes and the fan, and both the fan +12Vs from the #30s (else #87s) are joined together, then that's your cross-connect. IE - turn on either of the strobes and the +12V goes thru the fan +12V to the other strobe.

If so, then you need an "isolating diode" in each of the +12V fan feeds.

So what current consumption is your fan? That determines the current rating of the diodes. (Voltage rating isn't an issue since power diodes are usually rated for at least 50V.)
If under 1A, then 1N400x diodes.
If under 3A, then 1N540x diodes.

If above 3A - or even 1A - then using a 3rd relay may be better or easier than larger diodes...
OR if you don't want the ~0.7V diode voltage drop to effect you fan, then the 2 IN400x diodes join to energise a extra "fan relay" (#86) instead of the fan +12V.

Assuming you are switching/feeding +12V, then the diode line-ends are the joined outputs.
Click on the Diodes link at the top of this page and see the "Isolating Positive Door Triggers" example. The "door positive triggers" are (from) your switches and the "to alarm positive door trigger input" is your 3rd relay else fan.