Wiring Relays In Parallel
Printed From: the12volt.com
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=110568
Printed Date: May 02, 2024 at 4:01 AM
Topic: Wiring Relays In Parallel
Posted By: newgene
Subject: Wiring Relays In Parallel
Date Posted: January 11, 2009 at 7:15 PM
I have spent the last hour trying to find a schematic for wiring two SPDT relays in parallel without any luck. Could someone explain where everything goes? Also this will reduce the amp load for each relay-right? I am wiring up an electric fan that pulls over 30 constant amps and was thinking I may be asking too much of a single standard 40 amp relay especially considering the high but extremely brief spike at start-up. Thanks
Replies:
Posted By: i am an idiot
Date Posted: January 11, 2009 at 7:30 PM
Power terminal 30 of both relays, prefferably with a power wire of their own. Connect terminal 87 of each relay to the fan power wire. Once again 1 wire from each relay to the fan. Terminal 85 of each relay should be connected to the ground of your triggering system. Terminal 86 of each relay connects to the positive voltage of your trigger system.
Posted By: newgene
Date Posted: January 11, 2009 at 9:27 PM
Simple enough-thanks. I am assuming jumper wires are ok in these type of applications?
Posted By: i am an idiot
Date Posted: January 11, 2009 at 9:55 PM
Jumper wires on 85 and 86 are fine. For added current 30 and 87 should be jumped together at the fan and the point of connection to the power source.
Posted By: n2ixk
Date Posted: January 12, 2009 at 2:30 PM
Wiring multiple relays in parallel for added ampacity is generally a BAD idea.
One relay will always open or close a millisecond or so faster than the other one, leaving only one contact to carry the entire load until the other one "catches up". Add in the fact that motor loads have a high inrush current (a high current surge when power is first applied), and you will often find that the relays still burn up or weld their contacts, despite being paralleled.
In short, if you need higher current capacity, use a bigger relay.
Posted By: hotwaterwizard
Date Posted: January 13, 2009 at 11:45 PM
Use a Bigger Relay! Camdec Corp # 93285. 12 Vdc, 4 ohm coil. Heavy-duty, handles a 225 Amp load https://www.allelectronics.com/make-a-store/item/SOL-80/12-VDC-POWER-SOLENOID/-/1.html This is a sample it is intermittant duty you need a constant Duty Relay 
------------- John DeRosa (Hotwaterwizard)
Stockton California
When in doubt, try it out !
Posted By: howie ll
Date Posted: February 07, 2009 at 7:52 AM
Just a point but Bosch 4 pin SPNO relays are rated at 40amps. I've also pulled relays out of Fords with the same body and much larger contacts rated at 80+ amps
Posted By: ckeeler
Date Posted: February 07, 2009 at 11:13 PM
hotwaterwizard wrote:
Use a Bigger Relay! Camdec Corp # 93285. 12 Vdc, 4 ohm coil. Heavy-duty, handles a 225 Amp load https://www.allelectronics.com/make-a-store/item/SOL-80/12-VDC-POWER-SOLENOID/-/1.html This is a sample it is intermittant duty you need a constant Duty Relay
just saw this, and also gotta say Howie, once again you ar right. there is also a relay in alot of VW's and Mack trucks that is the same as the standard SPST relay with the 30 and 87 contacts rated at 70 amps. the terminals are bigger than the normal 3/8 terminals.
Posted By: ckeeler
Date Posted: February 07, 2009 at 11:16 PM
also, all riding mowers use the relay in the above picture for a starting relay. funny....
Posted By: howie ll
Date Posted: February 08, 2009 at 3:19 AM
By sheer irony or is it coincidence the UK page shows an ad on top from a company called raw components, they are showing a 100 amp at about $15 and a 70 amp normal casing, larger 30 and 87 terminals at about $10 see bottom of their relay page.
Posted By: howie ll
Date Posted: February 08, 2009 at 3:22 AM
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