ericfx1984

wiring relays in parallel to increase load capacity

I can not find much info on this... I have several Bosche 40 amp 12v relays laying around and I need to be able to run a 90-95 Taurus fan on high

from what I have been told a 40 amp relay will not cut it...

however from what I have read a pair of 30 amp relay wired in parallel will be able to handle 50+ amps with ease

but it sounds to good to be true... anything else I should know? any drawbacks to doing this? I plan to run a pair of 40 amp relays in parallel

SeriousOffroad

Why not just use a relay rated for the amperage needed?

http://www.weisd.com/store2/nterly/NTE_50Amp_RELAYS.php

Seems silly to to reinvent the wheel for a simple fan installation.

wildbill1

I don't think that will work. The current will follow the path of least resistance and burn out one relay at a time if they are overloaded. I think it's the same principle as trying to use numerous pieces of thin gauge wire instead of using one larger conductor.

ericfx1984

my clutch fan stopped working... I need something today... I can always order that and install it later...

ericfx1984

from what I have been reading it WILL work, but the problem is that one of the relays will always make connection first... only by a millisecond but still... once they both switch, it should be fine

TheJerm

just run the fan on low. I never use my high setting because low is good enough

SeriousOffroad

Sorry, but 2 relays in parallel won't do anything for you with regards to decreasing the amount of current flow. Wildbill nailed it. You can't alter basic physics.

Electron flow will always follow the path of least rresistance...PERIOD.

Electron flow cannot be divided at and rejoined at any point in any system...PERIOD.

Any auto parts house will carry a suitable relay for the job, it's up to you to provide the part number(s) though since your application is not a vehicle specific application.

TheJerm

Not everything you read on the internet is true

If you do find a higher amp continuous relay post it back on here, it would be nice to have the high fan setting again. btw 85A ford starter relay wont work, ask me how i know

SeriousOffroad

D'oh...never mind.

So I'm asking...How do you know?

TheJerm

Starter relays may be beefy but are not meant for continuous draw of fans and i found out while driving thru the mountains while it began to overheat. Now its a nice paper weight. When i did the initial install i follow an online write-up and they used a 85A ford starter relay cause it was like $5 at the parts store. yea dont believe everything you read

I had high setting on my taurus fan for about 3 days last summer and have never needed/used it since.

longship

Nothing wrong with using paired conductors. Parameters must be the same for both though.

As to the relays, it'll work. The motor current isn't instantaneous, it takes some mseconds to build up. The problem with the twin relay set up, is if one relay becomes faulty, how will you know? When the other one burns out.

Rob

jronald

Using multiple connectors to carry current is NOT a great idea. I have done it many, many times in an emergency, and been paranoid the whole time.
This is what you want, ok this one is a little overkill:

They are also used for Battery Charge lines in Travel Trailers.

If you must run 2 or more connectors, be prepared for them to fail.


Ron

waltermitty

Indicator lights can be wired to show "on" or "fault" or both for each relay. I concur dual relays to a single device is a bad idea however.

5-90

In a pinch - maybe. I certainly wouldn't run it as a standard practise - there's enough potential danger involved in a failed relay to cause problems.

Easier to get a higher-current relay and do it on a single circuit. It's like ChryCo fusing the alternator output circuit with a pair of MAXI fuses - I'm glad they got away from that idea!

What are you trying to find?

ericfx1984

nothing now... I found a fan that works fine and only needs around 30 amps...


also I found that if you use the Taurus 3.8 dual speed fan it CAN pull up to 70 amps , but that is only from a dead stop going straight to HIGH SPEED...

if you run 2 thermo switches with one 30 amp relay per thermo switch and make sure that the low speed (2500CFM) is turning before the HIGH SPEED (4500CFM) kicks on, then the fan will not pull nearly as many amps during HIGH SPEED spin up

BUT... like I said, I am using a Taurus 3.0 fan instead of the 3.8, it is smaller and a simple drop in, for the most part... that in conjunction with the stock A/C fan and I NEVER over heat...