relays for electric fan in truck

Sorry - I missed the update....

kaztheminotaur wrote: I don't follow you on the 2/3 A solenoid blows the ECU ?

A typical 12V 30A relay is usually at least 60 Ohms (coil/solenoid) - ie, ~200mA (12V/60R). That 100A relay/solenoid's coil (solenoid? ) is 8W hence ~0.67A (8W/12V). What can the ECU sink? I thought I read 200mA but I might be confusing threads.... But less is better. And though ECUs may switch more, they may only be designed for a typical automotive relay. Not that I expected that to be a clincher. Although this isn't an airconditioning or heating plant (where oversize is VERY undesirable!), and whilst I like "safe" (and reliable and economical) design, there is overkill. And I doubt your fan(s) total 360 Watts??

The fan I plan on using has an average amp draw of around 38 and a spike, when starting from stop to high, of around 50.  So that should be 547 watts average and a spike of 720 at 14.4 volts ?

Here is my 3rd. diagram with diodes added:

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Fair enough - my apologies. Though I still think a smaller "typical" 60A relay is nicer - though they probably have 9mm (3/8") spade connectors for the contacts Don't worry about Watts - relay contacts are current-Amps devices. And remember - not much more than 8-letter image filenames. FYI - I use a $13 60A (70A) relay to connect my 2nd battery. It is turned on by the alternator's charge lamp wire. Twice now it has handled jumpstarting my flat front battery via the 60A relay & 2x50A circuit breakers; the starter is a reduction type that normally takes ~ 120A excluding solenoid. Viz:

Filename fr3(?) looks ok, but maybe download to your PC first. I could be a permissions error. I do a Preview Post before Post Reply to ensure the image is there. There is no error indication - you just end up with the placeholder "stamp" (square). Ad rem - I think a 200k limit. I cropped, shrunk & resaved the relay image above, but all were larger than the original. So more screen space, but less bytes (~16kB?).

I uploaded it to the server also...that seemed to work.

Yes to that last diagramme, diode position is correct, wire all other leads to 85 on fan relay AFTER diode!

oldspark wrote: BTW - I was thinking the 1A diode was enough for the quenching. [And yes, it should be 400V; 200V can be a bit low. Besides, the IN4004 400V/1A is now generally "the common" lowest rated diode - ie, lesser rated power diodes cost more!] But it is also fine in series with any "normal" relay - even the oversized 100A relay with its 8W = ~0.7A solenoid/coil. I'm even thinking of buying a bulk pack of 1N4004 (a few dollar$ for 100) and throwing out those unlabelled 50V 1A I got years ago for 2c each - 50V "unpolarised" cleanskins just ain't worth it!) Rem: Hail Howie!!

Just a comment- The voltage transient supression occurs in the forward biased region of the diode, so the voltage rating doesn't matter for this purpose. They'll both clamp to the same 0.7V over rail. If you're just running 12V equipment, the 1N4001 will serve just as well as the 1N4004's. It's the same 1A rating for both, so they'll be equivalent.