47-55.1 MAD electrical

[Matt_50]

When I did my wiring a few years ago I used a basic kit along with Mark's advice from MAD electrical. Talked to him a couple times on the phone to for clarification on things and he talked my ear off for hours lol.

Anyways. I'm cleaning up some wiring, trying to make things look neater, and I found my wiring diagrams I made up BUT once I got to the relays I didn't finish the diagrams.

I dont remember why I used two relays together for my single fan. I know it was probably due to something Mark said but I don't have the tech books he sent me anymore. Can't find them.

I have a receipt. Not trying to get free info from someone who paid. See picture. But does anyone here have the MAD electrical tech and relay booklets?

I'd like to finish out my wiring diagram and put it in my build book for future reference.

[leegreen]

my guess:
one relay is for the engine thermal switch, which goes to ground when it is hot to trigger relay

one relay is to turn on fans when AC is on, using 12V+ from compressor clutch power circuit to trigger relay.

Painless sells a dual activation relay set for this. They have a manual for it online that might help you


I don't see AC in your under hood pictures, maybe you prewired for it. Texas does sound like an AC kind of place

[Matt_50]

They run together. I traced the wires off both those relays.

Both yellows splic together and go to the fan.

Both whites meet at the temp wire.

Both blacks also splice together and go into the wire bundle. Switch I think.

Both blues go to the circuit breaker.


It looks like I could eliminate one of the relays, but I know I followed instructions for this part so its driving me crazy not knowing why.

Its like a wired two relays for a dual fan but its only a single fan.

[joedoh]

if the outputs are spliced top the same wire on the fan its because of LOAD. most fans pull upwards of 40a and most automotive relays are 25 steady state 30a peak load. using two relays you are splitting the amperage over two instead of using one which will keep them alive a whole lot longer.

[Matt_50]

That kind of rings a bell. Thank you! I'm about to move the relays and make it look nicer and I started to think maybe I should remove one.

[mr48chev]

He explains the reasons for the relays and how many here http://www.madelectrical.com/catalog/rly-1.shtml

He does a good job of packaging and marketing kits that you can actually hunt down the pieces for yourself but a lot of guys don't have the time to hunt for the pieces or the knowledge of what they are actually hunting for. Plus there isn't a thing wrong with paying him for the knowledge that he used to provide a kit that will work.

Worth a look for a lot of folks. http://www.madelectrical.com/index.shtml

[Matt_50]

Ha! In his description. I was worried I'd need to buy it again to find out why I did what I did. I'm kinda tempted to anyway just for the material. I could use it for the next project .

For anyone wiring up their project I recommend not just buying through his website but calling him up. He gives a lot of advice and I remember working out part of my diagram with him over the phone.

[leegreen]

That Bosch style relay package is available in various ratings, typical overseas cheap stuff most likely 20-30ish amps, but you can get 60-80 amps ratings. that would be 60 amps normally open side , 80 amps normally closed side.

So you can wire for a 70 amp fan with single relay on NC side of relay - just get a good relay and socket.

From the few I have tested, the amperage rating is driven by marketing and real draw is considerably lower.

[joedoh]

i have wired a lot of electric fans in my time under the hood and even if i had an 80a relay i would still split the load over two, and here is why.

there is a big difference in the wiring required for a 40a fan and a 20a spilt load. two 14ga, one each on each relay terminal vs 8 ga on a single relay terminal. if you fuse the two 14ga separately at 20a you will have better protection than a single 40a fuse on an 8ga, because 20a fuses can use atc style which pass 15-20% more than their rated current before blowing, but a maxi style 40a (they make a 40a atc style but I would not use it in this application) will pass 30% its rated current before snapping. a dead short will snap atc and maxi instantly, as an addendum.

cost of the larger relay will be less than two smaller relays, but replacement cost will be higher. wire costs are higher, needing more expensive terminals.

do what you like, but for me i will split the load.