The Stovebolt Site Forums The Shop Area The Electrical Bay Alan - Radiator Fan Relay Question!

Alan:

I went to your website and looked at your article on running your radiator fan through two relays. This is probably a dumb question, but why two? Most commercial aftermarket setups are using just one 30 amp relay. Is it because there is a spike in amperage on fan startup?

This isn't Alan and I'm sure when he see this he'll reply, but if I were going to wire in a fan I'd have it set-up to run when the engine got up to temp, and a manual over-ride for when I thought it needed to run, 2 circuits.

Clint Lovell,

This isn't Alan either, and seeing as waldo53 broke the ice, I'll shoot the breeze too.

Alan is a big fan of Mad Electrical. If you visit the site and find the dope on fan installations, you will see that the owner (Mark) recommends two relays for this install.

The relays he spec's are rated at 30 amps...more than enough for the fan. So why use two? He indicates the the motor that powers the fan, when working hard, will draw enough current to heat the connections where the relay plugs into the socket. This will eventually 'crisp' things and lead to failure, which means no cooling.

In an attempt to 'half' this load, he recommends two relays, thus sharing current draw through the suspect wires. Simple, HUH!

The relays are merely the switch to turn the fan on..dumb. The temp sensor is a totally different component. It's the brains that turn the dumb relay (relays) on.

Stuart

This isn't Alan either .... but
YES you answered your own question.
Follow every above answer.
When you have a fan that runs off a thermostat and the engine finally comes up to temperature-HOT. The thermostat triggers the fan to ON.
the current draw is pretty high @ start-up so running two relays, spreads the current to two different relays lessing the possible failure if you only run one relay. When a fan is running the current draw is greatly lessened. About the last thing you want on a hot day is your fan not working cause you could not afford two relays and the one stops working. relays cost about $6.00, that includes the socket too. They're cheap and fairly easy to wire. sure beats a single 30 amp fuse.
DON'T run a fuse for this purpose! :hammering:
also consider using a fusable link that gets wired to the relay power source post #30. a roll of it runs about 6 bucks @ FLAPS and is 25 feet worth.

Fusable links should be 4 wire sizes (gauge) smaller than the circuit wire gauge you run for any circuit. solderless but soldered connections and heat shrink all terminals.
I run on my 51, 6 relays for various power using operations and have an additional multitude of fused circuits.

18ga. Fusible Link protects 14ga. or heavier wired systems
16ga. Fusible Link protects 12ga. or heavier wired systems
14ga. Fusible Link protects 10ga. or heavier wired systems
12ga. Fusible Link protects 8ga. or heavier wired systems
you can buy fusible link wire in bulk @ most any FLAPS and if you intend on doing a whole wire harness or have several projects going it's really cheap to buy bulk.
TRY:
A LOT of Information here...
http://www.madelectrical.com/catalog/rly-1.shtml
relay kit : http://www.madelectrical.com/catalog/rly-1.shtml
http://www.madelectrical.com/catalog/fusible-link.shtml
http://www.madelectrical.com/catalog/cn-1.shtml I highly suggest this.
my.02 :p

Alan must be in Cancun sunning 'his bad self'! That's OK, we can speak for him...I think.


Stuart

Heck, my middle name isn't even Alan. Bu I do have some questions for Atomarc, Waldo53, and Carolines truck. 1. If you run two relays for the reasons given and one does fail for whatever reason. How ya gonna tell? 2. Instead of running two relays, one for you to turn on and one for the heat sensor to operate, why don't you just run the "brains" or switch and sensor in parallel to one relay. 3. Fuses vs. fusable links. Blown fuses a a lot easier to trouble shoot. Fuses are generally located in a central location. There're easy to replace on the side of the road. A lot of guys don't carry VOM's or DVM's in their tool boxes. So why would you want a fusable link in this situation instead of a lowly fuse?

beltfed,

Don't shoot the messenger!

You couldn't tell if one relay failed, unless of course it failed 'closed'.

The thermo sensor (?) merely switches the control voltage for the two parallel relays that turn the fan on and off. The husky 30 amp contacts of the two relays handle the fan motor.

MAD contends if you split the motor load between two relays, the contacts will last longer, but more importantly, the load on the crimped terminals of the plug in sockets is now shared by two devices, so they won't overheat and fail.

It isn't uncommon for the spring clips on fuse holders to create a high resistance connection, heat up and loose their grip, so maybe a bolted or soldered connection on a fusible link makes sense.

As I remarked in my opening statement, I'm just reporting what I read on the MAD Electrical site. It is a interesting site, well layed out and full of down to earth info. It sounds like "Mark" has been there, done that, so I won't cast dispersions quite yet. That's my two cents!

Stuart

Clint
Stuart knows this stuff.

SO Carry a spare bosch relay in the truck. they're about $3 bucks
HERE is a good place to store those extras :::::
http://s67.photobucket.com/albums/h298/1951otter/?action=view&current=DSC00492_0008.jpg

http://www.stovebolt.com/bboard/cgi-bin//ultimatebb.cgi?ubb=get_topic;f=20;t=000655

LOL! This *IS* Alan ... and I have absolutely nothing to say because atomarc and carolines truck said it all.

Amen, Brothers!


PS - I've been playing with my new industrial sewing machine, working on recovering my armrests ... the 2nd time - because the aftermarket plastic - :mad: - broke when I slammed my door last week in freezing temperatures; I'm making new mounts out of red oak and covering them with elk leather.

This isn't Alan either, but now i'm going to go re-wire my fan via a couple of relays... it's currently hot wired to run all the time... like when i got the truck..

Rusty Rod,

Either you have a huge battery or you just got the truck if the fan has be running continuously since you got it! Seriously, put the relays in quickly if your fan is hard wired to the ignition switch, otherwise you will be replacing the switch soon.

OK. Talked me into it. I got two relays, ordered a screw in the manifold thermostatic switch and picked up a few fuseable links at the FLAPS.

Way to go, Clint!

Can I run my electric fan all the time when the engine is running? What are the down sides? I've tried using a Perma Cool temp control switch with a radiator sensor and it failed to kick the fan on...Perma cool replaced it and the new one wouldn't work either. So I hooked up the fan to run whenever the engine was on...I did use a pretty large relay however... The engine is a 350/330HP with an alternator/serpentine system and it does tend to run hot. With the fan on all the time temp stays about 180 degrees.

steveg,

It sounds like your cooling system is being overtaxed. If the fan runs constantly and will only hold 180&deg, it's just a matter of time until you overheat.

Your radiator is too small or plugged...or your fan setup is too small or installed wrong.

If all systems work properly, you should almost be able to select a operating temperature with a different temp thermostat.

I would investigate this problem before the first run up a steep hill on a hot day.

Stuart

Uhmmmm! I'm probably missing something here, and it's true I haven't had my nap today but running at 180 with the fan on all the time sounds normal to me. It doesn't seem to me that steveg needs to start working on his cooling system just yet. If his thermostat is 180, it doesn't matter if the fan is wired to be ON all the time or not, (just like a mechanical fan) the thermostat is controlling the temp. Right?

waldo53,

What you say does make sense..I have been having a tough day on the old Bolt. My thought would be, if the fan was running all the time, which it shouldn't be, just to maintain 180&deg, what would happen when the truck needed more cooling. You can't run the fan more than 100% can you.

If he has a 180&deg thermostat in it, then the electric fan should help hold this temp by running only part time. The hotter the rig got, the more the fan would cycle until it was on constantly. This would only happen when it was hot outside and the truck was working like heck.

Right now, there is absolutely no reserve, the system is operating at max!

I think the idea of a electric fan is to be too efficient..engine temperature is then maintained by cycling it on and off. Does this theory make any sense.

Stuart

[QUOTE]Originally posted by atomarc:
[QB] waldo53,


Right now, there is absolutely no reserve, the system is operating at max!


We don't know that, do we? It's only running at max if the thermostat is fully open. If the fan, radiator, water pump, etc. are all doing their job, the thermostat will regulate the temperature, by how much it opens up, even if the fan is on all the time. I'm not saying that running an electric fan continuously is a good idea, I wouldn't run one that way, but my old mechanical fan runs continually and once the ol' bolt warms up, it stays a constant temperature. Now, when the weather warms up, he's pulling a load or going up a steep grade and the thermostat opens all the way, and if the temperature guage starts climbing, then "Houston, we gotta problem" and he would be operating at max.

Waldo53,

I might be seeing the light. The fan isn't running continuously because of a temperature issue, but because it is switched ON and held on.

Ideally, the cooling system might be working a little harder right now just to keep the poor old engine at 180&deg with the fan on when it really shouldn't be on.

Is this your thinking...it makes sense to me, thanks.

Stuart

Thanks guys...Has anyone else had problems with the probes that you stick in the radiator fins not sending a signal to the fan controller?

atomarc; Yeah, the fan is running because it is switched on, not a temp. issue. The poor little fella has no choice but to be on. Mr. Thermostat is thinking to himself, "I'm gettin' tired of restricting the water flow to the radiator, I'd rather just open up, but that ##$%$& fan won't shut off, he keeps cooling my water down"!!

I definitely agree that Mad Electric is the place to visit. He sells great wiring hardware and an interesting and informative pamphlet on auto wiring.

http://www.madelectrical.com/electrical-tech.shtml

you can also pick up any Bosch relay locally, fusible link sold by single or bulk (U make) if you want,,,, it's very easy to do 6-8'' long. my thermostat switch is a napa one at 190 degrees napa #8750, screwed into the lower half of the thermostat housing. it's mlld cast iron, easy to drill and thread 1/4NPT. run your ground wire from it to both #85 posts on your relays. you can also keep a hand switch inside the cab, another option wired to ground, parallel circuit. just incase of a hot day.
but
have the radiator core rodded and cleaned.

dont forget to add a circuit to come on with the A/C for those running A/C.

Excuse me if this is a dumb question, but.......I'm also thunking of going with an electric fan on my 66, 292 I6. I currently have a brass temp sending unit that screws into the thermostat housing (factory) What do I need to purchase, that will still allow me to use my temp guage in the dash, and also act as a switch to turn the fan on when needed.......can this be done with one unit, or do I need to tap into another area of the housing for a second unit. Whichever the case may be, where do I get one, and a part number would be great as well......THEN, I will have lots of questions about how to wire it!

Kerry
NO dumb questions here as everybody learns, some may know and not respond while
others are too scared to ask. BUT it's how we all learn. been there done that...
my 51 has a 292

it gets it's temp from the sender in the head just above the intake/exh manifold. that should have nothing to do w/ the temp switch that needs to be placed below the thermostat located in the front of the engine.
http://s67.photobucket.com/albums/h298/1951otter/?action=view&current=19A-1-1.jpg
i drilled the cast iron lower piece and tapped it for my NAPA #3750 temp, 190degree switch. this switch closes to ground when the temp reaches 190.
It's wired to 2 relays (single wire to a dual wire @ the relay single relay spades) at position #85.
#30 dual relays gets power from the battery handoff, I use this...
http://www.madelectrical.com/catalog/cn-1.shtml
http://s67.photobucket.com/albums/h298/1951otter/?action=view&current=0732700-R1-036-16A.jpg ... (notice the two into one wire at the relay spade terminal.), as my handoff using a single wire to a dual wire @ the relay spade.
# 87 dual wire @ relay spades, goes to single the fan,
# 86 dual wire @ relay spades, to single switched fused ignition power (fuse block).

read how relays work
http://www.autoshop101.com/forms/hweb2.pdf
http://www.tune-town.com/relays.pdf
http://alanhorvath.com/54chevy/mad_electrical_2.php

That's very helpful........thanks! I'm going to ear-mark this post for future reference, when I actually put in my electric fan. Your truck is a beauty by the way!!

I have read thru most of the postings here and agree with them all but I will add alittle bit anyway.
I've had my fan set-up with the two relays for 1 1/2 years now and have not had too many problems with it. when I first set it up I was told not to use fuseable links because they create sparks in the engine compartment when they burn out so I put two 30 amp fuses instead. After going through 6 fuses I put the links in and have had no other problems. I am running a sbc 350 in mine so for the temp switches I put the fan switch in the water outlet above the thermostat and the the gauge switch in the intake jacket passenger side. Like I said been working fine for quite awhile now.

And just for the heck of it Kerry, I'm from just down the road from you, Whitesboro, but now live here in TX