Hi folks,

After burning through a bunch of fuses and relays, I've installed a cheap continuous-duty solenoid to control my electric cooling fan (which I plan to replace with a Lincoln or similar when I have the time). It uses a layout & 4-post post configuration like an old starter solenoid. Have two quick questions.

1) Right now it's working with battery positive going to one large post & the fan power to the other; with a switch in the cab wired to the "S" terminal and nothing attached to the "I" terminal. I'm reading conflicting information on whether in this application "I" should be grounded, jumped to "S", or something else.

2) I have a radiator temp kit to wire in, replacing the cab switch circuit. I'd like to install a dash light so that I know when the fan is running, but don't understand where to put it. If I run it in parallel with the fan (with a separate fuse), will that work, or will the big amps flowing to the fan somehow also blow out the fuse? I also considered putting it in line with the switch, but it seems to me that if the fan dies & the switch is closed, the light would still come on (and detecting failure is a big part of what i want to be able to do). Basically I don't know what I'm doing. I tried a lot of searches, but the second you put "light" and relay or solenoid in the same query, you get a million hits about headlights...
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please excuse the messy wiring, placement isn't final yet..

 

1. You can leave the 'I' terminal unconnected for this application. It stands for ignition and was used to provide a coil bypass during cranking. You don't need it for what you're using.

2. Using a starter solenoid as the fan relay will limit you in the type of temperature switch you can use because one side of the relay coil is permanently grounded. That means you can only control the solenoid by switching 12 volts to it. As such, you can't use the single-terminal temperature switches that ground out after a certain temperature. You'd have to use a two-terminal switch that opens or closes the two contacts based on temperature, then you'd switch 12 volts to the solenoid. Before we move on to the light, try to give us a model number or link to the style switch you're using first.

 

Toss the solenoid, and use a relay like this:
http://www.mcmelectronics.com/produc...9-150-/26-534B
Can be used in many configurations regardless of temp switch type. Wire a 12 volt light or led (with appropriate resistor) in parallel with the fan for an indicator. Actually, if you use a DPDT relay, (search the website listed) you can use one set of contacts for the fan, and the other for the light, thus avoiding any possible inductive kick from the fan to the indicator light. If the 30 amp relay shown won't handle the fan load, pick a 40 amp version, though I doubt the fan will pull 30 amps. What size fuse did you use for the fan?


"Who really cares about it being unconstitutional?" Pittsburgh Councilwoman Tonya Payne

 

A DPDT relay is making this too complicated. The light can be triggered using the same circuit that goes to the 'S' post of the solenoid, assuming he has a 2-terminal switch. The light and starter solenoid coil can be grounded, with switched 12 volts running the 'S' post and the light in parallel. This also isolates the light from the fan.

 

hey all,

thanks for the responses. i did wire the light in parallel to the fan and it seems to be working fine, although i'm experiencing new weird behavior (described below).

the fan switch i plan to install is not flex-a-lite, but otherwise similar to this one:
<IMG SRC="http://broncograveyard.com/images/catalog/zoom/ADJSTTEMPSNR.JPG" ALIGN="left">

...my kit comes w/ a 30 amp relay, which i planned to toss (well, not install, anyway), instead sending the relay signal to the "S" post on the solenoid.

I've posted about the fan before, FTE consensus is that it's dying, hence pulling huge amps and needs to be replaced.

the backstory, for those who are interested (feel free to skip ahead) is that the truck was previously owned by FTE user 'honkytonk', who installed the fan & an aluminum radiator. i've never met him, just found the gallery here. he apparently sold it to the PO, who didn't know the fan had an inline fuse (which was easy to miss). during Gustav evac, the fuse blew, followed by the radiator overheating & cracking. i bought the truck in November w/ a blown radiator covered in jb-weld and the fan wired directly from the battery to a toggle switch in the cab. i replaced the radiator with a 3-core 'super cooling' model, which seems to work OK. the switch subsequently melted. i replaced it with another, rated for 20A, which also melted after a few weeks. i replaced it with a new push-pull switch rated for 70A, and put a 30A fuse inline. fuses would last at most a few days, sometimes only a few minutes. i replaced the fuse holder with a 50A automatic circuit breaker, which lasted a few months before also melting (i didn't know circuit breakers could do that). i've now wired in the solenoid, and realized i could have saved a lot of time and money by just buying the lincoln fan back in November.

so obviously i'm gonna just get the new fan, but some folks have also needed to use solenoids with those too, due to the big initial draw. i wired the light in parallel with the fan today, and it's working great. that said, something else weird is going on- since this afternoon, sometimes i'll have to hit the switch a few times before the solenoid kicks in; and sometimes it's not going off right away after i kill the switch. it there like some kind of capacitor action going on? or is there a warm-up/cool-down period or something? i only paid $12 for the thing, so it's not like my hopes were up that high, but I just need this setup to work until the end of the month- I have all of August completely free to do more work/ replace parts/ go on junkyard adventures/ whatever.

 

Why do you think this is a continuous duty relay? With the "s" and the "i" terminals, it's obviously a starter relay, and I would not think it would be rated for continuous duty. I am not saying you should not keep using it, but keep this in mind if it does fail.

 

went to napa warehouse. said, "hello, i'd like to buy a ford-style solenoid, please." guy handed me one. i said, "is this one continuous duty?" he said, "no, you need this one." i said, "great, how much is it?" he said "$some astronomical amount of money." i said, "wow, is there a cheaper alternative?" he then sold me a NAPA ST81SB. cost about $10, which seems suspiciously low, but like i said, just looking to get through the month.

here's the link, which provides absolutely no useful information:
http://www.napaonline.com/NOLPPSE/(S...SB_0213380125#

 

That's a starter solenoid. The link didn't work, so I couldn't read any further on it, but as end-users, there's really no easy way for us to determine if it's rated for continuous duty or not. The difference comes down to whether or not the relay coil winding can handle the heat dissipated by current running through it for a significant amount of time.

Using a starter solenoid for this application is too much of a hassle. You're basically bending over backwards to install a relay that can handle the current draw of a fan that may be failing which is asking for trouble. You need to solve this problem the correct way. That means:

1) Look up the current draw of the fan from the manufacturer.
2) Use a relay with a current rating capable of handling the fan's current. It's good design practice to use a relay rated for 1.5 times the current that the fan will draw, to give you some headroom.
3) Use wiring capable of handling this current draw, and install an inline fuse that will blow below the wiring's maximum current rating.

I looked up the instructions for the fan switch, and it's still not clear to me how it should be wired. It says to connect the switch directly to the fan itself, but usually the switch is wired to the relay trigger. It's implying that you should hook the fan directly to the temperature control unit, but any description I can find says the unit does not contain a relay and there is no form of current rating for this item. Since you're not using that exact fan switch anyway, ignore any suggestions I've paraphrased from the instructions.

To tell you the truth, I don't recommend radiator sending units for electric fans. The only way to get an accurate reading of the engine coolant's temperature is to place the bulb directly in the path of the coolant, which you can only do with a temperature switch that threads directly into a water jacket.