Starter solenoids are usually very low duty cycle and will overheat & fail if you try to use them full time as a high amp switch. You can get 100% duty cycle solenoids, but this is only a solution if you're using a relay type of controller & then you replace one or both relays with these solenoids (they aren't cheap either).

If you use a digital controller (PWM), they have built-in solid state switches to feed the fan with the high amp pulses, so adding a mechanical switch like a solenoid isn't possible (the mechanical switches can't respond fast enough to give you the pulse train you need to run the fan - the ones I made generated at least a couple of hundred pulses per second). If you overload these solid state switches (they're a "form" of transistor) they will overheat almost instantly and then that's the end of your controller. Many of the PWM units are rated for around 30 amps max, the Painless unit is advertised to be able to operate with about 75 amps - they also state that it's designed for the Ford fans (Taurus).

 

Damn you state some valid points, is there a way to tell by looking at the fan sticker if they are over or under 30A?

I suppose this could all be avoided by installing a simple lighted flip switch for now, I was thinking about putting my fuel pump on a switch too so that there is no way I could forget haha and I would be one step closer to removing the factory computer and wiring to run aftermarket gauges. If I am running a standalone or carb with my own gauge system I think the stock wiring is all but useless at that point.

 

Often OEM stuff has no stickers. It strikes me that if you wanted to do your own research (often not worth it since much of it's already done), you could see if the electric motor(s) had any stampings on the cases - even the make & model could be enough to find the specs on that motor. Otherwise, I'd have a look at the wiring gauge and take a guess from that and then "err on the side of caution".

I wouldn't use normal switches (toggle or otherwise) to switch high amperage or even to start a device like an electric motor. Most switches aren't designed to handle the arc - you can add some arc protection circuitry, but it's far easier to use a relay. In this case the low amp circuit is run by the switch and the high amp side, by the relay that's designed to survive large arcs.

You could use a "solid state relay" which has no contacts as we know them, but is still wired up like a relay. Depending on what your electronic knowledge is, you could make one of these yourself with a MOSFET and a bit of monitoring & protection circuitry. These also use very little power and could be used to translate a lower amperage pulse train to a high amp pulse train, except for the point in my next comment on load sensing.

In my previous post, I mentioned that the solenoids wouldn't handle the pulse frequency needed for PWM. Well, even without that, it wouldn't work - most of the controllers that I tested some time ago, had a load sensing circuit (they needed to sense a draw of about 5 amps) so that if the fan motor failed, the controller would stop feeding power to it. Inductors like solenoids don't need an amount of power that would equate to a 5 amp draw.

There are various PWM kits that you could piece together (some of these kits are well made) that would allow you to run your fan in this manner, but it wouldn't have all the pre-programming smarts offered by the currently available controllers. If you're interested in any of this, I'll post a bit of a "diatribe" on these kits and what I'd suggest doing with them.

 

Hmm, well if I am going to go into piecing this together and it gets this complicated for the $ I might as well just buy a unit for $100 I mean I would do it myself if it was a simple on/off but if it requires building a circuit...maybe I can just use 4 low current fans in a push & pull setup.

 

You know, designing a cooling system can be complicated, but you've already got a baseline designed for you. The system for the dakota isn't hard to build on if you were going to keep the V6, but since you're going to an 8, you can look at one of the RAMs with that engine and use that setup as your design baseline and work from there. The biggest variable to doing this is your "usage scenario", ie, how do you want to use the truck. For most scenarios, you don't need the really high volume air flow offered by things like the Ford fans and can easily go for the lower power units along with a good sized rad, especially since you have the room to install a larger radiator. Once you're happy with the scenario, look for your components and this often can be broken down into 2 areas - finance and fabrication. If you're good with your hands, you can save cash. The important area related to fabrication is the air ducting (shroud), and if you consider yourself a reasonable worker plastics, you can easily build whatever you need to duct the air through the rad - I use ABS sheet (some 1/8" and some 3/8 or 1/2"), something to cut it with, a drill and bits, some self tapping screws, a heat gun, and ABS solvent. In addition, large sheets of paper are good to draw your templates.

When you decide to put your fan system together, I'd recommend that you not stack them - don't put pushers in front of pullers and avoid putting a pusher in the front of the truck - these configurations will often give you less than the sum of the components, and pushers give you best results in areas where you don't have air blasting right at the fan (like in front of the truck when driving). A puller configuration is the most efficient, and a dual speed, dual fan, or PWM for single or dual fans.

 

Is the fan system in a separate controller unit on the Rams or part of their ECM? I was actually thinking bout trying to squeeze a Ram radiator in since I have some leftover room and I can always cut some too:



They are wider but not sure how much wider, also a 5.9L Grand Cherokee had the same radiator as a 5.2L and they came with an efan. Thanks for all your help! I will deff fab something and keep you posted with pictures.

 

I can't tell you for sure whether it's a separate controller or PCM that runs the fan, but you could probably find out from your local dealership - the parts counter should be able to tell you. If your intended engine is using an e-fan in other models, I'd be looking for both the radiator (complete with all mounting brackets) and fan (complete with shroud and wiring to a plug). The size of the wiring on that fan should give you a good idea of what kind of controller you need to connect to, and also, there should be a fuse somewhere - the manual for that vehicle should be able to let you know the fan fuse value (owners manual should have it).

 

So my new efan came... $35 shipped from Amazon. It's from a Ford Escape, and it is within 1" in every direction of the factory shroud. It's also pretty low profile. I'll let you guys know how it works out once I get running again. Stupid hughes intake plate mod of DEATH!

 

Cool. Post the dimensions and the year and motor the fan is from. I'm really interest in how thick its it at it thickest point. Do you have any CFM's?

 

Will do... It's VDO FA70513. Normally $143 from Amazon, but there was an open box special for $35

Fits all 2.5l Ford Escapes, Mazda Tributes, and Mercury Mariners 2009-2011.

Will get dimensions tomorrow when it's light.