OK, If it's really that high, then go with 75 amp.

Of course, we are talking 12 - 15 volts and when I was thinking 10-20 amps, I was visuallizing 10 amps at 125 volt relays.

I was just looking at the relay in my wifes 85 Cutlas Ciera work beater and it has a very small relay in it. I don't know how it's rated.

 

The size of the relay does not always indicate the rating. I have seen plenty of the regular 1"x1" cube relays that are rated for 75+ amps. I'm with cjg here, I really think I need a higher powered relay, ALL of the writeups that I have read about this (A LOT) have called for higher amperage relays. Look:

http://highrpm.org/howto/taurus%20fa...taurusfan.HTML


And to Liemavick, I'm swapping to the electric fan because I have heard so many different expereince from people about the gains that they see. Most people say that optimally you will gain 1-2mpg and much better throttle response. I've heard people say you gain 10-15 hp but I don't think I trust that number very much. The logistics hold water because by removing the clutch fan you are removing drag from the engine. The clutch fan is pretty heavy and you're engine needs to get it moving FAST when you punch the throttle. If I don't see any gains from this mod, I am at least eliminating one component that causes THAT much more stress on the engine. Besides, its only like $20 for the fan!

And aside from that, I think my clutch fan might be on its way out so it's about time for this anyways.

 

I don't judge or rate relays by the size of the case, but by the size and construction of the contacts and armature.


If you are using 40 amps, you are loading your engine through the added drag of the alternator.

Actually, a fan is the most efficient because you are going directly from mechanical energy to the air flow. With the electrical fan, your energy is going from mechanical to electrical through the alternator then from electrical back to mechanical through the motor. Each conversion has a loss of energy.
Those claiming increased mileage are just wishful thinkers.

 

Chris, this is very simialr to how I had my relays wired when I ran the Taurus fan on my F-150. I actually hooked mine into the 12V+ wiring so it activates the system when I turn the key on and shuts off when I turn the ignition off (get forgetful sometimes if there is a toggle switch). I used the thermostat fan relay kit from jegs and purchased another kit w/o the thermal switch. Both came with 30A circuit breakers and 40A/ 30A relays (swapped to a higher amp relay on high side with a M-B fuel pump relay)which worked out very well ( I still use it with the Ramcharger fan that's on the truck now).

Kevin

 

Whelp! I downloaded an electrical circuit simulation program last night and I have been playing with circuits trying to figure out how this whole thing works. I have FINALLY successfully created a circuit that uses 2 relays and an adjustable thermometer switch to power a 2-speed fan!!!! There are a couple parts that are simplified (for my own purposes) such as saying that the thermometer is just a simple switch (yes I know it isn't, but can be treated like one) and that the A/C wire is INTERNAL on the fan controller. One last thing that might create some confusion, I wired in the ON-OFF-ON switch at the top right after the switched 12v source but the program didn't have a 3-way switch like I needed, so I just piggybacked 2 SPDP switches, again, just for the purpose of making my circuit work. Also, the 2 circles with M's inside are motors, and on my program they spin when they get power (like a fan... hmmmmm), I represented the 2 fan speeds with 2 separate motors. Feel free to make any corrections or criticisms!

 

Looks good Chris.
My only concern is connecting your indicator LED's across the motor windings at the outputs of the relays rather than the inputs.

The shunt diodes across the motors prevents inductive spikes when switched on as they should, and also will prevent the fan from spinning backwards, however If you are driving down the road and the fan is shut off, the air coming through the grill will keep the fan going in the forward direction, and will generate a positive voltage that will keep the LED's lit. Also, even though you have the high and low motor windings shown as two separate windings, I'm pretty sure they are one long winding with a center tap and when ever a voltage is present on one winding, there is a voltage present on the unused winding.

One remedy I can think of is to tie the indicator LED's to the inputs of the relays as I originally suggested to you.

This of course has drawbacks too, or perhaps an asset depending on how you look at it.

While you are in high speed override, the high speed LED will indicate.
If while you are in high speed override and your thermostat is in high temp mode, then current will flow backwards through it and down to the low speed LED and both LED's would be on.

So.......... with the override off your low speed LED would indicate that the system is on and in low speed.
And if the thermostat called for high speed, your low speed LED will shut off and your high speed LED will come on.

But if you are in high speed thermostatic mode, and switch to high speed override, both LED's will be on. This would alow you to monitor the thermostats mode while in override.

If the above is the preffered for you then just tie the LED's to the inputs of the relays.

If not, let me know because there is another workaround.

 

Nice schematic Chris. For the heavy duty relay this is what I used for the hi-speed of the fan at the local speed shop (plus not as expensive as the Bosch):


http://store.summitracing.com/partdetail.asp?autofilter=1&part=NEX%2D15515&N=700 +4294925143+4294839062+4294845465+115&autoview=sku

This is what I used for the low side when the A/C is off:

http://store.summitracing.com/partde...5&autoview=sku

 

This is not the case in my simulation. The motors gain momentum so even after the electricity to the motor is cut off it continues to spin down slowly to a stop (as would a fan), but the LED for that motor shuts off as soon as the power is cut to the motor, regardless of whether it is spinning still or not...


Isn't the freewheeling diode across the motor supposed to prevent the current from flowing backwards? Like a 1-way street?

If thats true, doesn't sound like a bad setup to me, as long as it is not damaging the circuit...


I'm not trying to tell you that you are wrong here netscaner, you obviously know what you are talking about. I am just telling you what my experience is in using this simulation program (and it's a pretty good one too). If you can download and install a free version of Crocodile Clips (I'm not sure if thats possible) then I can send you my circuit and you can play with the switches and LEDs yourself. Thanks for all the help dude, stay with me here

 

Chris, this is relatively simple stuff for me, so I handle it in my head.

Simulators are very shallow and only can handle situations that are programmed into them. They don't address situations such as air coming through the grill keeping the fan spinning when relay power is off.

Like you noted, diodes conduct in one direction, but not the other, that's why I noted that they will stop the fan from spinning backwards, but not forwards which would be your situation when driving down the road with no power to the fan.

You also have the simulator thinking it has two independant motors rather than one motor with two windings that are inner connected which is your actual situation.

The situation with the high speed override activation current flowing back through the thermostat has nothing to do with the motor spike suppresion diodes.

As an afterthought, you can connect the LED's to the inputs of the relays and prevent both LED's from coming on at the same time while in both high speed override and high temp thermostat conditions by putting a diode inline with the wire going to the input of the thermostat right at the thermostat.

So.............you can have it either way

 

Okay so I moved the hot side of the LED to the 85 relay pins and yes, it had the effect that you said it would, now both LEDs light on the high speed setting. I experimented with putting diodes around the thermometer and it did not make a difference... But I think I like it like this; basically the GREEN led is always on as long as the in-cab switch is set to thermo control, when the high speed is activated (whether by the thermo switch or by the A/C) then the red LED becomes lit, leaving the green lit also. Once the engine cools again the RED will go off and only the GREEN will be left glowing. The only time that the red will glow ALONE without the green is if I set the in-cab switch to manual override/forced HIGH speed, which is also fine by me. Here is the circuit as I have it:



Are all the diodes that I have necessary? Also, which part number should I be using for all those diodes?

 

I don't know what to recomend for the diodes across the motors, but 1n4004 or higher for the A/C and the two accross the relays.

You can probably get them two for a buck or so at Radio Shack.

 

1n4004 or higher. What does that number signify and which direction is "higher", 1n4005 or 1n4003?

 

How bout these, they are the highest amp rating diodes that radio shack has on their website:

http://www.radioshack.com/product/in...entPage=search

 

The 1n4000 series diodes are 1 amp which is plenty in the relay circuits.
It's the "prv" peak reverse voltage that you are concerned with because of the spikes they have to suppress.
A 1n4000 is 50 prv If I remember right and a 1n4001 is 100 prv.
1n4004, 4005, 4006 should work for your circuit.

I think the 6 amp diodes you are reffering to at Radio Shack would not be good because of their low prv.

 

Thanks a bunch netscaner, I'll keep you posted on how this project goes for me. Mind telling me your name?