Think I finally got this thing figured out, I hope. This questions apply to installing ford windstar fans in a 70. My questions:

1. Can I tie the power that goes to the #30 terminal of the relays(70 amp) together or do I need to run separate power lines to each relay from the horn relay buss bar?

2. Can I tie the ignition power that goes to terminal #87 of the relays together or do I need a seperate power line run from the supplemental ignition power distribution block?

3. What size breaker/fuse should I use in each of the power lines(constant power from the horn relay to #30 terminal and ignition power form distribution block to #86?

Thanks to all who have helped and for your patience with this electrically challenged individual. Pete

Think I finally got this thing figured out, I hope. This questions apply to installing ford windstar fans in a 70. My questions:

1. Can I tie the power that goes to the #30 terminal of the relays(70 amp) together or do I need to run separate power lines to each relay from the horn relay buss bar?
This is a high amp power feed so I would run seperate power lines.

2. Can I tie the ignition power that goes to terminal #87 of the relays together or do I need a seperate power line run from the supplemental ignition power distribution block?
This is a low amp power feed so it would be safe to combine.

3. What size breaker/fuse should I use in each of the power lines(constant power from the horn relay to #30 terminal and ignition power form distribution block to #87?
The #87 terms require peanuts for power so something as small as 5A would be more than sufficient. Truly it depends on what size wire you run, which often is sized to supply the power required. So a small wire would use a small fuse.

The #30 terms are a bit different. I am making a huge presumption here since you are talking about multiple relays that you are running one relay per fan? As I think about it here is what I would do:

1. I would measure the resistance of the fan motor with an ohm meter.
2. I would use E/R = I, or 14 divided by the number from #1 above, to calculate the startup current.
3. I would add a safety margin of perhaps 20% to the startup current.
4. I would size the wiring and fuses to the current calculated in #3.

Note that the wiring could be undersized by a bit since this is a startup surge current and typical operational currents will be much much lower. But then I would not undersize by too much because of the environmental parameters. Part of wiring current ratings is heat dissipation and that degrades in high temperatures, so we use larger sizes to compensate.

Or you could just figure you have 70A relays and wire/fuse for 70A :-)

Steve

Power wires to #30 & #87 are 10 gauge. Power wires to #86 are 14 gauge. All other wires are 14 gauge as well. Pete

10g should be fine. Some of the best cooling out there don't draw 70 amps so I doubt the Windstar fans do. Even if they do 10 should be ok. I assume the relays are close to the horn relay so you're talking about a foot or two of wire. This is not like house wiring where you have to consider voltage drop and the corresponding heat buildup.

Anyway the whole Chevelle electrical system, minus starter, was powered by a 10 guage wire originally.

The 14g wires are more than you need. They'll work fine but you could easily drop 1 or 2 sizes.

I assume 70amps is both relays, 35 each. If so you could go horn relay to relay 1 to relay 2 with no problem.

Also, I think you posted before about an alt upgrade, correct? Stock alt is not going to like those electric fans.

Power wires to #30 are 10 gauge. Power wires to #87 are 14 gauge. All other wires are 14 gauge as well. Pete
That sounds reasonable for the power wires and much more than you need for the control side. You could change that 14 gauge to 18 gauge wire and be fine.

You might want to clarify how you are setting this up... two fans, two relays, all in parallel or some creative high/low speed setup?

My Taurus fans are run in parallel with a high and low speed relay. The high is thermostatically controlled. The low is currently wired into a dash toggle switch. Two parallel control relays, one ground switched and one power switched.

I may revisit this in the future with the addition of EFI and A/C and a better understanding of the startup surge currents of these fans. If you have a way to either start them one at a time or first on low your electrical system will be happier. If I hit my system with the 70A startup draw it drops system voltage down under 10V momentarily, even with a CS-130 alternator. This drop is enough for the headlights to go out and the stereo to re-power up.

Steve

10g should be fine. Some of the best cooling out there don't draw 70 amps so I doubt the Windstar fans do. Even if they do 10 should be ok. I assume the relays are close to the horn relay so you're talking about a foot or two of wire.

I evidently misunderstood and have them in the middle of the shroud closer to the fans. There is approx 2 foot of wire from the relays to power(horn relay). Do I need to mount the relays closer to the horn relay buss bar? Also what size breaker should I use in the power wires? 30, 40, or 50 amp?

This is not like house wiring where you have to consider voltage drop and the corresponding heat buildup.

Anyway the whole Chevelle electrical system, minus starter, was powered by a 10 guage wire originally.

The 14g wires are more than you need. They'll work fine but you could easily drop 1 or 2 sizes.




I assume 70amps is both relays, 35 each. If so you could go horn relay to relay 1 to relay 2 with no problem.


No there are two presently soon to be three 70 amp relays. I've wired each #30 power terminal with it's own power line that will come from the horn relay. The three relays are set up this way; One relay for fan one(has it's own ignition power source). Thermostatically controlled to come on at 193.

There are two relays for fan two as it is set up to come on thermostatically at 205 with one relay. The second relay for fan two will be set up to come on when the A/C is turned on. These relays share ignition power to terminal 87.

Also, I think you posted before about an alt upgrade, correct? Stock alt is not going to like those electric fans.

Yes, alt is upgraded.

Take a look at this as a contol option, I am running it on my '66 and simply love the results.

http://hotrodhomepage.com/?p=57

It replaces the relays, switches, temp probe, etc all in one unit.

gchandler, nice setup, but at this time I'm going to stick with what I've already got purchased.

After my research and ALL the help I've gotten from TC members this is the way I have my electric fans setup:

Three 70 amp relays(bosch 0-332-002-156) side by side mounted on the windstar shroud. The larger fan I've designated fan #1 and the smaller fan #2.

I've wired the relays as follows:

Relay one for fan one,

Terminal #30(10 gauge) has it's own power source that comes from the horn relay buss bar. What size inline breaker or fuse should I use here?

Terminal #86(14 gauge) has it's own power source that comes from a supplemental ignition distribution block I've added to accomodate the six relays I'm using in this car(two for headlights, three for fans and one for supplemental vacuum pump). At the distribution block I need to use a fuse or breaker, what size should I use?

Terminal #85(14 gauge) goes to a double pole thermoswitch(NAPA FS-311) located in the thermostat housing water neck(80's monte that has threaded port for thermoswitch). Thermoswitch supposedly comes on at 193 degrees.

Terminal #87(10 gauge) goes to the positive fan lead

The ground, negitive terminal on fans, for both fans will be the core support. This is a 10 gauge wire.

Relay two is used for fan two and is wired as such:

Terminal #30(10 gauge) has it's own power supply line coming from the horn relay buss bar. What size inline breaker or fuse should I use here?

Terminal #86(14 gauge) is tied together with terminal 86 from relay #3 and goes to the supplemental ignition distribution block. At the distribution block I need to use a fuse or breaker, what size should I use here?

Terminal #85(14 gauge) goes to a single pole thermoswitch(NAPA FS-120) that supposedly activates at 205 degrees. This is located in the intake. A manual overide switch is also placed here and will be mounted in the car.

Terminal #87(10 gauge) goes to the positive terminal of fan #2.

Relay three is also used to activate fan number two when the A/C is switched on and is wired as follows:

Terminal #30(10 gauge) has it's own power supply wire coming from the horn relay buss bar. What size inline breaker or fuse should I use here?

Terminal #87(10 gauge) is tied into the power supply wire with relay number two's terminal 87 and runs to fan number two's positive terminal.

Terminal #85(14 gauge) will be grounded to the core support.

Terminal #86(14 gauge) will be tied into the A/C clutch power supply wire. This will activate fan number two when the A/C is switched on.

I have also put diodes(Radio Shack 276-1144) between the positive and negative terminals of the fan motors to protect agains EMF's. Banded side towards the positive terminal. I have also tied wires to the positive and negative terminal that will activate leds(Radio Shack 276-271) inside the car when the fans come on. The two ports in the heads are occupied by the original temperture sending unit as I've left the idiot light intact(visual for son to see) and the other head port has the mechanical temperture gauge in it.

I hope I've explained myself well enough for you to understand and to help anyone else who may be considering this upgrade. Pete

Pete,

Relays two and three can and probably should share a power feed and fuse for the fan supply since they are feeding the same fan.

All three relays can share a common fuse for the #86 terminals.

Relay three is in what I call a power switched configuration: put power to the relay and it turns on. Relay two is what I call a ground switched configuration: it always has power and just needs a ground to turn on.

Hook your override switch into the #85 on relay two and use switch to ground. This is a safer circuit design as any shorts just turn on the fan which causes no smoke. It also reduces the fuse and wire requirements.

I am guessing here (see my previous post about how to figure real values) but you probably want to fuse the fan power supplies at about 40A each. The relay controls would be fine with 5A.

Steve

Pete,
.... Hook your override switch into the #85 on relay two and use switch to ground. This is a safer circuit design as any shorts just turn on the fan which causes no smoke. It also reduces the fuse and wire requirements...
Steve

Steve thanks for the suggestions. I did have the over ride switch hooked up to relay two just made a mistake in my explaination above. I've changed my description/explaination above so it's accurate. But question the following.

"All three relays can share a common fuse for the #86 terminals".

Is this possible or should it be done? The reason I ask is the #3 relay gets it's power to terminal #86 from the A/C wire and not from the supplemental ignition distribution block. I do plan on putting in an inline 10 amp breaker between the A/C wire and relay #3. Do I understand this right or is your description of tying all three terminal #86's together still the way to go?

Again thanks to all who helped. :thumbsup: Pete

You are learning! You caught a slight faux paus on my part. Ok let me modify that slightly...

You can share a fuse on the ground switched relays for #86. The A/C switched relay will be fused as part of the A/C power supply so it should not really need it's own fuse.

So what you want to consider when deciding where to fuse is:

1. Circuit protection against shorts. For this you need a fuse as close to the power supply as possible. Minimize the wiring upstream and you maximize the protected wiring downstream.

2. Diagnosis capability. You could use just one really big fuse for the whole car :-) But we all understand that we really do not want to do that. So we divide the electrical system up into logical chunks. Part of this is so that if something fails it is part of a chunk and thus localized to reduce debug time.

3. Circuit overload protection. Smaller wires tend to be cheaper to run than big wires. And they take up less space. They do not however carry as much current. This is another reason we do not run one really big fuse, because then all the wires would have to be really big too. So we often fuse at the junction of a big wire to a small wire (or often several small wires). For an example look at the size of the ignition hot wire going into the fuse panel compared to the sizes of the wires going out of the fuse panel.

Your fan control relays share a common function, are localized geographically, and do not require significant current. Taken together these all suggest sharing a common fuse and power supply. The A/C control relay gets power from out in left field so to speak, so it gets fused seperately. But so long as you run the same sized wire to it as feeds the A/C it does not really need a seperate fuse.