Electric fan relays

7991LXnSHO

7991LXnSHO

wanna catch the space herp
10 Year Member
Sep 1, 2010
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Kearney, NE
#1
I have been reading about a Bosch 75A related for running the OEM style of fans. I was at Menards and saw what might be a cheaper, effective alternative. Electric start mowers have a smaller version of the Ford starter relay (aka solenoid). I am sure the amp rating of a starter motor for a 20+ hp engine is at least 75 amps. I am not sure about the constant duty cycle rating on it. Has anyone used these for another purpose than starting yard products or motorized toys?
Also, is this link for the right Bosch relay?
www.solidsignal.com

Bosch/TYCO Relay SPST 12-Volt 75-Amp with Mounting Tabs (V23232-D0001-X001) from Solid Signal

Bosch/TYCO Relay SPST 12-Volt 75-Amp with Mounting Tabs (V23232-D0001-X001) TYCO single pole, single throw relay. 12 volt, 75 A resistance load. For use with light bars. Case includes two molded mounting tabs. Typical applications: engine control, glow plug, heated front - and rear - screen...
www.solidsignal.com
 

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#2
I just wired up my contour fans with 2 30a relays. 1 relay for each fan. Its a simple key on fan on operation. (Coolant sensor red wire) The relays are $7 a pop on ebay. X2= $15. Add $15 in 10ga wiring from local oreillys, $10 for terminal assortment kit, $5 shrink wrap assortment from harbor/elec tape. $6 solder gun. $6 solder. Fans $50 at JY. Make brackets, $2 a pc out of the thin mending plate, easy to work with. X4 so $8. Bolts/nuts/washers/lock washers, Zipties, Thats about it. $120. Vs $3-400.

My car idled forever and never got over 210 ish. (@ 92+ degree ambient) Felt peppier also with the 5hp+ parasitic loss that got dropped.

I know this has nothing to do with the question, but i want to brag about my achievement. Lol.
 
#3
I believe I have the one in the photo (Bosch/Tyco), but this appears to be the same relay for a little cheaper price. I can go check later.

Amazon product ASIN B0117FAGVOView: https://www.amazon.com/Bosch-332-002-168-0332002168/dp/B0117FAGVO/ref=asc_df_B0117FAGVO/?tag=bingshoppinga-20&linkCode=df0&hvadid=&hvpos=&hvnetw=o&hvrand=&hvpone=&hvptwo=&hvqmt=e&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=&hvtargid=pla-4584276296427787&psc=1


I bought mine 20 years ago and it still works flawlessly today. I only run a single fan. I wired it so that my aftermarket fan controller (which only has a 30A relay) just turned the 75A relay on rather than directly powering the fan. I've measured the draw of my 94-95 Sn95 efan and it was only 35AMPs continuous.

When I go Megasquirt, I plan on using a volvo PWM fan controller with the MS3x to control the fan.


There are many many ways to skin a cat here in terms of fan control.
 
Last edited:
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#4
Leash sells a nice relay module which can be used for e fans. Comes with a 70a relay, and has provisions for a fuse so you don’t need to run one inline.

leashelectronics.com

1HO Single 70amp relay module

Single 70 amp relay module. Has heavy duty 70 amp industrial relay. Uses heavy duty J-case/FMX fuses (NOT INCLUDED). #10 battery input and relay output studs. Led indictor on output.
leashelectronics.com

I ran one of the big 100 amp relay when I required the sn95 fan I used. They’re the ones with the large pins on them, but they’re comparable to a standard size relay. Got it off amazon for around $12 for 2.
 
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#6
Mustang5L5 said:
I believe I have the one in the photo (Bosch/Tyco), but this appears to be the same relay for a little cheaper price. I can go check later.

Amazon product ASIN B0117FAGVOView: https://www.amazon.com/Bosch-332-002-168-0332002168/dp/B0117FAGVO/ref=asc_df_B0117FAGVO/?tag=bingshoppinga-20&linkCode=df0&hvadid=&hvpos=&hvnetw=o&hvrand=&hvpone=&hvptwo=&hvqmt=e&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=&hvtargid=pla-4584276296427787&psc=1


I bought mine 20 years ago and it still works flawlessly today. I only run a single fan. I wired it so that my aftermarket fan controller (which only has a 30A relay) just turned the 75A relay on rather than directly powering the fan. I've measured the draw of my 94-95 Sn95 efan and it was only 35AMPs continuous.

When I go Megasquirt, I plan on using a volvo PWM fan controller with the MS3x to control the fan.


There are many many ways to skin a cat here in terms of fan control.
Click to expand...
That's almost the same one as the -156. Don't know what the difference is.
 
#8
#9
7991LXnSHO said:
So is the diode is to prevent the motor working like a generator going down the highway or after the car is shut off?
The small engine solenoid is much cheaper, but if this is so reliable, the cost is not an issue.
Click to expand...
Wrong answer...

Using a diode as a dampener in automotive circuits:

Theory of operation:
The diode acts as a surge absorber or one way gate. Anytime you turn the power off an inductive load (coil, motor, solenoid, etc) the collapse of the magnetic field creates a voltage spike of opposite polarity to the voltage applied. The positive wire sees a negative spike and the negative wire sees a positive spike. The diode is wired backwards so that it does not conduct during normal forward operation. When the magnetic field collapses, the diode sees the reverse polarity spike and clamps it. This prevents the spike from possibly damaging the rest of the electronics in the car.
When used to clamp spikes in automotive circuits, connect the lead that comes from the end of the diode that has the band on it to the positive side of the circuit. Connect it the other way and you will make smoke.

Diode markings
attachments\586744\


A properly functioning diode will measure very high resistance or open circuit in one direction. Reverse the meter leads and it will measure a lower resistance.

attachments\50089\
 
#10
7991LXnSHO said:
So is the diode is to prevent the motor working like a generator going down the highway or after the car is shut off?
The small engine solenoid is much cheaper, but if this is so reliable, the cost is not an issue.
Click to expand...

It’s been in my car damn near 20 years. I realize the car sat for 10 of those, but the relay also sat and aged as well and I’ve never had a hiccup with it. I’m running about 35a through it
 
#11
Why the sarcasm, J.? I know how a diode works. I asked what it did in this circuit and appreciate the rest of the answer.


jrichker said:
Wrong answer...

Using a diode as a dampener in automotive circuits:

Theory of operation:
The diode acts as a surge absorber or one way gate. Anytime you turn the power off an inductive load (coil, motor, solenoid, etc) the collapse of the magnetic field creates a voltage spike of opposite polarity to the voltage applied. The positive wire sees a negative spike and the negative wire sees a positive spike. The diode is wired backwards so that it does not conduct during normal forward operation. When the magnetic field collapses, the diode sees the reverse polarity spike and clamps it. This prevents the spike from possibly damaging the rest of the electronics in the car.
When used to clamp spikes in automotive circuits, connect the lead that comes from the end of the diode that has the band on it to the positive side of the circuit. Connect it the other way and you will make smoke.

Diode markings
attachments\586744\


A properly functioning diode will measure very high resistance or open circuit in one direction. Reverse the meter leads and it will measure a lower resistance.

attachments\50089\
Click to expand...
 
#12
7991LXnSHO said:
Why the sarcasm, J.? I know how a diode works. I asked what it did in this circuit and appreciate the rest of the answer.
Click to expand...
No sarcasm or insult was intended.

Most of the people here don't understand electricity and I have limited ways of understanding the depth of electrical knowledge. Therefore I spell out the details to try to give them some understanding of how it works.
 
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#13
jrichker said:
No sarcasm or insult was intended.

Most of the people here don't understand electricity and I have limited ways of understanding the depth of electrical knowledge. Therefore I spell out the details to try to give them some understanding of how it works.
Click to expand...
you are very helpful to the 'electronically impaired' like myself. The only thing I'm sure is electricity is not like water and does not always run downhill. :jester:
 
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#14
jrichker said:
No sarcasm or insult was intended.
Click to expand...

I must have read “wrong answer” in the tone of my teenagers having a bad day.

The voltage spike from a collapsing field is what induces a higher, spark capable voltage spike in the secondary windings of an ignition coil.
The two diodes on the relay schematic diagram are both on the trigger side (terminal 86). It seems that a high current capacity diode on the load side (terminal 87) would be a more effective if the open points is not enough to clamp the voltage spike.

What I not understand, and may not be fully applicable here, are reports of electric fans causing run on in points and HEI carbureted cars. How a fan’s reverse voltage spike or generated power can overcome the open points and continue to power the ignition without being miswired Is an explanation I would like to hear. If the relay with the two diodes in the trigger side fixes this, I need to “relay” the info.
 
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