Circuit building pros needed!

[Corndoggeh]

I'm building a circuit for auxillary electric cooling fans for my truck that uses a capillary thermostat to control a relay, however, I wanted to tie said thermostat to only activate the relay when the truck is in the RUN position (the circuit will be open when the car is off or starting). I also wanted to include a manual override for the relay to turn the fans on at any time.

I was wondering if this circuit I drew will be satisfactory or if I should instead use two 10A fuses on each fan or keep the single 20A fuse. I was also wondering it it should be safe enough to tap into the hot lead on the blower since that will be the easiest wire to gain access to that is apart of the original circuit that will open when the car starts or is off. The blower originally has a 30A fuse so I assume it could take that tiny extra load on it.

NOTE: I used an overly simplified ignition and starting diagram on the circuit for simplicity otherwise there would be about 200 other things I would need to add.

 

[pedrodagr8]

The biggest change I would make is to add a second relay to draw power from your battery, simply tap the blower supply to activate the coil on this relay. This will give you the power switching you desire, without possibly overloading the blower circuit. Also add some reverse protection diodes to discharge EMF spikes.

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[rattle_snake]

2nd getting power directly from bat. also make over ride switch activate same relay, not transfer power.
GNDs are upside down..

 

[Corndoggeh]

Okay so here is the updated circuit, which is pretty much rattlesnake's with a little more detail for me to reference later on. Where should I place this reverse protection diode, directly connected with the battery or a grounding point on the body will suffice? Would it be better to place said diode after the paralleled fans?

 

[Corndoggeh]

Ah, I just realized why the diode goes where it does. Nevermind about that, I figured there was a way to wire the override better but I could only think of re-routing the power instead of just using it to activate the relay. Thanks guys!

 

[wyliesdiesels]

Funny timing. Im in the middle of designing the same thing for my FIL's RV.

What type of main fan do u have? Mechanical?

U want the fans to come on when the AC comes on? Im assuming this because youre tapping into the blower circuit. I wouldnt do this as the blower circuit is switched. Instead I would connect the fan motor relay to a fused line directly off the battery.

Connect the coil side of the fan relay to the coil side of the AC relay, temp sensor(hookup other side of sensor to an ignition switched source), and a manual switch(again connecting to an ignition switched source unless u want it hot all the time which in that case I would wire up some sort of warning light to keep u from draining the battery. Or go with an illuminated switch).

Use a multi-pin relay with socket that allows multiple feeds to the coil. This way the fan can turn on when the AC turns on, when the temp sensor closes and can be activated manually with a switch. Each source connects to a different set of coil pins.

 

[wyliesdiesels]

Okay so here is the updated circuit, which is pretty much rattlesnake's with a little more detail for me to reference later on. Where should I place this reverse protection diode, directly connected with the battery or a grounding point on the body will suffice? Would it be better to place said diode after the paralleled fans?

Forget the blower connection. Connect the 85 side of the coil to the frame or ground. Sensor and manual switch should connect to 86 and go to a ignition switched source as i explained above.

The diode, for proper protection, needs to go across 85 and 86, making sure the stripe is facing 86 AND also making sure 86 is the positive side of the coil. Of course u could reverse everything but the standard is what i described. If u reverse the diode and it goes in the wrong direction u could damage it.

Ah, I just realized why the diode goes where it does. Nevermind about that, I figured there was a way to wire the override better but I could only think of re-routing the power instead of just using it to activate the relay. Thanks guys!

Read above about the diode.

 

[Corndoggeh]

Forget the blower connection. Connect the 85 side of the coil to the frame or ground. Sensor and manual switch should connect to 86 and go to a ignition switched source as i explained above.

The diode, for proper protection, needs to go across 85 and 86, making sure the stripe is facing 86 AND also making sure 86 is the positive side of the coil. Of course u could reverse everything but the standard is what i described. If u reverse the diode and it goes in the wrong direction u could damage it.



Read above about the diode.

Where I'm connecting into the blower is at a constant hot wire before any of the switches but after the ignition switch, so the source of power to the fans will be an ignition switched source.

What I want from this is to be able to control the fans thermostatically and manually through a switch. However, I also want the fans to turn off when the truck is off or in the START position to avoid draining the battery when the truck is off and to cut the connection while starting the truck so that the starting circuit has all the amperage it needs.

Also, why does the signaling circuit need the diode and not the circuit that is tied with the battery, the truck is already equipped with protection diode for the electrical system, and since the signaling circuit is tied with the blower, it should be protected? I could see how the fans would need it since I'm creating a brand new circuit instead of paralleling an existing one that already has protection.

 

[pedrodagr8]

Where I'm connecting into the blower is at a constant hot wire before any of the switches but after the ignition switch, so the source of power to the fans will be an ignition switched source.

What I want from this is to be able to control the fans thermostatically and manually through a switch. However, I also want the fans to turn off when the truck is off or in the START position to avoid draining the battery when the truck is off and to cut the connection while starting the truck so that the starting circuit has all the amperage it needs.

Also, why does the signaling circuit need the diode and not the circuit that is tied with the battery, the truck is already equipped with protection diode for the electrical system, and since the signaling circuit is tied with the blower, it should be protected? I could see how the fans would need it since I'm creating a brand new circuit instead of paralleling an existing one that already has protection.

The diode across the relay is to get rid of the voltage spike created when the coil field collapses. This can cause noise in a bunch of other circuits as well as possibly damaging sensitive devices. It is considered best practices to add it, though it should function fine without it.

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[Corndoggeh]

I'm a bit confused whether to add the diode before or after the positive side of the relay on the signal circuit. A drawing of its placement would be big help!