Fan Delay Off Circuit

I've been wanting to put a latching delay relay in my van and found a solution that is cheap, simple and uses no power once off. I thought I'd share it here for anyone that needs it.

The $15 timer and info is from http://timers.shop/

The mode we are using is "4. Self latching Off Delay circuit"

Shouldn't cost more than $30 or so total to put together

I've modified the example schematic for our purposes:



It should be wired to 12v+ when ignition is on wire to the blue(trigger lead) of the timer. The other wire from the battery that powers the fan and the timer after ignition off should be sized and fused appropriately for whatever fan you are running to the fan and from the fan to ground(aux timer/temp switch wiring etc can be whatever), same with the relay rating. It will energize the fan, or fan circuit if going through a temp switch as I am, when the ignition is on. Once the ignition is turned off it will maintain the circuit for whatever time you program the timer to run. Once the time is up it kills all power to the fan and timer. The first diode keeps power from backfeeding into the ignition system and trigger circuit after shut down. The second diode ensures the fan is never powered by the ignition circuit. And with the only load on the 5 amp timer being the one relay it should hold up really well as long as it isn't in the doghouse. I haven't got this wired up yet. But will update when I do. If you are not using a temp switch you can simply wire the fans ground to ground.

I am preparing to do this and noticed an error I made in the original schematic posted. I have added a second diode to ensure the ignition circuit cannot power the fan while the ignition is on.

I also added a relay to the temp switch circuit to take the load off of the temp switch when the ground is made b/c I was worried it would shorten the life of the temp switch. And lastly, I combined both options(with or without a temp switch) into one schematic.

I should have this wired up in the near future, when I do I'll let you know how it works.

Could a moderator please delete the original post? Thank you.

Thanks Vanny

No Worries Seth, Bob's your Uncle!

So I got this wired up and it works great, does what it's supposed to. I used Bussmann 22903-6 6 amp diodes like these. But I'm sure they are overkill b/c we are just running the timer and a relay through the diodes. 1 amp diodes like these will work fine I'm sure. Programming the timer was simple once you get the hang of it.

Right now I've got it set to 3 minutes. I'm hoping it helps with shut down heat soak issues I've been dealing with. Up till now I've just been cracking the doghouse lid 4" when I exit the vehicle. Hopefully I won't need to do that anymore.

Super! I've been waiting in the wings to see how this worked out. I'm running one of these:

http://www.jegs.com/i/Flex-a-lite/400/160/10002/-1

Now I'll proceed with your findings. What I've been doing
is sitting in the cab (5-10 min) until my thermostat (170-180ish degrees) shuts down. This also takes care of all the stink and boil over/hard start issues. Now I'll be able to lock-up the van and walk away. Thank you for sharing!!

By the way

6cyl down flow rad re-cored to 4 rows
Electric fan is set-up as a puller
No mech. fan
No gap at top of doghouse
Studs for fan hardware (alum brackets) braised to tanks during re-core
Works awesome!

Your welcome. Your setup is similar to mine except I'm using a fan switch in the thermostat housing past the stat, i.e. engine output temp, which should be pretty similar if your probe is near the top of the radiator. While I was at this I decided to change from a 200 on/185 off switch to a 185 on/170 off and replaced the Motorcraft 180F oem style stat with a "high flow" 160F stat and found the high flow stat definitely moves more coolant. I just made a post about it HERE.

Here's a pic of the wiring installed near my ignition module under the drivers seat. I would recommend the $5 programming switch just to make programming the thing easier. With the bullet connectors you can hook it up and unhook it as need to change the program. And just alligator clip the ground lead of the interface. Other timers may work as well.

You know what would be really slick would be to pull fan power off of a smaller 12v battery wired in parallel to the starting battery with a relay in between that closes when the ignition is on for charging the smaller battery and opens when the engine is shut down so the fan doesn't draw from the start battery.

If you did that, you could actually do away with the timer all together and rely on one or more temp switches instead to cool until cooling isn't needed or the little battery goes dead, even air temp. Finding a battery that doesn't mind repeated complete discharging and charging on the alternator may be an issue, if that's what it takes to keep the doghouse in check. No worrying about draining the start battery though.

I also think maybe if you had a reversible fan and had it reverse @ shutdown so that the cool air is pulling across the engine/carb first before going through the radiator it would be more efficient at cooling the engine when parked.

That's what I like about you Seth, always thinking! From my research(for my UTV, initially) if the batteries are in parallel, they should be identical or one will drain the other. That is why they use isolators. A diode should keep the smaller battery from draining the main. The lithium batteries seem to thrive on charge>discharge cycles. You may be onto something!
Jim

Dag nabbit. The problem with a diode is that it won't block discharging, but if we open the circuit between the two at shutdown they are totally isolated. I'm thinking a cheap motorcycle or lawn mower agm or even a drill battery or battery pack. The battery won't be isolated at start up, it could be. But I think the starting battery will shield the other battery by it's size @ start up, path of least resistance. The smaller fan battery will draw on the starting battery as soon as the key is turned.

I think the concern was that the smaller battery would draw down the larger battery and eventually weaken it. It at least wouldn't do it when it was off, with your relay.

What if. . . The fan/battery were a separate circuit with only a charging wire coming from the alternator with a diode in it(it may need it's own regulator, though). This would be easier for me to visualize if I had a schematic, but alas when I draw them, they look like an angry modern art students drew them. This would allow more single points of failure. Maybe not, it might be alright on an evacuation fan but not sure I'd trust it with my cooling fan. Sorry, just throwing stuff against the wall to see if anything sticks.

Maybe you're right. Maybe the only safe way to do it would to use what they call an automatic charging relay. We use them in boats to separate the house from the start battery(s). It senses voltage and won't charge the house battery until the start battery is charged. I'm pretty sure you can't otherwise isolate them on the charging side unless you had another alternator. If the diode allows charging it will allow drawing from the start battery through the charging wire.

I'm having a problem with my fan timer circuit. It's seems to be working, but when the van is cruising I'm hearing one of the relay click occasionally for some reason. I don't know if it's a problem with the circuit or if there is a problem I wasn't aware of with my ignition switch or wire. The wire is new from the switch. Or if somehow the ignition module is causing it. I'm going to do some troubleshooting on it while I drive today.

I got the new fan switch installed yesterday and the vans temp guage hardly goes up, so that's pretty awesome. And I thought the fan would be running more but it isn't, just sooner for short periods.

If you had two charge wires to the alternator and each had a diode, would that not keep the batteries from discharging each other? Problem is the main battery would decide when both of them got charged. I dunno.

The problem with your fan timer circuit sounds like a loose ground or a flakey relay to me.

I think you have found the "cooling magic pill". Now it seems your off to slay the "heat soak/boiling carb dragon". We appreciate your advances in all things Econoline!

Jim

Seth G wrote:Maybe you're right. Maybe the only safe way to do it would to use what they call an automatic charging relay. We use them in boats to separate the house from the start battery(s). It senses voltage and won't charge the house battery until the start battery is charged. I'm pretty sure you can't otherwise isolate them on the charging side unless you had another alternator. If the diode allows charging it will allow drawing from the start battery through the charging wire.

I'm having a problem with my fan timer circuit. It's seems to be working, but when the van is cruising I'm hearing one of the relay click occasionally for some reason. I don't know if it's a problem with the circuit or if there is a problem I wasn't aware of with my ignition switch or wire. The wire is new from the switch. Or if somehow the ignition module is causing it. I'm going to do some troubleshooting on it while I drive today.

I got the new fan switch installed yesterday and the vans temp guage hardly goes up, so that's pretty awesome. And I thought the fan would be running more but it isn't, just sooner for short periods.

I was considering running dual batteries.....

Would either of these options help you guys out?

Isolator / Relay

Dual Kit

Yeah those are ACR's. I think that would be the solution.

I had some time to poke around and try and find my problem with the intermittent relay chatter. And I've isolated the problem to the coil. I tapped the power for this circuit on the ignition wire where it splits to power the ignition module and the coil. The coil is the source of the problem. What I'm going to do is direct feed the coil from the battery with a fuse through a relay and take it out of the rest of the circuit. I'm hoping this will also fix a problem I've had since the engine swap of the coil firing once(via the module which controls it's ground) when the key is turned to on. I'll leave the module and fan timer on the main ignition circuit from the key and see what happens. It's not a problem with the timer circuit or a ground or the relays themselves from what I can tell. If I disconnect or have disconnected the coil circuit with the key on and reconnect it, the relay on the timer circuit will click. And it shouldn't, b/c it never looses power or ground. Whether the diodes are in the circuit or not, makes no difference. If I take the wire to the coil off the ballast resistor and touch it back, click, every time, click. I think the inductive load of the coil is causing the problem and may be causing a problem with the ignition module itself and it's relays.

jrdunn96 wrote:If you had two charge wires to the alternator and each had a diode, would that not keep the batteries from discharging each other?  Problem is the main battery would decide when both of them got charged.  I dunno.

Jim

I love you're thinking, I didn't think of using two diodes, one on each charging wire. But the problem still exists that the start battery has to be connected to the starter, but if there were dedicated charging circuits, vs connecting the alternator to the start wire, that may work. This is why I like collaboration, it's hard to think of everything and someone else may see it another way. Lord knows, I'm no electrical engineer. If both diodes were on the alternator side of any other load from their respective batteries, it sounds feasible. But it would take some serious diodes. You've got a 60 or 90 amp alternator or more.

I have been keeping up with this thread but I don't understand the extra wiring, relays, diodes used?
I hooked up my fan to the horn relay wire with a in line 30 amp fuse and a light switch timer that is used between the ground wire to the Van.
The fan has constant 12 volts to it but shouldn't use any juice unless the fan is running?
At a 1/4 turn it will run 10- 15 minutes, that shouldn't drain the battery when it is parked to cool the engine bay.
While driving in heavy traffic I can turn it on or off as needed, the power comes from the alternator while running, right or wrong? Am I missing something?

I have a 12” electric fan (wired direct w/ 30 amp fuse) pushing through the radiator controlled by a

push-pull switch mounted on the doghouse where the choke control once was.

My E100 is seldom driven long distances and applying the fan manually covers any overheating issues…..

Nice setup. Me being the simpleton that I am, I just set the sensor, relay and fan to stay on all the time. On a really hot day the fan will cycle on for 2 or 3 times after shutdown for a minute or two at a time. I don't think 5-6 minutes of fan running has ever run down my battery. And, she always starts, even on a hot day, as it seems to have solved my boiling fuel problem in the overheated carb. Also, because I've found those cheap relays to be pretty undependable, I use a double relay to hand the load, about 10amps, and give me redundancy. Thanks for posting.

Russell wrote:I have been keeping up with this thread but I don't understand the extra wiring, relays, diodes used?
I hooked up my fan to the horn relay wire with a in line 30 amp fuse and a light switch timer that is used between the ground wire to the Van.
The fan has constant 12 volts to it but shouldn't use any juice unless the fan is running?
At a 1/4 turn it will run 10- 15 minutes, that shouldn't drain the battery when it is parked to cool the engine bay.
While driving in heavy traffic I can turn it on or off as needed, the power comes from the alternator while running, right or wrong? Am I missing something?

You're all correct, none of this is absolutely necessary. Wiring a fan is easy, it's up to the person doing the wiring to make it as complicated as possible



I'm showing you the way I'm doing it. I want to hear any thoughts on doing it better. The timer consumes somewhere along the lines of your radio memory in standby, so you could do away with the diode(s) and power the timer all the time with the fan circuit, and power only the trigger with an ignition 'on' wire. To simplify things further still, the fan could be always on when the van is running. The timer is an insurance policy against the relay, or temp switch, sticking and running the battery dead while you are away. It's an automatic method of doing what Don and Russell do with a mechanical light timer. The second relay that switches the temp switch ground is there to take the arcing load off of the temp switch. It's optional but if your fan is powerful at all I would advise you use it, if you're using a temp switch. Btw, I don't have a mechanical fan, my 16" electric fan is it and it's more than adequate for my setup, is off way more than on when running.

Now, having said all that, Russell has sparked a thought and shown me a better way to do everything with one relay, no diodes and still consume no power when off, iow, still be a latching circuit. By breaking the ground on the fan and the timer instead of the positive like the timer guy shows! Thanks Russell!! I will draw it up and post it later. Collaboration, I love it!

Me? I'm just pestering Seth until he builds a "better mousetrap". I've learned alot from his build, posts and ideas. Some of these guys(and Seth is one of them) can take an idea and make it work. He also makes me think. I'm not that familiar with it, but enjoy it.
Jim

Thanks JD. I had a 'business' meeting about a brewery with a friend that ran late and I'm going to Nashville to see my brother and Roger Waters concert this weekend. So I'm not going to get back on this until Monday or Tuesday. But basically the trigger wire is the ignition, power is always on to the timer and fan and the timer/fan circuit cuts the ground with the relay. I think it will work, but haven't had time to look at it other than the initial thought.

Ok I had some time before I leave today to work on this. After redrawing the circuit I saw that in order to make the circuit self latching a second relay is still needed to power the timer initially, but eliminates the diodes. I've also drawn a schematic that is the most basic, non latching circuit and will consume a minute amount of power that will in all likelihood take a month or two to drain the battery down far enough to not start the engine.

Here is the basic circuit:



Using a temp switch with the above circuit you would wire 85 on the relay to the temp switch instead of wiring it to 87 and ground directly.

Here is the self latching circuit:



Using a temp switch on this circuit is more complicated and will likely require a 3rd relay.

Seth,
I know you're "out of pocket" for a while but why did you tie the timer ground to pin 30 of the fan relay? I kinda understand the rest of the circuit(after a little studying up on the timer). It looks like if it wasn't tied together, you could just put your temp switch between 85 and ground like the first one. I have no doubt that you have a reason, it's just not soaking into my thick skull.
Jim

Yeah there is a reason. The temp switch may be intermittent, kicking on and off during the timing period after shut down, including not being made when you shut off the engine which would deactivate the timer b/c the trigger wire signal would also be gone, which starts the sequence. For the same reason it can't be tied in between 85 and ground on the lower relay. And it's also kind of the reason there has to be a second relay, but in reverse. You can't lose power to the timer until it's run it's course, or it won't reset the cycle until the trigger signal is re engaged. The timer activates when it has power and a trigger signal, then the timing sequence begins when the trigger is gone.

For the sake of simplicity I'll probably abandon the latching circuit b/c it draws so little juice anyway and use the second relay to take my coil off the ignition circuit and power it directly from the battery, fused of course. B/c I feel like I need to do that anyway.