I need to know what type of diode, and what number specifically, to use on a power line to a radiator fan so that current flows only one way. Please educate me. Thanks.

 

I need the current drawn by the fan to be sure but would hazard a guess that you’d find something in the 1N4xxx family.

I’m curious why you need a diode? Unless you are running a brush type permanent magnet motor, there shouldn’t be any back emf to worry about if the fan pinwheels.

Michael

 

Hey Michael. I have a 2,000 ford Contour dual fan set-up. Each fan draws 14 amps. They are single speed fans. I have them now controlled with a thermo switch in the coolant that activates relays. However, when the fans start there is a momentary spiks of about 40 amps that makes my MSD sputter. Believe me, I have moved both the fan + and the MSD + up and down stream to try to rectify the issue. Nothing worked. So I'm moving to plan B.

I have a relay pack that is oe on Volvos. It controls a 2 speed fan, turns low speed off when high activates. I was wondering if there is a way to use it with my dual single speed fans. It would mean running the low and high leads from the Volvo pack into the single + lead of each fan. But if low is live, it would send current up the high speed lead and back to the relay. Is that a problem? Would a diode solve that? Thanks.

 

I seen your concern. If the Volvo controller is just relays with no electronics on the output side of the contacts, there is no need for a diode but if there is a current sense function or other electronic circuit on the output, diode isolation does make sense.

Having said that, I think you might have the same problem with current spikes with the Volvo controller if it is mechanical relays. I can think of a scenario where the Volvo controller might help and that’s if it uses mosfets as the output device. That might provide enough of a soft start to reduce the spike. In that case, diodes make sense.

A diode will drop ~.7 volts which won’t make much difference in fan speed.

Let’s search for solid state cooling fan controllers. I’m at work now so I’ll try to get back to you later.

Michael

 

Attachment 278983

The volvo controller is a simple pack of relays. The low speed output is a smaller gauge wire that feeds less amps.

I can't find any 30 amp diodes for automotive use. I've searched Summit, Amazon, and ebay. There must be something I don't understand, and since I'm sort of an electrical dummy, that is a rather large possibility.

I may try to wire it up with the Volvo controller and try it as is.

I found a sort of Ma and Pa shop that is one guy making what seem to be good quality controllers. What do you guys think? www.autocoolguy.com

 

I’m thinking you’ll have the same issue with the Volvo controller. I’d guess that the fan motor has 2 windings to get 2 speeds although I could be wrong and it’s just a voltage drop due to the thinner wire.

The controller you linked to is how I’d do it and is probably how OEM’s do it on higher end and performance models. PWM is Pulse Width Modulation. Think relay or toggle switch suppling power. If you toggle it slowly, the fan will run slow. Toggle it faster and the fan will run faster. He also says it has soft start which means the current is limited on start to make the motor last longer and help prevent voltage drop due to high current draws.

You will have trouble finding a 30 amp diode in the shape you may be expecting. At that current, heating is a problem which means either a TO-220 package or a stud mount. At 20 amps, you will be able to find the normal cylinder with 2 leads that you might be expecting.

Michael

 

Could you use the slow speed to regulate 1 of the 2 fans, then use the high speed to turn on the second fan also?

I like the devices the AutoCoolGuy has, but dang are they friggen expensive... I can't justify paying that for a controller that will burn out one day when there are literally 1000's of free relays sitting in the local junk yard. I would go the relay route, but that's because I'm cheap.

 

Thanks for your help, Michael.
Not sure how to proceed. Having an inline six with the long block really limits my options with fans because of space. Things would be much easier if I had a two speed fan. But, maybe I should be using a PWM controller.
I have both a Volvo fan and a Taurus fan also. Maybe I'll experiment with location, and see if I can fit one of those around my p/steering, etc.
Thanks for the help.
P.S. It just occurred to me. Is there a way to delay the starting of one of the fans? If I could start them one at a time, with, say, a 15 second delay before the 2nd fan kicked in, that would really help with the current spike.

 

There are many ways to delay the turn on of a relay. You can get cheap timers from aliexpress and ebay that are adjustable and dirt cheap, you could cobble together a timer from a 555 IC and a handful of parts or you can use a capacitor and resistor as shown here. The circuit depends on what is known as the RC time constant. When power is applied, the capacitor acts like a dead short with the resistor limiting current. Since the capacitor is a short, there isn't enough voltage across the relay's coil to pull it in. As the capacitor charges, the voltage rises. At some point, it will be enough to pull in the relay. The values shown will give a delay in the range of 470 seconds depending on the relay coil's sensitivity. The capacitor will sit at B+ minus the .7 drop across the diode as long as power is applied. At turn off, the coil resistance will bleed off the stored charge in the capacitor. This very slightly delay the turn off but you won't notice it as the coil resistance is pretty low.

Another thought is, is it voltage drop due to high current that's knocking the MSD out or is it high frequency noise from motor brushes at high current? If it's noise, a capacitor or 2 across the motor leads might fix it. Search for rc brushed motor capacitor for examples but be prepared for a deep rabbit hole.

Edit, how expensive is the current temp controller you are using? Could you get another and set it 10-20° higher. That would delay the second fan, it may not even come on at all if the first one can keep temps down.


Michael

 

A diode is nothing more that a check valve for current to flow. DC motors use diodes to prevent reverse current flow to the circuit that feeds it.
30 Amp - 1000 V Diode - STTH3010W - TO-247 - 1,000 Volt - 30 A - Tj 175C - 42ns | eBay

 

Thanks for all the input. I believe the Volvo two speed fan relay controller is not for my single speed fans. I would need two diodes, and possibly one of the delay devices to make the volvo system work, and I don't know how reliable those components are.

I now use one Taurus relay to control each fan. The relays are activated by one thermo switch. I believe that a start delay of maybe 15 seconds to one of the fans might solve my problem. One fan starting would be half the amps (about 14 amps with an initial spike of 25 amps) and half the spike. If the engine doesn't hesitate when the single fans starts, or when the second fan kicks in, then I will have solved the problem. My 130 amp alternator should be able to supply plenty.

I'll let every one know how it went.

 

https://www.autocoolguy.com/

have to scroll down a bit to see his controllers.

 

i-w, see post #5. Thanks.

 

Well, I called theautocoolguy and it looks as though I'll be getting his smallest controller, the 85 amp unit. Although my fans on a hard jump to full power spike at 100+ amps, autocoolguy says that with his controller the fans will never jump to full power. Soft starts is the norm, even in failsafe mode, or so he says. I am a bit hesitant to make the purchase b/c I like having/using parts that can easily be replaced. That is not the case with a PWM controller.

 

I use a fan controller module from Be Cool/Derale (?) I forget but it had a delay when you start the engine and the ramps up slowly. It will then vary the speed as needed for cooling. Also has an input to force on high when A/C is activated.

I have a second fan.thermo/relaythat will come on full but only at a higher temp.

There are modules that will control two fans.