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someone help me with a diode?

whitneyj

whitneyj

NAXJA Forum User
Location
Mayville, WI
I'm looking for a diode to wire into my electric fan setup. When my high side would kick on it was acting as an alternator and backfeeding into the low speed side. I pulled the high speed wire and have just been driving it like that, but I overheated this weekend on the trail and couldn't keep the temp below 220*-ish. So. . . I need the high side back. I'm having a hard time understanding what all the terms and things are for the diodes. I'm not much of an electrical guru, so all I know I need is a diode that'll handle 12-18V. . . not sure about anything else. . . Someone wanna help a guy out?
 
whitneyj said:
I'm looking for a diode to wire into my electric fan setup. When my high side would kick on it was acting as an alternator and backfeeding into the low speed side. I pulled the high speed wire and have just been driving it like that, but I overheated this weekend on the trail and couldn't keep the temp below 220*-ish. So. . . I need the high side back. I'm having a hard time understanding what all the terms and things are for the diodes. I'm not much of an electrical guru, so all I know I need is a diode that'll handle 12-18V. . . not sure about anything else. . . Someone wanna help a guy out?
Click to expand...

How many wires does your fan has??
 
oh man. . it's been about a year since I wired it in. I'm not even sure I have the schematic of it anymore. I'm not sure. . . all I really need is a diode to keep the fan from backfeeding into the low side relay.
 
A diode is a "check valve" for an electronic circuit. They will have a maximum amperage and a rated voltage. They require a specific amount of voltage that is required for the diode to allow current to flow through it. In most cases it's approximately 0.7 volts. They can get saturated if too much voltage is applied in the wrong direction. Current will flow through a diode from the terminal furthest from the colored band to the terminal nearest to the band.
 
ok. . . I'm having a hard time understanding everything here. I know a diode is a "one way valve" of sorts, I understand that they're rated for certain V's and amps. What do you mean by they can become saturated? Do you mean burned up?

I'm really just looking how to match up a diode for my purposes. . .
 
Hallo. Do you have the plan to use the diode only for the switching of the relay or using the diode for the feed of the fan?
When you use the diode for the feed of the fan, you will need indeed a high current diode!
The fan is using by start a lot of current. (at least 20 Amps) :shhh:
 
I'm pulling 80 amps on the high speed startup, so yes, I need a diode to feed the high speed and low speed sign
 
lol! thanks. why would I want a zener diode though? I'm trying to prevent any and all flow to those relays.
 
whitneyj said:
lol! thanks. why would I want a zener diode though? I'm trying to prevent any and all flow to those relays.
Click to expand...

You dont,zener diodes perform a completely different function.You need a power doide!
 
ok, power diode check. I'll be needing a diode to handle up to 18V and 100 amps. . . that sounds correct? Is there anything else I'll need to know or want to take into consideration before I buy one?
 
whitneyj said:
ok, power diode check. I'll be needing a diode to handle up to 18V and 100 amps. . . that sounds correct? Is there anything else I'll need to know or want to take into consideration before I buy one?
Click to expand...

First, you dont need a diode,you need to fix your wiring method.Second a high current/ high PIV(probaly at least 100volts to be safe) diode would be extremely expensive!
 
Your fan could not possibly be pulling 80 Amps! That would take all the current your alternator can deliver, with nothing left for the lights or toys and no charge for the battery. You should figure out how to get an accurate measurement of start and run currents. I suspect your start is about 15A and run about half of that. I recommend pick up a diode with PIV of twice to three times the runing voltage and a current rating of about 15A.
The worst that can happen if it is way under rated, is the diode would short. Then you would be exactly where you are now, no smoke or fire.:flame:

If you are looking for a cheap source, you and try a surplus house, like here:
http://www.allelectronics.com/make-a-store/item/18TQ035/SCHOTTKEY-RECTIFIER-18A-35V/1.html
 
Here's the best I can do for a schematic:

I removed the high speed wire because I was getting 18-19V back at the low speed side relay. I'm running 80 amp relays with an 80 amp circuit breaker, the fan switch is rated at 30 amps I believe.
I shouldn't be getting 18V at the low speed side should I? I always here about people not worrying about it, but I'd rather get a definitive yes or no on this. I don't like taking chances that have catastrophic consequences.
 
From the looks of your diagram, when high speed is called for it shuts off the low speed. If that is the case, I don't see any harm if voltage is sent back to the low relay that is now open.
 
yup, low speed side is tempature controlled, high speed side is PCM controlled, and it has a cut-off switch for water crossings.
 
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