[mikes82GT]

I need help with figuring which way the freewheeling diode goes on the fan I installed.
Does the end with the stripe correspond with the end that is the vertical line in the symbol or vice versa?
I was following the tech articles in the cooling section and I realized I don't remember what I learned in high school science class (20-some years ago) about these things!

 

[tony]

The diode symbol has two parts: the triangle and the stripe. If a positive voltage is applied to the triangle side of the diode, the triangle is pointing the direction the current will flow meaning it will pass through the diode to the other side. If the positive voltage is applied to the stripe side of the diode, the stripe acts like a road block. It will not allow current to pass through to the other side. There is a small voltage drop across the diode (approx .7 volts). So make sure your source voltage is good. Time to go back to school.

 

[allenman85]

Ahhh...but he needs to know how to install it as a freewheeling diode.

The principle their is that you don't want the spike of the motors getting back onto your electrical system when you shut off the fans.

The way you do that is to install the diode ACROSS the fan inputs as close to the motor as possible. The cathode (stripe) needs to go on the Positive terminal of the motor and obviously the anode (triangle) goes on the negative.

This way the diode is reverse biased while the system is on and is forward biased when the system is off (freewheeling) and it conducts the spikes generated by the fan when the fans are spinning down.

 

[retyler]

It's a steering diode.

 

[mikes82GT]

Thanks Ponyexpress and Allenman85 for the info. Hey retyler, what's a steering diode?

 

[82GT]

Where did you buy your diode at.......Radio shack? Do you have a part # for that? I still need to put one on my taurus fan.

 

[retyler]

On 2006-03-25 23:25, mikes82GT wrote:
Thanks Ponyexpress and Allenman85 for the info. Hey retyler, what's a steering diode?

The diode is used to direct the flow of current. It can be used to shunt off spikes of current from motors, lightning , power surges, and so on but mainly used as a rectifier to convert from ac to dc.

 

[allenman85]

Nice replies. The freewheeling effect was explained by me already.
The 'steering' is cute. I wonder what he means too.

 

[mikes82GT]

On 2006-03-27 15:51, 82GT wrote:
Where did you buy your diode at.......Radio shack? Do you have a part # for that? I still need to put one on my taurus fan.

I found it at an electronics store called FRY'S Electronics in the computer components section. The part# crossed over from the one they used in the cooling section here.
It is part # NTE5809 by NTE Electronics Inc. and it says Si, Industrial Rectifier, Axial Lead, on the back of the card.
The specifications are:
PRV - 1000V max. IFSM - 200A max. IF -3A max. VF - 0.9V @3A
It says it replaces ECG5809, GE-512 and SK9010.
All I know is I gave the guy the part #1N5408 (or was it 1N5804? you'll have to look in the cooling section under junkyard fan install) and he looked it up, went over, picked this out and handed it to me. The price was $1.30, pretty low cost actually.
The problem I was having was relating the symbol to the part, as in which end was which.
Thanks again guys.

 

[slow-poke]

The 200A surge rating is only good for a very short time. You might want to look for a bit larger diode, because if it fails your fan will not work.

Digikey has a large selection

 

[allenman85]

Again, if it's installed as a freewheeling diode, the surge is minimal...

Follow the diagram in the article and you'll be fine. The aritcle also correctly details what a freewheeling diode does. Good luck.

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<font size=-1>[ This Message was edited by: allenman85 on 3/28/06 9:33pm ]</font>

<font size=-1>[ This Message was edited by: allenman85 on 3/28/06 9:35pm ]</font>

 

[mikes82GT]

Installed the diode and applied battery voltage to the fan. Held a test light to the positive wire as I touched it to the positive post and let off while holding the light to the wire. The light lit up brightly then tapered off as the fan wound down. Should it do that? I installed the diode as recommended, with the stripe end (cathode) towards the positive wire and about 1 1/2" from the fan motor. If I have to, I will try it the other way. A simple matter of undoing some tape and solder.

 

[Motorhead]

If you put it in the wrong way, you would have smoked the diode as soon as you put 12v across it... so the fact that the diode isn't vaporized means you did it right

 

[mikes82GT]

Ok thanks, MOTORHEAD. But isn't it supposed to keep all the juice from feeding back through the system? Or am I wrong and the light test I did says it's ok?