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What’s the Reason to Diode Isolate?


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evois 
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Posted: December 04, 2006 at 12:18 PM / IP Logged  
jpease wrote:

evois wrote:
it's easily accessible, at radioshack.

anyone have a part number/sku?   or link?

I used the 1N4001

bqe. 
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Posted: December 04, 2006 at 4:50 PM / IP Logged  
tvic 
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Posted: December 05, 2006 at 12:13 PM / IP Logged  
An ohmeter across a diode will show continuity for many reasons, as it could be the circuit on the other end of that + and - are still continuous.  (i.e. even across the + / - of a transformer will still show continuity).  Show just because hooking an ohmeter across a + and a - shows minimal resistance, or beeps, that doesn't mean there's a short across the device.
dualsport 
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Posted: December 05, 2006 at 10:18 PM / IP Logged  
evois wrote:
taking this diagram as correct, why is it that if you use an ohmmeter it shows continuity if I use the (+) of the ohmmeter to the (+) of the # 1 diagram and the (-) of the ohmmeter to the (-) of the diagram? Is it because electricity travels (-) to (+)?
Usually with a DMM you will hook up the red (+) lead to the side without the stripe, and the black (-) to the side with the stripe. With the meter on the diode check range (which puts out a high enough voltage to allow the diode to start conducting), it should show a reading. If you reverse the leads, it shouldn't show anything, if it's working properly.
Some old analog meters are different, however, the polarity of the resistance measurement is backwards, where the black lead puts out a positive voltage relative to the red one. If so, then you need to connect the red to the striped cathode side of the diode to check it.
jpease 
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Posted: December 11, 2006 at 9:16 AM / IP Logged  
thanks guys!  I appreciate your help.
dualsport 
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Posted: December 12, 2006 at 12:02 AM / IP Logged  
If you anticipate needing more than a few components, it'd probably be worth your while to order from mouser.com or digikey.com; the 1N4001 diodes there are about 2 cents each in quantities of 100.
alexlloyd 
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Posted: December 21, 2006 at 6:27 PM / IP Logged  

dea,can wrote:
What’s the Reason to Diode Isolate? - Page 2 - Last Post -- posted image.

Does this not appear to be backwards. Positive on the non-striped end and negative on the stripe forward biases the diode and it will conduct and effectively bypass the coil and not energize the relay. Refer to the diagram above. In order for the diode to quench the reverse spike generated when you remove the power from the relay, it would have to be reverse biased to energize it. That requires +12v on the stripe, ground on the other end.

dualsport 
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Posted: December 21, 2006 at 11:35 PM / IP Logged  
Yes, it should be the reverse of that description; it needs to always be reverse biased with the striped side connected to the higher voltage.
For a low side drive Trig(-) and high side drive Trig(+):
What’s the Reason to Diode Isolate? - Page 2 - Last Post -- posted image.
jacqueslacombe 
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Posted: December 30, 2006 at 3:57 AM / IP Logged  
4001 or 4004 should do  this is good for 1 amp     don't pay more than 10 cents a piece
cocolaboy
dualsport 
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Posted: January 08, 2007 at 8:11 AM / IP Logged  
1N4001 through 1N4004 are all rated for 1 amp, the only difference is that the higher numbers like 1N4004 are able to withstand a larger reverse voltage. You can always substitute a higher one for a lower one, so if you stock up on diodes, get the higher ones for the small diff in cost.
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