question on feedback

[bierluvre]

hello, newbie here. not much for electrical, I'm an IT guy with quite a few years of component level behind me.

My question is hypothetical. If you had two inputs from the same source voltage (DC) and they were shorted together, as in both inputs went to the same input point, would there be a feedback issue result if one input was energized after the other while the other remained energized? Or would there be no effect since they are of the same source voltage and in phase. To me, you're really not "shorting" anything since it's just the same voltage applied across two parallel conductors applied to one point. Correct? Not Correct? Stupid Question? Thanks.

 

[VEBill]

If the two signals are exactly the same, then just use one.

 

[bierluvre]

well, the purpose is to test two different paths for the same source to the same input. the reason for the question is to understand what would (if anything) happen if both paths were energized in a staggered sequence so where both would be on at the same time, this would be accidental.

 

[VEBill]

One trick, if the input Z is high, is to use series resistors to limit fault currents.

In other words, if the input circuit is 10M ohms, then you could probably use something like a couple of 10k series resistors to limit the current from the two sources without any effect on the signal.

You need to work out the optimum value yourself. Make it about twice the minimum value and make sure if doesn't impact the signal at the input.

 

[itsmoked]

I thing VE1BLL is thinking "signals".

If you mean could you plug two plugs who's cord ends meet at some device into the same outlet with no change in the device's operation? Yes. No problem. Plug and unplug all you want whenever you want. There will be no noticeable first order effect. AC/DC whatever.

Do not go demonstrating this haphazardly at the next party though, unless you bring the proper equipment to prove that the outlets really ARE the same phase. Any two outlets in a house are likely to be on different phases which most definitely will cause first order effects.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[IRstuff]

You've asked several questions. Tying two DC signals of the same voltage should present no problems, if they were BOTH on.

However, shorting them while one supply is off is a BIG problem, since that depends greatly on what the source looks like in the unpowered state. You could fry one or both of the sources, since you might be essentially shorting out the source that's on. The current surge might also damage in the unpowered source.

TTFN

FAQ731-376

 

[melone]

"the purpose is to test two different paths for the same source to the same input"...

Your boss want to spend time and money investigating this?

 

[bierluvre]

Thanks yall have answered my question, yes I wasn't referring to signals, just voltage (two lines, same source).

Melone: actually a couple of guys were adapting (via pigtail) an 18 wheeler trailer light tester to a regular hitch trailer. I over heard (wasn't involved with the wiring of the pigtail), the topic of having two lines ran to one connection point, yada yada ya, they weren't certain about it ...I don't know why really, I was just curious for my own personal sake. Thanks e'body.