Using positive rail as chassis ground 1

[JackZylkin]

Hey all. I have an interesting question:

I am making a very low budget piece of electronic equipment for mass production. We have circuits on two separate boards and it occurred to us that we could save big $$$ by sending Vcc (5VDC) to the second board from the first ***through the chassis*** (saving us a difficult wiring job).

I have seen people use the positive terminal of a 9V battery as chassis ground before. I am wondering if there is any reason I can't use a regulated 5V for chassis ground (the circuit is somewhat sensitive to radiated EMI).

What say you?

 

[eng1ne]

On what products have you seen this method employed before?

 

[Skogsgurra]

Have designed an HVAC control unit where every penny counts. Had to tie Vcc to grid phase (a lot worse than using it as common) because of triac triggering considerations. No probs, but we had to design the software so it recovered quickly and safely from repeated interference from switching interference on the grid. It was a non-critical application (WC ventilators) - but still...



Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[JackZylkin]

I've seen it on Japanese made guitar effect pedals like Roland and Boss.

 

[Noway2]

There is nothing magical about the concept of "ground". It is still a matter of how current flows and giving due consideration to the return current path. From an AC standpoint, both a positive DC supply and the DC ground will act as an AC ground return.

As another example of this type of setup is a diesel engine driven firepump, where positive (chassis) grounded systems are semi common.

 

[JackZylkin]

I want to believe that ground is an arbitrary concept, but I feel like a 5V regulator will not be able to source and sink current as well as the circuit ground.

 

[VEBill]

If you're going to use the chassis for the 5v power supply 'hot', then wouldn't you need to add a power supply return wire anyway (since you could no longer use the chassis for return)?

Save a foot of red wire, add a foot of black wire.

 

[MacGyverS2000]

The guitar pedals are most likely using dual-supply op-amps that need a (simple) negative supply... you'll often see reversed 9V batteries in there to act as the negative supply. Ground is an arbitrary concept, but as VE1 mentioned, what are you saving?

Dan - Owner

http://www.Hi-TecDesigns.com

 

[Comcokid]

Years ago even some cars used "positive ground". But eventually everything standardized on 12 negative ground. Positive ground and 6V automotive systems dissappeared.

 

[IRstuff]

Grounds can be whatever voltage, relative to the actual supply; that's a separate question than using the chassis for any current flow.

Using the chassis as a power rail is BAD; don't do it. The reasons are legion:

> Introduction of noise into the circuitry. The chassis is basically a giant antenna, and will pick up more noise than a wire will.

> Someone touching the chassis will add more noise, because people make good antennas as well.

> People are also great capacitors, and as we head into winter, electrostatic zaps to the chassis will go into the circuitry and possibly damage the transistors

> Non-ground chassis' may contact real grounds, thereby causing lots of sparks, damaged power supplies, and a fire hazard

nuf said?



TTFN

FAQ731-376