Relay question

[Lc85]

We have a panel for isolation relays. In this panel we have a 24v psu, and we are sending 24vdc from this panel to another panel(ESD Panel) where it will be switched back. We then have a relay (in the isolation relay panel) on the 0vdc. When this relay is energised it will close some contacts in the isolation relay panel.

My question is whether this is correct or should the relay be on the 24vdc side?

Thanks

 

[Skogsgurra]

Are you asking if it is better to switch on the positive (+24 V) side or on the 0 V side?

Normal practice is to have all loads, lamps, coils or what have you connected to ground (or 0 V) without any switches or relay contacts in-between. That implies that all relay contacts shall be between positive (+24 V) bus and loads, coils etcetera.

But there are many different special applications where all switching is done in the negative side and then others where the philosopy seems to be that it doesn't matter as long as it works. Automotive guys seem to be of the latter opinion.

Gunnar Englund

http://www.gke.org

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Half full - Half empty? I don't mind. It's what in it that counts.

 

[itsmoked]

It's very clear what the automotive guys opinion is:
"Do it in the most mind twisting absurd manner, of last to be expected, and the most illogical method to cause troubleshooting to require tools such as bleeding chickens and bone piles to effect repair."

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Skogsgurra]

Right, Smoked!

But we do have some automotive friends here. So I tried to be gentle. That is not me, usually. But I felt mild and forgiving after a few day's of utmost satisfaction. (New twist on old technology - power control with absolutely no EMI or harmonics issues, worked like a dream - customer paid bill and came back for more...)

Gunnar Englund

http://www.gke.org

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Half full - Half empty? I don't mind. It's what in it that counts.

 

[ScottyUK]

Skogs has re-invented the switch.

 

[Skogsgurra]

How right you are, Scotty! But with several twists. Ternary may ring a bell? There are a few more bells...

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[ScottyUK]

Long time since I did any coding work - ternary = conditional logic, correct?

 

[DanEE]

Corollary of itsmoked's humor... (love it!) From the computer digital design world, you see it done equally well in both ways.. active can be either pull high or active can be pull low; depending on the circuitry around the point in question.. do it in which ever manner that neither adds additional components, complexity or problem.

Always assumed in automotive world with all the handy sheet metal around to ground to, pull to ground, meant less wiring...

With digital logic had to be careful about float conditions (and noise immunity) and make sure proper pullups in place, not typically a problem with the higher current circuits where relays are involved.

One somewhat funny problem I found in a design... cable with 2 (16 bit + parity) memory data paths. Yank the cable and all data bits float high, so does parity bit says data path good! one case where easiest fix was to invert the parity bit to where all 1's in data path > 0 bit for good parity... now yanked cable parity checking works..

 

[waross]

Always assumed in automotive world with all the handy sheet metal around to ground to, pull to ground, meant less wiring..

Not alwys;
In my first car, the wire ran from the battery to a fuse panel under the dashboard.
A short wire from the fuse to the switch.
A long wire from the switch to the headlight.
A short wire from the lamp to nearby ground.

A newer car with ground side switching;
In a more recent car, the wire ran from the battery to a fuse panel under the dashboard.
A long wire from the fuse to the headlight.
A long wire from the headlight to the switch.
A short wire from the switch to nearby ground.
Let's not talk about the tail light wiring.
I'm with you Keith.

Bill
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"Why not the best?"
Jimmy Carter