detect 12 volt "in use"?

[jassing]

I have a transceiver -- when I turn it on, I want to trigger a relay to provide power to an amplifier.
I tried putting a relay "in line" -- but that sucked too much power out so that the transceiver didn't fully power up.

Any ideas?

 

[davidmc36]

I assume the transciever has a volume/on-off control and that is where you tried?

Just leave the volume knob in the on position and switch the power input to both the radio and the amp.

Or can't you get a smaller relay that does not draw as much current wherever you tried it?

 

[jassing]

a smaller relay -- so obvious that I had not thought of that. I'll give that a try. Thanks.

 

[kb2vxa]

Uh uh, it don't work that way. Your "in line" idea is flawed, current through the relay coil to the transceiver draws in the relay armature BUT coil resistance causes voltage drop so not receiving the full 12V it won't operate. Using a "smaller relay" will only exacerbate the problem. Hey guy, if the relay takes 12V to operate what's left for the transceiver?

Pardon my sarcasm but seriously, you're better off abandoning the relay and installing a good heavy duty switch in the common power source lead.

 

[davidmc36]

....Your "in line" idea is flawed,.....

I assumed he meant parallel but if done in series for sure it will never work.

 

[jassing]

Yes, I know my concept is flawed by the evidence collected: it didn't work.

It was something I could easily (and quicly) try... adding a switch is certainly an option; but one I want to avoid -- which is why I asked about detecting that the line is "in use"....

Thanks for input tho. Valuable and appreciated.

-j

 

[davidmc36]

You should be able to make it work depending on how much effort you want to put into it. Maybe using a transistor to switch on a relay. So long as it only draws a very tiny amount of current. Whatever you are doing it can't go through your "circuit" and then to the radio (series). Rather is needs to work "side-by-side" with the radio power (parallel).

 

[jassing]

Thanks -- I didn't have any transistors on hand...
I ended up wiring in a small wire off the off/volume knob to trigger an external relay... Seems to do the trick. Not as elegant as I had hoped for; but it's what I had around to work with.
-josh

 

[davidmc36]

Good to hear u had success. I can never resist a functioning mod, even if it is not exactly pretty. The guys at work know to ask if I have something electronic for sale, "Has the case been opened? What was the mod?"

 

[kb2vxa]

You lost me with the "detecting the line in use" bit so I fell victim to what they say about "assume".

"I ended up wiring in a small wire off the off/volume knob to trigger an external relay."

I was chewing on that idea but you came up with it first. What I had in mind avoided going inside the radio but you don't seem to mind having an extra wire, relay and associated wiring hanging about so go with it.

No David, the one he names in the will wins. (;->)

 

[com501]

This is what Elk relays are for....