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Old 11th November 2006, 02:00 AM   #1
SRMcGee is offline SRMcGee  United States
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Default Newbie Relay Question

Folks:

I am building a two chassis preamp that includes a 6V DC relay in the power supply chassis. The power source to trigger the relay is a 4.8V DC source in the preamp chassis. One wire in the umbilical between the two chasses carries the 4.8V DC from the preamp chassis to the 6V relay in the power supply chassis. The other side of the relay trigger goes straight to ground. I thought that the relay would operate with voltages as low as 4.2V DC (the relay is an Omron G2R-2-S(S)). When I apply a 9 volt battery across the relay, it works fine. Is the problem that the DC voltage is inadequate or is there a problem with applying the DC voltage through the relay to ground?

Any advice would be gratefully appreciated.

Regards,
Scott
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Old 11th November 2006, 02:59 AM   #2
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The wires between the two boxes are probably dropping enough voltage that you're falling below the minimum operating voltage/current for the relay. Measure the voltage at the relay terminals to check it.

Why not put a 5 cent transistor in the power supply box to drive the relay from the sort-of logic level signal from the preamp box? It seems a little round-about to generate the voltage in the power supply box, send it to the preamp box, then back to the power supply box.

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Old 11th November 2006, 06:02 PM   #3
SRMcGee is offline SRMcGee  United States
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I_Forgot:

The voltage at the relay is the same at the source -- 4.8V DC. This arrangement isn't as clumsy as my initial post may have made it sound: the purpose is to turn the power transformers for my Aikido preamp on and off using the remote control. Since the remote control is located in the preamp chassis and the power transformers are in the power supply chassis, I simply send 4.8V DC from the preamp chassis back to the power supply chassis to trigger the relay, which in turn powers the transformers.

Here's the thing: if I run two wires (4.8V DC and ground) from the preamp chassis to the power supply chassis to trigger the relay, the relay works just fine. If I just use one wire (4.8V DC) and use the ground already at the power supply chassis, the relay does not work. Why is that?

Regards,
Scott
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Old 11th November 2006, 07:15 PM   #4
dhaen is offline dhaen  Europe
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There is probably a small voltage drop in the ground wire, created by other circuitry, that is subtracting some millivolts.
I bet that if you use a digital voltmeter you'll see a small, but significant difference.

Also bear in mind that just because the 6v device can work on 4.5v, it doesn't mean it always will. Variables such as mains voltage, magnetic fields, temperature and even humidity can affect. Designing for centre tolerance will give you the best results, always.
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Old 11th November 2006, 07:58 PM   #5
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Is the ground the same ??
Otherwise your 4.8V is floating....
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Old 11th November 2006, 09:34 PM   #6
paulb is offline paulb  Canada
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I really doubt it's voltage drop in the wires that is causing the problem. There's something else. Any way to post a wiring diagram, even hand drawn?
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Old 11th November 2006, 09:56 PM   #7
wrl is offline wrl  United States
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How are you getting the 4.8 V signal?

Make sure that it is well rectified and filtered. I had this problem before... with some of my initial power supplies. Added bigger filter caps and its worked fine ever since.

-Wes
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Old 12th November 2006, 05:43 AM   #8
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Location: Wisconsin....what did you expect?
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And then, you have the Spasticteapot solution:

Use a reed relay designed for 2.5v use which will in turn trigger the 6v relay.
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Old 12th November 2006, 12:33 PM   #9
SRMcGee is offline SRMcGee  United States
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Folks:

ACD had the answer -- the Dantimax remote control system that was generating the 4.8V DC needed to drive the power supply relay had a floating ground; once I connected it to the ground common to the rest of the preamp, the relay worked perfectly.

Thanks to everyone for your suggestions!

Regards,
Scott
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Old 13th November 2006, 01:11 AM   #10
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Default 4.8V drives a 6v relay

Dear Gents:

I think you people make a big mistake. Omron relay 6V will works on +-10% of 6V, that means from 5.4-6.6v this relay must worked and guaranteed by the manufacturer, If use a 4.8v, that is far behind the spec. requirement, 5.4 - 4.8 = 0.6v. that means it's 20% below the requirement. of cause sometimes will work and some not.

the best solution is to provide 6v for the relay, indirect driven by reed is ridicious, consider the driven voltage is the best way to solve the problem.




WE DO THINGS BASE ON SPECIFICATION
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