Electrical question

[JG14_Smil]

Hello,

 

I am hoping someone here has enough electrical knowledge to help me with a problem I've come up against. I use some 6v bulbs in my cockpit and initially wired them up using a 7v 300ma power supply (PS). I got a new 5v 4 amp siwtching PS so I can drive more bulbs.

 

Without verifying polarity, I cut off the 3.5mm plug off the PS, assuming the white stripe would point to the positive wire as usual, then replaced the PS. When I fire it up, all my 6v lights come on and do not respond to my module that controls them (Epic cards).

 

I did troubleshooting and verified the original PS works the lights correctly. I separated the PS and used a LED with a 1k resistor wired in. When I wire the cathode to the non-striped ground wire, I get nothing. When I run the cathode to the wire I thought to be the 5v side, the LED lights up. The resistor is on the anode side and the cathode belongs on the ground wire, so it is acting like my PS wires could be reversed. I also verified this by testing the LED with my 7v PS: the striped wire is positive and works when wired to the anode and not with the cathode.

 

Maybe I have a fluke and the ground wire has the stripe, the way I cut it off I cannot verify one way or the other.

 

Enough talking... :) Could a reversed PS cause all my lights connected to it to light up at once?

 

Nothing appears to be fried and all works correctly in the original configuration. I have a multi meter but am not an electrician and am not sure how to use it to help out with the problem.

 

I would like to try all other tests before reversing the PS leads.

 

Thanks for any thoughts...

Edited November 28, 2011 by JG14_Smil

[Gadroc]

Use the multimeter to measure voltage on the leads from the new power supply. If it measures negative then reverse the leads. Once you get it reading positive the one connected to the ground lead on your multi-meter is your ground.

 

It really depends on specifics of how the controlling circuit is designed on the behavior of reversed power supply but it's usually a recipie for magic smoke.

[JG14_Smil]

Thank you Gadroc,

 

I put the meter on the wires and it seems to support my theory. Black lead on the ground PS wire gives me a negative number. Black lead on the "stripe" wire gives me positive numbers. All signs point towards reversed leads from the 5v.

 

My Output module has a "clamp" for the ground wire and highest voltage positive lead. The 12v and 5v ground wires were connected and "clamped" to ground on the module. The positive 5v leads go directly to the lights, which then return to the card.

 

If the wires were backwards, this means the 12v ground was wired to the 5v positive and clamped to the card and I am very lucky no smoke was 'let out' :) I am relieved the card still works in the original form.

 

I am waiting for an email from the card developer before I do any more. Will update when I get it figured out.

 

Lesson learned is never assume!

Edited November 28, 2011 by JG14_Smil

[Gadroc]

Glad it looks like you didn't damage your controller. Always double check you power supply before hooking it up to a circuit, both for polarity and to verify it's the correct voltage.

[JG14_Smil]

Problem resolved. Thanks for the advice Gadroc. I reversed the leads and it all works correctly. I can see I'll need to find a 6v power supply as the lights are dimmer.