Diode for Radio Power

[rich2202]

We have fried our share of Dlinks because of reverse polarity of the power connector. Any thoughts on putting a diode in the power cord to prevent current in the event of reverse polarity?

1) Anything in the rules that would prevent that (alter the power path, custom circuit to supply power, etc.)?

2) Is the voltage drop across the diode a problem? I think Schottky diodes have a 0.40 volt drop.

[Alan Anderson]

Originally Posted by rich2202

1) Anything in the rules that would prevent that (alter the power path, custom circuit to supply power, etc.)?

Yes, sorry. There's no room in the rules for anything except wires [edit] and connectors [/edit] between the VRM and the D-Link.

Have you found out who is reversing the wires on your D-Link power connector? If it has happened multiple times, it starts to sound intentional.

[jvriezen]

We had our briefly reversed and connected to 12v at the same time. Fortunately, nothing fried-- it was notices very quickly.

I'd suggest putting some red electrical tape on insulation near the end of the + lead to minimize the likelihood of it happening again and leave a tab of tape with "5v !" written on it on both sides.

[marshall]

Originally Posted by rich2202

We have fried our share of Dlinks because of reverse polarity of the power connector. Any thoughts on putting a diode in the power cord to prevent current in the event of reverse polarity?

1) Anything in the rules that would prevent that (alter the power path, custom circuit to supply power, etc.)?

2) Is the voltage drop across the diode a problem? I think Schottky diodes have a 0.40 volt drop.

I wouldn't recommend it because it could cause problems and I'm uncertain of the legality BUT I do have a suggestion for you. Don't use bare wires or rely on the often hard to see striping on the radio power cable. Use Anderson Power Poles on the ends of the wires and then run pigtails back to their respective ends (barrel jack pigtail for the radio and 24/22 AWG pigtail for the other). We then "key" the Anderson powerpoles differently based on 12v or 5v power. We haven't had any issues with blown components since we started doing this.

EDIT: To be clear, we use both red and black APP connectors to identify the polarity.

[rich2202]

Originally Posted by Alan Anderson

Have you found out who is reversing the wires on your D-Link power connector? If it has happened multiple times, it starts to sound intentional.

It happens during the initial wiring. We usually cut the cord from the AC power adapter and use that. The first year I became a mentor, I watched a Dlink get fried. I was told it happened before. Since then, I won't let the kids connect the Dlink to a newly wired connector until after the wire has been checked with a volt meter.

[Jon Stratis]

As Alan said, I don't think a diode would be legal. This is something we always cripple check, every single year. The stripe on the wire can be hard to see, and it's easy to forget what it indicates, so everyone on the electrical team does a visual verification when it's first hooked up. We ALWAYS check continuity with both the center and outside of the plug to ensure its wires correctly. Then, when we do the initial power on, the radio starts unplugged and we verify voltage on the plug before plugging it in.

[Alan Anderson]

Originally Posted by rich2202

Since then, I won't let the kids connect the Dlink to a newly wired connector until after the wire has been checked with a volt meter.

Originally Posted by Jon Stratis

Then, when we do the initial power on, the radio starts unplugged and we verify voltage on the plug before plugging it in.

Verifying proper voltage and polarity before plugging anything in for the first time should be standard practice.

If the problem is that the initial wiring was done incorrectly, I don't think a diode would help. It's just as easy to install the diode backwards, or in the wrong wire, as it is to swap the wires when first connecting them. You need to double-check the final connection anyway, and I think it is a lot easier to have just one thing that could be done wrong and which is easily corrected.

[JDL]

Enforce a 100% test policy and instill proper habits in the students instead of bodging in a diode. Everyone that is involved in the wiring should be able to use the DMM and check for proper polarity, voltage, shorts, ect.

God knows we need more EE's, tech and electricians that will take a second to ring it out before they just go flipping the switch.