If I were to choose two General Purpose Diodes for the locations noted in the diagram, what voltage and amperage would that diode need to be? The Head Unit (Radio) is capable of drawing 10A @12V, and the PSU (power supply) is rated for 40A @ 12V. Someone else recommended a diode with a minimum of 50V/1A, but I'm worried that that won't be enough, and I don't know how far above his recommended minimum I can go without unforeseen problems popping up, like heat or w/e.

A couple days ago, I read something along the lines of a diode should be roughly 2.5x the rated voltage AND amperage of the transformer/power supply. So should I get a diode with a minimum rating of 50V and 25A, instead of the 50V/1A that was recommended to me? Or is it all about the wattage? In other words, 10A@12V=120W, so it's only necessary to have a 50V/2.5A diode, or a 120V/1A, or 240V/.5A diode? Or is meeting or exceeding that 2.5X ratio necessary for both the voltage and amperage, even though a 50V/25A diode would equal a whopping 1250W overkill figure?

Thank you in advance.

 

Forgot the diagram, here it is.

[ATTACH=CONFIG]33134[/ATTACH]

 

Connecting 120VAC to a DC battery?

 

I understand your diagram, but if you will forgive me, I must say you are lost in term of your knowledge of diodes. Again I apologize, but you need to do some reading. Some modern day electronic pros will be along to correct me, but let me try to get you started.

Diodes are primarily rated for "forward current", "power", and "peak reverse voltage". In the application you are illustrating the peak reverse voltage of any diode you select will be in the hundreds of volts so not a concern.

The forward voltage will always be in the range of 0.7 volts so a 10 amp forward current with 0.7 volts would need a minimum of 7 watts capability, actually 10 watts for proper margin.

Your frequent reference to a voltage rating does not make sense. If it is a reverse voltage those numbers are far too low and in the reverse mode there is no current.

If your radio is going to draw 10 amps (which seems like a lot), then you need a standard silicone diode rated at about 15 amps and 10 watts. Recognize that your radio will see the source voltage less that 0.7 volts with your approach.

Let's see how I did when the pros show up .

Bud

 

I thought I made it clear in your other thread. No problem. You can use ANY general purpose diode. The diode needs to be at least 50v and can be up to 5000v. It needs to be 1A but can 3A, 5A, 50A.

1N4001, 1N4002, 1N4003 all popular and cheap.

Radio Shack sells a bag of diodes for a buck or two. You could probably open an old piece of electronic equipment and snip two out. They'd need to be black.... not clear glass.

The diodes are being used as a one way switch so that when your box is running on AC the battery is not being drained. Unfortunately the battery can't be charged as the voltage isn't high enough but at least it won't discharge. The yellow radio memory line is only drawing 10-15ma. of power.

 

Thanks PJ, that clarifies things a bit.

Bud

 

Ahh, ok. Thank you for the explanation, that helps a lot. I thought that the 10A circuit would be in the mix somewhere in there, but now I understand what's going on.