(Topic ID: 223361)

Help with dropping 12V to 9V from WPC Driver Board J116, J117 or J118?

By Walamab

1 year ago

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  • 18 posts
  • 12 Pinsiders participating
  • Latest reply 1 year ago by kbliznick
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#1 1 year ago

I'm working on a homemade mod for my Demolition Man. I found a set of 12V LED angle eye rings made for going around car headlights. At 12V they draw about 600mA and are INCREDIBLY bright. Using my bench power supply and dropping the supplied voltage to 9V produces a better brightness and subsequently lower current draw.

My question is...Can I simply connect 4 diodes in series to drop the 12V from J116, J117, or J118 on the driver board to ~9V (4X0.7V=2.8V; 12V-2.8V=9.2V)?

Is there a better (and simple) way to do this?

Thanks in advance!

#4 1 year ago

Diodes will get hot if you draw a lot current through them. If/when they get hot, the voltage drop of each diode is lower so you won't get a stable 9V at the output.

You could go with a simple voltage devider using two resistors but only if you know the exact resistance of your load.

At the end of the day, the most efficient way is to use a buck converter, as mentioned above.

You can get a set of 10 for cheap, with a variable or fixed ouput.
Good to have the around when needed!

#5 1 year ago

What sort of current draw does each draw at the 9V and how many do you plan to drive at once? The final current draw makes a world of difference.

Since you don't need an absolute 9V supply - the diode method would be by far easiest. But this will be a diode running at 100% duty cycle and a steady state (at 'TBD' level) current -- this has to be far less than the 600mA total or could be a huge temperature rise.

The linear regulator (LM2940) would also work and give a steady voltage at a level 9V. But, again, need to know current draw to make sure you aren't overloading. These will also dissipate a tremendous amount of heat and would need to have a pretty heft heat sink.

As the others mentioned - best bet would be to use the switching supply mentioned by SteveNZ. Since they are switchers - MUCH less heat. But since these are no-name Chinese assemblies, I wouldn't expect a tremendous life span out of them.

#6 1 year ago

I did some testing last night with the Diode idea with both LED rings connected. Current draw, as indicated by my bench power supply, was 10mA @ 12VDC. Voltage measured at positive connection to LED rings was right at 9.2VDC. I left it connected for several minutes and could not detect a temperature rise in the diodes.

#7 1 year ago


#8 1 year ago

This is looking like an easy/elegant option too. I think I'll order one to tinker with.

found these 6 for $12 @ amazon.com link »


#9 1 year ago

Why not just a wall-wart power transformer? Plug it into the service outlet and splice in the wires.

#10 1 year ago

Does the service outlet stay on when the main switch is turned off? If not this is also a good option.

#11 1 year ago

The service outlet is not switched.

#12 1 year ago
Quoted from Walamab:

Does the service outlet stay on when the main switch is turned off? If not this is also a good option.

Good point, but you could just tap into the 110AC, after the power switch, before or right at the transformer.

#15 1 year ago

And even cheaper yet!

ebay.com link

#16 1 year ago

It's unbelievable how cheap electronics are becoming. How the hell do people make money off of that?

#17 1 year ago

Yep, amazing how the Chinese can steal designs (why bother paying designers when you can just 'borrow' the completed design from somebody else?), pay slave labor wages, use inferior parts and still get subsidized by their government.

But that last ebay link. That's probably the easiest way for OP to do this. It appears to be nothing more than a rheostat.

#18 1 year ago
Quoted from DNO:

Good point, but you could just tap into the 110AC, after the power switch, before or right at the transformer.

Check the coin door wiring harness for the bill-validator power. Black wire and white wire that supply switched 110V. On most but not all WPC games.

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