How do I Modify a 9V universal to 8V?

Toolmaker · Post by **Toolmaker** » Wed Nov 05, 2008 3:01 am

I have one of those 9V power cords for small devices. Its only 9V and 800ma. The device I need to use it in is 8V 200ma.

What are my el cheapo hack options?

I would prefer something I could put together from Rat Shack parts.

gyre · Post by **gyre** » Wed Nov 05, 2008 11:25 am

What is the actual output of the supply?
What is the device?
Does it have a range of voltage?
It may work just as it is.
Are you running off dc or ac as a source?

Simplest way is a resistor, but it will be sized for one load only.

Be sure to check polarity at both ends unless all is ac.

The better converters have a range of voltages.
Try to find the usa made ones.
They are still around sometimes.
It's possible to get a variable power supply, but that costs more.

Or you might find a power supply that matches in voltage and power.
Again check polarity.

Dork · Post by **Dork** » Wed Nov 05, 2008 4:04 pm

You can get a voltage regulator chip - LMsomething. I know they have them at Fry's, as I just got one - might be at Radio shack as well. Get one with the appropriate input and output voltage range, check the application guide to see what resistor you need to get 8v out. It will require a little soldering and heat shrinking.

There's an instructable on this somewhere but I couldn't tell you exactly how to find it. I believe it was designed for powering something off 5v (USB power) that wasn't meant to be.

Or you can simply try plugging it in, maybe it won't fry. At least not right away.

Post by **mdmf007** » Wed Nov 05, 2008 4:10 pm

the 1 volt is no big deal - its the amps that are going to burn a circuit.

Gyres question is the most important, for good tips you need to tell us what your powering - and this would have been a perfect question for the Tech help thread.

later

Dork · Post by **Dork** » Wed Nov 05, 2008 5:09 pm

mdmf007 wrote:the 1 volt is no big deal - its the amps that are going to burn a circuit.

It depends where the volt is going - on cheap simple stuff the input might just go straight through a passive circuit to charge batteries, and the extra volt could overcharge them. Or something like that. In most cases it won't be a big deal, but whenever there's a weird voltage (eg not 5, 6, 9, 12) I wonder why.

Any chance you could crack open the item in question and post a picture of what the power leads connect to?

Toolmaker · Post by **Toolmaker** » Wed Nov 05, 2008 5:13 pm

Powering a wireless camera 2.4 ghz reciever. The device requires 8V 200ma. The Rat Shack adapter I have is 9V and "up to 800 ma" ac to dc plug into the wall. I was hopin there was a way I could just grab a resistor or something cheap and put it inline on the power cord and heatshrink the works or electrical tape it. The reciever powers up fine with the 9V 800ma and doesnt get too hot but I dont want to fry the thing from extended use.

gyre · Post by **gyre** » Wed Nov 05, 2008 6:12 pm

DC voltage?

Can you check the output from the supply?
What is supposed to be the source originally?

Dork · Post by **Dork** » Wed Nov 05, 2008 6:59 pm

Toolmaker wrote:Powering a wireless camera 2.4 ghz reciever. The device requires 8V 200ma. The Rat Shack adapter I have is 9V and "up to 800 ma" ac to dc plug into the wall. I was hopin there was a way I could just grab a resistor or something cheap and put it inline on the power cord and heatshrink the works or electrical tape it. The reciever powers up fine with the 9V 800ma and doesnt get too hot but I dont want to fry the thing from extended use.

The voltage regulator plus one resistor I mentioned will do it for a few dollars. Just solder the parts directly to the lead wires and shrink wrap the whole thing. You'll have to see what regulators are available at rat shack and look up the part number on the internet or in a catalogue to see what size resistor to use.

Since the power requirements of that particular device are probably pretty constant the inline resistor looks more appealing - do you have a multimeter to measure the current it's using now?

hsdavis · Post by **hsdavis** » Wed Nov 05, 2008 7:55 pm

I have dozens of transformers. If you are not in a rush for this, I can take a look through the pile and if I have it, I can mail it to you. Let me know if I should look for this.
PM me on this!

Toolmaker · Post by **Toolmaker** » Wed Nov 05, 2008 9:33 pm

Dork wrote:
Toolmaker wrote:Powering a wireless camera 2.4 ghz reciever. The device requires 8V 200ma. The Rat Shack adapter I have is 9V and "up to 800 ma" ac to dc plug into the wall. I was hopin there was a way I could just grab a resistor or something cheap and put it inline on the power cord and heatshrink the works or electrical tape it. The reciever powers up fine with the 9V 800ma and doesnt get too hot but I dont want to fry the thing from extended use.
The voltage regulator plus one resistor I mentioned will do it for a few dollars. Just solder the parts directly to the lead wires and shrink wrap the whole thing. You'll have to see what regulators are available at rat shack and look up the part number on the internet or in a catalogue to see what size resistor to use.

Since the power requirements of that particular device are probably pretty constant the inline resistor looks more appealing - do you have a multimeter to measure the current it's using now?

Looks like thats the way I'll go. I really don't wanna fork over 10 bucks to the vendor for the extra power supply cord. Plus I NEED to start foolin with this sorta thing since I will likely be doing bench work the rest of my days.

No more standing for 12 hours a day at CNCs ever again for me.

skibear · Post by **skibear** » Wed Nov 05, 2008 9:46 pm

two ordinary silicon diodes (eg 1N4005 or 4002 etc) wired in series
with the load should drop the voltage about 1 volt or a bit more.

The voltage regulation won't be great (maybe +/- .2 volts)
then again a rat shack unit likely has lousy regulation anyways.
check if this is a problem.

hth.

hsdavis · Post by **hsdavis** » Thu Nov 06, 2008 6:49 am

I found a 9VDC 200ma transformer if you can use it. I'm no Arthur Einstein, but I think you can use this because the miliamps are correct and the 1 extra volt should not have an effect on it.
Let me know if you want this and I will mail it to you!

Toolmaker · Post by **Toolmaker** » Thu Nov 06, 2008 10:11 am

I decided on making a variable power supply after poking around Instructables. 1) I need the knowledge and exp. 2) I am really stir crazy and need something to do.

Thanks for the help everyone. And I found this free learning site about circuits in case anyone want to bookmark.

http://www.allaboutcircuits.com/