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Drodriguez
10-22-2008, 02:58 PM
Hey guys- I had a question while setting up a grinch and thought that someone might be able to help me.

I'm going to power the grinch with an old computer power supply. However, I noticed that on the label on the case, it said
(RED) +5v, 25 amps
(Yellow) +12v, 10 amps
(White) -5v, .5 amps
(Blue) -12v, .5 amps
and (Black) Ground.

Why is there a -5 in addition to the +5? Is there a difference between the two? Which one should I use to power a GRINCH?

* Also, when I measure between +5 and Ground, I get something like 6.3 volts. Is that ok for a Grinch? My multimeter gives me 5v when I measure between -5 and ground.

toodle_pipsky
10-22-2008, 05:38 PM
The wiki has the answer to the question "is that ok for the Grinch" - http://www.doityourselfchristmas.com/wiki/index.php?title=The_GRINCH_Controller it will depend on what ICs you are using (half way down the page). 6.3 is a little high, you may need to install a diode to step down the power a bit. There's a thread around here with that info, I'll try and find it.

As for the + and - question, no idea sorry! You just need the red one, which I think is +. Someone smarter than me probably knows the answer to the + and - question.

rca
10-22-2008, 05:51 PM
You want the +5 connection. Also, 6.3 looks like it is high, but you are measuring it without any load on the power supply. Normally if you put a load on it, like powering your circuit it will drop closer to the specified 5V.

Just something to consider.

Ron

Drodriguez
10-22-2008, 07:35 PM
6.3 is a little high, you may need to install a diode to step down the power a bit.

So can I just use a standard resistor to step it down? I'd rather not blow any more chips.

toodle_pipsky
10-22-2008, 07:58 PM
You need a IN4004 diode - attached is a stunning diagram I did (thank you MS Paint). The yellow box is meant to represent the plug you plug into your Grinch.

Just to clarify - you need to put the diode in series with the red wire, with the grey strip pointing to the plug.

Add 1 diode and see what your power drops to. Then and compare it with what your maximum requirements are for the ICs you have.

daviddth
10-23-2008, 07:44 AM
So can I just use a standard resistor to step it down? I'd rather not blow any more chips.


In simple terms, NO!

In more detailed terms - NO!

A resistor will not drop voltage until current starts to flow. With the grinch sitting there with no outputs on the current draw will only be 10 to 20mA (Less if you dont have any LED for power installed), so the voltage drop will be SFA. With all the outputs turned on might give 1 to 2A of load giving a huge voltage drop on the resistor.

A diode will give a 0.6V (Give or take) voltage drop from 0A through to its max load. An IN4001 is good for 1A, 4004 is 4A and 4007 is 7A - keep half a dozen IN4004's handy for little things like this.

Also consider getting a 10 ohm 5W resistor and put it across the ground to 5V supply - that will draw roughly 0.5A and should be enough to load the supply up enough to give a good clean voltage out of the supply.

mark
10-23-2008, 04:32 PM
if you connect the red and white wires together, do you go back in time?

rstehle
10-23-2008, 05:04 PM
if you connect the red and white wires together, do you go back in time?

Only if you are traveling 88 mph............ :cool:

daviddth
10-24-2008, 08:23 PM
if you connect the red and white wires together, do you go back in time?

No but if you connect the Red with the White and the Blue your whole economy crashes, hundreds of thousands lose their jobs, and the lights just fade to black.

Now the question is.... OK who did it? :)

Aurbo99
10-25-2008, 01:49 PM
No but if you connect the Red with the White and the Blue your whole economy crashes, hundreds of thousands lose their jobs, and the lights just fade to black.

Now the question is.... OK who did it? :)

All the more reason to make sure OUR lights stay on. It's the big fish that messed up the ecomony in pursuit of greed.

It's the little fish that need to see there's still light.

Let there be lights!

dnesci
10-27-2008, 06:49 PM
Hey guys- I had a question while setting up a grinch and thought that someone might be able to help me.


Why is there a -5 in addition to the +5? Is there a difference between the two? Which one should I use to power a GRINCH?

* Also, when I measure between +5 and Ground, I get something like 6.3 volts. Is that ok for a Grinch? My multimeter gives me 5v when I measure between -5 and ground.

First of all the -5 volts are used for some chips in the computer. For the Grinch it is not needed.

With that said, 6.3 volts is not right. If you put a load on the power supply (such as a computer hard drive) and it stays at 6.3 volts, do not use it. There may be a problem with the power supply. It should read close to 5 volts with a load.

P. Short
10-29-2008, 07:20 PM
You might need more of a load than just a hard-drive to meet the minimum load requirements. I agree with everything else that dnesci wrote.

Drodriguez
11-05-2008, 10:32 AM
I put in a IN4004 diode and it works great.
Thanks!