Got my Keypower 250 watt ATX PS. - Page 2

SuperAJ · 02-12-2002, 07:31 PM

Has anyone successfully wired a Keypower DC-DC psu connecting the (-) and (g) to the ground?

Why would they have a (g) and (-) if you could just connect them both to ground? There's obviously some purpose behind having 3 connectors. I've set it up, it works, and that's all the proof I've heard so far on the forum.

LESLIEx317537 · 02-12-2002, 08:12 PM

I just tested the PS with my tester.

The (-) doesn't connect to the PS chassis or black leads on the molex connectors.
The (G) connects to the PS chassis and the black leads on the molex connectors.

I hope that helps diagnose what we Keypower owners should do. The unit won't be going into my car until I get everything running 100% in my room first on my regular ATX spare supply.

lifeboat · 02-13-2002, 01:40 AM

Good info, LW. Confuses my as to why it has been working for me without the G connected though. But it may explain why my LCD power lead from the PSU wasn't powering the display properly. I'm just going to make a bridge wire between G and -, the - is connected to chassis ground anyway, so it's all the same.

LESLIEx317537 · 02-13-2002, 02:00 PM

I'm going to go outside and place the meter on my trunk where I'm going to ground the cable and see if it completes a circuit to the (-) terminal on the battery.
If it does complete a ground and has very little resistance, I don't see any use in runing a (-) cable to the battery.
I just got my meter like 2 weeks ago too. I can't believe I've been doing soldering and elctrical work for so long without one.

jboy · 02-13-2002, 03:15 PM

Even a small amount of resistance can cause a bad voltage drop but it's probably not the car body at fault unless you drive a bondo buggy
"ohms law"
V/I=R
eg. a 12v supply draws 4 amps then it is a 3ohm load
any resistance between the battery and supply makes a voltage divider
R1/Rload=Vdrop/Vsupply (R1 is the car body or wire)
eg. 0.25ohm resistance in the car / the 3ohm load x 12v gives a 0.8v drop and 11.2v to the supply

make sure the battery connections are good and use a wire of atleast the same gage as you pos wire to connect the batery neg to the body of the car

LESLIEx317537 · 02-13-2002, 04:45 PM

Yes, but that amount of a voltage drop wouldn't affect the performance of my Keypower or Stereo amp right? The Keypower is meant to take +/-12 volts and regulate it.

So even if it was running on 10 volts it would still power my rig right?

Even so if Ohms law comes into play it helps me out because I recall that car battery usually puts out around 13.8 volts DC and after some resistance through my bondo buggy it should come out around 12 volts which is nice.

jboy · 02-13-2002, 05:12 PM

The problems may happen when you start the car w/ the carputer on the voltage may sag below the keypower rating of 9v minimum

mikeinsanmarcos · 02-15-2002, 10:52 AM

Ok, One thing I think we are missing here is that these power supplies are most likely designed for land based applications (ie: remote telecommunication stations ect...) and in those applications, a physical case ground is always required on any metalic casing products to protect the product and anyone who may be in contact with the product against possible shorts to the case of ac or lightning strikes (this is the same as the ground pin on any metalic cased home appliances). in this situation, the battery power negative might not be at the same potential as the physical earth ground and that is why they have separate terminals for earth ground and negative!