power suply problems

**jermaine** · 02-10-2007, 02:49 PM

He guys,maybe you can help

I have now an ebox carpc,it came with an AC adapter wich says "output 5v 4 ampere"

looking for a suitable dc pwersuply for in the car,I finded a powersuply to power up the playstation 1 in the car,it is an 7,5 volt 3 ampere.

I hooked up but fried my laptop hardisk.

So I putted some 6ampere diodes on the + cable and so I could pull down the voltage to 5 volt,but hooking up now,the ebox wil not start up,looks like not enough ampere.
But they are simple dioded,I used 7 diodes to get the voltage down.

any ideas what the problem is?????

greetzzzz guys

**bbalazs** · 02-10-2007, 03:03 PM

I think you need a stepdown DC-DC converter.
It is quite easy to build one, eg. LM2679 needs few external components.
You can use yor car voltage (regardless ignition, engine stops or runs) as a source. That converter chip does its part.

The simpliest method is to buy 2-3 7805 for 3A and wire them parallel, but it will produce anormous heat, so I do not recomend it, unless you are living in cold climate and can use as a heater, too

The main problem is (also true for your diode-method) that you have to 'dissipate' the excess voltage at the same ampere, and it means heat.

**jermaine** · 02-10-2007, 03:37 PM

Oke,but what I don't understand is why the pc doesn't boot in the car.

I have 5 volt and the diodes are not putting the ampere down ( I think)

anymore help???

**bbalazs** · 02-10-2007, 04:00 PM

As the label said that psone adapter is able to produce 7.5V 3A
Your pc needs 5V 4A
One ampere is missing...

**evandude** · 02-10-2007, 04:49 PM

Using series diodes is NOT an acceptable way to drop a regulated voltage at high current. Diode forward voltage varies with current so the voltage your PC sees is not going to be constant as the current draw changes.

Not to mention, even if diodes WERE a good solution here, if you put 7 diodes in series on the + rail as you seem to be saying, that's a combined forward voltage drop of probably 5v, but could easily be 7v or more depending on the diodes. If you're starting with 7.5v and dropping 5-7v, you'd end up with an output of less than 2.5v, not even close to the 5v you need.

Find yourself a proper regulator, because what you've done so far is going down the wrong path.

**jermaine** · 02-11-2007, 03:33 AM

oke guys,thanx for the help.

I have done what an electronicstore vendor said to me.

If I don't use the diodes,the ebox powers up,killing my harddisk.(so,the powersuply gives enough ampere and too much volts)

Using the diodes I get 5 volt on the +line,but I dont know how much ampere.

Does somebody knows a powersuply with those specifications?

Input: car (9-16 volt) output 5volt 4 amps

**jermaine** · 02-12-2007, 02:51 AM

well guys,Maybe I have the solution
I had a m2-atx somewhere and I hooked the black and purple cable to my ebox
(purple is the only one with 5 volt constant) and the ebox started up.
But does somebody knows if there can be problems doing this so?

greetzzzz

**ihzy** · 02-16-2007, 02:33 AM

I don't know how M2-ATX designed,but in theory,the +5VSB could only provide 2Amp or less,connect to the +5V is recommended.

However,M2-ATX might be a expensive solution for your ebox.

**Bizarro** · 02-16-2007, 03:51 PM

CAUTION!!! If you are not sure of the voltage / amperage required by an electronic item, don't hook it up till you KNOW what you are doing or you will ruin it.