12v supply split to 12v/5v molex output - loss of power, any ideas?

Hi,
Okay not the most common question you’re going to see on a ROOL board, but I’m hoping someone out there may have the answer.

I’m attempting to run a small, low powered, selection of equipment off one 12V power supply, the supply in question is a 12v 10A output, because some of the equipment uses molex connectors I’ve split the output into two lines, one that’s 12v and the other gets taken down to 5v, then they’re wired into a molex connector.

Using a multimeter when testing the output of each line they correctly give the expected amounts 12.x and 5.x volts (they actually read as good as a high end computer PSU I borrowed for testing with).

When I plug in any equipment however there seems to be a distinct lack of power (nothing I plug in can turn on) and I wondered if anyone had any clues?

I did wonder whether by splitting the 12v into two lines of power, when something then draws power it drops the lines well under the power I’m after, but for all I know (being a tad clueless about electrical things) a power adapter should give a constant output that shouldn’t drop.

So, has anyone got any ideas?

Thanks,
Chief :)

I’m attempting to run a small, low powered, selection of equipment off one 12V power supply, the supply in question is a 12v 10A output, because some of the equipment uses molex connectors I’ve split the output into two lines, one that’s 12v and the other gets taken down to 5v, then they’re wired into a molex connector.

You didn’t say how the one line “gets taken down to 5V” but if it’s voltage drop across a resistor you don’t have any current to speak of.

I’ve not done any of this stuff in years (most of the kit around at work has switched mode beasties)
There are plenty of simple voltage reg circuits around and even a low current voltage reg three pin device providing the reference voltage for an emitter-follower with a beefy transistor to carry the current will do for the stuff you are doing.
Start at one of the wikipedia articles:

http://en.wikipedia.org/wiki/Linear_regulator

Active regulators
http://en.wikipedia.org/wiki/Voltage_regulator#Active regulators

Hi,
Thanks for the reply, I hunted through my emails for the order, and yes it is a resistor in the cable (I bought the cable from a website long ago).
I didn’t realise that it was going to cut the current down as the cable is originally to allow people to plug in LCD screens to car/motorbike batteries (I presume for stuff like reversing cameras) and I figured LCD panels would require a fair whack of amps.
I suppose I should have checked the current output as well as the voltage when I had the multimeter handy.
Thanks for the links, I’ll have to look into those, hopefully I can work something out.

Chief :)

Okay, so having looked a bit further into it I looked on ebay to see if I got any results, and they came back with the following:

http://www.ebay.co.uk/itm/DC-DC-LM2596-Converter-Buck-Adjustable-Step-Down-Regulator-Power-Module-1-2-35V-/370624565910?pt=UK_BOI_Electrical_Test_Measurement_Equipment_ET&hash=item564af21296

http://www.ebay.co.uk/itm/DC-DC-Converter-Regulator-12V-Stepdown-to-5V-3A-15W-Car-Power-Supply-Module-/271038005969?pt=UK_BOI_Electrical_Test_Measurement_Equipment_ET&hash=item3f1b1fc2d1

http://www.ebay.co.uk/itm/Hobbywing-3A-UBEC-5V-6V-max-5A-Lowest-RF-Noise-BEC-S-UK-SELLER-005-/221155073673?pt=UK_ToysGames_RadioControlled_JN&hash=item337dde9e89

I decided to just check if these were definitely the type of things you meant, at least they all provide a a 3A output rating which should cover the equipment.

Thanks,
Chief. :)