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converted computer psu

nkgamer1990

nkgamer1990

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so im looking to get a computer psu that was converted for use in a scanner
and need to know a few more things before i buy.
Can anyone tell me how safe this is for powering lasers. ive read that computer power supplys that get converted for this reason have some downsides such as current spikes, there unregulated and are easily shortcutted( not entirely sure what that means).
-nick
 





Computer power supplies need a minimum 5 to 10% immediate load to run stable. To get that minimum load is simple, a 25W halogen lamp powering a GOBO eyecandy projector.
 
what exactly is a gobo eyecandy projector. if you were to build a projector would you use a computer psu, if so could you show me a diagram of how youd set it up?
-nick
 
Just put a nice big power resistor on the 3V line to ground, that'll keep it under enough load to keep it stable. Not really sure what you are wanting to buy though, why not just buy a computer PSU and cut the wires & solder them as you need? Theres nothing to using them as a normal PSU. On most computer power supplies, short the green wire to any of the black ones and it'll fire up :)
 
Thanks for the help on this Chris and Things-power suppplies of every type are often a topic that has more questions than answers-and the lack of knowledge can often lead to dead diodes.---hak
 
Doesn't every rail need a minimum load? I use the 3.3V, 12V, and 5V Rails...
 
the 3.3and 5V rails need a minimum load,the +,-12 ans -5 rails are derived from the 5V bus using a DC-DC type converter circuit in most current computer PSU's
 
I nearly killed a PSU without a load, avoid this. The smell of burning and clouds of white smoke are a pretty good indicator of when it's gone wrong. A standard 3.5in hard disk was load enough for me to prevent that. You can get plenty of guides online - and the output voltages and current limits are adjustable too, with a little bit of work and the right guide/chip combination.
 
Computer PSU's have their limitations.. the minimum load is annoying, but often required to make them run stable (or at all). You could load it with some power resistors, but if it goes into a projector project, thats also a lot of extra heat to remove.

I'd opt for ordering some power supplies online that don't have these requirements, and are guaranteed short-circuit proof etc.
 
theres plenty of tuts on the interwebz about how to mod a psu to make a benchtop psu. all i had to do was connect the standby wie to another wire... ive been using the another psu for a benchtop power supply for almost a year now that was modded the same way.
 
On mine I have a 10ohm 10 watt resistor on the mail 5v rail that went to the motherboard. On my PSU if you use that 5v rail that is the only load it needs to start but if you use one of them that went to a Molex or Mini Molex connected then it will not start
 
I must have an older one or something. As far as I can see, it works fine without any load

I've also got one in my projector powering a red and a blue. I just assume the drivers filter out any remaining ripple.
 
i spliced all my "like wires to gether. and the green to all the blacks. it is pretty stable. except i had never used my 3v socket till last week with my first lava driver. as soon as i applied power my psu went dead... luckily my psu resets its self if i unplug it.

michael
 
If you run it without a load, you'll notice the fan in the PSU start up, then go off slowly as the big capacitors charge up. The voltage then floats higher than the capacitors ratings, and thats when you end up with the very bad smelling electronics smoke!

I have a I think 10 ohm 10W resistor on either the 3.3 or 5V rail and it runs OK without a load with just that.

Some PSU's may already have some sort of internal load, that might explain your situation Cyparagon.
 
I'm in the process of converting a FSP 280W power supply.

I will be using two 10K 100W resistors, one on the 5V and the other on the 12V rail.

I'll let you guys know how it goes.
 
Uhm, almost all the 500W ones that i use as spare parts have internal loads, actually ..... when i turn them on connecting the remote (green) to the ground (black), they stay stable also without load .....

Probably the old models still requires an external load, anyway .....

As a crazy suggestion, you can take a 6V lamp from a car parts supplier, and hook it to the PSU on a flexible arm ..... so you have both PSU and work light, if you need it for a lab use :p :D ..... inside a projector / scanner, instead, i think there is already enough current request from the various parts, so you don't need to add any external load .....
 
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