PC PSUs - a handy hint

[powerlord]

Some of you might have read my diy observatory thread earlier in the year where I documented my use of a good quality PC PSU to provide 12v and 5v power to my whole observatory.

6 months in it has all been 100% reliable until about a week ago. In the hope of it being useful to others I'll just explain the issue.

When using a PC PSU for power of lots of low current use things it was recommended in some articles I read to put a bit of a load across both the 12v and 5v lines.

I thought this was a bit overkill, but did it anyway - putting a 10w resistor across the 5v and a 25w resistor across the 12v - these have big heat sinks and I screwed them to my main metal shelving to disapate heat (also gives me a warm shelf for putting stuff)

About a week or two ago my asiairs started to randomly reset them selves. which of course stopped any autorun plans, etc and caused me to lose quite a few nights imaging. I had got a new asi2600 in the meantime and initially though since that was the only thing that had changed, it must have something to do with it - and I swapped it to pull powe from the PSU direct rather than through the asiair.

However last night when it was doing it again, I had a hunch, and felt the power resistors - the 5v one was still fine, but the 12v one was cold.

Removing it showed that it was open circuit.

I've just replaced it with a new one for now, but will probably replace it with a number of power resistors to spread the load across more of them and keep them working longer.

So - turns out a base load IS important - don't skip it. And make sure you chose good quality power resistors and give them a good sink for the heat.

Now all running again and shooting darks.. though not sure how long that will keep up today as fan on asi2600 is already at 86% to keep it at -10 and it's only 9.45 !!

[rl]

Useful tip...thanks. 

I assume the 10 and 25w numbers refer to the maximum capacity of your load resistors. What were the resistances in ohms? If you were running them at their rated 10 and 25 watts the resistances must have been 2.5 ohms and 6 ohms respectively. But these rating often apply with some sort of forced cooling so that the mounting face sits at room temperature which is usually not possible to do....you might have been technically over-running them. 

RL

[powerlord]

yeh, I think the ratings are mince. I had used a 25w 12 ohm resistor - so it's running at 12w - figured a 1 amp load was ok and running it at 1/2 its power rating. but still gets very hot and clearly typical chinese fantasy rating (aka 10000ah batteries, etc).

so - I've just order a few 100w 12 ohm resisistors from amazon and will be replacing it with one of those - much much larger and maybe more realistic size to handle the 12W load.

 

[Dr_Ju_ju]

I use multiple supplies to drive various devices, and I've found that not all supplies require a dummy load, and if it does it, just a small load (0.25 mA) therefore 10-15 K ohms is more than adequate, and doesn't waste energy generating waste heat....