Re: Info on testing vintage power supplies
On 9/2/19 9:56 AM, Tony Duell wrote: On Mon, Sep 2, 2019 at 5:35 PM Alan Perry via cctech wrote: Can anyone here provide a pointer to info on testing vintage power supplies? Search results on the web may eventually lead to the kind of info that I am looking for, but I have to get through too many pages of modern PC power supplies first. Specifically, I will be testing the power supplies in my Sun 3/260, which has 24V, 12V and 5V. I am wondering things like what is suitable loads and do I need to put a load on all three or can I test them one at a time and what I haven't thought of with regards to testing them. With most classic computer switch mode PSUs (which the one in a Sun 3/260 is), you need to load the main output. The other outputs don't _need_ loads, but it doesn't hurt to have them). For 99% of classic computer supples (and true for the Sun 3/260) the main output is the +5V one. I'd try to draw perhaps 5A from that. So a 6V car bulb of 30-odd watts. A 6V car headlamp bulb, for example. It's not critical Have that connected between the +5V output and ground (the 0V rail of the machine, not necessarily mains ground) for all tests on the supply. In other words, connect up the bulb, power up (the bulb should light), then measure the voltage between each output of the supply and ground. The power supplies that I had been looking at were the two in the SMD disk cabinet. Still haven't tried powering them up. Today I opened the 3/260 cabinet. There was a nest made by some rodent on top of its power supply. It was composed of shredded material that went down into the power supply through the holes in its cover. From the surface rust, it looks like there was moisture in the nest. What should I do to the power supply before trying to power it up? alan
Re: Info on testing vintage power supplies
On 2019-Sep-02, at 9:35 AM, Alan Perry via cctech wrote: > Can anyone here provide a pointer to info on testing vintage power supplies? > Search results on the web may eventually lead to the kind of info that I am > looking for, but I have to get through too many pages of modern PC power > supplies first. > > Specifically, I will be testing the power supplies in my Sun 3/260, which has > 24V, 12V and 5V. I am wondering things like what is suitable loads and do I > need to put a load on all three or can I test them one at a time and what I > haven't thought of with regards to testing them. Regarding incandescent bulbs, 12V bulbs can be used on the +5. They tend to be cheaper and more readily available than 6V bulbs. Dual-filament tail-light-with-brake-light bulbs such as the 1034 and 1157 are common and inexpensive. The dual filaments allow for some load variation, the tail-light filament is lower current, the brake filament higher. Parallel a couple such bulbs (and the filaments) for more current. You don't have to buy sockets for them, you can solder wires to the base and contacts. Note the current draw is not a straight linear relationship with reduced voltage. At lower voltage they'll draw something more than the linearly-reduced current level. E.g. for the 1034: @ 5V@ 12V - - tail0.35A 0.6A brake 1.2A2.4A I don't know that you'll find any sort of generalised reference for your request. While some general rules may cover many models, the only way to be comprehensive over such a topic is to understand the principles and then look at the specific design of the supply one is dealing with. For switching supplies, usually only one of the outputs is actually regulated and the others will 'follow' in regulation (designed for a low enough source-impedance-to-load-impedance ratio that they'll be in range if the controlled output is in range). Sometimes lesser-current outputs actually have a linear regulator between the switching transformer and the output.
Re: Info on testing vintage power supplies
On Mon, Sep 2, 2019 at 5:35 PM Alan Perry via cctech wrote: > > > Can anyone here provide a pointer to info on testing vintage power > supplies? Search results on the web may eventually lead to the kind of > info that I am looking for, but I have to get through too many pages of > modern PC power supplies first. > > Specifically, I will be testing the power supplies in my Sun 3/260, > which has 24V, 12V and 5V. I am wondering things like what is suitable > loads and do I need to put a load on all three or can I test them one at > a time and what I haven't thought of with regards to testing them. With most classic computer switch mode PSUs (which the one in a Sun 3/260 is), you need to load the main output. The other outputs don't _need_ loads, but it doesn't hurt to have them). For 99% of classic computer supples (and true for the Sun 3/260) the main output is the +5V one. I'd try to draw perhaps 5A from that. So a 6V car bulb of 30-odd watts. A 6V car headlamp bulb, for example. It's not critical Have that connected between the +5V output and ground (the 0V rail of the machine, not necessarily mains ground) for all tests on the supply. In other words, connect up the bulb, power up (the bulb should light), then measure the voltage between each output of the supply and ground. -tony
Info on testing vintage power supplies
Can anyone here provide a pointer to info on testing vintage power supplies? Search results on the web may eventually lead to the kind of info that I am looking for, but I have to get through too many pages of modern PC power supplies first. Specifically, I will be testing the power supplies in my Sun 3/260, which has 24V, 12V and 5V. I am wondering things like what is suitable loads and do I need to put a load on all three or can I test them one at a time and what I haven't thought of with regards to testing them. alan
