mrpackethead
Full time elf
Theres a number of factors to consider, and you'll get some of these from a datasheet.. Of course some manufacturers ( or resellers ) may not provide a datasheet or even worse will provide a misleading one.. Heres a few important ones;
(a) efficiency.. how much of the energy that goes into the power supply (as AC) gets delivered out of the power supply onto the DC side.. This is normally expressed as a percentage.. What goes missing generally is lost as heat.. For example if you have a power supply thats 80% efficient, it would use 125W to supply 100W of DC Voltage.. This can be an issue and you need to think about how your power supplies will loose this heat.. Typically lower voltage DC outputs will result in lower efficiencies.. try to find somethign thats >85% if you can, higher is better.
(b) power factor.. (PF) Power factor is a whole topic of discussion. Try to find something thats at least 90% or higher.. Power factor is a ratio that describes how far the voltage and current lag or lead each other on the AC side of the power supply.. By nature switch mode power supplys will exhibit a inductive load to the ac side, and thus will have a poor PF. The result is that you end up with higher currents flowing than you woudl if the power factor is higher.. so called "good" power supplies will have active Power Factor Correction ( PFC ) built into the front end to compensate, and get the PF back closer to 100%.. "poor" ones often don't. If you start running lots of power supplies this really becomes a big issue...
(c) RFI/Ripple and Noise.. How much noise does the power supply produce on the power supply.. Does it produce lots of RFI? ( radio frequency interference ).. RFI can cause you all sorts of weird and wonderful problems that can be nightmare-ish to solve..
(d) Safety.. Is the power supply manufactured to a safe standard? This probably is the first criteria to consider.. i have seen power supplies that are simply unsafe.. ( the DC side floating at the Mains side! ).. Some of the construction standards of Power Supplies leaves much to be desired, and they are potential death traps.. If you dont' know how to do a "tag and test" type test on your gear, ( its pretty simple, but i'm not teaching it here cause i dont' want the death of your children on my shoulders) then find someone who does, and check it out..
Have fun..(safely)
(a) efficiency.. how much of the energy that goes into the power supply (as AC) gets delivered out of the power supply onto the DC side.. This is normally expressed as a percentage.. What goes missing generally is lost as heat.. For example if you have a power supply thats 80% efficient, it would use 125W to supply 100W of DC Voltage.. This can be an issue and you need to think about how your power supplies will loose this heat.. Typically lower voltage DC outputs will result in lower efficiencies.. try to find somethign thats >85% if you can, higher is better.
(b) power factor.. (PF) Power factor is a whole topic of discussion. Try to find something thats at least 90% or higher.. Power factor is a ratio that describes how far the voltage and current lag or lead each other on the AC side of the power supply.. By nature switch mode power supplys will exhibit a inductive load to the ac side, and thus will have a poor PF. The result is that you end up with higher currents flowing than you woudl if the power factor is higher.. so called "good" power supplies will have active Power Factor Correction ( PFC ) built into the front end to compensate, and get the PF back closer to 100%.. "poor" ones often don't. If you start running lots of power supplies this really becomes a big issue...
(c) RFI/Ripple and Noise.. How much noise does the power supply produce on the power supply.. Does it produce lots of RFI? ( radio frequency interference ).. RFI can cause you all sorts of weird and wonderful problems that can be nightmare-ish to solve..
(d) Safety.. Is the power supply manufactured to a safe standard? This probably is the first criteria to consider.. i have seen power supplies that are simply unsafe.. ( the DC side floating at the Mains side! ).. Some of the construction standards of Power Supplies leaves much to be desired, and they are potential death traps.. If you dont' know how to do a "tag and test" type test on your gear, ( its pretty simple, but i'm not teaching it here cause i dont' want the death of your children on my shoulders) then find someone who does, and check it out..
Have fun..(safely)
