Is on battery UPS output bad for power supply?

[NeoPTLD]

In the instruction manual of most UPS, they tell you to never plug a surge protector into the UPS. Surge protectors have an MOV that absorbs spikes and since UPS output is spikey it could absorb the power from UPS. PC power supplies typically have an MOV inside to absorb surge.

If I remembered correctly MOV is like a filter and it degrades with every abnormality it absorbs. When your computer switch over to UPS power, does it damage the MOV inside the power supply?

 

[Matthias99]

I would think that a line-conditioning UPS would provide *extremely* clean power relative to what you get out of a wall socket in most places in the US. Why do you think UPS output is "spikey", at least when running off of its battery?

 

[OrganizedChaos]

Originally posted by: Matthias99
I would think that a line-conditioning UPS would provide *extremely* clean power relative to what you get out of a wall socket in most places in the US. Why do you think UPS output is "spikey", at least when running off of its battery?

because almost all consumer UPSs have a modified sinewave output.

but anyway i wouldn't worry about it, i don't think the transformers(s) will care and the voltage regulators won't know the difference since it gets rectified anyway.

 

[OrganizedChaos]

http://www.fords-mtm.com/electric%20images/waveforma.jpg

example of a modified sine wave. i wouldn't worry in the least bit, but of your in doubt just check it with a scope, power supplies handle 230V usage just fine.

 

[uart]

The voltage output from a modified sine wave or PWM inverter don't have voltage spikes that will bother the MOV's of a surge protector. They do however have sharp edges that can cause resonant problems with certain types of passive filters included in some surge protectors.

 

[NeoPTLD]

APC's warranty conditions says if you use a "surge protector" in conjunction with their UPS, the connected equipment warranty is null.

 

[Jeff7]

Originally posted by: NeoPTLD
In the instruction manual of most UPS, they tell you to never plug a surge protector into the UPS. Surge protectors have an MOV that absorbs spikes and since UPS output is spikey it could absorb the power from UPS. PC power supplies typically have an MOV inside to absorb surge.

If I remembered correctly MOV is like a filter and it degrades with every abnormality it absorbs. When your computer switch over to UPS power, does it damage the MOV inside the power supply?

Assuming your PC has MOV's in the PSU anyway - not sure if they do or not. They do have a great deal of filtering though; I've only read that certain AC motors might have trouble digesting modified sine wave power, and that's about it.
Plugging a surge protector into a UPS - I think it has something to do with current draw in the event that something in the protector is damaged.

 

[Mark R]

PC PSUs generally do have MOVs in - although they are rather small, and would be destroyed by a single large surge. However, they are essential in protecting the main switching transistors which could otherwise be destroyed by the spike from a fridge switching off on a neighbouring circuit.

A PC PSU uses a simple rectifier and reservoir capacitor circuit as input - this will not behave significantly differently, with sine waves, modified sine waves or even DC input.

I think the concern with plugging a surge protector into a UPS comes from the fact that the surge protector has to absorb the surge by drawing an enormous current. Perhaps, the massive current flow running through the UPS could damage the electronics within it.