[GTALUG] mysterious restarts

[Alvin Starr]

On 06/14/2016 10:24 PM, Bob Jonkman via talk wrote:
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> Alvin Starr wrote:
>> A lot of UPSs switch from the mains to battery once the power drops
>> and that delay can be enough to cause some power supplies to lose
>> enough power to fail
> If that happens then your UPS is broken. The whole point of a UPS is
> to supply *uninterruptable* power. Even the simplest pass-through
> UPSes I know about can switch from line to battery in the space of a
> single waveform (ie. within 1/60th of a second). Not much point in
> having a UPS if it makes all your equipment reboot when the power goes
> out.
>
>
The answer "your UPS is broken" is a bit simplistic.

What I had is what you get from buying an inexpensive APC UPS and very 
heavily loaded server with a badly designed power supply.

I stole this from http://www.mpoweruk.com/ups.htm.

Off Line or Standby UPS
These are simple inexpensive systems providing only basic protection. In 
normal situations the UPS passes the mains power directly to the load. 
The mains power provides a single DC line which keeps the battery 
charged. When the UPS detects a voltage too low, it turns on the 
inverter to power the load from the battery. The system is relatively 
slow (longer than 4 ms) and the delay between mains power loss and 
inverter startup can be long enough to disrupt the operation of some 
sensitive loads. This technology does not normally provide full time 
power conditioning but it may use a simple filter to clip spikes and 
electrical noise.

On Line or No Break UPS
These are designed to provide a zero transfer time, with better voltage 
and frequency regulation than that can be achieved by off line and line 
interactive UPS. In on line systems the mains power is used to provide 
two DC power lines which feed both the charger and the inverter which is 
permanently turned on providing the AC power to the application. When 
the mains fails, the inverter instantaneously draws its DC supply from 
the battery instead of the mains.
The method by which the AC load is permanently supplied by the system 
inverter and not the mains is called "double conversion" since the 
charger provides the AC-DC conversion and the inverter converts the DC 
back to AC again.
On line systems typically provide full power conditioning, protecting 
the load from all forms of power disturbances, including brownouts, 
blackout, transient surges or sags. In the event of a mains power 
failure, there is no delay or transfer time to backup power. These 
systems are however more costly and have both higher power consumption, 
and higher heat generation.

Line Interactive UPS
These systems contain an off-line inverter but also use a transformer to 
supply to the load. In the event of a mains failure the inverter is 
started and switched to the transformer to provide the output. The 
transformer is used to provide line conditioning however it also 
maintains output on its secondary briefly when a total outage occurs 
increasing the hold up time of the UPS. This results in a break in the 
output of a few milliseconds or less and is thus faster than a simple 
off line UPS.


Also take a look at: 
http://www.repeater-builder.com/backup-power/ups-test.html

It provides a good look at what is actually going on when your UPS from 
CanadaComputers,NCIX,BestBuy... switches.
You will notice that the provided voltage lags a bit and depending on 
the timing you could lose up to a whole cycle.
This was also a test with a clean line drop.
In the case where the peak voltage drops before the power fails 
completely then you have a more complex set of problems.
I remember reading the specs of one UPS that would kick in if the input 
voltage dropped below 90V.
90V may be too low for some equipment and will cause power supplies to 
have even lower hold times.

This is why you need to test your UPS and equipment configuration from 
time to time and buy online UPS's when ever possible.


-- 
Alvin Starr                   ||   voice: (905)513-7688
Netvel Inc.                   ||   Cell:  (416)806-0133
alvin at netvel.net              ||

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