UPS: Compensating for a high input voltage.

[Mark Wyatt]

> 
> Message: 5
> Date: Wed, 13 Aug 2008 10:57:53 +0100
> From: Paul M <paul-clug at mansfield.co.uk>
> Subject: UPS: Compensating for a high input voltage.
> To: Cambridge LUG <clug at cambridge-lug.org>
> Message-ID: <48A2B021.3060006 at mansfield.co.uk>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
> 
> We seem to get a significant number of these warning messages from our
> UPS, an APC SUA5000 unit - appended.
> 
> I am wondering if this is a problem specific to the Science Park here in
> Cambridge or just us - is anyone else seeing mains voltage getting very
> high?
> 
> I am worried that there's a risk of damage to our systems. Here's a
> snapshot graph of power measurements; red line is output voltage, green
> is mains.
> http://www.mansfield.co.uk/misc/ups01.png
> 
> I reckon that what's happening is the power demand from the science park
> varies hugely and affects the grid's ability to regulate voltage, so
> after 9pm-ish, the mains voltage rises above the UPS's warning margin.
> According to my cheapo electricity meter we're currently seeing 236V,
> which is above the norm of 230V
> 
> regards
> Paul
> 
> -------- Original Message --------
> Subject: UPS: Compensating for a high input voltage.
> Date: Tue, 12 Aug 2008 21:24:12 GMT
> From: **@**
> To: **@**
> 
> Name     : ups01.***.***
> Location : **************
> Contact  : **@**
> http://ups01.***.***
> http://##.##.##.##
> 
> Serial # : ##########
> Device Ser #: ###########
> Date: 08/12/2008
> Time: 21:24:10
> Code: 0x010D
> 
> Warning - UPS: Compensating for a high input voltage.
> 
> ------------------------------
> 
> Message: 6
> Date: Wed, 13 Aug 2008 11:00:11 +0100
> From: Paul M <paul-clug at mansfield.co.uk>
> Subject: Re: UPS: Compensating for a high input voltage.
> To: Cambridge LUG <clug at cambridge-lug.org>
> Message-ID: <48A2B0AB.1060705 at mansfield.co.uk>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
> 
> p.s. times on the graph are GMT, so problem began at ~22:15 ended
> ~~06:45 BST
> 
> 
> 
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> 
> End of CLUG Digest, Vol 60, Issue 8
> ***********************************

>


This shouldn't be a problem, but it is slightly concerning.

The stated tolerance for the UK is 230 + 10% -6%, so a supply
up to 252 volts is allowable and anything that meets UK specs
should be happy with that (some of Europe is +6, -10% but 
the UK is not the only European Country that is 230 +10%).

Of course, for an 'installation' the equipment manufacturer
cannot test the cooling of the installation and if someone,
rather optimistically, has sized the cooling based on an exact 
230 V input, there could well be an issue. And it is well known 
that some cheap power supplies don't really meet their 
specifications, so that might be a concern, too, if you have 
equipment that doesn't have a UPS. While it is more usual for 
this to show up at high-ish loads and low input voltages, who 
knows? If someone 'cheats' by failing to honour one, fairly 
obvious, specification, who knows how seriously they take the 
others?

(But, on the other hand, what are you doing buying cheap power 
supplies, assuming that you do?) Of course, at this point I'd be
feeling more comfortable if my equipment budget had been spent 
with the 'big boys' like HP and Sun rather than 'no name' 
suppliers.

There might be some mileage in discussing this with your 
electricity supplier, but they may well just say 'Its in spec'
and you would probably respond 'It ought to be better and it 
might be a sign of an underlying problem'. (I agree with your 
analysis that it looks load dependant - possibly the demand 
from the Science Park has grown since the provisioning was 
sized [I don't know how re-sizing happens now that you could 
have several different agencies billing Sci Park orgs - in 
the old days at least one supplier had all the info]
but more likely there is a low level fault on one of the 
lines).

But if you can show them graphs generated overall several days 
and convince them that there is a pattern they should take you 
seriously - they probably get lots of seriously weird calls from
people who have mad conspiracy theories about the electricity 
supply and if they think you are one of those, you'll never get 
anything that resembles help. They might ask you whether any of 
your measuring equipment has a current cal cert and I'm guessing 
that it doesn't, but if the UPS and DVM agree it doesn't sound 
likely that both have the same fault.

If what is concerning you is the prescence of an error message,
be aware that you can probably reprogram the thresholds, as 
pretty much everything is re-programmable in an APC UPS, 
assuming that you are using the APC driver. (A slight caution is 
appropriate here: Most APCs don't work optimally out of the box
because the various limits aren't optimally set up - there are
limits on both run time and percentage charge remaining and if you
have a low or low-ish load, thinking that this will give you a 
long run time, the run time limit kicks in and shuts you down 
while you still have a large percentage of capacity left; if 
you are in any doubt, you would need to test the behaviour, but 
many people short cut this stage.)

But that won't alter the voltages - it only helps by minimising
'junk' warnings so that you might take 'real' warnings seriously.

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