UPS

[#1]

OK, now I have just had catastrophic failure. The whole thing was working perfectly running everything for about half an hour when the UPS cut out suddenly with quite a bit of smoke!
After looking inside I seen that the transformer has melted. It was obviously not designed to run for as long as I was making it run with the extra battery. It would probably cost me as much to replace this transformer as it did to buy the UPS so I am back to the drawing board with this one.
I think I will build my own UPS with a leisure battery, a 600Watt inverter like I have in my car and a double throw relay to automatically switch to the inverter when the mains fails.

[#2]

Now you have had your fun;
ebay.co.uk PowerWare 5125.
ebay.co.uk PowerWare 5125 with extra battery pack.
We install these on our larger systems (without the battery pack).
If you do go for your own external battery stick with Sealed Lead Acid, and it has to be 48V.
Single replacement batteries can be picked up of the internet for about £12, but it does use 4!!!
Chilly

[#3]

Thats a shame it packed up mate. I was looking forward to hearing a success story!
Unfortunately it looks like the UPS couldn't handle the amount of hardware you were using (I did say not to try powering your entire network like this!).
What about breaking it all down and using multiple UPS's to share the load?
I know you'd prefer one central power connection for everything but it doesn't look like it will be very successful (though I do understand the benefits of it all being connected to one central connection).
Good luck making your own customised version but I reckon the penguin might be suggesting a good idea so check it out. Also if you do make your own, the relay switching time could be an issue - Have you timed your hardware to see what the maximum powerbreak time is?

[#4]

Quote

OK, now I have just had catastrophic failure. The whole thing was working perfectly running everything for about half an hour when the UPS cut out suddenly with quite a bit of smoke!

I almost had one of those; during testing one of my UPS's switched over to battery power and shortly after started smoking. I managed to turn it off and get it replaced but I hate to imagine what might have happened if there was a power failure at night or when I was out.

[#5]

Generally speaking it's not a good idea to connect lead acid batteries in parallel. No two batteries have the same internal resistance so the battery with the lower resistance will take most of the available charge. Also if the system is without charging power, the lower resistance battery will take power from the other.
I've thought about using bigger batteries for my UPS and if I did it I'd wire a bigger battery outside the UPS and not use any internal ones.
Just my two pennorth

[#6]

Another good point.
I wonder how the PowerWare's with the external Battery's cope with this.
It would be worth checking before trying to hack your own extra battery pack across the connections at the back.
Chilly

[#7]

The resistance of each battery does not really affect it. The voltage is the main factor. If one battery is about say 12.5 and the other about 12.8 then the higher voltage battery will charge the lower one with a very small current until both batteries are at an equal voltage. Not really a problem.

[#8]

But what happens if (say) one battery developed a short circuit cell? Then there would be a high current flow from the good battery to the faulty one. I still say it's undesirable to connect lead acid batteries in parallel.

[#9]

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I still say it's undesirable to connect lead acid batteries in parallel.

I have worked on various electronic projects over recent years involving lead acid batteries and they usually always involve connecting multiple batteries in parallel. As a previous poster said the differences will be minor and only during the initial connection; the batteries can handle large discharge and charging currents so it isn't a problem.

Quote

But what happens if (say) one battery developed a short circuit cell?

That's one of many what if's that will probably never happen so unless its an cryitical aplication its probably not wirth worrying about.

[#10]

Instead of messing about buying more batteries for the UPS and extend the period of time until the comps shut down, go out and buy a small genny.
That way the UPS would give a short period for you to get the genny started then while it is running it recharges the UPS and if  large enough you could boil the kettle etc while the mains power is out

[#11]

Devon nice thought but you've missed something:
What happens if Sean is out when the power goes?
How is he supposed to start a generator from a remote location?
Not exactly going to work is it!

[#12]

What if its a major power outage of a day or so ? (Floods over the lask couple of months have proven this).
Even with larger batteries the UPS can only last for so long.
But you can get genny's with a remote start fairly cheaply nowadays. This could be configured to start the genny automatically within seconds of the power going off.

[#13]

Quote from: mgsmith

But what happens if (say) one battery developed a short circuit cell? Then there would be a high current flow from the good battery to the faulty one. I still say it's undesirable to connect lead acid batteries in parallel.

Each battery should be independently fused.
And even is connecting batteries in series has issue such as reverse charging should one cell fail.
James rules; Same Voltage, Age and Capacity. Sound good to me.
Looking on ebay, large UPS are going cheap. And if you are not fussy about the brand of replacement battery, are not too bad to maintain.
The company that I work more often that not replaces, the whole UPS rather than just the battery. As with discount new UPS's are not that much more expensive than the manufactures official replacement battery.
Which leave us with a UPS that for a 1/10 of the cost of the manufactures battery. We can replace the battery, with the same brand and model of SLA battery. But our quality system do not allow it.
Chilly