What is an acceptable transfer time for a UPS?

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Red Squirrel

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I guess this could go under power supplies but I'm thinking it may fit here as UPSes are usually used for network/server equipment so I figure most of you here will be familiar with them.

So my question is, what is an acceptable time to switch from AC to inverter for typical equipment?

An APC Unit will transfer in about 8-10ms according to their site. Some models less.

I was looking at this device here:

http://www.xantrex.com/power-products/inverter-chargers/freedom-458.aspx

Which is a 3000w inverter-charger, which is basically the heart of a UPS. It will handle big batteries and is designed for it.

According to a manual on that site it has a transfer time of 26ms-40ms. Would this actually work for server equipment? Or is that too long?

I'm debating on maybe getting one and building a decent battery bank and use that as my UPS for my servers and other circuits around the house.
 
No idea, but I'm going to guess that would be too much. Otherwise, I think commercial UPS suppliers would have that kind of delay also?

If I'm wrong, cool for you. If I'm right, cool for me.

Care to explain why you consider this an option? Is it the massive bulk of power it can move?
 
Transfer time largely depends on the equipment attached. The data you're looking for is hold time. This power supply http://www.pcpower.com/products/description/Silencer_Mk_II_950W/index.html
has a hold time of 20ms.

Not quite enough for that inverter you're looking at.

But more importantly, the inverters don't always produce clean enough power for your PC. I have a 800 watt inverter that produces 120volts from my car. But no UPS will run off it because the wave produced isn't close enough to a real sine wave as you get from utility power.
 
Hmm that's what I kinda figured.

What about if a proper UPS is attached to the devices that need faster transfer, or would that cause lot of issues?

The idea is I'd like to possibly set one of these bad boys up some day and have it power a couple house circuits like lights and what not, possibly the TV/HTPC, and the servers. I would have it power a sub panel then there would be a couple 15 amp circuits that come off that panel, one would go to the server room.

This one supposedly creates true sine, but I'd have to research that further.
 
Why not just buy a ups, with external batteries ?

A friend here has a apc 1500 like mine and uses external batteries, much better and safer idea, instead of inventing the wheel :)



How much uptime are you looking for ? how much equipment you have to keep up ? Whats the total draw of all the equipment ?
 
The problem with the renewable-energy oriented gear is that it's designed to power basic loads like lighting, appliances, and (very) light HVAC.

Modified sine wave tends to be pretty nasty stuff - loaded with harmonics. If you really want to roll a custom UPS solution, it would probably be best to just buy all 48VDC telecom gear and assemble a battery bank to power that. That way, you don't have to deal with switchover time at all, and since you don't need an inverter, that's one less component to buy.
 
Actually I was thinking of an "online" UPS solution as well but I'd imagine that equipment is hard to find and if I do find it it will cost an arm and a leg. But it would be the best bet.

My idea is I want to be able to buy some big ass lead acid batteries and build my own bank, instead of buying the small pricy UPS batteries. I can get a 100ah battery for maybe 100-200 bucks as opposed to a 6ah battery for close to 100 bucks. A $1000 battery bank would probably give me a good day or so of run time. Would be cool to be able to ride through long outages and still be able to watch TV or go on my computer. :) Now I know you can use your own batteries on an APC, but I just have trouble trusting that as it's not really an approved way. My main fear is how the charger and the runtime "calculator" will handle that.
 
Maybe our idea of a long outage is different but for something like this I'd rather get an LP generator and be done with it.
 
Yes, you can use a inverter for a UPS. I would recommend a good unit like a Outback, use the highest voltage model and get a matching charger. Set the voltage of the charger for the batteries optimal float voltage, get the largest batteries you can to limit the number of parallel banks. What you will end up with is a home made online UPS.
 
jschuricht said:
Yes, you can use a inverter for a UPS. I would recommend a good unit like a Outback, use the highest voltage model and get a matching charger. Set the voltage of the charger for the batteries optimal float voltage, get the largest batteries you can to limit the number of parallel banks. What you will end up with is a home made online UPS.
Click to expand...

I've thought of that, but would it work? Connect the charger and the Inverter in paralell on the bank? Wont the charger try to power the inverter directly and missdetect the battery charge status?
 
Macco said:
Maybe our idea of a long outage is different but for something like this I'd rather get an LP generator and be done with it.
Click to expand...

Well maybe a day was exagerating, but I'd like to get maybe an hour or so. We get a lot of short power outages at this time of year, probably because of all the road construction.
 
Here's another vote for an LP generator + transfer switch. I've got my servers on a UPS that holds the load for the 8-10 seconds it takes the transfer switch to realize something's up, fire up the generator,let it stabilize at 60 Hz, and transfer the load over
 
I've thought of that too, I'll have to weigh in the cost. The nice thing with the generator is it could do the whole house quite easily assuming I'm not using big appliances such as the oven and dryer at same time. Can get a Generac 7kw one for maybe 2k. Will do propane or natural gas. (has to be configured for one or the other)

I'm still curious about hooking up an inverter and charger to the same bank though, if that would work.
 
Red Squirrel said:
I've thought of that, but would it work? Connect the charger and the Inverter in paralell on the bank? Wont the charger try to power the inverter directly and missdetect the battery charge status?
Click to expand...

It will work just fine if you properly size everything. For instance, say the inverter can draw 200a at 100% load continuously. You use a 200a or larger charger, and don't plan on using more than 80% of the inverters capacity, 40a will still go to the batteries. It's the same way a online or double conversion UPS works.

Another advantage is you could subsidize the charger with solar, wind or even a DC generator, just set the voltage slightly higher on the preferred charging source.
 
Ahh I see, that is good to know. So as long as the charger is oversized compared to what is actually being used.

I do want to setup a wind or solar setup eventually so I could tie it in too.
 
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