Dawn/Ken,
There are a couple of issues you need to consider when using a computer style UPS with fish equipment. I use APC units to backup the power to my vital equipment and to surge protect non-vital.
First thing to think about is the size of the UPS. Ken mentions that a 350w heater would be OK on a 450W UPS - this is correct on the face of it, but bear in mind a lot of UPS are sized according to the VA rating. A 450VA UPS would only have 270w capacity and would therefore not be able to run a 350w heater.
From APC's specification for the Smart-UPS 420: Smart-UPS 420 has a 420 volt-amp, 260 watt capacity.
Here's part of a white paper explaining the difference between VA and watts - I didn't know this until quite recently.
Background
The power drawn by computing equipment is expressed in Watts or Volt-Amps (VA). The power in Watts is the real power drawn by the equipment. Volt-Amps is called the "apparent power" and is the product of the voltage applied to the equipment times the current drawn by the equipment.
Both Watt and VA ratings have a use and purpose. The Watt rating determines the actual power purchased from the utility company and the heat loading generated by the equipment. The VA rating is used for sizing wiring and circuit breakers.
The VA and Watt ratings for some types of electrical loads, like incandescent light bulbs, are identical. However, for computer equipment the Watt and VA ratings can differ significantly, with the VA rating always being equal to or larger than the Watt rating. The ratio of the Watt to VA rating is called the "Power Factor" and is expressed either as a number (i.e. 0.7) or a percentage (i.e. 70%). The Watt rating for a computer may not be equal to the VA rating.
The power rating of the UPS
UPS have both maximum Watt ratings and maximum VA ratings. Neither the Watt nor the VA rating of a UPS may be exceeded.
It is a de-facto standard in the industry that the Watt rating is approximately 60% of the VA rating for small UPS systems, this being the typical power factor of common personal computer loads. In some cases, UPS manufacturers only publish the VA rating of the UPS. For small UPS designed for computer loads, which have only a VA rating, it is appropriate to assume that the Watt rating of the UPS is 60% of the published VA rating.
For larger UPS systems, it is becoming common to focus on the Watt rating of the UPS, and to have equal Watt and VA ratings for the UPS, because the Watt and VA ratings of the typical loads are equal.
Examples where a sizing problem can occur
Example #1: Consider the case of a typical 1000VA UPS. The user wants to power a 900W heater with the UPS. The heater has a Watt rating of 900W and a VA rating of 900VA with a power factor of 1. Although the VA rating of the load is 900VA, which is within the VA rating of the UPS, the UPS will probably not power this load. That is because the 900W rating of the load exceeds the Watt rating of the UPS, which is most likely 60% of 1000VA or around 600W.
So when dealing with the load in watts you need to divide the total wattage by 0.6 to get an approx VA size.
For example if you have a 350w heater, an internal Fluval 4 at 10 watts and 40 watts of lighting this gives you a maximum load (when the heater is on) of 400 watts. This means you will need a UPS with at least a 667VA capacity. To be on the safe side I would aim for as least 700VA or even 1000VA.
A second thing to remember is that typical UPS are normally designed to run computers and other similar equipment. The output is not necessarily good for what we want to use them for as they do not always output a true sine wave AC volatage which can cause problems in some equipment such as motors.
From APC again:
APC's Back-UPS and PowerCell series all output a "stepped-approximated" sine wave when the unit is On Battery. While this kind of waveform is ideal for computers and computer-related equipment, it may not be compatible for other types of loads like motor loads. If you are using non-computer loads with one of the above-mentioned UPSs, consult the manufacturer's specifications to determine if the equipment can run off of a "stepped wave". If it can't, then it will require a UPS that outputs a pure sine wave when On Battery. APC UPS models that do output a Pure Sine Wave include: Smart-UPS, Matrix-UPS, and the Symmetra Power Array.
In my experience most aquarium equipment won;t have problems unless running for a long time on the battery output but it may shorten the life of some motors. If it is a concern you would need to pay a bit more for the better units.
Prices are guidelines from one on-line source - I am sure you can find better if you shop around. All prices inc VAT:
APC Back-UPS CS 350 - £55.21
APC Back-UPS CS 500 - £69.31
APC Smart-UPS 420INET - 116.31
APC Back-UPS Pro 650 - £146.86
APC Smart-UPS 700VA - £192.69
APC Back-UPS Pro 1000VA - £240.86
APC Smart-ups 1000 - £266.71
APC Back-UPS Pro 1400VA - £311.36
APC Smart-UPS 1500 - £351.31
Bear in mind that there are other brands out there which can offer good value for money but I don;t have the same level of technical information on them as I do for APC. For example a Belkin Regulator Pro Gold 625 VA is £106.91 from the same source as above.
HTH, Eddie
P.S. Forgot - the type of plug required for most UPS connections is called an IEC 320 connector. You should be able to get these from good electronic shops or on-line from RS Components or Maplin. If you need links let me know.
