Many consumers make fundamental errors when specifying UPS systems, which often result in costly long term consequences. Incorrect selection of a UPS can seriously impact on the daily running of your business, and as we are all too well aware, in this economic climate every cent counts. Below is a list of rules that have assisted me over the years. I am sure they will assist you in making the best selection when next acquiring a UPS system.
RULES:
- Use a UPS and not an inverter for sensitive load, as an inverter offers very little protection
- Check the name plates to establish the power rating for the equipment on which the UPS is to be installed, as a rule of thumb a standard PC is about 350Va, but don’t guess, it could be costly.
- Amps X Volts = Watts, Watts ÷ PF = VA
- If you are installing UPS systems onto servers, or any PC where sensitive, mission-critical data is stored DON’T COMPROMISE always use an online UPS
- Never overload a UPS system, loads in excess of about 80% of the UPS rated capacity, could result in poor performance or even total failure under no power conditions.
- Only True on-line UPS systems are capable of effectively filtering generator or poor mains supply. It is wise to test the power quality prior to specifying the type of UPS for the application
TYPES OF UPS SYSTEMS:
1. LINE INTERACTIVE MODIFIED SINEWAVE
- Low to medium levels of protection
- for your equipment
- Relatively inexpensive
- Sizes – 500Va – 1000Va
- Considered entry level units
- Most commonly used for PC back-up
- Not Suitable for generators
2. LINE INTERACTIVE PURE SINEWAVE
- Medium levels of protection
- for your equipment
- Sizes – 1000Va – 3000Va
- Considered industry standard
- Can be used as a long runtime unit
- Tower or rack mounted form
- Not Suitable for generators
3. ONLINE DOUBLE CONVERSION
- High levels of protection
- for your equipment
- Sizes – 1000Va – 3.6MVA
- Considered Up market
- Used for general AC Back-up and protection
- Can be used as a long runtime unit
- Tower or rack mounted form
- Only option Suitable for generators
CALCULATIONS
How to size a battery back-up systems:
AC power measurements are related as follows:
VA = Volts X Amps only if PF = 1, If PF is smaller than 1 then Volts X Amps = Watts, Watts ÷ PF = VA
Volts = 230 typical, lAmps = Load Current, Power Factor = between 0 and 1
Power factor is a number between 0 and 1 which represents the fraction of the load current which provides useful energy (Watts) to the load. Only in an electrical heater or incandescent light bulb is the power factor equal to 1; for all other equipment, some of the load current flows into and then back out of the load without delivering Watts. This current, composed of distortion or reactive currents, is the result of the nature of the electronic load. The important point to understand is this distortion or reactive current, which is forced to exist due to the load, causes the load V-A rating to be larger than the load watt rating. The Watt rating system can be thought of as a special case of the V-A measurement system, namely, the case where the power factor is equal to 1.
How to calculate battery runtimes:
From time to time people ask us what batteries do I need to get the runtimes I require from my UPS system, and unfortunately there is a lot of confusion surrounding this topic, so what we have done is list the most common way to calculate battery sizing and runtimes.
Step 1: define what type of UPS you need, either online or line interactive, if you are unsure please click on this link.
Step 2: determine the DC voltage of required UPS (number of cell or batteries the unit requires)
Step 3: take the VA rating of the UPS you require and divide it by the DC voltage this will give you the amp your require for 1 hour operation
Step 4: once you have the amps you require for an hour, multiply it by the number of hours that you want the unit to run for.
For example:
Lets say I need an 3kVA online UPS for 2 hours, so the ST3030 – L (Our online 3kVA range) has a DC voltage of 96 Volts (requires 8 x 12 volt cells to operate).
3000VA ÷ 96 volts (8 cells x 12volts) = 31.25 Amps
31.25 x 2 = 62.5 Amps required for 2 hours
Therefore to get 2 hours we would use 8 x 65ah batteries
Please note this is an estimation only.
