# I want to know about this UPS transformer with 7 wires and how to get maximum power from it.

Discussion in 'Power Electronics' started by AhmedCJ1, Aug 28, 2018.

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1. ### AhmedCJ1

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Aug 28, 2018
Hi, my father bought an old UPS APC Back UPS 300 which did not provided any back up. Maybe the battery was dead, so I opened it and disconnected a transformer from it. Now it has seven wires on it. On one side it has Black and White wires and on the other side it has : White / Yellow ( I am not sure) ,Purple, White ( Another white ) ,Brown , Blue.
Now I am not sure which is Primary or Secondary.
Question 1 How to get maximum power from it by using 3 parallel 6 volts rechargeable battery?

Note: I currently don't have access to a multimeter so its hard to calculate its electric flow.
Sorry for my bad grammar I don't speak English

2. ### kellys_eye

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Jun 25, 2010
The transformer has a low voltage secondary and a primary with multiple taps at the local AC mains voltage. Simply measure the resistance of the primary and use the two wires that give the highest resistance reading - this will be the highest voltage tap (probably the 250V AC tap) and will give the LOWEST output on the secondary. Other taps will be lower AC volts (say 230V, 210V and 190V - these are typical primary tap voltages) and give increasingly HIGHER outputs on the secondary - always assuming the input voltage (local mains) remains the same i.e. 240V ????

You can't apply DC volts (from a battery) to the transformer - you will burn it out almost immediately.

3. ### dave9

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Mar 5, 2017
I would put it back in the UPS and buy a battery since your father wanted an UPS, and make getting a multimeter a priority if you want to fiddle with electrical/electronics.

However before buying a 12V battery you could hook two of your 6V in series to achieve 12V for testing the UPS, provided those batteries are capable of several amps output (I assume it used a 12V, roughly 3.5Ah battery? That size does in the US.) keeping in mind that the live circuits in an UPS are at a dangerously high voltage.

4. ### AhmedCJ1

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Aug 28, 2018
Thanks mate that was I was looking for. I used 3 6 volts batteries in parallel and it gave a great shock to me. ( probably it was high amps) I will put back in UPS and buy a new battery

5. ### BobK

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Jan 5, 2010
Don't know how you got a shock from 6V. Was this battery in the UPS with line voltage coming in as well? That could give you a shock, even a fatal one.

Bob

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Sep 5, 2009