Lower 240 voltage a few volts

Thread Starter

catchingitwithcody

Joined Nov 18, 2021
1
I am working on a Air-conditioning unit. From the power box at the breaker I have 247.4 volts, due to the high end unit it requires 238v to 244v to operate, I have a error code saying power coming in is two high. Is there a way to lower the voltage just slightly to bring it within range to allow for it to work. Gulf power is no help and the electrical company said they couldn't do anything.
 

Papabravo

Joined Feb 24, 2006
17,642
I am working on a Air-conditioning unit. From the power box at the breaker I have 247.4 volts, due to the high end unit it requires 238v to 244v to operate, I have a error code saying power coming in is two high. Is there a way to lower the voltage just slightly to bring it within range to allow for it to work. Gulf power is no help and the electrical company said they couldn't do anything.
I'm not aware of one that is any of cheap, or easy, or even safe. Conceptually a variac transformer with an automatic adjustment to keep the output within the input range of the AC unit. That probably does not exist and even if it did, it might cost more than the AC unit. You might have more luck, and or insight from the AC manufacturer.
 

dendad

Joined Feb 20, 2016
3,987
You can use a 240V to, maybe, 6V transformer, and connect the 6V secondary in line with the mains to the aircon, but in the reverse polarity so it bucks the mains.
But, you need a transformer of sufficiently high secondary current rating to suit your aircon, and that could be a bit hard to find.
And if you can find a transformer, get one with a selection of secondary voltages so the best one can be selected.

Here is the first picture of the idea thet Mr Google came up with to demonstrate ...
1637265190398.png
EDIT: You could rewind a transformer to suit, like this for example..
https://www.hobby-machinist.com/threads/rewiring-a-mot-microwave-oven-transformer.57223/
BUT, add more insulation between the core and the secondary that shown here.
If you are not confident of doing a good job, please get outside assistance as this has the potential of being quite dangerous.
 
Last edited:

Externet

Joined Nov 29, 2005
1,741
Wondering if the sensing circuitry in its control board/diagnostics can be tricked by lowering the sampling voltage there... :(
 

Papabravo

Joined Feb 24, 2006
17,642
You can use a 240V to, maybe, 6V transformer, and connect the 6V secondary in line with the mains to the aircon, but in the reverse polarity so it bucks the mains.
But, you need a transformer of sufficiently high secondary current rating to suit your aircon, and that could be a bit hard to find.
And if you can find a transformer, get one with a selection of secondary voltages so the best one can be selected.

Here is the first picture of the idea thet Mr Google came up with to demonstrate ...
View attachment 252996
EDIT: You could rewind a transformer to suit, like this for example..
https://www.hobby-machinist.com/threads/rewiring-a-mot-microwave-oven-transformer.57223/
BUT, add more insulation between the core and the secondary that shown here.
If you are not confident of doing a good job, please get outside assistance as this has the potential of being quite dangerous.
He only has an 8 volt play with, this might be a major purchasing project.
 

Reloadron

Joined Jan 15, 2015
6,324
Your 247.4 for 240 volt service is well within the allowable tolerance as can be seen above. The national standard for utility voltage tolerance in North America is ANSI C84.1.
I am working on a Air-conditioning unit. From the power box at the breaker I have 247.4 volts, due to the high end unit it requires 238v to 244v to operate, I have a error code saying power coming in is two high. Is there a way to lower the voltage just slightly to bring it within range to allow for it to work. Gulf power is no help and the electrical company said they couldn't do anything.
With that in mind possibly your A/C manufacturer can explain why their voltage tolerance is much tighter then the US ANSI code calls out. The standard is +/- 5% which your AC unit should run on less any problem. Considering the current draw of an A/C unit there is no easy or inexpensive solution.

Ron
 
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