Water Heater
- Thread starter jbolen
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Assuming it to be a resistive electric water heater, the power will go up by about 18%.
chris kennedy
Senior Member
- Location
- Miami Fla.
- Occupation
- 60 yr old tool twisting electrician
Lets look at a 4500W heater.
Find element resistance
230??4500=11.8ohms
Find power at new voltage
250??11.8=5297W
Find element resistance
230??4500=11.8ohms
Find power at new voltage
250??11.8=5297W
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Am I correct in assuming the 60 cycle vs 50 cycle should not affect it at all?
- Location
- Massachusetts
Just curious, where are you getting a 250 volt 60 Hz supply from?
Not if it's just resistive.
chris kennedy
Senior Member
- Location
- Miami Fla.
- Occupation
- 60 yr old tool twisting electrician
How did you come up with this Mac?
Open Neutral
Senior Member
- Location
- Inside the Beltway
- Occupation
- Engineer
Unless it's very very different [1], it will matter not at all. You can run a resistive heater on 0, 25, 50, 60, 400 or 999 Hz and nothing will care.
The thermostats may balk at switching DC but the heaters won't care.
[1] As in "not resistive"....
- Location
- Illinois
- Occupation
- retired electrician
The power will change with the square of the change in voltage. 250 volts is 1.087% of 230 volts and the power at 250 (assuming that the resistance does not change with voltage) will be (1.087)(1.087) or 1.182% of the power at 230 volts. That gives you 5319 watts at 250 volts. That is the same answer your method would give you if you hadn't rounded the resistance up to 11.8 from 11.75 ohms.
kwired
Electron manager
- Location
- NE Nebraska
It has been a long time since I done any calculations of this type - like 20+ years, as far as power calculations for different frequencies.
From what I recall what matters most is the RMS voltage. For a resistive load the resistance will be constant therefore the current will be proportional to input voltage. RMS voltage is basically the effective DC equivelant while peak voltage and average voltage will be different values. So if you have 230 volts at 2 Hz RMS you will get same current through a resistive load as you will with 230 volts 60Hz RMS. The peak and average voltages will not be the same but the RMS voltage will be.
Most 50 Hz systems usually operate at around 220 volts instead of 240 volts nominal like most 60 Hz systems from what I understand. Therefore most 50 Hz rated equipment will likely be designed for 220 volts and not 240 (nominal voltage).
Jbolen: are you sure it is rated 230 volt 50 Hz? If so maybe it was designed to operate within its limits on a 60 Hz system at up to 250 volts? If you were to use it on a 208 volt system I don't see there would be any problem at all. 240 volt system it will probably work but will use more power than it is rated at, could shorten the life of it some.
From what I recall what matters most is the RMS voltage. For a resistive load the resistance will be constant therefore the current will be proportional to input voltage. RMS voltage is basically the effective DC equivelant while peak voltage and average voltage will be different values. So if you have 230 volts at 2 Hz RMS you will get same current through a resistive load as you will with 230 volts 60Hz RMS. The peak and average voltages will not be the same but the RMS voltage will be.
Most 50 Hz systems usually operate at around 220 volts instead of 240 volts nominal like most 60 Hz systems from what I understand. Therefore most 50 Hz rated equipment will likely be designed for 220 volts and not 240 (nominal voltage).
Jbolen: are you sure it is rated 230 volt 50 Hz? If so maybe it was designed to operate within its limits on a 60 Hz system at up to 250 volts? If you were to use it on a 208 volt system I don't see there would be any problem at all. 240 volt system it will probably work but will use more power than it is rated at, could shorten the life of it some.
Power is V2/R
The resistance stays the same (same heater)so the power goes up as the square of the voltages.
2502/2302 = 1.181
QED.
And you don't need to calculate the resistance or the current. Nothing wrong with doing that. It's just a bit longer.
Last edited:
kwired
Electron manager
- Location
- NE Nebraska
I think the OP is asking if a change of frequency has any effect on the power used, and if there is a change how does voltage come into play also. As I stated before I don't think frequency makes a bit of difference with a resistive load as long as voltage you are talking about is RMS voltage.
kwired
Electron manager
- Location
- NE Nebraska
I assumed (yeah I know) he knew that a change of voltage would make a difference. My guess is he was wondering if a change of frequency also made a difference. If it does maybe the combination of voltage and frequency change could end up with similar power consumed at the load. This is just what I get from his original question. Most people who deal with electricity know basic theory laws that deal with voltage, current, and power, throwing frequency in there gets to an area that most hardly ever have to do any calculations that will have end results that will vary if the frequency varies.
I am trying to say on a resistive load, RMS voltage is all that matters at any frequency. Change the RMS voltage with a constant resistance, and the amount of current will change proportionally. Correct me if I am wrong.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
I agree but the op's case is a water heater hence my response.
It just arrive here in Afhgansitan
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Did your question get answered? And be careful over there. :thumbsup:
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
Ditto. God bless.
Yes, so we don't know for certainty what the circuit comprises hence that conditional "if" in my response.
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