Converting 110 to 220 electrical question

[Inspector507]

I think with all the theory, we might confuse 'ol exeter. After reading his original post, I think his heater is fed with 110V but wired internally for 220V. He did say it was a combination unit.
But if he decides to replace it with a 220V unit, he can do it with the present wiring that is installed. The spare breaker from the water tank may be a bit too large for the heater. Some HWH need a 30 amp breaker, where the heater will only need a 15 or 20 amp breaker.
Exeter, let me know if you need anymore help with this.

Jerry

[exeter_acres]

My head hurts!!

Did the research.. Turns out that it was a 220 unit wired for only 110. Marked the white as hot, switched the breaker..(Yep the water heater was a 30 so I put in a 20 amp breaker) and Hey Hey!! I have heat in the mud room..
Thanks for all the info though. I truly have learned quite a bit from this!!!

there is no such thing as too much information... well there is! [img]/forums/images/icons/blush.gif[/img]
but not here!

Curtis

[Pat]

Hey inspector, I'm not going to underestimate Exeter's ability to learn/understand. Your emphasis on the mismatch of the DHW breaker with what he probably needs for his heater is RIGHT ON! Oversized breakers are nearly as dangerous as not having one.

Not trying to confuse anyone, just thought it might do a couple things:1. offer a reasonable explanation for why the output of his heater is so low (could be miswired) 2. explain some about how 110/220 heaters are inplemented. I know when I get into something where my experience is real slim, getting some background info helps me establish a general framework on which to "hang" pieces of info as I learn.

If a dual voltage heater is wired for 220 but powered by 110 it would only give 1/4 the normal output which seems to fit his observations. As far as wiring size, can't be sure from here but changing to 220 will double the amps in the current wiring. This might be entirely safe or not, it depends...

Pat

[hazmat]

<font color="blue"> As far as wiring size, can't be sure from here but changing to 220 will double the amps in the current wiring. This might be entirely safe or not, it depends...
</font color>

Well I'm a little confused:

For a given amount of power or heat, 220 vs 110 will half the amperage draw. But if it was wired wrong and only getting 1/4 the power, if it wire wired correctly for 110, he'd be using 4X the amps, but at 220 V this would only be 2X the amps (vs the "incorrect" wiring)

[Pat]

Hazmat, Confused? Maybe a little. Your statement of relative currrents is wrong. Your assumption regarding a "given amount of power or heat" is the likely culprit. The heater is a dumb resister or pair of resisters actually and has no active regulation to ensure constant output with varying input voltages.

Let us take a simple example: Let's say we have a heater built to run on either 110 or 220 volts and that it is rated at 4400watts (when correctly connected to either 110 or 220 volts).

If it is configured for 110 volts then each heater element (resistor) has 110 volts applied to it as if they were two seperate heaters each wired independantly to 110 volts. Each half producing 2200Watts.

I'll just write out a couple forms of Ohm's law for easy reference: P=IE and I=E/R Where P is power in Watts, I is current in Amps, and R is resistance in Ohms.

So we see that 2200 = I times 110 which with a little algebraic manipulation becomes I = 2200/110 which simplifies to 20 amps. This is 20 Amps to each resistive element and there are two so total current at 110 volts would be 40 Amps.

Now with the current (to one element) AND the voltage we can solve the second equation for resistance: I=E/R is restated as R=E/I. Substituting the known values we get R=110/20 or 5.5 Ohms for one element.

If we reconfigure the heater for 220 volt operation we have two resisters in series adding up to 11 Ohms (5.5 X 2). Combining the two equations we get P= ExE/R (power is voltage squared over resistance) and substituting in the knowns and solving for the unknowns we get P= (220x220)/11 which is 4400 Watts.

The heater, when correctly connected to either 110 volts or 220 volts, produces 4400 Watts. On 110 volts it draws 40 Amps and on 220 volts it draws 20 Amps.

Alternatively you can consider the two resistors in parallel to solve the 110Volt version. For two resistors in parallel you have 1/2 the resistance or 2.75Ohms. Using P=ExE/R (E squared over R) you get 110x110/2.75 which is (drum roll please) 4400Watts.

So you see if our imaginary heater was configured for 220Volt operation its R would be 11 Ohms which at 110 Volts gives (using P equals E squared over R) 1100Watts which is what we would expect, 1/2 the voltage so 1/4 the power.

Since I don't know the wire size (Ampacity), or run length I don't know that it is safe to just hook up 220Volts even if it is currently supplied with 110 while configured for 220. If the ooriginal wire was sized correctly to get rated power with 110Volts then the wire is generously oversized and safe to be used for 220. This needs to be confirmed before risking burninig the building down.

I have attached yet another precision engineering drawing depicting notional connections for a 110/220 volt heater. I did NOT show a ground wire which is for safety and does NOT get involved in our calculations. In the drawing NC means No Connection. I show a 110 and a 220Volt source but for simplicity did not show breakers etc.


If this was neither clear, helpful, nor seemingly correct to you, I'd be glad to answer any pecific questions or listen to any dissenting view. If continuing this topic risks boring too many folks or uses too much bandwidth (Censors/moderators please chime in) I'll be happy to take it to private email or drop it.

I can recall when I didn't understand some stuff and appreciated when others would take the time to satisfy my curiosity about how it was so I owe it to pass a little on as well.

Pat. (Note to Egon: This works in Canada too.)

[hazmat]

[blue]If this was neither clear, helpful, nor seemingly correct to you, I'd be glad to answer any specific questions or listen to any dissenting view. If continuing this topic risks boring too many folks or uses too much bandwidth (Censors/moderators please chime in) I'll be happy to take it to private email or drop it.[/blue]

Actually it was quite clear. Thanks for the explination, saved me from having to dig my physics book out of the attic.

I'm assuming E = Electro Motive Force also known as Voltage or V?

[Pat]

Hazmat, Yup.

And we didn't have to resort to using curl or the left or right hand rules or... Physics book? Doesn't the instructions for giving a physic come on the package?

OK, OK, I confess, in a past life I did physics (and electricity) before I found true religion (Software Engineering). Trying to be a specialist I studied more and more about less and less until in the limit (like in calculus) I knew everything about nothing. Then I tried my hand at being a generalist where the goal is to know less and less about more and more until you know absolutely nothing about everything. I'm nearly there!

Pat