Running 220v water heater on 110v supply

[mrm]

Originally Posted by wingless

All those who understand this have explained it, yet confusion still remains, so here is one more attempt.

Ohm's Law states V=I*R or I=V/R or R=V/I, where V is voltage expressed in volts, I is current expressed in amperes and R is resistance expressed in ohms.

Electrical power is the product of current and voltage, assuming a resistive load, like this water heater, expressed as P=V*I, where P is power expressed in Watts.

Because of Ohm's Law, by substituting for V or for I, the power equation can also be rewritten as: P=V²/R or P=I²*R.

So, because power is proportional to the square of the current and ½ squared is ¼, then half the current is one quarter the power.

Spot on (that is, for resistive loads, where W==VA, as is the case here).

Yes, some of the nanswers (spelling intentional) were most entertaining

To the OP: the heater element will be just fine, wiring too. What concerns me however is, that you report water to be noticeably warmer than usual (and also this plume of cloudy water you reported http://www.cruisersforum.com/forums/...ml#post1780031). Also that your safety release valve releases water (as you reported here http://www.cruisersforum.com/forums/...ml#post1780386) is of concern.
What is the exact model of your water heater? Are there any electronics involved in controlling the heater element or is it a plain mechanical (bimetal) thermostat? The gate valve you mention is used as a mixer to adjust temperature of water flowing into the hot water piping, but it does not adjust temperature in your water heater.

[Cadence]

Originally Posted by rwidman

Yes. Post #12

Yep, you did at the end. I see some for a few hundred dollars, I'll bet one can be had at the local electrical supply house for considerably less.

[monte]

Originally Posted by mrm

Spot on
What is the exact model of your water heater? Are there any electronics involved in controlling the heater element or is it a plain mechanical (bimetal) thermostat? The gate valve you mention is used as a mixer to adjust temperature of water flowing into the hot water piping, but it does not adjust temperature in your water heater.

It's a quick b3 boiler, pretty basic model and no electronics involved other than the element as far as I can tell. I think the gate valve is for the engine water heating system, allowing you to mix the engine coolant, but I haven't poked around to see if mine is plumbed that way. So I'm looking at the installation guide and I can't see how the unit can avoid being run low or dry if water if air is forced down the water inlet line by the water pump and allowed to evacuate through the shower head. Generally this wouldn't happen as we would stop using the water if it starts to splutter, but perhaps some air did get in the system, allowing it to steam. Strange for sure...
Thanks for the thoughts

[rwidman]

Originally Posted by monte

............. I can't see how the unit can avoid being run low or dry if water if air is forced down the water inlet line by the water pump and allowed to evacuate through the shower head..........

The cold water goes in to the bottom of the tank (usually through an internal dip tube). The heated water comes out the top of the tank. When there is no more cold water to pump into the tank, hot water is not forced out the top and the tank remains full. The element does not burn out.

Drain the tank through the tank drain and the element will burn out very quickly. Don't do that.

[mrm]

Originally Posted by monte

It's a quick b3 boiler, pretty basic model and no electronics involved other than the element as far as I can tell. I think the gate valve is for the engine water heating system, allowing you to mix the engine coolant, but I haven't poked around to see if mine is plumbed that way. So I'm looking at the installation guide and I can't see how the unit can avoid being run low or dry if water if air is forced down the water inlet line by the water pump and allowed to evacuate through the shower head. Generally this wouldn't happen as we would stop using the water if it starts to splutter, but perhaps some air did get in the system, allowing it to steam. Strange for sure...
Thanks for the thoughts

Well... Quick b3 is pretty basic, so I am stumped. Still looks like a temperature control problem to me, but no clue as to how...

I don't know if the gate valve you mentioned is the same as the valve delivered with a thermostatic mixing kit (optional, see Products | WATER HEATERS | NAUTIC BOILER | Nautic boiler B3) but with the mixing kit the idea is to heat water in the boiler as much as reasonably possible (say, 70-80 deg C range) and downmix to safer temperatures at the output.

[wingless]

Originally Posted by rwidman

More than once I have seen people use ohms law in a way that would have reducing the voltage in a circuit to zero result in an infinite current.

Like when short circuiting a battery?

Originally Posted by rwidman

You don't have to be an electrician to know that's not possible.

While the current from short circuiting a battery is not infinite, it is lots and lots, limited by the battery construction, the battery chemistry, the internal resistance of the battery and by the conductance of the shorting bar.

[Andina Marie]

Originally Posted by Andina Marie

Hmm. On 240 volts the resistor is 48 ohms and draws 240/48 = 5 amps. So the wattage is amps x volts = 5 * 240 = 1,200 watts.

It is current that heats it up, not voltage, all the voltage does is force the current to flow through the heating element.

If you have half the voltage you have half the force for current so you have half the current. So the element now has 2.5 amps flowing to produce heating = 2.5 amps. Since current produces heating it should be half the amount of heating = 600 watts.

BUT the volts x amps = 120 x 2.5 = 300 watts. Where did the other 300 watts go? Its the same piece of heating element with half the current. How does the voltage across the heating element produce heating watts, the heating element is insulated electrically from the water?

Thanks for the reply Wingless but I was not questioning ohms law, or questioning the mathematics, I agree 100% with the math and the conclusion.

I was questioning how the molecular action in the heating element produces less heat due to lower voltage. You can sprout formula and use that to get the (correct) answer but I like to understand HOW or WHY it works.

The voltage is reduced by 50% and therefore the current is reduced by 50%. I understand how the number of electrons moving in the wire is directly proportional to the current so that would account for HALF the number of electron/molecule collisions resulting in half the power loss. BUT how does the lower voltage (Part of the Watts = Amps x Volts) reduce the amount of heat produced? It is exactly 50% of electrons flowing in the element. Where did the other 300 Watts go? How did reducing the volts reduce the heating when all it does is force electrons through the element?

[cal40john]

Originally Posted by Andina Marie

Thanks for the reply Wingless but I was not questioning ohms law, or questioning the mathematics, I agree 100% with the math and the conclusion.

I was questioning how the molecular action in the heating element produces less heat due to lower voltage. You can sprout formula and use that to get the (correct) answer but I like to understand HOW or WHY it works.

The voltage is reduced by 50% and therefore the current is reduced by 50%. I understand how the number of electrons moving in the wire is directly proportional to the current so that would account for HALF the number of electron/molecule collisions resulting in half the power loss. BUT how does the lower voltage (Part of the Watts = Amps x Volts) reduce the amount of heat produced? It is exactly 50% of electrons flowing in the element. Where did the other 300 Watts go? How did reducing the volts reduce the heating when all it does is force electrons through the element?

Heat and amps are not related linearly. Solve the power equation another way. P=EI, E= IR, sub E from ohm's law into power law, P = I^2*R.

Why isn't it linear. I probably am making an improper connection here, but kinetic energy formula KE=1/2mv^2 says half the velocity is 1/4 the energy. Watts is energy per time, amps is coulombs (big number of electrons) per sec or otherwise more or less speed of electron.

OK, why is kinetic energy to velocity not linear? Here's someone's explanation that I'm still trying to wrap my head around:

newtonian mechanics - Why does kinetic energy increase quadratically, not linearly, with speed? - Physics Stack Exchange

[wingless]

Originally Posted by Andina Marie

I understand how the number of electrons moving in the wire is directly proportional to the current so that would account for HALF the number of electron/molecule collisions resulting in half the power loss. BUT how does the lower voltage (Part of the Watts = Amps x Volts) reduce the amount of heat produced? It is exactly 50% of electrons flowing in the element. Where did the other 300 Watts go? How did reducing the volts reduce the heating when all it does is force electrons through the element?

P=V*I.

In this example, half the voltage equals half the current, then the power calculation is half V times half I equals one quarter power.

[monte]

Good explanation cal, even I can understand that!
Also explains pretty clearly why the force on sails increases x 4 with increased windspeed.

[rwidman]

Originally Posted by wingless

Like when short circuiting a battery?

No. Usually they are trying to use ohms law to say that the current in a series circuit increases when there is resistance caused by too small or too long conductors or high resistance connections.

While the current from short circuiting a battery is not infinite, it is lots and lots, limited by the battery construction, the battery chemistry, the internal resistance of the battery and by the conductance of the shorting bar.

That's entirely correct. There can never be an "infinite" current. Their calculations (see above), if carried to the extreme, would result in an infinite current when the battery voltage reaches zero.

[Andina Marie]

I am NOT questioning the mathematics. You can write the equation any way you like and get the correct results that at half voltage you get 25% heating.

I'm trying to understand why half the current (= half the number of electrons flowing in the heating element) produce only 1/4 of the heating. I'm thinking that although the NUMBER of electron to molecule collisions is the same, at lower voltage perhaps the electron VELOCITY is lower so that is how the other 300 watts came up missing.

[cal40john]

Originally Posted by Andina Marie

I am NOT questioning the mathematics. You can write the equation any way you like and get the correct results that at half voltage you get 25% heating.

I'm trying to understand why half the current (= half the number of electrons flowing in the heating element) produce only 1/4 of the heating. I'm thinking that although the NUMBER of electron to molecule collisions is the same, at lower voltage perhaps the electron VELOCITY is lower so that is how the other 300 watts came up missing.

Isn't that what I said in my last post?

[sailorchic34]

Originally Posted by Andina Marie

I was questioning how the molecular action in the heating element produces less heat due to lower voltage. You can sprout formula and use that to get the (correct) answer but I like to understand HOW or WHY it works.

The voltage is reduced by 50% and therefore the current is reduced by 50%. I understand how the number of electrons moving in the wire is directly proportional to the current so that would account for HALF the number of electron/molecule collisions resulting in half the power loss. BUT how does the lower voltage (Part of the Watts = Amps x Volts) reduce the amount of heat produced? It is exactly 50% of electrons flowing in the element. Where did the other 300 Watts go? How did reducing the volts reduce the heating when all it does is force electrons through the element?

Hum, Think of voltage as pressure and amps as flow rate. 220V has twice the pressure as 110V, so if you drop the voltage by 1/2 the total power or pressure available drops by 1/2.

When you drop the voltage or pressure and there is resistance in the circuit, the voltage pressure takes longer to push through the resistance. so there are few amps (flow) making it through. In other words amps used is determined by voltage divided by resistance (I=V/R). Amps used does not stay constant but varies with voltage. That is why the amps used is not constant and why power (watts) is not 1/2 when you drop voltage by 1/2.

[transmitterdan]

Originally Posted by Andina Marie

I am NOT questioning the mathematics. You can write the equation any way you like and get the correct results that at half voltage you get 25% heating.

I'm trying to understand why half the current (= half the number of electrons flowing in the heating element) produce only 1/4 of the heating. I'm thinking that although the NUMBER of electron to molecule collisions is the same, at lower voltage perhaps the electron VELOCITY is lower so that is how the other 300 watts came up missing.

The traditional physics answer goes like this. The electric field within a material causes free electrons to move. As they move they bump into atoms that can't move because they aren't hot enough to break apart. Each of these collisions causes the electron to lose some energy and the surrounding atoms heat up because they could not move (they resist the electron's impact). The faster the electrons are moving the more heat they create with each collision. The energy of an electron according to Newtonian mechanics is 0.5*mass*velocity squared. When the voltage is twice as high the electron velocity is twice as fast. So the energy given up in each collision is 4 times as much. But since they are moving faster they don't hit as many solid atoms. But because the electric field is twice as high twice as many electrons enter and leave the material. These extra electrons account for the higher current and doubling the heat.

It's more complex than that explanation but the basic idea is correct.