thetankatwaterheaterrescue.com Home 
Home Search search Menu menu Not logged in - Login | Register
thetankatwaterheaterrescue.com > Forums > The Tank > Can I run an electric water heater on a 120 volt generator?

 Moderated by: Admin
New Topic Reply Printer Friendly
Can I run an electric water heater on a 120 volt generator?  Rating:  Rating
AuthorPost
 Posted: Fri Feb 18th, 2011 06:46 am
  PM Quote Reply
1st Post
murphy
Member
 

Joined: Sun Feb 13th, 2011
Location:  
Posts: 6
Status: 
Offline
I have a 19 year old 30 gallon water heater with a single 3500 watt element.

The power is out and it may be several days before it comes back on. Can I wire up the water heater to a 120 volt generator just so I can get some hot water? According to my calculations it will only pull about 870 watts so I'm sure it will take a while to heat the water but will it work? I don't need steaming hot water, just enough to take a quick shower with.

I'll wire the netural and the line wire from a 120 volt power cord to the junction box on the water heater where the 240 volt supply from my breaker box would normally connect then just plug it in to my generator.

Could this damage anything on the water heater in any way?

Back To Top PM Quote Reply  

 Posted: Fri Feb 18th, 2011 09:45 am
  PM Quote Reply
2nd Post
energyexpert
Member


Joined: Mon May 22nd, 2006
Location: Asheville
Posts: 646
Status: 
Offline
I've had mine wired at 120 volts for years.  When thermostats open, a spark occurs.  This burns the contact.  Contacts only have so much life.  One half the voltage and one half the current means one fourth the power and should mean one fourth the spark.  Element should also last indefinitely.

If I were doing it:  Turn off the main and backfeed both phases in the panel.  Turn off all breakers but the load you want to run.  Of course no 240 loads can (will) run.  In this case you would take the white wire (usually taped black) feeding the WH and lift it from the breaker and land on the neutral bar.

IF YOU FAIL TO TURN OFF THE MAIN WHEN BACKFEEDING, ELECTRICITY CAN GO BACK THROUGH THE TRANSFORMER AND KILL A LINEMAN WORKING.  BE CAREFUL!!!

Below is from my post yesterday, 17 Feb 2011, 1231 hours "New Dilema".  It describes how to wire both thermostats for parallel operation when wired at 120 volts.  This way you can can 1750 watts on normal power (or with the generator if generator output is big enough).

Scale on elements does not change water heater efficiency.  What it does do is to create an interference with heat transfer.  But the same heat MUST be transferred.  So the element center line temperature continues to rise over time to drive the heat flux through the crud until finally the element melts.

To eliminate this problem at my house, I have rewired the supply voltage from 240 volts to 120 volts.  Ohm's Law for a resistance circuit states E = IR.  For the equation to stay balanced, if E (volts) goes to half then I (current) also goes to half.  W (power) = EI.  So if both E and I go to one half, then power goes to 25%.

To offset this slow recovery I have paralleled the thermostats.
Look in Tanklets and Electric WH Issues.
There is a picture of the top thermostat.
First rewire supply to 120 volts.
Turn power off to WH.
Lift black wire from thermostat lower right screw.
Land black wire on thermostat one screw above where yellow wire is landed.
Restore power.

Each thermostat can now operate as needed at 25%.  Total output is 50% of nameplate.

Having a larger volume heater is helpful for this strategy.  I have a 105 gallon Marathon and heat off-peak only at $0.0515/kWh.

A 4500 watt element operating continually for 24 hours will produce 480 gallons of 90F rise water!

David

Back To Top PM Quote Reply

 Posted: Sat Feb 19th, 2011 09:27 am
  PM Quote Reply
3rd Post
undee70ss
Member


Joined: Fri Feb 8th, 2008
Location: Illinois USA
Posts: 123
Status: 
Offline
energyexpert wrote: If I were doing it:  Turn off the main and backfeed both phases in the panel.  Turn off all breakers but the load you want to run.  Of course no 240 loads can (will) run.  In this case you would take the white wire (usually taped black) feeding the WH and lift it from the breaker and land on the neutral bar.

IF YOU FAIL TO TURN OFF THE MAIN WHEN BACKFEEDING, ELECTRICITY CAN GO BACK THROUGH THE TRANSFORMER AND KILL A LINEMAN WORKING.  BE CAREFUL!!!


David


As stated, be VERY careful when backfeeding. The electric co will give you a hard time if you mess up and backfeed their lines. You are suppose to have a transfer switch when connecting a generator to house wiring. (they are designed to be dummy proof when properly installed so you can't backfeed the electric co lines) The safest way without a transfer switch is to disconnect all wires from house wiring for the item you want to power, and wire directly to the generator. (use a fuse or breaker of proper size if the generators breaker is to large for the item you want to power.  

Info on transfer switches. http://www.nooutage.com/manual-sw-help.htm

Back To Top PM Quote Reply  

 Posted: Sun Feb 20th, 2011 01:35 am
  PM Quote Reply
4th Post
murphy
Member
 

Joined: Sun Feb 13th, 2011
Location:  
Posts: 6
Status: 
Offline
I'm well aware of that. I'm not feeding any power in to anything that could back feed in to the power lines. The wiring from the breaker is disconnected at the water heater and I have a plug going from the generator directly to the water heater.

It works great by the way. It is slow at heating but at least I have hot water.

Back To Top PM Quote Reply

 Posted: Sun Feb 20th, 2011 02:19 am
  PM Quote Reply
5th Post
elenano
Member


Joined: Sat Sep 11th, 2004
Location: USA
Posts: 3252
Status: 
Offline
But don't you long for the good old days? A hundred years ago, nobody fretted about this because nobody bathed.

Modern life just gets more complicated and makes us long for things we really don't need.:P Hi-def TVs, computers, Ferraris, deodorant....

Randy Schuyler

Back To Top PM Quote Reply  

 Posted: Sun Feb 20th, 2011 10:39 pm
  PM Quote Reply
6th Post
eleent
Member


Joined: Sat Sep 11th, 2004
Location:  
Posts: 3456
Status: 
Offline
Hmmm:  Hot water soothes and possibly civilizes the wild beast.. or at least makes us a little less gamy :P  Also it reduces the need for deodorant!  I like much of what the good old days offered, but I'm keeping my hot water :cool:

Yours,  Larry

Back To Top PM Quote Reply

 Posted: Mon Feb 21st, 2011 12:35 am
  PM Quote Reply
7th Post
elenano
Member


Joined: Sat Sep 11th, 2004
Location: USA
Posts: 3252
Status: 
Offline
Are you accusing me of being high?;)

Randy Schuyler

Back To Top PM Quote Reply  

 Posted: Mon Feb 21st, 2011 03:51 am
  PM Quote Reply
8th Post
eleent
Member


Joined: Sat Sep 11th, 2004
Location:  
Posts: 3456
Status: 
Offline
Well:  I KNEW there was a reason I kept that ten foot pole around :dude:

:~)

Back To Top PM Quote Reply

Current time is 02:06 pm  
thetankatwaterheaterrescue.com > Forums > The Tank > Can I run an electric water heater on a 120 volt generator? Top




UltraBB 1.17 Copyright © 2007-2008 Data 1 Systems