Reply
 
Thread Tools Display Modes
Old 09-02-2012, 01:46 AM   #21
2012 Solera
 
Join Date: May 2012
Posts: 982
Lou used 1000 watts, which he indicated was what his water heater is equipped with, to demonstrate the math. I followed his example.
__________________

__________________
JLeising is offline   Reply With Quote
Old 09-02-2012, 06:58 AM   #22
Site Team - Lou
 
Herk7769's Avatar
 
Join Date: Oct 2009
Location: South Eastern PA
Posts: 21,154
Quote:
Originally Posted by jk31668 View Post
i have a 6 gal suburban elect/gas water heater. i am being told the elect mode has limited use particulary in the summer when the ac is being used as it pulls too much juice when the ac, refer, and other applicances are on. so, i guess my question is...what good is it? only use when weather is cooler?
Since this is the heater I have and my manual states it has a 1000 watt element and the amperage can vary up to 12 amps. I made the leap.
Attached Thumbnails
Click image for larger version

Name:	AC diagram.jpg
Views:	57
Size:	69.7 KB
ID:	19011  
Attached Files
File Type: pdf subsw06.pdf (2.23 MB, 17 views)
__________________

__________________

Lou and Laura with Bella - German Short Hair Pointer
2008 GMC Sierra 2500HD Crewcab SB Allison Duramax
2010 Flagstaff 8526RLWS - Superglide 3300
HAM CALLSIGN - KC3FFW
Herk7769 is offline   Reply With Quote
Old 09-02-2012, 07:29 AM   #23
Site Team - Lou
 
Herk7769's Avatar
 
Join Date: Oct 2009
Location: South Eastern PA
Posts: 21,154
Quote:
Originally Posted by JLeising View Post
By the way - love your posts - keep up the good work! This is only the second one I disagreed with ... gives you about a 99.9999% hit rate!
Well thank you.

I think I see what you are saying. That as the voltage drops, and since the resistance of the element is fixed, it forces the amperage to decrease as well effectively reducing the efficiency of the heater. IE you won't get the full 1000 Watts of heat transfer to the water. (Like a dim bulb trying to light a room).

I was not using Ohm's Law V (or E) = IR to do the calculations; but the one to calculate P (or Power). Power as you may remember is the application of electricity (in Joules) over time (in seconds).

1 Joule of electricity delivered in 1 second is a Watt.

The formula to calculate Watts is Amps times Volts or P=IV
The effective delivery of that electricity is over time is P or power.

So in order to calculate the actual effect of a voltage reduction we would need to use the equations in this article http://en.wikipedia.org/wiki/Power_(physics)) to determine the new current being drawn at the reduced voltage based on the "mostly fixed" - temperature dependent - resistance (R) in the heating element core at the lower voltage.

Then you can multiply the actual incoming voltage (say 100 Volts) times the calculated (or observed) amperage to find the actual watts being delivered to the water.

So if the heater at "standard conditions" delivers 1000 Watts to the water by consuming 120 volts at 8.33 amps we can use that amperage to calculate the resistance (R) of the element using Ohms's Law E=IR or 120=8.33xR

This gives the 6 Gallon Suburban heating element an R of 120/8.33 or 14.4 Ohms. So if the incoming voltage is dropped to 100 volts and the resistance stays "almost" fixed at 14.4 Ohms, then the current consumed will be V=IR or I=V/R or 6.9 amps instead of 8.333

Since there is only 6.9 Amps of current at 100 Volts being delivered to the heating element the Wattage of the element falls to 694 Watts (an almost 30% reduction in an already inefficient way of heating the hot water heater).

If I got that right, it makes even MORE sense to use propane to heat the water in the summer when delivered volts are reduced by the power company and the physics of the campground's power grid.

I assume that since a motor or "Inductive" load will not function at all at reduced power, the capacitors keep the watts being delivered pretty much constant and as such increase the amperage demand as the voltage drops until the breaker pops.

I got it now. Thank you.

HE CAN BE TAUGHT!
__________________

__________________

Lou and Laura with Bella - German Short Hair Pointer
2008 GMC Sierra 2500HD Crewcab SB Allison Duramax
2010 Flagstaff 8526RLWS - Superglide 3300
HAM CALLSIGN - KC3FFW
Herk7769 is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



» Virginia Campgrounds

Reviews provided by




ForestRiverForums.com is not in any way associated with Forest River, Inc. or its associated RV manufacturing divisions.


Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -5. The time now is 06:14 AM.