Dual-Purpose Batteries for high-draw applications?

dynaco1

Member
Great exchange in this string

Back to Hein’s suggestion of using a smaller 800W water kettle versus a larger kettle in order to use a smaller inverter.

Questions:

Given the same amount and temperature of tap water, wouldn’t an 800W water kettle take twice the time but the same amount of power to boil the water as does a 1600W kettle
 
Last edited:

john61ct

Active member
And with lead's Peukert coefficient you have a much higher total Ah capacity at a lower current rate. And less voltage sag, so later inverter LVC.
 

HarryN

Well-known member
Yes, and contemplate the words "a watched pot never boils".

Let's all go find some old 3G cell phones because no one needs 4G LTE.

Can we also bring along a computer with a spinning hard drive? After all, who cares if it takes 100 seconds to boot windows instead of 10?

I know that my wife will certainly enjoy that not only can she only use one appliance at a time, but that each one will take 2x as long to accomplish the same task. Can hear her bragging to her friends already about how great of job her husband did building out an expensive van and how great the vacation was.
 
Last edited:

rollerbearing

Well-known member
Windows boots in 10 seconds - NO WAY:lol:

I think it is perfectly reasonable to downsize the wattage in exchange for a little longer "cook" time. I used to have two coffee makers, one big - made all the coffee at once 1200W, and one small - made the coffee in two pots 600w. A pot took about the same time in either one.

If we had shore power we'd bring the big one. If not we'd use the smaller one. The smaller one always worked just fine and there was an excuse to make a 2nd fresh pot - we just quit ever bringing the big one.

So in addition to using less watts they often use less SPACE which is a benefit in a van.
 
Last edited:

GSWatson

2013 144
FWIW, here’s the kettle I use. And since I make my coffee in an Aeropress, I only boil the water I need for my travel mug.

Proctor Silex Compact Electric Kettle for Tea and Hot Water, Cordless, Auto-Shutof... https://www.amazon.com/dp/B07B51N79T/ref=cm_sw_r_sms_c_api_i_N5bZDbV3QXQMH

I also use a 2l InstaPor for the majority of my cooking.

I do have a Kisae 2kw inverter, sized originally rose he able to run a small table saw, but cordless tools now do 99% of what I need.


Cheers,
Greg
 
Last edited:

elemental

Wherever you go, there you are.
Given the same amount and temperature of tap water, wouldn’t an 800W water kettle take twice the time but the same amount of power to boil the water as does a 1600W kettle
To answer your question directly, yes... and at the same time, no.

Yes: The same amount of energy is required to heat a fixed quantity of water from one particular temperature to a second higher particular temperature no matter whether the energy is applied at an 800W/second rate or a 1600W/second rate, so the 800W kettle requires the same amount of power as a 1600W kettle, at 1/2 the rate, expended over twice the time. Theoretically, in an ideal world.

No: In the case of an electric water kettle drawing power from a lead acid battery storage system, given the same physical wiring, battery storage, etc., a higher current draw results in more losses in the system delivering the power to the kettle that heats the water than a lower current draw. The biggest practical loss may be the one mentioned by john61ct, Peukert's law. Simply put, the usable energy storage capacity of lead acid batteries depends on the discharge rate; higher discharge rates lower the usable energy storage capacity. So using the 800W kettle to heat the water reduces the usable energy stored in a lead acid battery system by less than using the 1600W kettle (but takes twice as long). Practically, in the real world.

Assuming, of course, that the rate of loss of heat energy from the system during the heating period isn't high enough to make a significant difference over the increased time required. I.e., that both the 800W kettle and 1600W kettle have decent insulative qualities and/or that the quantity of water is small enough that the desired increase in temperature can be achieved in a relative short period of time.
 

elemental

Wherever you go, there you are.
If one has time to kill, one can be even more efficient with this 1200ml DC electric kettle. 120 Watts on 12VDC (so only 10 amp draw)... but it takes 45 minutes to boil 40 fl. oz. of water (probably from "room temperature" and not a typical morning wake up van interior temperature in chillier ambient temperatures). I'm using my propane stove, since I don't otherwise need an inverter.
 

Midwestdrifter

Engineer In Residence
I'm probably guilty of using them interchangeably in common conversations, but power does not equal energy. Energy is power over time, power is an instantaneous measurement. Watt-hours is energy, watts is power.

So heating the water takes the same energy, but when you halve the power, you double the time.
 

elemental

Wherever you go, there you are.
I'm probably guilty of using them interchangeably in common conversations, but power does not equal energy. Energy is power over time, power is an instantaneous measurement. Watt-hours is energy, watts is power.

So heating the water takes the same energy, but when you halve the power, you double the time.
I used power in the colloquial sense at one point in my answer, the same as it seemed to be used in the original question. Had I been more on the ball, I might have made the same point as you have here in the interest of being totally clear and been more careful in my own language as well.

Thanks!
 

Top Bottom