How to convert reading of amps into amp hours

[donradcliffe]

Originally Posted by guyrj33

and
power watts = VxI which is an instantaneous reading, you need power for a length of time to do any work. That's why our electric bills use KWH Killo Watt Hours as the unit of billing.

12 volts x 1 amp = 12 watts
120 volts x 1 amps = 120 watts

with at 12v battery
1 amp x 1 hour = 1 amp hour or 12 watts (the 12 volts are implied)

with a 120v circuit
1 amp x 1 hour = 1 amp hour or 120 watts (the 120 volts are implied)

From the above it's easy to see how amp hour is an imprecise term and that's it's better to use watts and watt hours when converting between systems.

Just when the newbies were starting to understand, you had to muddy it up again.

at 12v, 1 amp x 1 hour= 1 amp hour = 12 watt HOURS = 0.012 Kilowatt hours

[guyrj33]

Originally Posted by donradcliffe

Just when the newbies were starting to understand, you had to muddy it up again.

at 12v, 1 amp x 1 hour= 1 amp hour = 12 watt HOURS = 0.012 Kilowatt hours

Don, i'm not sure, but I'll assume your comment is intended to be humorous.
I was just trying to supply some numerical examples of the points being discussed.

[Kelkara]

Originally Posted by guyrj33

Don, i'm not sure, but I'll assume your comment is intended to be humorous.
I was just trying to supply some numerical examples of the points being discussed.

Your example would have been excellent ... except you missed out the word "hours" ... you said "watts" instead of "watt-hours". Hopefully just an honest mistake that was well corrected.



There are people on this forum who happily use such erroneous units when discussing electricity, but when trying to teach a newbie what's what (pun intended) I feel this is a great disservice. Especially on this thread when the OP effectively asked in the title what is the difference between "amps" and "amp-hours" ... that "hours" is important.

[Jim Cate]

Originally Posted by Kelkara

Your example would have been excellent ... except you missed out the word "hours" ... you said "watts" instead of "watt-hours". Hopefully just an honest mistake that was well corrected.



There are people on this forum who happily use such erroneous units when discussing electricity, but when trying to teach a newbie what's what (pun intended) I feel this is a great disservice. Especially on this thread when the OP effectively asked in the title what is the difference between "amps" and "amp-hours" ... that "hours" is important.

Well said... complete agreement from me!

Jim

[Dave22q]

IMHO amps is a measure of electron flow, AH (amp-hours) is the product of flow times time. It is frequently used as a measure of battery capacity. Watts is a measure of power and is computed as volts times amps. Your cooker draws 1.7 amps at 110 volts so uses 187 watts. To get those watts from your 12 volt system you need to draw 15.6 amps (187/12). Inverters are not perfect so I would up that figure by 10 or 20%, say 18. the drain on your batteries is the amps time the hours used. e.g. 10 minutes at 18 amps is 10 amp-hours. Hope this helps.

[alansmith]

My Goodness, you fellas are gems. Honestly, reading all of the different comments are like warm free bread. It is interesting, da, how many ways a thing can be said... and you glean different things from different minds as they explain electrical theory. Even guys talking about other posts help illuminate 'watt' is at hand here. I've enjoyed this.

[alansmith]

See if I can post some pics of what I got here.

[alansmith]

So, fellas, you can see that it is reading amps in AC mode. You can see what the wattage is on this induction top. I followed the manufacturer guidelines in how to zero the line. No probes used. Just the yellow jaws. The 1.7 amps must have been from medium power.

So, the 2.47 amps @ 110 volts = 2.47 amp hr = 272 watt hr.
So when you guys are thinking house batteries are you thinking watt hours or amp hours?

Right now I have a trimaran, 30 foot Condor, in San Carlos. One battery is pretty dogged and another rather new. But there is less than 180-190 amp hrs. They are kept topped off with a pmm???? Controller and like a 50 watt panel.

So, me and the missus will retire July 2019. I will take a month in November to go down
And get familiar with her. I really don't mind throwing some money into her to make life comfortable. I also have a 28 foot Sharpie that Steadman found in Craig's list San Francisco. She is very rudimentary.

I have an Engle refridge. I am deeply interested in Lithium and solar panels. I have a lot of real estate to farm out with a 23 foot beam. So, the boat will never be a round tripper. I am 67. For comfort we want water, cooking, and some refrigeration. We won't have huge electronic arrays. Manual pumps are good for us. My wife likes to be clean before hittin the sack. Past skipper for quetzal used the Engle as a freezer. Then used a high quality cooler for mayonasise, luncheon meats, and what not. He would freeze water bottles and use them to cool the cooler. Most likely no more than a month at a time without running for supplies.

This is our agenda. So figuring out how much ampage is consumed... how much energy you use... how much can u store... how much can you put back in ...allowing for weather phenomenon... etc. it is heady stuff, da?

[Bleemus]

You can't measure amps with the ammeter wrapped around the whole power cord. You need to split the cord and only measure one leg (wire) not both.

Also you need to look how to zero your ammeter clamp before applying it. It should read close to zero when wrapped around both legs (wires) like you have pictured.

[Wotname]

Originally Posted by alansmith

So, fellas, .........

So, the 2.47 amps @ 110 volts = 2.47 amp hr = 272 watt hr.
So when you guys are thinking house batteries are you thinking watt hours or amp hours?

............ it is heady stuff, da?

You are not quite there yet (but getting closer )

2.47 amps @ 110 volts = 272 watts, not watt hr.

If you had it turned on for one hour, then you would have used 272 watt hours and so on - turned on for say 3 hours and you would have used 816 watt hours.

Regarding house batteries, it is assumed they are 12 Volts and we use amp hours. To get to watt hours, you have to times the the amp hours by 12 to get watt hours i.e. volts (12) x current (amps) x time (hours) = watt hours.

[Wotname]

Originally Posted by Kelkara

Your example would have been excellent ... except you missed out the word "hours" ... you said "watts" instead of "watt-hours". Hopefully just an honest mistake that was well corrected.



There are people on this forum who happily use such erroneous units when discussing electricity, but when trying to teach a newbie what's what (pun intended) I feel this is a great disservice. Especially on this thread when the OP effectively asked in the title what is the difference between "amps" and "amp-hours" ... that "hours" is important.

Originally Posted by Jim Cate

Well said... complete agreement from me!

Jim

These two posts sums up this thread perfectly

[Wotname]

Originally Posted by alansmith

........
I am a scientist in Health Care setting. ........

Thanks for your input...alan

@alansmith, clearly you know about maths and equations and so forth but you probably never had to apply those skills to electrical circuits, hence your questions on this thread.

The following might help...

Clearly how much electricity you can extract from you battery bank is defined by the capacity of the bank (I realised you already know this ).

The principle considerations to determine the capacity is to know the voltage, the current and the time they are used.

So:
the voltage units are "volts"
the current units are "amps"
the time units are "hours"

The relationship between them is simple.

Current times "time" is called amp hours.

Voltage times the current could have been called "volt amps" but we don't do that, we call them watts - historical thing really. However until you get your head around it, they are the same thing - a watt is a volt amp.

Voltage multiplied by the current multiple by the time could have been called volt amp hours but because we use the unit "watt" for "volt amps", it becomes watt hours (rather than volt amp hours).

As posted by others, the usage of the term "amp hours" usually refers to a 12 volt DC house bank and as the 12 volts is inferred, the term capacity of a 12 volt system is given as "amp hours" rather than a more correct "watt hours".

[Jim Cate]

Please note that the label on the cooker says "1800 watts". This is likely a good approximation of the power consumed at its highest setting, which is likely what you will use when boiling a kettle.

You should perhaps use that number when trying to calculate your battery usage with this device. Your measurement seems to have been in error in some way.

Jim

[Sailmonkey]

Originally Posted by Jim Cate

You should perhaps use that number when trying to calculate your battery usage with this device. Your measurement seems to have been in error in some way.

Jim

There is a HUGE error in measurement. Clamp meters don’t work unless on a single conductor. The OP is clamping both hot/neutral/ground at the same time.

[Kelkara]

Let's start by using the value on the manufacture's label, and see what you should expect.

1800W
120V

So if your induction top is working at full power it will draw 1800/120 = 15A ... This is the 120V draw on the inverter.

( if you're only measuring 2.47 amps ... either the cooktop is only simmering, or your measurement is faulty.)

But the inverter has to draw down the battery to supply that power ... on the 12V side, you still need to supply 1800W (plus some losses in the inverter): 1800/12 = 150A ... This is the 12V draw on the battery.

So ... if your batteries are 180Ah then, if they start out full, and you start drawing 150A...

after 10 minutes (1/6 hr) of cooking you will have used 150A * 1/6 hr = 25 Ah.
after 20 minutes (1/3 hr) of cooking you will have used 150A * 1/3 hr = 50 Ah.
after 30 minutes (1/2 hr) of cooking you will have used 150A * 1/2 hr = 75 Ah.
after 40 minutes (2/3 hr) of cooking you will have used 150A * 2/3 hr = 100 Ah.

by now your batteries are seriously depleted and you risk damaging them if you keep going

after 50 minutes (5/6 hr) of cooking you will have used 150A * 5/6 hr = 125 Ah.
after 1 hour of cooking you will have used 150A * 1 hr = 150 Ah.
after 1 hour 10 minutes (7/6 hr) of cooking you will have used 150A * 7/6 hr = 175 Ah.

And now your batteries are well and truly dead and likely damaged too ... in fact this assumes a hypothetically perfect battery, a real battery won't last that long at such a high current.