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Old 08-06-2018, 01:14   #1
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How to convert reading of amps into amp hours

Mr Brillance here,

Okay, so i bought a half way decent multimeter with the jaws. I have a new to me boat in San Carlos Mexico. I want to go Lithium, Solar, and maybe a small Ryobi or Honda generator.

I am a scientist in Health Care setting. But i have rebuilt 2 houses in the last 15 years with just about everything and anything you can think of. I ain't bragging. I'm just that poor. I have rewired multiple houses. One even had the porcelain knobs with bare wires up in the roof. What a miserable arse job that was. I digress.

Oh yah...back to the multimeter...sorry...So, I took one of our induction modules in the kitchen and placed a steel pan with water on it. Turned that sucker up to high power. Put the jaws of the multimeter on it and got an amperage reading. 1.7 amps.

To convert that reading to amp hrs I am assuming that i have to multiply that reading by 60 to see how many amp hrs it is consuming....did i get that right? So...1.7 X 60 =102 amp hrs?????

If i buggered that up set me straight...I am reading all the delicious threads on Lithium right now. It is amazing stuff. Thanks for your input...alan
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Old 08-06-2018, 02:04   #2
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Re: How to convert reading of amps into amp hours

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Originally Posted by alansmith View Post
Mr Brillance here,

Okay, so i bought a half way decent multimeter with the jaws. I have a new to me boat in San Carlos Mexico. I want to go Lithium, Solar, and maybe a small Ryobi or Honda generator.

I am a scientist in Health Care setting. But i have rebuilt 2 houses in the last 15 years with just about everything and anything you can think of. I ain't bragging. I'm just that poor. I have rewired multiple houses. One even had the porcelain knobs with bare wires up in the roof. What a miserable arse job that was. I digress.

Oh yah...back to the multimeter...sorry...So, I took one of our induction modules in the kitchen and placed a steel pan with water on it. Turned that sucker up to high power. Put the jaws of the multimeter on it and got an amperage reading. 1.7 amps.

To convert that reading to amp hrs I am assuming that i have to multiply that reading by 60 to see how many amp hrs it is consuming....did i get that right? So...1.7 X 60 =102 amp hrs?????

If i buggered that up set me straight...I am reading all the delicious threads on Lithium right now. It is amazing stuff. Thanks for your input...alan

Correct. Amps x hrs = amp hrs
Also Watts x hrs = watt hrs


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Old 08-06-2018, 02:08   #3
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Re: How to convert reading of amps into amp hours

Alan, it should be 1.7ah at 110v or 240v depending on the mains supply. Surprised the induction hob doesn't say how many watts it is, because that would be a way to check the amperage too.

1.7ah looks about right, our small 1.5 litre slow cooker is 120w at 240v, so 0.5ah. Or 120w at 12v so 10ah. However, and this may not affect you, a slow cooker has a thermometer so switches off when up to temperature and back on again when cooled slightly. This cycling makes estimating cookers and fridges tricky.

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Old 08-06-2018, 02:10   #4
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Re: How to convert reading of amps into amp hours

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Originally Posted by alansmith View Post
Mr Brillance here,

...........
To convert that reading to amp hrs I am assuming that i have to multiply that reading by 60 to see how many amp hrs it is consuming....did i get that right? So...1.7 X 60 =102 amp hrs?????

If i buggered that up set me straight...I am reading all the delicious threads on Lithium right now. It is amazing stuff. Thanks for your input...alan
G'day Mr Brillance, allow me to advise you that yes, you have buggered that up.

If your appliance is drawing 1.7 amps for one hour, you have used 1.7 amp hours. If you run it for two hours, then you have used 3.4 amp hours. If say it was only on for 30 minutes, then you have used 0.85 amp hours.

Simply put, you multiply the number of amps for the duration of use in hours, this gives you amp hours. Of course you could use amp minutes if you wanted to, but usually we don't
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Old 08-06-2018, 02:13   #5
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Re: How to convert reading of amps into amp hours

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Correct. Amps x hrs = amp hrs
Also Watts x hrs = watt hrs


Attachment 171271
I think you missed the fact that the OP multiplied the amps by 60 to get amp hours which of course is incorrect .
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Old 08-06-2018, 02:16   #6
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Re: How to convert reading of amps into amp hours

@alansmith, be aware that say 2 amp hours at mains voltage is much more power than 2 amp hours at 12V.
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Old 08-06-2018, 02:37   #7
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Re: How to convert reading of amps into amp hours

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I think you missed the fact that the OP multiplied the amps by 60 to get amp hours which of course is incorrect .

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Old 08-06-2018, 03:31   #8
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Re: How to convert reading of amps into amp hours

Ok, the rabbit hole just swallowed another clueless victim. So, let me see here if I understood. On dry land at 110 voltage my meter shows me 1.7 amps. If I used that induction stove top for one hour it would be 1.7 amp hours. If I used it for 30 minutes it would be 0.85 amp hrs. Do I have that correct?

Okay, if I take one of these induction tops onto a boat with 600 amp hr lithium batteries at 12 volts what am I doing with amp hrs after I run it through an inverter? Can the inverter handle that intense of a draw?
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Old 08-06-2018, 03:34   #9
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Re: How to convert reading of amps into amp hours

I can boil water in just a few minutes at home. I must be smoking something funny to be getting all happy about induction cooking. Bring me back to earth
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Old 08-06-2018, 04:06   #10
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Re: How to convert reading of amps into amp hours

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Originally Posted by alansmith View Post
Ok, the rabbit hole just swallowed another clueless victim. So, let me see here if I understood. On dry land at 110 voltage my meter shows me 1.7 amps. If I used that induction stove top for one hour it would be 1.7 amp hours. If I used it for 30 minutes it would be 0.85 amp hrs. Do I have that correct?

Okay, if I take one of these induction tops onto a boat with 600 amp hr lithium batteries at 12 volts what am I doing with amp hrs after I run it through an inverter? Can the inverter handle that intense of a draw?
Alan,

Let's say your induction heater uses 1.7A at 120V. That is 204 watts. It's going to take a long time to boil water at that low power. So I guess you need to put a pot of water on the cooker, set it to boil mode and measure the amperage again. You should get something like 5-7A. Remember that an induction top uses different current depending on the power setting and the type of pot.

Yes, an inverter can run an induction top. To compute the number of amp-hours the cook top will use you can use this simple formula. Let's call the number of AC amps A measured by your probe, and the number of minutes the cook top runs M then the formula is:

Amp-Hours = A X 12 X M / 60

Example: A = 1.7 and minutes = 30

Amp-hours = 10.2AH

This is a close approximation. The number 12 is a factor to account for the efficiency of the inverter as well as compensate for the fact that the battery is 12V and the cook top uses 120V.

But I think the value of 1.7A is not correct for a cook top that is actually heating water.
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Old 08-06-2018, 04:11   #11
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Re: How to convert reading of amps into amp hours

So at home 1.7AH at 110 volts equals about 187 watts.

When on the boat the stove still needs 187 watts but from 12v house bank which equals about 15.6AH.

Chances are the bank is nearer 13 volts so 14.3AH.

Then you need a fudge factor if you don't know how efficient the invert is, so lets say at 13v for each hour you use the induction hob is will take 16AH from the batteries.

The figures are slightly different from TD's above due to the different voltage and fudge factor, but are close enough for government work or a 600AH battery bank so not to worry.

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Old 08-06-2018, 04:55   #12
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Re: How to convert reading of amps into amp hours

amp hour is a measurement of charge in the battery. 1 amp hour equals the capacity of 1 amp draw for 1 hour. Those AH's are different depending on the rate of discharge. AH is not a measurement of power. We need to work with watts to get a closer approximation of power used during any work by appliances. Converting 120 volt x amps = watts to 12 volt x amps = watts is the only way to determine battery need. Remembering the loss during any conversion.
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Old 08-06-2018, 05:48   #13
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Re: How to convert reading of amps into amp hours

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Originally Posted by alansmith View Post
Ok, the rabbit hole just swallowed another clueless victim. So, let me see here if I understood. On dry land at 110 voltage my meter shows me 1.7 amps. If I used that induction stove top for one hour it would be 1.7 amp hours. If I used it for 30 minutes it would be 0.85 amp hrs. Do I have that correct?

Okay, if I take one of these induction tops onto a boat with 600 amp hr lithium batteries at 12 volts what am I doing with amp hrs after I run it through an inverter? Can the inverter handle that intense of a draw?


What are you clamping?

If itís anything thing other than 1-conductor then youíre not measuring the current correctly.
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Old 08-06-2018, 05:56   #14
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Re: How to convert reading of amps into amp hours

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This cycling makes estimating cookers and fridges tricky.
Easy peasy with the right tools.

A reasonably accurate AH-counting meter can be bought for under $60

If you will want to ongoing estimate SoC of your bank, a quality BM can also be used for the same purpose, more accurate, but costs a lot more.

They also show instantaneous Amps real-time like a clamp meter.
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Old 08-06-2018, 05:58   #15
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Re: How to convert reading of amps into amp hours

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@alansmith, be aware that say 2 amp hours at mains voltage is much more power than 2 amp hours at 12V.
Which is why Watts are a better unit for AC loads in a multi-voltage context.

AH usually implies DC only.
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