Two questions about amperage draw

[StuM]

Originally Posted by Wotname

TL;DR
Amp per hour = amps divided by hours (ie A/h). This is basically useless info!

A very simple numerical example.
10 amps multiplied by 10 hours is 10 x 10 = 100 amp hours (100Ah) (total consumed)

10 amps divided by 10 hours is 10 / 10 = 1 amp per hour (1A/h) (how fast the amperage is changing)

[dfelsent]

Oh. All this amps per hour and amps and amp-hours.

Again as many say amps (amperes) is a measurement of current. At the time you measure it. An amp. Two amps. a billion amps. A millionth of an amp.
Kind of like how sunny is it. Dim. Really sunny. Overcast. How is it RIGHT NOW.

Amp-hours is a measurement of current over a period of time.
My fridge used 5 amps for a day. (5 x 24 amp-hours) 120 Ah. My led navigation lights used 0.5 (1/2) amps for ten days. (0.5x24x10) 120 Ah. I used my battery as a welder for 14.4 minutes. (500 x (14.4/60) ) = 120 Ah.

It was really sunny and the temperature went up all day and it got hot. It was overcast and it never got warm. That’s about how much energy your surroundings absorbed during the day.

Amp hours are like that. How much energy was used over an hour.

All these examples use the same number of amp hours and discharge your battery about the same amount.

That is why amp hours is a useful measure.

Amp hours is the number of amps times the number of hours.

In the examples above, if you had a pair of 110 Ah capacity group 31 batteries you would take them from full to just less than half full.

220ah capacity minus 120ah used is 100 Ah left. Or 100/220 or about 45%.

Amps per hour is a different thing than amp-hours and not so useful for our boats.

[svfinlandia]

Originally Posted by StuM

"amp hours" is the energy consumed or generated at a steady rate of current flow (amps) for one hour. 2Ah is the energy comnsumed or generated with a current flow of 2 amps for 1 hour, or 1 amp for 2 hours ,or 0.1 amps for 10 hours etc, i.e. it is Amps multiplied by hours

Thank you StuM. A very clear and succinct explanation. I do greatly appreciate it.

Al, S/V Finlandia

[Tmacmi]

Thanks for the education.

[ErnestV]

Originally Posted by Tmacmi

We have one of those Costway 54 quart refrigerator/coolers. Someone on Amazon (not the best resource) says it draws 3.8 amps/hour. Does anybody have more confirmed data for that? Or does it at least sound plausible?

The Costway 54 offers, according to internet sources, 50W (38.5W in eco) performance. According to Ohms law this yields 4.17A (3.21A in eco) current draw, at 12V. Add your personal safety margin, e.g. 5%, and you're at 4.4A (3.4A in eco). Make sure you select the right cable for the bigger amperage, depending on length, and the correct fuse (at the battery side).

[PaulCrawhorn]

Amps is a flow rate, already has a "per unit of time" in the meaning, so water analogy, like 10 liters per hour.

Where AH "amp hour" has no "per", is not a rate but a static, fixed quantity of energy, like 100 liters of water in a container.

AH per time period makes perfect sense, as in "this device consumes 15 AH per 24 hours".

That could be from consuming at 100A for a sort time, or a 1A rate for longer periods, or varying continuously between those two rates.

"Amps per hour" is ambiguous and often verging on nonsensical, definitely to be avoided.

[PaulCrawhorn]

> Let's say that the refrigerator is cycling 50% of the time. When running its at 3.8 amps when off its at .5 amps (made that up for the example). That would suggest it would draw 129 amps in one hour?

3.8A for 30 minutes = 1.8 AH
0.5A for the other half is 0.25 AH

added together, 2.05 AH average per hour.

Which makes sense intuitively, halfway between 3.8 AH and 0.5 AH per hour.