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Old 05-10-2015, 05:16   #211
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Re: Why no Residential Fridges?

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That is the fundamental mistake you keep making and is the cause of all of this discussion. While gallon is closely related to volume. Ampere is NOT. It is closely related to Gallons per minute - it is the equivalent to Coulombs per second where the Coulomb is the equivalent of a Gallon (As clearly pointed out above, Coulombs can be directly converted to Amp Hours - not to Amps).

Gallons per minute has everything to do with speed. For a given pipe, the more gallons per minute you put through, the faster the water flows.
I won't get involved with fluids and such as I am not that good with them - apart from the beverages that is .

But I note that much of this thread is a units and dimensions and interestingly (to me at least), a Coulomb although the equivalent of 1 Ampere second is actually considered to be dimensionless quantity.

So comparing Coulombs to gallons may not be helpful.

Time for bed
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Old 05-10-2015, 05:47   #212
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Re: Why no Residential Fridges?

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Back in 1885 Sir Edmond Burbank was the first to discover that the longer an argument goes, the further is drifts from the topic.

I hope everyone has now learned a good lesson in how internet chat rooms work.

Ask about an apple...get answers on how to make a fruit salad.
Enjoy.

ALL threads drift, it's their nature, and sometimes there is a transfer of knowledge, but often it's just beating ones chest that goes on.

But I would differ with you on your point that an amp, is an amp.
I would argue that is not true, that in fact when I'm discharging my batteries and voltage is at 12.5 V, that amp is 12.5 watts, right?
But when I'm charging my batteries and the voltage is 14.3, then that amp is 14.3 watts.
Now I suck at math, but that is I think about a 13% difference.
I think we have a tendency to ignore that though as it's probably about the same difference that it takes to re-charge a battery. You have to put more current into a battery to recharge it, or it would be 100% efficient, and nothing is, or at least maybe very few things are.

I too wish we would use watts as voltage is accounted for in a watt, 1 watt is the same amount of power whether the voltage is 12, 14, 120 or 220 and I think that was to OP's point, and I agree, but then I wish the US would have adopted the Metric system back in the 70's when we were supposed to.


OK, all this arguments about refrigeration efficiency is really and truly almost all for naught, compressor efficiency is a very, very small portion of the problem, the overwhelmingly large variable is insulation, If I had a vacuum insulated fridge box, I could install anyone's ice box conversion and would have an extremely efficient system if I left the door closed. I like most have a box that was built 27 yrs ago, with spray in insulation, which is hit and miss at best, there are some voids. You can install anyone's system in my box and it will be inefficient, because of the insulation, and that is not the systems fault.

I'd even go so far as to say there is a rather large variation of R value from one identical boat ice box to the other, due to the fact they were hand made and some have wet insulation, some dry, some have more voids than others.
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Old 05-10-2015, 05:49   #213
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Re: Why no Residential Fridges?

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Originally Posted by Wotname View Post
I won't get involved with fluids and such as I am not that good with them - apart from the beverages that is .

But I note that much of this thread is a units and dimensions and interestingly (to me at least), a Coulomb although the equivalent of 1 Ampere second is actually considered to be dimensionless quantity.

So comparing Coulombs to gallons may not be helpful.

Time for bed
The dimensional formula you are referring to will depend on the unit system. In SI a coulomb is defined as an ampere times one second, with both ampere and second being base units. In cgs system the (stat)coulomb is a base unit.

You can make the comparison helpful by considering the analogy between:

- a coulomb is equal to 6240000000000000000 electrons, while
- a gallon of water has 1270000000000000000000000000 electrons.

The difference is that with the water you also get some protons and neutrons thrown in
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Old 05-10-2015, 06:31   #214
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Re: Why no Residential Fridges?

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Originally Posted by Wotname View Post
I won't get involved with fluids and such as I am not that good with them - apart from the beverages that is .

But I note that much of this thread is a units and dimensions and interestingly (to me at least), a Coulomb although the equivalent of 1 Ampere second is actually considered to be dimensionless quantity.

So comparing Coulombs to gallons may not be helpful.

Time for bed

Forgive me if I'm just enjoying the discussion at this point as the original question is long since answered.

I'm plagerizing a bit from the National Institute of Standardsand Technology website but:

Using SI (Système International [d'Unités]), everything boils down to
a combination of the fundamental units- meter, gram, second, ampre, kelvin, mole, candela.

The rest are derived units. To define a quantity of electricity, Coulomb is derived by the dimensions: Amp-Sec. Thus it is not a dimensionless quantity.

Since the typical cruiser has easier access to both the amperage and duration using the fundamental units is more convienent. (with the minor discrepency of using hours instead of seconds).
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Old 05-10-2015, 07:17   #215
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Re: Why no Residential Fridges?

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Originally Posted by a64pilot View Post

But I would differ with you on your point that an amp, is an amp.
I would argue that is not true, that in fact when I'm discharging my batteries and voltage is at 12.5 V, that amp is 12.5 watts, right?
But when I'm charging my batteries and the voltage is 14.3, then that amp is 14.3 watts.
An interesting thought, but unfortunately incorrect. The Amp is a base unit and is always a fixed quantity as defined by SI.

A more correct way to think about what you describe is that when you are discharging with 12.5V at 1 Amp, you are pulling 12.5 Watts out of the battery. When you are charging at 14.3 Volts and 1 Amp , then you are pushing 14.3 Watts into the battery. The Volts and Amps haven't changed in fundamental size - the number of Watts has changed.

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Originally Posted by a64pilot View Post

Now I suck at math, but that is I think about a 13% difference.
I think we have a tendency to ignore that though as it's probably about the same difference that it takes to re-charge a battery. You have to put more current into a battery to recharge it, or it would be 100% efficient, and nothing is, or at least maybe very few things are.

You don't have to put more current into a battery, you have to put more Watt hours into battery. You can do that in three different ways: with a higher voltage, a higher amperage or a longer time.

Added: your phrase "put more current into a battery" is another example of the misconception that you can "use", "consume" or "move" current. As has been pointed out several times it has no more meaning than "putting another 30 gallons per minute" into your fuel or water tank.
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Old 05-10-2015, 07:39   #216
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Re: Why no Residential Fridges?

This has been a fascinating thread, and I have read every comment posted. . Despite my low tech knowledge level, I have enjoyed reading the many comments. Some seem clear, but then another comment seems to refute the previous comments.

I am not sure what I have learned on the subject of correct terminology using terms for battery and electrical usage on boats, because it seems there is little agreement here, and the attempts at explaining it with definitions seems to change with each different member.

I wish there was an easy to understand (in laymens terms) explanation that would be approved and then posted on the Cruisers WIKI, so that in the future anyone (e.g. New boat owners) could go there to learn.

As it is now, when I read the differing comments here, some make intuitive sense, but then they are dismissed by others, who also speak authoritatively.

For a layman like myself, it is confusing, and I don't mind admitting that here, as I suspect I am not alone.

Speaking from a relative position of curious ignorance on this topic, I am bewildered and amused by what must be frustrating to those who feel they know the topic well.

It makes me appreciate those who chose a career in engineering or other technical fields.

I also appreciate that the discussion here has continued in a civil manner.
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Old 05-10-2015, 07:41   #217
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Re: Why no Residential Fridges?

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An interesting thought, but unfortunately incorrect. The Amp is a base unit and is always a fixed quantity as defined by SI.

A more correct way to think about what you describe is that when you are discharging with 12.5V at 1 Amp, you are pulling 12.5 Watts out of the battery. When you are charging at 14.3 Volts and 1 Amp , then you are pushing 14.3 Watts into the battery. The Volts and Amps haven't changed in fundamental size - the number of Watts has changed.



You don't have to put more current into a battery, you have to put more Watt hours into battery. You can do that in three different ways: with a higher voltage, a higher amperage or a longer time.

Added: your phrase "put more current into a battery" is another example of the misconception that you can "use", "consume" or "move" current. As has been pointed out several times it has no more meaning than "putting another 30 gallons per minute" into your fuel or water tank.


However you want to look at it or color it, 14.3 watts is "more" electricity than 12.5 watts is.
Just out of curiosity, why are Solar panels rated in Watts, not amps?
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Old 05-10-2015, 07:51   #218
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Re: Why no Residential Fridges?

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However you want to look at it or color it, 14.3 watts is "more" electricity than 12.5 watts is.
Just out of curiosity, why are Solar panels rated in Watts, not amps?
Wild guess but probably marketing.

120watts sounds like more than 10amps (at 12 volts) to those that don't understand the difference.

Even worse if you are feeding a 120v system say on land based household system, it's a 1 amp panel (ignoring conversion to AC and losses). God forbid you come from Europe where it's a measly 0.5amp planel.
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Old 05-10-2015, 07:58   #219
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Re: Why no Residential Fridges?

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However you want to look at it or color it, 14.3 watts is "more" electricity than 12.5 watts is.
Just out of curiosity, why are Solar panels rated in Watts, not amps?
They are not rated in Amps because Amp is not a measure of "power". It a measure of how fast electrickery is flowing in a circuit.

They are rated in Watts because that is the amount of "power" that they are capable of generating when 1000 Watts per square meter of solar radiation strikes them at right angles.
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Old 05-10-2015, 08:03   #220
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Re: Why no Residential Fridges?

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Wild guess but probably marketing.

120watts sounds like more than 10amps (at 12 volts) to those that don't understand the difference.

Even worse if you are feeding a 120v system say on land based household system, it's a 1 amp panel (ignoring conversion to AC and losses). God forbid you come from Europe where it's a measly 0.5amp planel.
Connect two 120 Watt panels in series and connect them to a load.
Now connect two more in parallel and connect them to another identical load.
Now measure the Amps and Volts in each circuit.

The amps and volts will be completely different in each case, but their multiple (i.e. Watts) will be the same - about 240 Watts in test conditions of insolation.
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Old 05-10-2015, 08:11   #221
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Re: Why no Residential Fridges?

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Connect two 120 Watt panels in series and connect them to a load.
Now connect two more in parallel and connect them to another identical load.
Now measure the Amps and Volts in each circuit.

The amps and volts will be completely different in each case, but their multiple (i.e. Watts) will be the same - about 240 Watts in test conditions of insolation.

He said it much more eloquently than I could, but what it amounts to is a Watt is a Watt, period. an Amp, well it depends on voltage as to how much power an Amp is. Assuming I am using the word power correctly
It's very easy for marketing types to "play" when quoting Amps, as are we talking the mythical 12V, the 13V+ of a full charged battery or the 14+ volts of a system being charged?
So in order for Amps to be useful, voltage also must be stated, but a Watt, is a Watt.

Now I am no Engineer, just a dumb arse mechanic, so I like to keep it simple so I can understand
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Old 05-10-2015, 08:18   #222
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Re: Why no Residential Fridges?

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Wild guess but probably marketing.

120watts sounds like more than 10amps (at 12 volts) to those that don't understand the difference.

Even worse if you are feeding a 120v system say on land based household system, it's a 1 amp panel (ignoring conversion to AC and losses). God forbid you come from Europe where it's a measly 0.5amp planel.
Actually it is to keep in line with standard land based power metering for simple clarity for the average person. You are charged for the electricity you use by the watt ( your bill says how many kilowatts you have used not how many amps you use) but this is just my personal opinion on that.
When I'm explaining it to customers I have to convert either the power used by them to watts or convert the panel output to amps to show the correlation between the 200 watt array being able to support a 50 ah daily usage.
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Old 05-10-2015, 08:25   #223
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Re: Why no Residential Fridges?

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Actually it is to keep in line with standard land based power metering for simple clarity for the average person. You are charged for the electricity you use by the watt ( your bill says how many kilowatts you have used not how many amps you use) but this is just my personal opinion on that.
Ashley, your bill says how many kiloWatt hours you have used.
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Old 05-10-2015, 08:32   #224
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Re: Why no Residential Fridges?

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Ashley, your bill says how many kiloWatt hours you have used.
Stu you are right and wrong im still on my first cup of coffee. My power bill did used to say kWh
The wrong is my name is Rob not Ashley that's my oldest boys ex girlfriends name
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Old 05-10-2015, 09:17   #225
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Re: Why no Residential Fridges?

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Connect two 120 Watt panels in series and connect them to a load.
Now connect two more in parallel and connect them to another identical load.
Now measure the Amps and Volts in each circuit.

The amps and volts will be completely different in each case, but their multiple (i.e. Watts) will be the same - about 240 Watts in test conditions of insolation.
I understand that but it's like small engines are that are often advertised by cc as opposed to HP.

Reality is most casual buyers could care less how many cc the engine is. They want to know how much HP it puts out (and secondarily torque) but the cc is typically a much bigger number and the bigger number sells better.
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