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Old 05-10-2015, 09:23   #226
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Re: Why no Residential Fridges?

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Originally Posted by StuM View Post

In that case: How many GPM does a standard fuel can hold? That would depend on the size of the fuel can and the GPM flow rate.

At last: you almost get the analogy! GPM is analogous to Amp. gallons per minute would be analogous to Ampere per minute.

So if GPM is analogous to Amp, it follows that Gallon is analogous Coulomb.

And you DON'T measure a days usage of fuel in GPM you measure it in gallons. An in exactly the same way, you dont' measure electricity use in Amps, you measure it in Coulombs or Amp hours or Amp days
But to get gallons per day to store you need to know the consumption rate in GPM or GPH. That then gives you the consumption rate in gallons per day. How else would you calculate the storage capacity required.

An ampere hour is the amount of energy charge in a battery that will allow one ampere of current to flow for one hour.
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Old 05-10-2015, 09:32   #227
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Re: Why no Residential Fridges?

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But to get gallons per day to store you need to know the consumption rate in GPM or GPH. That then gives you the consumption rate in gallons per day. How else would you calculate the storage capacity required.

An ampere hour is the amount of energy charge in a battery that will allow one ampere of current to flow for one hour.
By itself, GPM or GPH doesn't tell you storage capaity. Until you know how much of the day the engine is drawing X GPH, you don't know your storage capacity requirements as storage is measured in Gallons.

Similarly, amps by itself doesn't tell you much of anything in terms of storage and recharge requirments. You need to combine that with how long the amp draw continues (ie: amp-hr) then to charge, you need to run the inverse calculation. If you want to replace X amp-hrs and your system puts out Y amps, you need X/Y hrs or if you want to charge within Z hrs, you need a system that puts out X/Z amps. (very similar calcualtions are run for gallons and GPH)
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Old 05-10-2015, 09:39   #228
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Re: Why no Residential Fridges?

Size matters. AC/DC.
I looked hard at ac refers last time I replaced my Norcold. None would fit and it was not practical to redesign galley. Also, I believe marine refers use a dc powered compressor, with an ac inverter. AC to DC is not a problem when hooked to shore power, more effecient than DC to AC when using batteries. I have used a 5 cubic foot AC freezer for over a decade with good success. I have a 4,000 watt inverter to use underway, Key is to keep it full. I use 2 ltr water bottles to line the freezer box base. Also don't open unnecessarily. I run genny an hour am and pm at anchor to top off batteries and cool down refer and freezer. I usually turn off refer overnight.
Note the new Yeti type super coolers are very effecient for extra cooler spce. I have 2 on the boat and use them for beverage and produce. I rotate frozen water bottles from the freezer to keep cool. This is in Mexico with high daily temperatures.
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Old 05-10-2015, 09:41   #229
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Re: Why no Residential Fridges?

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Completely wrong. The only difference between "amp/hour" and "amp/day" is time. There is no other explanation.

I prefer, as do many others, to measure battery ins and outs in daily chunks. Makes much more sense because they can vary significantly during different times of the day. For instance, solar panels only charging during the daylight portion of the day.

The water analogy is helpful to people who don't or won't understand the practical application of this.
Now that is ridiculous! Attempting to apply some common sense.


The water analogy was mine in an attempt to make your point. Maybe, I got carried away and it didn't come across that way. Someone else saying you need to know the consumption rate? I wonder what measuring the pin hole flow amount was? I couldn't come up with an analogy for the varying pin hole size of usage. Nor the varying input. I probably could but when an analogy gets more complex that the point it becomes useless.
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Old 05-10-2015, 09:45   #230
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Re: Why no Residential Fridges?

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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.
I think it's not how fast amperes are flowing but how many electrons are flowing. The speed of the electrons in a wire (which in any case is very very slow) would be a function of current density in the wire. 100 amperes though 00 wire and the wire is cool and the flow rate slower then 100 amperes through say a 10 gauge wire.

Ampere speed at say 100 amps would be different in different wire sizes and in different wire material. That is 100 amps moves through a copper conducter slower then in a aluminum conductor.

So an ampere can't be a unit of speed when that speed changes with wire size.

For folks who want a bit more detail, see this Speed of electricity flow (speed of current.)
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Old 05-10-2015, 09:51   #231
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Re: Why no Residential Fridges?

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By itself, GPM or GPH doesn't tell you storage capaity. Until you know how much of the day the engine is drawing X GPH, you don't know your storage capacity requirements as storage is measured in Gallons.
But to get the storage capacity required in gallons of storage you must know the GPM or GPH flow rate required. In the case of the big prime movers they would run 24/7 so easy to define. Otherwise its a WAG or wild A$$ guess.
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Old 05-10-2015, 09:59   #232
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Re: Why no Residential Fridges?

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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.
Actually most engines are referred to by their displacement ( call a parts house and say you need parts for a 185 HP Chevrolet engine they will say what engine but if you say a 307 they will know exactly what engine (307 cubic inch displacement)
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Old 05-10-2015, 11:42   #233
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Re: Why no Residential Fridges?

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Actually most engines are referred to by their displacement ( call a parts house and say you need parts for a 185 HP Chevrolet engine they will say what engine but if you say a 307 they will know exactly what engine (307 cubic inch displacement)
In reality, ccs, cu. inches haven't a thing to do with HP.. I think on the smaller engines it sounds easier that I/10th HP, weed eater. beyond that it is nonsense other than stated above.

More for bragging rights and advertising for car and motorcycle makers.

I don't believe what they call HP today has anything to do with the real description of a horse power is, in physics, nor what it had been called until probably the 60s,with gas? Fortunately it seems the diesel industry hasn't seemed to fallen prey to it? Maybe that is why a rating of KW/Hour makes more sense unless you are drag racing. 900 hundred HP for nine seconds won't get your boat far when a rod comes out the side.
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Old 05-10-2015, 11:46   #234
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Re: Why no Residential Fridges?

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Originally Posted by SV THIRD DAY View Post

Ask about an apple...get answers on how to make a fruit salad.
Enjoy.
Close, Rich, but no banana.

The answer is always: "How to make a watch!"
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Old 05-10-2015, 11:56   #235
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Re: Why no Residential Fridges?

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I don't believe what they call HP today has anything to do with the real description of a horse power is, in physics, nor what it had been called until probably the 60s,with gas? Fortunately it seems the diesel industry hasn't seemed to fallen prey to it?
AFAIK nothing has changed since I was in engineering school, namely that:
  1. one imperial HP aka imperial HP is equal to 550 foot-lb/second = 745.7 watts
  2. one metric HP 75 kg force - meter / second = 735.5 watts


What is the difference between "what they call HP today" and "the real description of a horse power"?

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Maybe that is why a rating of KW/Hour makes more sense unless you are drag racing.
Did you mean to say that ratings in kW, which is the SI measure of power (not kWh, which is a measure of work, or kW/h, which is nothing useful really) would make more sense than the old HP that is also a measure of power?
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Old 05-10-2015, 12:05   #236
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Re: Why no Residential Fridges?

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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
I thought we went to drops of water.

I doubt anyone really cares or G a S, about how many coulombs went through that wire? I think we are on the same page but I'll check the next time I check the no. of electrons to a gallon of water.
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Old 05-10-2015, 12:42   #237
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Re: Why no Residential Fridges?

The recent question about why solar panels are rated in watts gets back to my point: amp-hours are only useful in the context of a specific system (or battery) voltage. And a single, specific system voltage is gradually going to become a thing of the past, because modern off-grid implementations freely intermix storage and transfer of energy at different voltages as convenience, chemistry, or solid state physics demand it.

In the specific case of the solar panels, the panels themselves vary considerably in output voltage and the downstream storage targets vary considerably in their design voltage. There is no implicit voltage that would make Ah an appropriate working unit for talking about this kind of system.

It makes sense that a battery vendor would use Ah to describe capacity. It makes sense that someone whose entire boat or RV runs on 12V would freely discuss consumption in Ah. But if you walk up to my RV's panel, you'll see a shore current meter registering amperes at 120V sitting right next to a charge controller displaying current being sent into a 12V battery. Those two current measurements, and any derived amp-time "volume" measurements, are not directly comparable. It gets worse when there is a 24V battery pack and a bunch of 5V components in there that I want to account for, too, although I recognize that these are much less common today.

It's been a matter of historical convenience that bandying about "Ah" as a substitute for an actual unit of energy (Wh, or BTU, or whatever) has worked. I posit that that won't be the case in the new world, and it is more straightforward to talk about W and Wh when power and energy capacity are of primary interest. You should already see large battery packs, solar arrays, DC motors, and of course heterogeneous systems all talked about using these more fundamentally appropriate units.
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Old 05-10-2015, 13:23   #238
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Re: Why no Residential Fridges?

I wasn't going to put in one more post on this 16-page long thread that has drifted to no where near the OP's original issue, but here I am.

Just gotta love the engineers and scientists who love to discuss how many angels on the head of a pin with kilowatt-hours should be how everything is rated. Or that HP is only interesting to nitro-headed fuel dragsters. Or that a 307 cu in engine doesn't tell you how powerful an engine is. I am not an engine geek but anyone who has been interested in cars in the "old" days knew that certain engines made more HP than others. A 454, properly tuned and set up, was one powerful beast. The old Ford 289 was a favorite. How about a Cleveland 351? It was an accepted lingo used in endless debates on what was the most powerful engines but it carried useful info. Chevy didn't have a 289 e.g. Some big engines were pigs for HP. A good 289 could smoke a 307 etc.

While using kW hours is may be the "best" in comparing engine power (or whatever it says), it is not commonly understood by the average person, at least in the US. HP is "understood" as being a general indicator of useful power in a boat, or a car, whatever. If you want to compare engines in a lab then you engineers and scientists can have at it. I have a Chemistry degree for all the good it is for me and I can convert units to other units, and I understand how units can be miscalculated, but come on guys.

You need to learn to talk down to the rest of us simple morons out here. You know the vast majority of cruisers. Just humor us a little bit.

And - amps, or Amperes, are a valid measure of the rate of flow of electrons at a given moment. I for one like to know what my net amps, at the time I look at them, are when I run my alternator while my watermaker is sucking up amps. Amp-hours are a useful measure of the total accumulation of amps but it isn't useful in relation to how much an alternator is putting out because that only matters if you know how many hours it ran. And only then if you are only running the alternator with no other uses or sources. Amp-hours are useful info on how much capacity your battery has as a result of the amps through the day, but that would be an amp-day then, but then you can misuse the units if you count a day as daylight or 24 hours. But then, without a thorough knowledge and understanding of calculus how would the rest of us know anything about rates and accumulations?

Horrors! The uneducated masses are ruining the cruising world as we know it. Better to be precise than accurate I always say.
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Old 05-10-2015, 13:38   #239
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Re: Why no Residential Fridges?

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Originally Posted by svlamorocha View Post
AFAIK nothing has changed since I was in engineering school, namely that:
  1. one imperial HP aka imperial HP is equal to 550 foot-lb/second = 745.7 watts
  2. one metric HP 75 kg force - meter / second = 735.5 watts


What is the difference between "what they call HP today" and "the real description of a horse power"?



Did you mean to say that ratings in kW, which is the SI measure of power (not kWh, which is a measure of work, or kW/h, which is nothing useful really) would make more sense than the old HP that is also a measure of power?
If it didn't put the /, per hr. it's my fault.

I guess the point being, HP and cc/cu. in. is BS. A 12V567A EMD locomotive engine/ GM LST engine is 6804 cu. inches, blown two cycle was rated at 900hp at 900 rpm. Now equate that to todays bogus claims of HP.
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Old 05-10-2015, 13:52   #240
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Re: Why no Residential Fridges?

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While using kW hours is may be the "best" in comparing engine power (or whatever it says), it is not commonly understood by the average person, at least in the US. HP is "understood" as being a general indicator of useful power in a boat, or a car, whatever.
kWh is a measure of energy. HP and kW are interchangeable units of power, and there's nothing wrong with either. You'll see kW used with combustion engines everywhere except the US, but I don't think anyone has a problem with HP.

Power (kW, HP) is often not what we are interested in when discussing energy consumption. I don't really care how powerful my refrigerator is, assuming it actually keeps stuff cold. I do care how much energy (kWh, BTU) it uses.

When you conflate these different units that measure different things in your sentences, it is hard to write a meaningful response, because your intention becomes unclear. Please don't take that personally.

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You need to learn to talk down to the rest of us simple morons out here. You know the vast majority of cruisers. Just humor us a little bit.
Everyone on this forum is more than capable of understanding and being clear with each other about basic physical terms. And no one deserves to be "talked down to," in my opinion. However, those of us who want to have a productive conversation do need to use accurate terminology, or things become unclear and nonsensical.

Quote:
And - amps, or Amperes, are a valid measure of the rate of flow of electrons at a given moment. I for one like to know what my net amps, at the time I look at them, are when I run my alternator while my watermaker is sucking up amps.
I agree: knowing instantaneous current is a very valuable piece of information in lots of situations. I'm not sure, though, what that has to do with what we've been discussing above.
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