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Old 03-10-2015, 05:07   #151
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Re: Why no Residential Fridges?

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Originally Posted by valhalla360 View Post
Maybe "O'engineering" has a different meaning but amps/day would imply you your system starts drawing Y amps and it steadily increases by X amps over the course of a day.

Example: You start the day drawing 10amps and you are increasing by 30amps per day, so after 1 day, you are drawing 40amps.

Over the course of the day, you will average 25amps over 24hours or about 600amp-hours.

I don't know what situation would have the amps steadily increasing like that over the course of a day on a cruising boat so I see no situation where it makes sense.

In the engineering world, sloppy thinking like that leads to bridges that fall down and space ships that explode for no apparent reason. In the cruising world, it just costs you a lot of money when you build a massively oversized system because the guy builds you a system that will handle 600amp-hrs rather than the required 30amp-hrs.
Thank you! At least someone else gets it.
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Old 03-10-2015, 05:10   #152
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Re: Why no Residential Fridges?

No, amps per day means exactly that, the amps drawn in a 24 hour day. The fact that the draw is not the same early in the morning as in mid afternoon makes no difference.

You need to rethink your post. Makes no sense from an engineering standpoint.
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Old 03-10-2015, 05:36   #153
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Re: Why no Residential Fridges?

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Originally Posted by onestepcsy37 View Post
No, amps per day means exactly that, the amps drawn in a 24 hour day. The fact that the draw is not the same early in the morning as in mid afternoon makes no difference.

You need to rethink your post. Makes no sense from an engineering standpoint.


No, Valaha360 is correct. It is your incorrect use of basic units that makes no sense, from any standpoint.

Once again: An Amp is a measure of instantaneous current flow.

Assume you have one of these:
T-1260 Plus | Trojan Battery Company

Read the specifications on that page: The capacity is shown as around 130 AMP HOURS (depending on how fast you discharge it - i.e. how many AMPS you are pulling from it)

If you have an average 2 Amp current flow for 30 minutes, you use 1 Amp hour of its 130 capacity . If you have the same 2 Amp current flow continuously for 24 hours, you use 48 Amp hours of that 130 capacity. i.e 48 Amp hours per day.


(Added: and just to be extra pedantic, the correct abbreviation is Amps with capital "A" since it is named after a person: André-Marie Ampère)
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Old 03-10-2015, 07:53   #154
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Re: Why no Residential Fridges?

Living on the hook is the easy part of sustainable cruising in my book. Consider a simplea passage for a couple of days to windward with only wind or solar supporting a battery bank that just went through a tropical night with chart plotter, running lights, autopilot, fans, refrigeration, etc... demonstrates a lot of savings supporting the investment in a well insulated top loaded box that doesn't require anywhere near the investment of charging sources to support. Not to mention the first random wave that throws the contents against the door, hopefully while you're not holding the door open enjoying the cold air falling at your feet.
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Old 03-10-2015, 07:54   #155
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Re: Why no Residential Fridges?

Apparently only cruisers/liveaboards know what amps per day means in the real world. Like if I use 90 amps per day while I'm on the hook I need to put back 90 amps per day to remain in balance. Simple.

I realize that the forum here is not 100% engineering background and I have no need to impress them with my education and work experience. Just provide straightforward real world useful information when I can.
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Old 03-10-2015, 08:25   #156
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Re: Why no Residential Fridges?

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Originally Posted by onestepcsy37 View Post
Apparently only cruisers/liveaboards know what amps per day means in the real world. Like if I use 90 amps per day while I'm on the hook I need to put back 90 amps per day to remain in balance. Simple.

I realize that the forum here is not 100% engineering background and I have no need to impress them with my education and work experience. Just provide straightforward real world useful information when I can.
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Old 03-10-2015, 09:10   #157
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Re: Why no Residential Fridges?

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Originally Posted by onestepcsy37 View Post
Apparently only cruisers/liveaboards know what amps per day means in the real world. Like if I use 90 amps per day while I'm on the hook I need to put back 90 amps per day to remain in balance. Simple.

I realize that the forum here is not 100% engineering background and I have no need to impress them with my education and work experience. Just provide straightforward real world useful information when I can.
You are missing the point. You didn't use 90 amps per day. You used 90 amp-hrs per day. So you need to replace 90 amp-hrs to remain in balance. Example: When you start your engine, you may draw 500 amps. That doesn't mean you need a charging system that puts out 500amps. Reality is you drew 500amps for maybe 10 seconds. 10 seconds is approximately 0.00278 hours. So you need to replace approximately 1.39amp-hrs. If you have a solar system that is putting out 10 amps, you need about 0.139hrs or about 8.3 minutes to put the amp-hrs back in.
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Old 03-10-2015, 09:17   #158
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Re: Why no Residential Fridges?

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Originally Posted by sailorchic34 View Post
Lets take a hypothetical fridge. Say, oh a 120V 3.5 CF fridge that if it ran for an hour would use 15 Ah at 12.7v. But it only actually runs for 1/6th the time so uses 2.5 Ah or roughly 32 watt hr. Not a great number, but not that bad.

Mind you the compressor only runs for 2.5 minutes in 15 minutes with 13 minutes for the condenser to cool down between cycles. There is a improvement in heat rejection for about 1/3 the short run cycle time before the condenser reaches a higher temperature.


Another hypothetical 12v fridge with might use only 1.8 Ah or 23 watt hr an hour, for the same work. It's more efficient in that it uses 9 watt hr less, but costs 5 to 10 times as much as a $140 120v fridge and $50 inverter. So, do you buy the fancy fridge or add one more 100 watt solar panel, for $120. Guess which I did....

I know that back in the old boat that did have a 12V fridge that the daily Ah used was just about what my 120V fridge uses, roughly 50-55 Ah.

Yes going with a variable speed 12V compressor and using a expansion valve in a small system can improve system efficiency. No question there. But for the poorer sailor without $1000 to $2500 for a compressor, expansion valve and holding plate, the 120V fridge can work well enough.

Mind you everything I read said you could not use a 120V fridge in a boat. But I thought for $140, lets experiment and find out. So I did. After 8 years on the boat, it still works well and has yet to show signs of rusting. Plus I've had zero maintenance. well other then replace the cooling fan in the inverter ($10 ebay)
OK to me your numbers don't make any sense let's see you have a dorm refer running on an inverter so that looses efficiency right there first what is the power draw of your inverter in standby mode.
Now for the fridge. You state it uses 15 amps when compressor runs it runs 2.5 min for each. 15 min so it runs for 10 min per hour which means it runs for 1 hour in a 6 hour time frame which means 4 hours run time per 24hour day so we have 15 amps x 4 hours per day = 60 ah usage per day my fridge (a holding plate system uses 4 amps and runs for about 2.5 hours twice a day so uses 20 ah / day right now with mid to upper 60's and mid 50's water ( air cooled system ) so I use about 40 ah less than you not even calculating the static useage of your inverter ( not even looking at the inefficiency and power usage of the inverter itself)
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Old 03-10-2015, 09:25   #159
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Re: Why no Residential Fridges?

Now I'm not trying to be mean or any of that crap it works for you do it however a dorm fridge wouldnt'like being tilted 15 to 20 degree heel for a week or more straight like on a passage from here Washington to Hawaii. It works for you and I see no reason it wouldn't work great for anybody on a local sailing boat.
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Old 03-10-2015, 09:39   #160
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Re: Why no Residential Fridges?

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You are missing the point. You didn't use 90 amps per day. You used 90 amp-hrs per day. So you need to replace 90 amp-hrs to remain in balance. Example: When you start your engine, you may draw 500 amps. That doesn't mean you need a charging system that puts out 500amps. Reality is you drew 500amps for maybe 10 seconds. 10 seconds is approximately 0.00278 hours. So you need to replace approximately 1.39amp-hrs. If you have a solar system that is putting out 10 amps, you need about 0.139hrs or about 8.3 minutes to put the amp-hrs back in.
I think everyone understands that. It's basic electrical. Really if we were all anal we would all use the term ampere-hour which is the correct textbook term, instead of amp hour. But I've yet to see anyone here use the proper term "ampere-hour". Nor do I loose a bit O sleep over it or care if one uses ampere hour, amp-hr or amps per hour. They oddly all mean exactly the same thing.

An ampere hour is simply the number of amperes (amps, A) used or stored in one hour. One could also use Ampere-day ( amp-day or amps per day) to define the number of ampere-hours used in one day. It's simple and quite clear.

But outside a university, amperes as a term is not used that much if at all. It's shortened to amp-hr, which is a contraction of the "proper" Ampere-hour term.

OK I am sooo done here. It's a lovely day at anchor, and I have many amps flowing into the batteries. I hope everyone else enjoys the day too.





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Old 03-10-2015, 11:20   #161
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Re: Why no Residential Fridges?

Yes, sailorchic, he misses the point. No use going on with this. I won't even mention to him that I use my voltmeter to keep track of SOC. Done that for the past ten years.
I'm on my way out to a race party at the sailing club....
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Old 03-10-2015, 11:35   #162
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Re: Why no Residential Fridges?

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I think everyone understands that. It's basic electrical. Really if we were all anal we would all use the term ampere-hour which is the correct textbook term, instead of amp hour. But I've yet to see anyone here use the proper term "ampere-hour". Nor do I loose a bit O sleep over it or care if one uses ampere hour, amp-hr or amps per hour. They oddly all mean exactly the same thing.

An ampere hour is simply the number of amperes (amps, A) used or stored in one hour. One could also use Ampere-day ( amp-day or amps per day) to define the number of ampere-hours used in one day. It's simple and quite clear.

But outside a university, amperes as a term is not used that much if at all. It's shortened to amp-hr, which is a contraction of the "proper" Ampere-hour term.

OK I am sooo done here. It's a lovely day at anchor, and I have many amps flowing into the batteries. I hope everyone else enjoys the day too.



Actually, no I don't think everyone understands it as we have people arguing that they are using amps not amp-hrs.

If they understood it, they would admit amps is the wrong unit but they are using it anyway. I believe we have several people who don't understand because we are getting vehement arguments that they are using X amps per day.
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Old 03-10-2015, 12:17   #163
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Re: Why no Residential Fridges?

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Actually, no I don't think everyone understands it as we have people arguing that they are using amps not amp-hrs.

If they understood it, they would admit amps is the wrong unit but they are using it anyway. I believe we have several people who don't understand because we are getting vehement arguments that they are using X amps per day.
You may wish to rethink that? hrs. and days are both time periods. Maybe they are using a monitoring of 24hrs? It may give a better overall assessment considering ambient temp.? Maybe not what they are doing? I haven't followed all of the posts.
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Old 03-10-2015, 12:23   #164
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Re: Why no Residential Fridges?

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You may wish to rethink that? hrs. and days are both time periods. Maybe they are using a monitoring of 24hrs? It may give a better overall assessment considering ambient temp.? Maybe not what they are doing? I haven't followed all of the posts.
If they were saying amp-days, that would be odd but as long as they follow with the correct math, it works fine. Likewise, you could use watt-hrs if you want to be voltage agnostic.

What is being proposed by several posters is amps/day, which makes no sense.
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Old 03-10-2015, 12:30   #165
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Re: Why no Residential Fridges?

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Originally Posted by valhalla360 View Post
Actually, no I don't think everyone understands it as we have people arguing that they are using amps not amp-hrs.

If they understood it, they would admit amps is the wrong unit but they are using it anyway. I believe we have several people who don't understand because we are getting vehement arguments that they are using X amps per day.
Which as cruisers of course means ampere hours per day. Quite clear. Amperes per 24 hours, is very much like summing up 24 hours of ampere-hours loads. Its a unit of measuring ampere hours in a 24 hour range. Which is oddly somewhat important to many cruising sailors.

An ampere-hour is simply the number of amperes used or stored in a unit of time called an hour. We can also use units of milliseconds, femto-seconds, days, weeks or years. To say that we can only use ampere-hours to measure the consumption or production of electron's is somewhat limiting.

I could just have easily said my fridge uses 2.05 moles of electrons in a day, which would be clear to chemists and almost no one else. A mole being equal to 26.8 ampere hours. Lets not use moles though. Someone might confuse that with small burrowing insectivorous mammals.

We could also use milliampere-second or coulombs, 3600 coulombs equals 1Ah. Lots and lots of units. How cool is that.
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