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Old 22-12-2014, 19:22   #91
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Re: Highest Output Alternator

As battery capacity is rated in AH using the term 50 AH per day is perfectly acceptable. It just means that, for instance, if you have a 100 AH battery that you have drawn it down by 50 AH in a single 24 hr. period. It is not the same as using the term knots per hr.

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Old 22-12-2014, 19:28   #92
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Re: Highest Output Alternator

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Originally Posted by rwidman View Post
You need to understand a little more about electricity. By definition, an amp hour (AH) is an amp of current flowing for one hour. An amp flowing for 24 hours (a day) would be 24 amp hours. Two amps flowing for 24 hours would be 48 amp hours, etc. It doesn't make sense to say "50 Ah a day".

The current consumed by your AP is the amount of current consumed by the AP multiplied by the hours used. If it draws two amps and runs eight hours, it has consumed 16 amps.

He did not say 50 amps per day

He did not say 50 amps per hour

He correctly identified that his autopilot alone uses a 50 ampere hours each day plus or on top of his other loads.. This AP consumption is actually not too bad for a sail boat at sea..

His fridge might use another 60 Ah's each day and the rest of the equipment another 40 Ah's each day. Add the three together and he's using 150 ampere hours each 24 hour period.

If you don't define how many ampere hours are used in what time period you only have half the story....

If he had said my AP uses 50Ah the question from most would have been; How long does it take to consume those 50Ah's? Four hours, 1 day a week?

I don't see why you felt the need to chastise the OP for how many ampere hours his AP uses per day when there is really nothing wrong with the way he identified the AP's consumption...?

Quote:
Originally Posted by JoeFish View Post
I'm looking for a new alternator for our motor.

In a perfect world I'd like to find one that I can push a lot of amps into our house batteries quickly, as I sail on AP a lot and that tends to suck up about 50Ah a day plus all the other normal loads from radios, instruments, etc. (I'll admit we use far less in that department than some).
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Old 22-12-2014, 19:48   #93
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Re: Highest output alternator

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Originally Posted by typhoon View Post
Just got it all up and running last week . This is what I am getting out of my alternator at generator speeds , 1800 rpm

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That is sweet! I only wish I had the room to do a direct drive or a J mount style large case....... 180A is about my upper limit with my space constraints.
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Old 22-12-2014, 20:27   #94
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Re: Highest output alternator

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Originally Posted by Maine Sail View Post
That is sweet! I only wish I had the room to do a direct drive or a J mount style large case....... 180A is about my upper limit with my space constraints.
Thanks Maine sail . I actually had to extend my engine room a little to make it fit but it all worked out just fine . Getting the lead out with your help was a bonus as we'll . Imagine trying to put 303 amps into a lead acid bank . 2 cycles on my lifepo4 bank now .

Sorry for the thread drift

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Old 22-12-2014, 20:31   #95
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Re: Highest output alternator

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Imagine trying to put 303 amps into a lead acid bank .

Regards
You'd hit absorption voltage in seconds....
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Old 22-12-2014, 20:36   #96
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Re: Highest Output Alternator

If one can find the room to put a a really big alternator on a small engine why not put a cut off switch on the alternator like MaineSail did. If you need power to the prop just shut down the alt. until it you have enough power to pull it. Don't some regulators also have the ability to cut the power by half?
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Old 23-12-2014, 03:13   #97
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Re: Highest output alternator

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Originally Posted by rwidman View Post
See anything wrong with the term "knots per hour"?

I think if you wand to discuss technical stuff and make any sense of it you have to understand and use the technical terms correctly.
AH per day is perfectly correct. Just as nautical miles per day is correct.
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Old 23-12-2014, 06:26   #98
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Re: Highest output alternator

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Originally Posted by rwidman View Post
See anything wrong with the term "knots per hour"?

I think if you wand to discuss technical stuff and make any sense of it you have to understand and use the technical terms correctly.
He does, you don't. Sorry for being blunt.

Some light reading:
What is ampere hour (Ah or amp hour)? - Definition from WhatIs.com
Battery ratings : Batteries And Power Systems - Electronics Textbook
Frequently Asked Questions (FAQ) - DC Battery Specialists

As a side note: a more appropriate unit to discuss energy consumption is a Watt-hour, but substituting Ampere-hours (while keeping in mind some simplifications like assumption of a constant voltage and forgetting inefficiencies in the system) is often acceptable in this sort of discussions.

@Mods: apologies if I sound harsh, but shouldn't this sort of techno-nonsense be avoided on quality forums?
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Old 23-12-2014, 06:52   #99
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Re: Highest output alternator

Quote:
Originally Posted by typhoon View Post
Just got it all up and running last week . This is what I am getting out of my alternator at generator speeds , 1800 rpm

Regards
Neat! How about more details on your installation including pics?
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Old 23-12-2014, 08:31   #100
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Re: Highest Output Alternator

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26 HP is not going to drive a huge alternator. Figure out what drag you can really tolerate. You can find the conversions for watts - HP. Remember to account for the inefficiency of the belts, alternator, engine etc. These are real numbers.
25 amps of alternator output uses about 1 hp
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Old 23-12-2014, 09:40   #101
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Re: Highest output alternator

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Originally Posted by mrm View Post
As a side note: a more appropriate unit to discuss energy consumption is a Watt-hour, but substituting Ampere-hours (while keeping in mind some simplifications like assumption of a constant voltage and forgetting inefficiencies in the system) is often acceptable in this sort of discussions.

I wish we would dump this whole Amp thing and use Watts, as the amount of power an Amp is, is dependent on voltage, whereas a Watt, is a Watt.
There is a significant difference with how much power an Amp is even between 12V and 14V
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Old 23-12-2014, 10:13   #102
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Re: Highest output alternator

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I wish we would dump this whole Amp thing and use Watts, as the amount of power an Amp is, is dependent on voltage, whereas a Watt, is a Watt.
There is a significant difference with how much power an Amp is even between 12V and 14V
Well, me too. But you see how it is...
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Old 23-12-2014, 10:16   #103
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Re: Highest Output Alternator

Quote:
Originally Posted by rwidman View Post
You need to understand a little more about electricity. By definition, an amp hour (AH) is an amp of current flowing for one hour. An amp flowing for 24 hours (a day) would be 24 amp hours. Two amps flowing for 24 hours would be 48 amp hours, etc. It doesn't make sense to say "50 Ah a day".

The current consumed by your AP is the amount of current consumed by the AP multiplied by the hours used. If it draws two amps and runs eight hours, it has consumed 16 amps.
Err... no, Joefish is correct. Actually one of the very few who use the terminology correctly too. It's refreshing to see, more people seem to get that one wrong than right. Go JoeFish.

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Old 23-12-2014, 10:25   #104
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Re: Highest output alternator

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Originally Posted by a64pilot View Post
I wish we would dump this whole Amp thing and use Watts, as the amount of power an Amp is, is dependent on voltage, whereas a Watt, is a Watt.
There is a significant difference with how much power an Amp is even between 12V and 14V

Amen...Amen....and AMEN!
In my warped view of the world, manufactures should give all the data, Amps, Watts and what voltage, etc. Why don't they? Well take wind generators for example.

They LOVE to give you nice graphs showing lots of data that is meaningless to you! That way you have a really hard time doing two things:
1. Accurately comparing their unit to the competition
and
2. Knowing that their output claims are (and excuse the language) full of **** since the data they are giving you is damn near meaningless to what you will actually see on your boat.

So the bottom line...the more worthless the data manufactures can give you...the more they can BS you. Call me jaded, but why else would a marine wind turbine give wind speed in units worthless and averaged like m/s? Why else give the Amps produced at 12v...when at 12v NONE of the power would go into your battery bank to start with...AHHHH..they do it to...well....I'll say it LIE and overstate what you will see in real life. THEN they will only really explain it to you after the fact when you call up and complain that you are seeing 20% less power produced than their graph at 12v..."oh ya" they will say, "that's normal because you are charging at 13.5v"...
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Old 23-12-2014, 23:41   #105
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Re: Highest output alternator

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.... "that's normal because you are charging at 13.5v"...
Worse yet, floating at 13.5, charging at 14.4
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