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Old 15-07-2009, 17:34   #16
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Quote:
Originally Posted by unbusted67 View Post
I thought Blue Sovereign was kind of teasing me and wasn't being really mean by saying that. I for one was just kidding around as well. No hard feelings guys. If you guys were serious then I hate you.
I was serious!

Had I known you were kidding, I would by no means responded as I did.

Addressing your refrig matter, my personal situation is based on my running my Genset 2x a day for about 1 1/2 to 2 hours, to both:
  • refrigerate
  • charge batteries
  • make water
This based on a 900A/hr house bank never dropping it below 60% charge level. If you have decent insulation surrounding your fridge/freezer, running your compressor 2x a day for ~ 1 1/2 to 2 hrs should be adequate to maintain a decent chilling/freezing temperatures.

BTW, Gracias for clarifying your intent was to be kidding.

William
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Old 15-07-2009, 18:45   #17
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Find the rated AmpHr capacity of your battery bank.
Let’s assume it is 450 AmpHrs (4 T105). Divide that by 20 hrs gives 22.5 amps, Figure out how to put a 22.5 amp load on your batteries.
Make sure your batteries are fully charged. Put the 22.5 amp load on your batteries for 10 hours.
At 10 hours turn off al loads and wait for a few hours, measure the volts. If you have 12 volts your batteries are in good shape. The table below gives voltages versus % charge. If you have 11.96 volts you have lost 20% of the capacity of your batteries.

,,,,,,,,,,,,,,,,,,,,,,,,,,,,,Percentage of Charge Open-Circuit Voltage
100,,,,,,,,,,,,,,,12.73
90,,,,,,,,,,,,,,,12.62
80,,,,,,,,,,,,,,,12.50
70,,,,,,,,,,,,,,,,12.37
60,,,,,,,,,,,,,,,,12.24
50,,,,,,,,,,,,,,,,12.10
40,,,,,,,,,,,,,,,,,11.96
30,,,,,,,,,,,,,,,,,11.81
20,,,,,,,,,,,,,,,,11.66
10,,,,,,,,,,,,,,,,11.51

Have fun
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Old 15-07-2009, 18:55   #18
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Quote:
Originally Posted by unbusted67 View Post
I have a Xantrex link 1000 system for monitoring my bank of 5 batteries
It's called an owner's manual. It's online, and its free.

http://www.donrowe.com/user_guides/x.../link_1000.pdf
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Old 15-07-2009, 20:29   #19
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Old 15-07-2009, 21:56   #20
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BS, not only were you snotty to the OP, you're being snotty to me, as well. Is this your normal communication style? Just because you have a slogan in your signature doesn't justify that kind of rudeness.

You expended a lot of energy tearing my post apart, line-by-line, in a definitely snitty tone, but didn't lift a finger to help the OP. I took fifteen minutes to patiently explain a concept to him, in a direct response to his question. Electricity is not an easy subject for many people.

How long he's owned a boat, what size it is, or how long he's been registered here has nothing to do with it, but it seems to make a huge difference to you. Maybe we should institute a two-tiered system here, only allowing access to the 1st tier when a poster has proven himself to the self-appointed gatekeepers by meeting whatever capricious criteria they establish. The rest can eat cake.

I guess we all have our own definition of laziness.
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Old 15-07-2009, 22:03   #21
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If you guys want to get back to answering unbusted's questions then I would be happy to keep the thread open.
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Old 16-07-2009, 06:27   #22
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Quote:
Originally Posted by David M View Post
If you guys want to get back to answering unbusted's questions then I would be happy to keep the thread open.
Thank you David M.

As to watt hours versus amp hours, the difference is rather moot when considering 12 Volt DC boat systems as the Volts aspect remains a constant (ie 12 V).
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Old 16-07-2009, 06:53   #23
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<chuckle> Must be the heat!

What we have done on many occassions to check system amperage utilization at the doc is to just turn off, unplug the shore power. We have seen what the systems consume or produce over 24 hour runs. We use the xantrex monitor, but I have also used a specific gravity meter, a VOM and clamp style amp meter (found my xantrex needed recalibrating, couldn't believe the figures! Thus the check).

The specific gravity meter is I believe the most reliable for measuring battery capacity. The amp meter will let you match capacity with usage. Volt meter is just a rougher gauge and rule-of-thumb device.
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Old 16-07-2009, 07:48   #24
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Quote:
Originally Posted by Strygaldwir View Post
The specific gravity meter is I believe the most reliable for measuring battery capacity. The amp meter will let you match capacity with usage. Volt meter is just a rougher gauge and rule-of-thumb device.
There is a problem with using a specific gravity "meter". Stratification occurs, the acid is denser at the bottom of the case and thinner on top. The only way to mix the fluid up its to charge the battery at a rate that produces a lot of gas bubbles. The rising bubbles drag up the denser fluid.

It is a good test though for seeing how badly sulphated your batteries. Fully charge your batteries, equilize and then measure density. The difference between what you read and the specs. for a fully charged battery will indicate the extent of sulphation.
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Old 17-07-2009, 08:55   #25
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Multi meter accuracy

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Originally Posted by mesquaukee View Post
[ If you have 12 volts your batteries are in good shape. The table below gives voltages versus % charge. If you have 11.96 volts you have lost 20% of the capacity of your batteries.[/SIZE][/FONT]

,,,,,,,,,,,,,,,,,,,,,,,,,,,,,Percentage of Charge Open-Circuit Voltage
100,,,,,,,,,,,,,,,12.73
90,,,,,,,,,,,,,,,12.62
80,,,,,,,,,,,,,,,12.50
70,,,,,,,,,,,,,,,,12.37
60,,,,,,,,,,,,,,,,12.24
50,,,,,,,,,,,,,,,,12.10
40,,,,,,,,,,,,,,,,,11.96
30,,,,,,,,,,,,,,,,,11.81
20,,,,,,,,,,,,,,,,11.66
10,,,,,,,,,,,,,,,,11.51

Have fun
Of course this is depending on how accurate is the measuring instrument (multimeter).
Also with battery monitor the accuracy of the monitor depend on where the shunt is placed.


Quote:
Originally Posted by hellosailor View Post
Don, beware of the "accuracy" of instruments. While a 420 meter may have a PRECISION of 0.02 units, it will not have that accuracy unless it has been lab calibrated as well.

Most of the less-than-expensive meters are not calibrated vey closely (within 0.1 perhaps) and have additonal errors such as a "float" of 2-3 digits in the least significant digit (LSD, rightmost digit) on the display. Plus an additional error of sometimes 1/2% on any given scale.

So while your meter may show "12.44" for a battery, and show it repeatedly, the real voltage could easily be 12.1 or 12.6. Sometimes the accuracy is important. Sometimes, it isn't. Just knowing "this is a full battery" "this is the normal charge" is enough, and you can approximate down 1/10th of a volt per 10% charge from there--if you are looking at a rested battery, or one in typical light use, so there's no question of surface charge or heavy loads deceiving you.

Voltage? If you read it in context, I'd say it makes a reasonably good charge indicator for several hundred bucks less than one of the total watt/hour monitors. But for some odd reason, you can buy a complete decent multimeter for $20, and a digital display meant to be bulkhead mounted, is $100+.
Quote:
Originally Posted by donradcliffe View Post
I use a radio shack minature digital multimeter, under $20, accurate to +/- 0.02 volts, but I think you are looking for a permanently mounted meter. Be aware that I found a new digital voltmeter installed on one boat which put out enough RF interference to completely wipe out their SSB reception.

After 15 years of watching my battery monitor, I can make a more accurate guess as to the state of the batteries from voltage alone than from their 'amp-hours remaining' display. After a couple of months of discharges and recharges, the amp-hour reading can be off by more than 10% of the battery capacity. Of course the voltage-based guess on the batteries also takes into account the ships load and charging currents from my solar and wind generator.
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Old 17-07-2009, 12:19   #26
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The other deceptive issue about voltage is the presents of loads. Theoretically you'd have to disconnect the battery to get an accurate reading of the voltage available from the battery.
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Old 17-07-2009, 14:18   #27
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It helps to pull checks monthly and keep a log of readings. This is the best way to keep track of performance trends and also helps you spot a battery that is failing under load. Verify (with a meter) that the string is floating within the proper optimum range per your battery's documentation. Do not always trust the meter on the charger (esp if it's a bit aged). Verifiy it with a hand-held as this helps you keep track of calibration. Also, check each cell individually in-string with load attached and log all these readings in a book or on computer. Checking them in-string and under load is more likely to show a battery failing than an unloaded test cuz they tend to fail under load rather than at rest. Once a year you can do a "hard discharge/whiplash" test (coup de fouet) with a full load to equalize them (unless your charger already has that capability). During this test take readings of voltage and current(total) at 1,2,3,4,5,10,15,20,25, and 30 minutes and log them. Mark the time and voltage amount the string "turns around" at (voltage drop stabilizes and begins to climb back up). this can tell you the string's ability to take sudden hard loads and not "fall out". If graphed, these readings can give you a visual representation of the initial discharge/recovery cycle.

Just my 2 cents.....

Ok dang it thats a nickels worth...
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Old 22-07-2009, 16:49   #28
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Quote:
Originally Posted by mesquaukee View Post
Find the rated AmpHr capacity of your battery bank.
Letís assume it is 450 AmpHrs (4 T105). Divide that by 20 hrs gives 22.5 amps, Figure out how to put a 22.5 amp load on your batteries.
Make sure your batteries are fully charged. Put the 22.5 amp load on your batteries for 10 hours.
At 10 hours turn off al loads and wait for a few hours, measure the volts. If you have 12 volts your batteries are in good shape. The table below gives voltages versus % charge. If you have 11.96 volts you have lost 20% of the capacity of your batteries.

,,,,,,,,,,,,,,,,,,,,,,,,,,,,,Percentage of Charge Open-Circuit Voltage
100,,,,,,,,,,,,,,,12.73
90,,,,,,,,,,,,,,,12.62
80,,,,,,,,,,,,,,,12.50
70,,,,,,,,,,,,,,,,12.37
60,,,,,,,,,,,,,,,,12.24
50,,,,,,,,,,,,,,,,12.10
40,,,,,,,,,,,,,,,,,11.96
30,,,,,,,,,,,,,,,,,11.81
20,,,,,,,,,,,,,,,,11.66
10,,,,,,,,,,,,,,,,11.51

Have fun
How does one determine the amp hour capacity of a battery bank?
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Old 22-07-2009, 17:01   #29
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What you see above is a sort of an approximation. In the olden days (like more than 20 years ago) they used voltage as a measure of discharge. It's sort of almost not accurate but it can be equated to a warm feeling. I can sense this is not what you wanted to hear. Battery monitors these days can measure the integral of the amps X time discharged. This is a better way. Even this isn't perfection.

Knowing that the battery only has so many amp hours inside means there is an exponent (based on the type and other battery details) that can convert the use to the amount of amp hours left, the existing amp hour load, and the percent capacity left. It's done by adding up the amp load over time (the integral). Yes, it's calculus. Don't worry you are a sailor and you do it all the time. Sort of like figuring out the moment before you smash into the dock long before it happens then figuring out what you need to do to stop. There are multiple integral calculations in doing that one exercise. Calculus is easy when you put it into practice.

The bottom line is the above won't do it really very accurate. What I told you is only accurate for batteries in good condition. If they get trashed even that won't work.
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Old 22-07-2009, 17:10   #30
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On the original question: If you have a gizmo that draws one amp, and you leave it turned on for one hour, your gizmo will consume one amp (for one) hour, that is "one Amp-Hour". Leave it on four four hours, it consumes four AH (Amp-Hours.) Use it for only fifteen minutes, and it comsumes 1/4AH. Which could be called fifteen amp-minutes but never ever is.

Amps are the instantaneous measurement of current being used, amphours measures that consumption over a period of time, normalized in hours.

Now, to make things just a little more complicated, when you are specfiying the capacity of a battery, you can't really just spec it in amphours. This is because the amount of power that the battery can supply changes depending on the internal chemistry of the battery, which is constantly changing as the battery is in use.

So if your battery can supply 100 AH...that's also "normalized". Typically the number is given for how many amp hours it can supply over a 20-hour period, so a 100AH battery really means it can supply 5A continuously for 20 hours.

If you draw higher current, the capacity is reduced, so a 100AH battery might have more detailed specs like these:
100AH, 5A for 20 hours
90 AH, 10A for 9 hours
75 AH, 25A for three hours
(numbers are real real ballaprk, don't memorize them).

Which is one reason why you'll get more economy and performance from one whopping big battery bank, than from switching between two smaller ones. The single bigger bank, gets the advantage of always seeing a comparably smaller load versus it's own capacity.
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