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Old 03-15-2015, 11:04 AM   #15
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Originally Posted by chboone View Post
Was the 100 amp question actual usage or just theoretical? Just curious of the need for that size battery bank on an RV. Thanks for the pictures.
just gave a round number to use.
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Old 03-15-2015, 01:27 PM   #16
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Originally Posted by tlaffourtit View Post
if you have fully charged batteries (12.8v) and they are rated at 1450 ah and are using 100 amps according to your amp meter. how long will the batteries last until they hit 50 percent level? 7.25 hours? thanks Tim
Sounds about right..BUT,,Is that 1450 at the Wal*Mart rate or the 20 hour rate (Wal*Mart rate they run down faster)

Here is why and, by the way a path to your answer. Peukert's law

Peukert's law - Wikipedia, the free encyclopedia

And to make it easy for you

Online calculator: Battery discharge time depending on load

Now what is the difference between C/20 and Wal*mart rates? NOTE: The batteries are the same, but the C/20 capacity of a Group 24 is around 73 amp hours.. Wal*Mart,uses the 1 amp rate,and at that rate a Group 24 can last 100 hours or more.

The links explain why.. Same battery, Different rating systems.
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Old 03-15-2015, 05:23 PM   #17
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Originally Posted by wa8yxm View Post
Sounds about right..BUT,,Is that 1450 at the Wal*Mart rate or the 20 hour rate (Wal*Mart rate they run down faster)

Here is why and, by the way a path to your answer. Peukert's law

Peukert's law - Wikipedia, the free encyclopedia

And to make it easy for you

Online calculator: Battery discharge time depending on load

Now what is the difference between C/20 and Wal*mart rates? NOTE: The batteries are the same, but the C/20 capacity of a Group 24 is around 73 amp hours.. Wal*Mart,uses the 1 amp rate,and at that rate a Group 24 can last 100 hours or more.

The links explain why.. Same battery, Different rating systems.

all I can tell you they are deka batteries. not sure at which rate
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Old 03-15-2015, 08:35 PM   #18
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The 1.2 inefficiency rating was in the formula in the manual of my Tripp-Lite inverter for estimating Amp Hr usage and battery recharge time. They didn't explain the 1.2 but I assumed it was for internal losses in the batteries. As you know, actual amp-hour capacities are less when batteries are discharged at faster rates. I probably should have stayed out of the conversation. The formula I posted would get you in the ball park, your's would get you to home base.
By all means jump in as we all learn form what other provide.

Me guesses that the 1.2 is some general number that some engineer may have added to some formula somewhere to compensate for something and to keep it simple left out the details which is fine.

In short it makes the consumed higher so one expects the batteries to not last as long so it builds some cushioning into the calculation.

Please do not hesitate from contributing as we all learn.
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Old 03-16-2015, 08:29 AM   #19
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how many watts (solar panels) would it take to recharge the same batteries?
How long is a string?

Seriously, how much are the panels exposed to the sun, hours at peak angle, further hours at a lesser angle, fully or completely exposed, etc. A 20 watt panel in full sun will eventually charge all those batteries, but more wattage will do it faster IF there is plenty of sun. If little or no sun reaches the panels, a million watts doesn't help.

Solar panels typically produce around 16v to do charging, so a 300 watt panel can produce around 18-20 amps/hour of full sun. That's not a lot if those 1450AH have been seriously depleted. If you needed to replace 700 AH using a single panel, it would take a minimum of 35 hours of sun, but towards the end (80+ % charge) the batteries slow down their acceptance rate, so it's probably more like 40 hours. Two 300W panels would cut that roughly in half. But if the batteries were only 25% discharged instead of 50%, the time is cut roughly in half.
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Old 03-16-2015, 02:51 PM   #20
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How long is a string?

Seriously, how much are the panels exposed to the sun, hours at peak angle, further hours at a lesser angle, fully or completely exposed, etc. A 20 watt panel in full sun will eventually charge all those batteries, but more wattage will do it faster IF there is plenty of sun. If little or no sun reaches the panels, a million watts doesn't help.

Solar panels typically produce around 16v to do charging, so a 300 watt panel can produce around 18-20 amps/hour of full sun. That's not a lot if those 1450AH have been seriously depleted. If you needed to replace 700 AH using a single panel, it would take a minimum of 35 hours of sun, but towards the end (80+ % charge) the batteries slow down their acceptance rate, so it's probably more like 40 hours. Two 300W panels would cut that roughly in half. But if the batteries were only 25% discharged instead of 50%, the time is cut roughly in half.
each string is made up of 2 batteries using 1 ga cable which is 8'to the bus bars from the bus bar the 4/0 is 16" long to the inverter. I doubt I would ever use up 50% of the batteries. I was just looking for the worst. the panels will be laying flat with no shade(hopefully).only shade would be if the fan covers are opened more than six inches. then that part of the cover might give the panel a little shade if facing the wrong direction. looks like 3 panels using 350 ah would still not fully charge the batteries. I was going to buy the renogy 300 watt panels instead I ordered the CS6X-310P from Canadian Solar.
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Old 03-16-2015, 03:56 PM   #21
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You need to forget the battery AH Capacity and do an energy budget, i.e. calculate the range of amp-hours used in a normal day off-grid. Once you have an idea how many AH you use each day, you can then figure how many AH you need to put back each day to maintain an adequate charge. That governs the amount and type of charging capacity you need. You can figure solar for general use and use a generator for extra charging when the days load exceeds the solar capacity. Trying to provide solar capacity for the worst case (dead batteries) is seldom cost effective.

I'm surprised there is any cargo capacity left in your ACE after adding nearly 1000 lbs of batteries and trays, plus solar panels. You can only cram so much extra weight into an 18,000 lb chassis.
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Old 03-16-2015, 04:50 PM   #22
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still around 3600 lbs left
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