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Old 05-10-2016, 06:46 AM   #1
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How to Figure Battery Capacities??????

I swear,, trying to figure out how batteries are rated is like trying to figure out a black hole.. OH wait they, scientist, haves a better handle on black holes than battery capacity, at least in my brain.

SO,,

currently I have 2-batteries (rv-marine type) rated at 109 amp hours @1 amp.
how do they compare to the trojans t-105 which are rated at 447 mins @ 25 amps. and they show capacity of 225 amp hours 20 hrs..

again blackhole stuff to me..

what is the difference and what is an easy to to get a handle on batteries capacity
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Old 05-10-2016, 07:12 AM   #2
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Quote:
Originally Posted by carl2591 View Post
currently I have 2-batteries (rv-marine type) rated at 109 amp hours @1 amp.
how do they compare to the trojans t-105 which are rated at 447 mins @ 25 amps. and they show capacity of 225 amp hours 20 hrs.
Batteries have two basic ratings:
1 - Cold cranking amps for using as a starting battery; and
2 - Amp-hours for use as a house battery.

The amp-hour rating is always for a 20-hour discharge rate unless otherwise specified. In other words, if you start with the batteries at 100% charged, then your 109 amp-hour batteries would provide 5.45 amps for 20 hours (20◊5.45=109), until they reach a 0% charge state. However, if you apply a larger load you'll get less than 109 total amp-hours out of the battery, and if you apply a smaller load you can get more than 109 amp-hours total before the battery is stony dead.

You could calculate exactly how many actual amp-hours you'd be able to use at a given discharge rate if you're willing to do some calculations using Peukert's Law, but for your purposes, that's not necessary. All you need to know is that the amp-hour rating is always for a 20-hour discharge rate unless otherwise specified, so you can directly compare one battery to another based on the listed amp-hours.
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Old 05-10-2016, 07:24 AM   #3
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Great explanation! Just to follow up, lead acid batteries such as the Trojan T-105 (excellent batteries BTW) or likely your marine RV batteries, don't like be be discharged below 50% of their capacity. Thus your 109 amp hour batteries have a usable capacity of 109/2 = 54.5 amp hours till next recharge.

The Trojan T-105 batteries are rated at 220 amp hours (20 hour rating). Since its a 6 volt battery you need two of them wired in series to reach 12 volts. In series the amp hour rating does not double though, only the voltage. Thus two T-105 in series are rated at 12 volts and have 110 amp hours (50% of 220) of usable capacity.
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Old 05-10-2016, 07:56 AM   #4
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The Trojan T-105 are golf cart six volt batteries. They are true deep cycle batteries, and are among the best for house battery. The RV-Marine batteries are relabeled, 12 volt heavy duty Starter batteries, not true deep cycle.
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Old 05-10-2016, 03:03 PM   #5
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Originally Posted by carl2591 View Post
currently I have 2-batteries (rv-marine type) rated at 109 amp hours @1 amp.
2 12 volt batteries in parallel

2 Parallel batteries provide: the same voltage with 2x the amp hours

You get: 12 volts at 218 amp hours.


Quote:
how do they compare to the trojans t-105 which are rated at 447 mins @ 25 amps. and they show capacity of 225 amp hours 20 hrs..
The Trojan T-105 is a six volt battery. You would connect two of them in SERIES.

2 series batteries provide: 2x the voltage with the same amp hours

You get: 12 volts at 225 amp hours.

There is relatively little difference between a capacity rating at 20 hours and a capacity rating at 1 amp. The 20 hour rating is a little more conservative but not by more than a few %.

The conclusion of all this is that there isn't much difference in rated capacity.

Whether your existing batteries still deliver anything close to their rated capacity is a separate question and hinges upon how hard or easy of a life they've had, and how old they are. The only way to know for sure is to do a drain test.
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Old 05-10-2016, 05:36 PM   #6
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OK, I give. How do you do a drain test?

Quote:
Originally Posted by Jammer View Post
2 12 volt batteries in parallel

2 Parallel batteries provide: the same voltage with 2x the amp hours

You get: 12 volts at 218 amp hours.


The Trojan T-105 is a six volt battery. You would connect two of them in SERIES.

2 series batteries provide: 2x the voltage with the same amp hours

You get: 12 volts at 225 amp hours.

There is relatively little difference between a capacity rating at 20 hours and a capacity rating at 1 amp. The 20 hour rating is a little more conservative but not by more than a few %.

The conclusion of all this is that there isn't much difference in rated capacity.

Whether your existing batteries still deliver anything close to their rated capacity is a separate question and hinges upon how hard or easy of a life they've had, and how old they are. The only way to know for sure is to do a drain test.
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Old 05-11-2016, 07:38 AM   #7
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thanks that make sense sorta..

so,if i apply that same equation to the t-105's i get 220/20=11.25amps or the batteries will provide 11.25 amps for 20 hrs or to prevent total draining the batteries 11.25 amps for 10 hrs.? with no recharging energy?.

I was thinking the RV/Marine batteries were mostly junk short of being hooked up to elec most of the time.

Now to figure out how to cram two t-105s in a 2005 classic 31D battery box.
any ideas.. they are under the front sofa in separate container on both sides of the a-frame from hitch head.



Quote:
Originally Posted by Protagonist View Post
Batteries have two basic ratings:
1 - Cold cranking amps for using as a starting battery; and
2 - Amp-hours for use as a house battery.

The amp-hour rating is always for a 20-hour discharge rate unless otherwise specified. In other words, if you start with the batteries at 100% charged, then your 109 amp-hour batteries would provide 5.45 amps for 20 hours (20◊5.45=109), until they reach a 0% charge state. However, if you apply a larger load you'll get less than 109 total amp-hours out of the battery, and if you apply a smaller load you can get more than 109 amp-hours total before the battery is stony dead.

You could calculate exactly how many actual amp-hours you'd be able to use at a given discharge rate if you're willing to do some calculations using Peukert's Law, but for your purposes, that's not necessary. All you need to know is that the amp-hour rating is always for a 20-hour discharge rate unless otherwise specified, so you can directly compare one battery to another based on the listed amp-hours.
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Old 05-11-2016, 07:41 AM   #8
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pull the plug..

knock knock,,, who's there,,, dwayne,, dwayne who,,, dwayne the bathtub

I'm dwoyning...

Quote:
Originally Posted by Kilroy View Post
OK, I give. How do you do a drain test?
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Old 05-11-2016, 07:43 AM   #9
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So what voltage is considered dead? You put a dummy load on the battery and measure how long it takes to get to what voltage or when it can no longer put out the require amperage? Keeping a constant amperage on a battery that is loosing voltage is nearly impossible. Most manufactures have discharge curves for their batteries at different loads.


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Old 05-11-2016, 08:21 AM   #10
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Find a battery place that uses a 'conductance meter' to measure your battery capacity. It sends a digital pulse thru the cells and interprets the result via a proprietary program to determine the battery health.

I use one regularly and they work well.


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Old 05-11-2016, 09:01 AM   #11
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This may help;
http://www.westmarine.com/WestAdviso...e-Battery-Bank
or this;
http://www.batteriesnorthwest.com/ba...ool.cfm?TID=10
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Old 05-11-2016, 09:30 AM   #12
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Quote:
Originally Posted by perryg114 View Post
So what voltage is considered dead? You put a dummy load on the battery and measure how long it takes to get to what voltage or when it can no longer put out the require amperage? Keeping a constant amperage on a battery that is loosing voltage is nearly impossible. Most manufactures have discharge curves for their batteries at different loads.


Perry






Quote:
Originally Posted by carl2591 View Post
Now to figure out how to cram two t-105s in a 2005 classic 31D battery box.
any ideas.. they are under the front sofa in separate container on both sides of the a-frame from hitch head.
I'm not a battery expert but I've heard standard lead acid batteries can off gas small amounts of explosive hydrogen under certain charging conditions. If your battery box is located inside the trailer you should avoid the T-105 and look at an AGM battery instead. Different chemistry, same performance more or less but no gas. Unfortunately $$$$.
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Old 05-11-2016, 10:35 AM   #13
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I remember my first experience with my current Classic and finding the batteries very low after a long period of non use with the master disconnect switch turned off. I borrowed a meter from a friend and tracked the current draw with the master disconnect switch turned on and off. Not to my surprise was that their was a power draw of .1 of an amp when the disconnect switch was in the on position. I attributed that to all of the appliances while turned off, still had some component that was alive. When the switch was in the off position, I saw a .01 of an amp draw, which is from the propane detector. If you know your amp hour capacity of your batteries, you can do the math and figure out how long it will take for the battery(ies) to fall into a lowered state.

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Old 05-11-2016, 01:55 PM   #14
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More to it than just batteries

I have a 2005 22ft. CCD with four solar panels and an excellent charge controller that lets the shoreline charge controller take over when plugged in. I have used Trojan 6v batteries in this for 11 years and also in a previous RV.

Trojan T105 batteries are excellent. They make a newer model with "Smart Carbon" technology that more than doubles the warranty and life of the battery. Those batteries are about 10% more expensive and are called T105 RE-B.

The T105 RE-B is just a little taller than the regular 105 so keep that in mind when expanding your battery box. I built a whole new battery box out of acid resistant PVC. If you're not a big DIY guy, find a weld shop after you get your batteries to fabricate something classy. There should be no flooded deep cycle batteries inside the trailer. Make sure the new battery box is vented and has good drainage.

Marine/RV batteries are generally not as efficient as true deep cycle which the Trojans are.

If you're worried about power, the very first thing that you should do is change all of your lighting to "WARM" LEDs. Warm LEDs have a "light temperature" of 2700. That is not heat but the type of light. 2700 will replicate warm incandescent lights and use about 10% of the power.

Superbrightleds.com is a great place for LEDs. For a few pennies more, Colonial Airstream has the exact replacements for older Airstreams. For a couple of hundred dollars they will create a kit for you to replace all of your lights. I went through Colonial because it was so easy and my power usage plummeted.

The next thing that you need to worry about is the charge converter. There are lots of discussions on this forum. You probably have a Magnatek or Parallax 7355 55 AMP charger converter. The trouble with the older converters is that they just put out one voltage. Newer converters have variable charge rates that will recharge the batteries much faster. This is really important if you are charging from a generator.

The second problem you have with your converter is that it has a charge rate of 13.6V. Modern converters charge at 14.4 -14.8 volts up until 90% of charge and then drop to the 13.6v until charged and then stay at 13.2v for a float charge. You not likely be able to fully recharge Trojan 105s with your converter at 13.6v. Those batteries require a ďBulkĒ of 14.4v to 14.8v and a float charge of 13.2v to 13.5v. BEFORE YOU BY ANY BATTERY, call the manufacturer and ask about charger requirements.
If you intend to be in weather below 40 degrees or over 80 degrees, that also will affect your charge needs and ideally, you might want a charger with a temperature sensor that will also adjust your charge rate. You can buy an upgrade kit for somewhere between $200 and $400. Make sure you stay with a 55 amp converter upgrade. Anything else could damage the trailer electronics.

I upgraded my shoreline charge controller to a Progressive Dynamics 4655 for $215. It has no temperature compensation but does sense the voltage with the charge wizard. There are other better ones out there but I only use my shoreline for one or two days per year. It was a little extra work to install this model as I needed more battery cable length which constituted a little extra work to pull the cable.

My solar controller senses temperature and charge charging at rates between 13.2 float and 14.8 bulk.

If you are not all that DIY minded, I would suggest bestconverters.com as they are competitive in price and offer all the Tech support you could want.

So, there is more to batteries when it comes to power.
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