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Author Topic: House battery question  (Read 7727 times)
Danny
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« on: May 29, 2007, 01:22:08 PM »

Getting ready to buy the house batteries.  What are the pros and cons of each (marine deep-cycle or 8D Deep-cycle)?

As always - thanks,

Danny
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« Reply #1 on: May 29, 2007, 01:25:20 PM »

Look here: http://www.busconversions.com/bbs/index.php?topic=3071.0

 ELECTRICAL SYSTEMS AND BATTERIES

Richard
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Dallas
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« Reply #2 on: May 29, 2007, 01:29:50 PM »

Pro's:

I can lift and carry Group 31 or Group 27 Marine Batteries.

I like the Ah of the 8D's.

Con's:

8D's weigh in at around 150 pounds each. I would just as soon not have to move them.

Marine batteries are a compromise between starting and deep cycle batteries.
------------------------------------------------------------------------------------------------------------------

You may want to think about using Real deep cycle batteries, something like L-16's (12V) or T-105, T-145, T-160 (6V)

good luck,
Dallas
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« Reply #3 on: May 29, 2007, 01:32:36 PM »

I also found that the warrenty on the 8D's was generally not as good as that on the smaller physical size batteries.
Richard

Pro's:

I can lift and carry Group 31 or Group 27 Marine Batteries.

I like the Ah of the 8D's.

Con's:

8D's weigh in at around 150 pounds each. I would just as soon not have to move them.

Marine batteries are a compromise between starting and deep cycle batteries.
------------------------------------------------------------------------------------------------------------------

You may want to think about using Real deep cycle batteries, something like L-16's (12V) or T-105, T-145, T-160 (6V)

good luck,
Dallas
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cody
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« Reply #4 on: May 29, 2007, 01:33:49 PM »

I have 2 golf cart batteries in my bus, they are huge and I'm not looking forward to the day I have to pull them out and replace them, they have been in the coach the 3 years I've had it and all I've needed to do is clean the posts and add some water now and then, I don';t even know what kind they would be called but they sure do a great job.
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Jerry Liebler
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« Reply #5 on: May 29, 2007, 01:55:14 PM »

Danny,
     The biggest questions are: How many amp hours?  12 volt house or 24?  Do you want the monthly chore of adding water?  How big is your budget?  Others have done lots of research and found that if you'll properly maintain them (water and charge) The T105 golf cart flooded cell is the most cost effective, They are 6volt batteries at about 200 ah.  If floor space is at a premium for them and you can use heavy batteries that are 16" tall the L16s are the choice, again 6volts per but about 400 ah. they have the same footprint as the T105  If you can afford them sealed L16 are a great choice but they cost about $400 each and weigh about 125 pounds each, 4 of them gets you 800 AH of 12 volt capacity.  The 8Ds are 12 volt and not a true deep cycle battery but many are in use and work well.  With any deep cycle battery it's life is much greater if only the top 1/2 of it's capacity is ever used so you'll want to recharge them after using about 1/2 the rated capacity. Marine deep cycles aren't a good choice their cycle life is compromised by the design trade offs that allow use as starting batteries.
Regards
Jerry 4107 1120
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Danny
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« Reply #6 on: May 29, 2007, 08:11:38 PM »

If a person got 4 - 6V golf cart batteries, would you wire two in series and then the set in parallel to get it up to 12V? 

Danny
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« Reply #7 on: May 29, 2007, 08:42:38 PM »

Danny,
    That's the general concept.  The batteries should all be the same age and as close to identical as possible.  In an effort to keep them all the same, throught their life of many charge and discharge cycles, the wire size and length should be the same when one traces the path from one load connection to the other through either of the paralleled pairs.  The Trace inverter manuals show several arangements that provide the equal length.
Here is my crude attempt to draw one of the arrangenents .
Load +---!---+  bat 1  --!
             !                    !
             !      !---------!
             !      !
             !      !+ bat 2  -------!
             !                             !
             !----+ bat 3  --!        !
                                  !        !
                      !--------!        !
                      !                    !
                      + bat 4  -------!---- load - connection

Regards
Jerry 4107 1120
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Sean
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« Reply #8 on: May 29, 2007, 10:38:56 PM »

Folks,

Let's not confuse battery type with battery size (which is also different from capacity).

Asking "What's better, marine or 8D?" is like asking "What's better, 92 Octane or 15 gallons?"

I don't want to irritate anyone by repeating here information that is readily available either in the archives of this board or other bus boards (e.g. BNO), or at various other excellent resources such as:
http://www.phrannie.org/battery.html
http://www.windsun.com/Batteries/Battery_FAQ.htm
and many others.

However, and with due deference to my good friend Jerry, I'd like to note that any type of battery, to include starting, deep-cycle, marine (which is a type of battery that, by definition, attempts to compromise between starting and deep-cycle performance), traction, float-service (emergency back-up batteries), AE (Alternative Energy), etc. can be made in any size, such as Group 31, 8D, L-16, etc.

It is a fact that most batteries in, for example, BCI Group Size 24 will be starting batteries, while most batteries made in size L-16 will be traction batteries.  However, there are a number of sizes, notably 8D and Group 31 (among others) that are very popular form factors for a number of different uses.

One can find 8D batteries that are pure starting batteries, strict deep-cycle batteries, marine batteries, and even traction batteries (especially in EV usage) as well as AE batteries.  And one can find "marine" batteries in a wide range of BCI group sizes and including 8D.

FWIW, as stated elsewhere in many places, I believe "marine" batteries are never the right ones to use in a motor coach.  Use starting batteries for starting, and use AE, Traction, or "deep-cycle" batteries for your house systems.  What size (form factor) you choose depends on many factors, including how much capacity (in amp-hours) you need or want, what the shape of the battery compartment will look like, how much weight you want to carry, etc..  Lastly, within "type", you will often be faced with a choice of technology, to include "traditional" flooded lead-acid (which, BTW, includes many "maintenance-free" batteries that are really flooded cells, just without user-accessible caps), gelled-electrolyte, Absorbed Glass Mat (AGM), and even Lithium-Ion (yes, there are AGM starting batteries, just as there are flooded deep-cycle batteries).  Choice of technology will be driven by ease of service access, availability of proper venting, laziness of the owner, and other factors.

Choosing the right batteries is one of the often-overlooked "critical" decisions in how well your coach will perform, especially if you spend considerable time away from shore power.

Good luck on your research.

-Sean
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« Reply #9 on: May 30, 2007, 07:00:49 AM »

"What's better, 92 Octane or 15 gallons?"

Sean - as always, masterful.

And a great quote, to boot! Smiley
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« Reply #10 on: May 30, 2007, 07:15:53 AM »

Sean,
     No need to defer, I agree fully with your statements, just didn't write those details in my previous post in interest of brevity and clarity. 

Danny,
    I'd like to add to what Sean said about the need for lots of consideration in choosing batteries, it's a choice many regret later.  Two attributes of the house bank are often regretted later so consider these extra carefully. Wet vs sealed; many choose wet for cost and wish for sealed soon after, you'll live with the choice for 10 years or so so think hard.  Capacity; many wish for more than they started with, batteries do loose capacity over their life, this is often not taken into account,so best to choose a capacity safely above what you think you'll need.
Regards
Jerry 4107 1120 
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« Reply #11 on: May 30, 2007, 03:55:26 PM »

What is the recommended charge level for AGM Batteries?  I normally try to keep my lead/acid starting batteries at 13.6 with the occasional run to 14.6 if they've sat untapped for a while....then let them settle back to the 13.6

The AGM's are a different matter...what's the good word guys?

NCbob
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Sean
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« Reply #12 on: May 31, 2007, 08:50:44 AM »

You should set your charger to the parameters recommended by the manufacturer of your particular batteries  -- every AGM is a bit different.

I am in the middle of changing out batteries right now, so I happen to have the specs handy on my brand new Trojan 8D AGMs, which require a bulk setting of 14.1 and a float setting of 13.5.  My old Xantrex AGM batteries wanted the same float, but a much higher bulk setting of 14.4.

If the required settings are not stamped right on the batteries, you can usually find them on the web site of the battery manufacturer.

-Sean
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« Reply #13 on: May 31, 2007, 09:11:28 AM »

Sean - did you get a good deal on the Trojan's ? - I will be interested in seeing how they work since the next time these Lifelines crash I'm leaning towards Trojan's - Thanks
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« Reply #14 on: May 31, 2007, 11:07:07 AM »

Niles,

I'm sworn to secrecy on what I'm paying.  Infinity is happy to sell me any of a number of batteries, but they do a ton of business with Trojan and so were able to give me a better price on those.  (To explain: I get special pricing from Infinity due to a long past relationship, and I'm paying installation and fabrication labor on top of the price for the batteries.)  I think Infinity's street price on these is $418ea.  Right now, we're crossing our fingers that we can make them fit -- they are just enough larger than the Xantrex units we took out, that it will be a tight squeeze, and we'll have to rotate four of them 90 degrees from the original plan, as well as make new hold-downs and jumper cables.

If the Trojan 8D's can't be made to fit, we'll go to Discover 4D's.  They actually have a higher 20-hr rating (245 AH) in a smaller package, but they're also another $35-$40ea.  BTW, Discover also makes an 8D size with a whopping 290AH 20-hr rate.  Pricey, but worth it if you have limited space or are trying to pack more AH into an existing rack.

FWIW, I consider $1.65 per AH (@12v, 20-hr rate), exclusive of tax, shipping, installation, etc. to be a rock-bottom price on deep-cycle AGM batteries, $1.75-$1.85 per AH to be average pricing from Internet and discount vendors, and roughly $2 per AH to be the going rate for bricks-and-mortar vendors, also known as MSRP.

Current status of the project, as always, will be on our blog.  That's also where I'll be posting about how they are working out, as we develop some experience with them, so stay tuned.

-Sean
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captain ron
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« Reply #15 on: June 01, 2007, 06:30:03 AM »

Sean, Would you please explain amp hrs/20 hr rate and how to figure your amp hrs. I'm going to need house batteries very soon and I want to know what I'm looking for when I buy them.
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« Reply #16 on: June 01, 2007, 06:55:32 AM »

Sean,
    I think I may have to get 4 of these.
http://www.hardysolar.com/shop/product.php?printable=Y&productid=17530&cat=47&page=1&js=n
At  $397 for 390 AH they sure beat your prices.
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Jerry 4107 1120
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« Reply #17 on: June 01, 2007, 07:03:12 AM »

Sean,
   Sorry I didn't pay attention to the 12 volt so the L16s do cost quite a bit more Darn.
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Jerry 4107 1120
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« Reply #18 on: June 01, 2007, 07:33:38 AM »

Captain Ron,
     I'll volunteer to answer your questions till Sean gets to it.  To estimate how many amp hours you'll need you'll need to determine how many watts of load you'll be running and how long you want to run them.  If you are running any of the loads through an inverter you'll need to add about 20 % to that portion to account for inverter efficiency.  Then you divide the total watt hours by your house battery voltage (either 12 or 24). The result of this calculation is amp hours you'll be taking from the battery.  For reasonable battery life you'll want a house battery bank with a capacity of 2 times that number, because for good battery life only 1/2 of rated capacity should be used. 

Batteries by their nature have higher capacity if they are discharged more slowly.  Because of this fact it matters how they are rated by the manufacturer.  In order to compare different batteries accurately the time to complete the discharge needs to be known.  The 20 hour discharge rate is available from most deep cycle battery manufacturers though some will feature higher capacity numbers but for longer discharge times.  For example the same battery may have a 390 AH rating at a 20 hr discharge rate and a 420AH rating at 100 hr rate. 
Regards
Jerry 4107 1120
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« Reply #19 on: June 01, 2007, 09:08:26 AM »

Ron,

This link:

http://www.windsun.com/Batteries/Battery_FAQ.htm#Amp-Hour%20Capacity

which is one of the pages from one of the two excellent references I posted in my first reply here, explains amp-hours pretty well.

To add to it, and to what Jerry said (and as emphasized by Jerry's slip regarding the 6-volt batteries), the concept of Amp-Hours is useful for comparison (because it is commonly published), but only at a specified voltage.  In reality, the energy capacity of a battery is better expressed in watt-hours, which is a measure that takes the voltage into account.  In other words, a 200AH 12-volt battery stores twice as much energy as a 200AH 6-volt battery.  One place where this effect comes into play is when using 12-volt batteries in a 24-volt system.  So while I just bought eight batteries, each with a 230AH rating, my total system capacity will be 920AH because it will be running at 24 volts, and that is what I have to use when programming my battery monitor.

Jerry is right about how to figure your needs.  But I understood your question to mean "how big are my existing batteries?"  Unfortunately, there is no easy way to figure this.  If you know the manufacturer, model, and size, you can probably look up the rated capacity.  The only other way to do it is with a load-tester, which is a long process that requires the batteries to be out of the circuit.  Commercial load testers are available, for a price, but you can make your own from a bank of light bulbs and a couple of meters.

What you might want to do instead is to get an energy monitor, which, really, you ought to have any way.  There are several good ones on the market, such as the Xantrex Link-10 and the Tri-Metric.  These meters actually "count" amp-hours going into and coming out of the batteries.  In order to work properly, in terms of their "gas gauge" and "hours remaining" displays, you need to know the total capacity of your bank.  But there is a trick -- set them to some capacity bigger than you have (by, for example, looking at published capacities of similar batteries, then adding 10-20%).  Fully charge your batteries, and reset the meter.  Then run your coach until the battery voltage drops to the level where the meter reports "low battery" (which it will do based on voltage, irrespective of what you set the capacity to).  Then you can read, from the meter, the total number of amp-hours used, and this will give you an idea of the working capacity of your bank.

HTH.

-Sean
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« Reply #20 on: June 01, 2007, 09:43:12 AM »

I did a bit of shopping, on the www, for AGM batteries.  It looks like the Toyo 6GFM200A is the most economical.  210 AH @ 20 hr. & Sunelec.com is asking $230.  It looks like it's about a 4D size.  19.53"x9.84"x8.15"h.   If I stood them on edge I could almost fit 4 where I have 4 L16s now, fortunately the L16s are still working fine.
Regards
Jerry 4107 1120   
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« Reply #21 on: June 01, 2007, 10:17:04 AM »

Sean,
Are those four batteries a complete change out of your house batteries or just part of them?

I am just trying to get an idea of your total pounds of batteries.

Never mind, I misread the posts.

Lee
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Sean
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« Reply #22 on: June 01, 2007, 01:01:08 PM »

I'm changing all eight of my house batteries.

I had Xantrex batteries, which we got cheap when Xantrex discontinued their rolling-cart inverter-battery system, can't remember what they called the product.  They had loads of these ~8D size 215AH AGM batteries with weird terminal arrangements, and they dumped them.

We've used them hard for three years, they were on Infinity's shelf for a year, and they were probably on Xantrex's shelf for two years before that.  For the price (a little over $100 apiece, IIRC), we definitely got good value out of them.

We came back here to have them replaced, because we knew that the weird terminal arrangement meant that new cables and tie-downs would have to be fabricated.  It's also turned out that the size was just enough different that we've had to modify the racking slightly as well.

The replacement Trojans are 155# each, so my new house bank weighs 1,240 pounds.  Cabling, racks, and tie-downs probably add another hundred pounds.  I'll try to post some photos of the installation on the blog when they are done.

Jerry -- the dimensions, specs, and even the terminal arrangement on those Toyos look almost identical to the Xantrex units we just took out.  (Xantrex, of course, simply OEMed the batteries from someone, maybe Toyo.)  And the price is right.

-Sean
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« Reply #23 on: June 01, 2007, 01:21:16 PM »

I found an on-line copy of the specs on my old Xantrex batteries, here:

http://www.partsonsale.com/xantrexbattery.pdf

After comparing them, I have to guess that the Toyo's you found are the same battery.  (I note Toyo claims a 210AH 20-hr rate, whereas Xantrex claimed 215AH.)  The dimensions, terminals, and power curves are identical.

So, probably, I could have just bought eight of those and had drop-in replacements.  Three years ago, I had done considerable research to try to find out who was making the batteries for Xantrex and how to get direct replacements, and came up empty-handed.  Oh well.

-Sean
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« Reply #24 on: June 01, 2007, 03:03:10 PM »

Sean,
     Dallas asked me how to compute the Peukert exponent, I didn't know but I do now.  Peukert defined battery capacity as the hours a battery could supply one amp and discovered that that discharge time  at any other current was the product of time, in hours,  and the actual current raised to the ' Peukert' exponent.  If one has two discharge conditions for any battery one can compute both the 'Peukert capacity' and the 'Peukert exponent'.  The ideal battery would have a 'Peukert exponent of 1, typical lead acid batteries are from 1.05 to 1.3.  The lowest exponent I've seen (1.05) is An MK AGM in size 8D.

Who cares?  Well if your usual loads take more than 20 hours to discharge then finding a battery with a higher exponent will mean you actually get more than you paid for, in capacity.  While the battery with the lowest exponent will most closely approach the predicted performance when discharge currents exceed the 20 hr rate.  BTW AGMs  generally have lower exponents than flooded batteries.  I calculate that your new Trojan AGMs have an exponent of 1.22
Regards
Jerry 4107 1120
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« Reply #25 on: June 01, 2007, 04:01:28 PM »

Jerry,

I was trying not to open the whole Peukert can of worms here :-)

The Peukert exponent is one of the parameters that also needs to be programmed into your battery monitor in order to get an accurate energy-remaining indicator.  My Link-10 has a default setting for this, IIRC, of 1.15.

One of my pet peeves is that battery manufacturers should, but usually do not, publish the Peukert exponent for their batteries.

An on-line Peukert calculator (along with some other good battery info) can be found here:
http://www.geocities.com/CapeCanaveral/lab/8679/battery.html

A lengthy technical explanation of Peukert's equation, and how it is often misused, is here:
http://www.smartgauge.co.uk/peukert2.html

And, yes, the Peukert Exponent of my new Trojans is about 1.221.  But, I can go around telling people that I have some of the largest Trojans around, or, alternatively, I use a bigger Trojan than so-and-so.  FWIW.

-Sean
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« Reply #26 on: June 01, 2007, 04:16:45 PM »

Thanks Jerry,

I have been looking for the Puekert exponent for my batteries (Walmart Marine) with an Ah of 125. Unfortunately, I've had no luck. They are built by Johnson controls who also make Optima, Diehard and many others.

To maybe make it a little easier for everyone to understand the importance of the Peukert Equation is to put it this way:

If you have a battery with a capacity of 100Ah that's what you can expect out of it under certain circumstances. The lower your current draw, the more actual useable amp hours there is.

Now if you add another battery to your first battery, it seems like you would have 200Ah. Well, not quite. What you may see is something on the order of 230Ah.

From my understanding, and it may be flawed, as usual, the reason for this is, instead of drawing say, 50A at the 20 hour rate, you are actually only drawing 25A per battery at the 20 hour rate. Since we know that the lower the current draw, the more Ah you get, you have effectively more than doubled you capacity by adding one battery.

There is a problem with Puekerts exponent as it is normally written, but I will leave that up to you dear reader to find.

For those interested here is the equation as copied form Smart gauge Electronics.com:

 Iⁿ T = C

Where:

I = the discharge current in amps
T = the time in hours
C = the capacity of the battery in amp hours
ⁿ = Peukert's exponent for that particular battery type

More on this at:

http://www.smartgauge.co.uk/peukert2.html

And another Puekert battery life calculator:

http://www.csgnetwork.com/batterylifecalc.html

Dallas

(Sean Posted before I got done typing) Tongue
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« Reply #27 on: June 01, 2007, 04:41:36 PM »

Dallas,
     The equation is fine BUT the capacity is the hours at 1 amp load NOT what is specified on most batteries.
That is the missuse Sean is referring to.  Be careful. 
Regards
Jerry 4107 1120
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« Reply #28 on: June 01, 2007, 04:48:50 PM »

Sean, 
     How does your battery monitor handle charging?  Is Peukert's equation appropriate to charging as well?
On my long list of someday projects is designing building a battery monitor.
Regards
Jerry 4107 1120
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Dallas
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« Reply #29 on: June 01, 2007, 05:40:17 PM »

Jerry,

Here is the Modified equation Smartgauge uses.

T = C/(I/(C/R))ⁿ X (R/C)

Where:
I = the discharge current
T = the time
C = capacity of the battery
ⁿ = Peukert's exponent for that particular battery type
R = the battery hour rating, i.e. 100 hour rating, 20 hour rating, 10 hour rating etc.

I tried it and it seems to be much closer to real life than the original.

Of course, that is using my cheapo Wally world batteries.
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« Reply #30 on: June 01, 2007, 05:59:43 PM »

Dallas,
     It's really the same equation but put in a form that doesn't require what is called the 'Peukert capacity' but instead uses what's usually given by most manufacturers amp hours achieved in a timed discharge.
if you have  two sets of  amps and time values to discharge a single battery you set up the first equation
twice then subtract one copy from the other dropping out the Cp(Peukert capacity) and solve the resulting equation for the exponent.
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Jerry 4107 1120
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« Reply #31 on: June 01, 2007, 06:14:49 PM »

Dallas -- sorry I beat you to the punch.  As Jerry noted, the page I posted cautions against the "simple" version of Peukert's equation -- the only "capacity" that works in that equation is the "Peukert Capacity" -- the amp-hours available at a 1-amp draw rate.

Jerry -- Peukert refers only to drawing energy out of the batteries.  Putting energy back in also has a "fudge factor" that must be applied, often called the "Charge Efficiency Factor (CEF)."  This measures how much of the input energy actually gets translated to chemically stored energy in the battery.  (To answer the obvious question, "where does the rest of the energy go?" -- it is heat, as can be easily demonstrated by measuring the temperature of the batteries as they are charging.)

The meter I use (which I highly recommend), the Xantrex Link-10 (not to be confused with the very similar but lower-quality Xantrex Battery Monitor), has settings for both.  The Peukert Exponent must be entered by the user -- the factory default of 1.25 (not 1.15 as I guessed earlier) is sufficient for most users if the exponent is not known.

The CEF may be manually entered, but the recommended setting is to allow the meter to calculate it on a rolling basis.  It does this by using a set of user-entered parameters to know when the charging process if finished, including final voltage of the system and amount of current flowing from the charger.  If you set these correctly, then every time the batteries charge up fully, the meter resets the amp-hours "used" to zero, and re-figures the CEF (since it knows how depleted they were, and how much energy was put back in).

The Link-10 also keeps a running total of the number of cycles your batteries have been through, what the average Depth-of-Discharge (DOD) is, and what the deepest-ever DOD was.  Very handy information.  I think I paid around $135 for mine on eBay -- a worthwhile investment.

-Sean
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« Reply #32 on: June 01, 2007, 06:40:28 PM »

Sean,
     Thank you!  Was/is the Link 10 originally the 'Emeter' from a Seattle area company named 'Cruising Equipment that was bought by Xantrex?  I'm quite sure it is/was.  I've had many lunches with the 'Emeter's designer as it uses a microprocessor made by my former employer.  The reason I kinda want to roll my own is  I don't want a resistor to sense current.  I've got some neat current sensors that measure the magnetic field around a wire, essentially lossless (it takes some power for the hall effect sensors and electronics).   
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« Reply #33 on: June 01, 2007, 11:26:34 PM »

Jerry,

You seem to have answered your own question... Yes, indeed, they are one and the same.  Only the screen-printed decal on the meter's face has changed.

As for substituting Hall-effect sensors for the shunt, you can probably still use the Link-10 (E-Meter) if you can translate your Hall-effect signal to a 0-50mV output (WRT ground) -- the Link shouldn't know the difference.  Just remember that you need to measure the current flow at the interface between battery negative and ground, rather than at the positive end of things.

FYI, installation and operating instructions for the Link-10 (in .PDF) are here:
http://www.xantrex.com/web/id/72/docserve.asp

-Sean
http://OurOdyssey.BlogSpot.com
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