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Old 02-23-2011, 10:27 AM   #1
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Acceptable voltage drop on 12V?

We recently got two 55w solar panels (paralleled) and a charge controller. When charging, the battery voltage reading is around 12.95 - 13.3, with a trickle charge from the controller. The morning after disconnecting the panels (about 14 hrs), the battery reading was 12.5 (no loads on either reading; battery disconnect switch in Bambi was activated during charging as well). The 2 paralleled batteries are oem (Oct. '06 purchase date). Do these readings indicate the batteries are holding a charge appropriately, or should I be looking at replacing them, and if so, what battery works best with solar?

Thanks for your input!

-Jerry
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Old 02-23-2011, 11:12 AM   #2
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From my expereince, your batteries are past their prime by a long way at five years old.

Now, a static voltage of a charged battery should be 12.6 volts after having been off the charger for a while and with no load. If your batteries won't read 12.6 volts for a good while (like a day or so) in this condition, I'd replace them.
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Old 02-23-2011, 11:58 AM   #3
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Question There are to many unknowns

Quote:
Originally Posted by ESCAPE POD View Post
We recently got two 55w solar panels (paralleled) and a charge controller. When charging, the battery voltage reading is around 12.95 - 13.3, with a trickle charge from the controller. The morning after disconnecting the panels (about 14 hrs), the battery reading was 12.5 (no loads on either reading; battery disconnect switch in Bambi was activated during charging as well). The 2 paralleled batteries are oem (Oct. '06 purchase date). Do these readings indicate the batteries are holding a charge appropriately, or should I be looking at replacing them, and if so, what battery works best with solar?

Thanks for your input!

-Jerry
Jerry,

There are really too many variables here to make a judgment on the condition of the batteries. Simply the age of the batteries is not an indication of condition. The care and use during this time period will greatly affect the condition and usability of the batteries.

In this case how long were they charging? Was there any load at all? etc?
Even if all the variables are known, the condition of the battery still is not really defined.

Unless a battery is obviously bad, the only way to truly evaluate it is by charging it with a high quality automatic charger. Then test it under load with a high quality tester. I have a tester that is essentially a large load resistor with electronic circuitry that translates the voltage to a value that can be read by a computer. Software running on the computer plots the voltage over time. comparing this curve to what a "good" battery's output should look like will give you the "condition" of the battery.

Auto electric shops should have equipment to test batteries under load.

My advice is to use the batteries as you intend to use them and see if they meet your needs. You can simulate camping for a couple of days, turning things off and on and see how long they last.

When solar charging is thrown into the equation, many more variables come into play such as weather, time of the year, where you are parked, etc.

You can replace your batteries now, and know where you are starting out, but you may be spending money unnecessarily.

As far as what type of battery, I will leave that to others, as there seems to be many rather firmly held opinions on that subject on these forums.

Personally, I do not replace a battery until it is no longer able to fulfill the need I have for it. I have often used batteries ten years or longer before replacement.

Regards,

Ken
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Old 02-23-2011, 12:11 PM   #4
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Originally Posted by w7ts View Post
...You can replace your batteries now, and know where you are starting out, but you may be spending money unnecessarily....
Concur.

The best (and quickest and cheapest and easiest) test is to use the batteries for a day or two under your typical load conditions, which usually means lights, mostly. If you come out the other side at or above about 11.9V, I'd keep 'em (the chart below is a little bit conservative). Remember, if you get below 20% charge, you are damaging the battery. If you completely discharge a lead-acid battery, it only takes a handful of times and the battery is worthless.

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Old 02-23-2011, 12:11 PM   #5
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Agree with w7ts. If your batteries have stabilized some after being off charge, 12.4 to 12.6 = 75 to 100% charge. Over 12.6 = 100%.

Well maintained batteries can last a long time if they are not discharged over 50%, kept watered and receive a periodic equalization charge.

Am new to Airstreaming and don't know if the converters in our trailers will even do an equalization charge(where voltage is brought up quite high to eliminate sulfation which inhibits a battery's ability either to accept a charge or to discharge). My experience is more with boats which can have good chargers with a equalization charge capability. On my boat, I disconnected all loads because the high voltages could damage electronics.
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Old 02-23-2011, 12:32 PM   #6
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Agree with w7ts. If your batteries have stabilized some after being off charge, 12.4 to 12.6 = 75 to 100% charge. Over 12.6 = 100%.

Well maintained batteries can last a long time if they are not discharged over 50%, kept watered and receive a periodic equalization charge.

Am new to Airstreaming and don't know if the converters in our trailers will even do an equalization charge(where voltage is brought up quite high to eliminate sulfation which inhibits a battery's ability either to accept a charge or to discharge). My experience is more with boats which can have good chargers with a equalization charge capability. On my boat, I disconnected all loads because the high voltages could damage electronics.
Your experience with boat electrical systems is exactly transferable to RVs. The stock converters in the Airstreams that I have seen, including mine, are not very battery friendly. The stock one in mine was a Parallax 7455. My trailer was only a few months old when I made to the decision to upgrade the converter to something more sophisticated. My main motivation was battery longevity. I choose an IOTA brand controller that does the equalization charge periodically. There is no provision for disconnecting the loads when this occurs and I have had no electronics failures. However electronics in travel trailers are not as necessary as those in boats.

Ken
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Old 02-23-2011, 01:10 PM   #7
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Jerry
I have a factory solar system on my trailer and my batteries are only slightly newer than yours(trailer manufacture date April 2007). My batteries are still preforming well. I periodically use a BatteryMINDer 12 Volt Charger/Maintainer/Conditioner; in the Pulse Mode to desulphate the batteries. Before replacing your batteries you might try this and see if you can extend their life. BatteryMINDer 12 V 1.3 A Plus
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Old 02-23-2011, 01:51 PM   #8
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Quote:
Originally Posted by ESCAPE POD View Post
We recently got two 55w solar panels (paralleled) and a charge controller. When charging, the battery voltage reading is around 12.95 - 13.3, with a trickle charge from the controller.
That high of a charge voltage at a low charge current (5 or 6 typically from a panel that size) is indicative of a high internal resistance in the batteries, which means they are old.

Quote:
The morning after disconnecting the panels (about 14 hrs), the battery reading was 12.5 (no loads on either reading; battery disconnect switch in Bambi was activated during charging as well).
As noted upthread that means that the batteries weren't quite charged all the way.

Quote:
The 2 paralleled batteries are oem (Oct. '06 purchase date).
It probably doesn't matter, but to be clear, I don't believe there is such a thing as an "OEM" battery, per se, except for the optional AGMs. It is my understanding that Airstreams are shipped without batteries. Dealers purchase batteries locally and install them.

Quote:
Do these readings indicate the batteries are holding a charge appropriately, or should I be looking at replacing them
The readings show that the batteries are several years old, which should be unsurprising, since they are several years old. You will have to decide for yourself how much battery performance you're willing to lose before you replace them.

Quote:
what battery works best with solar?
The fact that you use solar shouldn't affect your choice of batteries.

The choice you should be making is between flooded deep-cycle batteries and AGM batteries. AGMs cost more and work better. There are many threads discussing the tradeoffs.
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Old 02-23-2011, 02:42 PM   #9
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Hmm. When I push the battery button on the panel, ours reads 14.1 or a couple points higher right after we've been hooked up for a few days presuming they are fully charged.

After a day or two running we are around 13.8 or so depending on usage. Our 2 batteries are new last November, Costco Group 24 type.

Now I'm really confused seeing these numbers around 12 volts. I've used this PDF & graph http://www.scubaengineer.com/documen...ing_graphs.pdf to see where we're at percentage wise which seems to line up with the C20 graph on page 2.

I'm the first to admit I am a complete idiot when it comes to the math for electric stuff. But now I'm really confused as to why some are talking 12 volts and other in the 14 range but I have been thinking my bottom limit voltage number should be around 13.3 or so.

If anyone would be willing to dumb it down to toddler level for me, I'd appreciate it
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Old 02-23-2011, 02:55 PM   #10
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Quote:
Originally Posted by webtrippin View Post
Hmm. When I push the battery button on the panel, ours reads 14.1 or a couple points higher right after we've been hooked up for a few days presuming they are fully charged.

After a day or two running we are around 13.8 or so depending on usage. Our 2 batteries are new last November, Costco Group 24 type.
Probably, the panel is off by a volt or so. That's not unusual. The batteries won't stay up at that kind of voltage under load for more than an hour, max.
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Old 02-23-2011, 03:10 PM   #11
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The voltage when hooked up to the solar is very low. you should be at 13.5 to 14.2 . you are starving the batteries. how far is your controller from the batteries?
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Old 02-24-2011, 12:27 AM   #12
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The voltage when hooked up to the solar is very low. you should be at 13.5 to 14.2 . you are starving the batteries. how far is your controller from the batteries?
Being new to the terminology, I'm not sure what is meant by "starving the batteries". The controller is literally 3 inches from the batteries, just outside the battery box.
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Old 02-24-2011, 02:09 AM   #13
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as i understand it, a/s ships interstate batteries with new units from j/c,

so that's the 'oem' brand most of the time, and they are perfecting fine batteries.

when the upgraded agms are part of the order, then it's lifelines as oem.
________

by 'starving' i think arod' means the voltage from the solar (going to the batteries is JUST barely above threshold to charge.

in the simplest terms juice flows downhill.

so a charge voltage of 14.2 means a taller/steeper hill (gradient), which will fill the batteries faster.

if one thinks of a "full battery" at ~12.7v then anything above 12.8 is SLIGHTLY providing a fill.

but since the gradient is so small, it takes a really really long time to FILL 2 da'max (and maybe never if usage happens while filling)

another factor is WHICH solar controller is used and it's programing.

for example some don't KICK on the solar charging until the batteries DROP voltage to a predetermined level (for example 12.5 or 12.6 or ...)
____________

2 typical group 24s provides about 80-90 amps of useable juice.

110 watts of solar provides ~6.5 amps/hour under perfect/ideal conditions

so it takes 13-18 hours of GOOD sun exposure to replace 80-90 amps of usage.

realistically that means 2-3 days (or more) of quality sun or ~ 35-50 amps per day.

so, USE less than 35-50 amps per day and the solar MIGHT just barely keep up...

use more and the net will be a small LOSS in reserve each day, so the batteries slowly deplete.
_________

another way to think of it is this...

the trailer has about 2-3 days of useful juice, IF one is careful with it.

adding 110 w of solar means extending that to 3-4-5 or 6 days IF thrifty....

and the sun shines.

IF one wants 1. to use more daily or 2. want to greatly extend the days available...

the system needs LARGER or additional batteries, and perhaps more collection panels.

some of this was covered just recently...

http://www.airforums.com/forums/f448...wer-71048.html
________

while my unit has the agms and i do LIKE them, simply because of ease of maintenance,

the advice given so far to keep using the current flooded cells till they crap out is good.

some of that same discussion happened just last week...

http://www.airforums.com/forums/f449...ing-74098.html

IF u want more info on batteries, there really are dozens of good threads on this issue.

cheers
2air'
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Old 02-24-2011, 07:20 AM   #14
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The batteries need to be "fully" charged with a good battery charger before you can test for any condition.

To test to see if they can hold a charge.
Fully charge the batteries. After a full charge disconnect the batteries and let set for 24 hours. After 24 hours voltage should be 12.6VDC or slightly higher.

OR

Remove the batteries and take to a parts dealer like Auto Zone or any of the others they have equipment that will load test the batteries at no cost.
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