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Old 12-07-2013, 03:09 PM   #1
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RV battery charging

I have a 1994 Bounder with the original converter/charger still working fine. But it does take quite a while to bring back up my batteries. It does not put out like the newer ones. When dry camping I must run the generator for a long time to get them up.

I was looking at those newer battery chargers at wally world. 2amp maint...30a charge...100a starter assist. I was thinking of using it when dry camping and using the generator. Hoping that it would charge up the batteries quicker, thus saving generator run time.

I would use the original one when plugged into shore power.

What are your thoughts, experience, etc.
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Old 12-07-2013, 03:12 PM   #2
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The lower the amp. slow charge and over a longer period of time is better than a quick high amp. charge as the higher amp. charge tends to boil and gas the battery shortening its life span.
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Old 12-07-2013, 03:33 PM   #3
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I have always used a external battery charger for my batteries.Converter does not do the job.I have a $50 unit from Walmart that works great.Of note,I use this when hunting,temps down around zero.This has works very well for me for several years.
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Old 12-07-2013, 03:51 PM   #4
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You say the converter/charger is working fine, have you checked the voltage output at the different charging levels? (if it has them) The converter/charger should have enough power to charge and run house needs at the same time. It will require time on 120 AC to charge batteries because it does it the right way. Fast charging can 'boil' the batteries and damage them. Are the batteries in good shape? Have them load tested at any Auto Parts or Battery sales store. You might also look into LED lights and other energy saving steps to preserve battery power.
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Old 12-07-2013, 06:53 PM   #5
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It's unclear from your post how much you know about batteries and charging AND what the present system you have is and the shape it is in. So I will re-state the obvious points in determining what you should do.
1. Are you using your batteries in a responsible way that will not murder them? Do you know their exact state of charge (i.e. 60% full) and never go below 50%? Do you always Re-charge them to a full 100% which can take twice as long as 90%? Do you always keep the water levels up with DISTILLED water and NEVER allow the battery plate tops to be exposed to the air? Are they TRUE deep cycle batteries?
2. You imply that your converter is not charging quickly or properly. Do you know the amp hour capacity of your batteries and is the RATED capacity of your converter/charger at least 20% of this capacity? If it is...then a BIGGER charger is NOT the answer as wet cell batteries cannot be charged at more than 20% of rated amps without boil over. (i.e. a typical 200 amp hour battery bank needs no more than a 40 amp max charger.)
3. Does you present charger supply the right voltage? With a multimeter after using your batteries down close to 50%...turn the charger on and read the voltage at the battery terminals with a voltmeter. It should be around 14.5 give or take a couple of tenths. Anything below 14.2 should be cause for concern. If you DO get a low reading at the battery terminals...take the same reading at the output terminals of your charger...if they are significantly higher...that would suggest a voltage loss due to bad connections or corrosion.
4. Assuming you discharge to 50%, use a charger that outputs 20% of your battery capacity and does so at the proper voltage...it should take you 4-5 hours of charging to come to fully 100% . After about 2-3 hours...the voltage at the battery terminals should drop to 13.5 V or a few tenths LESS. This will stay the same as the battery completes charging which is when the AMPS going into the battery drop to about 1% of capacity (2 amps on a 200 amp battery bank. You can best check this with a clamp amp meter or a real battery monitor like the Victron (which also does a lot more).

NOW...if you don't like this answer and still want quicker charging...it is quite possible. Replace your existing wet cells with AGM batteries like Lifelines or Trojans at roughly 3 times the cost...Then you can buy a humongous charger that can charge at 50 to 100% or more of their capacity and cut your charging time by 75% or more. The only obstacle is money!

Hope you find this useful & good luck.

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Old 12-07-2013, 09:23 PM   #6
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Cool

I am currently looking at having to buy 1 Battery. The replacements can run $80 bucks up 6-$700 a battery. Ge-ssh, how do you guys that need 6-8 battery do it? The replacement I am looking at is 800CCA $125-$150.00 the old one being replaced has 650CCA and is a marine/rv battery. Can I upgrade like that?
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Old 12-07-2013, 11:15 PM   #7
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I have the 2 wet cell 6v Trojans in series to get 12v. They are in good condition, and distilled water has never gone to top of plates. I am watching DVDs on my laptop for about 3-4hrs at night, with nothing else on but a couple of LED lights, and the heater will come on a few times thru the night with the thermostat set to 70*F while up, and 60*F when sleeping. In the morning the voltage is at 11.7 to 12v. I am just wanting to run the generator less time to get them back up. That's why I was thinking a 30amp charger might do it in about 2hrs.
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Old 12-07-2013, 11:30 PM   #8
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A 11.75 v state of charge is down to 30%, 11.9 v = 40%, 12.06 v = 50 %. If you discharge a battery below 50 % repeatedly, you will seriously shorten it's life. To try to take a battery (or batteries) from 30% to 100% in 2 hours is a sure way to destroy them.
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Old 12-08-2013, 03:48 AM   #9
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11.7 to 12v is probably not a "rested" voltage. They need to sit for close to a day to get a true voltage reading. I wish someone would come out with a semi-loaded chart. Does Bob do that?

I use a 3 stage charger after my converter has done most of the bulk charge.
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Old 12-08-2013, 05:53 AM   #10
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Quote:
Originally Posted by mr300ce View Post
I have a 1994 Bounder with the original converter/charger still working fine. But it does take quite a while to bring back up my batteries. It does not put out like the newer ones. When dry camping I must run the generator for a long time to get them up.

I was looking at those newer battery chargers at wally world. 2amp maint...30a charge...100a starter assist. I was thinking of using it when dry camping and using the generator. Hoping that it would charge up the batteries quicker, thus saving generator run time.

I would use the original one when plugged into shore power.

What are your thoughts, experience, etc.
A multi-stage charger is best for charging batteries quickly and safely. They will charge at high voltage (14+ volts) for a time, then reduce to about 13.6 volts until the battery is charged, then reduce further to a float charge to maintain full charge without overcharging. If your existing charger is single-stage, it would be best to not use it at all and replace it with multi-stage.

Older converters tend to have single-stage chargers that put out a constant 13.6 volts, which can cook the batteries over time. Check the specs or measure the output of your current charger to see what kind it is.

Deteriorated batteries can also take longer to charge. If your batteries are in good condition, they will charge faster. As has been stated, it's best not to draw the batteries down lower than 50% to help maintain long life.
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Old 12-08-2013, 07:06 AM   #11
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Originally Posted by mr300ce View Post
I have the 2 wet cell 6v Trojans in series to get 12v. They are in good condition, and distilled water has never gone to top of plates. I am watching DVDs on my laptop for about 3-4hrs at night, with nothing else on but a couple of LED lights, and the heater will come on a few times thru the night with the thermostat set to 70*F while up, and 60*F when sleeping. In the morning the voltage is at 11.7 to 12v. I am just wanting to run the generator less time to get them back up. That's why I was thinking a 30amp charger might do it in about 2hrs.
Based on the depth of discharge, it would take about 2.5 to 5 hrs for a 40a charger to bring the batteries up to 100%. Deep cycles won't accept a fast charge.

However, that seems like a fairly low voltage after an overnight use. Do you also have a refrigerator drawing a load?

Before replacing anything I would perform an equalization charge. Many portable chargers can do this but it requires you monitor the battery to assess the specific gravity until all cells are matched. Usually takes 2-4hrs. Even new batteries should be equalized before being put into service.
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Old 12-08-2013, 02:11 PM   #12
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Quote:
Originally Posted by mr300ce View Post
I have the 2 wet cell 6v Trojans in series to get 12v. They are in good condition, and distilled water has never gone to top of plates. I am watching DVDs on my laptop for about 3-4hrs at night, with nothing else on but a couple of LED lights, and the heater will come on a few times thru the night with the thermostat set to 70*F while up, and 60*F when sleeping. In the morning the voltage is at 11.7 to 12v. I am just wanting to run the generator less time to get them back up. That's why I was thinking a 30amp charger might do it in about 2hrs.
If the 11.7 -12V V reading is legit and not simply a function of not letting the voltage come back up after use...then I'd say 2 things.
1. You're killing your batteries. Never go below 12.2.
2. You have about 220AMP HOURS in those batteries giving you (IF NEW AND FULLY CHARGED) about 110 amp hours to use before recharging. Assuming a large laptop the most you're gonna use is about 5 amps per hour or a total of 20 amp hours in 4 hours of DVD watching. You've also got some small loads and some parasitic loads that go all the time...but NOTHING that would take you down below 12.2V overnite from a full charge. Your batteries are showing an early death spiral. May I suggest you buy a cheap turkey baster hydrometer at AutoZone and determine the exact condition your batteries are in before doing anything else. To test...be sure to fully charge your batteries then disconnect and REST THEM for a full 24 hours before taking your readings. ALL cells should be tested and read within 50 points of each other. Ideal is about 1.250. Subract FOUR from this for every 10 degrees under 80 ...i.e. 1.246 for 70 degrees. Anything below 1.200 (at 80!) would be showing significant deterioration but is NOT a reason to throw the batteries out by itself...they should be load tested for that provided all cells read close to the same.

You don't say what your current charger puts out but putting back in 110amp hours from 50% to 100% with a 30 amp charger will take approximately 5 hours on new batteries.
You could use a 40/50 amp charger to improve things by maybe an hour.
Of course if you only lightly discharge in a nights use... you can cut down the recharge time based on the % of the battery you use vs. the normal 50%.
What size charger do you have now?
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Old 12-08-2013, 03:33 PM   #13
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I will second camaraderie, and add the only way to know with any level of certainty the SOC for your battery(s) is the use of a battery monitor and the Trimetric or Victron are the best. They measure the current that goes into and comes out of your battery not just the voltage. I went with the Victron will tell me instantly the %SOC. To the earlier individual asking about CCA, this means you are using the wrong sort of battery, a marine starting sort of semi deep cycle compromise battery. what you are looking for is a true deep cycle which will express capacity in Amp Hours. For our Teardrop trailer I have a 150AH AGM battery and we have never gotten below 64% SOC.
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Old 12-08-2013, 03:46 PM   #14
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Quote:
Originally Posted by mr300ce View Post
I have the 2 wet cell 6v Trojans in series to get 12v. They are in good condition, and distilled water has never gone to top of plates. I am watching DVDs on my laptop for about 3-4hrs at night, with nothing else on but a couple of LED lights, and the heater will come on a few times thru the night with the thermostat set to 70*F while up, and 60*F when sleeping. In the morning the voltage is at 11.7 to 12v. I am just wanting to run the generator less time to get them back up. That's why I was thinking a 30amp charger might do it in about 2hrs.
Well mr300ce,

The short answer is NO.

12.0V is about 50% charge
11.7V is about 40% charge
I suggest you do some reading, Trojan Battery Company would be a good place to start. Those people do know their business. If you want more then go to:RV and Marine Power Converters, Battery Chargers from Progressive Dynamics

When you read anybody's specifications, you will find that don't recommend charging at much more than the 20Hr rate. For your Trojans - if they are T-105, that is 22.5 amps. You can push that if they are cold, but but you will not recover the bank in two hours no matter what you do. The batteries just won't take it. You are trying to refill 100+ Amp/hours, you can't do it without hurting your bank. What you really need is a modern converter charger. Any one worth installing will cost more than the battery charger you are looking at, but you will get better charging and better life out of your house bank.

One of the new 3/4 stage from PD and Iota (look up Bestconverter.com) will do this as well as it can be done. There maybe others as good as those two, but read all the specifications for anything you consider. If it doesn't talk about bulk, finish and storage at least (the names may change) for charge levels, that isn't the one you want. If you get a PD9245, that will get your bank back about as fast as it can be had, but you still better count of 3 hours of charging to get an half dead bank to 90%.

This is what I did for yacht owners before the depression hit. It isn't over in Michigan yet.

Matt
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