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Old 06-25-2008, 02:53 PM   #1
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Converter test

Lately, After about three days of boondocking, my battery is going dead. I do not use if for much other than an occassional light at night and the water pump, and that never drained the battery before. How do I simply test to see if it's the deep cell battery gone bad or the converter? Both are pretty dated. It's a 1971 21 Ft GlobeTrotter, and I have owned it 4 years...and only the battery has been replaced in my tenure, about 3 years ago.

Thanks in advance.
Boltos
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Old 06-25-2008, 04:54 PM   #2
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Originally Posted by boltos View Post
Lately, After about three days of boondocking, my battery is going dead. I do not use if for much other than an occassional light at night and the water pump, and that never drained the battery before. How do I simply test to see if it's the deep cell battery gone bad or the converter? Both are pretty dated. It's a 1971 21 Ft GlobeTrotter, and I have owned it 4 years...and only the battery has been replaced in my tenure, about 3 years ago.

Thanks in advance.
Boltos
Remove the battery and take it to a battery shop.

Before you do, charge it up to maximum.

The battery shop has a load tester that they will clamp onto the battery terminals. That device puts a huge heavy load on the battery. If the battery is going south on you, that test will quickly point that out.

Three years for a battery is not bad, unless you bought an expensive type and then 4 to 5 years is about the limit of their life.

Generall speaking, if the warrantyon a battery is 2 years, then that's about all the life you will get from it. Most often, they fail very close to their warranty.

Rare exceptions, sometimes takes place.

Andy

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Old 06-25-2008, 07:01 PM   #3
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One problem with the old style charger is that it can overcharge and boil the electrolyte out of the battery. Check and see if the battery is dry. If it is, you'll need to replace it. Newer chargers are 'smart' and don't boil the batteries if left unattneded. Sometimes the old converter can fail in such a way as to increase the charging voltage and that will ruin batteries also.
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Old 06-25-2008, 09:49 PM   #4
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Brian,
I think I talked to you today. You do need to check the batteries and a load test is a free way to do it because the auto part stores have a calculated statistic that they are bad and and might be able to sell you new batteries. Hard to blame them. They will tell you if they are good too so we have to give those test some credit. Generally they are honest and will tell you the truth.
A better test in my opinion is a specific gravity test with a hydrometer. Sort of a pain in the ass but they tell the story better. The good part is that its only a few dollars for a hydrometer at any auto parts store and its a good investment if you plan to use flooded batteries in the future. They are handy for other batteries you might have not related to Rving if they are that type. Get one.
What I don't agree with is that batteries fail near the end of the warranty. They fail as soon as you or your charging system neglect them.
Here is the point I was trying to make. Neglect is partly our fault and partly the converter/chargers fault. You can throw batteries at an RV all day but without a multi-stage modern switching converter, it becomes a history lesson that repeats over and over.
I was that guy boiling batteries and watching everybody else do it at the same time when vendors and manufactures were telling us back in the day that we needed a new Univolt. They didn't understand (and quite frankly still don't) understand some people dry camp and need better charging profiles.
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Old 06-25-2008, 10:39 PM   #5
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Hi, I've been in the Battery Biz for many years...here's some highlights to look at, without trying to get too techicnal...

Most true Deep Cycle batteries on the market today are usually good for 4-6 years...IF...and that's a BIG 'If'... they are cared for properly; kept in a charged condition when the RV's not being used; keep fluid over the plates; don't overcharge, etc., etc...all that stuff you read about...trouble is, some don't take proper care of their batteries, and will then suffer from shorter service lives.

Yes, a load test is a good way to see if your batteries are still serviceable, or have enough capacity left to run your stuff...you MUST charge the battery fully BEFORE performing the load test....I always tell customers that you can't find a leak in a flat tire till it's pumped back up with air...same for batteries, you need to charge em' before the load test. The battery's usually still serviceable if the voltage reading on the tester remains steady....rapid drop-off indicates one or more cells are in bad shape and the battery needs to be replaced.

The hydrometer is a good device for finding the state of charge of a flooded cell battery...we use them all the time...we usually bring all cells up to about 1.275 SG, which indicates a full charge. A hydrometer won't tell you about the battery's longevity, except in the case of a shorted cell, in which case that particular cell will read much 'lower' than the others...when load testing, this same cell will usually 'bubble' profusely also indicating that the plates are touching, inside, probably because one or more separators between plates are torn, etc.

The number one problem I encounter often stems from the customer not fully recharging his battery. Often one will put a discharged battery on a small charger for a short amount of time, thinking that's all it takes...and the battery will only run stuff for a short time, causing the customer to think the battery is 'Bad'...I see it all the time...

I tell customers that what energy you use from your battery, has to be replaced in order for it to run all your stuff again! When boondocking, it may take 2-3 days for the batteries to run down...and running the TV's engine for an hour WILL NOT RECHARGE the batteries!

An amp hour is ONE AMP on the charger for ONE HOUR.. most common RV batteries are rated about 100 Amp Hours...do the math...for example, if you have a 40 amp charger (the charger will 'taper' that 40 amp rating as the battery becomes more charged) it will take about 4-5 hours to recharge, due to the way batteries will accept a charge as they approach a true full charge. If you have two batteries, it will take twice as long...many RV'ers just aren't aware of the time it takes to recharge battery banks in their rigs.

Another quick test involves looking at the ends of the battery...if it has not been fully charged during it's 'life', the lead sulfate will accumulate on the internal plates to such a degree, that it turns to a crystal form, forcing the plates to expand and make a hard 'bulge' at the ends...if this has happened, you will have to replace your battery, as it's capacity will be seriously reduced. If the ends are still 'pliable' when you push against them, you are still sulfate free.

Hope this long winded reply helps...
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Old 07-07-2008, 09:02 AM   #6
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Battery

Well I finally pulled the battery out and checked it for fluids, DRY AS BONE! So, I don't know if I killed it yet, I have filled the cells back up, and had it on trickle charge of 2Amp for 24 hours...it seems to be holding charge, but have not load tested it as yet.

Thanks for the generous advice, it was stupid of me to not have checked the fluids first, sometimes it's the simple things...but we'll see.
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Old 07-07-2008, 11:57 AM   #7
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I'm afraid if it went completely dry, you will not see the same service from it. They rarely survive once the plates have been exposed. I sure don't blame you for trying though, you might see limited service for awhile but not too likely.
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Old 07-09-2008, 11:54 AM   #8
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Converter/Battery

Well...I did fill it back up, fully charged it and took it to a friend who had the equipement to test it with a "load". They said it's dead!

So, I bought this battery at Sam's Club 3 years ago, and really don't recall if I had a real specification for a deep cycle battery when I bought it.

What is the recommended capacity for a deep cycle battery, for boondocking one weekend a month for 5 months a year and recharging in between?

Is the spec mostly about RC=Reserve Capacity, since CCA or CA seem inapplicable?

My old Deep Cycle said it was RC=205minutes, 115 Amp Hr.
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Old 07-09-2008, 12:50 PM   #9
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"group 27" batteries are usually around 100 amp-hours.

Q: if a battery goes dry (or at least, partly dry), will running it through the desulfate mode on a modern charger do any good? or is it just trash?
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Old 07-09-2008, 01:09 PM   #10
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It's really hard to predict how long your particular battery in your particular RV will 'last' for you....

A deep cycle battery is like an Amp Hr 'electron tank'...in that the higher your particular Amp draw is, the quicker you will run down your battery 'tank'...you can only find out yourself during your own 'use' cycles...

Group 27 deep cycle batteries are about 12 inches long and about 105 Amp Hr capacity.

Group 31 deep cycle batteries are 13 inches and can have Amp Hr ratings up to 140 Amp Hrs.

Generally, you should install the largest Amp Hr rated battery you can fit in your battery compartment if you are boondocking.

Don't forget to fully recharge your deep cycle battery at the first oppertunity...the longer a discharged battery sits in that condition, the greater the amount of sulfate becomes attached to the plates, reducing capacity...NEVER put your RV away in storage without fully charging the batteries!

With your old battery having the fluid 'boiled away'...it sounds like you have an older charger, and may be subjecting your battery to overcharging - another way to damage it. If you don't have a charger that shifts to 'float charge' mode when the battery's fully charged, you'll need to turn off the charger, or have a switch to remove the battery from the charging circuit when the battery is charged up.

Good luck..Ray
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