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Author Topic: Best way to charge battery?  (Read 6044 times)

ADKBOB

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Best way to charge battery?
« on: August 10, 2009, 03:49:20 PM »
Hi,  This forum is great!  I'm sure this question has been asked before. I'm new to RVing. I just bought a 2009 R-Vision 21 ft. TT. We just got back from our first 10 days of camping. (There were no hook-ups) Trying to find out the best way to charge the battery. The charger inside the trailer is a Parallax model: 7155. It says the output is 55 Amps at 13.6 VDC. The trailer battery is an Interstate Deep Cycle HD24-DP. I have a Honda EU1000i generator.  After about the fourth day the battery monitor in the trailer was showing two-thirds charge. I plugged the shore line into the generator a ran it for 1.5 hours a day therafter but could not bring the battery back up to full charge. Is there a better way to charge the battery? Also, should I try and "maintain" the battery by charging every day right from the beggining instead of letting it get to two-thirds and then trying to bring the battery back up? Thank You, Bob

Gary RV Roamer

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Re: Best way to charge battery?
« Reply #1 on: August 10, 2009, 09:09:05 PM »
Hi Bob and welcome to RV Forum.

1.5 hours isn't a lot of charging time. That's because the battery will not accept 55A of charging right up to the 100% mark. Once the battery reaches about 80% charge, the rate at which it will accept a charge slows way down, so in effect your 55A charger becomes a 3-4 amp charger in the latter stages. So yes, you are probably better off running it an hour a day.

You can only use about 50% of the available charge in a battery anyway. The voltage drops too much beyond that and it is harmful to the battery anyway. I suspect that you were pretty much down near the 50% level when you charged, regardless of what the gauge said. They are an approximation at best.
Gary
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Gary Brinck
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ADKBOB

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Re: Best way to charge battery?
« Reply #2 on: August 10, 2009, 09:51:38 PM »
Hello Gary, Thank You for the reply. I have been reading that a car charger used with the generator might be a better (faster) way to charge. Would that be the case here? Is the on-board charger in the trailer basically a trickle charger? Thank You, Bob

Lou Schneider

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Re: Best way to charge battery?
« Reply #3 on: August 11, 2009, 05:30:32 AM »
There are a couple of issues at play, Bob.

First, the internal Parallax converter isn't really a trickle charger, but it is a fixed voltage converter.   At 13.6 volts, you'll likely get about 10 - 15 amps of charging current into a single battery.   Adding a second battery will double the amount of current.

Converters that deliver a fast charge raise their output voltage to 14.1 volts during the bulk part of the charging cycle to push more current into the batteries, then drop back to 13.6 volts at the end to keep from boiling out the electrolyte.

Since the amount of current the battery will accept decreases as it gains a charge, you're better off recharging it to about 80% full.    Gaining that last 20% of a charge will take forever.  You'll be better off getting the battery up to full charge by plugging into electricity overnight when you get back from your trip.   Or if you have a charging wire going from your car to the trailer it will top it off while you drive home.  At 10-15 amps of current, you're looking at about 4 hours of running time to go from a 50% charge to 80% charge.

Adding a second battery will let you go longer before you'll have to recharge.    You'll still have to run the generator 4-6 hours to recharge but you'll only have to do it half as often.

Putting a car charger across the battery may or may not decrease the amount of charging time.   Most likely, the amount of current provided by the Parallax converter will decrease in direct proportion to the amount of current provided by the second charger, so the net effect is little or no gain in charging current.   This is because the Parallax has good voltage regulation - it's voltage stays the same regardless of how much or little current it produces.

How far is it from your converter to the battery, and what size of wire connects them?   Short, fat wires move more current into a battery than long, thin wires.  If the distance between the converter and the battery is more than a few feet, doubling up on the wire size will greatly improve the charging rate.

You can also put an automotive ammeter in line between the converter and battery.   This will not only let you see how much current is going into the battery while it's charging, it will also give you an idea of how much current you are using when you turn on a light, etc.

« Last Edit: August 11, 2009, 05:45:41 AM by Lou Schneider »

Gary RV Roamer

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Re: Best way to charge battery?
« Reply #4 on: August 11, 2009, 08:38:12 AM »
Your 7155 isn't a great charger, but it is definitely faster than most any automotive style charger you are likely to get. It is capable of sending upwards of 30A to the batteries, whereas the usual automotive charger is only 6-10 amps or maybe 15A-20A if you get a real expensive one.

The 55 amp output is divided between supplying the 12v needs of your trailer and charging batteries, so any lights or other 12v power uses that are on will detract from the charge rate. That's usually insignificant, though. The main problem is the one I described before - the battery simply won't except a charge very fast once it reaches 75-80% charge. The internal resistance increases as the charge builds up, so the current rate goes down.  For that reason, most people operate their batteries in the band between 50% and 80% charge while boondocking and don't get back to 100% full charge until they can hook up to a power source and let it charge for 24 hours or so.
Gary
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John From Detroit

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Re: Best way to charge battery?
« Reply #5 on: August 11, 2009, 10:31:09 AM »
I will add there are car chargers and there are car chargers

The other day (Friday) my car would not start.. I jumped it, twice, and when I got it back to the site I hooked up an old "Automatic" car charger.. This one is single stage voltage regulated

Well, by morning it would start but it was a long way from "Full"  I switched the plug to a battery minder I'd not plugged in (Let the blasted car sit all week w/o starting don't you know)

That only does 1 amp, but it is a 2-state (Absorption/float) charger so by time to go to church FULL UP.

My suggestion is always a good 3-stage charger matched to the battery.. Some of the "Smart" car chargers MIGHT fit the bill, but a Xantrex True Charge XADC or a Progressive Dynamics 9200 or several others is best.. These can replace your Parallex if you wish, or work with, or in place of it.

I'm most familure with the Progressive Dnamics line, they come in "Stand alone" (THey have a cord with a plug) and hard wired (Terminals you hook ROMEX to) models

To figure the size.. How much battery do you have? Group 24, 73AH (each) 27, about 80-85, 29, just shy of 100, 31 or 32 (forget which) just over 100, U-2200's (Golf car) Pairs, 220

Multiply by 0.30 and that's the size you need
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ADKBOB

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Re: Best way to charge battery?
« Reply #6 on: August 11, 2009, 05:00:41 PM »
Thank You everyone for all of your help. So, I will continue to charge using the shore line and generator, just make sure not to let battery get too low. One other question, I heard somewhere not to use the Eco-throttle on the Honda generator (EU1000i} to charge the battery. Is that true or could I set it on the Eco-throttle just to help keep the battery up? It is so much quieter that way.

Lowell

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Re: Best way to charge battery?
« Reply #7 on: August 11, 2009, 05:32:45 PM »
How well would a car alternator attached by belt to a 5 horse motor do in recharging a deep cycle battery?  My son has been thinking about rigging up something like that to recharge his deep cycle battery for Scanoe electric trolling battery.  He could pick up a used alternator for next to nothing and we have a spare motor. He tent camps so doesn't have the capabilty of using TT to recharge battery.
« Last Edit: August 11, 2009, 05:35:53 PM by Lowell »
Lowell

2005 Cherokee28A TT
pulled by 2009 Dodge 1500 Crew Cab 4X4
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Tempe, Arizona

Gary RV Roamer

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Re: Best way to charge battery?
« Reply #8 on: August 12, 2009, 12:02:41 AM »
The main problem with an alternator is that it is unregulated output. It just pours on the amps at a high voltage, a basic one stage charger. It should bring a fully discharged battery up to 70% fairly quickly, but above that it is really over-charging and not conducive to long battery life. On the other hand, it is a cheap alternative to buying a genset.

Car starting batteries are designed for short bursts of high amps and handle it ok, but deep cycles are the opposite.
Gary
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Gary Brinck
2004 American Tradition
2007 GMC Acadia
Homebase: Ocala National Forest, FL

Lou Schneider

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Re: Best way to charge battery?
« Reply #9 on: August 12, 2009, 11:13:49 AM »
The main problem with using an alternator with a small engine is having the alternator go to full output and stall the generator.   This usually only happens when you couple the alternator to a large battery bank.

An easy way to limit the current coming out of a car alternator is to pick one with an external regulator.  Set the voltage on the regulator to your preferred charging voltage (14.1 volts or so) then put a variable resistor in the field lead going back to the alternator.  As you increase the resistance the maximum current produced by the alternator will go down.

As the batteries gain a charge, the voltage will rise to the set point, the regulator kicks in and keeps it from rising further.

Other than that, charging the house batteries using an alternator should work fine.   You do the same thing via the main engine alternator every time you drive the motorhome or pull the trailer.

John From Detroit

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Re: Best way to charge battery?
« Reply #10 on: August 12, 2009, 11:46:41 AM »
My internet connection is by Electrolux, and "Nothing sucks like.. "

Actually a properly ALternator/Regulator pair is fully regulated and will both charge the battery properly and not too quickly.. The key is to get the PROPER size alternator (And the proper size motor, 5hp = about 4,000 watts by the time you convert to electricty (I am seriously rounding here)   That would be 30 somethign amps.  Good for batteries in the 100 amp hour range (1 group 29) up to a pair of six volts.. Much larer you gonna need more alternator/motor.

FORD makes a self regulating (one wire) alternator,,, or rather they buy and use one. 

GM alternators have some regulation "internal" I'm not sure what they need "external" of course considering the price...... Well,,, The price is kind of high less you get 'em used.

But a proper alternator/regulator pair, or a properly regulated alternator, Will do a very good job of charging the battery it is adjusted, or programmed for.  And when it comes to charging there is not a lot of difference between deep cycle and starting, save for the peak-amps (Which with a 5hp motor and at least 100 amp hours of battery should nto be an issue
Nothing adds excitement like something that is none of your business
My Home is where I park it.