Charging the Batteries

[Mapker]

I have a 30ft 5th Wheel that has an Onan 3.6K LPG generator.  I was parked in a remote part of Arizona this summer and we generated our own electricity and hauled our own water.  I was very dissappointed to find that I could not keep two 12 volt deep cycle Marine batteries charged with the generator.  it seems the generator takes more than it charges.  I have a MagneTek 3240 Converter Charger. 40 Amp and maybe that is the trouble.  It's not a new trailer.  A 1993 model Hitchhiker.  I have recently brought the trailer home and am charging with shore power.  After three days of charging, I am reading 13.3 on a digital tester.  The Monitor over the stove reads the battery as Good but not Full.  How accurate are these monitors?  I might add that both batteries were bought at Costco this summer and are brand new.  Several times this summer I had to bring the batteries home to be fully charged with a automotive battery charger.  The few times that I left the batteries in the trailer I disconnected the negative wire so that it wouldn't discharge while I was gone.  i would appreciate any suggestions that anyone wants to give.  I've been a member of this forum since I got the trailer in 1995.  The members here have been a wonderful source of information for me and others.

 

[John From Detroit]

I am surprised that the generator could not keep the batteries charged UNLESS there was another problem, such as a tripped breaker,  That said, i'd loose that converter in favor of a Intella Power 80 or 90 amp model with charge-wizard

 

[Ned]

It's not the generator that's the problem, more likely the converter isn't putting out enough charging current.  Also, marine deep cycle batteries aren't the best choice for your application.  They're designed as a combination deep cycle, starting battery, and don't perform well in deep cycle applications.  You would be better off with 2 6V golf cart batteries with the same combined AH capacity.

 

[Gary RV_Wizard]

The Magnetek 3240 is a mediocre converter/charger (I had one for awhile) and those marine deep cycle batteries are probably already tired from the frequent recharging. As Ned says, they are just slightly improved starting batteries and simply not well suited for the heavy use you are doing.

Get an  Iota    or Progressive Dynamics charger of at least 45 amps and with the optional Smart Charger feature.  A higher amp charger, e.g. 7-90 amps, will reduce charging time but won't charge any better in the long run. Then replace those batteries with good quality GC6 golf cart batteries or a real deep cycle 12V like the Lifeline AGM. They will hold up under the repeated deep discharge/charge cycles.

 

[edubb]

Is it possible that the generator was so busy powering the air conditioner ("summer in Arizona") that it didn't have much left for the battery charger?

 

[King]

I have a Magnatek 30, and you're right, it won't charge the batteries.  The engine alternator does a good job for me.  Now, if I'm not travelling, I charge with a standard automotive charger.  I will eventually buy a new design charger.

 

[Gary RV_Wizard]

Is it possible that the generator was so busy powering the air conditioner ("summer in Arizona") that it didn't have much left for the battery charger?

Possible but not likely. If there were not enough generated power available for the demand, a circuit breaker would probably trip. And a battery charger doesn't draw a lot of amps - a 30 amp 12V charger needs only about 3 amps @ 120 VAC to charge at full rate. Few of the basic Magnetek models can do that much - they may have a combined 30A or 40A available for charging and converter output, but are typically limited to something like 5-7 amps of charging alone. In other words, it can't actually deliver its full rated output to the charging function.  And if the batteries are tired or have high resistance, they may not actually charge even that much.

 

[fredethomas]

I echo what others have said.  Get rid of the 12V Marine Batteries and replace them with some good Trojan 105's, 125, or AGM [all six volt]  then invest is a good smart charger.  The AGMs can be installed anywhere [almost].  No need for ventilation and can mount them upside down is wanted.  But you will need a charger designed for them.

 

[Jeff]

All the recommendations are good ones but if you just invested in the two batteries you might start with either a good converter like the Intelli-Charger of a high output battery charger and see if that provides enough juice. If it doesn't you have not lost anything and you can get a good set of batteries. I had 2 12v in our 83 Pace Arrow and while they were nowhere as good as the 2 T105 6v in our 98 or the 4 6v we have now we did get by with them.

 

[Gary RV_Wizard]

Good suggestion, Jeff.  It would be smart to do the job in stages - and it spreads the cost out too.  But while a good 12V will certainly work, I get the impression that he is deep discharging and re-charging on a daily basis while boondocking long term. For that frequent and heavy cycling, he really needs batteries with thick plates designed for deep cycling. Golf cart batteries are definitely the way to go in that application - they will last longer and store/reproduce power more consistently over time.