Battery charger

Discussion in 'Power - Site Power/Batteries/Generators/Solar' started by Lagman, Jan 12, 2019.

  1. Lagman

    Lagman Member

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    Sep 29, 2016
    Bucks County, PA
    I have a pop up that I recently added 2 6 volt batteries in series. My converter doesn't have a built in charger. My question is, I have a 4 amp Battery Tender and was wondering if 1. Will it work of a Honda 2800i genny and 2. Will it be enough amps to charge it in a reasonable amount of time. I bought it for the algorithm 4 mode feature. I do have a 10 amp charger also. The batteries are the ZTrojan T105's. I have a breaker between them and the inverter also. Also I need a switch for use between the house and the inverter. Any recommendation will help emensely as I have one of those dual battery marine switches, maybe that will work?
    Thanks for the help,
  2. JimmyM

    JimmyM Well-Known Member

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    Jun 5, 2014
    Franklin, MA
    The generator will run either charger easily. The 4 Amp is small as the primary charger. But when the batteries are low, you just want to get amps in them as quickly as possible. You can safely connect both chargers. Once fully charged, you can disconnect the 10A and use the 4A to top off / maintain the batteries. T105s are 225AH batteries IIRC. The max recommended charge rate for flooded batteries is .2C. So if your battery bank is 225AH then 225*0.2 = 45A. You could charge them at 45A and you'd be fine.
    Don't use a breaker between the batteries. Use it as close to the positive terminal that goes to the camper as possible. You can use the breaker as the switch. Keep in mind that the inverter will draw 10A for every 100W drawn from the inverter. Wire accordingly.
    225AH (Assume you've drawn them down to 30% SoC) means you have to put 157AH back in. They'll have a charge efficiency of ~90%. So for every 10AH you put in only 9 AH actually stay in the battery.
    157/.9=~175AH. 175AH/10A = 17.5 Hours. But in reality, that math only works until the battery gets to 90% charged. That last 10% tales a while.
    I may get flames from the "50% discharge floor" LAW folks. But that's just a rule of thumb. Trojan T105s are built for DEEP cycling. You'll still get 100s of discharge cycles going down to 30%. I have GC2s (same size as T105s) in my hybrid and I don't flinch gown down to 30%. They're going to last YEARS.
    tombiasi likes this.
  3. joet

    joet Well-Known Member

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    Mar 16, 2011
    Elkins WV area
    The 4 amp tender will take forever to charge the batteries, and the 10 amp isn't much better. I would find a manual charger that is capable of putting out 40 amps. Then use the 10 amp for a finish charge.

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