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Recharge rate

countrykids
Explorer
Explorer
We will be boon docking at the same location for several days and I am concerned about maintaining battery.power. We have two group 27 batteries, a 4 KVA on board generator and a 40 amp 3 stage converter. If batteries are dropped to 50%, how long does the generator have to be run to refill the batteries assuming little other power usage?
2004 Born Free class c
11 REPLIES 11

pianotuna
Nomad II
Nomad II
Hi,

Charge acceptance rate at 85% state of charge is 12.5 amps per 100 amp-hours of storage for flooded batteries. The closer the bank gets to 100% the more the charging rate drops.

Attempting to charge faster by increasing voltage simply causes the cells to gas. You do want some bubbles--but one per second is what to aim at.

Solar is definitely a boondocker's friend.
Regards, Don
My ride is a 28 foot Class C, 256 watts solar, 556 amp-hours of Telcom jars, 3000 watt Magnum hybrid inverter, Sola Basic Autoformer, Microair Easy Start.

2oldman
Explorer
Explorer
3 hours
"If I'm wearing long pants, I'm too far north" - 2oldman

countrykids
Explorer
Explorer
Thanks for all your help. As LWDDIS cleverly pointed out it makes solar look pretty good.
2004 Born Free class c

PNW_Steve
Explorer
Explorer
wa8yxm wrote:
If you run those batteries down to 50 Percent it's not good for 'em. 75 percent is about the minimum for MARINE/deep cycle beyond that they age very fast.

Now I would not replace them till they need it but when they do consider GC-2 Golf car batteries or GC-12's these are True DEEP CYCLE and do not mind 50% at all that's the design limit though.

To recharge
You have about 200 amp hours (Bit less) so at 40 amps to replace 100 AH would take about 3 hours .. But that will only get you to about 90%. the next 3 hours should top you off.. So I'd go 6 hours Might get there in 5 but I'd say six.


What he said ๐Ÿ™‚

One thing to add. Discharging and partially recharging (not reaching 100% SOC) will shorten your battery life.

Common recommendation is make sure you charge to 100% at least once a week.

When it comes time to replace your current batteries I would recommend looking at something like the Duracell GC2 or Trojan T105. They are "true" deep cycle where the typical group 27/31 "marine deep cycle" is a hybrid starting/deep cycle.
2004.5 Dodge 3500 5.9 Cummins, NV5400, 5" turbo back stainless exhaust, Edger programmer & 22.5 Alcoa's
2002 Forest River 36 5th Wheel (staying home)
1992 Jayco 29 5th Wheel (Mexico veteran & headed back)
2002 "faux" Wanderlodge 40' My new toy....

wa8yxm
Explorer III
Explorer III
If you run those batteries down to 50 Percent it's not good for 'em. 75 percent is about the minimum for MARINE/deep cycle beyond that they age very fast.

Now I would not replace them till they need it but when they do consider GC-2 Golf car batteries or GC-12's these are True DEEP CYCLE and do not mind 50% at all that's the design limit though.

To recharge
You have about 200 amp hours (Bit less) so at 40 amps to replace 100 AH would take about 3 hours .. But that will only get you to about 90%. the next 3 hours should top you off.. So I'd go 6 hours Might get there in 5 but I'd say six.
Home was where I park it. but alas the.
2005 Damon Intruder 377 Alas declared a total loss
after a semi "nicked" it. Still have the radios
Kenwood TS-2000, ICOM ID-5100, ID-51A+2, ID-880 REF030C most times

theoldwizard1
Explorer
Explorer
If you are manually charging, the max charge rate should not exceed 30% of the battery capacity. A dual purpose Group 27 batteries is rated at 90Ah so charging at the max rate would be 30A. At max charging rate, it should take about 3 hours, probably a bit longer if you have a good multi-stage charger.

If you battery has been discharged to 50% SOC, you have shortened its life.

time2roll
Explorer II
Explorer II
If your converter is putting 14.4+ volts on the battery you need a solid three hours.
If you have the typical WFCO or parallax at 13.6 volts it will be 12+ hours.

Bobbo
Explorer II
Explorer II
With a good 4 stage converter/charger, 4 hours. WFCO is not a good converter/charger. Magnatek/Parallax is an absolutely s****y converter/charger. My preference (put in 2 RVs) is Progressive Dynamics, although there are others that are as good.
Bobbo and Lin
2017 F-150 XLT 4x4 SuperCab w/Max Tow Package 3.5l EcoBoost V6
2017 Airstream Flying Cloud 23FB

philh
Explorer II
Explorer II
WFCO charger is a POS

Lwiddis
Explorer
Explorer
Four hours of recommended generator time per day. Not too pleasant if your neighbors are close or even for you. Gee, could there be another way to silently recharge FULLY almost every day? That would be heaven sent.
Winnebago 2101DS TT & 2022 Chevy Silverado 1500 LTZ Z71, WindyNation 300 watt solar-Lossigy 200 AH Lithium battery. Prefer boondocking, USFS, COE, BLM, NPS, TVA, state camps. Bicyclist. 14 yr. Army -11B40 then 11A - (MOS 1542 & 1560) IOBC & IOAC grad

DFord
Explorer
Explorer
Just run it an hour or two in the morning while you're making coffee or heating something in the microwave. Then again in the evening for a couple more hours before retiring and you should be fine. The 12v batteries you have won't have a very high capacity so try to conserve while the generator isn't running. If you need heat, they should be able to run the furnace overnight.
Don Ford
2004 Safari Trek 31SBD (F53/V10 20,500GVW)
'09 HHR 2LT or '97 Aerostar MiniVan (Remco driveshaft disconnect) for Towed vehicles
BlueOx Aventa II Towbar - ReadyBrake Inertia Brake System