beavergod1
austin, texas, usa
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Joined: 05/05/2004
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Boondocking in Utah this past summer with 1 group 31 wet cell battery. Charged for 2 hours in morning with stand alone 3 stage charger. Would get 85%- 90% charged. 4 hours for 100% charge. Would discharge it 50% p/day...
Friends: Easy to make and hard to get rid of.
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Boarhog
Los Angeles California
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Joined: 03/10/2004
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I agree with Sailbad, use a good three stage battery charger.
Before your "how log" question can be answered, the battery capacity and its state of discharge must be known. The expended A-H have to be replaced. The greater the A-H the longer it will take.
You should slow charge your battery in the first stage so as not to warp the plates. The other two stages are requited to get it to a complete charge.
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wa8yxm
Wherever I happen to park
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Joined: 07/04/2006
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Group 24 is 83 amp hours. I don't know your WFCO converter so can't say if it will fully charge it or not.. I do know WFCO makes some good stuff that can.
Assuming you keep the battery at 50% or more SOC then you need to replace about 40 amp hours.. You divide 40 by the "Excess" output of your converter.. (hopefully that's less than 15 amps) and you should find at least 3 hours to 90%,, then add 2-4 hours to full
I would suggest a 2nd battery be jumpered in while dry camping. you can jumper in another G24 or go with a G-31 for more capacity.
Nothin adds excitment like something that is none of your business
Kenwood TS-2000 housed in a 2005 Damon Intruder 377
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red31
Bryan
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I'd charge two hours daily depending on nightly use. I keep hauling along a gen but never have needed it on my group 24 since I schedule hookups after 2 nights in the cold. Of couse can go much longer without running the 3.4A/40 watt/12v furnace fan.
Someone compared a Xantrex 40 to WFCO 8735
Charge Test Preliminary Results - WFCO 8735
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pnichols
Santa Cruz Mountains
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"Of couse can go much longer without running the 3.4A/40 watt/12v furnace fan."
I'm curious as to what kind of furnace you have. I thought most RV propane furnace blowers use more than 3.4A ... more like 6-7 amps. Or did you mean an average of 3.4A per hour because it's only ON an average of one half the time when heating your rig?
Phil, 2005 E450 Itasca 324V Spirit
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CJW8
Arizona
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Salvo wrote:Hurricaner wrote:Quote:There has been mention that the WFCO will work fine "if it is set up right". The issue with proper setup is not exclusive to WFCO but applies to any three stage smart converter. The wire size from the converter to the battery must meet a minimum size for the converter to function properly. The WFCO has its own issues in addition to wire size. If the converter is sized too large in relationship to the battery size, I don't care how big the wire size is, the WFCO will not go into boost. On a single group 24 the WFCO better not be larger than a 35 amp or it will never go into boost know matter how large the wire size is. The WFCO will only go into boost if it is loaded so severely that the voltage drops below 13.2 and those things do a darn good job at holding that voltage.
This isn't rocket science. There are 3 factors which determine if the 35A WFCO goes into boost: battery voltage, battery resistance, and line resistance.
If the discharged battery voltage is still too high it will not go into boost.
If the combined battery and line resistance is too high it will not go into boost.
This equation must be met to get boost:
V_bat + I_charge * (R_bat + R_line) < 13.2V
If the battery is discharged to 12.0V (~50%), then the combined resistance is:
R_bat * R_line < (13.2V - 12.0V) / 35A = 34 m ohm
The Group 24 battery has about 20 m ohm resistance. That means the line resistance must be less than 14 m ohm.
Sal
Salvo,
Where were you when I was trying to get my WFCO to work a couple of years ago? Does this formula just apply to WFCO? I tried all the then current suggestions, bigger wire, all new connections etc. I even tried another WFCO. I finally gave up and got a Xantrex XADC and am extreamly pleased. Is there a different formula for different chargers? Do you know the formula for Xantrex? Something about it is different because it works where the WFCO would not.
Pnichols,
How do you "completing one's charging equipment's output feedback loop at the batteries (instead of on the equipment's PC board) so as to drive "R_line" to zero!"
Thanks gentlemen.
2004 F350 PSD FX4 SB CC, Banks Cold Air Intake, Banks 5" turbo back exhaust
18,000 Superglide
2003 37SP Forest River Sierra Toyhauler
2008 Polaris RZR
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red31
Bryan
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pnichols wrote:"Of couse can go much longer without running the 3.4A/40 watt/12v furnace fan."
I'm curious as to what kind of furnace you have. I thought most RV propane furnace blowers use more than 3.4A ... more like 6-7 amps. Or did you mean an average of 3.4A per hour because it's only ON an average of one half the time when heating your rig?
Atwood 7916-II, spec on page 1
It's gotta be very cold to be on half the time!
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Salvo
California
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Joined: 06/01/2008
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CJ-
The equation:
V_bat + I_charge * (R_bat + R_line) < 13.2V
is valid for WFCO converters only. WFCO has a power-up algorithm to determine if it should go into boost (or not). Other converters do not have this routine. During this algorithm, the converter supplies max current (in this case 35A) into the batteries. The converter then checks the voltage that's present at the converter's output terminals. If the voltage is less than 13.2V, it goes into boost mode. If the voltage is greater than 13.2V then the converter goes into absorption mode.
It's not a bad algorithm, except for one detail. The decision to enter boost is highly dependent on converter cable resistance. If you have a long cable run, or some contacts are corroded, or the cable isn't big enough then you may never go into boost. In other words, charge times will be very slow. The WFCO 3-stage converter now becomes just a 2-stage converter (absorption & float).
We can modify the equation to make it work for any converter.
V_converter = V_bat + I_charge * (R_bat + R_line)
Where V_converter is the output voltage at the converter terminals.
The equation isn't that important for XADC. I believe it only has 2 stages: bulk (same as boost) and float. XADC will go into bulk every time it's turned on, regardless of line resistance. So that's the big difference between WFCO and XADC.
Line resistance is still a factor for XADC. It will limit current to less than converter's max rating.
I_charge = (14.2 V - V_bat) / R_line
R_bat is no longer in the equation. It is hidden within V_bat value. The larger R_line is, the smaller I_charge becomes. R_line is still very important, but not as critical as for WFCO.
I'll also answer the second question (Pnichols reference). It would be great if we can make R_line = 0. In this case, when we're in bulk mode, I_charge = I_max_converter. If you have a 60A converter, then 60 amps gets pumped into the batteries. Regardless of line resistance.
That's what I did to my sorry-ass'ed (Parallax 7345) converter. I have about 23 feet of 8 awg cable going from converter to the battery. The line resistance was high. This cause the converter (which was already slow) to be even slower. I had two options, chucking the converter or fixing the problem (high line resistance). I fixed the problem by taking the line resistance out of the equation.
To make a long story short, I moved the voltage regulation feedback location from the inside of the converter to directly at the battery terminal. Line drops are now compensated by the converter.
Sal
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big_murph_279
Concord, NC
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Lots of good info. I took my boats new group 27 with me. I also took my power pro 3500. I got to the camp site about 4:00 on Sunday afternoon. The sun didn't shine until lunch time on Monday, so we had to run the lights. The temps where in the upper 60's during the day and mid 40's at night. We ran the gen for about an hour so I could watch the nightly news. Then in the morning it would run for about 30 mins so we could use the microwave to warm up left overs. Last night there were no other campers in the campground so we ran the gen for about 3 hours to get a full charge. I think as long as I don't go camping when it is real cold I should be fine with my single battery.
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pnichols
Santa Cruz Mountains
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"I have about 23 feet of 8 awg cable going from converter to the battery."
Sal,
As you probably know, the Parallax 7345 output lugs are specified to fit up to and including 2 awg cable. I'm really curious as to what current my 7345 would pump into my 200 AH AGM coach battery bank with the batteries down to 50% SOC and 8 feet of 2 awg cable between the 7345 and the batteries. I think I have it written down somewhere what cable drop I measured with the Winnebago stock 8 awg cable in place (about 8 feet) in parallel with a large battery jumper cable strand I ran in parallel to the stock 8 awg. I'll have to look it up. I'd prefer to have real data along with the equation's prediction.
I'm on somewhat of a mission to force/show/prove my 7345 to be "just fine" with my 200 AH AGM batteries. I'm reluctant to modify it's output feedback so as to rule out cable resistance cuz I prefer not to mess with the 7345 internals. Currently, with about 30 minutes of V10 idling alternator charging time through 7 feet of 6 awg cabling plus 2 hours of converter charging through 8 feet of 8 awg cabling I think I'm getting up to 90% SOC from around 50% SOC with the fast AGMs.
I can of course pick up another expensive 3-stage charger it I ever need it - but I want proof it's cost effective to do so. I have a sophisticated and pricey solid state switching 3-stage trolling motor charger but it's only 15 amps, but I can't really see any way of using it along with the 7345 to emulate a 60 amp 3-stage charger.
P.S. Don't be so hard on your 7345. After all, don't they set one back $150 to $180 new? I think it's notorious "charging problem" is merely one of speed (charge time) with dinosaur-technology wet cell LA batteries and too-small cable sizes. I'll bet the 7345 would have a different reputation if manufacturers had been installing them with 2 awg cabling all along. 
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