Battery charger vs converter January 06, 2013, 12:19:22 pm Yahoo Message Number: 136018Hi gang, there's a few existing threads on converters, battery chargers, etc, but they seem to have grown fairly long & dispersed, so I thought I would post a new question. On our '93 22' MP, the original Magnetek 6336 (36 amp) linear converter was replaced with a Parallax 7345RU (45 amp) upgrade unit back in 11/2006. We're developing a pretty good sense of our RV usage characteristics, so I thought would share this information in order to get some input on the best way of charging & maintaining our twin "T-105 type" 220 Ah Costco golf cart batteries. As an aside, Costco doesn't post the Ah, but they each weigh 60+lbs, which comes in @ 1,320 watt hours [22 watt hours/lb] or approx 220 Ah @ 6vdc.In essence, we're using (and expecting to use) the RV two-ways: 1. Take it out of storage every other week for a quick 1-2 night trip 30-60 miles away from home. 2. Take it on the road 2-3 times/year for 7 days averaging around 300 miles per day ie 5-6 hours/day driving. (Old time road trippers/campers here.)In both cases, we try and find places that don't necessarily require hook-ups. If they have them, great, but we'd prefer to run off battery power in a 'regular' camp ground space. In scenario #1, we bring the RV back the night before and hook it up to the house in order to both (a) cool the frig; and (b) re-charge the batteries. I have a wingnut on the negative terminal to disconnect the battery while in storage - after 14 days, the self-discharge shouldn't be greater than 5% or 11 Ah. When we return, we once again hook up the RV to re-charge the batteries before driving it back over to storage. Since we're only out 1-2 nights and fairly frugal with 12v usage, the battery is typically around 80-90%. Even at 175 Ah, we would only need to re-charge 45 Ah. My understanding is that you don't want to exceed a 20% re-charge rate, or 30-45 amps, so at that rate, we could re-charge in under 2 hours. Since the Parallax max re-charge rate is 13.8v/10 amps, the batteries never really get to 100%. My options are to either get a stand-alone 3-stage battery charger or upgrade the Parallax converter. However, I've heard that even the Progressive power wizard has issues that effect its stages if you're running any AC (eg the refrigerator) other than just re-charging batteries. If this is true, then a stand-alone charger might be the better option. That is, hook up shore power for the frig, and another line for the batteries. OTOH, it doesn't seem very efficient to have a separate device if a new converter/charger can do what is needed. In scenario #2, we'd only be spending 1 night per stop, and driving around 5 hours per day. Even if we consumed 50%, or 110 Ah in some kind of wild orgy of energy consumption, 5 hours driving/day on a 105 amp alternator should be more than sufficient to fully re-charge the coach batteries. More realistically, at 80-90%, 4-5 hours driving will have no problem re-charging. Assuming these calcs are correct, I wouldn't need to drag along a battery charger, nor would I necessarily even need an upgraded 3/4-stage converter-charger. OTOH, if I'm off, then I'd want something to quickly jump the re-charge back to 100% It looks like the real variable is the semi-weekly overnight trips. In that case, it comes down to either getting a battery charger, or upgrading the converter. If I went with the converter, which ones are the faves? Progressive, Xantrex, Iota, others? What amps would you get? 30 or 45? (220Ah * 20% max re-charge rate = 44.)If I went with a battery charger, which ones are popular?As usual, TIA for any tips/advice.Karl
Re: Battery charger vs converter Reply #1 – January 06, 2013, 04:55:49 pm Yahoo Message Number: 136024QuoteWhen we return, we once again hook up the RV to re-charge the batteries before driving it back over to storage. Since we're only out 1-2 nights and fairly frugal with 12v usage, the battery is typically around 80-90%. Even at 175 Ah, we would only need to re-charge 45 Ah. My understanding is that you don't want to exceed a 20% re-charge rate, or 30-45 amps, so at that rate, we could re-charge in under 2 hours. First, it is important to understand how a battery accepts charge - charged at a constant current, the voltage at the terminals will continue to rise, so if the charger voltage is limited - as it should be - then the charge current will drop as the limit voltage is reached. To achieve full charge could take several hours at 14.3V, as the charge current dwindles from full current output to a few hundred milliamps. Typically, a multi-stage charger - which yours is not - will switch to about 13.6V once the charge current drops to an amp or so. If a 45A 3-stage charger is used, it will replace almost that in A-hrs, per hour, until it limits at about 80% full replacement charge in the batteries. Then count several hours more beyond that. With a single-stage charger at 13.8V, current will begin to drop off well before the 80% mark, so charging will take considerably longer. You might consider investing in a good battery monitor. That way, you can determine if you can get a satisfactory recharge with your converter or need to upgrade.Steve
Topic: Battery charger vs converter (Read 12 times)
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Topic: Battery charger vs converter (Read 12 times)
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