If a 250 AH Battery is charged with a Sprinter Alternator over a few hundred miles how long should it be expected to take to fully charge with a Magnum Energy MS2000 and EU2000.

Depends on the state of charge before you started driving, and the state of charge after you started driving. Do you have any way to read the house battery voltage?


Herb

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SMB-less as of 02/04/2012. Our savings account is richer, but our adventures are poorer.

Yep, a bunch of factors to dwell over. Is the plan to drive and top off at camp? I can only give a wild guess based on my system that might be no use to you. I guess with some research you could do the math. In a perfect world, if the alternator supplies a positive charge to the battery, then really the batteries or battery should be at about 95% state of charge pulling into camp. Shouldn't take long for a good charger to bring the battery system to the float level. An amp meter would be a big help. I actually found that my stock Ford alternator didn't supply enough when driving at night with the Starcool running. The amp gauge showed a negative charge and I had to upgrade the alternator.

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2006 Ford 6.0PSD EB-50/E-PH SMB 4X4 Rock Crawler Trailer

Sportsmobile 4X4 Adventures..........On and off road adventures

Starting from the same state of discharge, I would not be at all surprised to find the ME charger takes about the same time overall as charging to full capacity when driving. The reason is that once the battery is about 80% +/- charged, depending on the battery type, charge rate has to cut way back to finish topping up the battery. In either case, after the so-called "bulk charge" phase up to about 80%, the charger can't continue to deliver anywhere near its rated current into the battery. The ME is probably more "intelligent" about the charging curve than the stock Sprinter alternator controller, but in practical terms it's generally not feasible to fully charge batteries from a generator, unless you can tolerate the extended run time.

Check with your battery manufacturer's online tables for your specific type of battery to see how the charging curve works out.

Trying to estimate how many AH I would really have to "play with" I we really only want to discharge to 50% I would have 125 AH from 100% for a 250AH Battery (Lifeline AGM) but if I am only likely to start from 85% I would base available on only 87.5 AH. That battery got a lot smaller.

I wonder if it depends on the regulator of the alternator. My alternator takes my batteries well into the absorption state. My battery voltage will actually stay above 12.8 for several minutes W/O load on them after the engine is shut down, even at night when the solar is dead. But I've never let the batteries sit w/o load for the required several hours to see where they stand after an alternator only charge.

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2006 Ford 6.0PSD EB-50/E-PH SMB 4X4 Rock Crawler Trailer

Sportsmobile 4X4 Adventures..........On and off road adventures

Yep, that's the way lead-acid batteries work. On our rig, the batteries get pretty near if not fully charged on driving days. Or when we happen to camp with an electric plugin. Otherwise, we run the generator about an hour per day, which seems to be sufficient for our battery needs, as well as letting us use some 110V stuff while it's running. We have 200-220 ah of AGM batteries, and our biggest draw is furnace fan on cold nights, a bit for the absorption fridge, and not much at all for the LED lights. If we are boondocking for only a couple-three nights, and have no other reason to run the generator, often we don't (especially in warm weather), and just plan for the next driving day to bring them back up.

A plug-in digital voltmeter that reads to .01 volt helps a lot in keeping track of the batteries, if you don't have a monitoring system which measures charge/discharge current (which we don't).

Works that way on our Sprinter, too. After a few hours of driving, the batteries always show 12.8x for a while. I've checked them on "clean-up day" after a trip, when they've been turned off at least overnight, and they are sitting right at 12.7 volts, indicating a full charge. But I don't credit the Sprinter alternator controller with much intelligence, rather it HAS to eventually top them up, if you drive long enough. From maybe 50-60%, "long enough" seems to be any drive of 3-4 hours or more, give or take. YMMV. But the OP was asking about charging from a generator, which is tougher if you want to dribble in that last 15-20% charge.

Are you in the building stage? One of the reasons I went to twin 4-D batteries rather than one was I wanted to be able to run outside lighting, a microwave for limited time w/o the engine running, and still have enough to run a fan or heater all night. A single 4-D was slightly too light for some of the loads I was running. Adding the extra battery was one of the better upgrades I've done. But I guess it all depends on what you actually use. Some find a smaller battery system enough for them.
Having a battery monitor is a good idea and the best way to find out where the battery sits by morning. With all the LED lighting going into the new builds maybe you would be fine with a single battery but having a spot to install a 2nd battery is a nice option.

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2006 Ford 6.0PSD EB-50/E-PH SMB 4X4 Rock Crawler Trailer

Sportsmobile 4X4 Adventures..........On and off road adventures

Thank you for your inputs. Good to hear some real world experience inputs. Still in planning stages. I will be planning to carry a Honda EU2000 or even the Yamaha EF2400 if much more useful. There will likely be times I will want to run the A/C without shore power. SMB standard 200 AH battery seems a bit light. May end up with the 2 x 6 volt Lifelines for 300-400 AH. Just thinking that with the Honda EU2000 I can get away with the 8d 250 AH