Using high-idle to recharge house batteries.

[Wrinkledpants]

The Sprinters come from the factory with a 200 amp alternator with an option of a second alternator. If high-idle is used to ensure 200 amps are put out, how long would it take to recharge a 200 Ah battery if it's at 50%?

The 2nd alternator option is 280 amps for a total of 480 amps at high idle. Does this drastically reduce charge times, or is there a point of diminishing return in regards to how current a battery can take during a charge?

[arctictraveller]

It would depend on the battery chemistry, amp hours of the batt bank and the temp. The manufacturer should have a graph of recharge time verses amperage.

[BroncoHauler]

IMO the high idle would best be utilized to offset high demand items like a microwave, coffee pot, or space heater for a limited time. Even at high idle, I don't think the engine rotates the alternator anywhere near the maximum stated capacity of the alternator, so to fully charge a battery (or batteries) could take some considerable time. Batteries can also only absorb a limited rate of current at a time.


Herb

[arctictraveller]

Charging Information For Lead Acid Batteries – Battery University

[arctictraveller]

Extensive idling even at high idle is not good for diesels either

[BroncoHauler]

No matter what concerns you might get in this thread, as a general rule I do think higher output alternators are a good idea. I think most stock alternators are adequate for stock vehicles, but the addition of electrically operated options and possible extended low speed driving (e.g. dirt roads) does not make for a good combination.

Herb

[Wrinkledpants]

Originally Posted by arctictraveller

Extensive idling even at high idle is not good for diesels either

It's a factory option from Mercedes. Both the fixed high-idle, and the adjustable high-idle. With a 5 year/100K mile engine warranty, I'm not too worried about occasionally using it.

Some of the Class B Sprinter folk on other forums talk about topping up their batteries in an hour with high-idle and a 2nd alternator. I've read in a few places that a deep-cycle battery can take 250 amps for awhile until you get to about the 80% charged mark.

One of the SMB representatives stated 30-60 min to recharge from high-idle and dual alternators. But, then from digging in threads here and from the posts in this thread so far, it seems like that's not possible. I haven't come across any charts from the manufacturers that state charge times with a current over 5 amps.

SMB states the high-idle power charges your 12v system first, then to the inverter for 110v to the house batteries. SMB advocates this setup over a generator. Am I missing something?

[LenS]

Originally Posted by Wrinkledpants

The Sprinters come from the factory with a 200 amp alternator with an option of a second alternator. If high-idle is used to ensure 200 amps are put out, how long would it take to recharge a 200 Ah battery if it's at 50%?

The 2nd alternator option is 280 amps for a total of 480 amps at high idle. Does this drastically reduce charge times, or is there a point of diminishing return in regards to how current a battery can take during a charge?

Five hours +

[arctictraveller]

[QUOTE Am I missing something?[/QUOTE]

Probably only that once a battery reaches about 80% of a full charge, the current it will accept (the acceptance rate) declines, dramatically extending the time needed to replace all the missing amp hours to get to 100% recharge. As a result, most folks never fully recharge their batteries until the plug into shore power. Once again I refer you to Nigel Caulder:

"Even with quality “deep cycle” batteries, repeated deep discharges dramatically reduce life expectancy, so typically systems are designed to limit discharges to no more than 50 percent of rated capacity. This takes care of the deep discharge issue. It’s not so easy to ensure adequate recharges.

Unfortunately, irrespective of the power of a charging device (alternator or battery charger), a battery’s charge acceptance rate (CAR) declines rapidly as it comes to charge. This makes it difficult to fully recharge batteries without either plugging into shorepower for several hours, or else running an engine (or an AC generator powering a battery charger) for long hours. For much of this time there is minimal electricity production.

In order to avoid these unproductive engine run hours when away from the dock, it is common to cease charging at around the 80 percent state of charge (SOC) level, but then the failure to fully recharge on a regular basis leads to something known as “sulfation,” which results in premature battery death. Like it or not, and regardless of how inefficient it is, if the batteries are to stay healthy, periodically they must be driven to a state of full charge."

[LenS]

Many of the better 3 stage chargers have desulfation cycles built into them. So does the Renogy MPPT solar charge controller.