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Old 09-01-2015, 01:36 PM   #43
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Originally Posted by twinboat View Post
A late model Grand Cherokee, like the OP tows with, has a 160 amp alternator as standard equipment, with options up to 200 amps.

With at least 80 amps available, he can charge his 80 AH trailer battery with booster cables, without worrying about overloading and overheating his alternator.

Just don't turn on every electrical item in the Jeep while doing it.

But the trick is how to limit the alternator to just 80 amps or less 😃

It WILL ramp the amps up to max in an attempt to get the voltage to 14.2 or higher
depending upon temperature.
which on a severely discharged battery will not happen for awhile. You may feel comfortable risking your equipment .....however it is a substantial risk that damage will occur if the load is maintained long enough to overheat the diodes.

Better to get something like Amp-l-Start, which will limit the charging amps to 15, and then there is no worry.

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Old 09-01-2015, 02:36 PM   #44
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The paralled battery in the Jeep will limit this condition. Besides no alternator will output full capacity until it's RPM's are increased to around 2000 engine RPM's.

With 15 amp charging current, it will take the OP over 3 hours to charge his battery, from 50% discharged.

If this was a permanent setup with large gauge cables, a battery combiner sold by "Yandina.com" would serve him well.

It is full of features needed to charge 2 battery banks from one source.

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Old 09-01-2015, 07:57 PM   #45
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Short term at most. I will be putting solar panels on after this month-long trip. I don't plan to run the trailer battery down much and do carry a battery charger.
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Old 09-01-2015, 09:53 PM   #46
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The simple answer I see is neither one is more efficient than the other. You should either go to a campground with electric or spend money on all suggestions mentioned here.
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Old 09-02-2015, 05:53 AM   #47
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Originally Posted by elkski View Post
200 watts of PV charging at 14 amps?? wow! my 100 watt grape PV has only given me 4 amps so far :( But I guess that means 4.3 incl My parasitic.
Did you have yours tilted for that 14 amps?
Flat on my roof and when cońnected to my friends dead batteries I saw as high as 15 amps at 14.8 volts to the batteries. I do have an MPPT controler.
Summer sun can charge very well. Winter sun not so good.
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2005 Ford F250 SD, XL F250 4x4, Long Box, 6.0L Diesel, 6 Speed Stick, Hypertech Max Energy for Fuel mileage of 21 MPusG empty, 12.6 MPusG pulling the BC. ScangaugeII for display..
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Old 09-03-2015, 09:13 AM   #48
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Originally Posted by Davdeb1 View Post
The simple answer I see is neither one is more efficient than the other. You should either go to a campground with electric or spend money on all suggestions mentioned here.

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Old 09-04-2015, 08:53 AM   #49
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I would not be as worried about efficiency as I would be about plate damage at really high charging rates one gets from jumping the two batteries together. The alternator output is only part of the equation. The starting battery will also be a current source trying to equalize the voltage with the camper battery through the jumper cable. Current limiting is the resistance of the connection plus the internal resistance of the batteries.

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battery, boondocking, charging

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