Best way to recharge batteries while boondocking ?

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patsdad

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Joined
Mar 28, 2006
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85 Minnie Winnie 22  -  two new deep-cycle batteries
This summer I'll be boondocking a couple of times, and I'm wondering which would be the best way to put some juice back into the coach batteries  if necessary.  (The charging section of the stock electrical system is not working - batteries do not charge when the coach is plugged in to shore power.  I just top them off before I go on a trip. )

Should I run the gennie, and hook my garage battery charger ( 6 amp ; multimeter shows about 13v when charging ) up to the coach batteries, and do that for a couple of hours ?

Or, would it be better to put the 'battery' switch  ( on the driver's bulkhead - positions are "Both" , center, and "Momentary" ) in "Both" , and idle the main engine for a little while ?

As I understand it, the 'both' position links the engine battery to the coach battery load, so I guess it comes down to three things:
1 - Would the "both" position send a charge from the engine circuit to the coach batteries ?
2 - at idle, does the engine alternator put out any meaningful charge ?
3 - Would the engine method get more volts to the coach batteries more quickly than a 6 amp garage charger powered by the gennie  ?

As always, thanks for any insights.  I'm happy to say that my old girl, looking spiffy with some fresh paint on it,  is getting a LOT of use this summer  . . . . .
 
patsdad said:
Should I run the gennie, and hook my garage battery charger ( 6 amp ; multimeter shows about 13v when charging ) up to the coach batteries, and do that for a couple of hours ?
Click to expand...

With gas at $3.00/gallon, the Winnie engine would be a very inefficient way to recharge.  The automotive chargers you mention are also not good to charge deep cycles with. They drop off from their maximum input very fast and would then take forever to charge. When boon docking, batteries take much longer to recharge than they do to drain.

The ideal solution, to me, is a 3 stage charger. Mine is a 40amp, but they make smaller models. These chargers give you, in my case, 40amps full charging power through about 75% of the charge cycle. They then go into stage two that tops them off, and then a 3rd maintenance stage that keeps them topped off. This then uses minmum genset time.

If you are not using that much power while boon docking, you may also want to consider solar panels. I have 2 - 80 Watt panels that give me about 8amps into the batteries on a good day. I write, on a good day, because unlike the genset, charger, if the day is cloudy, solar is useless. Also, 2 80 watt panels will cost over $1,000 -- whereas a good 3 stage charger would be much less.

You could also just leave the charger plugged in when hooked up to power (as the one in your converter is not working) -- and it would then keep you batteries topped off all the time.
 
Gas may be expensive but I always thought the engine electrical system was better at charging a low battery.
You'd have to run the generator and a battery charger for many hours to get the effect of running the engine at idle for say 30-40 minutes .
Unless they have solar power I'd just fire up the engine for a while and see how many  amps you get.
Correct me if I'm wrong.
 
Well lets look at some facts.  Our 7.5 Onan burns .5 gals at full load and 0.3 the way we normally load it when using it. Now just how does that fuel burn compare to a 6 or 8 cyclinder engine that produces much more horsepower?

Genset is the way to go.
 
Alternators will put out some decent current even with the engine idling. I would set the switch to "Both" while driving, then "Center" when parked (Don't want to drain the engine battery). Get a decent 40A charger, as Bob mentioned, and run it off the generator rather than using the Winnie engine or that anemic 8A unit you have now.
 
If you love this old thing so much why don't you go & buy a converter? Being pluged in every thing goes through the converter/ battery charger. If you don't want to buy a new converter go buy some solar. The generator also will put about a 3 amp continues charge also. [ Go buy a new converter.]
 
At idle your engine alternator probably doesn't put out much current - maybe 3-5A in a 1980's vintage unit.  I'd replace the converter if you paln to keep the Minnie - you can get a good one for under $200. Or buy a 20A or better charger at the local auto parts store. 40A is better but they get pricey in a hurry.
 
OK - thanks for all the replies.    I hear you -  First, get a decent charger  ( need one anyway ), and also fix the converter.

Makes sense.  With 2 good deep cycles, I find that it takes quite a bit of use to run the batteries down.  But, as I said, with the whole family boondocking for 3 days, I just want the backup plan in place. 

Thanks for the help, as always. 
 
Bob,
If you paid over a grand for two 80 watt panels then it must have been long long ago! I can buy two 190 watters for that! $520 each!
 
what are your winter solutions? I WILL be going solar this spring, but full timing in the winter in Canada can be COLD :eek:.
my propane furnace and water heater are on 24/7 due to freezing temps. my RV has 2 brand new 100 Ah batteries.
I do have an onan 4Kw generator, and have been using it. I can get the batteries to 3/4 in the display after about 1.5 hours of run time. then the meter slowly drifts back to 1/2 on the meter; in the morning it drops to 1/4.  :(
I think I might have to go on a longer drive for a few hours, and see if this helps.
if that doesn't, i'm going to have to find a shore power source to plug in weekly, I think.  :(
 
Starting with FULLY charged batteries will help you. Please read below to get a better idea what fully charged batteries are all about:

https://handybobsolar.wordpress.com/the-rv-battery-charging-puzzle-2/
 
1.5 hours isn't a lot of charge time for 200 AH of battery.  You need to let the genset run longer and get that batteries to at least 80% and 100% if possible.  Discharged batteries accept a fairly high rate of charge initially, but the rate slows down as the charge increases. It may take an additional couple hours to get near 100%. Shore power won't be any quicker, since the charger and the batteries are identical whether the 120v comes from genset or shore power.  The Onan just provides power to the charger, same as the shore cord.

What size converter charger is in the RV - that's what determines the charging amps available.

Driving the RV engages the engine alternator to charge rather than the house converter/charger, but the principle remains the same: the battery charge rate slows as charge builds up above 60-70%. You would have to drive for more hours to get a greater charge. May as well run the genset and save the driving.
 
After 11 years I think the OP probably has figured out how to charge his batteries.
 
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