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Old 09-18-2008, 07:53 AM   #1
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Battery Re-charging by tow vehicle?

Good morning! Would appreciate some advice - We dry camped for 3-4 days using battery power for occasional use of interior lights, all-night playing of the built-in radio, and use of the power jack to raise and lower the trailer from the tow vehicle hitch. Then drove 2-hrs on interstate at 50 mph back home and parked trailer for a week, after which we found the battery had drained completely. I believe we have a marine battery and think it less than 2 years old.

Question: Wouldn't that drive home with the battery connected to the tow vehicle have pretty much re-charged the battery completely? Or was the 2-hour drive just not long enough?

Thanks.

Roadlou and Paul.
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Old 09-18-2008, 09:20 AM   #2
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Someone will explain this, but in the meantime I can tell you that Steve did some analysis and determined that it takes a LONG time to charge the battery by driving. This analysis caused us to buy an additional battery, and only plan on charging by either plugging in, or using a generator.
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Old 09-18-2008, 01:09 PM   #3
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I use 2 batteries myself that I charge at home by plugging the camper in to a 30 amp circuit. I did find that 90 minutes on the road charged one battery. I haven't tested it since I added another battery. While your unit's parked, do you turn off the battery switch? The light on the radio and the CO2, Smoke, and Propane detectors use some current which will drain the battery in a few weeks. I leave my unit plugged while at home so anything running is on house current.
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Old 09-18-2008, 03:49 PM   #4
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Quote:
Originally Posted by pwb01
I use 2 batteries myself that I charge at home by plugging the camper in to a 30 amp circuit. I did find that 90 minutes on the road charged one battery. I haven't tested it since I added another battery. While your unit's parked, do you turn off the battery switch? The light on the radio and the CO2, Smoke, and Propane detectors use some current which will drain the battery in a few weeks. I leave my unit plugged while at home so anything running is on house current.
I have to agree, 1.5 -2 hours on the road, hooked up to the tow vehicle, should have the battery mostly recharged. That is presuming that you left the battery switch in the "on" position during the ride and your tow vehicle has a good electrical system. If you left the switch in the "on" position after you got home, your battery then started to discharge by keeping things powered even minimally.
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Old 09-18-2008, 08:00 PM   #5
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What are you using for a tow vehicle? Have you checked to see if you have 12V at the trailer connection?
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Old 09-19-2008, 04:15 PM   #6
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The amount of time you can get from a charged battery is easy to calculate. Remove the cable from the positive terminal. Place a voltmeter betwen the battery's positive terminal and the cable just removed. Have the meter on the current scale. Meaure the current flow.

A very good battery might provide 200 amp hours, approximately that means 20 amps for 10 hours or 5 amps for 40 hours or 2 amps for 100 hours.

If you know the current the trailer draws at idle, (by idle I mean nothing unusual on but sensors, alarms, control boards) you can easily calculate how long the battery will last when fully charged.

Simply divide 200 by the current flow to get the number of hours.

Of course a week has 168 hours in it and for a battery to be powering the basic systems of the trailer without being charged means about a week if you're only drawing an amp or so.

Hope this helps.

Norm Milliard
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Old 09-19-2008, 05:57 PM   #7
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Please note that the 200 amp hour number I posted in the previous email was for illustratiuon purposes. You need to look up the amp hour rating of your specific battery.

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Old 09-19-2008, 10:22 PM   #8
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Hi Roadlou and Paul.

See if this helps some as TV battery charging the TT coach battery can some times be tricky pending a few things.

A few things 1st.

1 As others have stated the battery switch if you have one needs to be on.

2 Do you know if your 7 wire TV receptacle actually is putting out voltage on the battery terminal? Some TV’s need a fuse installed to make that pin hot. Yours may or may not even be working.

3 On the newer Sunlines and maybe even the older ones, they have a fuse, generally 30 amp, in the TV charge line to the battery. This protects the TV if a short comes in the camper wiring circuit. It needs to be good.

Once past these 3 things comes the battery itself. Depending how far drained the battery is, the odds are not in your favor it will recharge off the TV by what you said you used the battery. If it is deeply discharged, odds are it will not come up unless you put it on an actual battery charger. If you are below 50 to 60% charge you might be in that requirement.

Part of the problem is the small 30 amp rated wire used in the 7-wire plug. On the TV battery it has very heavy cables capable of 60 plus amps in some cases to the TV alternator so it can put a level of charge to a discharged battery some if you drive long enough and the battery is in good shape.

But with that little 30-amp wire some 30 feet away, the voltage and current may not be high enough to recharge a deep discharged battery.

Here are some comparisons on time. I have a higher end 3-stage convertor I upgraded to on the TT. This Progressive Dynamics convertor can put out 60 amps of power at 14.4 volts to quick charge a 125-amp hour battery in 2 to 3 hours to about 90% IF it started out at around 10.5 volts which is about 50% discharged. If this bigger battery is even more discharged, it takes even longer. This larger 125 amp hr battery is bigger then most. You probably have a group 24, 85 amp hour battery unless you know it is bigger.

To go from 90% to 100% my charger then drops down in voltage and power and it takes about 15 hours to reach full 100% charge. That is if you are after a full 100% charge. Most RV chargers stop in the 90 to 95% range which is still good, but technically not 100% full charge. The newer 3 stage chargers get you higher.

The TV charging system cannot reproduce this to your TT if your TT battery is deeply discharged in most cases.

Check your battery for water, put it on a charger and try bringing it back to life. Ideally do not drain your battery down to below 50% (about 12.06 volts) before recharge while using it. It will last longer if you do not heavy drain it and recharge.

See this web site The 12 volt side of life It is helpful in explaining a lot of these battery type questions.

Hope this helps.

John
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Old 09-22-2008, 06:03 AM   #9
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THANK YOU!

Wow! Thank you for educating us and providing great practical advice. That link to the 12-volt side of life was a bonus and helped us understand what the critical decision criteria are for our camping needs and how to adjust our current practices. And, we may just pick up a few more tips at the Adirondack Meet & Greet this weekend. We're enjoying learning as we go!

Louise and Paul.
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