Charging on the road

[SCBillandJane]

Normally we would be in a campground with electrical supply to run the air conditioner where we camp. However, we are planning a trip to Alaska where the temperatures would allow us to not use air conditioning. We will probably want or be forced to camp without electricity. Our group 27 deep cycle battery is located under a kitchen cabinet and is vented to the outside. Adding another battery would put it in the living area unvented. We have good sleeping bags and would use the heater as little as possible. I have read on other posts that the one battery can last 24 hours with conservation, but it is stretching your luck to try and make it for 48 hours. I have the following questions and welcome someone thinking outside of the box.

1. How long does it take to recharge the battery when plugged into 30 amp or sometimes to 15 amp at a campsite?
2. Factoring in running the refrigerator on battery while traveling, will the tow vehicle be able to give the battery much of a charge in say 8 hours of driving?
3. Buying a second battery and keeping it in the back of the truck seems to be the cheapest and easiest solution until I think about the weight changing it in and out and figuring how to keep it charged.

Ideas?

[ShrimpBurrito]

1) Charge time will be the same regardless of whether or not you are plugged into a 15 or 30 amp service. The charger is going to draw whatever it needs, and it wouldn't be anywhere near 15 amps.

2) The refrigerator takes about 10 amps at 12VDC. In my experience, the battery does not charge very much while towing if the fridge is running, but I can provide more detailed info next week after we get back from our trip. But since the fridge takes alot of power, note that it puts a significant drain on your battery while you are setting up and taking down. If it takes you 30 minutes from the time you disconnect, level, set up, etc., and finally turn it to gas, that's 5 amp hours. Same thing when you take down. You could easily consume 10% of your battery charge by doing this during setup and tear down. Someone posted some pics of a switch they installed on the outside to turn the fridge off.

3) I put two 6v batteries in the rear compartment of my 2720SL, and they perform great. I don't have to worry about running out of juice, even over 4 days running the furnace several hours a night and modest use with the lights.

Dave

[TREXHUNTERS]

Hi,
I think that figuring out how to add a second battery (or a system that gets 200+AH) will be very helpful. We have 2 Grp 27 12v batteries (≈230AH) and can go 3 or 4 days running the heater 1-2 hours/night similarly to what ShrimpBurrito indicated. I agree though that keeping one of the two in the car is a difficult proposition. We have the KB instead of the KS. Can you not fit the batteries on the front-end?

We have a 1kw generator that we use to charge the batteries every day or two. If you're going to Alaska and will have to dry camp a lot this will be a good investment as you can charge for an hour or two every couple of days.

I agree that you may not get a good charge from your TV while running the fridge. I say "may" because I haven't measured it but have had two batteries go bad, i.e. completely discharged when we arrived at a destination, during the last month. We bought the batteries at Costco so they replaced them. I don't honestly know if I killed them or they were bad to begin with.
You can get a battery powered fan to put in the fridge(Walmart or else) to save that power but I think the big sink is the fridge itself.

The switch idea that shrimpburrito mentioned sounds like a good one too.

cheers
trexhunters visiting california

Originally Posted by ShrimpBurrito

1) Someone posted some pics of a switch they installed on the outside to turn the fridge off.

Can someone point me to this post? I'd like to add such a switch to mine but I have searched and cannot find this.

Thanks.

[ShrimpBurrito]

I looked for it for about a half hour, but it has thusfar eluded me.

Dave

Do you mean a battery switch? I put one of these on our dual battery setup:

http://www.amazon.com/Guest-2111A-Un...2382188&sr=8-5

BK

[ShrimpBurrito]

This was a switch that was mounted underneath the trailer directly under the fridge. The idea was that when you make a stop for an extended period, you can turn off the fridge and fan so it doesn't eat the TM battery (or the TV battery if the hitch power isn't turned off when you turn off the engine). Then before you hit the road, you turn it back on.

A battery disconnect switch would accomplish the same thing, but has a few disadvantages:

- it would turn off your radio and probably erase your presets (not a big deal to me)
- if you forgot to turn it back on before you hit the road, you would not have any breakaway brakes nor would you be charging your TM battery (a big deal)
- or, if you wanted to keep the fridge off for a few hours, then turn it back on for a few hours, then off, etc., if an effort to dedicate more power to charging the TM battery, you need need a dedicated switch to prevent the above problem.

This switch would only disconnect the 12v supply to the fridge and fan. You could use that switch referenced in BK's post to do it, but it only has to be an on/off switch.

Dave

The battery fuse is 30A (12V). If you could charge at that rate, a 100AH battery would take 3 hours. FYI

As discussed in other threads, if you have a proper connection between TV and TM the average 55A vehicle alternator can charge and supply the fridge.

[ShrimpBurrito]

Originally Posted by larsdennert

The battery fuse is 30A (12V). If you could charge at that rate, a 100AH battery would take 3 hours. FYI

True, but I don't see how you're going to get 30 amps to the TM battery from the car. On a 30 amp load run 70 feet (35 feet out and back), the voltage will drop over 4 volts over #10 wire. The drop is definitely more than that due to additional resistance in connectors, and even more if you smaller than #10 wire. You won't be able to charge a battery or run the fridge with that, so I don't see how you can charge a 100AH battery in 3 hours from your alternator without some wire that is about the diameter of your finger. You could use smaller wire if you have a DC to DC converter, however, a suggestion Bill has offered previously (which I am considering).

Originally Posted by larsdennert

As discussed in other threads, if you have a proper connection between TV and TM the average 55A vehicle alternator can charge and supply the fridge.

Indeed. But if you are not running the fridge, you can charge the battery faster. If you camp somewhere for a few nights, and then move and want to arrive elsewhere with a full battery, having the option to charge faster is nice if you're not driving far. But the limiting factor here is resistance and voltage drop, not alternator capacity. My alternator is 150 amps, but right now, I can only get about 8-9 amps from the TV before the voltage drops below ~12v. Also, your alternator is not as efficient after it gets warm. My alternator output gradually drops 0.5v over the course of the first 20 minutes of being started, so if you're doing testing, be sure you test it while it's warm for a more real-life reading.

Dave

Yep my point really was that no matter how good or bad your hookup it will take a long time to charge. Even on shore power. That could be why people think they aren't charging off he TV.