Battery Charging Question

Go ask your dealer how much current is available at the RV plug. I think mine is like 30A because of wire size. The 62A is a max draw. Look at the current draw of the fridge to determine if it would keep it fully charged....

While assuming that your answer is in good faith, my experience with the dealer(s) has not been positive. I have found quite a bit more expertise here than at dealers.

I have not yet had an experience that did not require multiple trips for simple issues, and questions more complex than "is the sun shining" have more often than not been been met with "slack-jawed" looks.

Open your trucks owners manual and go to the FUSE section
It will identify the fuse/relay used and size for trailer charge line
Most likely 30A max

BUT the issue is resistance...due to length of charge line and small size of wire
So 'charge' lines are OK for maintaining normal trailer battery demands while in transit

Your residential reefer will probably NOT demand much because it will cycle very little........it is already cold, nobody is opening/closing it while in transit and even if it does cycle it should be very short run time.

IF large demand occurs then you will have to run a larger size charge wire

We have a residential refer with a 1000watt inverter. We have never had a problem with the batteries being low at the end of the day. We have 2 group 27 12 volts.

No worries. Worst case they could be a bit low as you arrive and plug in. You will never even know unless you have a voltmeter and make a point to check.

Mr. Biscuit, dmck and time,

Thank you for the replies.

Our 5 has two Group 24 batteries, each rated at 60 amp hours. Since they are in parallel, I am assuming that keeps the voltage the same, but increases the amp hour rating to 120 (Based upon being fully charged after a night on shore power.)

When these batteries reach their end-of-life, I have thought about going to 4 six-volt deep cycles (space permitting).

I welcome any and all knowledge regarding these issues, and thanks again.

Old-Biscuit wrote:
BUT the issue is resistance...due to length of charge line and small size of wire.

Or to say it another way, "voltage drop" over the length of the wire.

I am a retired automotive engineer.

First, let's start with modern light vehicle charging systems are design to replace the energy consumed from starting the engine and running other electrical devices ON THAT VEHICLE. Once they "sense" (and many vehicles do now have some kind of battery "state of charge" sensor) they cut back the voltage on the alternator to just enough to keep the vehicle battery charged, which is typically between 13.2 and 14.0 volts.

Even at 14.0V, the "voltage drop" (loss of voltage over a specific size and length of wire) is likely to be INSUFFICIENT to keep your fifth wheel batteries charged. If you want to prove this to yourself, hook up a voltmeter to your trailer batteries, hook the trailer up to your vehicle and take a drive.

You have 2 choices:

• use a DC-DC boost converter
• buy a special DC powered battery charger.

There are literally thousands of DC-DC boost converters for sale on eBay. Make sure to buy one that is powerful enough. You simply install it in between the wires coming into your trailer and your existing battery charger and set the output voltage to about 14.8V.

DC battery chargers are harder to find, but they do exist.

62 amps is *way* too high for a fridge that you can fit in an rv, that's peak power. Your battery bank will handle the surge, you need average current.
The measured power use I've seen for residential style fridges ranges from like 900 to 1400 watt hours per day. Taking the high number and rounding off the voltage to 14 and a day to 25 hours and ignoring the inverter efficiency (85 percent?), yes I lazy today, your average current is more like 4 amps.

Planning wrote:
I have thought about going to 4 six-volt deep cycles (space permitting).

Two should be plenty sufficient unless you change your camping style. With some conservation two GC2 should even get you through a quick overnight.

Yes you need 4+ if you are going off grid for an extended period. Also need to consider solar and generator.

Wizard,

"Make sure to buy one that is powerful enough." How much is "powerful enough"?


Horton,

The sole reason that I listed the 62 amps was as a rough worst case draw, converting about 110v/6 amps AC to 12v/DC.

I figure that we drive somewhere around 8 (average), and max of 10 (unusual) hours per day; that time being the most that the inverter/batteries would be powering the reefer.

What would you say that equates to in terms of watts and amp hours?