Battery charge when pulling down the road

[oldelmer1]

I happened to check the idiot lights for the battery after pulling for about 5 hours with the inverter on and or course the refrigerator on. I noticed that the lights were down to 2/3 charge.

I have checked the outlet on the truck and I have 12.79V there, and checked the cable on the camper and it has 13.1V when plugged into the AC.

So, has anyone else checked their voltage after pulling for about 5 hours?

I need to check the levelup display before I unplug from the truck and after I unplug but before I connect to AC.

THANKS,
Tom

 

[Oregon_Camper]

Tom...it is not the voltage that is the issues, it is the amps being used by the residential refrigerator. You'll have to look up your refrigerator model to see amp usage, but normally the refrigerator will consume more than your truck can deliver to the battery.

Some have solved this by installing solar panels on the roof.

 

[oldelmer1]

Jim, I went out and looked at the label on the fridge and it says it draws 8.5 AMPs at 115 Volts.

 

[mlpeloquin]

8.5 AMPs at 115 Volts
Assume 89% efficiency of the inverter
8.5 X 115V = 977.5 Watts
977.5 / 89% = 1098 Watts input to inverter
1098W / 12V = 91.5 Amps at 12V

So you must have some really good 12V batteries. The current maybe less do to the output of the inverter should be 125VAC. You can get a AC power/voltage monitor. They do not cost much. https://www.amazon.com/P3-P4400-Ele...1512335729&sr=8-4&keywords=ac+current+monitor

 

[Oregon_Camper]

Jim, I went out and looked at the label on the fridge and it says it draws 8.5 AMPs at 115 Volts.

I am guessing here, but the truck probably only puts out 3-4 amps...take into account some loss for wiring, battery quality, etc...then it is clear the refrigerator is going to draw more than you can create with the truck alone.

While your trailer “umbilical” cord does have a “charge wire” in the connector, typically the size of the wire is quite small. To adequately charge an RV battery, a heavy gauge wire is required.

Think of it this way: Your RV is on fire and the firemen arrive. However, the hose they use is only a garden hose. It provides water......but it just can't get enough through the hose to put out the fire.

 

[JMP]

I am guessing here, but the truck probably only puts out 3-4 amps...take into account some loss for wiring, battery quality, etc...then it is clear the refrigerator is going to draw more than you can create with the truck alone.

While your trailer “umbilical” cord does have a “charge wire” in the connector, typically the size of the wire is quite small. To adequately charge an RV battery, a heavy gauge wire is required.

Think of it this way: Your RV is on fire and the firemen arrive. However, the hose they use is only a garden hose. It provides water......but it just can't get enough through the hose to put out the fire.

Thank you for explaining this in a manner this is easily understood. I did not think about the residential refrigerator drawing more AMPs than the truck provides to the battery. I was on a 2-3 day trip recently and noticed my battery idiot light down to 3/4 and wondered why... Thanks again for explaing this Jim.

 

[cemill]

I installed a third battery in our 2015 Big Country at Heartland's suggestion and after pulling 5to 7 hrs a day for three days. No problem.

 

[Bob&Patty]

This discussion has me wondering about the statement that " the truck only puts 3-4 amps to the coach". My truck has a 140 amp alt and a 40 amp fuse to feed the coach. Am I missing something?? The OP states that he has a "voltage reading of 12.77 at the truck. But what is the amp reading? Voltage does not charge a battery....it's the amps.

 

[Oregon_Camper]

This discussion has me wondering about the statement that " the truck only puts 3-4 amps to the coach". My truck has a 140 amp alt and a 40 amp fuse to feed the coach. Am I missing something?? The OP states that he has a "voltage reading of 12.77 at the truck. But what is the amp reading? Voltage does not charge a battery....it's the amps.

LOL...Ya missed the disclaimer... "I am guessing here, but the truck probably only puts out 3-4 amps"

Even if your truck could generate 1,000,000,000,000 amps...the wiring to the 7-way plug and then from 7-way plug to battery is simply too small to carry a sufficient amount of amps to the battery. (see post #5 for example) Think about the wire size that you see on your battery, coming from your converter....then think about the wire size coming in on 7-way plug.

 

[RFOneWatt]

As mentioned above, if you have any significant amp draw in the RV and you want your batteries to charge adequately while traveling you must run an additional charge wire (4GA or larger, depending on the length of the run) from the vehicles battery all the way to the battery bank on the trailer.

I use 2/0 welding cable with Anderson-style quick disconnects along with a hefty fuse/breaker under the hood of the TV.

Once you decide on the gauge of wire you plan to use, double it.

~RF

 

[bwdt]

You don't need 1100 watts of power to the batteries for the fridge. It draws this kind of power only while running. Figure that it probably runs for about 20 minutes per hour unless you are in a very hot climate so the total amount of power you would need not calculating losses and start current would be about 330 watts. If this is the case then you probably need about 35 amps at 12.5 volts or more to stay close to even. This is totally doable but you need to up the wire size in your wiring to compensate for resistance losses. The terminal connector in the plug should carry the current but might run a little warm.

You should also check the fuse on your trucks trailer circuit? If its to small you can put a relay in the circuit with a larger charge wire off the batteries that ties into the coach to get more current. Just put a large fuse on the wire that goes back to the coach.

Instead of buying additional lead acid batteries you should look into putting your money into LiPo batteries as they are much easier to charge and discharge. There are some awesome comparison videos on youtube with comparisons between all of the types of batteries.

 

[oldelmer1]

OP here, I have a AMP meter, the kind you put over the wire for a reading, but I cant find it....

I will keep looking and see what it says on the wire going to the camper.

 

[Oregon_Camper]

OP here, I have a AMP meter, the kind you put over the wire for a reading, but I cant find it....

I will keep looking and see what it says on the wire going to the camper.

Should be able to find it via the junction box on your king pin.

 

[shiggs68]

This discussion has me wondering about the statement that " the truck only puts 3-4 amps to the coach". My truck has a 140 amp alt and a 40 amp fuse to feed the coach. Am I missing something?? The OP states that he has a "voltage reading of 12.77 at the truck. But what is the amp reading? Voltage does not charge a battery....it's the amps.

Voltage and amperage are directly related. It’s just fundamental Ohms law. Consider the current open circuit battery voltage, any voltage higher than that will cause current to flow into the battery (charging). The resistance of the battery, the wires and connectors, and the voltage difference is needed to do an actual calculation. When you consider 12.6vdc is a fully charged battery, 12.77 is not much charging current.

This chart art shows the state of charge

 

[avvidclif]

OP here, I have a AMP meter, the kind you put over the wire for a reading, but I cant find it....

I will keep looking and see what it says on the wire going to the camper.

Make sure it's a DC Ammeter. The regular ones are for AC and won't work.

 

[Bob&Patty]

All statements are true. As amp draw goes up...voltage goes down and visa versa. At least it always has in my world of a DC voltage system. JMHO

 

[oldelmer1]

OKAY... I found my Mini AC/DC clamp meter, now it it only stops raining....