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12 volt charge line from HDT to RV


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I was checking the wiring on my Volvo 610 which I am using a Jackalopee. I have the 12VDC needed to charge the RV batteries hooked up on option one which is BLU 12v AUX line pluged in to the +12V direct which gives me 12V going to the trailer with the switch key on. I am getting the correct voltage at the rear plug on the truck which is about 13.6 with truck running. If my rv batteries are showing 12.6 when I plug in to trailer, it does not seam to raise this any. I checked the trailer plug and correct 12V in the trailer plug is going to the batteries. How many amp charge should I get to the trailer, I have 4 6V batteries on the trailer and a 2800 watt inverter, also a residential fridge. Is their a better way to wire the Jackalopee like option two or option three so I can get more amps to the trailer batteries? Should I ever be able to bring the trailer voltage on the batteries to what I am showing on the truck batteries? The only thing running off the trailer batteries is the inverter which is only powering the fridge.

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This is what I would do for starters. Kill all the DC loads in the RV, especially that inverter. You might have to remove all the DC fuses. Turn off the converter in the RV (or disconnect from shore power) so that no DC is being generated from the RV. Then disconnect the battery lead ground from the batteries in the RV so that no DC is seen on the trailer plug coming from the RV. Then plug in the trailer plug and measure from the removed ground lead to the positive side of the battery. This way you can see what is really getting through the trailer plug.

 

Now you should have the truck's DC into the RV. If you get DC from the truck and it appears to be somewhere around 12V then put a small load on the trailer's DC panel. Like turn on one DC light. Then measure the volts where you did before (ground cable to the positive side of the batteries). If you still have DC volts and your light load works then it should be good.

 

If you have 12VDC before you turn on the small DC load and then have none (and the load does not work) let me know and I will tell you how to proceed.

 

Chet

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This is what I would do for starters. Kill all the DC loads in the RV, especially that inverter. You might have to remove all the DC fuses. Turn off the converter in the RV (or disconnect from shore power) so that no DC is being generated from the RV. Then disconnect the battery lead ground from the batteries in the RV so that no DC is seen on the trailer plug coming from the RV. Then plug in the trailer plug and measure from the removed ground lead to the positive side of the battery. This way you can see what is really getting through the trailer plug.

 

Now you should have the truck's DC into the RV. If you get DC from the truck and it appears to be somewhere around 12V then put a small load on the trailer's DC panel. Like turn on one DC light. Then measure the volts where you did before (ground cable to the positive side of the batteries). If you still have DC volts and your light load works then it should be good.

 

If you have 12VDC before you turn on the small DC load and then have none (and the load does not work) let me know and I will tell you how to proceed.

 

Chet

Will do, thanks Chet

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OTR - Chet has the right idea on the 12 volt. I have a different problem with 12 v. Your just not going to get much back there.

 

Using the alternator as the starting point, your batteries are - call it 50' - back there. Remember all the twists and turns the wire takes. Now, double that!! (the 12 v has to come back to the alternator also). So 100' of we'll say #10 wire (what most folks run). Then you have the Bargman plug. (Not really suited for large wire or serious power). You have a 1 volt difference? (13.6-12.6) And this is when no other 12 volt loads, running lights, trailer brakes, stop lights are using part of that 12 ground path.

 

Tech stuff

From the table - http://en.wikipedia.org/wiki/American_wire_gauge - 1000' of #10 wire has a resistance of 0.9989 ohms per foot. So 100' is 0.09989 and plugging it into the formula

I=E/R ---- 1 volt difference / .09989 (resistance of the wire, it will be greater with the various connections) = The best your going to get is 10.011...amps back to the trailer.

 

You do have other loads - propane detector, A/C-furnace controls, 1.5 amps for the inverter standby, so I would figure about 2.5+ amps idle current leaving 7.5 amps for charging. Then, the fridge hits the inverter. Guesses here --- you drive for 4 hours, stop for lunch for an hour so with unhook and hook up time your unplugged for 6 hours. Let's say the fridge hits once during the 6 hours and runs for ~1 hour. And let's say the fridge uses 2 amps at 120 volts running.

 

So, the inverter is using 20 amps - conversion is never 100% so call it 90% efficient - 22 amps for that hour. - 22 AH (amp hours)

 

Summary

I can supply 10 * 4 hours engine time 40 ah

I use 6 * 2.5 (idle loads) so -15 ah

fridge load - 22ah

 

ideal conditions - 40ah-15ah-22ah = 3 ah going into the batteries if your lucky!!!

 

I have a sine wave inverter in the truck and power the trailer at 120 volt (limited @ 5 amp) and let the trailer inverter / charger charge the trailer batteries (AGM) and run the freezer and such. It works much better. I can put 200 ah back there in the 4 hours of driving. And, I've seen the solar adding another 80 ah.

 

We have 800 ah of 12 volt capacity in the trailer.

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Greetings - Charging the coach batteries from the tow vehicle is a trickle at best. Even with the 10 AWG wire in the harness, there will be 30 or 40 ft of length, each way between the truck battery and the coach battery, plus the impedance of any fuses or connector pins in line.

 

 

This is a little voltage drop calculator that one can play with to see how much voltage is lost, at a given amp draw with what seems like "big" wire.

 

 

http://www.powerstream.com/Wire_Size.htm

 

 

I have experienced the same thing; the truck charge line cannot keep up with the draw from the residential refrigerator going down the road. In 10 or 12 hrs off the grid, with the truck charge line hooked up, I have about a 70 to 100 amp hr deficit according to the Magnum system.

 

 

I planned for this by running some 2/0 to the back bumper of the truck but haven't wired it up to the trailer yet as I haven't figured out how to fish two 2/0 wires from the pin box to the belly of the coach.

 

Any suggestions short of pulling the skin off the coach?

 

 

 

thanks

Rich

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"I planned for this by running some 2/0 to the back bumper of the truck but haven't wired it up to the trailer yet as I haven't figured out how to fish two 2/0 wires from the pin box to the belly of the coach.

 

Any suggestions short of pulling the skin off the coach?"

 

I tried to do this with the camera wire. Pretty near impossible. Then I tried to pull down just a corner...and managed to really mess stuff up. Finally I just unscrewed the whole panle and took it down and was glad I did--so I could fix all the rubbed places where the OEM wiring was going thru rough torched-out holes in the framing! Honestly, If you don't want to move the skin (and it is a REAL PITA!) I would seriously consider some rigid electrical conduit (probably use plastic) neatly clamped up under the belly. Drill a hole and run the conduit straight into the storage compartment (If you have one).

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Greetings - Charging the coach batteries from the tow vehicle is a trickle at best. Even with the 10 AWG wire in the harness, there will be 30 or 40 ft of length, each way between the truck battery and the coach battery, plus the impedance of any fuses or connector pins in line.

 

 

This is a little voltage drop calculator that one can play with to see how much voltage is lost, at a given amp draw with what seems like "big" wire.

 

 

http://www.powerstream.com/Wire_Size.htm

 

 

I have experienced the same thing; the truck charge line cannot keep up with the draw from the residential refrigerator going down the road. In 10 or 12 hrs off the grid, with the truck charge line hooked up, I have about a 70 to 100 amp hr deficit according to the Magnum system.

 

 

I planned for this by running some 2/0 to the back bumper of the truck but haven't wired it up to the trailer yet as I haven't figured out how to fish two 2/0 wires from the pin box to the belly of the coach.

 

Any suggestions short of pulling the skin off the coach?

 

 

 

thanks

Rich

I used a electrical fish tape to mount a 110 volt plug in from the inverter so I could use the rv inverter in the truck. I have a 1400 watt inverter in the truck and it works fine for a small fridge and microwave. I put a 110 volt outlet on the fifth wheel hitch next to where the box is for the 12 volt tie in.

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I have installed a separate 3-0 welding cables from the truck batteries to the fifth wheel and it works good. The residential fridge with the ice maker off and all 12vdc at idle draws 27 amps from the truck when the compressor is running. A though that maybe when the batteries are fully charged and shortly after the compressor has settled down.

I did install a disconnect from the truck batteries for when we are boon docking. But forgot about the trailer plug. Yes the truck batteries would not start the truck several days ago at the Kayenta Az. so had to start a generator to get going

Also it does take 6 plus hours or running time to bring the batteries back up. and we sometimes shut the fridge off late at night and back on in the am.

 

safe Travels, Vern

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I have installed a separate 3-0 welding cables from the truck batteries to the fifth wheel and it works good. The residential fridge with the ice maker off and all 12vdc at idle draws 27 amps from the truck when the compressor is running. A though that maybe when the batteries are fully charged and shortly after the compressor has settled down.

I did install a disconnect from the truck batteries for when we are boon docking. But forgot about the trailer plug. Yes the truck batteries would not start the truck several days ago at the Kayenta Az. so had to start a generator to get going

Also it does take 6 plus hours or running time to bring the batteries back up. and we sometimes shut the fridge off late at night and back on in the am.

 

safe Travels, Vern

Vern what kind of connection do you have to connect the 3/0 from the truck batteries and the rv batteries? Also do you have this wire fused in any way?

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I have installed a separate 3-0 welding cables from the truck batteries to the fifth wheel and it works good. The residential fridge with the ice maker off and all 12vdc at idle draws 27 amps from the truck when the compressor is running. A though that maybe when the batteries are fully charged and shortly after the compressor has settled down.

I did install a disconnect from the truck batteries for when we are boon docking. But forgot about the trailer plug. Yes the truck batteries would not start the truck several days ago at the Kayenta Az. so had to start a generator to get going

Also it does take 6 plus hours or running time to bring the batteries back up. and we sometimes shut the fridge off late at night and back on in the am.

 

safe Travels, Vern

Also are you connected directly to the battery bank on the truck and directly to the battery bank on the rv?

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When I was considering adding a 12VDC trailer connector from my trailer to my truck I was considering these 300 amp connectors. Since I installed a Magnum MS2012 inverter in the truck and one in the trailer the connection was not needed. I do run a cord from the A/C outlet from the trailer to the truck to power the charger in the inverter to keep the truck batteries charged.

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When I was considering adding a 12VDC trailer connector from my trailer to my truck I was considering these 300 amp connectors. Since I installed a Magnum MS2012 inverter in the truck and one in the trailer the connection was not needed. I do run a cord from the A/C outlet from the trailer to the truck to power the charger in the inverter to keep the truck batteries charged.

That looks like a connection I already have on the back of the cab of the truck. I will have to go check but it may already be there. Not sure what size wire goes to it

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I have a sine wave inverter in the truck and power the trailer at 120 volt (limited @ 5 amp) and let the trailer inverter / charger charge the trailer batteries (AGM) and run the freezer and such. It works much better. I can put 200 ah back there in the 4 hours of driving.

I did the same things a few years ago using a cheap modified sine wave inverter I bought in a truck stop, before true sine wave inverters were commonplace. Worked fine once I figured out I needed to mount the inverter away from the engine heat. The switching supply in the converter really doesn't care what kind of waveform you feed into it.

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For the heavy stuff you want to use Anderson connectors. Here is an EXAMPLE. Then make them in all ratings.

 

I've done a bunch of high power hookups from tow vehicle to trailer in the past. You have to be careful of your alternator overheating. It can EASILY happen. I've even gone so far as to upgrade the alternator to exotic high output continuous usage alternators. They can REALLY crank out the power.

 

In the end, it is (on balance) probably easier for most people to do what Bill did - send 120 volt across. But you need to do that the RIGHT way or you have a big safety issue.

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I've done a bunch of high power hookups from tow vehicle to trailer in the past. You have to be careful of your alternator overheating. It can EASILY happen. I've even gone so far as to upgrade the alternator to exotic high output continuous usage alternators. They can REALLY crank out the power.

 

In the end, it is (on balance) probably easier for most people to do what Bill did - send 120 volt across. But you need to do that the RIGHT way or you have a big safety issue.

I did it that way because I have an expensive charger (inverter) in the trailer tailored to my AGM's, and I can limit the battery charge through a 'power share' feature that turns down the charge load to the trailer batteries to limit total 120 v incoming to 5 amps (or 50 amps out of the alternator). The truck also has 400 ah of AGM's

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I have a sine wave inverter in the truck and power the trailer at 120 volt (limited @ 5 amp) and let the trailer inverter / charger charge the trailer batteries (AGM) and run the freezer and such. It works much better.

 

Without going to great expense and dedicated equipment, this is really the most efficient way to use your rig for charging your house bank. DC doesn't travel well and just can't push enough amps over that distance with much effect.

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Your right Yarome - see post #4 where I did the calc's on it. And I only use it while actually traveling. The Honda does a much better job.

 

This was / is just a continuation of the other posts. OTR the OP was asking that very ? to get to this point.

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I think for the money invested, safety and I need them anyway will be to add the solar panels. I will go to Jack's web site and start trying to figure out how many I need to maintain the coach battery bank. I never thought about overloading the truck alternator and burning it up.

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I think for the money invested, safety and I need them anyway will be to add the solar panels. I will go to Jack's web site and start trying to figure out how many I need to maintain the coach battery bank. I never thought about overloading the truck alternator and burning it up.

 

Guaranteed you certainly won't ever regret it. You also have the added advantage of continuous charging instead of start and stop charging only when your rig is running... not to mention power on demand during the day without having to dip into your battery bank. :D

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I think for the money invested, safety and I need them anyway will be to add the solar panels. I will go to Jack's web site and start trying to figure out how many I need to maintain the coach battery bank. I never thought about overloading the truck alternator and burning it up.

I'm happy to work with you on the design of your system. Once you get some ideas just email me.

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