Charging with Tow Vehicle

mcpaul · 11-10-2014, 12:20 AM

I've been reading for quite a while, first post, probably not my last. I know this has been gone over many times but I think my situation is a little different. I have a '14 3200 with a '15 F350 6.7. The dealer installed a 3000w inverter & 4 six volt batteries for me. I have +/- 14v at the output of my plug at my truck when running but it is not making it to the batteries in the 5th wheel. Meter reads +/- 12.6 or so at the batteries when hooked up. Just want to keep my batteries topped off while running. Any ideas where to start looking??

**wahoonc** · 11-10-2014, 01:30 AM

Make sure the relay and fuse that lead to the trailer charge cable are installed and not blown. I had that problem with our F150... relay was in the glove box.

Aaron

MartyG · 11-10-2014, 02:16 AM

Aaron, if he had "14v at the output of my plug at my truck when running" then there is nothing wrong with his TV; it is sending voltage to the back end. But if the batteries in the trailer say 12.6, then they are not getting the charge. Check plug connection, and all wiring to converter.

mcpaul · 11-10-2014, 04:33 AM

Correct Marty, the TV is working correctly. All the other functions of the plug are good. The inverter now charges the batteries so i believe the converter is no longer used which is what is confusing me. What happens to the 12v lead from the plug now that the inverter is involved.

**wahoonc** · 11-10-2014, 10:34 AM

Quote:

Originally Posted by MartyG

Aaron, if he had "14v at the output of my plug at my truck when running" then there is nothing wrong with his TV; it is sending voltage to the back end. But if the batteries in the trailer say 12.6, then they are not getting the charge. Check plug connection, and all wiring to converter.

You are right Marty... my brain shuts down around 9pm.

Something didn't get hooked back up when they installed the inverter and new batteries.

AFAIK the converter should still be hooked up, all most inverters do is take the battery power and convert it to 110/120v. They usually don't go the other way.

Aaron

MartyG · 11-10-2014, 07:11 PM

Wow, this can get confusing. The converter takes 120Volt shore power, and changes it to 12 volts DC, which is used for lights, many circuits, and also keeps the trailer batteries charged. When it is on, there very well may be a relay that cuts OFF the connection to the trailer plug, so the converter isn't also trying to charge the vehicle battery. As mentioned earlier, there is in many cases also a relay in the truck to also break this connection when the truck is not running. In short then, the only way to get the truck to charge the trailer's batteries is to have the vehicles connected via the plug, the truck running, and the converter either off or not plugged in to shore power. This is the configuration of driving down the road. In that condition, the voltage measured at the trailer battery terminals should be (virtually) the same as measured at the truck battery terminals.
An inverter is another thing altogether. It takes 12 volts DC from the trailer batteries, when not hooked up to shore power, and steps it up to 120vac for some circuits and outlets. It DOES NOT try to feed the converter. Attempting that would create a power-robbing power feedback, i.e. battery to inverter to converter and back to battery. The only thing the inverter does to your 12 volt battery pack is to put a load on it, so in an unhooked, i.e. no truck, no shore power scenario, your battery voltage might drop a little when the inverter is turned on. They do consume a lot of power. Hope this helps.

DesertRat · 11-10-2014, 07:42 PM

Quote:

Originally Posted by mcpaul

I've been reading for quite a while, first post, probably not my last. I know this has been gone over many times but I think my situation is a little different. I have a '14 3200 with a '15 F350 6.7. The dealer installed a 3000w inverter & 4 six volt batteries for me. I have +/- 14v at the output of my plug at my truck when running but it is not making it to the batteries in the 5th wheel. Meter reads +/- 12.6 or so at the batteries when hooked up. Just want to keep my batteries topped off while running. Any ideas where to start looking??

The place to look is the charge wire that runs from the rv plug & should go directly to the + post on your rv battery. Check the connection in the rv plug first.

mcpaul · 11-11-2014, 01:32 AM

Quote:

Originally Posted by DesertRat

The place to look is the charge wire that runs from the rv plug & should go directly to the + post on your rv battery. Check the connection in the rv plug first.

Thanks for all the input, I believe this is the answer. I talked to Voltage & my dealer today & both agreed the line from the plug should go directly to the batteries. That's what I didn't know. Seemed like it should be much more complicated than that!! The dealer said there should be an in-line fuse but no one said anything about a relay or anything else to prevent back-feeding the truck when the ignition is off. The plug from the TV has no power when the ignition is off so I suppose it might have something built-in to prevent that? There is no smaller gauge wire going directly to the batteries so they must have forgot that detail when installing the inverter & batteries. Now I just have to track down that wire. Should be easy right??

**wahoonc** · 11-11-2014, 10:55 AM

The relay is on the truck end. It is to keep the trailer battery(s) from draining the tow vehicle battery when the ignition/engine is off.

As long as the charge line is dead when the truck is off and hot when it is running you are good to go.

Aaron

mcpaul · 11-13-2014, 04:19 AM

Kinda interestering findings in tracing the 12v lead from TV to trailer. I'm not sure if this is how its supposed to be or if it's the same on all the trailers. Before I tried tracing the wire all over the small world of my trailer I figured I'd try a continuitity test from the 12v lead at the plug to the cables already connected to my batteries. I disconnected one smaller wire (although still a large cable) & tested it, sure enough there was a direct connection. So with the cable disconnected I went into the trailer & checked the 12v systems (lights, pumps, refer, etc.)... nothing worked. So out of curiosity I reconnected the plug to my truck & started it. Everything in the trailer worked, with the cable disconnected from the battery still. Shut off the truck & nothing worked again. ALL the 12v systems were running off the 12v lead from the truck. Hope I explained that well enough. I started out trying to see if my batteries were being topped off while driving. At least I know that the systems are not draining the batteries & there is maybe something eventually making it to the batteries.

MartyG · 11-13-2014, 04:29 AM

ASSUMING SHORE POWER WAS OFF, then the wire you disconnected was the one that connected your trailer 12V system to the battery. It was, somehow, still connected to the trailer plug, and then when the tow vehicle was on, power was applied to your 12V system. If you were to reconnect that wire you disconnected, it should also charge the 12 V battery when the truck is running, and also with the truck not running or unplugged, your 12V items in the trailer should work. ALL STILL WITH NO SHORE POWER. If you connect shore power or turn the converter on, then you have 12V coming from different directions and you'll never be able to troubleshoot from one source or another. For the purpose of this discussion, keep your shore power off, and tell us how it works with your disconnected wire back together. Unless your batteries are dead, you should be able to work your 12 v stuff without shore power and without truck plug-in. If you can't do that, once reconnected, you've got battery problems.

mcpaul · 11-13-2014, 05:38 AM

Yes, shore power was off & yes it was the wire that connected to the entire 12v system & yes it all works fine when reconnected. My orignal intent was to make sure my batteries were being charged when driving. With 14v+ at the plug I expected close to that at the batteries. Now that I know it is powering the ENTIRE system 12.6 v back at the batteries makes more sense. I suppose there is a small trickle charge going on but at least I know the system is not draining while driving. Still not sure it is right as both Voltage & the dealer said it should be connected directly to the batteries, instead it is connected somewhere else & eventually makes it back to the batteries.

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