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Old 05-31-2017, 11:10 AM   #1
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Does TV charge TT?

Stupid question time. We’re first timers… Just picked up our 2018 Rockwood 2703WS and 2017 RAM 2500 CTD. A family emergency is requiring us to employ it much sooner than I’m ready.

So -- will be doing some boondocking over next week. Question is – will the RAM recharge the 2 trailer batteries while hooked up and towing down the highway? Or will only “RV park” shore power recharge the trailer batteries? RAM has optional dual upgraded alternators and trailer has optional 2nd battery (12v deep cycle).

Will travel about 1000 miles over the course of 3 days, stay 3-4 days (next to a house - no RV style 50 amp plug in – but a 5KW generator). Then travel about 1000 miles back over the course of 3 days. Not part of my newbie RV training plan, but it’s going to happen.

Understand leave the 2 ACs off, but can run maxx air fans for a while. Propane for frig. Use a couple LED lights sparingly.

So will the truck recharge the trailer batteries while traveling? Or will the trailer be electrically dead within a couple days and remain that way the whole trip?

Bob
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Old 05-31-2017, 11:17 AM   #2
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If properly installed, the 7-pin cable from the TV to the TT will provide battery charge. Now, it is NOT a high-current thing but it will do the trick over those 1,000 miles. Your dealer / installer may have put a fuse in the line to the +12 terminal, so might be good to make sure that is checked and you have a couple spares.
We absolutely do use this method to top off our battery.
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Old 05-31-2017, 11:21 AM   #3
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As said above, it will but it's not going to be a fast charge. Also as eluded to above, make sure that it's working correctly before you leave.
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Old 05-31-2017, 11:53 AM   #4
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Good article on why a generator and dedicated battery charger is needed to boondock.

Alternators make lousy Deep Cycle Battery chargers.
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Old 06-01-2017, 06:17 PM   #5
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I just posted this replay to a similar question. My answer is evern more appropriate here:

I'd like to describe what I've done to keep my batteries fully charged while traveling. We have a 31' bumper pull Rockwood. We have 2 6v Trojan T-105 batteries and a whole house inverter that keeps our outlets at 110v so when not hooked to shore power we can run everything except the A/C.

When we travel we usually spend the nights at Walmart and often go for a week without shore power. At first we would always run out of battery power after the 2nd or 3rd night. To solve that I ran a 2 gauge hot wire from my battery to a solenoid (keeps the voltage from traveling backward from the trailer to the truck), solenoid to a 100 amp breaker, from the breaker to the back of the truck. Ran a 4 gauge ground from under the truck to the back to join the hot wire in a heavy duty connector that connects to 4 gauge cables that run to my trailer batteries. Now when we travel our batteries are always 100% charged when we pull in for the night.

In our experience that small gauge wire in the 7 pin connector cannot handle the serious amperage needed to charge heavy duty battery systems.
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Old 06-01-2017, 07:32 PM   #6
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Check your manual and verify the output. My F150 came with a relay you had to install, my Silverado says the wire is not connected from the factory. So it should have the capability but you may have steps to enable it.
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Old 06-01-2017, 08:21 PM   #7
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It should. But check b 4 you go to make sure it's charging by unhooking from shore power. Plug in TT to ram check battery voltage, then start TV , voltage should increase 2-4/10s.
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Old 06-01-2017, 09:37 PM   #8
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Quote:
Originally Posted by OldBob View Post
I just posted this replay to a similar question. My answer is evern more appropriate here:

I'd like to describe what I've done to keep my batteries fully charged while traveling. We have a 31' bumper pull Rockwood. We have 2 6v Trojan T-105 batteries and a whole house inverter that keeps our outlets at 110v so when not hooked to shore power we can run everything except the A/C.

When we travel we usually spend the nights at Walmart and often go for a week without shore power. At first we would always run out of battery power after the 2nd or 3rd night. To solve that I ran a 2 gauge hot wire from my battery to a solenoid (keeps the voltage from traveling backward from the trailer to the truck), solenoid to a 100 amp breaker, from the breaker to the back of the truck. Ran a 4 gauge ground from under the truck to the back to join the hot wire in a heavy duty connector that connects to 4 gauge cables that run to my trailer batteries. Now when we travel our batteries are always 100% charged when we pull in for the night.

In our experience that small gauge wire in the 7 pin connector cannot handle the serious amperage needed to charge heavy duty battery systems.
I don't understand how doing this negates the voltage regulated current output of the alternator.

How are you determining "100%" charged?

Voltage of 12.7+ volts (4 lights on the display) could just mean that there is residual surface charge on the plates from the drive. You would need to measure the voltage after a load was placed on the battery(s) to dissipate the surface charge and then measure the voltage or wait 24 hours with no load for the batteries to equalize. 3 lights on the display could mean anything from 50% of capacity to 100% with no way to tell the actual state of charge.

Here is the voltage range of the "4 light system" (the voltages are when that light "goes out" and what the stabilized voltages mean regards to capacity.
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Old 06-01-2017, 10:09 PM   #9
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Sorry Herk, by saying 100% I only meant that it seems like 100% compared to when I didn't have my charging setup. I no longer take a look at those idiot lights as I've come to distrust them over the years. When I only relied on the 7 pin connector to charge the batteries I would have frequent alarms from my inverter and I would have to cut down on our electrical usage. Since installing this system we never get complaints from the inverter no matter how much power we use. So I am assuming from that...the batteries are fully charging while driving. We only drive between 300 and 350 per day so we are thankful that this setup has worked for us. We carry a 2000 watt Yamaha generator for when we'll be boondocking for more than a few days.
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Old 06-02-2017, 07:57 PM   #10
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Originally Posted by Herk7769 View Post
Good article on why a generator and dedicated battery charger is needed to boondock.

Alternators make lousy Deep Cycle Battery chargers.
In reality the linked article is pretty inaccurate.

There are no constant-current chargers, nor do any chargers cut back or adjust the current. This applies to car/truck alternators, converters, and stand-alone chargers.

Most vehicle alternator regulators (in the past 10+ years) are 2 stage alternators to better protect your battery. They put out a charge voltage in the low 14s to rapidly recharge the battery, than cut back the charge voltage to around 13.6 - 13.8 volts as the battery voltage builds. This avoids "boiling" the battery on a long day of driving. The charge current is determined by the battery's internal resistance, which increases with the battery charge (decreasing the charge current).

Most RVs (past 10+ years) come with 3 stage converters. They have a 14.4V boost or bulk mode, a 13.6-13.8V normal mode, and a 13.2V trickle mode. The bulk mode is for faster charging when the battery is low (50-70% state of charge). Trickle mode is entered after a couple of days in normal mode to protect your battery from "boiling" away the water.

There are 2 things that limit how much charging the TV alternator can do.

First is voltage drop from the alternator to the RV battery from the wiring. If the alternator is putting out 14.4V, but the RV battery only sees 13.6V, it's not going to charge very fast. If your RV fridge is running on DC, and the RV running lights are on, the 10+ amp draw can make these wiring voltage drops very real.

The second limit on RV battery charging by the TV alternator is the TV battery. If the TV battery is not as discharged as the RV battery, the alternator regulator will see the higher TV battery voltage, and cut back to the lower charging voltage. When combined with the voltage drops in the wiring, the RV battery may only be getting a trickle charge.

I have found that turning our fridge off while towing for the last 2 hours before we arrive at the site makes all the difference in whether or not the RV battery is fully charged when we arrive.

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Old 06-09-2017, 05:40 AM   #11
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I'm not too technical on stuff like this but it works for us. (Ram with 2 batteries and high output alternator). My simple answer is to get a tester and see if you have power at the TV pin at the 1 o'clock position. If you do you're good to go.
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Old 06-16-2017, 12:04 PM   #12
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Back from our emergency trip.
Pulling a brand new trailer with a brand new truck 1000 miles up the Appalachian Mountains wasn’t my idea of a good first trip.
Trailer arrived at destination fully charged (4 of 4 lights on panel).
After using a couple lights & fans sparingly over the course of 1.5 weeks, I basically depleted the 2 batteries (panel showed 1 of 4 lights).
Trailer arrived back home fully charged (4 of 4 lights on panel).
Thanks for all the feedback.
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Old 06-16-2017, 01:53 PM   #13
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I am sorry to disappoint you, but 4 lights does not mean the battery is fully charged. It means a charging voltage is being applied. Or that the charging voltage was just removed - there is a surface charge in the battery which takes a few hours to dissipate.

The lights are a pitiful excuse for a voltmeter. The lights measure system voltage, not battery voltage. Since my A-frame does not have a panel with the lights, I don't what voltages they represent. A fully charged battery, if measured 24 hours after being charged, will read 12.7V. Your converter, while camping, normally keeps the 12V system at 13.7V to charge the battery. If the battery is low, the converter may push system voltage to 14.4V. If the battery is full, the converter should back off to 13.2 volts (trickle charge).

Your vehicle alternator also normally outputs about 13.7V to recharge the vehicle battery. It may go higher if the regulator senses low battery voltage. These voltages may be lower at the camper because of voltage drop in the wiring. Voltage drop are especially likely if you are running the fridge on DC while towing. Running lights on the camper add to the load on the ground wire when turned on.

hope this helps
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Old 06-16-2017, 02:02 PM   #14
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New GM PUs have all wiring connected to the rear trailer plug. Also, for full voltage to the trailer, drive in either Tow Haul Mode or with your headlamps On. In those two conditions the computer does not cut output to the trailer power wire.
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Old 06-21-2017, 01:28 PM   #15
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Lots of theoretical info above, let's add some empirical data:
Camped two nights, barely 3 lights on the panel (dropped to two when pulling some load) when leaving. Drove 2.5 hrs, 24 hrs later the battery showed 12.60V which according to the table posted earlier is a charged battery.

Obviously the tow vehicle needs to supply some current on the 7 pin connecter, in my case up to 20A which is plenty for a single battery.
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Old 06-22-2017, 01:16 PM   #16
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Thanks to all for the feedback.

Going on another trip this weekend. Will experiment some more.

Will start by measuring both trailer batteries before I hook up.
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Old 06-26-2017, 06:46 AM   #17
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Pick up a DC clamp meter and measure it.
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

I ran the battery's down to 80% and found the truck is putting a good 20 amps to the battery's.
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Old 06-26-2017, 07:19 AM   #18
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Even if your alternator is in charging mode full time, most trucks have 16 or 18 gauge wire going to the trailer. There are also numerous connections along the way. With each foot of cable, and with each connection, you loose voltage. The alternator also does not stay in charge mode all the time. These are the biggest reason a tow vehicle does not make for a great TT battery charger. Just for the wires/connections, figure 20 feet of cable (it doesn't just go straight to the back bumper) and at least 6 connections between the battery/alternator and your battery, you are lucky to even get 12v to the back bumper.
Voltage Drop Calculator

If your truck can do it, you obviously don't have the standard cables to the back. Most people's setup can't do it, so just trying to let people know not to rely on this method!
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Old 06-30-2017, 09:07 AM   #19
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Thanks for continued feedback.
Will look at measuring it.
TV has the Cummins with upgraded dual alternators (part of snow chief package). Assume that helps.
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Old 06-30-2017, 09:20 AM   #20
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Quote:
Originally Posted by Bob.n.Denise View Post
Thanks for continued feedback.
Will look at measuring it.
TV has the Cummins with upgraded dual alternators (part of snow chief package). Assume that helps.
Bob
Yes it should. I always upgrade my charging system when I buy new tv. Later RJD
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