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Jtermini30 · 02-25-2017, 07:58 PM

I have a 2017 Classic and wanted to know if the batteries are charged while plugged into the 7 pin connector and towing? I used to tow my pickup truck behind My motor home and the truck batteries were charged.

Flht2k · 02-25-2017, 08:04 PM

It should, won't charge to full, but will maintain and improve current charge

Jtermini30 · 02-26-2017, 05:44 AM

Thank you.

Al and Missy · 02-26-2017, 07:43 AM

In my experience, the answer to the OP's question is "maybe". My F-150 had a relay to control power from the TV to the TT. I understand it was originally supplied in an envelope in the glove box but was not installed by the previous owners of my truck and lost. The purpose of the relay was to ensure that there was no drain on the truck's batteries unless the engine was running. In order to get power to charge the batteries while driving I had to buy and install the relay. The best bet is to use a meter of test light to check for the presence of 12V on the connector. Looking at the connector on the truck, with the index key up, there should be 12 volts on the pin at 1-o-clock, just to the right pin number handy, but with lights off, no brakes applied

My new (to me) Ram 2500 charged the batteries when I bought it and does not turn off the voltage supply when the engine is not running. As a result, if the 7-pin is left in when parked and the TT batteries are weak, it is possible to drain the truck batteries to support the trailer. I always unplug, even is just stopped for a night en-route.

Al

lsbrodsky · 02-26-2017, 08:15 AM

To echo those comments above, maybe. My Chevy came with the factory towing package but one wire had to be connected at the fuse block and a fuse had to be installed for the charging connection. The dealer neglected to do it, so I did. GM did not install a voltage relay so the connection was always hot, even with the ignition off. I bought a relay from Atkinson connects the charging current only when it sees alternator voltage.

Larry

greenflag · 02-26-2017, 12:24 PM

My GMC does not charge Airstream batteries while towing.
It is wired for it but the wire has to be connected into the under hood fuse box.
I never had it hooked up. Electricity is Greek to me.
The answer to your question is maybe.

us3rnam3 · 02-26-2017, 03:17 PM

If in good condition the battery charging system in your TV will put out 14.7 volts to keep your car's 12volt battery fully charged but you AS battery will not see this much voltage because of losses in the vehicle wiring.

Vich · 02-26-2017, 04:53 PM

If GMC or Chevy Tow vehicle see - http://www.airforums.com/forums/f37/...-149371-2.html post #23

Vic H

Pressdr · 02-27-2017, 06:35 AM

Good morning Airstreamers..
This is not an easy question to answer. There are many conditions that are specific to each and every tow vehicle. The above answers are all correct depending on what tow vehicle you are using, and how it is set up...

Chevy trucks of the 2008 and newer have a "Tow Haul" mode on the shift lever. This mode prevents the transmission from over shifting at low speeds, but also------Engages the circuit that will charge the battery on the tailer.

Check the manual for the tow vehicle. Look for items such as: location of fuse, charging wire circuit, and connections. If that does not work, a good trailer hitch installation company is well equipped with knowledge and reference material to get accurate information.

"Peace in our time"
pressdr

lsbrodsky · 02-27-2017, 07:23 AM

I think you are a bit misinformed. If the factory wiring is connected and fused, the charging wire on a 2012 GM truck is energized all of the time, ignition off or on. Of course if the engine is not running, it is at battery voltage. If the engine is running, it is at alternator voltage. My understand is that Tow-Haul assures that the alternator stays in high output, which will assure better charging of the trailer battery, although there still has to be some significant voltage drop with that wire size and the distance.
Larry

Jtermini30 · 04-12-2017, 05:37 PM

Update. My 2014 RAM Ecodiesel does charge the batteries while connected to the trailer. I appreciate all your responses.

LAWBC · 09-17-2019, 08:28 AM

Update on this thread and FYI for others that may consider this. We where boon docking in the pacific north west (cool and very wet ) for a extra unplanned night and by the next morning the house batteries where running below 70%(per my Go Power PWM 30).I thought to start up the truck as we where still hooked up and see if it would charge the house batteries, and voila ,,

it did start charging .
Now-feeling comfortable to continue using the furnace to warm up the trailer while running the truck but more importantly dry us out .

I have read where someone mentioned that having your umbilical plugged into the tow vehicle would deplete the battery but I have kept mine plugged in when hooked to and never had that problem. I just never knew that running my tow vehicle (2012 Dodge Ram) is like having a mini generator.

cru-in · 09-17-2019, 08:54 AM

I use a Dc to DC 3 stage battery charger to charge my AS batteries from the TV. It will work over a wide range of voltages (8 to 16 volts) from the TV and puts out the correct voltage for the AS batteries. Works very well.

https://www.renogy.com/12v-dc-to-dc-...ttery-charger/

cru-in · 09-17-2019, 09:43 AM

Quote:

Originally Posted by lsbrodsky

I think you are a bit misinformed. If the factory wiring is connected and fused, the charging wire on a 2012 GM truck is energized all of the time, ignition off or on. Of course if the engine is not running, it is at battery voltage. If the engine is running, it is at alternator voltage. My understand is that Tow-Haul assures that the alternator stays in high output, which will assure better charging of the trailer battery, although there still has to be some significant voltage drop with that wire size and the distance.
Larry

Concur....to overcome that voltage drop is one reason I installed a DC to DC charger between the TV and AS.

Plus I went to LI batteries and had incompatible charging voltages between the Lead Acid batteries on the TV and the LI Trailer Batteries. But that is a topic for another thread....don't want to hijack this one...

lsbrodsky · 09-17-2019, 10:59 AM

Quote:

Originally Posted by cru-in

I use a Dc to DC 3 stage battery charger to charge my AS batteries from the TV. It will work over a wide range of voltages (8 to 16 volts) from the TV and puts out the correct voltage for the AS batteries. Works very well.

https://www.renogy.com/12v-dc-to-dc-...ttery-charger/

Did you install this in the trailer? It doesn't seem to me that an install in the TV would be possible. First, you would still see the voltage drop over the long cable length back to the trailer, second, this does not seem to have a temperature rating suitable for under the TV hood in hot weather.

Larry

uncle_bob · 09-17-2019, 11:54 AM

Hi

Pretty much every *trailer* is hooked up to charge when it comes from the factory (it's Airstream so never say always ....). As wired, there is a lot of (likely number 10) wire between your trailer batteries and the truck alternator. The alternator will do it's thing based on the needs of the battery in the truck (it knows nothing about the trailer batteries). The amount of current you get from the truck probably isn't gong to be a whole lot (like < 10 A) as a result of all this.

What you have to do to get the truck to put power onto the "charge" wire on the 7 pin varies all over the place. Back in the mists of time, indeed all there was between the truck battery and the 7 pin was a fuse. Those days are long gone. Different makes / models / years of trucks have different "rituals" you go through to get them to charge the trailer battery. What works on a 2015 may not work at all on a 2018 truck of the same make / model.

One way to make sure you get the max current is to use jumper cables. Yes, that *is* a PIA and it involves more than a little gymnastics. It also is more than a little inconvenient. A DC/DC converter approach still leaves you with the whole "ritual" thing to get your truck to deliver voltage.

Back in the good old days a clamp amp meter would tell you that the truck was doing its thing. If your truck needs to be going more than 5 mph down the road ( who knows .... ) that probably isn't very practical. A bluetooth enabled battery monitor may be your only answer in that case.

Bob

lsbrodsky · 09-17-2019, 12:05 PM

Bob,

One edit to your comment is that, at least on GM, Tow-Haul prevents the alternator output from dropping down to float on the truck battery measured voltage. This is what I have observed over 6 years of towing. The voltage stays up at acceptable charging voltage the entire time the engine is running. Of course there is still the long run of #10 wire.
Larry

cru-in · 09-18-2019, 05:25 AM

As mentioned, this is a two fold issue
1) The AS has the hot wire on the 7 pin connector wired to the battery
2) Different TVs handle the hot wire differently.

So here is where the electrical engineer in me gets overly picky:
1) The TV Alternator system is set up to run a ton of electronics and recharge the starting battery of the tv.
2) it is not well optimized to charge a Deep Cycle Battery like in the AS
3) The voltage drop could lead to the TV not charging the AS battery at all.

For reasons 1) thru 3) above, if one really wants to optimize TV charging, a Dc to DC charger (that takes in 8 to 16 volts and provides appropriate charge voltage to the AS battery) is necessary. This is especially true with LI batteries. Due to the higher voltage of LI batteries, the AS LI batteries end up charging the TV's lead Acid battery. Lots of threads on here and rv.net discussing this. A few with data showing the effect using a bluetooth battery monitor.

cru-in · 09-18-2019, 05:31 AM

Quote:

Originally Posted by lsbrodsky

Did you install this in the trailer? It doesn't seem to me that an install in the TV would be possible. First, you would still see the voltage drop over the long cable length back to the trailer, second, this does not seem to have a temperature rating suitable for under the TV hood in hot weather.

Larry

Concur, installing in the TV makes no sense. it is not intended to go in the TV. Mine is placed in the TT near the battery bank.

It works very well. Accepting anywhere between 8 to 16 volts from the TV (hence dealing with the long wire runs and associated voltage drops). Provides the appropriate 3 stage charge curve for the AS batteries. IMHO, for $130, it is well worth it.

RVDreamer · 05-10-2021, 03:42 PM

Quote:

Originally Posted by cru-in

Concur, installing in the TV makes no sense. it is not intended to go in the TV. Mine is placed in the TT near the battery bank.

It works very well. Accepting anywhere between 8 to 16 volts from the TV (hence dealing with the long wire runs and associated voltage drops). Provides the appropriate 3 stage charge curve for the AS batteries. IMHO, for $130, it is well worth it.

I know this is an old thread but I am having lithium batteries installed in my airstream and I am still a bit confused by this.

Even if you direct wire a DC to DC charging system from the TV battery, how does this prevent the Airstream from drawing power thru the 7 pin connector?

Instead, it seems like you would have to draw the power from the 7 pin connector to run the DC to DC charging system so that it would then output the correct voltage to charge the lithium batteries. Otherwise you would not only be charging the batteries with DC to DC charger wired directly from the TV battery but in addition you would also be getting charge from the 7 pin connector. This seems like it would worsen the load on the TV alternator.

Am I missing something? or are you wiring the DC to DC charger only on the trailer side drawing power from the 7 pin connector. It sounded like most people are wiring directly to the TV battery.