Charging Through the 7 Pin Cable

[vanderwielen]

Originally Posted by uncle_bob

Hi

The typical 7 pin is limited by a slow blow fuse at 30A. Your 15A diode will be long gone before that fuse gets into the act. Since it's not a fuse designed to protect a diode, you will need a diode rated to well over 30A to have any chance of it surviving. How much over depends a bit on how big a heatsink you put it on and maybe how big a fan there is on that heatsink. If you have a diode that is rated to drop 1V ( check that spec sheet !!! ) at full current. It will dump 30W at 30A. That's a lot of heat.

Why do we talk about 10A of charge current on the 7 pin? The battery only accepts current above a certain voltage. You can't hook a 12V battery to a 6V source and expect it to charge. The wiring drops voltage as the current goes up. In the typical case ( alternator at this, battery in that range ) you get 5 to 10 A.

... but ... hook up a near dead battery and you can get a *lot* more current. Flip on a load of some sort ( that power jack on the front of the trailer ....) and you get a pretty good current hit. Your poor diode needs to survive all that.

Bob

True Bob. I hear alot of work arounds that are more hassle and less of an integrated solution that a simple DC to DC converter.

[field & stream]

Originally Posted by vanderwielen

Battleborn is in conflict with their integrators, such as me, who can attest to the fact that you can absorb 100-150 watts via a Victron Orion DC to DC converter even with the factory wire. It is also not necessary to unplug your 7 pin with or without a DC to DC converter since most current tow vehicles have a qualifying circuit that only provide power to the charge wire while running...among other qualifiers.

I am a bit confused by your blanket statement that it is “not necessary to unplug your 7 pin”.

The reason you give is that “most current tow vehicles” have a circuit that provides protection. MOST! CURRENT! What about the current TV owners who don’t have that circuit, and how would they know? What about all of us who do not own “current” (whatever that means) tow vehicles?

Seems to me that any blanket advice would be to unplug.

[vanderwielen]

Originally Posted by field & stream

I am a bit confused by your blanket statement that it is “not necessary to unplug your 7 pin”.

The reason you give is that “most current tow vehicles” have a circuit that provides protection. MOST! CURRENT! What about the current TV owners who don’t have that circuit, and how would they know? What about all of us who do not own “current” (whatever that means) tow vehicles?

Seems to me that any blanket advice would be to unplug.

Put a voltmeter on the charge pin with your vehicle off. If no voltage is present, you have a qualifying circuit. With a DC to DC Orion charger, any vehicle is ok to use and it will not 'drain' your TV. Simple. 5 minutes.

[LowOnCash]

I found that different type of trucks have different charging protocols, best bet is to clamp an Amp probe over correct wire and check it with the battery slightly discharded at idle and high idle.


Mike

[field & stream]

Originally Posted by vanderwielen

Put a voltmeter on the charge pin with your vehicle off. If no voltage is present, you have a qualifying circuit. With a DC to DC Orion charger, any vehicle is ok to use and it will not 'drain' your TV. Simple. 5 minutes.

OK, so the blanket advice should be: unless you have performed and passed the above test, you should unplug your 7 pin.

[Boxite]

I have a heavy 28V-80A rectifier/power-supply (Collins) used to feed an avionics repair bench. I rescued it from the airport dumpster when the Austin Mueller airport closed. (Does that make me a “dumpster-diver”..??)
It consists of a 120VAC - 28 VAC transformer (weighs almost 90 lbs.) and a single diode… the diode is the size of a D-cell flashlight battery.

Doesn’t get any simpler than that.

However, if you leave it hooked up to your Beechcraft Baron charging batteries while you drink beer with your buddies …. when you return to the plane you’ll have a distinct smell of sulfur and acid will be dripping onto the concrete floor of the hangar thru the battery-box overflow tubes and you’ll be “out” a pair of $280 ea. batteries. (and 4-lb box of baking-soda)
Of course, that’s somewhat better than hearing fire-engine sirens and returning to a burnt-out hangar and airplane and glares from volunteer firemen.

The concrete floor will have a rough-puddle reminder of your forgetful-ness 20 years later.

I.E. supplying power to batteries requires regulation. Get a DC-to-DC converter.

[uncle_bob]

Originally Posted by vanderwielen

Put a voltmeter on the charge pin with your vehicle off. If no voltage is present, you have a qualifying circuit. With a DC to DC Orion charger, any vehicle is ok to use and it will not 'drain' your TV. Simple. 5 minutes.

Hi

That's a start, but it's not really a full test. There's going to be *something* hooked to that pin. How happy is it when it sees 14.6 V coming back on the charge wire? There's really no way to know.

The risk here isn't really frying the alternator. The fuse on the charge wire will take care of that. The gotcha is some very expensive solid state "module" somewhere in the truck. It sees this or that ( 14.6V, current ... ) and dies. Should it be sensitive to this sort of thing? probably not. Folks have killed them this way.

Bob

[LowOnCash]

Hello Guys - It's important to note the output you receive to the trailer is determined solely by the needs of the tow vehicle as well as engine rpm. If the A/C, radio and lights are on, the alternator first feeds these requirements, plus the battery voltage is reduced providing less voltage and amperage to secondary loads such as your Airstream. Most newer vehicles now have smart alternators which limit secondary loads such as for charging lithium batteries in RV's.

Finally, heavy loading of the alternator can also lead to heat-related failures such as windings or bearing failures. You'll want to protect your tow vehicle especially now when there is little to no service nor parts.

If you plan on charging lithium batteries or large banks of AGM, you should consider separate running fused cables direct to the battery which protects the alternator.

You should consider the use of a Victron DC to DC charger module which limits draw to 30 amps max, protecting the alternator. Another advantage of the Victron module is you get to control the charging and voltages as well as when its active Bluetooth right from your phone. This way once the engine is off there is no more draw from the battery. This way when you get ready to leave in the morning, your truck battery is happy and your on your way to your next destination.

Regards - Mike

[Ndcctrucks]

Just to add to the noise:

An automotive alternator’s voltage output is regulated, in part, by outside temperature. The warmer it is, the lower the voltage and the colder it is, the higher.

32 degrees F will see about 14.6 volts, while 100 degrees F will see about 13.4 volts.

I agree that charging lithiums off of the 7-pin is unlikely to give satisfactory results.

And yes, a diode WILL prevent backward-flowing current and voltage.

[pfm41]

Originally Posted by uncle_bob

Hi

That's a start, but it's not really a full test. There's going to be *something* hooked to that pin. How happy is it when it sees 14.6 V coming back on the charge wire? There's really no way to know.

The risk here isn't really frying the alternator. The fuse on the charge wire will take care of that. The gotcha is some very expensive solid state "module" somewhere in the truck. It sees this or that ( 14.6V, current ... ) and dies. Should it be sensitive to this sort of thing? probably not. Folks have killed them this way.

Bob

This is what I consider of prime importance. I do want to have some charging ability but, like Bob says, who knows what the feedback will be tickling. I did take the covers of the battery box and such and found that the logical place to mount the DC-DC converter is stuffed full so that will need some creativity. Looks like I will use the 20A Renogy so I can limit it to 10amp if I want and use only the original 7 pin wiring. There will be a second 100AH Battleborn installed before the Alaska trip. Thanks for all the insight.

[uncle_bob]

Originally Posted by pfm41

This is what I consider of prime importance. I do want to have some charging ability but, like Bob says, who knows what the feedback will be tickling. I did take the covers of the battery box and such and found that the logical place to mount the DC-DC converter is stuffed full so that will need some creativity. Looks like I will use the 20A Renogy so I can limit it to 10amp if I want and use only the original 7 pin wiring. There will be a second 100AH Battleborn installed before the Alaska trip. Thanks for all the insight.

Hi

The 7 pin cable comes into the inside of the trailer. It connects to the DC bus ( along with the thermal breakers) that is buried up there somewhere. The logical place for the DC is in that same area. Even the devices that look like they are sealed up have connections that are just hanging out in "the environment". The muck and whatever from the road is going to be a problem if you mount things outdoors.

Bob

[CandK]

For those of you who have intercepted the 7-pin power wire: How did you wire the two neutrals - input and output - of the DC-DC charger? Per the schematic, the 7-pin ground is connected to the neutral bus of the trailer. So if I connect the input side of the charger AND the output side to the same bus, seems I will be ok. Do you all agree?

[richard5933]

Originally Posted by CandK

For those of you who have intercepted the 7-pin power wire: How did you wire the two neutrals - input and output - of the DC-DC charger? Per the schematic, the 7-pin ground is connected to the neutral bus of the trailer. So if I connect the input side of the charger AND the output side to the same bus, seems I will be ok. Do you all agree?

There is no need to keep the two negative connections isolated. Some of the DC-to-DC chargers have the capability to do this, but in most Airstream situations they can both ben connected to a common negative, assuming that the 7-wire harness is properly connected to the negative bus in the trailer.

For clarity, the two conductors in a DC circuit are the positive and negative, not neutral. It's AC circuits that have a neutral, since AC circuits don't have a negative and positive (they keep alternating, hence the 'alternating' current).

[Vagabond62]

Originally Posted by ROBERT CROSS

You won't charge any significant amount charging thru the 7-pin while driving.

POI...We do charge two Zamp 160w panels thru the 7-pin.

Bob
🇺🇸

What adapater(s) do you use to attach your panels to the 7-pin connector?
Thanks!

[Aironius]

Not familiar with the Nissan, but my 2013 Expedition has the factory towing option pkg which includes a trailer relay. This connects the TT battery directly to the TV charging system while the TV is running and disconnects the TT when the TV is not running, so no need for a DC / DC converter and full charging amperage available. You should consult your owners' manual or a shop manual and find out if you need anything beyond what you already have. If no relay on the Nissan, you can still just unplug the TT connector while stopped.

[uncle_bob]

Originally Posted by Aironius

Not familiar with the Nissan, but my 2013 Expedition has the factory towing option pkg which includes a trailer relay. This connects the TT battery directly to the TV charging system while the TV is running and disconnects the TT when the TV is not running, so no need for a DC / DC converter and full charging amperage available. You should consult your owners' manual or a shop manual and find out if you need anything beyond what you already have. If no relay on the Nissan, you can still just unplug the TT connector while stopped.

Hi

Pretty much all modern TV's work that way. The reason you need a DC/DC is because of the voltage drop in the cables combined with the voltage you need to deliver to actually charge the batteries. This is problematic with lead acid. It is really crazy with LiFePO4's. The difference can be an average of <5A of charge going up to > 20A.

Bob