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Old 11-13-2023, 02:01 PM   #1
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Smile Can I put the DC/DC charger in my truck instead?

I've not seen much discussion on putting the DC/DC charger within the truck vs the trailer. Any reason this would not work or is a bad idea?

I'm old and not a contortionist, which seems to be the pre-requisite for electronic upgrades in Airstream trailers. Like things simple and easy to get too. I have a cab on top of the truck and thinking of mounting it somewhere inside and running a pig tail to the bumper side that can mate with the AS.

This would also allow me to charge something besides my AS. I don't have a need as of yet, but gives me the option.

Mike
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Old 11-13-2023, 02:41 PM   #2
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You can, but you will still have to be a bit of a contortionist. You'll have to pull the charge line from the 7 pin. Run a new ground wire to the charger. Run a new charge wire to the 7 pin.
Not nearly as clean as doing it inside the trailer.
I assume you're limiting yourself to an 18 amp charger.
If you are running a larger converter, you'll have to run larger wiring from the TV batt all the way back to the trailer batts (buss). In that case put it where you want, keeping in mind voltage drop from.convertr to trailer.
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Old 11-13-2023, 02:42 PM   #3
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Originally Posted by Mr Wonderful View Post
I've not seen much discussion on putting the DC/DC charger within the truck vs the trailer. Any reason this would not work or is a bad idea?

I'm old and not a contortionist, which seems to be the pre-requisite for electronic upgrades in Airstream trailers. Like things simple and easy to get too. I have a cab on top of the truck and thinking of mounting it somewhere inside and running a pig tail to the bumper side that can mate with the AS.

This would also allow me to charge something besides my AS. I don't have a need as of yet, but gives me the option.

Mike
Victron says to locate it as close to the battery bank being charged as possible, allowing for ventilation, protection from the elements and not on top of any batteries. Voltage drop due to wire resistance might play a role here resulting in the batteries not receiving a high enough voltage to top off.

I look forward to comments from others on this.
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Old 11-13-2023, 03:06 PM   #4
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It will work better if put in the trailer.
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Old 11-13-2023, 03:45 PM   #5
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How much of a drop?

How much of a drop in voltage are we talking about, and is it still charging the battery(ies) as long as it's in operation?


TR Anderson
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Old 11-13-2023, 03:56 PM   #6
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How much of a drop in voltage are we talking about, and is it still charging the battery(ies) as long as it's in operation?


TR Anderson
Great Lakes
We'd have to know wire gauge and length in order to figure out voltage drop. It will still charge as long as the charging voltage is greater than the battery voltage. From what I have learned a LiFePO4 will need somewhere North of 14.2 volts to fully charge. So if the alternator is putting out the standard 14.4 that doesn't leave a lot of room to spare for voltage drop. Also at lower voltages it may take longer to charge.

Someone will correct me if I'm wrong but the voltage drop along the charge wire from the alternator will experience voltage drop in all cases, but the DC-DC charger will compensate for this and boost voltage output but if the DC-DC is too far away from the battery the boosted voltage will drop by the time it reaches the battery so in a sense putting the DC-DC at at the supply end seems like defeating it's purpose and you may as well not even install it at all.

That's my thought anyway, I too am still in the LiFePO4 learning stages.
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Old 11-13-2023, 04:25 PM   #7
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Originally Posted by ITSNO60 View Post
Someone will correct me if I'm wrong but the voltage drop along the charge wire from the alternator will experience voltage drop in all cases, but the DC-DC charger will compensate for this and boost voltage output but if the DC-DC is too far away from the battery the boosted voltage will drop by the time it reaches the battery so in a sense putting the DC-DC at at the supply end seems like defeating it's purpose and you may as well not even install it at all.

That's my thought anyway, I too am still in the LiFePO4 learning stages.
I agree. The purpose of a DC to DC charger is adjust the output charge voltage according to a particular battery profile. This assumes a proper gauge charge wire with a short run to the batteries. If your charge wire to the batteries is long and or wire gauge is insufficient, resistant will be high enough to drop the charge voltage, preventing your batteries from being fully charged.
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Old 11-13-2023, 09:33 PM   #8
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We'd have to know wire gauge and length in order to figure out voltage drop.
Also need amps, more amps equals more drop on same wire, gauge and length.
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Old 11-13-2023, 09:57 PM   #9
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This kind of question always reminds me of why we use AC to power our homes and not DC. As Tesla and Edison battled things out years ago, the fact that DC power doesn't travel well over long distances became an issue.

Same thing here - the DC-to-DC charger should be as close to the batteries as possible since it doesn't travel well over long distances. The amazing feature of a DC-to-DC charger is that it can take in whatever your tow vehicle throws at it and still deliver the proper voltage to the batteries. But the further you move it away from the batteries the less it's able to do its job. You could upsize the wiring between the DC-to-DC and the batteries to compensate for this, but then you're back to doing the contortionist thing.
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Old 11-14-2023, 07:18 AM   #10
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Also need amps, more amps equals more drop on same wire, gauge and length.
That's where it gets complicated, the Li will draw heavy amps during bulk charging which will increase voltage drop significantly but as it nears the end of the charge cycle the amps will drop to nothing and the voltage will go high, so it's kind of a moving target and how much voltage is needed at any time during the charge is yet another calculation. The length of time to fully charge is another variable dependent on the combination of available amps and volts.

There are folks who can figure all that out for a given scenario but I'm not one of them.
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Old 11-14-2023, 08:02 AM   #11
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Originally Posted by ITSNO60 View Post
That's where it gets complicated, the Li will draw heavy amps during bulk charging which will increase voltage drop significantly but as it nears the end of the charge cycle the amps will drop to nothing and the voltage will go high, so it's kind of a moving target and how much voltage is needed at any time during the charge is yet another calculation. The length of time to fully charge is another variable dependent on the combination of available amps and volts.

There are folks who can figure all that out for a given scenario but I'm not one of them.
This is my understanding as well. And most LFP batteries don't like to stay up over 14V for very long, which is why most chargers have a timer for that cell balancing phase, after which they drop back to a float voltage in the 13.6 range. Your charger will be able to time this more accurately if it knows the actual battery voltage, not the voltage several feet away.

Some of the Victron products have VE.Smart networking to help manage this--they can use the voltage measured at the battery terminals by the shunt, sent to the charger via Bluetooth. But I don't think their DC-DC chargers do this (yet?). They have a new Smart Buck Boost coming out that I'm hoping may get that feature. https://www.airforums.com/forums/f37...er-248200.html.
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Old 11-14-2023, 10:08 AM   #12
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Hi

Simple answer:

You put in the DC/DC to take care of few things:

1) The wire drop due to the current

2) The somewhat variable output of the TV alternator

3) The voltage needs of your LiFePO4 batteries

Of the three, number 1 is the biggest issue. Unless you run very heavy wire back to the bumper *and* in to the trailer it will still be a problem. Putting in all that wire through all those places is not going to be easy.

Compared to the rest of the "fun" switching to a lithium setup, the DC/DC part was by far the easiest thing I did.

Bob
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Old 11-14-2023, 10:11 AM   #13
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So, I have actually done this, partially. '06 Ram 2500 Cummins, '68 Overlander, '92 Hallmark truck camper, truck topper. Put the Victron Orion 18 in the truck bed where it is 3 feet from the truck camper battery (a regular FLA). Ran double 6 AWG from truck battery to charger and then to battery. I've done several good trips and it's worked great. Plan is to be able to extend to the trailer when needed, that hasn't happened yet but is a big reason I went with the 6 AWG. I suppose I could move the Orion to the trailer or just put a second one in the trailer and by-pass the one in the truck. I've taken it in and out a couple times and takes 5 minutes.
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Old 11-14-2023, 10:19 AM   #14
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Thinking about this a bit more, could make a big difference if the batteries are on the tongue or like mine, 15 ft. further back mid-trailer.
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Old 11-14-2023, 10:24 AM   #15
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What about putting an inverter in truck, then running an AC cord to a modern battery charger in trailer?
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Old 11-14-2023, 11:19 AM   #16
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You mentioned that you're not so young and not a contortionist, thus making installing the DC-to-DC in the trailer difficult.

What about hiring someone younger and more able to contort to do the install?
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Old 11-14-2023, 12:17 PM   #17
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Quote:
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You mentioned that you're not so young and not a contortionist, thus making installing the DC-to-DC in the trailer difficult.

What about hiring someone younger and more able to contort to do the install?
Haha yes, its only $$$. I will likely find a place on the trailer.

Some additional info. I have a 2021 Globetrotter. 2 100a batteries in the battery box. The thought was to but the DC/DC converter right inside the tailgate mounted on the side. Im not envisioning to much of difference in cable length (maybe a few feet)

Anyway, I appreciate the feedback. Will likely find a spot on the AS in the storage area up front.

Thank all!
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Old 11-14-2023, 04:07 PM   #18
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What about putting an inverter in truck, then running an AC cord to a modern battery charger in trailer?
That would be very inefficient. You'd be paying the energy conversion tax 2X - once from DC to AC and then from AC back to DC
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Old 11-14-2023, 04:23 PM   #19
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Location of DC-DC charger

Mr Wonderful, I can share where I put my DC-DC charger in our 27 GT FBT. I have a Renogy 40A unit and put it under the curb side bed, just above the DC junction box.

Ive got a Battle Born GC3 inside the street side compartment extending into the front compartment. I did run a pair of 4 AWG cables under the truck to the bumper and used Anderson 150A connectors to the trailer.

I think youre right about the distance being close to the same if you installed the DC-DC charger in the truck bed vs. inside the trailer. That said, inside the trailer the charger is protected and not that hard to get to.

By the way, the DC-DC charger worked great and allowed us to run the 3-way fridge on 12V instead of propane when on the road. Well worth the effort!

Hope that helps!
-Jeff
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Old 11-14-2023, 06:32 PM   #20
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Love ya Jeff! But I get fixated on that upside down mount. Lol
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