Do I need a DC-DC charger for towing?

[Zwy]

Thanks for this info, do you have any links to more information about isolators and solenoids?

Wouldn't it be more wise to install a DC to DC charger that would perform both functions plus would allow the battery to be charged to full?

Think of it this way, you're using an alternator that is meant to maintain (not charge) a LA battery. It really isn't meant to charge all the time. What you can do is pull some watts off the alternator and use it to charge another battery. But you really want isolation between the 2 batteries when the alternator isn't running so when you go to start the tow vehicle to leave, it starts.

As for the solenoid, you get one like this, no matter what you buy, make certain it is continuous duty and not a starter solenoid. https://www.etrailer.com/Accessorie...Tf94DhDNl_pe6cMXsZW6af_9yoJc55OBoCIbAQAvD_BwE

I would add a manual toggle switch to it. I have wired my work trucks that pull a trailer this way for years, but I have a LA battery in those. And this was done before DC to DC chargers really came around.

For a little more money, you could move to this or one higher amp rated. https://www.amazon.com/Victron-Ener...SWYFPDGACBGDHPEM5&qid=1619526293&sr=8-20&th=1

It's isolated and it would allow you to fully charge the auxiliary battery. Output voltage is set by a screw on the back side. This is not the Smart version and the price reflects it. But really, it solves the inherent problems of just running a wire back to a auxiliary battery.

 

[YBen]

Wouldn't it be more wise to install a DC to DC charger that would perform both functions plus would allow the battery to be charged to full?

Think of it this way, you're using an alternator that is meant to maintain (not charge) a LA battery. It really isn't meant to charge all the time. What you can do is pull some watts off the alternator and use it to charge another battery. But you really want isolation between the 2 batteries when the alternator isn't running so when you go to start the tow vehicle to leave, it starts.

As for the solenoid, you get one like this, no matter what you buy, make certain it is continuous duty and not a starter solenoid. https://www.etrailer.com/Accessories-and-Parts/Tow-Ready/TR118665.html?feed=npn&utm_source=google&utm_medium=cpc&utm_campaign=Google | Smart Shopping - Accessories and Parts - Prospecting&adgroupid=78005013485&campaignid=6886913949&creative=389615232711&device=c&devicemodel=&feeditemid=&keyword=&loc_interest_ms=&loc_physical_ms=9022938&matchtype=&network=u&placement=&position=&gclid=CjwKCAjw7J6EBhBDEiwA5UUM2pUOiJsabDknDkk2xowAr2Tf94DhDNl_pe6cMXsZW6af_9yoJc55OBoCIbAQAvD_BwE

I would add a manual toggle switch to it. I have wired my work trucks that pull a trailer this way for years, but I have a LA battery in those. And this was done before DC to DC chargers really came around.

For a little more money, you could move to this or one higher amp rated. https://www.amazon.com/Victron-Energy-Orion-Tr-Isolated-Converter/dp/B07L6H8VKL/ref=sr_1_20?dchild=1&keywords=dc+to+dc+battery+charger&pd_rd_r=9ffdf12a-e042-46ce-8c09-ab898daff7ec&pd_rd_w=6TYEN&pd_rd_wg=9w15F&pf_rd_p=4fa0e97a-13a4-491b-a127-133a554b4da3&pf_rd_r=06ZSWYFPDGACBGDHPEM5&qid=1619526293&sr=8-20&th=1

It's isolated and it would allow you to fully charge the auxiliary battery. Output voltage is set by a screw on the back side. This is not the Smart version and the price reflects it. But really, it solves the inherent problems of just running a wire back to a auxiliary battery.

Thank you for all that information!

 

[YBen]

Towed the camper for 3 hours each way last weekend, battery was 99% full on the way there. Max amp I saw being pulled through the shunt was 2. On the way back battery was about 85% charged, max amps I saw as about 8.
Just my experience.

 

[Jasgeer]

I tow with a Mazda CX-9, 30amp fused directly from the battery.

I am not really worried about charging the battery as much as not burning out the alternator.

I use a 20 Amp Renogy DC - DC Charger and it does an excellent job. They run approx $100 and can be used to charge from the converter or from the trailer. The Lithium batteries may not properly charge from the converter.

 

[bshackcreative]

Will it hurt anything if I have a 12/12 18amp dc-dc charger installed if the trailer wiring will only support a max of 10 amp from the 7pin? 10AWG trailer wiring. Safety issue? I find the Victron smart 12/12 dc dc chargers start at 18 amps. My truck is a Tundra with a 30amp fuse for the trailer 7pin power.

 

[rickst29]

Will it hurt anything if I have a 12/12 18amp dc-dc charger installed if the trailer wiring will only support a max of 10 amp from the 7pin? 10AWG trailer wiring. Safety issue? I find the Victron smart 12/12 dc dc chargers start at 18 amps. My truck is a Tundra with a 30amp fuse for the trailer 7pin power.

Your 10-AWG "trailer wiring" can support a maximum of 30A, so that's not a problem. The "Trailer Battery Charge" wire within the Tundra is possibly smaller than the fuse rating, but should be OK - maybe causing moderate Voltage Drop when carrying all 18 amps. (In my own 4Runner, Toyota installed a smaller gauge TBC wire at the factory, and I later upgraded it to 10-AWG.)

Your highest risk of "burnout", when pulling all 18A into the DC/DC charger, will occur within the Bargman power cord - and especially at it's wire ends, connecting into the 7-pin terminal for the Tundra connection. But your DC->DC charger will probably not need all 18 amps. The Victron "smart" unit may also allow for tuning to a smaller power limit.
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In my own configuration, I boost the alternator/engine "under-the-hood" voltage from its original value, typically around 13.5 Volts, up to 36.0 volts for the Bargman TBC wire connector. (This is under control of dashboard switch, which allows me to leave the switch "OFF" when towing other Trailers.) In my Trailer, I use a 30A MPPT Solar Charge Controller to receive the high-voltage TBC input, converting down to LFP battery charging Voltage in accordance with battery state-of-charge.

The resulting current load (within my Bargeman Power Cord, The 4Runner TBC wire, and the Trailer-internal "run" to the Solar Charge Controller) is only about 12 Amps maximum. It offers maximum output of almost 30A, rather than only 18A. But the installation under the 4Runner hood was complicated - involving the new dashboard controller switch, a high-power Relay on the path between the Battery and the "Booster" unit, plus BIG wires (AWG-8) and a 40A fuse for the leads into the Booster.
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The advantage of my personal scheme is a 3x reduction in current on the TBC wire. The disadvantages are higher cost and very complex installation. I think that your use of the Victron would likely be problem-free, although it creates significantly less maximum power.

 

[willo]

FYI The Victron DC-DC charger does not allow for current adjustment. It allows for intelligent operation - can tell if the engine is running, adjustable voltage parameters, etc. I'm using a Victron 12/24 DC-DC smart charger.