Charging while towing - Dedicated 12V-12V Charger

[AzAv8r]

Renogy is now selling chargers for towing. Discovered this on their website a few days ago, and a day or two later saw a product announcement. Hmmm. This is what I need...

You might think that when you tow (with an aux wire in your harness) you are charging your house battery, but this rarely occurs (to near-full charge levels) because it takes excess voltage to force current into a battery, and you are likely dropping too much voltage across the wiring harness (between your TV and your trailer) to achieve significant charge.

The solution (discussed here before) is a step-up converter in the trailer, which converts the TV 12V to something like 14V to push current into the trailer battery. Such devices (as DC-DC voltage converters) are plentiful and relatively inexpensive on Amazon, but not optimized for the battery-charging task. They require some engineering both to install and get to work. I have an LiFePO4 battery (and am a particularly persnickety engineer), and the products I've found on Amazon (and other sources) basically become trickle chargers, or risk triggering my BMS to deactivate my battery.

Renogy now sells a device specific for the task. Not cheap, but designed for the task, and configurable for various battery technologies, including Li. I'll probably ditch my planned Amazon solution.

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

Now, if you want to go the engineer-it route, contact these folks:
https://www.powerstream.com/

[iggy3860]

G'day AvAz8r

I have found the attached link to be very useful when deciding if a DC-DC charger is required.

Thought I needed one to charge my pair of Optima D33M batteries under the tray of my vehicle until I read this article & worked out my alternator output. Also helped to talk to the old bloke that actually wrote the article at a 4x4 show

http://www.home12volt.com.au/uploads/2/ ... arging.pdf

I have a hard wired system through a selectable 100amp relay from my main battery to a pair of battery switches used to isolate each battery if required. Separate outputs from each battery are used to operate a number of services: 12v fridge, UHF CB, HF radio [VKS737], & a pair auxiliary outlets to operate a CPAP machine & other 12v appliances. Solar input is via a 50amp Anderson plug to the battery switches. Overall length from main to auxiliary batteries is about 15 feet, used 6 B&S cable.

I intend to build a teardrop sometime in the future & I expect that I will charge the teardrop batteries via a selectable relay / VSR from the main battery through an Anderson plug connector to battery switches. The alternator output & cable length should be able to handle this.

Regards

[John61CT]

This functionality has been bog-standard in off-grid mobile living for many years, both on land and marine use.

The generic name for the product category is DC-DC charger. The leading vendor worldwide are Sterling and CTEK, Australia also has Redarc and others.

Many people get convinced they need one when they really don't.

I doubt Renogy is bringing anything new or special to the table, more of a mass marketing company of existing cheap-Chinese gear,

but if so I look forward to learning more.

Adjustability in user-custom setpoints is an important feature to me, few offer that.

And total current capacity of course.

[John61CT]

More details I just posted in a boating forum

http://www.cruisersforum.com/forums/sho ... ?p=2867949

[featherliteCT1]

After reading the manual, I am impressed by the fact that the Renogy unit has adjustable charge parameters using dip switches and is temperature controlled. The 20amp unit at $130 is a great price.

[John61CT]

Yes, that's cheap if 20A is enough.

But no user custom setpoint option? I like to vary (.01 increments) between 13.15 and 13.95. . .

[featherliteCT1]

Yes, that's cheap if 20A is enough.

But no user custom setpoint option? I like to vary (.01 increments) between 13.15 and 13.95. . .

Are you aware of a unit that will do that level of fine tuning?

[John61CT]

In DC-DC? Sterling BB series (my reco), someone told me Enerdrive as well, and dozens of "hobby chargers" from the RC and e-bike worlds, I use a iCharger 4010-Duo myself for maintenance protocols while off grid.

Many if not most decent solar units, and shore power chargers with addon remotes.

But of course once you have a DCDC then the others are just raw input, don't need anything fancy.

[featherliteCT1]

I looked at the manual for the Sterling unit and see that it has the following charge parameters that can be chosen:

Picture1.png (118.41 KiB) Viewed 8764 times

Nice unit for $320.

[John61CT]

The ones prefixed with BB are the user-custom adjustable models.

[featherliteCT1]

The ones prefixed with BB are the user-custom adjustable models.

Thanks! I read the manual for one of the Sterling BB units and see, like you said, where the units are adjustable to almost any conceivable charge parameter using the remote device. Wow!

[John61CT]

They make good stuff, very robust. Good support too, worldwide

[Shadow Catcher]

Voltage at the battery is 13.7 to 14.7 volts and the alternator is 130 Amps, but the killer is voltage drop for me at about 1.2V. I have however never checked.

[John61CT]

Voltage at the battery is 13.7 to 14.7 volts and the alternator is 130 Amps, but the killer is voltage drop for me at about 1.2V. I have however never checked.

You mean without a DC charger or converter right?

What type and size bank, model batts?

What gauge wire and what total (round trip) distance?

Is the alternator output adjustable? Any idea amps actually getting pulled?

[greygoos]

I am old school and it works fine with no issues. I run a 10 guage,wire fr8m my postive post on my battery to a el cheapo 15 buck Rv selnoid which is powered by a toggle,switch under my dash on my tow vehicle then then I run a 10 gauge wire back to my 7 way plug thats,wired into to the postive post on my tears battery..no issues charges up my tears battery totaly A-okay... ... slow...

Spoken by a man who has actually built and camps in his own creation. Thanks Slow