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Open Roads Forum  >  Truck Campers

 > Why do I need a DC to DC charger?

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theoldwizard1

SE MI

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Posted: 09/18/20 04:30pm Link  |  Quote  |  Print  |  Notify Moderator

Kayteg1 wrote:

System powers 260 W refrigerator when on the road and with smart charging operating at 13.2-13.4 v it works well.
In conclusion >> what's your business in promoting B2B chargers to people who don't need them?


You are changing my words ! I said :

theoldwizard1 wrote:

If you just want your house batteries to not run down (further than they are), you don't need one.


3 tons

NV.

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Posted: 09/18/20 04:44pm Link  |  Quote  |  Print  |  Notify Moderator

Kayteg1 wrote:

theoldwizard1 wrote:



YOU ABSOLUTELY DO NEED A DC-DC CHARGER !!


Now I wonder how could I survive 34 years of RVing without one? [emoticon]


Agree, 16 years and three trucks on, never the slightest hint of a problem while having two 6v Golf Cart batts.... Far better to invest in some solar...

Freep

Wisconsin

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Posted: 09/18/20 05:00pm Link  |  Quote  |  Print  |  Notify Moderator

3 tons wrote:

Kayteg1 wrote:

theoldwizard1 wrote:



YOU ABSOLUTELY DO NEED A DC-DC CHARGER !!


Now I wonder how could I survive 34 years of RVing without one? [emoticon]


Agree, 16 years and three trucks on, never the slightest hint of a problem while having two 6v Golf Cart batts.... Far better to invest in some solar...


Are they LiFePo4 batteries? That's the key here. You don't need a DC-DC charger for FLA or AGM but you definitely need it for LiFePo4 if you want to be able to charge the batteries from your truck.


2014 Lance 992
2014 Ram 3500 DRW Turbo diesel

towpro

Compass PA

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Posted: 09/18/20 06:57pm Link  |  Quote  |  Print  |  Notify Moderator

I did not know that DC to Dc charges could RAISE the voltage?

but anyway, as I did say in original post, I am hooking up a toad. it should be fully charged and I just don't want it to be dead after a days towing.
so were not charging batteries, were maintaining.

but by the way, it IS a Mercedes sprinter. Using the FACTORY 7 pin harness.
The RV side of the fuse line is already fused. I will install a 20A inline on the Toad side for safety and see how it goes.

Thanks everyone


Forest River Forester 2401R Mercedes Benz.

Sold: 2016 Arctic Fox 990, 2018 Ram 3500, 2011 Open Range

Kayteg1

California > Nevada

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Posted: 09/18/20 07:07pm Link  |  Quote  |  Print  |  Notify Moderator

Only 4-cylinder Sprinters of last decade has smart charging, so figuring it out might be useful information.
So is the Sprinter TV, or toad?
There are several ways to wire toad to TV.
Pretty popular is adding bulbs, or taillights who are powered directly from trailer pin.
This way toad electric system is not used and no worry about battery charging for weeks.
Than you might have electric toad brake, who needs to be recharged. But those don't take much current and standard 30 amp charging wire is plenty.





NRALIFR

Truck Camping Out West

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Posted: 09/18/20 07:27pm Link  |  Quote  |  Print  |  Notify Moderator

Freep wrote:

Are they LiFePo4 batteries? That's the key here. You don't need a DC-DC charger for FLA or AGM but you definitely need it for LiFePo4 if you want to be able to charge the batteries from your truck.


I have to respectfully disagree with you here. I have a single group 31 AGM, and a DC-DC charger, and If I were asked whether to install solar or a DC-DC charger, I would recommend the DC-DC charger. With one caveat though: install one that has a solar input as well. DC-DC chargers are nothing more than an MPPT voltage controller. Install the right one, and it will do double-duty for you, and it will always prefer the solar panels over the truck alternator if the sun is shining. Up to the limit of what the panels can produce, anyway.

When I’m on the road, I’m running the fridge in either DC mode, or in AC mode from an inverter. Before I installed the DC-DC charger and was just relying on the truck alternator to charge the camper battery, I’d typically find the camper battery to be at 75-85% charged at the end of the day. And that was after installing 6 AWG charge wires from the truck to the camper battery. The fridge was working fine, but pulling in to a primitive camp without a fully charged camper battery doesn’t work for me.

With the DC-DC charger, I can run the fridge on the coldest setting while driving if needed, and there’s still enough charging capacity left to keep the camper battery as close to fully charged as possible.

Another unexpected benefit of the DC-DC charger is that the fridge DC mode works noticeably better than before. The voltage to the 12v heating element is being maintained at 2-3 volts higher than before, and it actually gets hotter, and can maintain a lower temperature inside the fridge, even in extremely hot ambient temps. It could never do that before. It worked so poorly I pulled the fuse on the fridge controller board for the 12v heater so I wouldn’t accidentally switch it to DC mode.

They’re getting more and more reasonably priced too. There just isn’t a down side as far as I’m concerned.

[emoticon][emoticon]


2001 Lance 1121 on a 2016 F450


cewillis

Tucson, az, usa

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Posted: 09/18/20 09:47pm Link  |  Quote  |  Print  |  Notify Moderator

There's a lot of ridiculous advice in this thread. Maybe a little good too -- but I'm way too smart to keep reading when I see horse- I mean nonsense.


Cal


adamis

Northern California

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Posted: 09/19/20 08:06am Link  |  Quote  |  Print  |  Notify Moderator

I'm surprised this wasn't mentioned already... A DC to DC charger on a camper that has solar is an excellent backup if the sun isn't shining. Think cloud / smoke coverage or camping in thick tree coverage. Your alternator is concerned about charging your starting battery. Hooking your camper battery straight to it leads to two different loads and the camper battery at best is maintained but charging properly can be difficult.

AGM and lead acid batteries on a DC to DC charger probably isn't as necessary but for LiFePo4 it is. They charge at a higher voltage than the standard alternators are going to provide. They are also expensive so a charger that is dedicated and has the proper charging profiles is a worthwhile insurance plan.

What the unit does is it regulates the voltage to the camper battery to be consistent with the charging profile appropriate for your battery type. It does that regardless of what the alternator is doing. By the way, the alternator voltage at least in my 99 7.3 Super Duty is anything but constant. It is constantly fluctuating and changing every few seconds. Not a great way to charge a battery.

The way these things regulate the voltage to be constant is they pull more current when necessary and through fancy electronic engineering that others could explain better raise keep the voltage constant on the output side. V=IR is the equation you are hunting for. If the voltage is dropping because of a load, you increase the current pull to maintain that voltage.

In short, you may not NEED one unless your use or battery type make it necessary.


1999 F350 Dually with 7.3 Diesel
2000 Bigfoot 10.6 Camper


Kayteg1

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Posted: 09/19/20 08:58am Link  |  Quote  |  Print  |  Notify Moderator

Beware adamis, that 7.3 powerstroke has very weird charging program, who is design for glow plugs protection.
On cold start alternator will not start charging for several minutes as 14-15 V wold shorten glow plugs life.
Took me a while to figure out why my truck, who was idled for 10-15 minutes every month would have dead batteries after 3 such charging cycles.

time2roll

Southern California

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Posted: 09/19/20 10:48am Link  |  Quote  |  Print  |  Notify Moderator

towpro wrote:

I did not know that DC to Dc charges could RAISE the voltage?
Yes as long as the thin wire has 11 volts the DC-DC will charge the auxiliary battery properly at about 14.4 volts and once charged float at about 13.4 volts.

Here is the Renogy version to get more details. The 20 amp is generally plenty for a single battery.

https://www.renogy.com/12v-dc-to-dc-on-board-battery-charger/


2001 F150 SuperCrew
2006 Keystone Springdale 249FWBHLS
675w Solar pictures back up

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