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 > Why do I need a DC to DC charger?

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NRALIFR

Truck Camping Out West

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Joined: 11/27/2005

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Posted: 09/19/20 11:34am Link  |  Quote  |  Print  |  Notify Moderator

In most cases, you should plan on installing heavier gauge wires than what you will find on the OEM 7-pin wiring harness. In fact, I wouldn’t recommend using the standard 7-pin RV plug at all for this circuit. The connectors are a poor design for this IMHO.

Also, don’t underestimate the total length of the wire required to connect the DC-DC charger, which should be as close to the battery it’s charging as possible, and the truck battery it will be drawing from (not the alternator!). You’ll be lucky if you can keep the circuit length under 25 feet on a crew cab pickup. Mine is closer to 30 feet.

This is from the Renogy installation guide. The recommendations for my Redarc were similar.

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2001 Lance 1121 on a 2016 F450


Kayteg1

California > Nevada

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Posted: 09/19/20 12:04pm Link  |  Quote  |  Print  |  Notify Moderator

On practical note for B2B charger is inverter combined with converter.
So if you already have converter adjusted for lithium, or whatever batteries and on-board truck inverter >>> you already have the system. All it takes is to learn how to use it.
To clarify - I am talking about 400W inverter Ford installs on newer trucks and potential for adding 1 on truck who doesn't have it.
400W inverters run for like 35 bucks.





kohldad

Goose Creek, SC

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Posted: 09/21/20 10:08pm Link  |  Quote  |  Print  |  Notify Moderator

Quote:

YOU ABSOLUTELY DO NEED A DC-DC CHARGER !

Prove it to yourself. Start your truck. Check the voltage at the battery. Immediately after starting it should >13.8V. Let the truck idle for about 10 minutes and check the voltage again. Probably <13.2V ! Have some one hold the engine at a high idle. I'll bet it is still <13.4 !

13.2V - 13.4V at your house battery bank will not let it discharge but it will NOT re-charge the house battery bank !


I don't need one but would like to have one for faster charging. My truck will recharge my battery faster than 10a/hr even when running the fridge on 12V. Now I did upgrade the wiring from the truck battery to within 10" of the camper battery to #2 and go through a 175A Anderson connector which helps greatly.

Most modern alternators have over 75% capacity at idle. The old days of having to rev the engine for a good charge are gone. At idle, my alternator turns 3,000rpm thanks to pulley size which is 90% of it's 220A capacity so has plenty of output at idle.

Now, I would like one so I can recharge a dual battery bank at 40A/hr when I upgrade my next camper to a DC compressor fridge as I hope to sit more and drive less.


2015 Ram 3500 4x4 Crew Cab SRW 6.4 Hemi LB 3.73 (12.4 hand calc avg mpg after 92,000 miles with camper)
2004 Lance 815 (prev: 2004 FW 35'; 1994 TT 30'; Tents)


toddb

az

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Posted: 09/21/20 10:26pm Link  |  Quote  |  Print  |  Notify Moderator

Kayteg1 wrote:

On practical note for B2B charger is inverter combined with converter.
So if you already have converter adjusted for lithium, or whatever batteries and on-board truck inverter >>> you already have the system. All it takes is to learn how to use it.
To clarify - I am talking about 400W inverter Ford installs on newer trucks and potential for adding 1 on truck who doesn't have it.
400W inverters run for like 35 bucks.


I don’t think you’ll find a converter that’ll run on 400w.

I use a small Orion 110w dc-dc that covers my fridge draw at about 85w. Runs on the factory wiring so no need for jumper cables.

S Davis

Western WA

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Posted: 09/22/20 06:56pm Link  |  Quote  |  Print  |  Notify Moderator

I am getting ready to install two of the 50amp Redarc dc to dc chargers on my truck, they are charging four Trojan T105s to start.

time2roll

Southern California

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Posted: 09/22/20 07:02pm Link  |  Quote  |  Print  |  Notify Moderator

100 amps seems like a lot even on four batteries and especially a lot on the alternator.


2001 F150 SuperCrew
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S Davis

Western WA

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Posted: 09/22/20 08:54pm Link  |  Quote  |  Print  |  Notify Moderator

time2roll wrote:

100 amps seems like a lot even on four batteries and especially a lot on the alternator.


The alternator can handle it, I have a high output alternator. I drive a couple hours a day and want to take advantage of that.

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