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 > Tow vehicle charging RV batteries

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Lwiddis

Williams AZ area

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Posted: 12/04/20 05:59pm Link  |  Quote  |  Print  |  Notify Moderator

What’s for lunch, wanderingbob?


Winnebago 2101DS TT & 2020 Chevy Silverado 1500 LTZ Z71, 300 watt solar-parallel & MPPT, Trojan T-125s. TALL flag pole. Prefer boondocking, USFS, COE, BLM, NPS, TVA, state camps. Bicyclist14 yr. Army vet-11B40 then 11A - (MOS 1542 & 1560) IOBC & IOAC grad


Seon

Lake Camanche, CA

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Posted: 12/04/20 06:31pm Link  |  Quote  |  Print  |  Notify Moderator

I bought from Amazon a 20watt solar panel charger/maintainer connected to battery #1 while the trailer powers off #2 battery then next day switch to #1 battery and transfer the solar connectors to #2 battery to charge.
As a backup I carry a 12v charger powered by a 2K generator.

Works for me.

theoldwizard1

SE MI

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Posted: 12/04/20 06:50pm Link  |  Quote  |  Print  |  Notify Moderator

blaczero wrote:

How slow is it? Is there a mod you can do to make it charge quicker?

The real issue is how large is your battery bank and how depleted is it (what is its "state of charge" SOC ?)

Sometime around 2000, the entire auto industry switched to "smart charging". Smart charging is when the PCM controls the output voltage to the alternator to limit the voltage to "just enough" to replenish the battery after a start and not left the voltage go so low as to discharge the starting battery.

This means that about 5-10 minutes after starting you vehicle the output of the alternator is about 13.2V-13.4V and there is not much you can do about that !

So if your RV battery is at the end of 25' of wire (actually double that because you have a ground connection) you will be darn lucky to get 13.0V, probably less. You can NOT charge a lead acid battery on that little voltage. USING HUGE WIRING FROM THE VEHICLE BATTERY TO THE RV BATTERY DOES NOT SOLVE THIS PROBLEM !

The only solution is a DC-DC battery charger mounted close to the RV battery. Most can accept voltages as low as 10V-11V and boost them up to the proper voltage (>14V) to charge a battery.

theoldwizard1

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Posted: 12/04/20 06:51pm Link  |  Quote  |  Print  |  Notify Moderator

old idaho guy wrote:

If you are trying to charge your battery while camping, use jumper cables from battery to battery

A DC-DC charger will do it faster because of what I just described.

theoldwizard1

SE MI

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Posted: 12/04/20 06:53pm Link  |  Quote  |  Print  |  Notify Moderator

Seon wrote:

As a backup I carry a 12v charger powered by a 2K generator.

The 12VDC output on most of today's generators does a poor job of recharging a lead acid battery. You are better off plugging in a AC battery charger.

pianotuna

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Posted: 12/04/20 10:17pm Link  |  Quote  |  Print  |  Notify Moderator

dc to DC voltage boosting may be the best way to improve charging.


Regards, Don
My ride is a 28 foot Class C, 256 watts solar, soon to have SiO2 batteries, 3000 watt Magnum hybrid inverter, Sola Basic Autoformer, Microair Easy Start.

jdc1

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Posted: 12/05/20 09:50am Link  |  Quote  |  Print  |  Notify Moderator

Dual alternator. Best you could ever do. Some super duties come equipped that way.

time2roll

Southern California

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Posted: 12/05/20 09:57am Link  |  Quote  |  Print  |  Notify Moderator

Single alternator has plenty of amps. The trick is getting the proper voltage on the battery that needs charging. A DC-DC charger will work excellent for this purpose. Still takes 3 to 5 hours to get a flooded battery from low on charge to 95%+.

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

Also consider some solar. This works all day with no effort. Works in motion or stationary. Does need sun of course. 200 to 400 watts works well for most people. Even if it does not provide all the power solar will significantly reduce generator or alternator run time.


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valhalla360

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Posted: 12/05/20 10:10am Link  |  Quote  |  Print  |  Notify Moderator

theoldwizard1 wrote:

Seon wrote:

As a backup I carry a 12v charger powered by a 2K generator.

The 12VDC output on most of today's generators does a poor job of recharging a lead acid battery. You are better off plugging in a AC battery charger.


I presume he meant a generator putting out 120v AC power a dedicated charger outputting 12v.

Charging with the truck has a few major limitations:
- Wiring is too small and voltage drop limits both the voltage and amperage that gets to the battery. You can run what are effectively battery cables back to the batteries but 30-40ft of good quality battery cable ain't cheap.
- Multiple connections are prone to corrosion or just general poor connection, so they often don't work well.
- Standard alternators are designed to put out their rated amperage for a few minutes to replace the short but high amp draw from starting the motor. After that they tend to drop way back. You can buy specialty alternators that put out more amps but again, not cheap.

A couple hundred watts of solar is a much cheaper solution and if you are stationary, it still feeds the batteries.


Tammy & Mike
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JCK

Ohio

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Posted: 12/05/20 11:27am Link  |  Quote  |  Print  |  Notify Moderator

I’ve seen as high as 18 amps going to trailer batteries on start up of truck. And hour later or so still seeing 6 amps. Even if voltage is 13.2 to 13.4 amps is what gets the job done. Sure it won’t fully charge but on a 4 to 6 hour run I’m usually close to full charge.
I’m using AGM batteries with low charging resistance. The charge line on my truck carries a 40 amp fuse so manufacturer has to size charge wire to carry load.


2019 GMC Denali 2500 Duramax
2018 Grand Design Imagine 2500 RL

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