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 > Use a solar controller as a DC to DC charger?

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Son of Norway

Denver, Colorado

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Posted: 06/15/19 09:50pm Link  |  Quote  |  Print  |  Notify Moderator

I have been thinking about installing a DC to DC charger to properly charge my coach batteries from my alternator while driving. I have a dual-output alternator that delivers a constant voltage of about 14.4 V to the coach batteries. The DC to DC chargers I see are pretty expensive. I had the idea, why not just install a properly-sized solar controller, maybe about 30 amps, for the job. Is there something that I don't understand about this or will a solar controller work? Thanks for your advice.


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2oldman

New Mexico

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Posted: 06/15/19 10:00pm Link  |  Quote  |  Print  |  Notify Moderator

Not sure if the 14.4 is enough to properly operate a controller, never seen a minimum voltage spec.

BFL13

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Posted: 06/15/19 10:46pm Link  |  Quote  |  Print  |  Notify Moderator

An MPPT controller is a buck converter so output is lower in voltage than input.

We had some threads about using controllers with other than solar panels as input such as a DC power supply, and it does work in some cases (not all) I forget the details. Idea was to take advantage of the controller's adjustable settings ISTR.


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time2roll

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Posted: 06/15/19 11:02pm Link  |  Quote  |  Print  |  Notify Moderator

Not all controllers will limit themselves to the rated power.
By the time you pay extra for MPPT you may as well get an actual DC-DC charger.

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


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MrWizard

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Posted: 06/15/19 11:36pm Link  |  Quote  |  Print  |  Notify Moderator

all solar controllers 'buck' the voltage that is reduce the input from somewhere above 15+ even 12v panels have an open circuit voltage 21+

no solar controller i have read the specs on will increase voltage on the output side
MPPT will take higher voltage and make more amps at battery charging voltage
but that is still less voltage than what is on the input side

you need DC to DC voltage BOOST, output volts higher than input volts

that doesnt come cheap


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twodownzero

NM

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Posted: 06/16/19 11:51am Link  |  Quote  |  Print  |  Notify Moderator

If you're going to spend money on a solar controller, why not put on a few panels? My moderate battery bank is full within a few hours of the sun coming up. Why make it complicated?

wopachop

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Posted: 06/16/19 12:42pm Link  |  Quote  |  Print  |  Notify Moderator

Fun topic i like learning here. Isnt the limitations wire size and amp output? How many amps would you guys expect he could get to the house batteries assuming he had proper wire gauge?

I think with a tow behind setup isnt it only around 2 amps back to the trailer plug? That is due to wire size correct, not the alternator output?

pianotuna

Regina, SK, Canada

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Posted: 06/16/19 01:02pm Link  |  Quote  |  Print  |  Notify Moderator

wopachop,

The alternator and "brains" see the starter battery. When it is full (which happens quickly) very little charging happens.


Regards, Don
My ride is a 28 foot Class C, 256 watts solar, 556 amp hours of AGM in two battery banks 12 volt batteries, 3000 watt Magnum hybrid inverter, Sola Basic Autoformer, Microair Easy Start.

2oldman

New Mexico

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Posted: 06/16/19 01:08pm Link  |  Quote  |  Print  |  Notify Moderator

wopachop wrote:

Fun topic i like learning here
Let's hope the OP does too.

Lwiddis

Near USFS Glass Creek CG, Inyo County, CA

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Posted: 06/16/19 05:07pm Link  |  Quote  |  Print  |  Notify Moderator

Why stay out in left field cobbling together charging method? Install an adequate solar system. It will charge driving or not.

“That is due to wire size correct, not the alternator output?”

And the batteries in absorption phase accepting less and less amps.


Winnebago 2101DS TT & 2019 Chevy Silverado LTZ Z71, 300 watts solar-parallel & MPPT, Trojan T-125s. TALL flagpole for flags. Prefer USFS, COE, BLM, NPS, TVA, USF&WS, state & county camps. Bicyclist! 14 year Army vet - 11B40 then 11A - old MOS 1542 & 1560.


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