Solar Charging Question

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bigbluedoggy
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Solar Charging Question

Postby bigbluedoggy » Mon May 01, 2017 4:13 pm

Oh, great gurus of solar power systems, I entreat you to answer my simple question.

We've had a basic 12 volt solar charged system for years which consists of 4 - deep cycle 6v batteries, wired in series pairs to combine for a 12v total output, and 4 off the shelf 100w to 140w solar panels with a Sunforce 30amp charge controller... very basic. This system has worked very well for us for a number of years. We also need to run our little 2k Honda genny in the evenings to power up some items in our camp. I'm curious if using my plug-in battery charger will work for helping keep our batteries charged during the heavy evening draw. Can I just connect it up to the plus and minus poles on either end of one of my pairs of batteries? Is it likely to damage the charge controller? I can't see how, since it's used to seeing voltage on those terminals, and it seems like it wouldn't hurt anything to do this, but I'm wondering if it's feasible or just silly. Since the gas is burning anyway, why not augment the 12v system with it?

Thoughts?
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asr9754
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Re: Solar Charging Question

Postby asr9754 » Mon May 01, 2017 4:37 pm

Read the specs on your battery charger to make sure the Honda 2k will support running all the direct-connected gadgets and the charger at the same time. It will pull take more power from your generator and will make it run harder/take more fuel. Is the additional juice to charge your batteries worth the extra gas? That's up to you.

Are the solar panels not able to keep up with battery power demand (AKA, are you waking up every morning with drained batteries? If so It might be worth it to charge off the genny at night then. Other hand, If your solar output is keeping up with demand, it would be a waste of gas to unnecessarily charge the battery overnight, because once battery is full, the solar panel can't put anymore juice in, so what's the point of even having the solar panels?

The better alternative might be to keep an eye on your battery levels and only recharge them via genny when needed. They at least you know you are replacing power that you have used, rather than creating excess power and making your solar panels obsolete.

I don't know about damaging the charge controller if you run the charger at the same time-- but you can just unclip the charge controller from the battery when needed if you're worried about that.

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bigbluedoggy
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Re: Solar Charging Question

Postby bigbluedoggy » Mon May 01, 2017 4:46 pm

Thanks for the quick response. Our batteries do alright although they are often down to about 11+ volts or so by 1am. I suppose the correct thing to do if we keep adding load to our 12v stuff is to add more batteries and panels. But you are right, I could just run the charger a bit during the day when there is no output load on the 12v stuff. It's almost all LED lighting.
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Captain Goddammit
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Re: Solar Charging Question

Postby Captain Goddammit » Mon May 01, 2017 5:00 pm

I would absolutely use your charger whenever the generator is running anyway.
The amount of extra fuel you'll use is insignificant, probably immeasurable.
But let's say you burned two extra gallons in a week, just to be ridiculous. What's that, $6?
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asr9754
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Re: Solar Charging Question

Postby asr9754 » Mon May 01, 2017 5:16 pm

Agreed! a few gallons of gas is way cheaper than another 100w panel and a great way to "stretch" your solar battery kit.

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bigbluedoggy
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Re: Solar Charging Question

Postby bigbluedoggy » Mon May 01, 2017 5:42 pm

Thanks for the advice!
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some seeing eye
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Re: Solar Charging Question

Postby some seeing eye » Mon May 01, 2017 7:06 pm

Since you have the Honda 2K generator, you could expand your battery bank and have more silent running time off the batteries. You can use the generator to charge lead acid cells more efficiently through a battery charger, than through the generator DC connector. The Honda is limited to about 100 W on the DC port. Lead acid batteries like a current source while charging, converting to a voltage source maintaining/topping off. A battery charger does that, while the DC output of the generator does not.

(Technical: https://www.maximintegrated.com/en/app- ... mvp/id/680)

You might think what future use cases you are building to. Then you can design an stepwise economic evolution path.

Do you want it for home for power outages? Attach to an RV? More camping trips?

If you want more panel capacity, it is cheaper to buy new pro panels well sub- $1/Watt. That number is likely to go lower in the coming year, if we don't have a change in import taxes. The monocrystalline pro panels are larger ~40x70-80" and #40-50, and 300-400W per panel, 25-30 year guarantee, if that works for you. You can often get more than $1/W selling your panels. Shipping adds cost to panels, so local pickup is better. There are opportunities to buy American panels.

Do you want more battery capacity? Flooded lead acid, sealed or AGM? Other battery technologies? Chargers specific to the battery system with the capacity to grow?

Do you want cleaner inverters? Dust enclosures? Meters? Fuses/breakers?

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