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Old 12-28-2016, 12:56 AM   #1
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Laptop charger + solar controller = cheap shore charge/battery tender

I'm sure someone has already discussed this, but I wasn't able to find anything with a search so I figured I would post up the idea in case its helpful to anyone.

More and more of us run a strict 12V only system with solar and alternator charging only - the shore power side of things doesn't make sense for our typical wants and needs to explore off the grid. However, sometimes it is nice to park in the garage, leave the fridge going, or just ensure that batteries are topped off without having to make sure you are parked in a location that gets you good solar gain.

By adding a laptop charger (or similar power source) going in to your fancy solar charge controller, you can safely trickle charge your house batteries. I was recently looking for a power source to diagnose my solar panel and charger controller system and saw that an old laptop charger had an 18V / 5A output. This would be about equivalent to a 100W panel on a sunny day, so by connecting it to the charge controller it should safely charge your batteries.

Don't get me wrong, a battery tender isn't all that costly; however, I think this is a good solution for folks that might only need to charge from shore power rarely and don't want/need to invest in a more costly charging system. YMMV!
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Old 12-29-2016, 06:05 PM   #2
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And how would that device know when the batteries are full and shut down?
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Old 12-29-2016, 06:10 PM   #3
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And how would that device know when the batteries are full and shut down?
That's why it's run through the solar controller.
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Old 12-29-2016, 06:14 PM   #4
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So the laptop charger, at least mine draws 90 Watts. So while the solar charge controller shuts to input down when the batteries are full but Thing is still drawing 90 Watts from your house which you are paying for. If you use a car charger or trickle charger it would shut down to charge the batteries as needed and would minimize the draw from the house current.
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Old 12-29-2016, 07:45 PM   #5
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Quote:
Originally Posted by rallypanam View Post
That's why it's run through the solar controller.
Yep that would solve the problem and essentially make the charge controller act as a trickle charger and not overcharge.

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So the laptop charger, at least mine draws 90 Watts. So while the solar charge controller shuts to input down when the batteries are full but Thing is still drawing 90 Watts from your house which you are paying for. If you use a car charger or trickle charger it would shut down to charge the batteries as needed and would minimize the draw from the house current.
That isn't a problem actually, if there is no draw on the laptop charger it doesnt draw 90watts. In fact it probably draws less than a watt. There is a very good test on phantom/vampire power consumption here.

That said a decent trickle charger to keep the batteries topped off doesn't cost to much:
KeyLine Chargers KC-75A-MP 12V 0.75 Amp Automatic Mini Pro Car Battery Charger 25.00
or a bit more power
Battery Tender (022-0186G-DL-WH) 12V 5 Amp Battery Charger
60.00

Now a laptop charger is under 8.00 since the model doesnt really matter,
Exxact Parts Solutions®Acer 65W 19V 3.42A Laptop AC Adapter Power Supply Charger
Usually the power supply outlives a laptop so a used one could be next to nothing, if you ask around or visit a thrift store but either way it would be a pretty cost effective solution for the problem.
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Old 12-29-2016, 07:48 PM   #6
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I learned something new!
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Old 12-29-2016, 08:07 PM   #7
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Question:

Does your solar charger not run its "charge strategy" based upon a presumed "solar cycling" of input current? As in...the available voltage from a solar panel peaks once a day (and then drops to zero overnight) so a solar charge controller would be built to work around (and optimize battery charge) with that schedule.

Since the laptop charger puts out a *constant voltage/current*, I wonder if that would cause hiccups with charge optimization. Would it confuse the solar charge controller.

Hmmmmm....honestly just curious! I like the simplicity of your solution.

(Had a similar discussion in a thread a couple months back, "One Charger To Rule Them All?")

http://www.sportsmobileforum.com/for...all-18197.html

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Old 12-29-2016, 08:12 PM   #8
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Josh, or whoever, where do you plan to tap in to the solar controller? Just piggyback off the panel inputs?
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Old 12-30-2016, 12:23 AM   #9
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I actually have an inverter/charger, so I don't plan to implement the plan on my personal rig (at least this build!). If I did, I would do exactly as you are implying, Eric - piggyback right on top of the solar input into the charge controller. I am operating under the assumption that it would not backfeed and take power from the solar panels during their normal operation when not plugged in.

I was simply troubleshooting my solar panel and charge controller when I thought about this. I hooked the laptop charger up to the charge controller to verify that it worked (and that my solar panel was truly toast) and thought there was no reason this couldn't be a good permanent and affordable solution for folks that are operating off of a 12V only system. If/when I swap vans or need to replace the inverter/charger in the current van, I would highly consider using this method to charge my batteries.
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