How can I charge a laptop computer with a Solar Fence Charger?

How can I harge a laptop computer with a solar fence charger? Thanks.

Assuming the solar fence charger has a 12V battery, you can get a car charger for the laptop and connect it to the battery.
But in the long term a laptop uses much more energy than an electric fence, so the battery will probably drain rather quickly.

Thanks Sebastian, thats very helpful.

The charger designed to charge the computer has a third terminal, usually a center pin.  This allows the laptop to communicate with the charger to let it know when to alter/stop charging.  Without communication, so random power supply is likely to damage the battery.

Agreed. I'm not sure other posters were actually advocating shortcuts. But  if I want to reliably and safely charge a laptop battery from solar, the path I would always use is:

Solar panel > 12vdc lead acid battery > 12vdc to 120vac inverter (pure sine if possible) > plug in appropriate laptop power supply > connect to laptop.

That said, I have also picked up a couple of 12vdc universal laptop chargers, with all the various tips. I don't use them much, but have no qualms doing so. I suspect they would be more efficient since there are fewer conversions.

Along similar lines, it's that time of year again when I need to rig up the trail cams to see what's snacking on various garden delights in the middle of the night.  A big lament of trail cams is the number of batteries they eat in the process, but there are solar powered units that are sold so that you can just plug the cam into a larger power supply.  I've always assumed that there must be charge-controller circuitry to keep the charging of the battery on an even keel in addition to the discharge of the battery to power the camera.....correct?

It's a nifty idea.  I wish I knew more about electrical stuff to be helpful.  But if a solar fence charger is what you've got to work with, then it's a fun place to start.  I'm a learn-by-doing person, so I've taken apart a few gadgets to make different gadgets.  Some work, some not. But this is going to be a great thought experiment if nothing else.

Solar trickle charges a battery.
Electric fence uses power from the batter, constantly, but not very much.  
Laptop charging uses power from the battery for an hour or two, but uses a lot of it.

There needs to be something to protect the laptop battery from using too much power at once.  Possibly from using too little power.  Something to regulate the power out.  For some reason, the word in my head is "controller".  This may not be the correct word.

I've had more than one battery die due to power fluctuations in the mains (wall plug - it's called hydro here).  I've had one laptop explode due to work being done on the line caused a surge.  When plugging the computer into the wall, I always use a surge protector.  So I'm feeling strong that protecting the battery is an important element.

Next is to find out if the size of the battery in the solar charger is big enough to charge the laptop.  I don't know how to do this.

And then find out if you can get at the battery.  On my solar charger, the battery and controller are one unit.  I would have to break it open to get at the battery without the controller for the fence.  

I almost wonder if there could be a third element.  I often use this for my gadget.  I have a solar charger in the south-facing room which I use to charge a portable battery which is used to charge my gadgets in the north-facing room.  The big problem is I charge the gadgets during the day but the solar charger only lets me draw power from its batteries when the sun is down, so I compromise.  

From what I have read the pin is to tell the notebook what charger is connected .. usually to refuse charging unless it is from the correct brand.
But the correct car charger for a notebook will have to handle that, so I don't see any risk there. It is also designed to be connected to a 12V lead-acid battery and the wide voltage ranges found in a car. The only risk would be to over-discharge the battery.

As to sizing the solar panel, I would look at what rated power of normal power supply is and double that, so it doesn't only work under lab-conditions.

Sebastian Köln wrote:From what I have read the pin is to tell the notebook what charger is connected .. usually to refuse charging unless it is from the correct brand.

I have only seen this once. I have an older HP laptop that complains when I plug in a Dell power supply by mistake. The plugs (barrel connectors) are largely identical.  The HP starts up fine, but gives an error message saying it can't charge the battery because the power supply can't provide enough amperage. I checked the specs, and it's correct.

So it's an issue of capacity, not about the manufacturer -- which makes sense, because there are all sorts of third-party chargers that work just fine.

r ranson wrote:There needs to be something to protect the laptop battery from using too much power at once.  Possibly from using too little power.  Something to regulate the power out.  

You're right. To charge properly and safely, lithium ion batteries need to be charged in a specific way. The charging circuitry that controls charging is usually built into the laptop and the battery pack itself.

A car-type inverter will have a circuit that shuts it off when the 12V battery voltage dips too low, to avoid deep-discharging and damaging the 12V battery.

I just did a quick web search for solar fencers. A lot of them use a 6 volt battery, which would not be easy to use to charge a laptop. Best to check the specs of your unit before going any farther.

Hi Douglas,

To run with your previous post. Let’s assume we are using a 12v system.  What would be the minimum wattage panels to charge a laptop in .....say.....4 hours or so on a cloudless day?

Hi Michael,

I like the pathway that Douglas took earlier in this post.  If you were feeling really ambitious and wanted to cut out a step/possibly conserve electricity, you could try something like this:

Solar Panel >12 Lead Acid Battery>Adjustable Buck Converter>Cut off DC Supply to computer (I would get this separately).

The advantage is that you wouldn’t have to step up voltage to 120v just to bring it back down again in the brick part of the computer AC power supply. Also the inverter can be skipped.

Buck converters are cheap and available on Amazon.  They can be adjusted to a very precise voltage output.  But before taking this route, I would very carefully check the exact voltage requirements for the laptop.

This is not a necessary route to go, just an option that might be worth considering.

Eric Hanson

When I had a laptop, I chared it every second day.  

If one assumes 6 hours of direct light per day, that's 12 hours of sun to charge the battery that charges the laptop.  (I always underestimate when building a system like this).  You'll know your location better to know your hours of direct sun, but then again, fence chargers usually come with their own built-in solar panel and since the thought experiment isn't building a system from scratch, we would need to know ... how much the fence battery holds.  How long it takes to charge with the solar panel the charger has, and how much power the laptop takes.  

I'm feeling it's going to be a way of topping up or reducing the mains usage.  Maybe use the solar system every second time you charge your laptop?

Most people don't fully drain the battery before charging it again.  So maybe you are a person who charges their laptop when the battery is over 50% empty?  Behaviour influences your needs.

I've burned through three or four laptop batteries in the last five years charging them with a car charger hooked to 12V batteries. You need a pure sine wave inverter if you're going to be charging it off the batteries all the time.

It's true, a pure sine wave inverter is much nicer to your electronics.

Eric Hanson wrote:Buck converters are cheap and available on Amazon.  They can be adjusted to a very precise voltage output.  But before taking this route, I would very carefully check the exact voltage requirements for the laptop.

Wow, the price on these has come way down. Thanks! I want one to play with!

With that in mind, I just did a survey of my assorted laptop power adapters. They are all rated at 90W, with output voltages ranging from 18.5 to 20 VDC and amperage in the 4.5 to 5 A range.

Edit: the amperage is to run the laptop and charge the battery pack simultaneously. It takes fewer amps to run the laptop itself without the battery installed. I have lots of old systems around and I remove their almost dead batteries to save energy.

Douglas,

I wonder how much power is required to simply power the brick itself.  Or put another way, how many watts are being lost to heat through the power brick.

I have my little battery box that I built about a year ago.  It is powered by a 12v 14 ah SLA battery.  I deliberately made it with a generic DC output and I am thinking/wondering about connecting a little buck converter to it.  All mostly just for fun.

Eric

Eric, the mid-range buck boost converters (50W continuous) are claiming conversion efficiency up to 93%, which is amazingly good. That refers to an ideal situation, of course; it will be somewhat lower in practice.

Edit: oops, I misunderstood the question. I'm really not sure how efficient the laptop power supplies are, though my experiments lead me to think they aren't too bad. I would need to monitor actual amps in and out to give a proper answer.

Douglas,

Actually, given how warm a laptop power supply can get I am thinking that they aren’t all that efficient.  Maybe a small battery contraption like what I built would stand a chance?

Eric

Totally crazy question:  Is it possible to charge a laptop battery outside a laptop?  

Back when I was a student, I often wanted to have two batteries so I could charge one while the other was in the laptop.

I don’t see why not.  There are charge controllers designed for lithium batteries so I would think that with a little bit of research and ingenuity a battery charger for a laptop battery would be perfectly possible.

Eric

I'm hoping it's okay with the OP to tuck this question into this thread.

Consider the following help statement:

"When do I need a charge controller and why?

The safest way to figure out if you need a charge controller is to take Battery Amp Hour Capacity and divide this by the Solar Panel max. power amp rating. If the quotient is above 200, you don't need a controller. If the number is less than 200 than you need a controller.

For example if you have a 100 amp hour battery and a 10 watt panel, you take 100 and divide it by .6 (600mA) and you get 166.6. Since this is less than 200 you need a charge controller. If you have a five-watt panel in the above example you take 100 divided by .3 (300mA) and you come up with 333.3. Since this is larger than 200 you do not need a charge controller. However you still need a blocking diode, to prevent the battery from discharging to the panel at night. So as a general rule of thumb you don't need a charge controller unless you have more than five watts of solar for every 100-amp hours of battery capacity."
-- https://www.mrsolar.com/content/faqs/when-do-I-need-a-charge-controller-and-why.html

From what formula or set of concepts is the 0.6A being derived?  Wouldn't it be 10W/12V = 0.833A?  Or is there a fudge factor being considered for average efficiency of the panel?  Thanks!