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New project don't know where to start!

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tkbell34

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So I want to create a portable power supply, something rechargeable through solar panels, large enough to power a laptop for 5 or 6 hours. I've been looking at various types of solar panels, but my biggest concern is the battery. What's the best kind of battery for large capacity and will last through a lot of recharges?
 
my son asked me about running his labtop from panels a few yrs ago, so I figured how many watts he'd need and when I showed him the price for the panels and the size of them,
he just said forget it, ? I think the battery that you are looking for will win the "X"prize of 10 million dollars, that has yet to be invented, :) good luck.
 
I guess if I were to think about it I would look at the currently used AC adapter used with the particular laptop. My laptop for example is a Dell Precision M90 that uses a 130 watt AC adapter delivering 19.5 volts at 6.7 amps to the laptop. Pretty power hungry laptop, however, the actual demand will vary from laptop to laptop. The laptop uses a 3 wire system and is well aware of what is out there, anything less that the 130 watt AC adapter and it gets very unhappy real quick with messages telling me so.

That said, if I were to consider such a project my first choice in battery would likely be building a hell of a large LiPo battery pack. The use of LiPo batteries has several drawbacks as caution is needed designing and building the charging circuit. Great batteries but can be a problem to work with. A more friendly battery would likely be a SLA (Sealed Lead Acid) battery. SLA batteries take well to solar charging systems. However, depending on the laptop power demands there is a good possibility you will be building a large and heavy SLA battery pack. If I used two 12 volt 7.5 AH SLA batteries in series it would give me 24 volts and about a few hours on a good day with my laptop.

When I travel I use a 300 watt DC to 120 VAC inverter in my truck and just plug the laptop AC adapter into it. Not efficient but it works.

Looking at solar panels we get into what Joe G mentions. You are going to need one heck of a large solar array to power the laptop and charge the battery pack. If you want 12 volts at a few watts it is one thing, if you want 24 volts at a few hundred watts it's another animal all together. Not easily or inexpensively done. Maybe other forum members have some ideas but I do not see a simple viable way to go about it. :(

Ron
 
It's been years since I had my first electronics class in college, and unfortunately I never really had a chance to use that knowledge.

My laptop is rated at 19V at 3.42A, so the W is about 65, right? So powering it for 6 hours would require a battery with a capacity of of at least 400W. I was thinking of going with an AGM battery at 12V. As for the solar panels, I was planning on lining the roof of my car with them. I've seen some 6"x6" panels providing 3W for under $10. 8 panels could fit on my sunroof and could recover about 5 hours worth of usage (on a good day, not accounting for actual draw of the system itself.)

Obviously I'll want a battery with a high enough capacity that running it for the target of 6 hours doesn't take it below 20% capacity. I'd like to include a circuit to monitor battery life, and will have to include a way for the power from the solar panels to be dissipated if the battery is fully charged. To make things simple, I'm considering using a COTS DC to AC inverter, so that I can simply plug my laptop into it (or any other device I might want to use)
 
I can buy a 400 watt 12 VDC to 120 VAC inverter like this one for about $50 USD. Similar to the one I currently have in my truck. The current drawn by the inverter will only be a function of the current delivered plus any inefficiency. If I want longevity above and beyond what I have without the engine running I can add a deep cycle marine or RV battery to my truck for less than $100 and add it to my truck. Deep cycle or deep discharge batteries are designed and built for applications like this.

In reality you only need 65 watts so a simple 100 watt inverter would be adequate. Max current at 12 volts for a small 100 watt inverter would be well below 10 amps so a 100 amp hour battery would give about 10 hours of operation. The automotive system has an alternator which will easily maintain the battery or batteries occasionally. I guess I just don't get the reasoning for solar panels? Charging a 12 volt battery requires about 14 volts, solar panels short of a large array will not do it and a large array is costly to the point and well exceeding the point where any gain is outweighed by cost.

Ron
 
I think that if you want to have a PSU that can run your laptop that will deliver 400W of power your best bet is to have several smaller battery packs connected in parallel to deliver the current that you need. The solar pannels would charge these as a group but they would have to be disconnected from each other in order to charge properly.

It does beg the question though, if you are somewhere that you need to have solar pannels charge your laptop, should you even have it out there in the first place?
 
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