Solar Thinkpad Charging Station for T30s or similar vintage

[voneschenbach]

Hi All,

This topic has come up in various places in the past but without specific hardware and/or the IBM solar solution which seems pricy. I wanted to ask folks what they thought about the feasibililty of a DIY solar charging station.

I have a T30 which appears to draw 4.5 amps through it's 16 volt adapter for a total of about 72 watts. I have no idea what the watt draw of a sleeping T30 would be when it is recharging the battery, but thought it would probably be in the range of 10-15 watts.

Amazon sells a 12-volt 20 watt solar panels for about $100 - $150 or two 15-watt panels for about $150.

Would it be feasible to purchase a 20 watt panel and 100 watt inverter and directly plug in the Thinkpad without a charge controller? I am under the impression that the charge controller is designed to help avoid overcharging large auto or deep cycle batteries but is not needed if you are not charging a battery. Would the inverter and the IBM AC power adaptor protect the laptop from the voltage and amperage variations? I hear these panels vary in voltage from 10-20 volts depending on sunlight intensity, etc.

What would be ideal is if someone who is running a similar set up or has done projects like this in the past can report back with the specs of their system and the components they are using.

For the purposes of this discussion, we are assuming charging a sleeping or turned off T30 over the course of 8 hours with one 20-watt monocrystalline panel in direct sunlight with 100 modified sinewave inverter for a total project cost of under $200. If costs can be SAFELY reduced, that would be great as well.

Finally, any other non-grid power options would be interesting as well, such as wind, water turbine power. Off course, anyone with a DIY fission or fusion reactor is welcome to post as long as their setup cost less than $200!

[RealBlackStuff]

Plenty info here: http://forum.lenovo.com/lnv/board/messa ... sage.id=44

[voneschenbach]

Actually, I saw that discussion and it doesn't have the detail that is needed, specifically whether anyone has verified that you can go directly from solar panel to DC inverter to Thinkpad without damage, etc.

It also is a lot more expensive that $200.

Low in posts, but do know how to use Google ;o)

[Paul Unger]

voneschenbach,

I'm not too electrically savvy, but I have some experience that may prove helpful. I live and work in Solomon Islands in an entirely 'off grid' setting. I have three 85W panels (255W total), 4 x 110Ah 12V batteries, a 30A charge controller, and a 1000W modified sine inverter. Obviously, I'm running more than my computers on my system, but they do run!

In my and my colleagues' experience here, I've never heard of anyone doing what you propose (and, believe me, we're all interested in getting by with as little as possible!) I think you will need a battery (at a minimum) and a charge controller (ideally) to even out the power fluctuations before it hits the inverter (unless you have a very capable inverter). As you mentioned, variability of sunlight is an issue and the inverters I've had experience with do not like fluctuating voltage. Having said that, I do run everything I can directly from the outlet side of the charge controller (i.e., not passing through the inverter, which is inherently inefficient): lights, fans, CD player, HF radio--all these run directly from 12V. But again, this is evened out by the charge controller so that it does not fluctuate with variable sunlight.

I'm interested to learn what you discover elsewhere!

[voneschenbach]

Thanks Paul - that is exactly the kind of experience I was hoping we could hear about!

So, it sounds like the charge controller is definitely needed to even out the voltage. I also hear you that the inverter will waste energy (probably in heat), so it sounds like going from a the charge controller to a 12 volt DC adapter might work better. Would a Thinkpad car adapter do the job, or is it essentially just an inverter? If it just converts the voltage from 12v to 15v, then this would seem to be the least wasteful in energy vs. an inverter. It also sounds like a modified sinewave inverter would work without frying the machine.

So the question is how much panel wattage would be needed, what size battery would be needed, and the recharge time for a T30 or similar spec machine to run a few hours a day...

3 hours x 4.5 amps would be 13.5Ah
20 watts x 8 hours at 12 volts would be 12.8Ah

Assuming a 30% energy loss from resistance, etc. It looks like one would need to use at least 30 watts in solar panels (assuming you get full rating), a 100Ah battery (to minimize wear on the battery in discharge/recharge cycles) to support a T30.

[frankiepankie]

Nice project!

I would use a big solar panel, to charge a SLA battery (Sealed Lead Acid), then use a thinkpad car adapter to charge the thinkpad.

This way, you can charge your thinkpad even if its cloudy.

By using an inverter, you are wasting energy.

[voneschenbach]

Thanks all!

After some research and reading the posts, I thought I would go with something like the following:

Duracell DPP-600HD Powerpack ($99)
Coleman Solar Backup Power Kit (3x 18 Watt Panels and 8A Charge Controller) #CL-3600 ($319)

I thought the Duracell Powerpack (or it's Xantrex equivalent) would work well because it has a built-in inverter, contains an 28Ah AGM battery and can be recharged from AC, Solar or the Car.

The Coleman solar panels are amorphous, so not as efficient as monocrystalline, but are a little cheaper per watt.

This set up should keep a T30 running for several hours a day.