Jun/071
Solar charging. Lead Acid vs Li-Ion
In a recent comment here, someone asked why the Lead-Acid battery was needed. Its probably not too clear in the video why I use it so I reproduce my answer (which comes from the best of my knowledge!) here.
There are two main problems with charging Li-Ion batteries from Solar panels.
Firstly, Li-Ion batteries (in notebooks and battery bank) charge using a constant current (stream) of power. For common notebook batteries and battery banks such as the Tekkeon MP3400, this is around 1A. A lot of the 12V portable solar panels only reach this power at high sun levels meaning you can only use them for a few hours mid-day. In fact a 12W panel might not be enough to even start the charging process. Secondly, if you have a huge panel that could deliver, say, twice as much power as needed, its not used. Only the power needed is taken. The rest is wasted.
These two problems can be overcome at the expense of weight with a lead-acid battery.
L-A batteries are more flexible. You can charge them with a trickle and also with a higher charge rate. They are much more suited to pairing with a solar panel. The problem with this solution is weight. Small 12v L-A batteries are over 2KG in weight!
What’s needed is a flexible Li-Ion battery charging solution. Currently there are no products on the market that can archive this but I’m searching hard!
In summary there are 2 solutions.
1 – Get a panel powerful enough to charge a Li-ion battery at 70% of its rated output. For example, a 25W panel and the Tekkeon MP3400 Li-ion battery. This will give you about 4 hours of charge time on a sunny summer day. (Mid-Europe) This should be enough to completely fill up the Li-ion battery.
2 – Go for a heavier solution with a L-A battery and give yourself more charging flexibility.
Jun/079
Video: How to use a solar panel to power your gadgets.
Before I talk about the video I just want to say “where’s the damn weather!” Lesson number one in the Solar-UMPC project is that the weather is chaos and if you live in mid-northern Europe, you can’t rely on it as a source of instant energy. You’ll see how I’ve had to adapt my solution in my first Solar UMPC video. In the video I present the solar charging and storage setup that I’ve decided to use for the tour. Its based on the fag-packet drawing I did a few weeks ago after deciding that Li-Ion batteries weren’t really the best solution.
I’ve introduced the lead-acid battery as a buffer and despite the 100-year old technology and 2.6KG weight, provides the perfect stabiliser to the whole architecture.
A quick rundown of the equipment I’m using (mostly bought from my home country, Germany.)
- Sunlinq 12v / 25W foldable solar panel.
- Sonnenschein 12v / 6.6Ah lead-acid battery.
- Solar charge controller. 12v / 4A
- Samsung Q1b UMPC.
- TabletKiosk MP3400 Li-Ion battery pack.
- Voltcraft dual-mode 12v battery charger.
- Voltcraft 12v DC-DC adaptor.
The 20-min Video is below (800kbps divx, 120MB) and also downloadable here. If you can handle a 1.5mbps stream or 200MB download, take the WMV version from here. YouTube version also below. More pictures in the gallery here. Blip.tv link here for sharing. Many thanks to SelectSolar for their help in preparing this solution.
Now available at YouTube:
Jun/072
UMPC Tour Pack-list
Despite the terrible weather forecast (rain, clouds, heat, thunder) It’s time to finalize the pack-list and buy the last items, prepare the solar equipment (which should turn up today) and do some test loading and test cycling. Over the last weekend I fitted the baggage to the bike and loaded it up with random heavy items including the new tent, sleeping bag etc. There should be no problem with space or loading weight. I also tested out the tent and it seems OK although some dampness came through from the floor. Is that normal? I’m surprised.
I’ve written the pack-list in Google docs and shared it for everyone so you can always see the latest version. Its organized into sections. Feel free to take a copy for your own use.
I will go through it and weigh each section before I go and add that to the pack-list. Despite the sub 1kg PC, it won’t be a light load! Here’s the list of electronic equipment I’m taking.
12v AA battery charger,12v charger for Nokia phone,12V lead-acid battery (70W/hr),Adaptor cables and tips, Batteries 8xAA for camera, Batteries (2xAA for GPS), Camera case, Camera USB cable, DC-DC adaptor, Digital Camera + 2GB mini-SD card, GPS logger and holder, GPS serial cable and USB-serial adaptor, Li-ion battery (56W/hr), Mini battery tester, Multimeter (voltage, amps, sun, temp), N800 (spare web-access kit), Nokia headphones / adaptor. , Nokia phone (6280) + 2GB mini-SD card, Nokia USB cable, Passive USB mini-hub, Solar panel (25W) +cable kit, Spare mobile phone (voice only), Standard UMPC battery, Torch, Tripod, UMPC (Samsung Q1b) + Extended battery, case + keyboard, USB LED Lamp.
Later today I should have more details about the solar panel/battery to post. Pictures too.
Jun/070
An evening outside with a Samsung Q1b.
The new tent has arrived, the bike baggage, and finally, some warmer weather so I’m taking the chance to test things out in the garden. My daughter is nearly asleep in the tent and I’m perched outside with the Samsung Q1b and organizer pack resting on one of my panniers, a clip-on LED lamp a paraffin lamp and a bottle of Germanys best beer!
This is the perfect time to be writing because its dark and you only need the minimum of backlight on the UMPC. As I write this with WiFi on, I’m taking between 6.5 and 8.5W on the UMPC. Its also wonderfully quiet.
Behind me, in the spare bedroom, I have started to lay out everything I need for the tour. I’ve written the pack list and there are only a few more things to buy before I’m ready to go. I hope it all fits into the panniers I bought for the bike which, incidentally, is going to be the blue Kronan.
A few things that haven’t turned up yet are the Lead-Acid battery and the solar panel. They should be here on Monday which will allow me to build the frame that the panel and battery will sit in on the back of the bike. I’ve ordered a could of panel meters too because I want to see what sort of drain each component puts on the panel.
One thing I was a little disappointed to find out tonight is that in theory, DC-DC conversion will cost at least 25% of my energy. That’s rather a lot to be wasting just to transfer energy, especially if I charge the Li-Ion battery from the 12V lead acid battery. I could lose an hours computing time just in that process.
I’ll finalise the packlist (V1.0) in the next few days and post it up. I’m also planning to do a video overview of all the equipment I’m taking, a picture-set of the bike and the charging setup and as many other images as I have time to take. The 9-day forecast is looking OK (not perfect, but OK) and so I’m quite confident that the tour will start at some point next weekend.
May/075
Refining the Solar equipment. Li-Ion or Lead-Acid?
I’ve just had a nice conversation with my energy advisors, Select Solar, about some of the issues I’ve seen with the tests I’ve done so far. The main problem being that Li-Ion batteries will not trickle charge. They require a certain level of stable voltage/current before they start to charge and this wastes the possibility of charging a battery at lower sun power. In fact, on a hazy day or with light cloud cover, the sun power might not actually go above 70% and you have no chance to charge anything. This could be major problem and I’ve decided to try and address it.
A solution to this problem, as I mentioned before, is lead-acid batteries. These are the type you will find in your car and are a tried, tested, reliable and relatively cheap solution. The problem is that they are also extremely heavy – at least 400% of the weight for like-for-like power storage. They also operate at 12v which means voltage conversions (and more electronics and power-wastage) in order to operate the UMPC.
The decision I’ve made is to buy a 70W/hr 12v lead-acid battery (2200g) and to try and use this as a charge buffer. Here’s a little sketch of the planned set-up.
The idea would be that I connect devices to the lead-acid battery as the solar power increases during the day. For example, I might add a couple of AA batteries or my mobile phone in the morning. At mid morning I might replace it with the Li-On battery and during the peak hours I could re-attach the AA battery charger with 2 or 4 batteries depending on sun power.
Two problems I can see here:
- How do you know the charge on the lead-acid battery?
- Will the lead-acid battery be able to feed up to 1.5 Amps?
There’s only one way to find out. I’ve just put an order in for a 70W/hr lead acid battery and charge controller along with some fresh AA batteries, a powerbank tip adaptor for the Samsung Q1, a 12v charger for the mobile phone and something I’ve always wanted, a flexible USB LED-lamp!!!
Later today I will probably be ordering the solar panel. I won’t be using the P3 Panel as the only advantage with that was that it could drive 19V into the PowerBank. Now that I’m going for a 12V source solution I’m going to be looking at the 25W version of this Sunlinq panel which is the same price as the 15W version of the P3 panel. There’s a risk that its going to be too big for the bike at 1m long but even if I fold 25% of it away, its still going to give more power than the 15W panel and during mid-day pause and work sessions I hope to get the full 25W out of it.