DIY Solar tablet charger?

[TirNaNog]

I'd like to make myself a decent solar charger for my tablet. I'd like to build it into an A4 sized folder. I'm thinking about 10 of these in parallel will give me around 800mA at peak which should be good for charging on the go.

http://www.dealextreme.com/p/0-44w-s...-5v-80ma-12988

So a Q for the electronics fundis - I assume I need more than just solar panels to do the charging - like something to regulate the output to some degree. I'm not sure if the tablet itself can handle the charge cut-out to prevent overcharging or if I need something like that on the panel side too?

Thanks in advance!

[FlatspinZA]

I am not an electrician, or electronics expert, but I think you're pushing the envelope hoping for 800W on 8 x A4 solar panels. I stand to be corrected.

[TirNaNog]

I am not an electrician, or electronics expert, but I think you're pushing the envelope hoping for 800W on 8 x A4 solar panels. I stand to be corrected.

No, it's A4 total and they're rated at 80ma each and I was thinking 10 of them in parallel - perhaps that's incorrect?

Here's another - 4 of these should produce 6v 800mA at peak if I'm not mistaken. Total size 220x190 roughly.
http://www.dealextreme.com/p/solar-p...6v-200ma-18168

[FlatspinZA]

It can never be the size of an A4 given your first option when you're already looking at 10cm x 4cm on one panel?

[Robertvv]

Do you use a regulator as well.

[Rudimental]

[Tacet]

No, it's A4 total and they're rated at 80ma each and I was thinking 10 of them in parallel - perhaps that's incorrect?

Here's another - 4 of these should produce 6v 800ma at peak if I'm not mistaken. Total size 220x190 roughly.
http://www.dealextreme.com/p/solar-p...6v-200ma-18168

Try using proper units - mA, rather than ma, and V rather than V. This sounds silly, but is actually quite important in a technical discussion to avoid making a fool of yourself by claiming 800 W from an A4 sized panel. An A4 sized panel will give you roughly 15 W.

If you put four of those 6 V, 200 mA panels in parallel, you could get 6 V, 800 mA. That is 4.8 W, a far cry from 800 W.

You'll basically need a voltage regulator to make sure that you supply exactly whatever your charger wants. I would also suggest a circuit to cut off the solar system whenever it can't give sufficient charge. You don't know how intelligent your charger is, and for some batteries a charger running low can cause problems. The charger should handle the overcharging cut out - you don't always take the power off the moment it is fully charged, do you?

Oh, and remember that you'll get losses in your regulating circuit, and that you're unlikely to get good sunshine for more than a few hours per day. If your panels can supply 4.8 W under ideal conditions, you're not going to see 4.8 W onto the charger ever.

[TirNaNog]

Try using proper units - mA, rather than ma, and V rather than V. This sounds silly, but is actually quite important in a technical discussion to avoid making a fool of yourself by claiming 800 W from an A4 sized panel. An A4 sized panel will give you roughly 15 W.

I'm quite prepared to make a fool of myself to get the details I want - that 800W was a typo - 800mA is what I meant, thanks for pointing it out.

If you put four of those 6 V, 200 mA panels in parallel, you could get 6 V, 800 mA. That is 4.8 W, a far cry from 800 W.

Good logic. As above

You'll basically need a voltage regulator to make sure that you supply exactly whatever your charger wants. I would also suggest a circuit to cut off the solar system whenever it can't give sufficient charge. You don't know how intelligent your charger is, and for some batteries a charger running low can cause problems. The charger should handle the overcharging cut out - you don't always take the power off the moment it is fully charged, do you?

No I dont, it works off regular USB or an equivallent charger which probably uses a PWM of sorts.
I'm deciding between a pre-assembled PWM charge controller or DIY using an LM312T to control the current. I'm not sure if it offers cutoff for low input.

Oh, and remember that you'll get losses in your regulating circuit, and that you're unlikely to get good sunshine for more than a few hours per day. If your panels can supply 4.8 W under ideal conditions, you're not going to see 4.8 W onto the charger ever.

True, I'm charging an eink device that has a battery life of up to 2 months without Wifi usage so it should be adequate.

[nevadayz]

Depending on how clues up you are , the best type of regulator to use would be a buck-boost regulator , it can step down high peak voltages and stepup low voltages.
These are available in a normal DIP chip, and fairly inexpensive, but they also need some power, either 3.3/5V .
Google around a bit and check instructables.com , they have lot of diy projects and you might fond something close to what you want.
Also for components, try Mantech , think they based somewhere in jhb.

Happy Soldering

[TirNaNog]

Depending on how clues up you are , the best type of regulator to use would be a buck-boost regulator , it can step down high peak voltages and stepup low voltages.
These are available in a normal DIP chip, and fairly inexpensive, but they also need some power, either 3.3/5V .
Google around a bit and check instructables.com , they have lot of diy projects and you might fond something close to what you want.
Also for components, try Mantech , think they based somewhere in jhb.

Happy Soldering

Cool, I'll look out for something. Mantech are awesome, I've got plenty of free samples from them in the past for other projects.

[Yotch]

Have you had a good look at the Dealextreme site? They might have something suitable. It's not usually cost effective to build something these days unless you really need to.
http://www.dealextreme.com/p/1800mah...-gadgets-26720
http://www.dealextreme.com/p/12000ma...rs-white-70713
http://www.dealextreme.com/p/dual-po...-adapters-4799
http://www.dealextreme.com/p/solar-p...-adapters-4813
http://www.dealextreme.com/p/solar-p...ed-light-42139
http://www.dealextreme.com/p/4200mah...-gadgets-40210

[Tacet]

True, I'm charging an eink device that has a battery life of up to 2 months without Wifi usage so it should be adequate.

If you're using USB as power input, then you at least know the worst-case scenario power draw: 1 A at 5 V. I have a little 15 W panel at home which is slightly longer, but also slightly thinner than A4. You should be able to get something that gives you enough power in A4 size to design for 5 W effective output power. Add a USB receptacle (spelling?) to that, and you can build a fairly universal charger.

[TirNaNog]

If you're using USB as power input, then you at least know the worst-case scenario power draw: 1 A at 5 V. I have a little 15 W panel at home which is slightly longer, but also slightly thinner than A4. You should be able to get something that gives you enough power in A4 size to design for 5 W effective output power. Add a USB receptacle (spelling?) to that, and you can build a fairly universal charger.

Yeah, that's kind of what I had in mind. The idea of multiple panels is pointless if I can find something suitable in near A4 size in a single panel. Where did you get that one from? Of course the major headache is the undervolt cutoff and charge regulator - Perhaps I should look at bastardising a regular Nokia charger (same rating as the eink charger). I'm just not sure if the intelligence to prevent overcharging is all in the charger or in the device itself (Nook touch).

[TirNaNog]

Have you had a good look at the Dealextreme site? They might have something suitable. It's not usually cost effective to build something these days unless you really need to.
http://www.dealextreme.com/p/1800mah...-gadgets-26720
http://www.dealextreme.com/p/12000ma...rs-white-70713
http://www.dealextreme.com/p/dual-po...-adapters-4799
http://www.dealextreme.com/p/solar-p...-adapters-4813
http://www.dealextreme.com/p/solar-p...ed-light-42139
http://www.dealextreme.com/p/4200mah...-gadgets-40210

Nice ideas but the reason I want to DIY is because it seems I can't get what I need without going bulky. I'm building the charger into the device's folder - something like this:
http://www.instablogsimages.com/1/20...ipad_lz6zo.jpg
Now I'd consider that except it's designed for iPad which is different size / dimensions. Also, these things have batteries that they charge independently of the device - kind of pointless IMO except that I guess it's easier to regulate the power from batteries than from a solar panel and in the event of issues with the solar output at least the external batteries take a knock and not the more expensive device.

Having said that, I don't see why I shouldn't be able to build a safe and reliable circuit for charging my device directly from the sun and I like a challenge

[nevadayz]

+1 for your attitude, you'll get it done..