Author Topic: Ruggedized Solar USB charger  (Read 1846 times)

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Offline HDL_CinC_DragonTopic starter

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Ruggedized Solar USB charger
« on: March 09, 2011, 02:46:04 PM »
I need to build a ruggedized solar powered battery charger. It needs to be able to charge any standard USB device plugged into it such as handheld camera, cell phone, iPod, etc.
Heres what Im thinking I'll need for the meat and potatoes of the thing:
Rugged case: Pelican 1030 case (Already have. Solarcell and regulator circuit should all fit within just the lid nicely. The device being charged can be stored/protected in the case with it)
Photovoltaic: Parallax 6v 1W Solar Cell 750-00030
VREG: Radioshack 7805(Conveniently same as the $50 robots board)
12v .1uF Electrolytic capacitor (To filter any potential noise)
2 Diodes(because im paranoid) to ensure current doesnt flow in the wrong direction
USB port (Recovered from an old PC motherboard)

.:Charging indicator:.
LED
Resistor calculated to supply proper current

I drummed up a quick schematic in Eagle Lite to show what Im thinking as far as my circuit goes. You can kinda ignore the values I entered in for the resistor on the LED path. Im going to see what LEDs I have available to me at home before I pick a resistor of proper value

P.S. Its been just over a year since Ive been able to tinker around with my electronics so Im sure theres a few things ive forgotten or something I did that was just plain a dumb idea or w/e. Thats the main purpose of my posting this here. Any thoughts on fixes and improvements would be highly appreciated
« Last Edit: March 09, 2011, 02:50:00 PM by HDL_CinC_Dragon »
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Offline Soeren

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Re: Ruggedized Solar USB charger
« Reply #1 on: March 09, 2011, 09:30:45 PM »
Hi,

I need to build a ruggedized solar powered battery charger. It needs to be able to charge any standard USB device plugged into it such as handheld camera, cell phone, iPod, etc.
So, you just need a 5V out?


Any thoughts on fixes and improvements would be highly appreciated
The 7805 has to go, as it needs around 8V on the input. You need an LDO regulator.
When you have that, move D2 to the ground connection of the regulator (forward biased) to get 5V at the right side of D1 - I'm not sure how an LDO will deal with that though.
Use Schottky diodes for a lower loss (compared to plain silicium diodes)
Use around 22µF for C1 (consult the data sheet of the LDO for exact value) and use 100..200nF at the regulator input.

The best way would be a SEPIC, a Ćuk or a Buck/Boost converter, as the solar panel will provide it's best only at max sun in the correct angle (and kept as cool as possible etc.).

Although the text for the panel claims 1W, it sounds a bit small for a 1W solar panel and there's a lot of sellers that simply multiply the unloaded max. voltage with the short circuit current to get to very optimistic numbers (plain fraud if you ask me). I cannot make any claims as to how it is with that particular panel, as I haven't seen it, but to compare, I have a high quality panel that gives 1W and it is 300mm x 100mm.

All that aside, if you don't wanna chase maximums and always have plenty of sun, a Schottky diode is all the circuit you really need, as modern phones etc. have got their own charge circuits and will charge from anything from around 4.5V to 5,5V (or slightly higher).

Just don't count on it as your sole charger, as Lithium based batteries really ought to get a larger charge current.
Regards,
Søren

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Offline HDL_CinC_DragonTopic starter

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Re: Ruggedized Solar USB charger
« Reply #2 on: March 09, 2011, 10:14:19 PM »
Thanks for the reply Soeren. I completely forgot about LDO VREGs :-[ It really has been a long time since ive messed with this stuff! Unfortunately having batteries isnt going to be something ill be able to manage often. My unit is going on a combat deployment in about 18 days and this thing is going to supply pretty much a whole platoon plus sized element with the ability to charge an iPod or w/e we manage to be able to have. Ill make those changes to the schematic tomorrow and update everything as per spec. Thanks again Soeren!
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Offline Soeren

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Re: Ruggedized Solar USB charger
« Reply #3 on: March 10, 2011, 06:32:20 PM »
Hi,

Unfortunately having batteries isnt going to be something ill be able to manage often.
Meaning ???


My unit is going on a combat deployment in about 18 days and this thing is going to supply pretty much a whole platoon plus sized element with the ability to charge an iPod or w/e we manage to be able to have.
Assuming this panel do give 167mA, it still isn't much for an entire platoon.
You could buy more than one panel, stack them in your box and break them out when you need to charge - that would give you a higher charge current, but will be more cumbersome to use of course.


A wind-up charger made from a stepper motor would be smaller (although a bit heavier) in the back pack, you could all take tours charging and you can use it on rainy days and at night.
Regulating it for charging is easy.


Depending on how long you are out there (wherever), a setup with 4 primary D-cells goes a long way too (and spares are easy to come by) and it's my understanding that 6V lantern batteries are easy to get by in the US.
D-cells or lantern batteries should last a good number of charges, perhaps with a diode to cut a bit of voltage at first and that could be bridged out by a switch when voltage falls.
I used a 2 x D-cell setup for a Walkman back in the eighties and had very good results, but that was feeding directly - not charging anything.

Not knowing the size of your platoon, but if each guy carries a single D-cell, except for the guy carrying the battery holder/diode/switch setup, you should have a substantial number of canned charges. Just be sure to get alkaline cells (rather than carbon/zinc).
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
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Offline HDL_CinC_DragonTopic starter

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Re: Ruggedized Solar USB charger
« Reply #4 on: March 10, 2011, 08:34:54 PM »
Were going to be gone for 11 months and most of those 11 months will most likely be without easy access to batteries(eg. in the middle of a desert). I was indeed thinking of making a hand crank generator in addition to the solar one though. I was thinking of having this solar one and adding 2 terminals that I could wire a standard battery to with a switch that selects between the two different power sources. If the solar cell does give 167mA, it should be just enough to charge a handheld device in decent lighting conditions. As much as I like the idea of having batteries to charge these devices, its not a reliably feasible idea in this particular situation.

Changes to the schematic:
New LDO VREG: SPX29150
Added a wheatstone bridge to the data pins because the newer iPhones apparently set their charging rate based on voltage accross the data pins.(Scroll literally all the way to the bottom) I will most likely have to change the values of the resistors to alter the charge rate making it lower...
Added proper capacitors on the VREGs legs as per the datasheet for the VREG
Moved D2 to the leg of the VREGs ground connection as per Soerens wisdom

-EDIT-
Forgot to add the schematic
-EDIT again-
Forgot to add the junctions showing which joints were connections and which were not connected
« Last Edit: March 10, 2011, 09:28:43 PM by HDL_CinC_Dragon »
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Offline Ro-Bot-X

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Re: Ruggedized Solar USB charger
« Reply #5 on: March 11, 2011, 06:16:15 AM »
I know you want to build one because you can. But sometimes it's easier to just get what it is already available. Here is a list of solar chargers with built in rechargeable batteries for phones, mp3, etc. I bought from these guys before and they are not scammers.

http://www.sinadeal.com/cheap-wholesale/solar-charger/
Check out the uBotino robot controller!

Offline Soeren

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Re: Ruggedized Solar USB charger
« Reply #6 on: March 11, 2011, 09:09:40 AM »
Hi,


Were going to be gone for 11 months and most of those 11 months will most likely be without [...]
-EDIT-
Forgot to add the schematic
-EDIT again-
Forgot to add the junctions showing which joints were connections and which were not connected
I have to prepare for going out to dinner (since it's my Bday tomorrow), so in a hurry now, but will look at it when I return tonight.
Is it possible you could post the Eagle files? (makes it easier to show you changes I'd make).

Before I read Ro-Bot-X's answer, I had meant to tell you to use two panels and 3 cell lithium as a buffer - then you can have a higher charge current on the devices you connect and it can charge all day in the dessert. I'd still think a home made unit gives you a better chance of repair if somethings go wrong with it when you're away from shop.

Apart from that... Wouldn't you have vehicles with either 12V or 24V batteries that you could charge from?
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline HDL_CinC_DragonTopic starter

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Re: Ruggedized Solar USB charger
« Reply #7 on: March 11, 2011, 05:50:41 PM »
@Ro-Bot-X: Those are some pretty sweet and cheap products! But I wouldnt trust them to not get completely destroyed in the environment we are going to be in. The main reason im building it myself is because I know how strong the device will be and am very confident its not going to shatter into a million tiny pieces at any point during the deployment. It also has to be water proof to a decent extent. Hence the pelican case. Crush resistant and water proof enough to work.

@Soeren: Ill post up the EAGLE files for you. We wont always have access to vehicles either. Because of what we do and where we go, vehicles will often become too much of a liability and can actually hinder our missions. There will be periods of a couple weeks straight where we cannot get so much as a food supply drop in some areas.

In the interest of time I had to cheat a little bit on my first solar charger though. I had an old battery powered phone charger that used 2 AA batteries to charge a phone. It wont work with 6v (I hooked up 6v volts from batteries and tried it but it wouldnt charge my phone) so i ordered two 3v solar cells and will wire them in parallel and solder their leads where the battery terminals were. The circuit is also tiny, taking up the foot print of a quarter. Im assuming the circuit makes a square wave and steps it up using what looks like it could be a mini transformer smaller than an M&M on the little PCB. Im going to be using that one on my first build and then probably build another solar charger from scratch as per this project
« Last Edit: March 11, 2011, 05:52:06 PM by HDL_CinC_Dragon »
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Offline Soeren

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Re: Ruggedized Solar USB charger
« Reply #8 on: March 11, 2011, 11:46:17 PM »
Hi,


First off, in Eagle, use Draw->Net rather than Draw->Wire, or just press this button when you wire up a schematic, then you get the junctions needed and don't have to manually dot out the schematic afterwards, possibly forgetting some.


In the interest of time I had to cheat a little bit on my first solar charger though. I had an old battery powered phone charger that used 2 AA batteries to charge a phone. It wont work with 6v (I hooked up 6v volts from batteries and tried it but it wouldnt charge my phone)

Did it survive?

I have a couple of different makes of a cylindrical charger that use a single AA and while they're good for emergencies, they're not that efficient in getting all the juice out of a cell and/or conversion efficiency isn't something to brag about - never got around to testing them... Yet.

I guess a 3V version might do better.


Im going to be using that one on my first build and then probably build another solar charger from scratch as per this project

Too bad you don't have more time, as a SEPIC converter would be ace here.

Anyway, I rearranged a bit on the schematic and added a "too high input voltage" LED that would be prudent if you make a crank genny, as I imagine some people will just see how fast they can go  ;D
It kicks in at close to 14V and at 16V the LED would see around 45mA.
I decreased the LED current in the other LED. Since it's just an indicator, there's no reason to burn too much of the hard earned current in a LED. A black tube around it may help in sunlight and at night, it won't be that strong a beacon for snipers.

I made a PCB as an example as well. The Schottky diodes aren't as large as they looks, I just took a symbol that had width and length to work.
The mounting holes probably don't fit your box, so it'll be better to mount the PCB on some foam or similar - never just mount a PCB with screws in 4 corners. Under vibrating conditions, it behaves like fire fighters holding a sheet for catching people - very elastic... And the possible death of components by physical breaking off.
RTV silicone "strings" bonding the components that doesn't heat up to the board helps too.

The revised schematic and example board layout.

Look at it and we can discuss what you might wanna change.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline HDL_CinC_DragonTopic starter

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Re: Ruggedized Solar USB charger
« Reply #9 on: March 13, 2011, 04:52:44 PM »
Ah ok, ill use nets from now on. Thanks for the tip ;)

And yes the little circuit board survived a 6v source but it wouldnt let it charge the device. I hooked 3v back up to it and it began charging.

I really wish I had more time, but even more than that I wish I had access to my work bench >_< where im stationed right now, ive been 730+ miles away from all my electronics for just over a year now >_< If were lucky, ill get a few days of leave before we deploy and Ill get to go home for a little bit and maybe work on some stuff.

And you are definitely right. They would without a doubt see how fast they could go haha. Unfortunately they would also see if they could make the LED explode so I dont think the LED will help in too many situations :P :P Ill have to rig an old fashioned governor up to it :P (James Watt was a genius for such a simple design)

The schematic looks great! I dont think theres anything else Id change on it. In the board layout though, I think the two outer power pins got switched around... unless im just being retarded lol... but im fairly certain they got switched around......... mind looking at that for me before I accidentally hurt myself by staring at it too long? lol

-EDIT-
Oh and putting LED2 on the wrong side of the diode was such a dumb mistake! >_< The worst part is I was looking at that knowing the LED would illuminate using the USB device as a source if the current wasnt there for charging it and wondered what I needed to do to prevent that... I really am retarded sometimes... I seriously need to get some quality time with my workbench again :(
« Last Edit: March 13, 2011, 05:51:53 PM by HDL_CinC_Dragon »
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Offline Soeren

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Re: Ruggedized Solar USB charger
« Reply #10 on: March 14, 2011, 02:21:12 PM »
Hi,

In the board layout though, I think the two outer power pins got switched around... unless im just being retarded lol... but im fairly certain they got switched around......... mind looking at that for me before I accidentally hurt myself by staring at it too long? lol
Not sure which you're talking about?
Is it the USB power pins?
Going from the schematic to the PCB won't swap anything, so they are consistent.

If it's the input, you're correct (I just did that to make the wiring more tidy), but this is just a switch and you can swap them freely.


I seriously need to get some quality time with my workbench again :(
Yes, it's hard to be away from the good stuff :)
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

 


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