Home charging station

[symon]

Hello,

my goal is to setup my own solar powered charging station for my smartphone/ipad/camera battery...
I gathered lot of information from Internet but I need your advice, perhaps I'm missing something...

Equipment:
3.4W solar panel (output 6V at 530 mA) with DC jack connector
Battery Li-on TeckNet iEP392 Dual-Port 12000mAh (input 5-12V, 2A (DC jack DC) and 2 usb output 5V 1A and 5V 2.1A)

I especially chose this battery because I don't need to build a charging circuit to protect against short circuit, over charge, over discharge, over current, over temperature, am I right? Moreover no conversion circuit so no loss of power, correct?

I think I only need to connect the solar panel to the battery, right?
Do I need to add a zener diod in any case?

[Bruce S]

Lets see if I can help as I have helped one of our recumbent travelers do something similar.
That unit is a very nice one! we have something similar here.
To charge that unit the very first time , it would be best to plug it into the wall, as even then it will take hours for it to fully charge.
On the solar panel(s) (AND YES you will need a diode to keep from draining it back into the panel), it will take a week, and that's provided you get 4 full hours of solar and the full 0.530A .
See, the battery is a 12Ahr battery and the panel is a 0.530A panel, to find how long it will take at full sun its 12/0.530. = 22+
Fully charge it the first time then use the panel to keep it charged.
YOU can however, use the panel to fully charge it, just  that you'll need to let it sit until charged. WE did use our without a full charge and it did not seem to bother it. It will take a few charges to get it to full capacity. We've yet to see the full 12Ahr ability, but when he can charge his phone a GPS with occasional camera batt and let it recharge  its okay.


The panel: If it's one of those that has the red LED to tell you its got enough sun to start charging stuff then you will not need a diode, the LED acts like the diode for you.

Hope this helps;
Bruce S

[Simen]

I disagree about the diode.
Since it is a Lithium battery with an integrated charge controller, it's not likely the power can go the wrong way.

But you asked about a ZENER diode...
That would be to protect the battery's charger from overvoltage from the solar panel. Have you measured the Open Voltage from the solar panel in full sun? If it exceeds the chargers max 12V input, you should add a 12V Zener.

Otherwise i'd agree with Bruce. I would have considered a second panel in parallel to reduce charge time, if you have the space and money.

[Bruce S]

From taking a closer look at the specs of that unit; you should have no problem with the solar panel.
The input shows to be 5v - 12v DC so the panels should be just fine. Will still take a bunch of days on that panel, but the blue lights can help you tell when it is charging  .

Cheers;
Bruce S

[OperaHouse]

I'd  look at some of those M2596 regulator / chargers on ebay.  One is sold with 3 pots and 3 LED that are set up for charging batteries.  I got one shipped to me for less than $4US.  I will also be working with the single pot version and modify it for power point operation.  These seem like an ideal controller for systems about 1 amp.

[JW]

I've done alot of work using both ziener and rectifier diodes, to clamp colapse voltage on inductors.

At one point I was useing a blue led to trigger the gate on a very large mosfet array.

The reason the blue led worked is because it operated at 4 volts dc, which was enough to trigger the gate. So I couldnt use a red or yellow led since they operate about 2 volts.

In the case with a solar panel wouldnt you need a rectifier diode, with a turn on voltage between 12 and 24 volts? If you did use the led as a rectifier diode, wouldnt a resister in series be needed and how would this affect power factor?

[symon]

Hello,

thanks all for your answers!
So here is the solar panel I intend to use: http://www.adafruit.com/products/500

I agree with you It'll take a long time to charge the 12Ahr battery so I'll probably buy another one to get ~1A in full sun.
Or perhaps I have to find a more powerful solar panel...and more expensive...

Since it is a Lithium battery with an integrated charge controller, it's not likely the power can go the wrong way.

I want to be sure my installation is safe, I've read many posts on lion batteries and it can be very dangerous 
The battery come with UK USB power adaptor so I don"t think there is a charge controller inside it, I can't find any specs. How can I verify all of this?

My first choice for the battery was this one: http://www.tecknetonline.co.uk/products/TeckNet-iEP389-10000mAh-External-Universal-Power-Bank.html
: No AC charger is included, but TeckNet iEP389 is compatible with original iPhone AC charger or Other 5V 500ma-1A USB Charger
So I thought the charge controller was builtin, what do you think?

[Simen]

Let's guesstimate a bit about the technical layout of your battery.

To deliver 5V reliable from LiIon batteries, one would normally need at least 6.5V. (I'm here assuming an older LM7805 type regulator are being used, but probably a newer, more efficient regulator are being used...) One type 18650 size LiIon battery delivers nominel 3.6V-3.7V, so two in series are needed. Six 18650 4000Ah cells in 3p2s configuration would give us 7.2V, 12000Ah, and fit nicely into the 108x105x23mm size of the battery pack.

Now, this battery pack are protected against over/undercharge etc., and to safely and properly charge LiIon cells in series, the charger has to have access to each cell in the series string to make sure each cell are balanced etc., and this would be hard with a 2-pin DC jack, since one need at least 3 wires for 2 cells in series.
So my guess would be that all charging and monitoring electronics are integrated inside the pack, and the wall-charger are just a dc power-supply.

This is my guess.

[symon]

fantastic explanation Simen! I just bought the battery 

Regarding the solar panel: one or two 6V 3.4W. In this case I won't need to add any extra circuit, right? It's a kind of plug'n play installation.

Let's imagine I buy a 20W solar panel like this one: http://www.amazon.com/Instapark%C2%AE-High-Efficiency-Mono-crystalline-Solar-Panel/dp/B004FX1192/ref=pd_sbs_lg_6/186-3676384-3901060
Maximum power voltage ( Vpm ) : 17.5V ;Maximum Power Current: 1.17A

In this case I'll need a circuit with a step down voltage regulator (18v/12V), correct?

[Simen]

Regarding your '6V solar panels'; from the pictures, i can count 12 cells, which should be at least 6.00-6,36V, which is perfect for your battery; just plug it in. (Just make sure the +/- from the solar plug match +/- on the battery. (A very common standard are + on the center pin and - at the sleeve...))

Note:
Your battery box MIGHT have a Current (ampere) limit at the input, so when ordering solar input, make sure you don't exceed that limit. It should state the limit in the manual... (I couldn't find the max charging current for your battery box in the specs on the net...)

And Yes; a solar panel that exceeds the max 12V input for your battery would need a circuit. Often called a Buck Converter. (The other way; converting lower voltage to an higher one, are often called a Boost Converter. )

There is, of course, much more to say of this subject, but i'm sure you'll manage to ask...

(Edit: Spelling) 

[Bruce S]

Last pic of this device on Amazon shows 5-12Vdc 2A, best to stay at or under this.
Your current one maxes out at 0.560 so that one is okay. IF you're going to jump higher with with 12V and stay under the 24Watt section , you'll be safer, but you could go a little higher to offset any lower outputs of the panel. Really depends on your pockets 
Cheers;
Bruce S 

[symon]

Hello,

I have received my battery (12000mAh, Input: 5-12VDC)  so I worked a bit on my project this weekend.

2 solutions to charge it:

1) buy two 6V 3.4W solar panel (550mA each), wire them to get max 1,1A@6VDC on sunny day and plug directly on the battery and it should work properly.

2) buy a 12V 20W solar panel:

Open Circuit Voltage: 21.4V 

Short Circuit Current: 1.32A 

Power Allowance Range: 5% 

Max Power Voltage: 16.94V 

Max System Current: 1.18A 

Max System Voltage: 300VDC 

Number of Cells: 36

with this solution I need a 'buck converter' to lower the voltage to 12VDC.
After some research I find out that a circuit based on a LM317T voltage regulator can help me.
It can handle max 1,5A with an input voltage from 1,5V to 36V.
If I use this solar panel as source power:
Vi is between 12V (nominal) to 16,94V (max)
Ci is between 0A (night) to 1,18A (max)
so (17V-12V )* 1,18 = 6W to dissipate, correct?
Vo will be 12V
Co will be 0A - 1,18A
I understand that this kind of regulator need an input voltage at least +3V than the output voltage so in my case 12V+3V=15V. 
So I should better use a low dropout regulator?
http://www.linear.com/product/LT1086

What do you think?

[wooferhound]

Careful not to charge your batteries too fast
In General, batteries like to be charged at 10% of their capacity
A 2000mah battery wants to be charged at 200ma

Battery chargers for little batteries are closer to a Current Limiter than a Voltage Regulator

[OperaHouse]

Buy a 20W panel and dissipate 6W in a regulator!  Save some money.  Buy an assembled LM 2596 regulator board for $3 and get a 10W panel.

[Simen]

DO NOT listen to Wooferhound, regarding charging... (He's still in the 'lead' age )
(Sorry Woof... )
Your battery pack have Lithium batteries inside, and even the lowest/oldest type of lithium batteries prefer at least 60%; or 0.6C charging current (of total Ah capacity)
That said, the charging electronics in your pack might set a limit to the current you might charge with... (Should be specified in your documentation...)

[Bruce S]

Your battery pack have Lithium batteries inside, and even the lowest/oldest type of lithium batteries prefer at least 60%; or 0.6C charging current (of total Ah capacity)
That said, the charging electronics in your pack might set a limit to the current you might charge with... (Should be specified in your documentation...)

What Simen said.
The picture on the side says 5 - 12Vdc 2A  so the internal BMS will hold it to what it wants 10W or 24W will do. Personally, depending on cost of 12V 20W panel I'd go with it so you can recover battery full quicker.
YMMV
Bruce S

[symon]

ok let's go for a 20W (not more expensive than 2x3.4W)

The picture on the side says 5 - 12Vdc 2A  so the internal BMS will hold it to what it wants 10W or 24W will do

So what do I need to regulate?

[Bruce S]

ok let's go for a 20W (not more expensive than 2x3.4W)

The picture on the side says 5 - 12Vdc 2A  so the internal BMS will hold it to what it wants 10W or 24W will do

So what do I need to regulate?

Nothing :-).
MAKE sure the panel has the correct plug for the input side of the battery and that it is the correct polarity; and you're all done.
The internal electronics of the battery BMS will take care of the rest.
Might come back with pics of the setup and a few records of how long it took to charge it from new to full.
Cheers;
Bruce S

 

[Simen]

You're sure he won't need a dc-dc downconverter, Bruce?

A standard '12V' panel have an output of around 20V...

[Bruce S]

You're sure he won't need a dc-dc downconverter, Bruce?

A standard '12V' panel have an output of around 20V...

Simen;
Yup I'm sure. the Vo is a relative number. I have a couple 20W polys that I'm testing for a neighbor and even though they show 21Vo when just putting a meter to them they quickly drop to about ~14V - 13V when plugged in. The BMS system for the Li based batteries are pretty robust, the ones built into the laptop batteries are what I'm using as a test bed for that panels, and I'm impressed.
What I've seen on the laptop batteries( the cool ones that have the little push button to tell power level) is that they go full 15Vdc then quickly ( 2mins for a empty battery) start stepping the voltage back down, in a complex Voltage controlled & Current controlled kind of algorithm.
It then stabilizes and does a tamper top off charge.
I was worried that the PV would be trying to push too much into the BMS, but it didn't evem seem to notice OR even get hot.
This was using a 12V 20W poly panel that is still siting. My cheapo 1 wire temp gauge on a $3 meter did not show any real temp rise either.
 

The big issue will be when his pack is fully charged and all that extra power is going nowhere :-(.
Since the pack has a LED indicator built in to tell when full, and IF it was mine, I would have a GHURD controller, plus some other rechargeables around to keep from wasting all that SOL power :-)

Hope that helps
Bruce S

[independent]

Hello a bit late to this conversation. I've been charging a li-ion battery through directly through a carefully calibrated LM2596 buck converter by gutting a external battery charger for the device I use (dealextreme) and putting my own one in.

The problems I've found in charging electronics not designed for solar is that as a cloud goes past and the voltage drops the electronics go into error mode and usually the device needs resetting every time this happens. Also, the current draw is not usually limited on the device and so without some sort of clamping (impedance matching the solar panel to the load) then it just doesn't work cloud or no cloud as soon as the current draw ramps up.