Hi guys,
I need an idea for a clever and effecting setup. I would like to charge my Li-Ion battery packs with a few solar panels I bought.
The first plan was to connect my panels to my iMax charger B6 charger which accepts 11-18V input but this didn't work. The iMax is very voltage specific so whenever a short term under- or overvoltage occured the iMax stps charging.
So my question is: Do you have an idea for a cheap setup of an li-Ion charger which accepts ideally 8-30V max?
Thanks

Hi Happyguy,

well, where should I start... LiIon Batteries are not the easiest to charge, to begin with. Basically, LiIon accumulators are charged the same like a lead acid type. BUT: you need exactly 4.20V (pay atention to the 0 :), tolerance per cell is 0.5%) per cell. Per 01.V lower, you loose 10% of capacity. 0.1V over, and your cells are burning.
But the situation is not as bad as it might look right now. What I wrote is true for bare, unprotected cells, like the ones that are used in RC applications. If you got a self-protectet pac, then things are getting smoother:
just use a current-limiting resistor, a zener diode matching the maximum alowable voltage for your pack and hook both between your pack and the solar cells:

+--resistor--+----------+
p z ¦
a e b
n n a
e e t
l r ¦
+-------------+----------+

Now the probelm is, that you don't use the maximum aviable power from the sun (keyword/google search word: MPP tracker). So idealy (and if you know a little electronics), you use the following setup:

[PANEL]--[MPP-TACKER]--[VOLTAGELIMITER]--[LIION-BALANCER]--[BATTERYPACK]
(the balancer you only need if you use an unprotected battery pack).
The MPP-Tracker and voltage limiter, you can build with an arduino uno and some bird feed (resistors, capacitor, inductor, n-fet). If you like to, I can provide you with a bachelor thesis I shortly tutored, but it would be in german. but the schematics and source code are "international" :)

Regards, Edi

Could I get a copy of that? Also: Subscribed.
@Happyguy what cells did you buy?

Hi Edi, Prepperandflash,
@Edi - I would be very interested in the bachelor thesis, german is no problem. How can I send you a private message here at DX? I would like to avoid to post my email address publicly.

@Prepperandflash - Well actually I have a number of 18650 and some flatpack Li-Ion cells. Mostly Sony G7/G8, Panasonic, Samsung and Sanyo cells.
I am pulling them out of used notebook battery-packs.
Attention: This works only when you exactly know how to open these packs, so I do not recommend this as not everyone can do that safely.
After measuring the capacity and checking the fitness of the cells with the iMax I am building battery packs (mostly parallel cell setup). I am also using under/overvoltage protection circuits (eg SKU 26113) to protect these battery packs.
Attention: Whenever someone puts together such kind of battery pack, watch out: The combined cells must be carefully selected. It is NOT recommended to join random cells to a battery pack! Always use cells from same brand, capacity and about the same range of real (measured) capacity.

So far I have a solar charging setup using a DC-DC voltage step down circuit connected to my solar cells. I am feeding the 6V to my DSD charger (SKU 00936) then and charging the battery packs. I am achieving a charging currect of about 800-900mA with this setup. I would love to achieve a charging setup of at least 2 Ampere or some parallel setups to charge several battery packs.

Best
Happyguy

Subscribed.
Pretty interesting!

Well I'm looking for a fixed setup that can charge protected 18650's for my Fenix flashlight, and also charge an iPhone. And run some 12V lighting...

@Happyguy I think easiest will be if I put the thesis on some web space and publish the link here. You are lucky: they used 18650 cells from DX (my recomondation :)). Also the AVR microcontroller was ordered from here. Just give me some time, I am a little messy with my digital archives and I have to search the thesis...

@Prepperandflash: They use a setup with a intermediat DC link. So you can build it up until the intermediate and then use something like sku.47817 to provide 5V for the IPhone. Not quite sure, I think they even implemented a discrete 5V DCDC converter.

@all maybe we can design a low cost MPP solar tracker which DX can sell then :)

Regards, Edi

2A from solar panels, not an easy task...

After reading the first post the only question I have is how powerful is the solar panel? Oh, and what charge current on the iMAX B6 did you try charging them at? I agree with Sirius9 - 2A from solar panels, not an easy task... You're talking quite a large panel.

I would like to avoid to post my email address publicly.

And it's against forum rules anyway.

Well I have 4 panels with 20W each and two smaller panels with 5W each.
Voltages are 18V, 1.11A for the larger panels and 9V, 0.5A for the smaller panels.

The iMax B6 charging rate was 0.3A which worked for a couple of minutes... as long as there wasn't the smallest cloud passing by. When that happened the input voltage fluctuated and the iMax stopps shows the error "Input voltage error" and makes some beeps. Very anoying. I couldn't find an easy method to cover these voltage drops.
Still I was surprised that the iMax seems to consume quite a bit power itself as increasing the charging current to 0.4-1A let the iMax display flicker and it reboots.

My actual charging setup with the two smaller and one large panel gets the DC-DC step down + DSD charger working with the reported 0.8-0.9A. So my conclusion was/is that the iMax is ineffective despite its fancy display features (charging current rate, time and actual voltage) which I will miss for sure.
For the matter discussion the drawbacks of the iMax: One have also to start the iMax always manually. So you have to go through the iMax menu and start the charging process. This isn't smart at all as I would like to have a setup which starts charging with first sunshine without manual attention. End of charging and overvoltage controll is still covered by the protection PCBs.

Best,
Happyguy