DIY Charger - Possible Project

I bought a Litokala 500 engineer from Alibaba for $14 shipped, taking one of them apart might be instructive. The insides of one of the USB doctor measurement devices might be useful too.

i ll check back in 3 months if the project is still going strong.
i will be off on Xmas season vacation until mid January, enjoying ski trip with family and friends.

have phun :person_facepalming:

bye.

I ordered two LTC4015E samples. (commercial temp range)

Time to get on with block diagrams and Rev. 0 schematic.

I may need to update Eagle on my machine. I own a paid license.

Good idea. I’ve got an Lii-500 on the way :slight_smile:

I’ll open it up and post in this thread. That may not happen until after Christmas or it could be next week. Shipping from China is unpredictable.

Any suggestions on form factor?

My initial thoughts are 100mm x 100mm 2 layer to hit the $5.00 for 10 deal at PCBWay. 4 layers takes the price to $49.00 Still a bargain.

OR

Arduino shield.

OR

suggestions?

They are also running an $88 for 10 PCBA deal. That puts the impossible to DIY TI and On Semi parts back into the running.

I generally use Eagle early in the design process to get a rough schematic and block diagram. Eagle is a bit quirky but works better than any freeware I’ve tried. I also use LTSpice to simulate parts or all of a project. I don’t much care for the schematic capture in LTSpice. I often use Eagle to get my ideas down and then go on to simulations.

Cadsoft GMBH sold out to Autodesk last year. :cry: My Cadsoft EAGLE 7.4.0 doesn’t play nice with MacOS 10.12. :disappointed: I’ve installed Autodesk Eagle 8.4.3. I’ll need read up on what’s new and then merge my device library.

EAGLE 8.4 includes spice. I may stop using LTSpice and do capture and simulation in Eagle.

For those following along, here is the product page:

There are plenty of tutorials on YouTube and now support from Autodesk.

Eagle runs on Windows, MacOS and Linux.

Subbed and following this thread.

Are you making these to sell? Will you be sharing your Eagle files here? If you’re not doing this as a community shared project, then do whatever works best for you. If you ARE going to share the files, then it might be nice to keep in mind OSH Park pricing as well, which is $5 per square inch with free shipping for three copies on all 2-layer boards. A lot of members here use Eagle, and also OSH Park. With that fixed pricing, the smaller the design is, the better.

Probably not. I don’t want to string anyone along. I’m doing this in my spare time.

If I get as far as having boards made, I’m open to selling extras at cost. I live in Wales. Postage to the US is going to be a few £’s.

I’ve been satisfied with PCBWay and haven’t looked elsewhere.

I’ll keep OSH park in mind. I’ve never used them. At a minimum I’ll check against their design rules.

Absolutely YES. I’ll also share my bill of materials.

Thinking about including this optional module in the project. Stay tuned.

I would consider a PCBA (assembly) group buy for a bare board with sub-mm pitch parts installed. The LTC4015 is QFN38.

I need to get a rough schematic / block diagram up.

I opened up my Lii-402. They sanded off the numbers.

Almost blank sheet of paper. I’ll make the untested LTC4015 library available if anyone wants it.

Mine arrived yesterday. They sanded most of the part numbers… I’m not going to post any images. There are a couple of videos on YouTube if you are curious.

It is about what you would expect. A micro controller for the display board and another one on the mother board. There are a few power transistors and chokes. The USB power out circuit is at the top by the jacks.

LTC4015E arrived. I’m working on the design. Stay tuned.

…maybe downscale your pictures:

Thanks for that. I didn’t know the syntax.

I use a 27” display, and sometimes forget to scale.

:+1:

You can make it clickable too, linking to full size:

(opens in new tab)

I made two design choices yesterday. Both are open for discussion. It is easy enough to undo this early in the design.

The LTC4015 can reduce charge current if Vin drops below a hardware set threshold. Typical use would be when Vin also powers a device. If the device starts drawing more power, the charger will throttle back. In this application, it would be used if we program a current that is too big for the power supply.

I decided not to implement under voltage current limiting. I will leave it up to the end user to source a suitable power supply. Leaving it out simplifies the board.

Cell count is set in hardware by three pins. The LTC4015 does not monitor individual cells and cannot balance a series string. I’m leaning towards hard wiring this to one cell only.

The other option would be to tie Cells 2 low with jumper selection on Cells 0 and 1. That would allow 1,2,3…6 all the way to 9 cells in series. 3 and 6 would be for 6 and 12V lead acid. If I do that, I’ll design for 15 or 20V Vin Max and 8A I charge max. The higher current would make this more useful for Pb batteries.

Thoughts?

One more thing about jumpers:

The optimal size of the inductor depends on the charge voltage and current. An inductor sized for 13.8v 8A is non-optimal for charging to 4.2V.

Even if I put in cell and chemistry jumpers I will optimise for 4.2V 4A.

The switching frequency is adjustable between 200kHz and 1MHz. The reference designs switch at 500kHz.

The AM broadcast band starts at 520kHz. 500kHz is the upper range I’m going to consider. Anything higher means I need to worry about interfering.

Here in the UK and EU, we also have AM Long Wave from about 148kHz to 283kHz. Many AM radios use 455kHz IF. I don’t want that either.

That leaves me with 300kHz - 430kHz and 480 - 500. Aiming for 500 could end up with at 525kHz or even a bit higher.

525kHz isn’t a problem in the UK.

*F = 47.65/Rt
*

Where F is in MHz.

Trying some standard 1% resistor values:

93.1k = 512kHz Too high. Worst case will be around 540
95.3k = 500kHz
97.6k = 488kHz
100k = 476kHz :slight_smile:
102k = 467kHz
105k = 453kHz
107k
110k = 433kHz