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Daox 08-24-19 12:05 PM

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I got my dc-dc converters last night. So, I printed up a little bracket for them. It went quick and easy and they fit great.

I started tinkering with them this morning. I started by connecting the dc-dc converters up to the battery bank with alligator clips. I then set the open circuit output voltage to 5V for the USB.

I was delightfully surprised that the dc-dc converter power draw with no load is a very low ~.35 mA. This will eliminate the need to switch them off and keep things simpler. It will loose .014 Ah per day with the two dc-dc converters hooked up. I think this is acceptable.

I also hooked up an old phone to the circuit. As expected, it started charging at about 5W.

However, when I plugged my newer phone into the charger it also charged at only 5W. I specifically got dc-dc converters that can handle more power output so I can charge at faster rates. So, I need to figure out what is required to activate the faster charging. If you guys have any info on this it would be much appreciated. :thumbup:

NiHaoMike 08-24-19 02:33 PM

You'll have to short the data lines to each other to signal fast charging and adjust the voltage to a bit above 5V, probably 5.2V or so would be ideal. Also, if you're putting USB-C sockets on the charger, the CC line pullup has to be 10k.

Daox 08-28-19 03:17 PM

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I had some sun today, so I worked on the charging system.

Here was the setup for today. The sun was come and go, but I did have a few periods of full sun.

I got things adjusted okayish. It definitely still needs some work. Under full sun I got the charge controller to charge at 2A. It was clearly capped at 2A as no adjustment would bring it higher than that.

Apparently there is a resistor that controls the max charge current. At 2A the charge controller transistor, inductor, and diode all got too hot to keep my finger on for more than a second or two. The ebay listing does say:
"Constant current charging current is set by external resistor Default 2A (3A / 4A / 5A)"
"If the charging current is greater than 2A, it is recommended to attach the heat sink on a good aluminum or heat sink installed!"

They weren't kidding. :) So, I would love some suggestions on how to do that. I'm not familiar with how you slap heat sinks on chips. I assume there is some sort of thermal paste / glue that you can use. Suggestions are welcome.

ThomSjay 08-29-19 12:17 AM

How-to video to apply tape...

Links to possible tapes. 12mm is approximately 1/2", and 25mm is about 1"

Daox 08-29-19 09:13 AM

Tape! That sounds easier than glue. I didn't even know there was such a thing. Thanks!

As for how to go about things. Is it better practice to make individual heat sinks, or one larger one? The diode and transistor are the same height, so I could combine that heatsink. But the inductor is higher, so it will need it's own anyways.

I also checked out the datasheet for the charge controller chip. It says "In constant current charge mode, the charge current is set by the external sense resistor Rcs and an internal 200mV reference, so the charge current equals to 200mV / Rcs." I traced the pin and it looks like that big R100 resistor is our Rcs. 200/100=2 so that makes sense. I'll need to replace it with a 40 ohm resistor to get the full 5A out of it. However, I am hesitant to go the full 5A because of how hot it is already getting. Should I be concerned, or is it okay to have things run that hot?

ThomSjay 08-29-19 10:49 AM

For simplicity's sake, I would use one larger heatsink, but, make sure that it is large enough (too large is never a problem....unless there are size constraints:) )

As far as heat goes, I have read that 60 degreesC, maybe 70, is about as high as one wants to go for a Raspberry Pi when overclocking. I think the same would hold for most electronics.

Daox 09-03-19 09:39 AM

I have been using the power bank as is for a few days now. I really haven't been monitoring the battery voltage or anything. It has been charging at 2A or less during the day, and charging my phone up at night. With the current settings it actually requires very little light to start charging the pack which I think is very cool. I haven't measured amperage at low light but I can only imagine it's quite low. I just grabbed another multimeter so I can look at amperage and voltage at the same time. It will be interesting to see how it does.

I also got my LED bar graph circuit kits this weekend. I assembled one and it seems to work. However, I can not seem to get it working the way I would like. It is supposed to have two modes; bar and dot mode. Bar lights up multiple lights, and dot only one. I can seem to only get it working in dot mode. This works, but is not what I was hoping for. I also have yet to adjust the circuit to the correct minimum and maximum voltages.

Daox 09-16-19 10:21 AM

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I am continuing on with the LED bar graph not working the way I'd like. I added a symbol on the faceplate to indicate what side is charged vs discharged.

So, I printed up a new faceplate and mounting piece for the LED gauge. It looks like it'll work out pretty well.

Daox 10-31-19 08:41 AM

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I got back to tinkering with this project the other day. I changed up the face too plate a little. I like it a bit more.

I still need to set the charge controller correctly. I overcharged the pack the other day to just over 4V. Lifepo4 is not supposed to be charged that high. I'm thinking I should hook up the dc-dc converters to some power supply and tweak it that way. I also have to swap out the resistor so it can charge at 5A vs 2A.

Daox 11-30-19 04:49 PM

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Disaster strikes! I told my wife she could use the battery bank, so she did. But, I didn't recharge it because I wanted to monitor the high voltage settings on the charge controller.... The DC-DC converters claimed to have a low voltage disconnect built it, but there was no adjustment so I kind of doubt that... In any case, my cells got overdischarged and puffed up sadly. :( As of now, this project is as dead as my batteries!

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