Charging those 18650 cells---without blowing things up - Page 1
Forum section: electronics / projects

author: qrper
author_rank: Contributor
timestamp: April 27, 2017, 04:52:24 pm
content: Gang...Many projects going on, and one that I've been kicking around is a small battery bank made up of series/parallel 18650 cells.I've been doing research and know that I'll need to balance the cells, not charge them over 4.2 V, or discharge them under 3.0 or so.What I haven't seen is a constant current charging circuit.The words 'simple, safe, and Li-ion' should never been used in the same sentence.So I've been looking for a single IC that will charge 18650 cells (li-ion) when configured as 3S6P. I can find single cell charger ICs, but not so much multi-cells. The ones that I do find are solder ball footprints, something I can't deal with.Yes, I know about the TP4056, and ebay has them by the thousands. I've seen BMS and protection circuits as so on.And yes, I know you can buy a charger that will do the 3S6P configuration, but that's not what I want. I somehow suspect those china chargers aren't what they claim to be.So, any one up for some ideasMike

author: mrjoda
author_rank: Regular Contributor
timestamp: April 27, 2017, 05:14:35 pm
content: check this. Maybe you can find somethink interestinghttp://cds.linear.com/docs/en/solutions-manual/Linear-Battery-Charger-Brochure-2016.pdfhttps://www.intersil.com/content/dam/Intersil/documents/an13/an1333.pdfhttp://www.ti.com/lit/an/slaa478/slaa478.pdfi want to design cell managment for 5S bateries and use it as replace in Hilti drill but.... no chance to find time for this.

author: IanJ
author_rank: Unknown
timestamp: April 27, 2017, 05:54:56 pm
content: Hi,I use the MAX1873 (16-pin QSOP) Lion charger IC in my Precision Voltage Source.......will do 2, 3 & 4S (unbalanced setup).Nice thing is it acts standalone but will also allow some external control & monitoring. I use it in a 4S1P config.For the extra safety I use batteries with the protection circuit built-in.........the idea being that if a cell goes bad/weak then the other cells won't have to deal with the increased voltage because the protection in the other good cells will cut in and go open circuit and the MAX1873 cuts out. Without this you can have accidents! I tested this with a weak cell and it's great to see the charging shutdown.I also have the uC monitor the charge current (an output from the IC) and can cut the charging if it goes over a setpoint.On top of that, as well as setting up the charge current on the IC you can also set up the incoming power max current.......so if all goes wrong your incoming current to the whole product is limited.Ian.

author: Seekonk
author_rank: Super Contributor
timestamp: April 27, 2017, 06:54:16 pm
content: Just more China bashing regurgitation parroted from people who don't know what they are talking about. I buy those TP065 boards ten at a time and have not had any problem with them. Far better than something you will build. If you are smart you will use at least a half ohm resistor in series with input power.

author: suicidaleggroll
author_rank: Super Contributor
timestamp: April 27, 2017, 07:02:19 pm
content: FYI - While it's not a single chip solution, you can add a small MCU, current monitor, and DAC to a typical DC/DC converter to make it follow any CC/CV charging profile you like. Add the DAC and a series resistor into the DC/DC converter's feedback network to control output voltage, and have the MCU gradually step it up to maintain your desired charging current until you hit the float voltage. It's more complicated than the single chip solution you asked for, but it's incredibly flexible and scalable to other battery configurations and chemistries.

author: ebclr
author_rank: Super Contributor
timestamp: April 28, 2017, 05:02:59 am
content: TP4056 simple work'sWhy people are so xenophobic, just because is made in china does not mean is low quality or don't work, China have all class of goods, high end, bad quality, fake, used, new you can't define all as same group, this is simply not true, People who blame china things are not so well informed, fly to there and stay a while there than you can differ who is who

author: vealmike
author_rank: Regular Contributor
timestamp: April 28, 2017, 06:51:52 am
content: The 6P is irrelevant.Firstly you need to consider your battery protection circuit. You'll need under voltage, over voltage and possibly over current protection. Cell balancing would be wise.The exact voltages that your cut offs kick in will depend on your chemistry. All Li-ions are not the same.Consider one S8253 , three S8209 and five transitors (two power, three balancing)http://www.sii-ic.com/en/semicon/products/power-management-ic/lithium-ion-battery-protection-ic/Once you have worked out where your safety cut offs sit, you can design your charger. You don't need a constant current charger. You need constant current/ constant voltage.If you have a micro to drive your circuit, then the easiest way is to use something like a BQ24725a smart charger.HTH

author: qrper
author_rank: Contributor
timestamp: April 28, 2017, 02:30:40 pm
content: Quote from: Seekonk on April 27, 2017, 06:54:16 pmActually, I do know.Purchased 250 74LS47 decoder/drivers for a project.NONE! Absolutely NONE worked.It was cheaper to reorder new pcbs than to pay for the labor to remove the defective ICs and replace them.Then there were the Ni-Cd batteries. They sure weren't the capacity they were sold as.Let's not forget the fake CD2545 HF transistors. While they tested out of circuit as fine, two hours later after they were installed, they didn't perform, drawing huge amounts of current for little RFoutput.One more? Sure!The 500, 16 pin machined IC sockets that didn't have holes drilled in the pins so the IC would set inside. Those I sent back.On the other hand, I've received some very good parts from China. My smart phone is made in China.

author: ebclr
author_rank: Super Contributor
timestamp: April 28, 2017, 08:19:14 pm
content: I would suggest that you change your China supplier, I buy thousands of IC's from China regularly, and the failure rate is negligible, but i didn't bought the cheapest ones available