LiIo-Cell - Protection and charging - Page 1
Forum section: electronics / beginners

author: PeterFW
author_rank: Frequent Contributor
timestamp: June 16, 2014, 06:18:05 pm
content: Hello Folks!I can not say if i am at the right place to ask suchs questions.But i thought i might as well visit the forum wich is often referenced in one of my favorite youtube channels.My undertaking is not realy a newbie task and i am not new to electronics but since this particular subject is somewhat new to me...In the past i worked and build stuff with single LiPo cells and a charger, a Max1811.The cells all had a protection circuit and it was pretty easy.But now i would like to build a 3S-series LiIon pack from 18650 Cells, i know i can but something like that from the shelv but were is the fun in thatAnd there in lies the Problem, i can not find a suitable charger or protection IC.3 Series LiIon Cells10A continuous drainbuild in 1-2A charge circuit, so i just have to connect a wall adapter.Overcurrent protection for the packsingle cell undervoltage and overvoltage protectionI will be using Sony US18650VTC4 cells, they are capeable of safely delivering the needet 10A and they are pretty stable in this configuration.Noone needs to take me by the hand and spoonfeed meIf you could point me in the right direction to some data sheets and a manufacturer who will send me a few samples i will be more then happy.I can basicaly solder anny IC that has legs and 0603 is not that much of a problem, im capeable of producing my own PCBs as well.TI has some pretty ICs, Maxim as well but they are either legless, got waaaay too many features or are out of production.Edit:Oh... if it is important, im working in a dark shed, just for myself and i am my only customer. I just do this for funGreetings,Peter

author: JoeO
author_rank: Frequent Contributor
timestamp: June 16, 2014, 09:33:41 pm
content: Peter:I will attempt to answer your question from what I know. I am not a battery charging expert.1-Turn on your country flag.2-It is difficult for an individual to buy real 18650 batteries from a manufacturer or distributor. Most sold are recycled from China or somewhere else. They look good but they are repackaged.3-18650 batteries are very dangerous. If you are going to charge them, you need to know what you are doing. I suspect that the battery IC companies will not release specs on their chips unless they know who you are and that you are competent.4-Google 18650 batteries. Mouser, Digikey and Farnell do not sell them. Amazon and ebay does. Adafruit does also but I suspect they are repackaged.A few references for you:Adafruit sells a charger:http://www.adafruit.com/products/259They also have others.http://www.candlepowerforums.com/vb/showthread.php?257543-LiIon-18650-battery-comparison

author: Paul Price
author_rank: Super Contributor
timestamp: June 17, 2014, 03:21:48 am
content: If you have a pc laptop power supply (17-21V 2-4.5Amp are typical) you can drop down the output voltage with a switching regulator to float charge the e liPo cells in series. Since the max output current of the laptop supply is much lower than the C capacity of these batteries (10amp) you don't have to worry about overcurrent, but you must regulate the float charging voltage to always be lower than the max charge voltage for three batteries in series. You also must keep the charge current within the capability of the laptop power supply.I limit the current to C/20 if the batteries are almost completely discharged, and switch over to full charge current once the cell voltages reach 3.3V.I use a PIC MCU to create a SMPS power supply by PWM control from the MCU. To control a PNP power transistor switch, I have its base connected through a 150-ohm 1W resistor to a 2N3904 transistor collector that interfaces to the PWM output of the MCU through a 1k base resistor. The PNP power transistor (MJ2955, only a small heatsink is required) is pulsing a 330uH coil with a 5-amp schottky catch diode to ground. A 100uF output capacitor filters the output to the batteries in series. With 10-bit resolution PWM, it is easy to write the LiPol charging code used to regulate the output to any voltage or current desired. I use a .01 ohm sense resistor in series with the minus lead of the bottom battery of the series Li-ion stack whose voltage drop is amplified x 100 by a LM358 op-amp and feed this signal into a MCU A2D input to monitor charge current and also determine end of charge. I use simple math to calculate each batteries precise voltage by adding/subtracting relative measurements of the three battery voltages and the sense resistor voltage drop.I have found that charge balancing is not needed since Li batteries are and stay very closely matched in voltage if they are not damaged by improper charging or use.If I were to implement charge balancing, I have used the following scheme:Parallel each of the three Li-ion series connected batteries with a power N-Chan MOSFET (I use 6N03, P3055L "pulls" from a discarded desktop PC motherboard), each drain in series with a 10-ohm 1W resistor to charge balance the batteries. I use the 10-bit A2D inputs of a PIC MCU (16F886 using 20MHz xtal) to measure each battery's voltage (voltage dividers are needed for the "top" two cells)and the series charge current amplified by an op-amp. I control each MOSFET for balancing with a 18V gate bias signal developed by a 18V zener connected through a small limiting resistor(330ohm) to the laptop P/S output. I use 2.2k pull-up resistors to +18V to each of 3 outputs of a ULN2004 open-collector darlington array (or a 74LS07) to interface the MOSFET gates with the MCU 5V outputs. I also use a 78L05 to develop the 5V required for the PIC MCU and 74LS07. The 78L05 connects directly to the laptop 15-21V output to get the 5V needed. For a 78LS07 a 7805 is a more robust choice for the 5V supply. For ULN2004 the 78L05 is ok.If you don't like a MCU approach, you can use the circuit attached to float charge this large capacity LiPol battery.

author: poorchava
author_rank: Super Contributor
timestamp: June 17, 2014, 07:26:24 am
content: Quote from: JoeO on June 16, 2014, 09:33:41 pm2. Not entirely true. Yes, it is hard to buy genuine name brand primary cells, but it is entirely possible to buy protected cells based on those genuine cells. For one there is a Polish company BTO.pl, who sells them. I have eeven verified some LG-Chem-based batteries, and the cells are genuine. You can always buy a protected cell and strip it down, saving the protection sicrutry for later. Or you can use them with protection circuit if you find one that can handle the current3.ORLY?http://www.sii-ic.com/en/semicon/products/power-management-ic/lithium-ion-battery-protection-ic/http://www.ti.com/paramsearch/docs/parametricsearch.tsp?family=analog&familyId=413&uiTemplateId=NODE_STRY_PGE_Thttp://www.ic-fortune.com/upload/Download/DW01x-DS-15_EN_51313.pdfhttps://www.ricoh.com/LSI/product_power/bmu/multi.htmlhttp://www.intersil.com/content/dam/Intersil/documents/x310/x3102.pdfbesides-LiIos are not dangerous. Idiots handling LiIons are. If one makes sure that batteries are operated within spec, stored as they should and so on, they are rather harmless.4. There is also ton of other stuff that mouser or digikey don't sell. Big guys don't sell batteries because quite often shipping companies will charge a large premium as they deembatteries of all types very dangerous, potential chemical disaster and so on. This applies to anything from coin cells to 30kg truck batteries (at least in EU). Fry to order a coin cell from Farnell - I dare you. You'll most likely get a separate box literally wallpapered with all sorts of hazard stickers.There is a good set of Application notes from Cypress concerning charger/balancer/supervisory circuits using their PSoC series of chips.

author: BravoV
author_rank: Super Contributor
timestamp: June 17, 2014, 07:59:22 am
content: Quote from: poorchava on June 17, 2014, 07:26:24 amHigh quality 18650 cells such as Panasonic are available and easily bought mostly at developing/less developed or poor countries where laptop/notebook batteries recycling is a big business.The place where I live, fresh & genuine Panasonic or Samsung 18650 cells even the highest capacity are available and can be bought relatively cheap. And last time I bought few of them have a really fresh manufacturing date code too. Less than 2 months, proof that the business turn over in consuming this kind of battery is quite high here.

author: KL27x
author_rank: Super Contributor
timestamp: June 17, 2014, 10:00:53 am
content: For undercharge protection, you pretty much need a switch and a voltage detector(s). The switch is typically a MOSFET. The voltage detection can be done with a comparator or an ADC. A microcontroller is ideal, because you can do it with an internal comparator/ADC circuit and then put it to sleep after it switches the fet off. If you do it right, there is almost no drain on the battery while it's depleted.A simple method for a single cell is to use a 3 pin voltage detector circuit. They are made specifically for this application and have very low quiescent draw. TC54 is one I have used. They only go up to 4.5V or so, though. I'm not sure how that would do for 10A if you used 3 of these in series with 3 FETS. That is not going to be very efficient on the FETs.I have also used the brownout on a micro to switch the FET. If you drop the VDD with the right combination of diodes, you can get the PIC to brownout at just the right battery voltage. For a such a high drain app, you would need more than just a small pulldown resistor on power FET to switch it off when the PIC browns out. You would probably need a two stage transistor setup. This method is dumb if you don't already need a micro to do something else, of course. I just add it as a curiosity.I agree you don't need to worry all that much about balancing. Basically, you need to limit maximum voltage to 4.2 per cell. And max current drain to w/e you think is right, usually 1/10C is fine if you are not in a hurry. If you have all night, you can just use a voltage regulator at 12.6V and a power resistor on the output to limit max current. (12.6V- ~8V)/R = 1/10CThe crudest method I can imagine for charging fast as possible is as follows. You will need plenty of overhead voltage, say 17-18+V. Take a constant current circuit at 1/10C. Feed a linear voltage regulator with that current source. Voltage regulator is set to 12.6V. Feed that to the battery. (I think if you omit the constant current circuitry and instead rely on a lappy SMPS to not be able to delivery much more than a few amps, you will either trip the short protection on your PSU, or you may send it to an early demise.)

author: JoeO
author_rank: Frequent Contributor
timestamp: June 17, 2014, 05:25:12 pm
content: Even SONY has problems using SONY batteries.http://www.theverge.com/2014/4/11/5603862/sony-vaio-fit-11a-battery-fire-risk-warning

author: sequence
author_rank: Newbie
timestamp: June 20, 2014, 03:52:39 pm
content: http://www.fasttech.com/category/1420/batteries/MTI1PTE4NjUw/Fasttech is an excellent source for 18650 cells. They carry Panasonic, Sony, LG, Sanyo and Samsung batteries, in both protected and unprotected formats.