A a ICless charging off circuit @4.2V for lithium - Page 1
Forum section: electronics / projects

author: dave_j_fan
author_rank: Regular Contributor
timestamp: June 21, 2015, 05:36:50 am
content: STory :Wanted to make a reliable power bankmodified a 1$power bank , swapping reliable cellsIssue :The cheapy somehow dont cut @4.2V ...need to add a tiny thingy preferably BJt+mosfet circuit so thatthe cut happens @4.2Vcomment on the cut circuit .. i want to swap he mosfet with IRLML2502TRPBF[I help many to make useful circuits and they cant procure special chipsso bjt mosfet as they are available all d placeswill be suitable for every one, more over even small loss while charging is no issue]

author: mariush
author_rank: Super Contributor
timestamp: June 21, 2015, 05:43:30 am
content: I'd suggest just using a MCP73812 :http://ww1.microchip.com/downloads/en/DeviceDoc/22036b.pdf(or a similar IC)It's easy to find at stores like Digikey, Farnell / Newark or even directly from Microchip's store :http://www.microchip.com/wwwproducts/Devices.aspx?product=MCP73812#pricindAndSamples(may even be able to request one as sample but it may take a long time or may be denied)

author: dave_j_fan
author_rank: Regular Contributor
timestamp: June 21, 2015, 09:54:32 am
content: we have a slight problemto get a 0.44$ chip .. need to pay digikey 40-50$suggested chip just goes 0.5Amps or lessit will take ages to fill 10400mAH

author: JoeO
author_rank: Frequent Contributor
timestamp: June 21, 2015, 10:20:26 am
content: If you turn on your country flag, someone may be able to help you by directing you to a place you can buy the parts from.

author: amyk
author_rank: Super Contributor
timestamp: June 21, 2015, 12:54:52 pm
content: What IC does it use and what voltage does it actually output? Note that the typical "absolute maximum" voltage for lion cell is actually 4.25V and typical charging ICs have a tolerance of 1% which fits within this range.There are also some 4.30V and 4.35V cells around.

author: mariush
author_rank: Super Contributor
timestamp: June 21, 2015, 02:12:33 pm
content: dave_j_fan , i suggested several online distributors so that you could pick which ever works better for you, since I didn't know your country.Farnell has an online store customized for your country, in.farnell.com , and here's the IC you want on that site:http://in.element14.com/microchip/mcp73812t-420i-ot/ic-li-ion-li-poly-charger-sot23/dp/1627187Shipping will probably be a few dollars (in your Rs currency), just make an account (it's free, no obligations) and check how much they charge for shipping. They have a warehouse in Singapore and one in UK, if the products are only in the UK warehouse, they may charge an additional fee per package to ship it to you. But it says so before you complete the order.If you don't like that chip because it's limited to 500mA, just search for another one that can do more, there's 459 ICs listed on the website:http://in.element14.com/battery-management_battery-chargersJust filter to see only ICs that charge lithium batteries, then if you want filter by the amount of current they can do. I suggested that one because it was stupid easy to use and solder, and you needed just that chip and a couple of ceramic capacitors and a resistor.Here's two that can do 1A :http://in.element14.com/microchip/mcp73833-ami-un/ic-battery-charger-1a-msop-10/dp/2146603andhttp://in.element14.com/microchip/mcp73834-fci-un/li-ion-li-poly-charge-controller/dp/1332162and this one can do up to 2A:http://in.element14.com/texas-instruments/bq2057sn/prog-battery-charger-2057-soic8/dp/1101403

author: dave_j_fan
author_rank: Regular Contributor
timestamp: June 21, 2015, 06:05:23 pm
content: USES hotchip HT4921http://www.hotchip.com.cn/en/Product.asp?tid=2&SortID=33acc specs it sd cut at 4.22V but accuracy 3% .. that may be risky ?mariush,that web links look they ship but here in INDIA they are hassledont take orders w/o VAT TIN (only business holders can have ) numbers etcplz suggest a MOsfet bjt solutionPlease rule out ALL IC solutionscoz people living in small towns also sdhould be able build at low cost !(i some how get element 14 delivery butnot for all)

author: dave_j_fan
author_rank: Regular Contributor
timestamp: June 27, 2015, 10:09:53 am
content: A mosfet SI2302 Has been ordered ....Until it comes 2-3days to go .I could guess the cut off 3% tolerance making the china power bank go till 4.35Vmean while i took few other cheapy power banks to try .Some of these will have perfect cut at 4.2VFor others my simple circuit will do that !This arrange ment will give reliable power bank @16$ cost to all ..Many of the branded ones are like 30-39$..People from small towns loosing money in fake ones for 8-20$

author: dave_j_fan
author_rank: Regular Contributor
timestamp: July 05, 2015, 08:54:42 am
content: mosfets mounted ..will test soon

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 05, 2015, 07:27:39 pm
content: I wonder if you could add a small bias voltage to the voltage sense terminal, so that it reads 4.35V when the cell is actually at 4.20V. It could be from a trimpot, so the awful 3% range can be calibrated correctly...Tim