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| General Electronics Chat This forum is for general chat about electronics, eg: Dont know what a part does? Dont know how to read a circuit? Want to get an opinion? |
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9th September 2007, 12:31 PM
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Battery Charger - DS2714 - Current Source?
Hello,
I am wanting to make a super safe, nimh/nicd smart battery charger. After looking around, I've decided to use the DS2714 chip for my design. If you have any other chip suggestions, please let me know. http://www.maxim-ic.com/quick_view2.cfm/qv_pk/5297 I think I pretty much have the schematic of how to get the DS2714 working, except for the current source. I found no information on the current source in the data sheet, except "current source". Does anyone know what current rating my current source should be? Also, I will be using a regulated 5V to power this charger, how can I turn that into a current source? Thanks! |
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9th September 2007, 12:50 PM
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hi Fred,
Have you checked Maxims application notes? http://search.maxim-ic.com/search?ie...h/search3.xcgi Whats the voltage/AHr capacity you want to charge? You can configure a 7805 or LM317 as a current source.
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Eric "Good enough is Perfect" PIC tutorials: Gramo's: www.digital-diy.net/ Bill's: www.blueroomelectronics.com/ Last edited by ericgibbs; 7th July 2008 at 11:21 AM. |
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9th September 2007, 02:04 PM
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The current source in the datasheet is 2A. it charges each of 4 cells for 1/2 a second each 2 seconds, minus a small amout of time where each cell is tested.
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Uncle $crooge |
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9th September 2007, 02:46 PM
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hi,
as 'agu' points out a 2Amp current source is required for the 4 cell charger in the application data. A 7805/L317 isnt upto the job, you require a similair regulator but with a minimum continous current of say 3amps. Extract from data sheet.
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Eric "Good enough is Perfect" PIC tutorials: Gramo's: www.digital-diy.net/ Bill's: www.blueroomelectronics.com/ Last edited by ericgibbs; 7th July 2008 at 11:21 AM. |
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9th September 2007, 03:09 PM
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Thanks for the information guys! I didn't see that 2A in the datasheet anywhere, I must have been blind.
Unfortunately, my source power has a maximum current of 500mA. Would that work with this chip (just take 4x as long) or do I need a totally new chip? Any recommendations? Thanks again! Last edited by Fred.Amoson; 9th September 2007 at 03:27 PM. |
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9th September 2007, 04:30 PM
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The IC is a fast charger for individual Ni-MH cells. It times out after a max of 10 hours. 2500mAh AA cells need 20 hours or more at 500mA/4.
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Uncle $crooge |
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9th September 2007, 07:59 PM
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How many cells do you need to charge?
If it's just one then you could use a switching regulator for your current source and get 1A@2V from 500mA from 5V@500mA which would cut your charging time in half. You really need a much higher current power supply, I'd recommend a PC power supply which can supply a lot of current and is quite cheap to.
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