Adding resistor to USB LiPoly Charger

by rawfuls on Fri Jan 04, 2013 9:13 pm

Got one of the USB LiPoly chargers to put in another Altoids box to take on the road incase I can't come home to use my Bantam BC6 charger to charge up the big 6600mAh battery.

I got the charger in and it says to add a resistor to maximize it's charge rate.

Which and where does this resistor go?
Not the greatest at reading diagrams so some step-by-step explanation would be nice, thanks!

http://www.adafruit.com/products/259#tutorials
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Re: Adding resistor to USB LiPoly Charger

by adafruit_support_bill on Sat Jan 05, 2013 6:25 am

The max charge rate of the USB charger is about 1000 mA. To acheive this charge rate, you can either solder a 1.3K resistor on top of R4 (default 4.7K) - this will make the total parallel restance 1.0K or you can remove R4 by desoldering it or cutting the trace to it and solder a 1.0K resistor in its place.


http://learn.adafruit.com/li-ion-and-li ... r-charging
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Re: Adding resistor to USB LiPoly Charger

by rawfuls on Sun Jan 06, 2013 12:31 am

adafruit_support wrote:
The max charge rate of the USB charger is about 1000 mA. To acheive this charge rate, you can either solder a 1.3K resistor on top of R4 (default 4.7K) - this will make the total parallel restance 1.0K or you can remove R4 by desoldering it or cutting the trace to it and solder a 1.0K resistor in its place.


http://learn.adafruit.com/li-ion-and-li ... r-charging


Excuse the ignorance but where exactly is R4?

Having trouble locating it, I'm assuming it's the one which says PROG?
Soldering a resistor (linked below) right on top of the resistor is fine?

http://www.parts-express.com/pe/showdet ... r=002-1.3K

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Re: Adding resistor to USB LiPoly Charger

by adafruit_support_bill on Sun Jan 06, 2013 6:26 am

Yes. R4 is labeled RPROG on the board. You can solder a standard through-hole a 1.3K resistor over it using the adjacent holes.
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Re: Adding resistor to USB LiPoly Charger

by jonsleepy on Fri Jan 25, 2013 6:06 pm

Hi, did you ever follow their suggestion of soldering a 1.3K over RPROG or removing RPROG and adding a 1.0K in its place?

I had the same question and was wondering if this worked well for you..

Thanks
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Re: Adding resistor to USB LiPoly Charger

by adafruit_support_bill on Sat Jan 26, 2013 6:13 am

A 1.3K resistor will work fine. In parallel with the existing resistor, the total equivalent resistance is 1k.
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Re: Adding resistor to USB LiPoly Charger

by jonsleepy on Sun Jan 27, 2013 2:02 pm

Thanks for replying. I'm trying to learn and not nitpick, but something doesn't add up..

According to the datasheet for the control chip ( http://ww1.microchip.com/downloads/en/D ... 22005b.pdf ), the charge current is 1000V/Rprog (equation 4-1, page 14), so a total of 1k resistance between the pads will give you 1000mA.

There is currently a 2K surface mount resistor, and if I add a 1.3K resistor in parallel as you suggest, that'll give me 787 ohms resistance, leading to a charge current of 1.3 amps. Wouldn't I want another 2K resistor over the existing 2K resistor for 1 amp of charging current? If not, help me find my mistake?
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Re: Adding resistor to USB LiPoly Charger

by adafruit_support_bill on Sun Jan 27, 2013 3:26 pm

There is currently a 2K surface mount resistor

The docs I'm looking at say it should be 4.7K. I'll try to verify that.
4.7K in parallel with a 1.3K gives you 1K.
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Re: Adding resistor to USB LiPoly Charger

by rawfuls on Tue Jan 29, 2013 4:08 pm

To be honest I have yet to even touch the charger.

I find it much more useful to use my Bantam BC6 charger to charge it up, as it will read out the amount of mAh it puts back into the battery.
If the USB Charger could display this information, I'd be on it in a heartbeat.

Reading the live mAh input gives me a rough ETA of when the battery will be done, or if it's able to be used temporarily to charge something else.

However, I am currently building it into a secondary Altoids tin which will pair with the mintyboost which will allow me to charge other devices and itself self-sufficiently.

Just a matter of finding the time to solder the leads together (JST connection on battery), and getting a resistor.
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Re: Adding resistor to USB LiPoly Charger

by adafruit on Thu Jan 31, 2013 6:34 pm

Typo fixed - it should say 2K, that's what we're currently shipping with. Perhaps a really old version of this product was with a 4.7K? Its been a few years, not sure!
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Re: Adding resistor to USB LiPoly Charger

by rawfuls on Mon May 13, 2013 1:03 am

Still a little new to all the resistors and electronic wiz.

I'm going to need a 2k resistor, at what wattage? 1/2? 1/4? 1W?
Any other information I'd need to know? Do all the wattages have different types of color bands or is the RED/BLACK/GOLD going to be universal for all 2k resistors?
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Re: Adding resistor to USB LiPoly Charger

by adafruit_support_bill on Mon May 13, 2013 5:41 am

1/8 or 1/4 W should be fine. There isn't much current going through it. The higher wattage resistors will work just as well, but they might be a tight fit on the board.
Color bands should be the same for all wattages. There are also 5-band color codes for higher precision. These will work also, but the added precision is not needed.

http://www.hobby-hour.com/electronics/r ... r_code.php
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Re: Adding resistor to USB LiPoly Charger

by CalebEng on Mon May 13, 2013 9:08 am

I've got a question about this board as well, but I think a quick look at the schematic would answer it. I see the schematic is available in the downloads section, but I cannot open the file with my expressSCH software. What software should I use to look at it?
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Re: Adding resistor to USB LiPoly Charger

by adafruit_support_bill on Mon May 13, 2013 9:33 am

The files are in EagleCAD format. It is a free download.
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Re: Adding resistor to USB LiPoly Charger

by CalebEng on Mon May 13, 2013 11:50 am

Thanks. I downloaded EagleCAD and was able to open the file.
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