MintyBoost with Low Battery indicator (seems to be affecting

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mistertek
 
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Joined: Fri Dec 28, 2007 11:30 pm

MintyBoost with Low Battery indicator (seems to be affecting

Post by mistertek »

I have added the Low Battery Indicator option to a MintyBoost but have noticed I don't seem to get as much charge to the external USB device before the batteries run flat.

I tried charging a BlackBerry that was 60% charged (based on the BB battery indicator). After about 15 minutes, the batteries got slightly warm and the went flat. The BB did charge an additional bar (~20%). The Low Battery indicator came on as well.

Here is the timeline of events:

0 mins: 3.1v across 2 batteries resting (nothing connected to MintyBoost)
1 mins: 2.7v across 2 batteries with BB connected
15 mins: 2.1v across 2 batteries (Low Battery Indicator on)

Here are the parts I am using:
R1 = 100ohm
R2 = 110ohm
R3 = 300ohm
LED = Red SMT LED
*side note... with these resistor values, battery voltages of 2.3v or lower is when the LBI illuminates.


Any thoughts? I might connect a data logging DMM and run another test and then another with the LBI removed.

Thanks!
Last edited by mistertek on Sat Jan 12, 2008 2:31 am, edited 3 times in total.

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mistertek
 
Posts: 22
Joined: Fri Dec 28, 2007 11:30 pm

Blackberry at fault

Post by mistertek »

It turns out it was the BlackBerry causing and incredible drain on the MintyBoost. It was drawing .95 amps! far more than the USB spec. It looks like the BlackBerry isn't current limited. At least not limited to USB spec. I connected the MintyBoost to a bench power supply that is voltage and current limited. I connected a few devices and here are my results.

BB = .95 amps!
AT&T Tilt = .53 amps
Mot H700 headset = .12 amps

I think if I used rechargeable batteries in the Minty I wouldn't have had such a problem delivering that high current as NiMH or NiCD are able to deliver more current over a short period of time vs alkaline batteries due to their lower internal impedance.

Perhaps I'll run more tests if anyone is interested.

Entropy
 
Posts: 472
Joined: Tue Jan 08, 2008 12:43 am

Post by Entropy »

Many devices will happily bump up (or remove) their current limit if they detect a "dumb" charger.

For example, I'm surprised the Tilt only took 0.53 amps - It would have either taken almost nothing (extra pin on the MiniUSB plug not grounded, indicating a sync cable and not a dumb charger to the Tilt), or I would have expected far more if the "dumb charger" pin was grounded.

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