Batteries get HOT and phone is DISCHARGING!

by kscharf on Mon Jan 07, 2013 9:43 pm

It seemed to work for a while, it was charging by daughters Samsung Android smart phone, but the batteries started to get hot, and then the phone started to show discharge (percent charged going down). At this point the batteries were removed and measured 1.2v each. These were Kirkland (Costco) brand Alkaline AA batteries. What is the minimum voltage that minty boast needs? Well my daugher admitted she had the phone ON while charging, which you advise against. We will try it again with the phone shut off.
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Re: Batteries get HOT and phone is DISCHARGING!

by adafruit_support_bill on Mon Jan 07, 2013 10:03 pm

The Minty will handle input voltages down in the 2.5v range - with decreased efficiency. The real question is what was the voltage output of those cells when they were still under load. Given the heating, I'm pretty certain it was lower than 1.2v.

For modern smart-phones with their high-capacity batteries, I like the 3x NiMH cell configuration. The 3.6v output is right in the MintyBoost's efficiency sweet-spot, and the cells hold up much better than alkaline cells in high-drain applications. If you do stick with Alkaline, look for cells designed for high-drain usage. Check here for more details: viewtopic.php?f=15&t=22377
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Re: Batteries get HOT and phone is DISCHARGING!

by kscharf on Tue Jun 25, 2013 7:31 am

I modified one of the minty boost's to use three AA batteries in series. I purchased a single AA battery holder from 'rat shack' and found a larger tin that would house the three batteries and the Minity Boost. This seems to work much better and charges the phone using alkaline batteries. I agree that using NiMh rechargable's look good, but this brings back the 'chicken and egg' problem. AA batteries can be found in ANY drug store or supermarket. If you are in the middle of any urbun area and your phone is dieing, the minty boast can be a life saver. If you build it with the rechargeable batteries you need to plan ahead!
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