Hint for keeping the batteries from discharging

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clarkj
 
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Joined: Thu Aug 08, 2013 12:34 pm

Hint for keeping the batteries from discharging

Post by clarkj »

I recently built a couple of MintyBoost units -- one for myself and one for my girlfriend. Our scenarios for use are dramatically different, but the MintyBoost is good for both of us. I travel some, and need a way to charge my tablet. She lives in "snow country" and may need to recharge her cell phone during a "snow emergency" (when the power grid is down). In both these scenarios, the ability to get power from AA cell disposables into our "gadget" is a good thing. (I considered, briefly, the commercial units with built-in rechargeable batteries, but those only give a "one shot" if you can't recharge THEM.)

Anyway, one of the down sides on the MintyBoost is that it uses a tiny amount of power even when it's not charging something, and this can eventually (like as in a month or so) kill the AA cells. In both of my scenarios, the MintyBoost may go for months without being used, but it would be nice to not have to hunt for batteries when it's needed.

So, here's the simple solution I came up with: I took a 3"x3" "Post-It" note and folded it up until it was about as wide as a AA cell. I wrote "Remove to use" on both sides, and then was able to slip this between the positive end of the AA cell in the battery holder and the contact on the battery holder at the end away from the circuit board. The paper is then long enough to stick out of the closed tin and be obvious. Since paper is an insulator, it keeps the circuit open and the batteries from being discharged. Just flick open the case and pull out the paper strip when you need to use the MintyBoost.

I'm toying with modifying my MintyBoost by adding an "earphone" jack that when a plug is inserted, it will disconnect the "internal" battery and allow another battery holder (maybe 3 D cells!) to be connected. Using a plug with nothing connected would just disconnect the "internal" battery and keep it from discharging.

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steverobey
 
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Re: Hint for keeping the batteries from discharging

Post by steverobey »

I just caught your post here and that seems like a good solution to me too. I also have a Mintyboost that I bought a while ago and put together to see how long it would power a raspberry Pi. I honestly wasn't surprised by how well it didn't do but that really wasn't what it was designed for. I would consider this just as you speak of it from personal application as an emergency power supply, your phone / tablet is dead and you don't have another charger source, this is perfect for that. Have you had a chance yet to try out any of the Powerboost products? https://www.adafruit.com/products/1944 I've got one of these on the way so I haven't gotten to try it out yet but I'm thinking you might be able to replace your Mintyboost with one.

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clarkj
 
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Re: Hint for keeping the batteries from discharging

Post by clarkj »

I haven't personally tried the PowerBoost 500 product. Just glancing at it, it looks like it is designed to be used with a LiPo rechargeable battery. One of the things to be aware of when working with things like this, if you want it as a "standby" (think Uninteruptable Power Supply) source, carefully check out the portion that charges the LiPo. I was working for a company a year and a half ago that made a product that often would be used connected to a computer, but could also run from its internal LiPo battery. Folks were complaining because they would have it attached to the office computer for two or three weeks, then when they detached it to use it on the LiPo, the battery would quickly die. Turned out that the charge controller wasn't as smart as it thought it was: it would turn the charge to zero after about 24 hours, and leave it there, and worse, cause a small drain on the battery, leading to a dead battery after a couple of weeks. (We advised our customers for this product to unplug it briefly every day or two.) Some more "modern" controllers will at least check the voltage on the "charged" LiPo every few hours and eventually will detect that it's gone down far enough to need recharging.

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steverobey
 
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Re: Hint for keeping the batteries from discharging

Post by steverobey »

Yeah I get what you're saying. For my intended application I would only be connecting the battery when it is low or dead though. I'm going to try to make a portable handheld computer of sorts with a Raspberry Pi. Unfortunately I started asking questions after I had already purchased the 500c and it sounds like it won't be able to power a Pi with a GPIO attached display. Having said that I'm going to try it anyway.

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