Battery hack and Gamma M0/QT PY question

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michaelmeissner
 
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Battery hack and Gamma M0/QT PY question

Post by michaelmeissner »

I should preface this with the disclaimer that while I do know which end of the soldering iron to grab (at least most of the time), I am a software guy. My knowledge of electronics is rather shaky. But that doesn't prevent me from blazing ahead, blithering into things.

Any way, I've been using neopixels for some time now, starting with the original Arduino Uno, going on through the original Gemma/Trinket, various Teensies, and most recently Gemma M0, Trinket M0, various feathers, and various QT PYs.

I go to long steampunk events and science fiction conventions that can last quite a bit of time. I've made various do-dads involving neopixels, such as wooden bowties with a neopixel ring, goggles with 2 rings, and suspenders with 40 leds or so. Plus I've used the two Hallowings (M0/M4), Eyelights LED glasses, and the Monster M4SK. However, having the battery not last for the full day of the event is a drag. While in theory, the lipo batteries are inter-changeable, I find it hard to unplug the battery. And a lot of the times, the battery is attached to the cosplay gadget. Unfortunately, I have ripped the wires off of several lipo batteries.

I like to try and hide the battery on the gadget, but a lot of times space is an issue. In particular for the googles, I would like to find a battery that fits within the eyepiece of a standard goggle (roughly 45mm in diameter), but has at least 1000mAh power (1200mAh or 1700mAh is better of course). The 500mAh and 350mAh lipo batteries that Adafruit sells will fit, but they don't have the power to drive neopixels for 8 hours or so. The 1200mAh battery in the past has lasted long enough (depending on how long I go, which microprocessor I use, and how bright the LEDs are).

I also am a camera user, mostly with the Olympus and Panasonic brand of cameras. While most of the camera batteries are based on 2 li-ion cells and deliver 7.2 - 8.4 volts, the smaller cameras use single cell batteries. In particular, I have an Olympus TG-5 camera which takes a LI-92B battery. I bought several third party batteries (Kastar 3.7 volt 1300mAh), so I decided to sacrifice one for testing.

I soldered a JST cable across the +/- pads of the battery. Using my multi-meter, I verified that it was producing 4.1 volts of power. But I was disappointed when I plugged in the battery to the goggles (which is using a Gemma M0), it didn't turn on. Then I attached it to one of the QT PY's I've been using for doing the suspenders. At the moment, I'm using a QT PY M0 with the lipo BFF attached. Again, the battery would not power the QT PY.

I put a third party lipo and booster (lipo rider plus from seeedstudios) and both the Gemma M0 and QT PY M0 worked fine with the boosted voltage. I then put the Adafruit Powerboost 500 on the battery and connected each of the processors in turn. Both worked fine. Just to be clear, both processors run fine with normal lipo batteries and/or USB power.

So the question is why does it work if I boost the current, but it doesn't work when I connect the battery directly to the JST port. Is it a safety issue? It can't be that I didn't connect the third battery terminal, since the booster runs fine without it. While I know I'm losing power doing the boosting, it will at least work. It is also is convenient in that I can turn the microprocessor off at the booster, and just charge the battery during downtime.

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argonblue
 
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Re: Battery hack and Gamma M0/QT PY question

Post by argonblue »

What voltage do you measure across the battery terminals once you plug it into the board and power on the board? (assuming the terminals are still accessible)

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michaelmeissner
 
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Re: Battery hack and Gamma M0/QT PY question

Post by michaelmeissner »

The voltage that the battery produces at the moment is 4.0 - 4.1 volts. It is freshly charged, and the nominal voltage is 3.7 volts, so I assume it will drop down to 3.7 volts as the battery is depleted some. I assume it has a standard li-po single cell battery inside. Running the charger from the power booster seems to charge the battery. I don't (yet) have a meter setup to measure the amps for lipo batteries before it goes into the power booster.

The power booster produces 5.02 volts. Running a QT PY M0 with a neopixel led strip with 30 neopixels (https://www.adafruit.com/product/3919) uses about 80-82mA. I generally restrict my LED projects so that the sum of the R + G + B levels is 30 or less.

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argonblue
 
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Re: Battery hack and Gamma M0/QT PY question

Post by argonblue »

Thanks. I was asking if you had measured the voltage, not the current, across the third-party battery terminals once you attached the JST connector and plugged it into the board, and turned on the board.

Sometimes batteries have high internal resistance, or built-in current limiting circuitry. Microcontroller boards sometimes have large filter capacitors can that draw a large surge current when power is initially applied. This "inrush" current surge can cause a sudden voltage drop due to internal battery resistance (maybe enough to cause the board to misbehave) or cause any protection circuits in a battery module to kick in (which might also reduce or cut off the battery voltage).

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michaelmeissner
 
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Re: Battery hack and Gamma M0/QT PY question

Post by michaelmeissner »

That is sort of what I was asking. I was just hoping I could find a battery that met my size and power requirements without too much work. I was surprised when it just didn't work. I was curious what it might be. As I said, I'm a software guy, and I tend to not know the details of how things are setup, other than at a block level.

Now, in terms of including the booster along with the battery, isn't much of a problem. Except, with the loss due to boosting the current and the efficiency of the booster, it means I might get 8 hours of run time instead of 11 hours. One convention does last all day, so I still might need to change the battery. But it is better than the 4 hours that 500mAh battery gives me.

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adafruit_support_mike
 
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Re: Battery hack and Gamma M0/QT PY question

Post by adafruit_support_mike »

For what you're doing, using a multi-cell battery and dropping the voltage to 3.3V (or 5V) will work to your advantage.

DC-DC converters are constant-power devices: to get 1W of power out of one, you have to send at least 1W in. Boost converters draw more current than the load and use it to generate a higher voltage. Buck converters do the opposite, turning excess voltage to more current. That works in your favor because a smaller high-voltage battery will give you the same charge lifespan as a larger low-voltage battery.

There's also a technical advantage because it's easier to make an efficient step-down converter than an efficient step-up converter. The central theory of buck conversion is basically PWM with a really good ripple filter. Today's buck converters are usually 95% efficient or better.

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michaelmeissner
 
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Re: Battery hack and Gamma M0/QT PY question

Post by michaelmeissner »

Thanks. I do have 2 cell camera batteries that might fit in the size requirements. The nice thing about the seeedstudios unit is it combined recharging and boosting, so I could just plug in the unit into a USB cord overnight without taking out the battery.

I'll think about trying one of those, but many of those are in use -- perhaps I need to order some third party batteries just for this.

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adafruit_support_mike
 
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Re: Battery hack and Gamma M0/QT PY question

Post by adafruit_support_mike »

Check the market for quadcopter hardware, especially the miniature ones. Those prioritize size and weight, and it's usually easy to find the charger that goes with a given battery.

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