Can I briefly pull more than 500mA from minty boost?

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creatify
 
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Can I briefly pull more than 500mA from minty boost?

Post by creatify »

I've confused myself trying to find this answer in all the minty docs — will minty boost allow me to pull more than 500mA from brief periods (ms)?

I am using a minty boost (powered by 3 Ni-MH AAs) to power an arduino micro, 1 neopixel ring, PCA9685 servo driver, and 3 MG90 micro servos. The circuit currently, surprisingly, works fine but I wonder if I'm minutes away from frying the minty-boost. I glossed over the fact that minty boost supplies up to 500mA when I hooked all this up. When I start driving the 3 servos, I'm seeing spikes over 1.8A of current used (I'm using the adafruit Mini Power Meter to view the volt/current) and I'm wondering how I can even see that much draw coming from the minty boost?

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Re: Can I briefly pull more than 500mA from minty boost?

Post by adafruit_support_bill »

With reasonably fresh batteries, it should handle brief current spikes. 1.8A is pushing things a bit though. A large-ish capacitor between GND and 5v would help smooth those peaks out somewhat. But a PowerBoost 1000 would be a better match for that load.

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creatify
 
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Re: Can I briefly pull more than 500mA from minty boost?

Post by creatify »

Thank you, again, this is helpful. Ha, I was just looking at that power boost 1000, it does seem like a better fit, but I wonder if I need to rethink 3X AAs powering this all. When this project is turned on, the servos will only move for a few ms every 1-2 minutes maximum, but 36 neopixels will continuously animate. I'm trying to balance those brief, rather large, servo spikes against the majority of time when <200mA are consumed. 8-10 hours of runtime is what I'm aiming for from the batteries. I plan on a secondary DC jack input for a wall wart for long run times, but it will be much more practical to use easily accessible (AA) batteries (in limited chassis space) in this case. Any thoughts are appreciated.

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Re: Can I briefly pull more than 500mA from minty boost?

Post by adafruit_support_bill »

NiMH cells typically have a capacity in the 1200-2000mAh range. Let's assume the lower end of things to be safe.

A 3s NiMH pack will give you nominally 3.6v. Boosting that to 5v at 95% efficiency gives you an effective conversion factor of 0.684. So you will need about 300mA @3.6v from the batteries to get 200mA @5v for your circuit.

So, at 200mA continuous draw at your circuit (300mA from the batteries), you will get about 4 hours of run-time (4h x 300mA = 1200mAh). Factoring in brief excursions to 1.8A, you can expect somewhat less.

You could go with a higher capacity NiMH pack to extend the runtime. 5000mAh C cells should get you closer to your goal.

Another option would be a LiPo cell. We have these as large as 10050mAh. That would be a good match for a PowerBoost 1000-C - which has a built-in charger.

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creatify
 
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Re: Can I briefly pull more than 500mA from minty boost?

Post by creatify »

Awesome advice, and thanks for that math regarding the conversion, I should be able to make one of these options work!

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