[Dprglist] For your next robot - handy dc-dc converters - 3S LiPo to RPi

[Carl Ott]

These packs show ratings of 8 ~ 20 volts, or 8 ~ 50 volts so, even when
starting at a full 4.2v charge, 2S probably wouldn't work, at least not for
long...

In terms of voltage monitors, I've been using one of these for a while -
they're pretty nice
https://us.banggood.com/Wholesale-Warehouse-0_28-Inch-2_5V-30V-Mini-Digital-Voltmeter-wp-Usa-974258.html?akmClientCountry=America&rmmds=myorder

The 2016 club robot came with one of these
https://www.amazon.com/Battery-Monitor-Voltage-Checker-Indicator/dp/B013U1CP08/ref=asc_df_B013U1CP08/?tag=hyprod-20&linkCode=df0&hvadid=167139094796&hvpos=1o1&hvnetw=g&hvrand=8040392104640112483&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9026796&hvtargid=pla-304998738630&psc=1

looks like it can work nicely if your battery has a balancing port. it
monitors the voltage on each cell in the pack. you can set the alarm
threshold voltage to your preference.  But it does beep every time you
power it up, and seems to cycle the display through each of the cell
voltages - so it looks like a good alarm but is not as simple as a voltage
gauge on the entire pack.

- Carl


On Wed, Feb 6, 2019 at 7:02 AM <deltagraph at aol.com> wrote:

> Hey Carl/All,
>
> Looks nice, but would be nice to have auto disconnect of converter on low
> voltage -- of course that can be addressed separately, up line at the input
> of the dc-dc converter.
>
> Voltage monitoring by MCU (with suitable voltage divider)  or display with
> one of those $1 LED display modules is handy, just thinking more about
> accidental leaving converter/load connected to battery.
>
> Maybe someone can shed some light on how many li-po packs have auto
> low-voltage shutoff these days.
>
> At first I was thinking about this converter being used with a 3 cell
> pack, wonder if it would work with a 2 cell pack?
> If so, at least the pi would die before the battery. You still would need
> to disconnect battery, but at least brain death would precede battery death.
>
> Ron
>
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> -----Original Message-----
> From: Carl Ott via DPRGlist <dprglist at lists.dprg.org>
> To: DPRG D-List <dprglist at dprg.org>
> Sent: Tue, Feb 5, 2019 8:07 pm
> Subject: [Dprglist] For your next robot - handy dc-dc converters - 3S LiPo
> to RPi
>
> FWIW
>
> Found these - should come in handy powering Raspberry Pi from a 3S LiPo
> pack.  Haven't powered them up yet - but the specs look good
>
> this one is a little smaller, with just Micro-USB out
>
>
> https://smile.amazon.com/gp/product/B00O6RJLQC/ref=ppx_yo_dt_b_asin_title_o03__o00_s00?ie=UTF8&psc=1
>
>
> this one has both a micro-USB and a USB female:
>
>
> https://smile.amazon.com/gp/product/B016XI9CZQ/ref=ppx_yo_dt_b_asin_title_o03__o00_s00?ie=UTF8&psc=1
>
> it's also branded DROK
> DROK sells a ton of handy modules like this - dc-dc converters of all
> sizes, I/O, control & display options. I've used them a bunch and haven't
> been disappointed yet.
>
> - Carl
>
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