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

deltagraph at aol.com deltagraph at aol.com
Wed Feb 6 06:43:08 PST 2019

Looking at gizmos to disconnect pack from load

Something like this (only prob did not see price and 1000 units here... )
Here $10 -- would assume not getting put in most hobby li-po batteries.

Of course more interest would be simply monitor and disconnect due to discarge, not  overvoltage protect during charge since that is managed by charger... 

-----Original Message-----
From: Carl Ott <carl.ott.jr at gmail.com>
To: Ron Grant <deltagraph at aol.com>
Cc: DPRG D-List <dprglist at dprg.org>
Sent: Wed, Feb 6, 2019 7:26 am
Subject: Re: [Dprglist] For your next robot - handy dc-dc converters - 3S LiPo to RPi

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 nicehttps://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 thesehttps://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.


-----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

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


this one has both a micro-USB and a USB female:
it's also branded DROKDROK 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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