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max72
05-19-2010, 09:19 PM
I would like to ask for suggestions about using a battery combined with a DC external supply or an USB charger.
I would like to use a 3.3V LCD and the sensirion, so I'm requiring 3.3V only.

The idea is to have the system running out of the battery when on the go, or using an external power supply. The power supply should be able to charge the battery while the propeller is running.
The battery could be either a Li-ion, 1-2 NiMh, a LiFe, or anything else suitable.
Ideally I could have:

Wall mart --> Battery_Charger --> Battery --> Regulator --> Propeller

Depending on the battery type the regulator would change (or be missing in case of LiFe), but the general idea is there.

I found also ready to use components like LTC3558 or similar. Unfortunately the package is not hobbist friendly, and they are difficult to find.

I would like to ask the forum if there is a proven set-up, a couple of guidelines, or a component ready to be used better suited.
For instance, if I use a Li-ion battery I must pay attention to the undervoltage.
If I use 2 NiMh and I charge at constan current (<0.1C) will it work with no management or am I missing an obvious point?

Thanks in advance.

Massimo

Rayman
05-19-2010, 10:08 PM
For simplicity, I like using three NiMH cells, which are easy to trickle charge with USB +5V.

But, if smallness is the main point, then Li-ion is better...

Also, trickle charging is slow...

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My Prop Info&Apps: ·http://www.rayslogic.com/propeller/propeller.htm

My Prop Products:· http://www.rayslogic.com/Propeller/Products/Products.htm

max72
05-19-2010, 10:31 PM
Do you current-control the charge? Even with the propeller running?
Do you use a buck-boost to have the 3.3V?

Massimo

Rayman
05-19-2010, 10:36 PM
You can see a messy schematic here for a 2-cell NiMH circuit:

http://www.rayslogic.com/Propeller/Products/PAB/PAB.htm

There, I take 5 V, regulate down to 3.3 V for constant voltage trickle charging through a small (1-Ohm ?) resistor.
Then, I do use a MAX chip to boost the voltage back up to 3.3 V (and another one for 5V).

A bunch of diodes make sure power goes in the right directions...

But, more recently I did a 3-cell system and there I charge from 5V directly and then output straight to a 3.3V LDO·regulator...


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My Prop Info&Apps: ·http://www.rayslogic.com/propeller/propeller.htm

My Prop Products:· http://www.rayslogic.com/Propeller/Products/Products.htm

BigFoot
05-19-2010, 10:40 PM
We are using the Lt1513 with an 8 cell Ni Cad battery pack. The nice thing about this chip is that
it is both an up & down converter.

We run our PoS terminals off a 9 Vdc wall supply and the battery can be from 7.5v when dead
to 11.5v fully charged. The charger puts out around 850 ma and just uses a small Smt heat sink.
I used the Vc line from the charger chip to drive an inexpensive Lm339 charge indicator
(gas gauge) that has 5 led's.

Russ

Botdocter
05-20-2010, 11:21 AM
And still the question remains unanwered.

I have the same issue. I want my bot to sense if the battery is low. Then drive to the charging dock. And when full he's on it's way again.

But indeed, can the propeller ( by software) charge a battery? Even when staying on?
I use a 12V sealed lead acid battery through 'Vin'.

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1 Parallax Propeller Robot Control Board
1 Memsic MX2125 accelerometer/ tilt
1 Parallax Ping))) ultrasonic sensor

a few motors and a whole lot of chaos!

Post Edited (Botdocter) : 5/20/2010 3:26:18 AM GMT

Mike Green
05-20-2010, 11:31 AM
Botdocter,
The Propeller can measure battery voltage with a few external passive components. You need to wire up two I/O pins as an ADC. There's documentation on this in the application note on the cog counters (AN001) that's downloadable from Parallax's Propeller download webpage. The documentation includes sample code.

You'll have to figure out what to do with the voltage information. You will find lots of information on various types of batteries and their discharge voltage curves and charging information in the Wikipedia and elsewhere on the web.

The Propeller by itself can't charge a battery. You'll have to provide external power control circuitry to do that. It's possible to use diodes to isolate the Propeller and other logic circuitry from the battery such that it all runs off the highest voltage source whether that's the battery or the external power source and the battery will charge from the external power source when it's present. The details depend heavily on what type of battery you're using and what type of charger you want to use for it.

Leon
05-20-2010, 06:26 PM
Rayman said...
You can see a messy schematic here for a 2-cell NiMH circuit:

http://www.rayslogic.com/Propeller/Products/PAB/PAB.htm

There, I take 5 V, regulate down to 3.3 V for constant voltage trickle charging through a small (1-Ohm ?) resistor.
Then, I do use a MAX chip to boost the voltage back up to 3.3 V (and another one for 5V).

A bunch of diodes make sure power goes in the right directions...

But, more recently I did a 3-cell system and there I charge from 5V directly and then output straight to a 3.3V LDO regulator...


NiMH cells should be charged with constant current.

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Leon Heller
Amateur radio callsign: G1HSM