Author Topic: biferent power source idea for 50$ bot. is it good?  (Read 946 times)

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Offline 123laurensTopic starter

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biferent power source idea for 50$ bot. is it good?
« on: November 26, 2010, 11:56:29 AM »
so now im building the 50 bot brain,and getting realy exited (its my current and only goal) and had a idea.irecently got this ''solar charger prenium'' and it has abuilt in battery and advanced circut protection and regulator. it is designed to suply a stable 5v suply to charge cell phones an whatnot.it has a usb-tiny adaptor(designed to charge blackberryies) wich fits in the pocket avr programer,so iwas thinking...

if i use that to replace the 9v battery and regulator,whud it work while its attached???

Offline 123laurensTopic starter

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Re: biferent power source idea for 50$ bot. is it good?
« Reply #1 on: November 26, 2010, 12:14:37 PM »
some specs

the battery can be charged by a computer
battery capacity  700mA/3.8V(LI)
output vooltage  5V6
output current  700mA(MAX)
output power  3W9(MAX)

optional question 

can this also power the servos?

Offline VegaObscura

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Re: biferent power source idea for 50$ bot. is it good?
« Reply #2 on: November 26, 2010, 01:51:27 PM »
This table from the Atmega8 datasheet should help you

Voltage on any Pin except RESET
with respect to Ground ................................-0.5V to VCC+0.5V
Voltage on RESET with respect to Ground......-0.5V to +13.0V
Maximum Operating Voltage ............................................ 6.0V
DC Current per I/O Pin ............................................... 40.0 mA
DC Current VCC and GND Pins................................ 300.0 mA

With a 700mA maximum output, this battery can not power your servos.

Offline Soeren

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Re: biferent power source idea for 50$ bot. is it good?
« Reply #3 on: November 26, 2010, 10:47:04 PM »
Hi,

[...] and getting realy exited (its my current and only goal)
Nice to hear you've got your priorities sorted  ;D


irecently got this ''solar charger prenium'' and it has abuilt in battery and advanced circut protection and regulator.
Just to keep you pointed towards your goal a little longer... In case you are counting on making a solar 'bot, here's the lowdown on these chargers.
The solar panel charges the internal lithium cell slowly and when fully charged, the lithium cell will be able to convert this to 5.6V for charging.

It's not a well regulated 5.0V output, but a 5.6V output and I don't think regulation is all that.
(It certainly isn't in the one I have - a Chinese make designed to open to expose the dual solar panel).

But... The laws of thermodynamics still applies, so the lithium cell (of 700mAh capacity) converted to 5V will be 700mAh * 3.8 / 5.6 = 475mAh.
And since the voltage of a lithium cell declines during use, a more realistic calculation would be:
 700mAh * 3.4 / 5 = 425mAh

One thing is clear, they mix mA with mAh and that won't work.

A lithium cell with a capacity of 700mAh can easily supply 2A (much more in fact) for some time, some are rated up to more than 30C (which for a 700mAh cell would mean 30*700mAh = 21A)
Perhaps the box includes a simple resistor for current limiting, perhaps it's only meant for charging  cell phones and personal music players and perhaps it's not that wise to experiment too much with badly spec'd lithium cells without proper knowledge...

Far better to buy a lithium cell for the purpose, built and spec'd well, with a overcharge/-discharge protection built in and such (and a matching charger) and be more safe from fireballs and agitated parents, that don't see eye to eye with having your home burnt crisper than your X-mas dinner (now consumed under open skies) in the name of "getting really exited".
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline 123laurensTopic starter

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Re: biferent power source idea for 50$ bot. is it good?
« Reply #4 on: November 27, 2010, 02:09:00 AM »
well,to me, it seems better than a 9v battery,it can charge by plugging in this usb charge cable,and can power this usb fan purely battery power.i dont need it to power the servos,i just cant find a decent 9v clip thing,and the regulator i got localy im not sure of,it whud be cool if i actualy found a uce for this thing.and i hate buying 9v bats all th time,and we only have a AA battery charger,and 9v rechargebles are inpossable to find in south africa.

i dont want a solar bot,just a DIY battery suply

Offline 123laurensTopic starter

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Re: biferent power source idea for 50$ bot. is it good?
« Reply #5 on: November 27, 2010, 04:52:49 AM »
plz reply,whud it work,or shud i get a 9v battery instead?
and it can charge the beattery and supply the things with power,the battery is there for 2 reasons

if there isnt inuf sun,it will youse half the power from the battery and combine it with the solar power

its also advertized as an external battery when there is no sun,and can charge my cell fo 15 mins

it also seas in the manual ''advanced over charge and over discharge protection''
« Last Edit: November 27, 2010, 12:30:52 PM by 123laurens »

Offline Soeren

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Re: biferent power source idea for 50$ bot. is it good?
« Reply #6 on: November 27, 2010, 07:10:28 PM »
Hi,

Whatever you read in the manuals might be true... But I wouldn't bet on it though.
You could test the unit by measuring the voltage while discharging it (perhaps with the fan you mentioned).

If it holds 5.6V for most of the discharge time, you can add a diode that can handle the total curernt used (1N4001..1N4007 handles up to 1A and is a very common diode), to get it down to ~5V and then you can use it without a regulator.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

 


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