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Author Topic: Multiple power supplies  (Read 1042 times)

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Offline rbtyingTopic starter

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Multiple power supplies
« on: August 19, 2011, 11:02:47 PM »
Hey all,
   My robot currently uses a 14.4v lithium-ion battery pack (made following MadSci's tutorial) for its primary power supply, and is charged by a standalone 14.4v Li-Ion "smart" charger. Right now, it's got a pico-itx motherboard stuck onto it, and updating the software requires that I detach the charger and run the board off battery power - undesirable for long upgrade processes (such as my recent kernel upgrade).

  What I'd like to know is if there would be any problems if I hooked up the charger (which charges at 16.8 volts) while having the battery still connected to the motherboard. The regulator I've got can handle the voltage, but I don't know what it'd do to the "smart" charging system. Any information would be greatly appreciated.

Offline corrado33

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Re: Multiple power supplies
« Reply #1 on: August 20, 2011, 09:53:25 AM »
If possible, why not just use a wall wort that provides 14.4V at whatever amps you need?

Offline rbtyingTopic starter

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Re: Multiple power supplies
« Reply #2 on: August 20, 2011, 02:20:18 PM »
Lithium-ion batteries need "smart" chargers - constant voltage charging can cause explosions. Also, seeing as this is a mobile robot, tying it to a wall when not necessary is rather undesirable.

Offline corrado33

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Re: Multiple power supplies
« Reply #3 on: August 20, 2011, 06:18:42 PM »
Lithium-ion batteries need "smart" chargers - constant voltage charging can cause explosions. Also, seeing as this is a mobile robot, tying it to a wall when not necessary is rather undesirable.

Yes, I meant bypass the battery and use the wall wart when you need your bot on for long periods of time like when you are updating it. 

Offline rbtyingTopic starter

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Re: Multiple power supplies
« Reply #4 on: August 20, 2011, 07:05:19 PM »
I do that right now, but it's relatively annoying to have to keep swapping around power supplies. I'm hoping for something more like a laptop, where you can charge and work simultaneously, then pull AC out and run purely off battery without a reboot.

Offline Soeren

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Re: Multiple power supplies
« Reply #5 on: August 20, 2011, 10:26:19 PM »
Hi,

  What I'd like to know is if there would be any problems if I hooked up the charger (which charges at 16.8 volts) while having the battery still connected to the motherboard. The regulator I've got can handle the voltage, but I don't know what it'd do to the "smart" charging system. Any information would be greatly appreciated.
It wouldn't do anything bad to the charger.
"Smart chargers" are actually pretty dumb and will just see the added load as if the battery was more depleted than it is and, depending on its algorithm, may try to up the current (if there's any in reserve).

Depending on the current draw (which is fairly low on the Pico) vs. available charge current the Pico will probably draw all the needed current from the charger, so the battery will be full or pretty close to full when you disconnect.
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 rbtyingTopic starter

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Re: Multiple power supplies
« Reply #6 on: August 21, 2011, 10:05:26 AM »
Thanks! That sounds like a good solution for me then.

 


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