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[DPRG] Robot Pb battery charging question

Subject: [DPRG] Robot Pb battery charging question
From: Quinones, Jose jquinones at ti.com
Date: Sun Jan 24 05:10:41 CST 2010

Hi Paul,

I will be honest here; whether what you attempt to do (tap out of the lower 12V battery that is connected in series with another 12V battery to power 24V motors) is a good idea or not, I have no clue. But there is like a gut feeling which tells me it is not the most efficient way to do this.

I had your problem, precisely! Which is why I came up with the AE-PWR1 board. I think you may still have one of the bare boards. The beauty of this concept, is that all you have is a single 24V power source and the PWR1 generates 2 other voltage outputs. Per example, you could have 3.3V and 5V derived from the 24V and both batteries would be subjected to the same loading. Plus the PWR1 gives you multiple connection points to route your two rails.

Each PWR1 output can support up to 2A loading, which I believe should be more than enough to power up your electronics (unless you are driving a PC on the 12V). I have not tried wiring them in parallel, but I supposed there has to be a way. That would give you 4A of current loading.

Sorry to ask this, but could you copy-paste this question on the www.robot-talk.com forum? I think it is a very good question and since I am trying to fill it up with content, it would help quite a bit! Thanks!

Best regards,
Texas Instruments - Applications Engineer
13560 North Central Expressway
Dallas TX, 75243
Office: 1-214-567-7275
Mobile: 1-214-240-3179
-----Original Message-----
From: dprglist-bounces at dprg.org [mailto:dprglist-bounces at dprg.org] On Behalf Of Paul Bouchier
Sent: Sunday, January 24, 2010 4:39 AM
To: dprglist at dprg.org
Subject: [DPRG] Robot Pb battery charging question

Robot Illuminati - I'm seeking advice on a robot battery power/charging
conundrum. I'm building the electronics for a robot which has 24V motors but
12V electronics (Mowbot, for those who know him). The natural way to wire it
is to put two 12V batteries in series, tap off the lower one & feed 12V from
it to the electronics, and wire the upper one to the motor power circuit. 

The concern I seek advice on is charging the two 12V lead acid batteries.
The lower one will discharge faster, especially during development, because
it's running the electronics as well as its share of the motors. If I just
hook up a 24V charger to the two batteries I'm concerned charging will leave
the batteries unbalanced because the upper one will be fully charged before
the lower one. 

Is this something I should worry about? If it is an issue, does anyone have
any ideas on how to address it?

I imagine the electric R/C guys deal with this, because they sometimes have
separate motor & radio batteries. What are the standard techniques for
handling this situation?

Thanks for any ideas

Paul Bouchier

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