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[DPRG] charge and forget

Subject: [DPRG] charge and forget
From: Dennis Clark dlc at frii.com
Date: Tue Mar 30 12:46:24 CDT 2010

The BGmicro cells are good for project I think.  A temperature monitor  
and one of those low current chargers would be perfect for you.  To  
save effort you could use the Sparkfun PRT-00726 single cell LiPo  
charger and have what looks like a great setup.


Dennis Clark
While traveling

On Mar 30, 2010, at 10:27 AM, Ed Paradis <legomaniac at gmail.com> wrote:

> And I guess I've come full circle.
> My original idea was to build a small NiMH pack with an integrated
> charger that'd keep me out of trouble for over charging.  (Can you
> spot the "fire and forget" design requirement? :D )
> It sounds like for these small LiPos, I can charge at a reasonable
> rate with a temperature monitor on the battery for emergency shut off
> and sleep well at night.
> Really, the NiMH would charge the same way.
> I suppose one of my reasons for moving away from NiMH was the long
> charge time, but if I say "reasonable charge rate" with a LiPo, I've
> lost the benefit of using LiPo, since NiMH has no memory effect and I
> should be able to charge at will.
> It sounds like I would benefit from concentrating on a generic charge
> management system that supported enough brains to charge various
> chemistries.  Ok, just NiMH and LiPo.
> Here is the algorithm for LiPos: http://www.powerstream.com/li.htm
> Requires current monitoring and voltage monitoring and some brains to
> switch betwixt the two.
> Here is the algorithm for NiMH: http://www.powerstream.com/NiMH.htm
> Requires voltage monitoring but only current regulation and some
> brains to shut things down.
> Both require temperature monitoring for unattended charging.
> Ah! One benefit of not using NiMH is cell balancing.  For a 3.3v
> system, a single LiPo will suffice with one of the Pololu switching
> regulators I love so much.
> Right now I use three NiMH in series, and theoretically I'd want to
> cell balance them.  You know and I know that no one does that and I'm
> not looking at charging fast enough to cause troubles.  Temperature
> monitoring would catch trouble if you were to mount the thermistor
> such that the three NiMH cells surrounded it.
> As far as Lead Acid batteries, my robot is significantly wussier than
> yours, David.  With a lead battery I'm afraid I'll be tearing treads
> off and putting a good deal of wear on the Tamiya gear box.
> Beating my head against the same problem again,
> Ed
> On Tue, Mar 30, 2010 at 10:36 AM, David <dpa at mail.isem.smu.edu> wrote:
>> I spent a lot of time doing battery comparisons when we built
>> jBot, and settled on NiMH (two 12 volt packs) as the best  
>> compromise.  They
>> are safe and truly charge and forget.  They can be topped of (no  
>> "memory
>> problems" like with NiCads) and provide all kinds of current when  
>> needed.
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