[Test-Equipment] RE: MAHA battery cooker

[Hsu, Aaron (NBC Universal)]

Primarily because many people don't want to wait 16 hours to charge a battery <g>.  Trickle charging a NiCD or NiMH battery is the absolute best way to do it, but everybody wants it done *NOW* these days.  So, force 800mAh through a battery, watch it heat up, and hope it takes a full charge and doesn't melt or blow-up in the process.  Be thankful it's not a Li-ion battery - overcharge/overheat these things just a tiny bit and they'll cause trouble!

I think part of the problem with the auto-detection circuitry in the C777 type chargers is that they don't take battery age and internal resistance into account.  I've noticed that my older NiCD/NiMH batteries will report a higher voltage when first "analyzed" by the C777.  For example, 4 AA NiMH batteries show as 6.2v when first "analyzed" by the C777.  It then thinks it's a 5-cell 6v (1.2v x 5) pack and will attempt to charge as a 6v pack (@ >7v).  When I start the discharge analysis, it cuts out at 5v thinking there are 5 cells rather than 4.  I know the analysis is applying a slight charge (3 minutes?) to the battery before determining cell count.  I'm thinking it should "rest" the battery without charge for a minute after the analysis before determining the cell count.

Perhaps what Maha needs to do is to add the ability to "force" the cell count.  The charger should then bulk charge the battery upto 1.4/1.5v per cell and then put the charger into a trickle charge mode to top off the battery.

Anyways...

73,

  - Aaron, NN6O



-----Original Message-----
Sent: Wednesday, November 28, 2007 5:27 PM
Subject: Re: [Test-Equipment] MAHA battery cooker

On Wed, 28 Nov 2007, Brooke Clarke wrote:

> I too had that problem with the Maha C777 and sent it back because it was not 
> properly figuring out the number of cells in a pack.

Over the years I have had a real mental problem wondering why battery 
charging for NICADS and Nimh batteries had to be so involved. I use a lot 
of battery powered devices (mostly 2-way radios) and all I have ever done 
is charge them with a power supply and current limiting resistor at the 
standard 16 hour charge rate (1/10 the amp/hr rating) and I have never had 
a problem. Sometimes, if I want to keep one topped off, I leave it on what 
I call "super trickle" which is 1/10 of the standard charge rate.

                               Bob Roehrig
                     Aurora University    Telecom dept.
                            broehrig at aurora.edu
                          K9EUI  W9ZGP  WD2XSH/19
                     630-844-4898      fax 630-844-4222
                     "Nostalgia is a thing of the past"
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