any merit in running dual battery packs ?

[Dean Pappas]

Hi Tom,
That's why you turn on one switch, then the second, then turn the first off, then turn it back on. At each step, check for signs of life.
That was what Bob meant when he said, "like a magneto check in full scale".
Later,

Dean Pappas
Sr. Design Engineer
Kodeos Communications
111 Corporate Blvd.
South Plainfield, N.J. 07080
(908) 222-7817 phone
(908) 222-2392 fax
d.pappas at kodeos.com


-----Original Message-----
From: discussion-request at nsrca.org
[mailto:discussion-request at nsrca.org]On Behalf Of Tom Simes
Sent: Monday, January 24, 2005 5:29 PM
To: discussion at nsrca.org
Subject: Re: any merit in running dual battery packs ?


On Mon, 24 Jan 2005 14:45:32 -0500
"Dean Pappas" <d.pappas at kodeos.com> wrote:

> LEDs have large voltage drops. Something more interesting would have
> to be done. You have to figure out what is most likely to fail. My
> high-falutin' analysis, done ages ago, showed that switches and
> connectors are the worst culprits. I use one battery withtwin leads,
> and cvarry the twin leads all the way to the RX. Of course, I don't
> buy the cheapie batteries. Hello SR! Dean

So I can see that your method likely reduces the probability of failure,
but as far as I can see you still have no indication that a failure has
occurred in the primary system until a failure occurs in the secondary
system as well - although when the notification occurs it's a doozy!

Checking Digikey it looks like even the high efficiency LEDs are
still in the neighborhood of 2 V forward drop and the drop is fairly
consistent across their operating current range (darn physics!).  

It looks like one might be able to use something in the TI TPS61010 thru
TPS61016 family to drive the LED (although obviously at the cost of
increased input current).  Or what about using a dropping resistor and
tapping the current flow downstream of the regulator with the lowest
voltage setting?  Should I crawl back in my hole with this?  I'm just
thinking that some kind of visual failure indicator would really be
a beneficial addition to a two pack design.

Of course that wouldn't show you that the backup pack had a failure
while the primary pack was still operating...  Although you could have
an LED on both regulators and as long as the expected one was on...
Vague memories of statistics class, MTBF calculations and the effect of
adding components to a system are starting to crop up about now...

Nevermind, straight back to my hole it is - now where did I put that
tinfoil hat?


Tom

_____________________________________________________________________

       |  ,  |               Tom Simes
---------(@)---------        AMA 230068
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          '                  nsrca at shinymetalass.com
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