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[DPRG] Re: 9 volt batteries in parallel
Subject: [DPRG] Re: 9 volt batteries in parallel
From: Chuck McManis
cmcmanis at mcmanis.com
Date: Tue Mar 27 16:58:14 CDT 2007
Hi Rick,
This is a good example of where the requirements can be harder to get right
than the design! So you wrote:
> You are correct - 9V batteries are short on current capacity, which is
> precisely why I need to use them. There's more to the story. The circuit
> I'm building has to be mounted in an intrinsically safe area, so I have to
> limit the total power capacity of the batteries.
On the surface this appears to be a design requirement that defines the
design to be impossible. On the one hand you state "I use 9v batteries
because they have less power capacity for saftey reasons" on the other hand
you state (not in this message but to start this thread) "I need more power
capacity than a 9v battery can provide, can I use them in parallel?"
This is further complicated by the inference that "intrinsic safety" and
"power capacity" are somehow related. I expect you will be much more
successful if you treat each of these requirements separately, power
required and safety level required. It may be possible that what you are
trying to do is impossible given the requirements at which point you have to
go back to the folks who created the requirements in the first place and
explain their choice in terms of changing requirements or picking a
different project.
The reason this is such a good example is that it crisply demonstrates a key
component of the engineer's life. Asking the question "Is there a solution
(design) within the volume constrained by the following requirements?"
--Chuck
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