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From: Tony Williams
Subject: Re: Current draw of several light bulbs?
Date: Wed, 11 Dec 2002 07:45:03 +0000 (GMT)
NNTP-Posting-Date: Wed, 11 Dec 2002 08:39:15 +0000 (UTC)
User-Agent: Pluto/1.14i (RISC-OS/3.60)
In article <firstname.lastname@example.org>,
> My first guess would be to simply add the current draws (i.e.
> 6 bulbs in parallel would draw 6 x 0.15 or 0.90 amps). Can
> I assume that 42 bulbs will draw 6.30 amps (i.e. 42 x 0.15 amps)?
> Another question, what is the difference between driving them with
> DC rather than AC? I know that the bulb doesn't care and I'd like
> to use AC because it simplifies the power supply.
To get best life I think you would need to ensure
that the voltage never exceeds 6.3V. So the
transformer has to be designed for 6.3V unloaded
voltage (1 bulb), reducing to (say) 6V when all
bulbs are on..... in transformer terms this would
be a 6V transformer, with 5% no load to full load
5% regulation is not normally achieved in low-VA
transformers, but can be obtained by accepting
a larger transformer with (say) 10% regulation and
only running it at half load. Toroidal transformers
give better regulation because of the reduced leakage
Perhaps split the total load into groups, each group
using a 6V 20-25VA transformer, driving 8-12 bulbs.
(Avoids having to unplug 42 bulbs to find the s/c one.)
That would be a 1.2-1.8 A load. Fuse with about a 3A
Slo Blo (or motor current breaker) to allow for the
switch on surge current.
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