Subject:
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Re: DCC for the RCX
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Newsgroups:
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lugnet.trains
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Date:
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Thu, 29 May 2003 12:45:38 GMT
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Viewed:
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2512 times
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In lugnet.trains, James Powell wrote:
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As I run 12v stuff I dont know the 9v motor good enough to comment on the
capacitors but I dont think it’s that good an idea to use a resistor to
drop the voltage. Use one or more (zener)diode’s instead.
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Resistors work fine due to the relative difference in cost. The accessory
outputs of the earlier decoders are 100ma or so @28V or less, so at most you
are dealing with 2.8 w loss (or 100 ma current draw). In order to drop from
14V to 9V, you are loosing 5V/.5W at 100ma, (and 50 ohms) which is not really
a signifigant load. The more recent decoders with 500 ma accessory outputs
are trickier, since you are getting into more serious power draws (like 14 w,
which is darn’d near what my soldering iron is...)
James Powell
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Huh??!? Your basic resistor can only handle 1/4 watt (0.25W), so your
worst-case 2.8W is more than ten times the rated maximum current. Even dumping
an “insignificant” 0.5W across a resistor is probably not adviseable unless you
are also trying to heat your house. With fire. And don’t forget that all of
this power is being supplied by the motor driver circuit of your precious RCX
which has limits of its own.
Is it worth trying to save a few pennies using a resistor to do a diode’s job at
the risk of doing dammage to your RCX?
-Chris.
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Message has 1 Reply:
 | | Re: DCC for the RCX
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| (...) I don't know about you, but I tend towards .5W or bigger for most of my resistors, and diodes have exactly the same problem if you use them as a voltage drop. Load is not really signifigant on a 5A booster (soon to be 10 amps total...2 (...) (21 years ago, 30-May-03, to lugnet.trains, FTX)
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Message is in Reply To:
| | Re: DCC for the RCX
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| (...) Resistors work fine due to the relative difference in cost. The accessory outputs of the earlier decoders are 100ma or so @28V or less, so at most you are dealing with 2.8 w loss (or 100 ma current draw). In order to drop from 14V to 9V, you (...) (21 years ago, 29-May-03, to lugnet.trains)
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