Re: [MV] 24 volts at Blazer Relay

From: chance wolf (timberwolf@wheeldog.net)
Date: Mon Nov 06 2000 - 23:04:48 PST


----- Original Message -----
From: "Emmett Thompson" <kt4al@worldnet.att.net>
To: "Military Vehicles Mailing List" <mil-veh@mil-veh.org>
Sent: Monday, November 06, 2000 4:09 PM
Subject: Re: [MV] 24 volts at Blazer Relay

> You will read 24 volts there because there is no load (current) to find
out
> if the resistor is bad put an ohm meter across it. Dropping voltage with a
> resistor is wasteful. 99% of the time a transformer is used. I believe it
is
> a pair of 100 ohm resistors. Investing in a good trouble shooting manual
> would be well worth your time. I have found that time spent
troubleshooting
> is much cheaper and less aggravating than throwing parts/money at the
> problem.

Erm? A transformer dropping DC to DC? That'd be a neat trick <grin>. There
are, of course, DC-to-DC converters used from 12VDC to 6, and
24 to 12, and other variants for use in 25 sets and the like, but they all
involve
chopping up the DC feed voltage through transistors (until it's a
very square-wave sort of AC), feeding that voltage into the primary of a
transformer, realizing a secondary (also AC) voltage from the transformer
output, then rectifying it back to DC again.

Fine for relatively low current draws, but the CUCV glow plugs suck an
immense
amount of current, hence the resistor of a wattage I could only guess at.

The wasteful part is dead on though - as dropping 12V resistively at that
sort of
current would generate some kinda heat!

Andy Hill
MVPA 9211
Vancouver, B.C.

(For instance, put your hand on a 151 heater resistor while the fan is
operating
  in 'low' position. That resistor is likewise a dropping resistor,
effectively
  cutting the fan supply voltage in half - and with the expected heat
dissipation.)



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