The Fs and early GPs had to have a field loop cable to excite the DB and without it they would not work, much later they were modified to take the signal off the 27 pin MU cables but by then most Fs were gone.
From: CBQ@groups.io [mailto:CBQ@groups.io] On Behalf Of Tom Mack via Groups.Io
Sent: Friday, February 28, 2020 2:56 PM
To: CBQ@groups.io
Subject: Re: [CBQ] Dynamic Brakes
On Fri, Feb 28, 2020 at 11:41 AM, John Olson wrote:
Since all of the Q's freight F-units (including FT's) were delivered with Dynamic Brakes and none of the GP-7's or GP-9's were- when the 'Q' spliced one or more of these GP's in the middle of a 4-unit set of F's, for extra horsepower, could the Dynamic Brakes still be used... and would it activate on all four of the F-units?
Yes. Dynamic braking is controlled on MU cable pins 17 (Dynamic Brake Control), 20 (Dynamic Brake Warning), 21 (Dynamic Brake Interlock), and 24 (Dynamic Brake Excitation). All units with MU, whether they have DB or not, should pass all MU signals through. Thus a non-DB unit would not affect the DB on any other units in the string.
The problem is if you have a non-DB equipped diesel leading a consist with DB equipped locomotives. In that case you disable DB on the entire consist since the non-DB equipped unit does not have the DB lever or wiring to control DB. Hence very seldom would a railroad that counted on DB put a non-DB unit in the lead.
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Tom Mack
Cincinnati, OH