marflow wrote:The ETH supply is 1000 volts (ish). Designed to give lots of watts at a lower amperage for heating down a long rake. (It's the amps that cause losses in cables). So I wouldn't have thought ETH supplies were suitable for galley use etc.
As Mike has pointed out 1871 is currently fitted with a motor-alternator set which is powered by the ETH supply. The MA set will operate in the 800 - 1000V range. The output from this is 240V AC which is used for powering the various equipment in the galley as well as battery charging. This is the same method used on later Mk2 and Mk3 stock to supply power to the air conditioning.
The issue with 1871 is the MA set is u/s and requires repairing. Not a problem but that would mean an ETH loco would always be needed to give a supply to the MA set. Here is the biggest problem as we currently only have one loco, 50015, that is capable of supplying a constant output on ETH that will run the MA set reliably. Whilst there are other locos that can supply ETH, they do not give a constant output.
D1501 (47402) outputs 800V which is at the bottom end of ETH requirements. More critically, to supply ETH, the engine idle speed is raised, but, when moving away from a stand, the engine revs drop back to the lower idle speed to prevent an overload of the main generator. This obviously cuts the ETH supply. MA sets do not like having variable voltage supplies.
As for Deltics their issues stem from the fact that ETH is supplied directly from the main gen. This had to be done as there was no room for an ETH gen to be fitted. At idle the main gen will only supply 425V so to provide ETH both generators are connected in series to give an output of 850V. When under power the ETH is supplied by the generator of the leading power unit. This was
achieved as follows, with the power handle closed both generators are connected in series supplying ETH output of 850V, opening the power handle cuts off the ETH supply and a time delay relay of three seconds prevents traction current being drawn whilst the ETH contactors switch over to supply from the leading power unit, BUT ETH is not switched back on until a minimum of 600V is being supplied from the generator, this to give maximum starting power. When closing the power handle there is a ten second delay before the ETH supply is switched back to both generators connected in series, this is to prevent unnecessary switching should power be shut off momentarily for a signal etc. As can be seen Deltic ETH is very variable in output, regularly being switched off and varying from 600 - 850V.
There were MA sets which had modified control systems which allowed them to work with 47401 - 20 and Class 55. These were fitted to batches of ER based vehicles but following the withdrawl of, firstly Deltics and then the 20 47/4s, just became part of the common user pool.
Class 33s cannot supply ETH to MA sets as they have the same setup as 47401-420 and some of them had the output derated for SR stock.
) when the coach was 'plugged in'
