Class 57/0 Update Discussion

[Ooveecouk]

One more from me ! The amps should drop to zero when the controller is put in the 'Off' position and the tractive effort should drop to zero because the motor contactors are open in that position. At the moment the amps drop slowly to zero and the loco feels as if it's still under power when the controller is moved to off. I suspect this is due to the way the delayed response of the engine to the controller is modelled.

Andy L

Hi Andy the amps is taken off the alternator not the traction motors. Amps is literally determined by engine RPM this is as close to accurate as any Diesel Electric that RW has had the pleasure of simulating.

But if the motor contactors are open there is no circuit between the traction motors and alternator - therefore no current can flow hence the ammeter should read zero.

Andy L

Don't worry, the ammeter now drops to zero when throttle is closed.

[phill70]

Don't worry, the ammeter now drops to zero when throttle is closed.

Good, because that is what is should happen.

I think the first 47's (47401-25) or whatever it was, had Westinghouse brake equipment.

[wolly1380]

Humm your right I missed the contractors bit.
I did think it would just be a case of letting the field drop off I think EE's did this. makes sense since this is a loco developed in 1990's rather than the 1950's

[Kariban]

From the chats I've been having to old EE drivers ( the EE are old, not necessarily the drivers ), if you shoved the power controller closed past the On notch that would open the contactors too; and then your amps drop to 0 again. I've hacked this into the 37, it makes it quite interesting when you have to fish around for the On notch to close them again.

[wolly1380]

From the chats I've been having to old EE drivers ( the EE are old, not necessarily the drivers ), if you shoved the power controller closed past the On notch that would open the contactors too; and then your amps drop to 0 again. I've hacked this into the 37, it makes it quite interesting when you have to fish around for the On notch to close them again.

I'll get me coat

[Kariban]

Well there still appears to be a problem with RW that the throttle seems to control amps rather than (just) engine RPM; not sure if that's meant to represent some load controller thing or it's just plain wrong.

[AndyUK]

In RW with a fixed controller setting the current will drop off as speed increases modelling the effect of back EMF. So it's not a case of throttle setting 'x' gives amps 'y' which is what I inferred from your post.

Andy L

[Kromaatikse]

No, but there is an unprototypical current limiter associated with throttle position. This can be seen in operation on several of the default diesels.

Constant-current operation did exist on some American locomotives, but did not enter mainstream British practice.

[Ooveecouk]

So amps should drop smoothly with RPMs? - At the moment the amps reflect the same as default stock let me know and I will see what can be done.

[Kariban]

Cosmetically that's not hard to correct; I'm a little concerned that it's a bit more than cosmetic for the default stock, and thus for the Regulator controller. I guess you throw out all the builtin RPM spool up/down & script that too, eh.

Modern ( well reasonably ) diesels would use thyristors though, I guess? then you might well have some direct current control.

[AndyUK]

So amps should drop smoothly with RPMs?...

Apologies if my post above led you to that conclusion, I was guilty of over simplification. The current will drop with increasing speed once the generator excitation is at maximum, but then weak field stages (if fitted) will cut in which will cause a slight increase in current before it drops again with increasing speed. A picture being worth a thousand words the theoretical curve on upper graph in this post by Kromaatikse shows what should happen (http://forums.uktrainsim.com/viewtopic. ... 1&t=107773). The values of current and speed etc will vary for differnt locos but the overall effect is the same

As you can see RW models this after a fashion in the default stock.

Andy L

[Kariban]

That is current/speed for constant RPM though; we're talking about current/RPM at any speed, and whether indicated current should be linked with RPM rather than controller position ( barring Off notch at least ) as it seems to be. I'm going to speculate that for an old installation current should drop with falling RPM rather than controller position, but when you get to electronic controls there's no reason why you can't do whatever you like, and I've no idea.

[AndyUK]

That is current/speed for constant RPM though; we're talking about current/RPM at any speed...

Sorry I misread Oovee's post.

...and whether indicated current should be linked with RPM rather than controller position ( barring Off notch at least ) as it seems to be. I'm going to speculate that for an old installation current should drop with falling RPM rather than controller position, but when you get to electronic controls there's no reason why you can't do whatever you like, and I've no idea.

but as engine RPM is linked to the controller position both in RW and in the prototype I'm not sure I get your point.

Andy L

[Kariban]

Yes, but current doesn't drop smoothly with RPM if you close the controller, it drops *immediately*, proportionally to your controller movement; meanwhile the engine and generator are still spooling down. I see how you could do this from an old type load controller, but I don't know if it actually was done.

Actually now I go back and check, amps rise with controller position before the engine spools UP too, although it's not totally independent of engine RPM.

[AndyUK]

Sorry I'm a bit slow on the uptake today, I now see what you mean. If the engine speed, increase or decrease, follows the controller setting change with a time delay then yes, the current should follow the engine RPM rather than the controller position, except in the case already discussed when the controller is put to 'off'.

Andy L