Thu 24th / Fri 25th - Maintenance
Thanks again to Graham, especially as it means Alex doesn't need to do Saturday's report until tomorrow now!
Friday
The usual gang of 5 in attendance. More legionella avoidance flushing activities, draining flushing and refilling the overhead water tanks. Cleaning and lubricating the tracks of the sliding window quarter lights…
Thursday
The two Richards went looking for a suitable dynamo and fixings to fit on the CK16621. It’s a case of finding items on carriages that have no hope of being refurbished any time soon so they made a trip into the far end of the yard to take the swinging arm and spindle from a carriage suitably low down on the restoration list.
Once the dynamo had been cleaned up a bit it was ready to be mounted and painted.
Unfortunately finding a key for attaching the pulley securely is not so easy - we’ll have to ask someone to make a key or get our own files out!
Why can't alternators be used instead of dynamos?
ReplyDeleteThe batteries on the carriages are 24V and requires DC (direct current) to charge them.
DeleteAlternators produce AC (alternating current) which needs to be converted to DC using some form of rectifier. A dynamos produces DC automatically as the commutator internally acts as the rectifier. In the 1950-1960's solid-state rectifiers were not invented and the only other form of rectifiers available at the time were mercury-arc, not suitable for mounting on carriages.
The dynamos fitted to MK1 carriages were either 70A or 125A (used for high loads, eg restaurant/buffet cars), which at 24V means 1.7kW or 3.0kW output. With the LED lighting now fitted to the carriages, the maximum current taken is about 20A, and we probably could find a modern alternator to be suitable, but that would require a fair bit of engineering modifications to fit, as the drive has to be taken from the wheelset.
Is there no easy low cost means of fitting an intermediate small to large suspended pulley arrangement in order to provide a faster turning speed of the generator rotor; and ensure that the speed the carriages now run at can generate the output voltage needed to maintain lighting and battery charging?
ReplyDeleteTypically the dynamos will only provide output if the carriage is travelling at a speed in excess of 18-20 mph. With a maximum speed of 25mph allowed for heritage railways, there is little opportunity to provide adequate charging of the batteries. Smaller diameter dynamo pulleys have been tried in the past on our and other railways to compensate for the slower running but this also has complications with belt tension.
DeleteAn intermediate gear-up pulley arrangement might be possible but there is little room under the carriage between the dynamo and the bogey to mount a suitable lay-shaft and tensioning system. The dynamo is currently aligned to the wheel mounted pulley and would need to be off-set to allow for the additional mechanical equipment.
It sounds to me like every "how about this" suggestion is more complicated than the one we've settled on! :)
ReplyDeleteYou state: "the dynamos on the GWSR are not functional as the speed of the trains is not normally enough to charge the batteries reliably - this is why we use battery chargers on each carriage and recharge the batteries overnight" So why bother fitting the dynamos at all? One less item to maintain I'd have thought!
ReplyDeleteGood point! However we are led to believe many visitors like to see carriage that are complete with the dynamo pulley and belt turning as the carriages go along, even though they are electrically isolated with the fuses removed!
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