Electrics on Mk1 Carriages for GWSR

 Right, a technical one today, sit up and pay attention folks, apparently it's more complicated than just blue smoke! Thanks to Richard I and Richard II for this article, over to them - Ed.

A number of people ask why the electrical maintenance team is so involved in work on the carriages and what has been changed from the traditional ex BR Mk1 carriage. 

With the typical speed of the trains being under 25 mph – and only when exceeding 18 mph would the on-board batteries be charged – and the carriages being at a standstill for a good few hours in a day, the traditional method of charging the batteries with the on-board dynamo is inadequate. For the last ten years the carriages on the GWSR have had through-wiring allowing each carriage to have its own charger, thereby ensuring the batteries were fully charged at the beginning of the working day.

Over the last couple of years, these charger units were starting to become unreliable. An alternative charger was sourced and we have been modifying the 240V wiring on the carriages to accept the new charger, taking the opportunity of standardising where possible.

The new Victron chargers are fully weatherproof and have the added functionality of Bluetooth connection to a smartphone via an App, enabling us to view the key parameters of the charging cycle.

Typical results from Victron Bluetooth enabled charger via smartphone app.

The chargers are electronic and have a seven-step charging algorithm. After a battery test, the first part of the charge works at constant maximum current (5A - bulk charge) with increasing voltage until the battery is 80% full, followed by a period of constant voltage, decreasing current (29 Volts – absorption charge) until the battery is fully charged. It will then run at a trickle charge (float) and finally go into storage mode, dropping into a short absorption charge once per week. Above is snapshot of the typical main charge profiles shown on the smartphone App.

The carriages are wired with a through cable from one end of the carriage to the other, terminating in a 16A plug at the south end and a 16A socket at the north end, with the charging cable always connected to the south end of the rake. The cable is brought to behind the battery box and a multi-way connection box with 13A socket allows easy connection of the battery charger. 

We have now changed over two-thirds of our carriages to the new type of charger.

Batteries – and the use of a data-logger

We have been challenged over the past few years about the way some of our batteries have performed during the season. Charging overnight and not relying on any daytime charge, works for the majority of the batteries. However the high-demand carriages (eg Restaurant/Buffet cars or where we still have fluorescent loads) during the winter months where the lights have to be on, the batteries have not performed so well.

In order to get some empirical data to justify any appropriate investment, we purchased a voltage data-recorder. This is a small USB stick that samples an external voltage which can then be downloaded on a computer to be analysed. The data-recorder captures over 32,000 records and can be set to sample at different time intervals, from one per second (approx. 9hrs capacity) up to sampling on an hourly basis. We have found 20 sec sample rate giving 8 days capacity is useful as we can review weekly, or 1 min sample rate giving 22 days for the longer analysis.

We found two suspect carriages, the RBr (1672) and the RMB (1876) where the batteries would not last the operational day. Furthermore, if the battery voltage is allowed to drop lower than 24V, not only is this a sign of deep discharge, the batteries can be permanently damaged.

Output from data-logger on RBr during September 2019

Also, we were getting reports from the RCS staff that whilst the lights were still operating (these will work to a voltage as low as 10 Volts), the protective gas solenoid would not stay open at the end of the day, therefore the water heater would fail.

Using this report, it convinced us that we needed to upgrade the batteries and charger and that such investment would be well targeted. This was planned and completed in the month before the Santa 2019 use of the train.

Having upgraded the batteries to 385 AHr and installed a larger charger (25A) on the RBr, we found the performance was significantly improved. 

Output from data-logger showing voltage maintained above 24 Volts.

One advantage on the RBr was that a gas powered generator is installed to provide power to an electric toaster to provide toasted teacakes. The use of the generator can be seen in the post-Christmas period, but not during the Santa trains.

As a result failure of the batteries in the past, we have designed and built a battery monitoring alarm panel which gives a visual and audible signal should the battery voltage go below 24V, instructing the RCS staff to start the on-board generator in order to restore battery voltage.

The other carriage which has presented us with problems is the maroon RMB (1876) which has fluorescent lighting. We have not yet updated this to LEDs and so the battery drain is significant, taking about 20A load when all lights are working. This became the next candidate to investigate with the data-logger, and the characteristics of the battery voltage were clear to see…

Output from data-logger on RMB during Race trains 2020

After the summer season where the RMB had not been used due to being COVID-19, we connected two data-loggers, one to each of the batteries, to see whether it was just one or both batteries were giving us problems.

Individual data logger results of the two batteries of the RMB 
 
We show the two data recorders with the blue cursor at the minimum voltage recorded (1/11/20 17:33:06) to see the resulting terminal voltage amounting to 12 V (instead of 24V).
The plan (before the latest Lockdown-3 kicked in at Christmas) was to use the RMB as a carriage on the north of each rake to provide refreshments at Broadway and Cheltenham. In early December we were permitted to change to batteries and charger to similar configuration to the RBr in preparation of the post-Christmas use of the carriage, but have yet to report on the outcome.

When we are allowed to return to the C&W works following this latest lockdown, hopefully before too long, we shall measure the operating current and run a load test on the carriage with the data-recorder connected (effectively switch on the total lighting and kitchen load) for a period of about 3-4 hrs to assess the performance of the new batteries. With this data, we should be able to identify if we need to progress a planned future project of modifying the fluorescent fittings (to convert them to LEDs) sooner rather than later.

Richards Bates & Budd