TfW class 398 Stadler Citylink tram trains

[Peter Sarf]

I doubt the batteries on a 398 are meant to be anywhere near the same cpacity as on a 756. After all the batteries in a 756 are fitted in a module the same size as an engine and occupy space above the floor.

 

[VR494]

I doubt the batteries on a 398 are meant to be anywhere near the same cpacity as on a 756. After all the batteries in a 756 are fitted in a module the same size as an engine and occupy space above the floor.

Traction batteries on the class 756 are (LTO) supplied by ABB, they and located in the centre ‘power-pack’ vehicle along with the diesel generator.

The 3-car units have an installed battery capacity of 447 kWh, whilst the 4-cars have a capacity of 559 kWh.

The class 398’s have lithium titanium oxide battery as well, with a capacity of 138 KWh. With no diesel generator.

Tfw does not use the electricity from the overhead wires to power the traction motors directly. Instead they operate in battery mode and the pantograph is used to top the battery up. Yes you read that right.

The wires on the valleys are not the same as you’d find on the mainline, they are not capable of producing enough power to run a full electric service and the flirts are pushing them to capacity. It’s not uncommon for the system to trip out on a daily basis. If it was not for the diesel generator many services would have to be terminated.

The system is also fed from a limited supply of sub stations, and if you were to turn wires off in Cardiff, near enough the whole of TAM would go down. Yes, you read that correctly too. They didn’t install enough neutral sections and it’s all connected.

 

[AdamWW]

I doubt the batteries on a 398 are meant to be anywhere near the same cpacity as on a 756. After all the batteries in a 756 are fitted in a module the same size as an engine and occupy space above the floor.

Quite. There is clearly a lot more space on a 756 dedicated to batteries, and they were designed to have a much larger battery capacity.

 

[VR494]

Out of interest, why does a fitter need to be there to uncouple units?
Is it not like normal trains where a button is pressed and move unit?

They are coupled and prepared on depot, to uncouple them requires physical assistance from fleet. They also cannot be assisted by anything other than another 398.

 

[AdamWW]

Tfw does not use the electricity from the overhead wires to power the traction motors directly. Instead they operate in battery mode and the pantograph is used to top the battery up. Yes you read that right.

I have seen this said before but I do not understand how it can work - I can't visualise the circuit that lets a battery simultaneously be charged and be providing power to the traction motors without this constituting a direct link between the overhead power and the traction motors.

I realise that from an operational point of view there may be a "direct power" mode and one in which the batteries are in the circuit, but I can't see how a battery can simultaneously be charging and discharging.

I can see that depending on whether the power demand is greater or less than the overhead can supply the battery can either be providing power in addition to the overhead power, or some of the overhead power can be charging the battery and some being used for traction.

 

[43096]

They are coupled and prepared on depot, to uncouple them requires physical assistance from fleet. They also cannot be assisted by anything other than another 398.

That is just dumb beyond belief, but it isn't a surprise.

 

[VR494]

I have seen this said before but I do not understand how it can work - I can't visualise the circuit that lets a battery simultaneously be charged and be providing power to the traction motors without this constituting a direct link between the overhead power and the traction motors.

I realise that from an operational point of view there may be a "direct power" mode and one in which the batteries are in the circuit, but I can't see how a battery can simultaneously be charging and discharging.

I can see that depending on whether the power demand is greater or less than the overhead can supply the battery can either be providing power in addition to the overhead power, or some of the overhead power can be charging the battery and some being used for traction.

They had a software update prior to introducing them at the request of tfw, we do not use the full feature of the units.

The units have a combined battery and overhead mode, which charges the batteries. They can be switched to full electric mode for mainline, but this is prohibited on the CVL. That’s all they do is charge and deplete a battery pack. On battery mode only, when the charge reaches 20% or lower, the generator is supposed to automatically kick in and charge the batteries. It will then shut down once the battery is around 70% charged.

The issue with the 398’s is they are expected to be able to run the same way. The batteries aren’t strong enough for one, and the units were designed for full electric power, which they will not be receiving.

Plus when the wires will eventually go, it’s going to be a major incident if the 398’s end up stranded with no charge. When you can only be rescued by another 398, who’ll also have the same capacity.

Whoever ordered these 398’s at the time clearly didn’t know what they wanted, or just saw something in a catalogue and went, yes, we’ll have them!

Now they’re asking Stadler to explain why what they ordered is not working. After they cut costs on discontinuous infrastructure.

Unfortunately, put all their eggs in a basket and dropped it from a great height at the expense of the tax payers.

 

[390112A]

Class 756 units for comparison can do 70-80 miles on a charge where these can do roughly around 6 miles.

The 3-car units have an installed battery capacity of 447 kWh, whilst the 4-cars have a capacity of 559 kWh.

The class 398’s have lithium titanium oxide battery as well, with a capacity of 138 KWh. With no diesel generator.

Welcome to the forum your posts are very intriguing as to the set backs this program faces however I do find your statements regarding the battery performance of the 398s confusing.

398 has approximately 30% (138/447) of a 3 car 756 battery. Yet you state the 398s only have around 8% (6/70) of the range of a 756 this is unexpected and confuses me.

This is a proportional guess assuming similar rates of energy consumption
756 Energy Consumption 447kwh/70miles = 6.39 kWh per mile
398 range 138kwh/6.39 = 21.6 miles
In practice, the 398 has potential to do better than this because:

• It’s shorter and lighter than a 756 and likely has a lower resistance

On the other hand, frequent stops and lower speeds can also hurt efficiency. So realistically I would expect something in the range high teens low twenties triple your stated range.

What is causing a dramatic increase in the amount of power a 398 uses? 138/6= 23 kWh per mile approximately triple 756s

[For 320kwh 35 mile class 777 with similar LTO batteries 320/35=9.14 and 138/9.14= 15 miles 398 expected range]
[This is still more than double your stated range again based on a longer and heavier train]

 

[mrmartin]

Yeah that doesn't make any sense why it would be 6 miles.

Also the project afiak is fed from Pontypridd not Cardiff. And I'd be hugely surprised if given the discontinuous electrification bits couldn't be turned off in pieces! It's not fully connected!

Not sure about the power supply not being up to par either. Pushes credibility imo that it would struggle with just the flirts - it is a fraction of the total design power. Obviously there's some real problems with these units but the 756s are performing pretty well so I highly suspect it's faults with the tram trains rather than inherent problems with the electrification.

The running only off batteries doesn't sense. Maybe he means they have to use some battery power to "top up" the OHLE power. It requires more power to charge a battery AND run the train itself (by nature of simple maths), you couldn't "run the train off batteries but also charge the batteries". There's no way you could run anything if they had 6 mile range but also didn't use the OLE?

That's not to say there isn't potential issues with discontinuous electrification.

 

[norbitonflyer]

Has regenerative braking been included in the calculations in oprevious threads. I imagine it could be an important factor on a route with lots of stops, and gradients.

 

[AdamWW]

Also the project afiak is fed from Pontypridd not Cardiff.

There is a feed at the junction just north of Queen Street station. I don't know if it's normally in use or if it's just a back-up. There are some extremely heavy duty looking switches.

And I'd be hugely surprised if given the discontinuous electrification bits couldn't be turned off in pieces! It's not fully connected!

So far as I can see the discontinuous sections just have the power carried alongside the track - electrically it's fully connected it's just that in some sections it isn't carried through the overhead wires.

What I do find interesting is that the later electrification (Coryton/Rhymney) has fully powered sections that must have been originally planned to be permanently earthed. It looks as if they have been able to get away with smaller clearances than originally expected by using surge protectors. (My understanding is that the clearance is based not on the planned line voltage, but the potential voltage during a lightning strike).

This does suggest that should money become available, it might well be possible to reduce the number of permanently earthed structures on the lines that the 398s run on.

 

[positron]

I’m afraid the source of this information is not dubious in anyway

With respect @VR494 you joined the forum this week and we have no way to verify who are. Given inconsistencies around what you've said regarding air conditioning not existing, but actually existing but perhaps being broken (or misused). Along with lots of other hard to verify claims. So in my opinion the source is dubious. I'm not saying you're outright lying just I can't know either way.

What I do find interesting is that the later electrification (Coryton/Rhymney) has fully powered sections that must have been originally planned to be permanently earthed. It looks as if they have been able to get away with smaller clearances than originally expected by using surge protectors. (My understanding is that the clearance is based not on the planned line voltage, but the potential voltage during a lightning strike).

This does suggest that should money become available, it might well be possible to reduce the number of permanently earthed structures on the lines that the 398s run on.

It is interesting how the spec for rhymney does seem to have changed a few times as they've developed and implemented the plan at one point it was no wires past bargoed for example. So it shows they had flexibility, potentially that was late on enough in the project to make changes, but id have expected they could have changed TAM lines if it became clear it wasn't up to scratch.

 

[Wyrleybart]

That is just dumb beyond belief, but it isn't a surprise.

No. It definitely isn't a surprise. It's simply "the railway".
Absolutely shocking really. We always though the 1955 modernisation plan was a textbook on how never to do that again, yet here we again placing stumbling blocks in the way to logic.

I bet Stadler must be pizzing themselves after the Brits leave their boardroom

 

[Peter Sarf]

Traction batteries on the class 756 are (LTO) supplied by ABB, they and located in the centre ‘power-pack’ vehicle along with the diesel generator.

The 3-car units have an installed battery capacity of 447 kWh, whilst the 4-cars have a capacity of 559 kWh.

The class 398’s have lithium titanium oxide battery as well, with a capacity of 138 KWh. With no diesel generator.

Tfw does not use the electricity from the overhead wires to power the traction motors directly. Instead they operate in battery mode and the pantograph is used to top the battery up. Yes you read that right.

The wires on the valleys are not the same as you’d find on the mainline, they are not capable of producing enough power to run a full electric service and the flirts are pushing them to capacity. It’s not uncommon for the system to trip out on a daily basis. If it was not for the diesel generator many services would have to be terminated.

The system is also fed from a limited supply of sub stations, and if you were to turn wires off in Cardiff, near enough the whole of TAM would go down. Yes, you read that correctly too. They didn’t install enough neutral sections and it’s all connected.

If the 756s are running up the TAM lines without using their engines then I can guess the overhead is strong enough to deliver power to lightweight 398s. How much use do the 756s make of their engines on the TAM lines ?.

I am not an electrification expert BUT surely there HAS to be a neutral section and isolation between electrification supplied from different substations ?. There may well be switches to isolate a substation and then connect its overhead lines to an adjacent substation/section. An expert on electrificaton will be along soon I hope to correct me.

I have seen this said before but I do not understand how it can work - I can't visualise the circuit that lets a battery simultaneously be charged and be providing power to the traction motors without this constituting a direct link between the overhead power and the traction motors.

I realise that from an operational point of view there may be a "direct power" mode and one in which the batteries are in the circuit, but I can't see how a battery can simultaneously be charging and discharging.

I can see that depending on whether the power demand is greater or less than the overhead can supply the battery can either be providing power in addition to the overhead power, or some of the overhead power can be charging the battery and some being used for traction.

It will be how a description is being interpreted.

A rash thought but I guess perhaps during regenerative braking the 398s are being isolated from the overhead ?.

That is just dumb beyond belief, but it isn't a surprise.

Thinking about recent events with a 701 that lost its pickup shoes (overnight engineering work left things in the way I believe). A second 701 could not rescue all day, but that night a different 701 could. Coupling and uncoupling seems to be an art these days reserved for the chosen few. Things are just too damn complex and I doubt the problem(s) are exclusive to 398s, other fleets are suffering teething problems.

Mention up thread of union sign off not yet sought on the 398 training made me immediately think of the 701 saga. So I think patience is the best approach. Patience that should not be required I suppose but I do not think the 398s are necessarily the basket case they seem (or no worse than other projects).

 

[VR494]

The battery on the 398 are capable of 10 km (about 6.2 miles).

The electrification on the TAM is fed from Trefforest (Power station hill), Queen street and a small section north of Merthyr Vale. They have run the 25Kv cables alongside the track in cable troughs from these feeder stations to other areas. And switching the power off brings near the whole network down.

I think it’s unfair to compare this project to the 701’s, it’s more than a dispute over door operations. The 398’s are sadly not fit for purpose, and rather than continue to throw money down a well on pointless test runs that keep failing, they need to make a decision soon whether to go for a rebuild, upgrade the infrastructures or another form of rolling stock.

== Doublepost prevention - post automatically merged: 25 Jan 2026 ==

There’s also the issue of Quakers Yard down platform, which still slopes towards the track. This was somehow overlooked during the planning of the rebuild, and it could not reopen. It could only reopen under interoperability provided there are persons there to warn the public of the risks of items running away towards the line. So we now have to pay security to stand there 24/7 as well. There are many other interesting things that would have you laughing for hours. But now let’s get back to these 398’s

 

[Peter Sarf]

The battery on the 398 are capable of 10 km (about 6.2 miles).

The electrification on the TAM is fed from Trefforest (Power station hill), Queen street and a small section north of Merthyr Vale. They have run the 25Kv cables alongside the track in cable troughs from these feeder stations to other areas. And switching the power off brings near the whole network down.

I think it’s unfair to compare this project to the 701’s, it’s more than a dispute over door operations. The 398’s are sadly not fit for purpose, and rather than continue to throw money down a well on pointless test runs that keep failing, they need to make a decision soon whether to go for a rebuild, upgrade the infrastructures or another form of rolling stock.

== Doublepost prevention - post automatically merged: 25 Jan 2026 ==

There’s also the issue of Quakers Yard down platform, which still slopes towards the track. This was somehow overlooked during the planning of the rebuild, and it could not reopen. It could only reopen under interoperability provided there are persons there to warn the public of the risks of items running away towards the line. So we now have to pay security to stand there 24/7 as well. There are many other interesting things that would have you laughing for hours. But now let’s get back to these 398’s

They will struggle on - tis the British way.

In reality I do think that even 18 months ago the 701s were looking pretty dire. Led to talk (on forums) of the 701s just being abandoned. Was not likely with the 701s and will not be likely with the 398s. Never underestimate the scale of teething problems these days and the fact that solutions will be found. Hindsight is a wonderful thing.

Personally I wish TfW had gone with proper trains (756s) and had a separate tram network like Croydon did. But thats just water under the bridge.

 

[43096]

The battery on the 398 are capable of 10 km (about 6.2 miles).

The electrification on the TAM is fed from Trefforest (Power station hill), Queen street and a small section north of Merthyr Vale. They have run the 25Kv cables alongside the track in cable troughs from these feeder stations to other areas. And switching the power off brings near the whole network down.

I think it’s unfair to compare this project to the 701’s, it’s more than a dispute over door operations. The 398’s are sadly not fit for purpose, and rather than continue to throw money down a well on pointless test runs that keep failing, they need to make a decision soon whether to go for a rebuild, upgrade the infrastructures or another form of rolling stock.

I assume there is a blame going on between TfW and Stadler on this? And I bet the odds are that TfW have not specified them correctly...

 

[Malkemy]

View attachment 196333

My quick phone grab at Old Dalby yesterday from the footpath and I saw 398020 waiting to be collected, along with two 398s coupled together (seen above) with pantographs raised and staff onboard, so testing must be ongoing.

To answer your question therefore, I can confirm there are more than just one 398 left at Old Dalby.

Is that an 810 in the background there?

 

[norbitonflyer]

They are coupled and prepared on depot, to uncouple them requires physical assistance from fleet. They also cannot be assisted by anything other than another 398.

Jus5t like the 458s as built. I understand that came as a surprise to the operating department at SWT

 

[VR494]

If anyone would like more information on tram-train, then please see the attached link to the light rail safety standards board: https://www.lrssb.org/news/comprehensive-guidance-on-tram-train-design-and-operation

== Doublepost prevention - post automatically merged: 25 Jan 2026 ==

They will struggle on - tis the British way.

In reality I do think that even 18 months ago the 701s were looking pretty dire. Led to talk (on forums) of the 701s just being abandoned. Was not likely with the 701s and will not be likely with the 398s. Never underestimate the scale of teething problems these days and the fact that solutions will be found. Hindsight is a wonderful thing.

Personally I wish TfW had gone with proper trains (756s) and had a separate tram network like Croydon did. But thats just water under the bridge.

I think the long drawn out vision is for TAM to be exactly that. You could be looking at an Oldham loop project on a greater scale, and one that could potentially come with a huge impact on terms and conditions for future of train crew based out of Taffs Well.

 

[800001]

Is that an 810 in the background there?

Yes.
810003 and 810004 long term residents as test units for Hitachi.

 

[chargesmith]

The battery on the 398 are capable of 10 km (about 6.2 miles).

The distance between Cathays and Ninian Park is under 3 miles (2 miles 53 chains according to RailMiles) which I think is the largest non electrified section they would need to bridge.

Given they will also leave the electrified section at line speed in either direction in normal operation this likely helps too. Are the units capable of regenerative braking to recover some lost energy between stations?

 

[VR494]

The distance between Cathays and Ninian Park is under 3 miles (2 miles 53 chains according to RailMiles) which I think is the largest non electrified section they would need to bridge.

Given they will also leave the electrified section at line speed in either direction in normal operation this likely helps too. Are the units capable of regenerative braking to recover some lost energy between stations?

The brakes on the 398’s are not the same as the 756’s and the wheels are also of a resilient design, the tyre has a rubber band lining which reduces noises and vibration for on street running. The wheel profile is also different to regular train wheel, and are not as robust.


I’ve been told the 398’s do have regeneration braking combined with a friction brake, they also have the below style braking system:

• Electromagnetic Track Brakes: This is a safety brake that drop magnets directly onto the rail, using magnetic force and friction to stop the vehicle rapidly, regardless of wheel-to-rail adhesion. (This has been tested by the current drivers trialling them, and they advised it was so violent it could cause injury to any standing passengers)

Aberdare to Merthyr loop services are the primary concern regarding the batteries, and delays occurring at Cardiff West, awaiting platform clearance etc. They will also not be permitted to occupy a platform under permissive working in conjunction with a heavy rail unit, such as a 756.

I’ve checked today and the battery capacity is actually 128Kwh. They’ve also been standing for so long that a replacement set of batteries from storage that came with the units are apparently now being fitted.

The test runs to accumulate hours at old Derby have also taken place apparently with the absence of the beacon system they will run under on the CVL.

Ive attached below a diagram of the system designed by Sella Controls

 

[MikePJ]

@VR494 's comments about Stadler made me think of this Modern Railways article from March last year:

Transport for Wales Chief Executive James Price says he wants ‘political and social pressure’ applied to train manufacturers because the financial penalties in contracts do not produce all the desired results.


He told a Senedd committee in January that TfW was still: ‘experiencing delays from our manufacturers, both Stadler and CAF, and it’s important to both work in partnership with them and to hold them to account in every way possible.’

His briefing paper for the committee, dated 13 January, recorded that 58 out of 77 Class 197s were in service, along with all 11 of the Stadler Class 231s, 10 out of 24 Stadler Class 756s and none of the Stadler Class 398s. Delivery of all new fleets, apart from Stadler Class 398 tram-trains, was expected to be completed by the end of the year.

Modern Railways invited CAF and Stadler to respond to Mr Price’s comments. CAF declined the invitation.


A Stadler spokesperson said: ‘We are proud to have successfully delivered all trainsets on time from our factory, demonstrating Stadler’s can-do attitude and commitment to reliability. Our strong partnership with Transport for Wales has been instrumental in achieving this milestone.


‘We are particularly pleased that Transport for Wales has begun introducing the innovative tri-mode FLIRTs into passenger service on the Core Valley lines. These state-of-the-art trains represent a significant advancement in rail technology, offering enhanced flexibility and significantly reduced carbon emissions.


‘Stadler’s sister fleet in operation on the Greater Anglia network now boasts record performance levels. Through our Strategic Partnership Agreement with Transport for Wales, we are working with our client to enable the new state-of-the-art FLIRTs reach and hopefully exceed these enviable measures of success, ensuring that passengers in Wales enjoy a seamless and high-quality travel experience.’

It's worth noting here that the Stadler PR spokesperson talks exclusively about the FLIRTs and makes no mention at all of the 398s. Given that they would have said something positive if they could have, it suggests that James Price was unhappy about the 398 situation at least 12 months ago.

 

[Prime586]

I have seen this said before but I do not understand how it can work - I can't visualise the circuit that lets a battery simultaneously be charged and be providing power to the traction motors without this constituting a direct link between the overhead power and the traction motors.

This is exactly how industrial online/double conversion UPS systems work. The key is that the AC supply is rectified to DC to charge the batteries (via the Battery Management System), and the DC from the battery bus is connected to an inverter to convert it back to AC to supply the load, so there is no direct link between the AC supply and AC output (or traction system on a train), though it has the disadvantage of conversion losses at each step.

Under light load conditions, the Battery Management System detects when the batteries are topped off (Lithium cells can't be trickle charged like lead acid) and no longer need to be charged, the rectifier is basically directly connected to the inverter via the DC bus. When the mains input is lost, the inverter draws current from the batteries instead. When the mains input is restored, the BMS will control the recharging of the batteries using any excess mains input current capacity available from the rectifier that is not being drawn by the load on the inverter.

 

[CapitalStar378]

@VR494 's comments about Stadler made me think of this Modern Railways article from March last year:







It's worth noting here that the Stadler PR spokesperson talks exclusively about the FLIRTs and makes no mention at all of the 398s. Given that they would have said something positive if they could have, it suggests that James Price was unhappy about the 398 situation at least 12 months ago.

I guess the question is, what's the alternative? I imagine that any change in rolling stock would be 3 years down the line, if that's even an option. Unless Stadler have a load of spare FLIRTs knocking about.

 

[1D54]

Realtime Trains | 6Q37 1355 Old Dalby to Kings Norton Ot Plant Dept | 26/01/2026

Real-time train running information for 6Q37 1355 departure from Old Dalby to Kings Norton Ot Plant Dept on 26/01/2026. From Realtime Trains, an independent source of train running info for Great Britain.

www.realtimetrains.co.uk

Realtime Trains | 6Q38 1000 Kings Norton Ot Plant Dept to Pengam Sidings | 27/01/2026

Real-time train running information for 6Q38 1000 departure from Kings Norton Ot Plant Dept to Pengam Sidings on 27/01/2026. From Realtime Trains, an independent source of train running info for Great Britain.

www.realtimetrains.co.uk

Realtime Trains | 6M39 1544 Pengam Sidings to Kings Norton Ot Plant Dept | 27/01/2026

Real-time train running information for 6M39 1544 departure from Pengam Sidings to Kings Norton Ot Plant Dept on 27/01/2026. From Realtime Trains, an independent source of train running info for Great Britain.

www.realtimetrains.co.uk

6Q37 was activated earlier on today so i take it this will be on the move in an hour or so.. Any idea which one it is?

 

[Cowley]

I guess the question is, what's the alternative? I imagine that any change in rolling stock would be 3 years down the line, if that's even an option. Unless Stadler have a load of spare FLIRTs knocking about.

Before this strays too far, it would better to ask in this thread really.

TfW class 398 train introduction delays: what could happen as a result?

I'm quite alarmed by the latest information about class 398s posted on the TfW class 398 Stadler Citylink tram trains thread. Does anyone know if 4 tph would still be a possibility with 756s? I'm trying not to turn this into speculation about the 398 rollout being abandoned, but it does beg...

www.railforums.co.uk

Thanks

 

[Covshire1]

43467 + 43468 with 398015...

 

[1D54]

Thank you Covshire 1.