Triumph 955i Charging Problems: 2

Triumph Sprint 955i Weak Charging System

Part 2

Following on from Part 1, when the problem first manifested.

Alas my difficulties in getting home the previous evening were nothing compared to the following day… The Sprint behaved beautifully after a full overnight charge, but on my 100 mile commute the battery dwindled almost completely – first hint of trouble when the tachometer and speedo both fluttered & died, second hint of trouble when the bike followed suit.

I should, of course, have performed a little testing the previous evening instead of confidently assuming that the problem was the loose battery cable. Had I done so I would probably have noticed that she wasn’t charging at all.

After a 5 hour wait in Colne a recovery vehicle finally turned up – apparently 6’4″ angry looking bikers in a Sainsbury’s car park are considered neither ‘vulnerable’ or ‘high priority’ – he confirmed that the Sprint was indeed dead (down to <11 volts), loaded me on the wagon and took me home, to the apparent relief of the circling Police Patrol - overall, a tiring 6 hour 50 mile trip home. The Problem: Weak Charging System
It would be easy to be critical about this, but most motorcycle manufacturers are guilty of these same cost saving shortcuts…

1. The Sprint uses a Shunt Regulator/Rectifier – not very efficient and tend to run very hot – I know there has been a spate of these failing (maybe down to the recent hot weather), seriously – if you still have the original shunt type Regulator/Rectifier then I’d consider changing it to a MOSFET one before it goes and takes your alternator stator with it.

2. The nice, thick, high current DC cables out from the Regulator/Rectifier disappear into the wiring loom, becoming much thinner (hence hotter and inefficient under load).

3. Alternator Stator insulation not quite as good as it should be.

Sorry looking burned out Triumph Sprint 955i alternatorResult of all this is that my sudden stint of high mileage commuting burned out the shunt Regulator/Rectifier, which shorted.

The duff Reg/Rec then pulled too much current from the 3-phase alternator.

The Alternator Stator got so hot it burnt out its insulation and shorted the coils to ground (pic to right).

So… No DC back to the battery 🙁

Resolution: Option 1
Pay Triumph nearly £600 for replacement alternator stator and shunt Reg/Reg, plus about £300 for fitting – which would get me back to a fully functional, but potentially still temperamental charging system..?

I don’t think so…

Which leads us to…

Resolution: Option 2
Purchase of higher quality Electrosport ESG959 Alternator Stator and Electrosport ESR535 MOSFET Regulator/Rectifier – from M&P in the UK, less than £170 for both items.

Naked Triumph Sprint 955i with duff alternatorFitted them myself:

– Tank and all bodywork (except headlight unit) removed
– New Reg/Rec bolted inside of right hand frame & cabled in
– Alternator replaced
– Spliced Reg/Rec output direct back to battery (30A fuse)
– Put everything back together and prayed

Not quite as simple as it sounds – took me best part of a day in all, with much grunting and cursing. Still, <£200 versus >£900 for a less efficient system – the work was worthwhile.

Not to mention the warm glow of satisfaction from a job well done.

Putting out 14.4 volts at the battery from tick-over right across the rev range; at every start the motor spins like she’s being jump-started by a truck.Electrosport ESR535 MOSFET Regulator/Rectifier

The ESR535 MOSFET Reg/Rec runs cool enough to touch (just try that with a shunt Reg/Rec).

Bike seems more alive.

Me too….

** Important Note **
The first alternator purchased – described as correct for year, model, manufacturer & VIN range – did not fit. It bolted into the alternator casing OK, but at several mm deeper it prevented the cover fitting flush with engine casing. Fortunately I test fit everything before torquing down and thread locking so the incorrect one was refunded without quibble. You can see the difference below:

My 2004 Sprint 955i stator vs standard

My 2004 Sprint 955i stator vs standard

After carefully checking dimensions I ordered the ESG959, although this was described as a 2010 Triumph Tiger 1050 Alternator Stator (115mm x 42mm x 22mm) – The moral being check measurements before you buy, don’t rely on the description (cost me an additional 3 days no riding).


Naked Triumph Sprint 955i with duff alternatorHere you can see the direct feed from the Reg/Rec back to battery – ran 30 Amp cable (fused) from the output ~10 inches to battery positive and ground.

Much more efficient rock-solid regulation and charging now as no losses from passing heavy current through the loom as before – the good stuff has an easy path right to where it does most good.


Triumph Sprint 955i alternator magnetsDon’t forget – as I did – you’ll need a gasket for the alternator casing.

Fortunately the excellent Philip Youles Blackburn Triumph Dealership is only a 20 minute blast from Westhoughton and Wooly sorted me out in short order.

The problem with Youles is you go in to spend £10 and leave wanting to spend £10,000.

As an aside, whilst at Youles I met and fell in love with what will be my next bike – the rather magnificent, moody yet comfortable looking Triumph Thunderbird..!

If anybody wants to swap a Triumph Thunderbird for a low mileage Sprint ST 955i, you just let me know 😉

2013 Triumph Thunderbird - awesome

Thanks to…

DEcosse on for his excellent article on Triumph charging system diagnostics – most helpful (although I went for the ESR535 Reg/Rec)

zam70 on for his insight into charging loads through the loom and remediation – splicing into Reg/Rec output and running direct to battery posts. I have noticed much crisper response from my Sprint following the mod, and no dimming of the headlight at tick-over.

32 comments to “Triumph 955i Charging Problems: 2”
  1. Many thanks for a great writeup about the Triumph charging propblem you had. I have a similar problem with the same model year bike which can be seen here:

    My problem seems to be that the stator I have is too small (104 mm dia), the inner diameter of my rotor is 117mm leaving a gap of around 6.5mmwhich I think is too large. You suggest using the ESG959 which you gave the dimensions as 115mm x 42mm x 22mm, I take it the 115mm is the diameter of the stator, what do the two other dimensions refer to. Many thanks for your advise. Regards Sam

    • Hi Sam,

      115 is the total diameter, 42 is the central hole diameter & 22 is the stator depth.

      The original gasket should be fibre, suggesting as you suspect that yours has been changed at some point.

      The 6.5 mm gap you refer to is way too high – on mine the gap is so small that the original stator was polished by the magnets and the replacement had no measurable gap.

      Finally, yep – 70 volts AC out from each coil.

      Good luck 😉

  2. Hi William
    Was out on a run with my local IAM group today when my beloved Sprint ST955i slowly died – with symptoms very much as in your article.

    Would you kindly tell me what year yours is?
    Mine is 2004 and thus has the wider engine and NO oil level sight glass. I’m thinking the alternators on these later (dip stick) models may be different to those on earlier Sprints.

    Thanks in advance

    • Hi Peter – Mine’s a 2004 model with no sight glass too 😉 Guess that’s why my first alternator didn’t fit (despite correct year and model in description).

      If coils also gone I’d heartily recommend the ESG replacements – Electrosport ESG959 Alternator Stator and Electrosport ESR535 MOSFET Regulator/Rectifier – both still working a treat on my Sprint..! I’m also aware of at least 2 riders who’ve fitted these (without the splice direct to battery tip referred to in the article) where they are still showing 14v at the battery and experiencing no further issues.

  3. Hiya I have a 2004 also and am having the same problems can you please email me mxxxxxxxxxxxx33 gmail so I can send you a pic of my bike to make sure its the same model. Thanks K

  4. Yet another one! – Mine just did the same on day one of a European tour. Gutted is not the word. It’s stuck in a french garage at the moment but when I get it back I’ll definitely be fitted both the stator and the rec you recommended.

    • Day 1..! Now that’s what I call a downer… Hope it’s not spoiled the trip too much..?

      Took mine round France (post-fix) and she didn’t miss a beat. Hoping to do something similar on the Thunderbird soon.

  5. Thanks for this great write-up. I’m having what sounds like the same problem on my 02 model Sprint ST 955i (dipstick). You start off with a fully charged battery, within 60 miles battery’s so gubbed the bike doesn’t start 🙁 ….

    Do you reckon fitting a new ESR535 MOSFET Reg/Rec on its own first might be worth a shot? I’d remove the side fairing panels etc and check the alternator, but just last year I fixed the broken lugs on the panels and I’d rather not fiddle too much if I don’t have to…
    Any help would be appreciated!

    • If you’re alternator’s OK then sure, just change the reg/rec for the ESR535.

      When it’s running you should be getting about 70 volts per phase out of the alternator… if so then no worries.

      You’re a lucky man if you just blown the Reg/Rec..! As in ‘it could have been worse’.

      Good luck…

      • Hiya, just got some time tomorrow to do some more work on the sprint. You said 70 Volts per phase out of the alternator: Got to say that is deeper knowledge than I have of bike electronics… Is there an easy-ish explanation to how I can measure this? All I can see are a couple of leads coming from the alternator, one of them has a connector that is easy to access (that I’m going to open to check resistance of the alternator parts/coils). The other connector is trickier to get to under the tank…

        Thanks for any help. I appreciate if it’s too complicated to explain.

        • Or do I just take the connector I’m talking about and measure the voltages at idle and 5000rpm between the 3 pins…? simple as that?


          • If it’s the connector with 3 wires (yellow I think) from the alternator, then 70v AC from each pin to ground (frame or engine metal). First set your multimeter to ohms and check that none of those 3 pins are shorted to ground – if they are then it’s goosed…

      • Hi, tiger 2004, I’ve seam to have a problem with my all my lights flickers, worse at 5000rpm. Charging the battery is not a problem, found this out at Calais after leaving Sat nav on (wired direct to battery but forgot to remove) after bumping of and 100 miles bikes stared up fine but it’s this light flicker that’s my problem, dash lights too. Any ideas please.

        • Hi Paul,

          Well if recharging after a run, safe to say it’s not the charging problem discussed here.

          If the problem is just headlights and clocks I would suspect a loose connection on the feed or earth for this area. Revving at 5,000 probably vibrates the connection looser than it is at tick-over.

          Manual investigation of cables/connectors in this are is where I’d start… good luck..!

          • Hi William
            Not sure if I was supposed to do this but I disconnected the connector block with the 3 yellow wire from regulator, ran the bike at standstill for a very short period, no flicker, switched of, reconnected, flicker was back. Thanks for reply and any further help.

          • Hey Paul,
            Sat by a pool in Malta and drinking beer so please excuse any rambling..!

            No problem with disconnecting alternator (3 yellow wires) – you can do this to check output voltage.
            If your lights do not flicker with alternator disconnected, but do when it is connected, then I’d suspect your regulator/rectifier (referred to in the article).
            I’m guessing that all lights/electrics flicker..?
            I’d change it now to be on the safe side – if it goes short it will burn out the alternator too.

            If it were any other electrical issue it would manifest regardless of the alternator connection state.

          • Hi William
            Why that sounds fantastic sat by the pool with beer. I got back yesterday from San Marino and a week in the Alps on said motorcycle.
            Yes I best change that R/R. What with your help and my findings on internet it’s looking very likely.
            Thanks again

  6. *fairing lowers I mean, not side panels – the big plastic bits below the tank, not the seat 😛

  7. Hi William,
    I have a 2005 Tiger 955i which has displayed the same symptoms as your Sprint. I have purchased the parts in your article and was wondering how you wired the reg/rec directly to the battery. Thank you

    • Hey Neil

      Unfortunately this post is 5 years and two bikes ago – honestly don’t remember the exact details.

      I do know people who didn’t take it that far and had great success just changing the hardware so would not worry if you don’t fancy tackling that part.

      As I recall – ring connector on high current cable for battery post connection, to an in-line 30 Amp fuse, spliced into the original DC feed near the connector. Additional precaution of cable management sheath to protect from damage – only about a 10” run.

  8. Hey William, I appreciate the post is 5 years old but still very helpful. I have as I said purchased what the post recommended although the stator doesn’t appear to fit in my fly wheel! It is too big. I may have to return it, unfortunately, I need the bike in 3 days to ride to Germany. I feel a road trip coming on lol. Thank you for the reply

    • Well two things I hope:

      1. That the post was helpful
      2. That you get the bike sorted in time

      This was why I included the important note to confirm measurements and not go off the supposed part number – same thing cost me 3 days.

      Would love to take the Rocket abroad…!

      • HI William! It was a very helpful letter. Do you have some additional photo or description how can I implement the direct (plus) wire from REC/REC to the battery “+” pole? Thank you in advance. Laci

        • I’m afraid not – this was a few years ago 🙁
          Based on feedback, couple of users did not implement this final mod and had no issues

          It may have been a little overkill

  9. Hi I can find the referred Tuneecu you referred to. Im looking to buy a 2014 Thunderbird. can you point me in the right direction please?

  10. Hi All

    Wondered if anyone could help me out? I had the same problem on my 02 955 daytona. On inspection the three yellow wires from the alternator had completely melted at the regulator plug end. I had to cut the plug off it was so bad! Alternator showed no resistance to ground so I fitted new regulator but I now have three yellow wires that are not on a plug (mine are not yellow actually but by the by). presuming these three will go in any order I fitted the regulator, plugged in and away. Problem I have is it now overcharges, showing up to 19v at the battery at 5000 rpm. I pulled the three wires one at a time and can get
    1 wire=no charge
    2 wires = correct charge
    3 wires = overcharge.

    Does anyone know if the three wires need to be in a correct series or if it shouldn’t matter?

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