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Discussion Starter · #1 ·
Not been convinced recently that the alternator on my 72 T100R is doing its stuff. Battery was showing 12.4V last night after not being used for a week so put it on charge overnight. Showing 12.9V this morning. Went out for a near-home 7 miler and left it 20 minutes when I returned. 12.55V. Hmm..

Went out on the same ride and checked it again. 12.41V. Nope, that's not good, despite giving it plenty of beans on both rides.

I did buy the hefty 1 ohm resistor a while ago to test the alternator but never got around to rigging it up. I need some better croc clips and leads so I'll get some and then look out Don's guide to alternator testing and see if it's that, or the reg/rec, or some other gremlin.

Having said that, the stator's original, as is the rotor, so I wouldn't be surprised if it's died over the winter layoff. Didn't particularly want to spend £300 on a replacement alternator though.

Ho hum.
 

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Didn't particularly want to spend £300 on a replacement alternator though.
Assuming you’re looking at the LPW kit (?) Andy you would be upgrading to 3 phase at the same time so there would be additional benefit to just new parts. Thinking of buying one myself for next time the primary cover’s off. LPW no longer sell UK made alternators, they haven’t been available for some time so they’re Wassel items though Phil has used them without any issues. My Wassel RM21 stator is still going after two years along with the 50 year old rotor.

Anyway you’re not at that point yet, would it be worth doing the quick test of voltmeter across the battery terminals to see if anything is getting through to the battery when you rev the bike?

Chris
 

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Discussion Starter · #3 ·
Hi Chris, no I wasn't looking at any alternator in particular just yet until I know if that's what's wrong. But I would go 3 phase though.

Did put a voltmeter across the battery terminals and it showed 13.3V but very unsteady. Previously I've seen up to ~15V doing that test, and I know a digital VM can be confused when testing across the battery terminals. I have got a cheapo analogue meter but the scale is so poor as to be less than helpful.

Has to be Don's method for testing the alternator output first I think.

My bike was dismantled for 37 years so who knows how the rotor was stored, but it does seem to have an affinity for loose spanners, so maybe it's OK. Stator continuity etc first to be checked.

I put a new primary chain on this winter so the stator had to come off and I wonder if moving the cable was finally a bridge too far.

Fortunately I have my TR7RV and a 2015 T100 Bonnie to ride when I need a head clear.
 

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I had a rotor lose all magnetism after about 45 years. Fitted another old one and its been working ever since. Andy, if you do mostly day riding, a single phase alternator is fine. Mine runs 3 rear LED lamps, i have a row of 5 white high power LED on the front, it all runs very well on the fire alarm battery and never goes low. I have 13volt indicated on my digital voltmeter on the handlebars with everything on and running at just 2500 rpm. At idle, it drops to 11.5volts. I can run around green lanes for 10 miles with no problems and the bike is mostly under 2000 rpm on the lanes. A few minutes at higher road speed and the battery is fully charged again. Used rotor cost £10. Harder to find now though.
If i do ride home 30 miles at night with headlight on, there are still no problems with the battery going flat or dimming lights. Single phase alternator has always been sufficient.
 

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Hi Andy,

Hope things are OK?

alternator on my 72 T100R
did buy the hefty 1 ohm resistor a while ago to test the alternator
need some better croc clips and leads so I'll get some and then look out Don's guide
No offence intended to Don but the "guide" is in the Triumph workshop manual - Section H4, manual page H10, you just don't have to construct your own resistor! :)

Given the standard 2-wire alternator on your bike, it's even simpler - connect one stator wire to each end of the resistor, set your meter to AC Volts and connect each of its leads to different ends of the resistor, rev. the engine to 3,000 rpm, meter should display at least 9V. (y)

did buy the hefty 1 ohm resistor
How many Watts?

or the reg/rec
Risking telling you things you know already:-

. Don't disconnect the reg./rec. DC output and then try to test it. Reg./rec. only rectify enough to satisfy the detected DC load; disconnect reg./rec. DC, it doesn't detect any load so it regulates most or all of the AC into heat ... :oops: Test the reg./rec. output by connecting the meter (set to DC Volts) across the battery.

. Don't test with a fully-charged battery - if it's fully-charged, the reg./rec. doesn't have to rectify anything to charge it ... Part-discharged battery and all the lights on should show the most charge.

stator's original, as is the rotor, so I wouldn't be surprised if it's died over the winter layoff.
If it's "died", you should be; the bike's '72, not '62 or '52.

Didn't particularly want to spend £300 on a replacement alternator though.
The "died" to which you refer above is the rotor losing magnetism; if that's the problem, you don't have to replace the stator. The only reason to replace the stator is because - even with the newest, shiniest rotor - its output was always pants, all the more so in the 21st century's third decade.

Hth.

Regards,
 

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Discussion Starter · #6 ·
Hi Stuart,

Taking each day as it comes, up and down. It'll just take time, thx. Still in the disbelief stage.

It's a 100W resistor - I think value that came from Don's notes. Waiting for a better set of test wires with insulated croc clips to minimise the potential for inadvertent shorting when running the engine and checking the alternator outputs at the battery.

I wasn't sure how to test the reg/rec, but since it's only 2 years old I was hoping it'll be OK, so thx for that.

Easy enough to start testing the stator - it may be open circuit or shorted to earth.

The alternator was fine last year, charged well, so not sure why the rotor would lose its magnetism when standing for 5 months. I'm still suspecting a failed stator connection when I moved it to change the primary chain - even though I was careful to avoid straining the wires - but they are very stiff now.
 

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Hi Andy,
100W resistor - I think value that came from Don's notes.
Mmmm ... original suggestion by "Magnetoman" on BritBike; iirc Don couldn't obtain either of the higher-Watt ones (there's also 175W and 225W) when he bought?

not sure why the rotor would lose its magnetism when standing for 5 months.
Unlikely. Rotor magnetism attenuates gradually, more likely is there just comes a time when something like battery charging/not charging is noticed.

suspecting a failed stator connection when I moved it to change the primary chain
:(

Regards,
 

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Discussion Starter · #8 ·
Hi Stuart,

Mmmm ... original suggestion by "Magnetoman" on BritBike; iirc Don couldn't obtain either of the higher-Watt ones (there's also 175W and 225W) when he bought?
Think you are implying then that 100W is too small? Which I could understand given it's a 120 or 200W alternator.

The WM Section H4 doesn't suggest the wattage rating of the 1 ohm resistor so not sure what I need to do.

Looking on FleaBay, I can get 0.5 ohm 100W resistors, which in series would give 1 ohm and presumably 200W. Would they be better?

Goffy gives a test method for the single phase stator using a car headlamp bulb, which would typically be say 60W.

Suggestions pls?

Thx.
 

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Andy,
The aluminium-clad 100W power resistors, such as those on eBay, will be perfectly OK. They are rated at 100W continuous power: the several seconds it takes to measure the voltage and current on the alternator test are not likely to make them fail - but they would get a bit hot, so mind your fingers!
P.S. bolt them to a piece of aluminium sheet for increased heat dissipation and lower surface temperature.
 

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Discussion Starter · #10 ·
Thanks Brian. Not wishing to turn this thread into a fault finding thread, but one last post here on this topic from me: correct me if I'm wrong, but I have an open circuit between the green/white and green/yellow wires from the stator, and similarly between each wire and the crankcase. That tells me that the stator wiring has failed.

Yes?
 

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Hi Andy,
There should definitely not be any reading between the two wires and the crankcase.Yes it sounds as though your stator wiring has an open circuit, however it's unlikley to be the coil windings as the wire is quite thick so it would take a lot of current to burn it out (like a fuse). You said your wires were very stiff: I think it's more likely one of the connecting wires has broken, most likely where they go into the potting. I recently had the stator on my Daytona fail like this and it was giving annoyingly intermittent charging for some time.

I was in two minds to dig out the potting and connect two new leads, but in the end I settled on a nice new 3 phase stator and rotor. The main thing I noticed was that the original stator wires were bent round from where they exited the potting on the outboard side, around the laminations, and then through the hole in the primary chaincase. This seems to be how the factory fitted them and is dumb as it stresses the wire when it gets stiff with age. For the new 3 phase one I turned the stator over/round so that the wires came straight out the back and through the hole on the chaincase.
 

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Discussion Starter · #12 ·
Thx Brian. Thought so. That bike only has an LED pilot and an LED headlight/tail light and a Boyer and I never ride at night, so decision time. 3 phase or a straight RM21 stator......As Rambo says, the RM21 should be fine, if the rotor is OK......

If......
 

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I expect you know this Andy, the rotor should be able to pick up a fairly heavy spanner. I was surprised when mine failed and i was still riding around and the battery became flat every 3 rides. I suspected the battery but Triton Thrasher suggested connecting a lamp across the 2 alternator wires. I got a dim light so alternator was poor. I have spare old alternators and rotors in my stash of old parts so took the stator off ready to fit another old one. Then i noticed virtually no magnetism in the rotor. I also found that a Norton Commando rotor is the same unit but has a different part number. My BSA alternator also looks the same type.
Just 10 years ago there were loads of these parts at the autojumbles so i stocked up on some engine parts just in case. Its all getting rare now.
At one sale, i bought a brand new gearbox layshaft and 4 new gears. New Renold primary chain and a random collection of other new parts all at £40. That never happens now.
Still have a perfect T120r crankshaft ready to fit one day maybe. That was just £70.. . When i did need one a few months before i bought the £70 one, i paid £240 for another ready to fit crank which has been in use since 2012. Cant wait for the auto jumbles to start again as i have a great day out and often buy some old rusty rubbish to sell on which pays for the day out.
 

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Hi Andy,
100W is too small? Which I could understand given it's a 120 or 200W alternator.
Mmmm ... one of those questions to which the answer is the "Irish" joke punchline, "Ah, If I was going dere, I wouldn't start from here." :)

You have the the 100W; as @BrianG posted, use it, worst that could happen is it annoyingly goes phut.

3 phase or a straight RM21 stator...
bike only has an LED pilot and an LED headlight/tail light and a Boyer and I never ride at night,
Murphy's Law says, "If anything can go wrong, it will." Who knows what in the future, if not for you, the next potential owner? Paying similar money, I'd never set out to restrict my potential options in a future situation I can't possibly predict or envisage.

Similar money:-

. high-output 3-phase, only current option is Wassell, (n) no other downside; (y)

. low-output single-phase RM21, only current option is Wassell, (n) other potential downsides (n) are why 'original Lucas' produced high-output single- and later 3-phase;

. high-output single-phase from TMS, NOS 'original Lucas', (y) 12% less (1.45A) than high-output 3-phase @ 2,400 rpm.

Hth.

Regards,
 

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high-output single-phase from TMS, NOS 'original Lucas', (y) 12% less (1.45A) than high-output 3-phase @ 2,400 rpm.
That’s interesting Stuart, I looked at the TMS site before posting a response to Andy and found the listings quite confusing. Their code used to be “UK” = not Wassell, “Lucas” = Wassell, listings would be supplemented with a picture of the item with no packaging (UK) or the green box (Lucas). Now they’re listing a stator as “UK” but the picture includes a brown box labelled “Genuine Lucas”? Is the NOS item you’re referring to?

Chris
 

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Hi Andy, I made a "fancy test rig just because I wanted too. You could just lay resistor on concrete floor. I got the 100w spec from Magnetoman. All I can say is the 100w works fine & gives the desired test action.

I got an Ohmite brand as that's what Magnetoman recommended as durable. About $20 US. There are other 100w on market for even $6 or so. A fellow got one & used it. Worked equally as well. A larger one may be better, I don't know, but I know in real life the 100w works good enough to give good test. If you have the 100w use it. Be aware all the electricity is turned to heat. So it will get hot. You'll find test only takes 10-20 seconds or so. My resistor got hot, but not smoking hot. As I recall I could still barely touch it in that amount of time. The stator wires get warm also, so don't extend run time. Take your readings & let things cool. If you want to test again, do it after it cools. That's what I did right or wrong all 3 times. I feel I got accurate results.

Of course you need good jumper leads. I made my tool to use snap connectors so a simple direct hook up. Of course you are correct, you must insulate connectors such they don't short on anything. My snap connector uses the normal rubber sleeves. Again, you don't need that. Just tape them up such no shorts.

If you don't have tach you make your best guess as to rpm. You'll see how rpm effects ac volts. I've only tested 3 so far. All passed fine. In real life all 3 charged good on the road.

If bike is overcharging this test in not needed, but undercharging it indeed will test both magnet & stator.

If test shows good, both are good. If test shows weak, or fail it does not tell if rotor is weak or stator has failed.

Thing is, if it tests good, you can know both are good. That's a very valuable thing to know. Now you can move to other faults knowing the heart of the charging system is good. Takes guess work out of the alternator output.

You can very accurately bench test the rectifier under some load also. That's another subject. I've only tested zener on bike motor running using amp & volt meter at same time. I just wanted to learn in real life what zener does. I've only tested 2 of those. In real life if all else is good the zener operation will show on volt meter hooked to battery.

I find it a little puzzling why more owners with problems don't do the alternator test. Once you get the resistor & some test leads, it's so simple & tells if alternator has enough output.

Don
 

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Hi Andy, You spec is in shop manual for your stator type. I took a lousy video of a real life test. I don't know if I have your email or not. I didn't carefully organize them by user name... Dumb! Now I always do. PM it if you want to see vids. Next time I'll take proper video. My old phone was out of storage so vides were very limited. 265g phone is only way to go.
Don
 

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Hi Andy,

Before you go too far into your problem, it is worth checking every single connector associated with the charging system. When I first had my bike, I had a strange intermittent charging problem that I eventually traced to a badly soldered bullet connector done by a PO that had got so bad that the wire had been arcing inside the loose connector.

Here is a test sheet that I put together for testing the whole DC side of things for carrying out a full test on the battery condition and whether the charging system is up to scratch. The numbers recorded are from a test that I did to establish a base line for my bike with the system working well, so that I can have something to measure it against at some point in the future if I suspect I have a problem.

The charging system is a standard modern "Lucas" single phase 120 Watt stator and Rotor with a Sparx Rectifier/Regulator, the type that looks like the old Zener heat sink under the headlight.

I expect that figures should be typical for a standard alternator working correctly:

753985
 
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