The BSA A7-A10 Forum

Technical => Lucas, Electrical, Ignition => Topic started by: BSA500 on 13.01. 2012 15:40

Title: E3L dynamo not charging
Post by: BSA500 on 13.01. 2012 15:40
Have tested the dynamo and I am only getting 0.5-0.7 volts. What I need to know is what is likely to be the issue the field coil or armature. The coil gives no resistance on the meter as does the armature and from the written word its more likely to be the coil. Is there any other tests to try(doesn't motor either). If it turns out to be the coil how easy are they to remove and replace? And its now off the bike.
thanks in advance Andy
Title: Re: E3L dynamo not charging
Post by: bikerbob on 13.01. 2012 16:58
Hi there
Assuming you have done the test correctly then with that reading it points to the field coil winding being the problem if you had reading of 1.5 to 2 volts then it would be the armature winding and no reading would be the brush gear. They are relatively easy to strip down and replace the parts you can buy a complete kit to replace everything except the casings for about £100 off ebay I have done this myself but if you have never done a dynamo before it maybe better to give the job to a professional and get the job done properly as the retaning screws for the field coils have to be really tight and there is a special tool needed to  press the coils to the casing. I made my own temporary one.
Title: Re: E3L dynamo not charging
Post by: beezermacc on 13.01. 2012 20:18
Nine out of ten problems with old dynamos are due to armature problems. If you disconnect the field coil leads and test them for continuity you should get a reading of about 2 ohms resistance. There should be no continuity between the field coil and the dynamo casing. The field coil is usually OK. Old Lucas armatures give the same problems as magnetos due to the break down of the insulation i.e they burn out at the core. Also the wires become disconnected from the commutator. If your dynamo has not had a new armature before it will almost certainly need one now. Presumably you have checked for worn out brushes, broken wires and loose connections etc. You would also be well advised to fit new bearings of the sealed type.
Title: Re: E3L dynamo not charging
Post by: BSA500 on 14.01. 2012 09:13
I have changed many armatures and this one is only 3 years old(the others were burnt out by a c**p JG regulator). I now have a V Reg 2. It looks like the coil is an original I know for a fact its at least 20 years old. My worry is I replace one and find they are both dead is there any more tests I can do with the dynamo armature?
thanks Andy
Title: Re: E3L dynamo not charging
Post by: beezermacc on 14.01. 2012 13:55
There are two types of armature on the market at the moment (predominently, there may be others). The cheaper version, probably made in China, struggles up to 6.5v at 1400 r.p.m., the better one gives about 8.0 - 8.5v. at 1400 r.p.m. I find some people are trying to use the cheaper armature in 12v systems which they can't cope with. Even the more expensive one isn't really designed to give 12v. but it will and seems to last reasonably well so, if you're trying to run 12v. this may be a contributary problem. If you haven't got a 'growler' to test the armature you can try 'probing' adjacent segments on the commutator. The resistance beween one segment and the next is probably about 1 ohm. Try testing each segment with its adjacent segment - the readings should all be the same. Sometimes you find that, as you work your way round the armature, the ohms reading gradually increases and then starts to fall again. This shows that one of the armature windings is open circuit, usually caused by burnt out wire or disconnected from the commutator. The easiest thing to do is substitute a good armature into the dynamo and test with a hand flick spin and your voltmeter set to 0.25v. You may achieve 0.05 - 0.1 v even with a hand flick. If you want some advice over the phone you're welcome to give me a ring.
Title: Re: E3L dynamo not charging
Post by: BSA500 on 14.01. 2012 20:12
Thanks for the replies so far I am leaning towards a complete rebuild as the parts alone for just the armature and coil is about £120 (and I am not sure if these are the Chinese versions). A very nice link was sent to me and a complete refurb including bearings/brushes etc is a very very good price. Esp seeing if I have bought the field coil alone I need to pay someone to fit as I do not have pole expander.
Title: Re: E3L dynamo not charging
Post by: beezermacc on 15.01. 2012 00:26
Give me a ring on Monday!
Title: Re: E3L dynamo not charging
Post by: groily on 15.01. 2012 00:47
I wonder if I could prevail upon your good nature for a bit of extra clarification beezermacc, on the point you make about armatures?

The options I see available at the moment seem to be 'standard-wound' items designed to run at 6v with a standard Lucas field coil - but capable of supporting 12v subject to our tolerating higher cut-in rpm; or finer-wound after-market armatures (to run only with matching finer-wound higher-resistance field coils) designed to support 12v systems and which cut in at the same sort of rpm as the coarser-wound original. (They would, of course, deliver different voltages at the same rpm owing to the number of turns etc.)

I've got dynamo bikes running both ways, as well as one running still at 6v, and I reckon 'standard-wound windings at 12v' is a good option despite the higher rpm needed for cut-in (in fact it's my favourite). No idea where all my armatures were made (except they aren't original parts), nor am I sure it matters much, as observation suggests to me that proper regulation and management of the field is the key. For which I and many others give thanks for Dynamo Regulator's DVR2 and its derivatives.

Have I misunderstood your description of the types of armature commonly available (as in you are talking suppliers and I'm talking windings), or are we saying much the same thing from different angles? Be grateful for your thoughts.

Title: Re: E3L dynamo not charging
Post by: beezermacc on 15.01. 2012 00:56
Groily - Speaking from my experience there is not much varience of spec on field coils, most of which are about 250 turns of 0.63 insulated magnet wire. Most of the field coils available in the UK are described as 6V, direct replacements for the original Lucas items, and people use them with the better quality armature to achieve 12v. Most people seem to focus soley on the spec of the armatures which, regardless of physical properties, give different voltages at output. Visually, the better performing armatures have exposed wires between the windings and the commutator; the lower output armatures have epoxy coated wires which conceals them, also red solid epoxy insulation down the length of the lamination blocks. Original Lucas 6v armatures worked just as well (but probably didn't last as long) as the better quality armatures on the market now. I have an unused dynamo, refurbished by Lucas, in the workshop which I have tested at 8.3v at 1400 rpm and 22v at about 4600 r.p.m.- very similar output to a refurbished dynamo with all new good quality parts, and much better output than a refurbished dynamo fitted with the cheaper armature. You're absolutely right about DVR2's - a vast improvement on the old twin coil arrangements!
Title: Re: E3L dynamo not charging
Post by: groily on 16.01. 2012 14:17
Thanks for that Beezermacc. I was thinking of the finer-wound coils that are available nowadays, which call themselves '12v' although it's really a bit of a misnomer. Those field coils have a resistance of 11 to 12 Ohms (as you'd expect for '12v' so-called) and are of rather thinner stuff with more winds although I haven't unravelled one to count. The finer-wound armatures also sold as '12v' are supposed to be a good match to ensure low rpm cut-in, which they do indeed give - but obviously a strict power limit. I'm quite sure it would be pretty easy to throw a winding off the commutator if one tried and I try to hold max loads to around 50W on one of my AMCs so equipped. I use standard Lucas-style at 12v on another AMC (and have for best part of 30 years). That takes a few more rpm to cut in and then again to get to full regulation - but is fine in rural areas and can safely give 70+W continuously. Which is a main reason for my liking it. My A10 remains, for the moment, at 6v. All run DVRs, and any of the three is just as reliable as anything in my shed with an alternator. In fact, being like you a magneto lover, they're rather better from the get-you-home point of view!
Title: Re: E3L dynamo not charging
Post by: trevinoz on 16.01. 2012 20:53
            The resistance values you Quote for 12V field coils seems rather high.
Standard 6V coils are around 2.8 ohms. The 12V coils that I make are 5.6 ohms.
I wind the 12V armatures with 0.7mm wire as compared with approx 0.8mm wire of the 6V item.
80W output is readily achieved.

Title: Re: E3L dynamo not charging
Post by: groily on 16.01. 2012 22:46
Yup, quite a few ohms there but 'tis true Trev. No idea of wire thicknesses or number of turns though. Std field coils I've got are indeed 2.7 or 2.8 ohms. This aftermarket so-called '12v' field isn't 'made here' - I bought it from Feked in the UK I think, along with a finer-wound armature allegedly made to go with it. In combination they've been OK, but strictly limited in power to 60W or a flimsy 4.5A-ish at operating system voltage. Cut-in supporting a 12v system is not far off tickover. Nice. It reaches its fully regulated state by about 1850 rpm. Nice too I think, from the windings' point of view because the thing is running fully regulated for most of the time out on the road.
By contrast, my 'std wound' set-up supporting 12v kicks in at higher rpm, and doesn't get to a state of being fully regulated until well over 2000rpm. This obviously implies some burden on the dynamo under full loads at lowish rpm. However, the windings would be happy to take as much or more current at 6v, so OK so far. This is actually my favourite dynamo option in winter (it was -5° this morning here), as it is robust (25 years on the same dynamo guts says it has to be) and supports a 35W halogen light plus some Oxford HotHands which use 32W (a concession to thickening knuckle joints). 72-75W seem quite supportable continuously without stressing anything unduly - 80W? Hey, maybe! In summer it supports a 60/55W halogen easily. No other dynamo option I have in my shed can do these things, and some smaller alternators would struggle too, what with ignition loads to worry about on top.
Both these 12v options are imo better for night work than the std 6v system on my A, although that's not at all bad, especially with belt drive.
The funny thing is, when I was young I could see in the dark  . . .
Title: Re: E3L dynamo not charging
Post by: BSA500 on 26.01. 2012 12:41
Beezermacc in his other guise as Priory Magneto's turned around a rapid repair in a matter of days. Put it on the A7 last night with the belt drive(20% faster) and she is balanced and showing a charge at 38 mph top gear with the 55 watt headlamp. So a big thanks to beezermacc and time to blind the car drivers back !!
Title: Re: E3L dynamo not charging
Post by: A10Boy on 22.09. 2013 21:19
Note the comments on the two types of armature, could you advise which this is please? (

Title: Re: E3L dynamo not charging
Post by: beezermacc on 22.09. 2013 21:32
The armature on the ebay link is the standard 6v, UK made, replacement armature for an A10. I can supply these if you want one. Andrew
Title: Re: E3L dynamo not charging
Post by: A10Boy on 23.09. 2013 12:14
PM sent
Title: Re: E3L dynamo not charging
Post by: beezermacc on 23.09. 2013 12:46
PM received. If you want anything please send me an e-mail and your phone number from my website. Best wishes, Andrew
Title: Re: E3L dynamo not charging
Post by: Gerry on 25.09. 2013 12:12
Just a thought that might not be relevent but on the build of my A10 the dynamo had not been used in God knows how many years and according to what I have been told the field coil core loses its residual magnetism over time. I replaced the bearings with sealed ones, fitted new old stock Lucas brushes, checked the resistance of the field coil and the armature after a light skim and undercut segments looked really good. On assembly used my variable speed drill with socket on the shaft nut and checked with an analogue multimeter........1.5~2.00 volts!!! "Flashed" the field coil with a lead from the battery plus a + lead from the battery to the case and then ran it again with the D and F terminals bridged together and got 25 volts on the meter!! Had a good nights sleep after that *lol* Gerry