When I first got the 1931 TT car back on the road the Lucas DFL (yes LUCAS ) dynamo charged ok and was adjusted to 8 amps .Now will only charge if you push the cut out points together ,still at 8 amps .Whats the problem? As car is blown has magneto type charging set up .

Hello David,

With a bit of luck and a fair breeze, I think you may just have to re-adjust the Cut-Out, which I am assuming is a Lucas CF1 or something very like that.

Do you have a voltmeter?

If not you will probably need to beg, borrow or steal one.

Simple matter to adjust. The more pressure extended on the armature by the sping, the more volts are required to attract the armature to the core. Also the wider the "at rest" armature gap, the more volts are required to attract the armature to the core.

Cut in voltage should be a tad under 7 volts. Stick your voltmeter across "D" and earth.

You also need to ensure that Cut-Out releases when Dynamo voltage drops below just under 6 volts, although that normally looks after itself if you get Cut In right.

Another problem can be a poor earth connection to Cut-Out (quite a common problem with all electromechanical Cut-Outs and Regulators)

And then of course, you may have an open circuit "Voltage Coil" on the Cut-Out bobbin. (Have seen/heard of three such cases in last month! First I have seen for about 20 years.)
To check the latter you will really need an ohm meter.

I can send you some notes I have here on Cut-Out operation if you would like me to. I think they are in PDF format.

There has also been some discussion on this subject on A7OC Forum over last month or so.

MOST IMPORTANT
PRODDING ABOUT CUT-OUT WITH BATTERY CONNECT IS A BIT OF A WORRY!!!

YOU NEED TO BE VERY CAREFUL EVERYTHING RELEASES AGAIN

I HAVE SEEN THEM LOCK UP AND DMAGED CUT-OUT AND DYNAMO CONSEQUENCES.

PLEASE MAKE SURE BATTERY IS DISCONNECTED WHEN YOU MAKE ANY PHYSICAL ADJUSTMENTS AND IT IS EVEN A GOOD PLAN TO DISSCONNECT THE BATTERY WHEN PULLING THE COVERS OFF THE CUT OUT IF THEY ARE THE METAL TYPE.

regards,

Barry R.

Hello again David,

It was great to see you and the car going so well at Wiscombe last weekend – the sunburn is beginning to fade! Your problems with charging could well be as Barry suggests, a poor earth on the cut-out, so I would check this first. However, cut-outs are generally pretty reliable items, so I would look for other causes before fiddling with its insides. I think that it is more likely that you have set the charging rate of the DFL too high and it has overheated, causing the solder to melt where the armature wires meet the commutator. I recommend that DFLs are set to charge at a maximum of 4-5 amps for reliable operation.

First, clean the commutator with a clean rag moistened with petrol. Then check the cut-out earthing and improve this if necessary. Finally if it's still not working properly, take the DFL apart and check the brushes are OK and moving freely in their holders. Inspect the soldering at the commutator; if it looks thin or missing, it is fairly simple to repair if you use a good modern hot soldering iron to resolder the joints.

David

.


Barry, and others!

Slight change of direction, but still with dynamo's.

I have recently removed the brush cover band from the casing of the dynamo. I noticed that there are three small brass washers (1/4 dia x 1/32 thick appro)secured with bifurcated rivets, more or less equi-spaced, positioned on the inside face. I have never noticed these previously.

What purpose do these serve? Two line up with the brush access gaps whilst one lines up with the casing. Doubtful that they are a stand off for ventilation, but what else?

Mike

David Thanks for your reply ,dont think its the dynamo because if you push the points together with engine on fast tick over a charge is registered on the ammeter. First task is to check the earthing. Oddly enough whilst checking the instruments after Sawbench at Wiscombe on the way up noticed a charge of 8 amps was showing . Starting engine to run down again no charge.David

Hello Mike,
Have a DEL Dynamo on the bench here at the moment Mike but am fairly certain that the band is "plain" but will look shortly.I would have to say that I haven't noticed rivets anyway. On the earlier stuff, DEL anyway, on one or two occasions,I have found a layer of greyish insulation paper underneath the band, presumably to act as a seal around the band, so I doubt that ventilation is the answer. There again, maybe the brass bits were to help locate that paper.In the early days, there seemed to be a fetish for "sealing up" the electrics, and the benefits of airflow to keep things cooler was not considered. I will have a look at what info I have here in due course.
You might like to tell me what model of Dynamo are you "examining?"

Regards
Barry R.

David, I agree with your logic on that, and think that you have "proved" the Dynamo, and the state of the Cut-Out contacts by the fact that manually operating the armature results in a healthy charge.

I think you have also eliminated the "D" terminal connection on the Dashboard switchbox, which can and does give problems from time to time.

What I failed to mention in my earlier response is the fact that depending upon the actual type of Cut-Out you have, the "wiring" under the base can give trouble, and the solder which joins the metal conductors can give way. Might be worth a look if you test the voltage coil and think it is open circuit. Hopefully, your "earthing" experiments will bear fruit.

As an aside, the fact that your Dynamo has a Lucas branding is probably not that surprising. Lucas actually took over CAV in the late vintage period (commencing around 1926 from memory) and by early 1930's its CAV "arm" was almost totally focussed on the more specialist Commercial vehicle market. The early Ignition Distributors are a similar case (Model DS4) and appeared under both CAV and Lucas banners. Badge engineering was alive and well even then.

Regards,

Barry R

Mike, I have these on some of my bands and I assumed they are all that's left from a band of thin paper or card protector.

Naomi

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Barry and Auntie,

Yes, between you I am sure that you have hit the nail on the head. They were the retainers for the resin paper seal. I should have worked that out for myself.


Mike

And I have now cleaned my glasses and turned the workshop lights on. The DEL I have on the bench does have rivets on the band, but they appear to be well rusted steel, not brass, which is my excuse for not seeing them.

Does anyone know where you can buy Bifurcated Rivets?
I have had no joy locally (That is Taswegia)

Barry R

Hi Barry. Golly, you Tasmaniacs are always causing trouble ! I have had some for many years, don't know if new still available here in Melbourne. Let's know how many you want and if urgent I'll post, if not I'll re-visit you & deliver when I traverse the Pond in October, probably in '23 Chummy (might be just enough room !). Cheers, Bill

Don't know if this helps, but my 1927 chummy was only charging now and again and finally gave up altogether.
I too found that I could only get it to charge by pushing the points together. I checked everything I could think of, but the dynamo would produce no volts at all unless I pushed the points together. That puts battery volts on to the dynamo and I can only assume that it gives it a wake up call! What I did next is to fit a switch under the dashboard (where it cannot be seen) and wired in in parallel with the points, with a fuse to protect everything in case the switch is operated without the engine running, or on tickover. As I toodle along, all I have to do is to flick the switch on and off and the dynamo starts charging OK. The cut out opens as normal on tickover and will close again if you rev up. But if you stop the engine, you have to go through the procedure again. My conclusion was that the dynamo had lost its redidual magnetism and as I do not know how to fix that (+ I live in south west France), I have lived with my little botch up - and it still works fine.

Bill ..... '23 Chummy!

I'm sure you must be writing this up somewhere else, but as they are like hen's teeth, we look forward to a full report, or have I missed it (again and again...).

Naomi

Naomi - long story coming up, nothing to do with dynamos !! Am (very) slowly building up a "kosher" '23 which required much of a new body tub, but I have many bits of another, nearly completed, which perhaps in the above I should have called a '23 Chummy Special, as it will have many updated bits so I can hopefully stay alive in using it regularly. The floor, body, wings, radshell to sparewheel drum, even the petrol tank, etc are all aluminiumn much from a lightweight Chummy I made & raced many moons ago, have rebuilt it all to the shape & dimensions of a '23. Work on this & Ruaridh's '23 body has been held up by other recent events, including impending marriage, but hope to finish off all soon. Should get selected in State veterans' table tennis team again for Aust. championships, next is in Hobart , thought instead of ferrying Celica across Bass Strait, could take the Special instead. Have already driven a '25 around Tas - although there's very few spots level enough to check the oil, it's a great State for touring Sevens - would recommend. End of life story - if you're still awake, must say I enjoy your contributions on the site. Cheers, Bill

Hello Donald.

As a matter of interest, "remagnetising" a Dynamo (ie ensuring that there is sufficient "Residual Magnetism" lurking around the Field Poles of the Dynamo to enable the Dynamo to "start up" providing current when spun) is easy.

Take a piece of suitable insulated "cable,” bare the ends a little, and connect one end to the "live" side of the battery, and then "dab" (to use the technical term) the other end onto the "Field" connection to the Dynamo several times. The Dynamo would then have its residual magnetism revitalised "in the correct magnetic polarity" to suit the way in which your battery is connected (that is negative or positive earth as the case may be) I must say that I have only ever known the process to be required on very rare occasions, except where a dynamo has languished unused for aeons, or else, of course when a change of battery earth is made, and even then you often get away with "doing nothing."

Regrettably, I don't think all the above has much to do with your problem, for which you have so artfully contrived a remedy.

You obviously have some problem with the Cut-Out, the job of which is to automatically ensure that the Dynamo is only connected to the battery when there is sufficient output from the Dynamo to commence charging the battery. If there was no Cut-Out switching, the battery would tend to discharge itself into the Dynamo ( Dynamo would want to "run" as a "motor")

So Donald, what you are doing is replacing the "wizard" who lives inside the Cut-Out with yourself, and you are doing the switching. The risk you run is forgetting to open the switch at the appropriate time and flattening the battery. There is an admittedly remoter risk of damaging the Dynamo, whilst driving, even with your "switching" efforts because everytime the dynamo speed drops down below what would normally be charging speed, reverse currents will flow into the dynamo from the battery. It was for all these reasons that the Cut-Out was originally devised.

The Cut-Out can be replaced by a modern semi conductor Diode. That is not quite as simple a solution as may first be thought, but it can and has been done.

I think you probably are suffering from the same "-Outitus" as that faced by David, the originator of this particular thread. There is every chance that you have an "earthing" problem with your Cut-Out, particularly given the fact that you report that the problem was originally "intermittent" charging.

It could be that the Cut-Out has somehow "gone out of adjustment," although normally that results in the Armature coming in at too low a voltage (because of a weakened spring)

There again you may have a defective "Voltage Coil" on the Cut-Out.

In your case, you may be happy to continue in your role a "wizard" and switch manually. This is also understandable as I notice that you are a "Maxwell" - and Maxwells are after all international units of Magnetic Force!

May the force be with you


Barry R

G'day Barry,

Thanks for your response. However, I am not quite doing what you think I am! By flicking my switch on and off (very quickly)I am merely saving myself the bother of getting out of the car, opening the bonnet and pushing in the points and then getting back in again. As soon as I do my "flick", the dynamo starts charging and the points close - my switch is now open, so things are working normally. When I go down to tickover, the cut out opens as it should. The only danger of frying something is if for some reason the switch is closed when the engine is not running or when the cut out should be open - that's why I put a fuse in the switch circuit.

However, I'm going to have a good look again, including the earthing as you suggest. Then if still no joy, I will repolarise the dynamo. I have an old American Fergie tractor and on the Website Forum for this beast, they are always talking about "replorizing" in answering cries for help about dynamos not charging.

But first I have to change the leaking top water outlet and fix the stipped thread that the bolt goes in to - that's this morning's job.

Lastly, I am one of the thicker Maxwells - I could never understand his electromagnetic theory. The "swimming man" rule was dead easy though!

Hello Don,
Well......

From your description of what is going on , that is, in essence, the Cut-Out is "hanging in" OK after you have remotely closed the Cut-Out contact circuit with your remote switch suggests the following:

1. Your Dynamo is working properly
2. The mechanical adjustments on the Cut-Out are wihin spec.
3. The Cut-Out is obviously "holding" OK on the series coil (The coil on the Cut-Out bobbin which has realtively few turns of relatively thick wire and which is connected from the "output" side of the contacts to the "A" terminal on the Cut-Out)
3. Your problem is likely to be associated with the voltage coil on the Cut-Out. This is the Coil which is wound on the Cut-Out bobbin and has relatively many turns of relatively fine wire, and which is connected between the "D" terminal on the Cut-Out and "earth")It is the coil which "senses" the dynamo output, and which creates the initial magnetising effect in the core, which, at an "exact" voltage, is sufficient to latch the armature closed and operate the contacts.
4. As you have indicated you intend to do, the "Earthing" arrangements need a good check out. I think your Cut-out will have a dedicated "Earth" terminal post. I can't check this at the moment because I have broken my glasses and am operating on a pair which are at least 3 prescriptions old!
If you have access to a multimeter you could check for continuity of the Voltage coil from "D" terminal to Earth Post or frame, but I guess you may not have such a device.
(If your Cut-Out does not have a seperate earth post, but relies on contact between the frame of the Cut-Out assembly and the bodywork then you can almost back it in that you will need to take some drastic action to ensure good earth contact.I have seen Cut-Outs made this way, but I don't think I have ever seen one in an A7)
A look underneath the Cut-Out might also be revealing. It is not unknown for corrosion etc to wreak havoc with the wiring there.

If I were a betting man I would take a punt on a poor earth!

Good luck with your water works - that is a real weak point on early A7 heads

regards

Barry R

Don,
In my immediately previous post I said, in part:
(If your Cut-Out does not have a seperate earth post, but relies on contact between the frame of the Cut-Out assembly and the bodywork then you can almost back it in that you will need to take some drastic action to ensure good earth contact.I have seen Cut-Outs made this way, but I don't think I have ever seen one in an A7)

I have now been down to my workshop and had a look at the Cut-Out whih is destined to go into a 1929 Chummy I am slowly bringing back to life.

Please ignore by rantings a quoted above, to the extent that I claimed that I had not seen a Cut-Out without a dedicated earth post in an A7.

The Lucas CF1 Cut-Out which is the usual vintage era fitment in A7's definitely only has two terminals. That is the "D" and "A" posts, the earthing being via the frame. Later types ( I think the CF2 and definitely the CF3) have a dedicated earth post.

So, if your Cut-Out does not have a decent cable bonding the frame of the Cut-Out to a good electrical earth then you task is probably very clear and simple.

Sorry to be so confusing.

Yet another Senior Moment.


Regards

Barry R.

Barry states he had a Senior Moment... like most of use, but does there come a point where we can have a 'Youthful Moment' within the context that most of the time we are in a near perpetual state of seniority.

Just wondering, as Finland seemed to have won the Euro Song Detest, with a noise that must turn on it's head all the previous formulea for a winner...... CSI on Channel 5 seems to be all that's left to watch, that's were I was anyway. Perhaps I've become a grumpy old man, but I can't remember when or why.....

Algie.

I'm with you Algernon. Thank God I've got my own old cars little world to escape to.

Barry R

Having read all the comments I'll throw my tuppence worth in.
What is the dynamo voltage at the D terminal before closing the cut out? If it is only 1 volt and will not rise (without closing the cut out) then the dynamo has retained it's residual magnetism but is unable to self excite due to a high resistance in the field circuit. Try checking all the connections for cleanliness and security from the third brush to the switchpanel and back to the D terminal on the dynamo.

Have put separate earth on the cut out and adjusted the coil contacts to a min will try out the car at the weekend.The neighbours dont appreciate the car being run up so trail it to local car park.will advise outcome.

Had the car out today much fiddling and adjusting and nothing still only charging with points held together. Very puzzling, still its got a mag so Ok.Starting from cold a supercharged engine seems to need 12v which I jump.When hot will start on handle!!!!

There has been quite a bit written about dynamos failing to charge unless the cut out is manually closed (a decidedly risky busness) so I looked into the problem.
Obervation
In the December 2004 a friend reported that his dynamo wouldn’t charge unless he closed the cut out. It produced just 1 volt at the output terminal at a fast tickover after which he dismantled and cleaned the dynamo and, hey presto it worked. I suspected that this 1-volt is the voltage generated solely by the armature conductors passing through the residual magnetic field. So I retired to the workshop and ran a dynamo with the field disconnected, this produced 1 volt at approximately 1000RPM and 1.5 volts at 2400rpm (dynamo & electric drill speed). Now normally with a link between the D and F terminals of the dynamo, for bench testing only, I expect to get at least 18 volts at 2400rpm on no load, i.e. not connected to the battery through a cut out.
Conclusion
After cleaning his dynamo this friend reported it now produced 2 volts and 3 volts on half and full charge respectively at tick over and wants to know what was really wrong with his dynamo. From the forgoing it would appear that the original fault with the dynamo was a loose or dirty connection in the dynamo field circuit. This could have been at the F terminal or the third brush connection both of which would have been disconnected and reconnected when he cleaned the dynamo and in the process resolved the fault.
Explanation
When you start the engine the dynamo will produce about 1 volt due to the armature conductors moving through the residual magnetic field, this voltage then circulates the field coils to increase the magnetic field which in turn increases the output voltage. This increased voltage circulates the field coils etc etc until the system stabilises for that particular speed. Now if there is a high resistance in the field circuit that the 1-volt cannot overcome the voltage will not build up, however if an external force (human digit) closes the cut-out this will apply the battery voltage to the field circuit which may overcome the high resistance in the circuit. Similarly an operational ignition warning light circuit could also provide enough voltage at the dynamo to kick-start a unit, especially early cars that do not have the 30-ohm (approximate value) resistor, or later cars which have it bridged out because it had failed.
So may I suggest checking all the field circuit connections from the third brush through the switch panel back to the D terminal.
Regards Dave Mann

Dave Thank you for your reply this coupled with a few things I noticed on the dynamo yesterday has prompted me to have the dynamo seen to ,but not before one last effort- new brushes.David

An afterthought to my last reply anyone know a good rebuilder of DFL dnamos in the south of England

Hello David,
Sorry I can't help you with events in the South of England, but if you want to reasonably surely test the dynamo, remove the leads from the "D" and "F" (may be labled "SH")on the dynamo. Bridge these terminals together. If you have a voltmeter, you can then gently rev the engine up, with the voltmeter connected between these bridged terminals and earth. If the Dynamo is in good fettle it will produce quite a high voltage even at modest revs. 20 volts would not be out of the question.

If you do not have a voltmeter, then a 12 volt headlamp or similar bulb, connected between the bridged terminals and earth should be glowing brightly with even quite modest revs.

The bridged "D" and "F" terminals are the condition for maximum dynamo output (Full Charge) so, if you do the above test and find matters OK, you could TEMPORARILY leave the bridge in place and reconnect the wire to the "D" terminal, leaving the "F" wire off. Then see if the the Cut Out will cut in normally. If it does, then there is indeed something wrong with your field wiring/switch box etc.

If you can beg, borrow or steal a multimeter, you could test whether or not the Cut-Out "Voltage" coil, which is the coil on the Cut-Out bobbin that is designed to operate the Cut-Out when the Dynamo output is sufficient (approx 6.5 volts or a tad more).

With everything at rest, the battery disconnected, and the wire going to the "D" terminal on the Cut-Out temporarily removed, you should be able to measure around 40 ohms between the "D" post on the Cut-Out and earth (frame) Up till Easter this year, I had only known of one Cut-Out with an open circuit voltage coil since circa 1960. In the last three months I have found three.

From a position of logic, if the "Voltage coil" was open circuit, then the Cut-Out would not operate on rising voltage from the Dynamo, but, when you bridge the contacts with your momentary switch operation, then it would be possible for the armature to operate on the series coil (the thicker wire coil around the bobbin, which is what you see when you look at the Cut-Out.)

There is at least one UK firm who I know specialises in Cut-Out repairs, not cheap but good. I have also just though of someone in UK who might be OK for Dynamo repair. Please Email me if you want details of either.

I am not dismissing Ron's obviously well thought out considerations, but I try and practice what I term the "divide and conquer" rule when trying to fix electrical problems. By that I mean trying to eliminate bits and pieces as I go through by reasonable testing, on a stage by stage basis, to prove where the fault lies.

There is also not doubt that the connections in the switchbox and the switch mechanism itself can give problems.But the tests outlined above should prove that one way or the other.

regards

Barry R.

Have been told that if you disconnect the wires from the cut out then run wires from the battery, earth to body of cut out then touch other on the D terminal the points will close if cut out OK ....well by this test my cut out is OK. So have taken dynamo off cleaned it up ,fitted new brushes we shall see if it makes any difference tomorrow when I take it out.

Hello David,


That test would definitely seem to prove the Voltage Coil on the Cut Out is OK (and that your Battery is in pretty fine fettle, in theory anyway above 6.5V)

The "Brigding 'D' and 'F' terminals" trick should test the "field control/switch" wiring as it will bypass all that area and push the Dynamo into full output.

Don't forget that you can also test the Dynamo "off the car" by bridging "D" and "F" terminals and connecting accross a battery - "Bridged "D-F" to normal "live" side of Battery and frame to earth side of battery. Dynamo should act like a motor and spin quite fast.

Good Luck

Barry R

The dynamo does run as a motor with teminals connected to the pos battery and neg to dynamo body. Will run the car up next weekend .Have also put a piece of card inside the end cap to prevent any shorting ,the brush fingers look rather close

Thats a positive David. I look forward to the next installment of your "current" problems (pun intended)

I have just found some info on DFL Dynamos in an ancient test I have here. Haven't had time to read it yet, but will do and will send you a scan if it seems to add anything to this whole affair.

regards

Barry R.

Well its charging now but I wonder for how long ,thank you everyone especially Barry.