Circuit diagrams

[ian Howell]

When I rewired my Long four I followed the '1935 van' diagram in Newnes 'Motor Engineering' volume II, which has circuit diagrams for a wide variety of cars including various Jowett models from 1935 and 1936 and I KNOW that since then I have run the engine and got a 'charge' indication.

But not now!

Threatened with an MoT test before long (and NOT before time some might say!), the beast now refuses to show any signs of charging.

I have checked all connections - including the mechanical/electrical one between the cut-out and the dynamo body - and everything appears to be in order. The cut-out appears to be mounted and connected the right way round (there are no markings on the terminals except '6V' on one).

Newnes helpfully? mentions in passing that failure of a dynamo to charge may indicate 'loss of polarisation'. I assume this means the residual magnetism in the body of the dynamo. What they don't say is what to do about it!

I expect that one has to apply a voltage feed - presumably from the battery - to the field connection, but I don't want to do any damage, so any advice?

Just a thought, the battery is definitely 'shot' but it does hold enough charge to run the ignition and even the headlights for a short time, so could low battery voltage be a cause?

Also, ALL the diagrams show THREE connections to the dynamo, but only TWO of them appear to have any internal connection within the dynamo itself, with no internal connection to the terminal labelled 'POS'.

Shome mishtake shurely?

[Forumadmin]

Polarisation can be accomplished by flashing the terminals across a battery in the desired polarity. I very much doubt that is the cause if the system was previously working. I would start by putting a meter across the dynamo to check continuity and resistance. Not having a dynamo the same as yours I cannot give the ohms to expect. Then I would spin the dynamo with meter on 10v DC range and see if I got a few volts. You will not get much because there is no field current. You can put a battery on the dynamo and it should spin like a motor.

Having established volts are coming out of the dynamo. You should check the continuity of the cut out coil or check to see if it is cutting in when the dynamo puts out about 7v on a 6v system. Is the charging warning light coming on and then going out when the engine is running?

And yes a shot battery would upset the cut out and could even not give enough field current initially.

I guess the three connections are for positive or negative earth; but that is only a guess. Are you sure the Pos connection is not connected to the body of the dynamo.

[Keith Andrews]

Just a thought, the battery is definitely 'shot' but it does hold enough charge to run the ignition and even the headlights for a short time, so could low battery voltage be a cause?

yes...
A shot battery can have high or even low internal resistace, this determines the current and voltage draw and how the relays switch...unlike a modern alternator be it internally or extenernally regulated.
In saying that still caustion, because if the generator is putting out incorrect voltages / current it can do damage to the battery....
Flashing of generators is covered in detail in older posts.. a thread about converting from +ve to -ve ground.

[Forumadmin]

If you disconnect the D wire from the dynamo and run up the engine or spin at 1500rpm the volts on the D terminal to dynamo body should be between 1. and 3 due to residual magnetism. If less than 1.5v suspect an internal connection fault.


Disconnect wires from D and F, put ammeter across them. Run up engine until volts read either 6 or 12v. The field current should be about 2 A. If not probably need new field coil.

[george garside]

have you tried closing the contacts on the cutout by hand ( or preferably with aa suitable instruiment- insulTED SCREWDRIVER OR WHATEVER) with the engine at around 1500 rpm with aan assistant watching the ameter.

george

[Tony Fearn]

Hello Ian.

1:- If you have the brass cover on the cut-out when there's no charge, try it again with the cover off the cut-out. Don't ask me why, but I've had the same problem. I got a charge without the cover on, but see item 2.

2:- For some reason, when I start the cars and set off, the ignition light doesn't go off for quite some time, and then it does. If you're just running the engine for a few minutes, then this won't be apparent. Other pre-war owners have told me that they experience this phenomenon as well.

3:- If you have a three brush dynamo, make sure that all the brushes, especially the thin one are touching the commutator and move freely in their slides (?WD 40). The thin 3rd brush wears away relatively quickly and the spring can't make it touch the commutator.

4:- With one of the brushes removed, put a piece of fine wet and dry on a thin piece of wood that will fit into the brush holder and polish the commutator. Get someone to turn the engine by hand using the handle. Then, using something like carb cleaner on a piece of cotton on the same bit of wood, do the same to clean it up.

5:- Buy a new battery, you're going to need it anyway!!

If these don't work, then the more esoteric answers might hold the key.

Tony

P.S. She's hardly 'a beast'! What are you going to call her?

[Keith Clements]

If the ignition light does not go off then it means the dynamo is not generating more voltage than the battery, unless the cut out is open and the current is flowing to the battery via the lamp rather than from it! This suggests a lazy cut out that may need to heat up to operate. Try putting an ammeter in series with the lamp.

[ian Howell]

WOW! Loads of useful stuff there! Thanks a lot!

Things already done (BEFORE my original post): -

Commutator cleaned.

Brushes checked for wear and free movement in brush boxes.

Cut-out contacts cleaned and cut-out set to operate at 6.5V by means of a variable voltage power supply unit.

A couple of points mentioned: - My car does not have an ignition warning light but it does have an ammeter which is in full working order - both 'charge' and 'discharge'. It shows about 3 amps discharge with the ignition 'ON', which goes to 0 as the engine is turned and the contacts in the distributor open. With the engine running it sort of averages out at about 1.5 amps discharge as you might expect.

There are three brushes on the dynamo.

I have a recollection that at some time in the past there was a 'post' that warned of the risks of manually closing the cut-out contacts and causing damage to the dynamo windings. I think this would be unlikely as there is probably not enough oomph in the battery to do much damage. (It will operate the ignition for a prolonged period but the headlights 'kill' it after about 1 minute.

I think I will try the 'flash' idea but with a low rating - say 5 amp - fuse in line, just in case.

Back to the actual circuit diagram - is it right? What about the contact arrangements of the 'ignition' switch? This appears also to select 'half' or 'full' charge for summer or winter operation but the actual internal connections seem to be missing.

I feel an opportunity coming on for a clearer diagram, if only for later generations - once these problems are sorted.

I will let you know what progress - if any, but I am orf to Wales again next week so things might be on 'hold' for a while.

Many thanks for your (collective) interest and encouragement.

Name for the 'beast'? Well there was a suggestion that as the registration letters are PG it might be called 'Miss PiGgy', but as that has already been done there is now a tentative bias towards 'Miss PeGgy'.

First things first, I want to get an MoT done but I think that will not now be before they become a (compulsory) thing of the past!

[Forumadmin]

Why not attach the diagram ?
Is this something like the operation?

[Tony Fearn]

The 33/34 wiring diagram is in my album in JowettGallery.

here

[ian Howell]

Yup.

Thanks Tony - that diagram is similar to the ones I was referring to, at least as far as the dynamo connections are concerned.

Look VERY carefully at the third (right hand side) terminal. See? Only two external connections shown and NO internal connection. Hmmm . . .

The ignition switch is different but that does not affect the dynamo.

[Forumadmin]

Well I cannot make head nor tail of that diagram! The ignition switch needs a lot of explanation and the wires into the dynamo are ambiguous as to where they go. Give me a clue.....

[robert lintott]

Ian, Going back to the start of this item, if as you say , the charging system worked in recent times it is very unlikely that the dynamo or cut out has failed of its own accord . However a dud battery--and yours sounds very dud--- will stop the system working . As a first step therefore it would be best to buy or borrow a good battery and you may find all is well.

Just for curiosity what number PG do you have ? I have PG 5897, a 1930 Austin 16/6 Tourer owned since 1970 ish, it does not have a name except as "Chitty" by grandchildren! Bob Lintott

[ian Howell]

Bob (et al): -

Well now - progress of a sort?

Today I managed to get in about 1 hour of investigation and found: -

There are TWO wires coming from the dynamo 'innerds' - one goes to the 'F1' terminal and one to the 'pos' terminal of the three way block attached to the dynamo. No connection from the dynamo itself to the 'pos' terminal.

On the circuit diagram there is NO internal connection shown to either the 'A' or the 'pos' terminal.

When I touch the lead from the 'A' terminal on the dash panel to the 'A' terminal on the dynamo - with both the ignition/dynamo and the light switches on their 'off' positions, there is a spark, therefore there is a CONSTANT drain on the battery through the dynamo, at least until the dynamo starts to charge the battery.

This circuit is broken when I lift the bottom brush away from the commutator.

I cannot see any means to move the 3rd brush assembly - all three brush holders appear to be rivetted to the end cover (I can't actually see one fixing as it is under the distributor mounting).

I have now disconnected all the external wires from the dynamo and the plan is to make a jury rig with remote connections to make them easier to get at and then to experiment with various connections and meters in the appropriate positions.

Bob: - The reg is PG 7956, so some way from yours but interesting nonetheless. If you were at Wakefield you may have seen my 'project'. If not, in Google Images enter 'ian howell jowett' and the first image is of the car with my son and myself at Wakefield - courtesy of Tony Fearn I believe.

I have had great fun? trying to track down the original registration date of my car as I had no paperwork with it in 1966.

A plate on the dashboard shows 'Hunts of Guildford' as the supplier (presumably when new) and they had a site in Woodbridge Road Guildford but more that that I don't know - yet!

I received the following very helpful information from Malcolm McKay, Hon. Sec. of the Bull Nose Morris Owners Club: -

Hello Ian, PG xxxx was used between May 1929 and May 1930 by Surrey County Council. PG 284 May 16 1929, PG 2740 Aug 28 1929, PG 5834 Jan 30 1930, PG 6994 Feb 20 1930, PG 9441 Apr 15 1930, and PG 9882 May 5 1930.

Hope this helps, Regards Malcolm, Hon. Secretary BNMC.

So PG 5834 is quite close to your car. I am orf to Wales tomorrow so everything will be on hold until early November at the best.

Keep Jowetteering!!

[robert lintott]

Ian, Thanks for the PG info. My PG 5897 was registered on 03/02/30--I have the original Reg. Book--and looking at the Vintage Austin Register I see PG 7047 registered on 04/03/30 and PG 9691 on 19/05/30, The latter illustrates that because numbers were issued to Dealers in a block, numbers can be issued out of order when one block is used up faster than another. The last number you showed was after 9691 but was issued earlier.
Some counties have retained the old records , I suggest you approach Mike Worthington -Williams ( the Automobile ), he will know what happened in Surrey and may be able to point you in the direction to get the actual date.
Good luck with the electrics Bob