Dynamo and regulator wiring

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db2d
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Location: Monmouthshire

Re: Dynamo and regulator wiring

Post by db2d » Wed Apr 17, 2019 4:49 pm

I would be surprised if you can successfully charge a 12V battery with the 6V CAV dynamo on your tractor.

ddclutch
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Location: nr. Kendal, English Lake District

Re: Dynamo and regulator wiring

Post by ddclutch » Wed Apr 17, 2019 7:42 pm

So would I. But did you see that I am getting 13.8v output from that third wire from it? I am wondering if it has been modified or rewound at some stage. I can't think how else it would be putting out a steady 13.8v.

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rid54
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Re: Dynamo and regulator wiring

Post by rid54 » Wed Apr 17, 2019 8:31 pm

A reflection on dynamo working principles:

The output of a dynamo of the type used in vehicles comes from the armature, the rotating part. It is taken out via the commutator segments and the brushes, one of which is connected to chassis (+ or -) and the other to the system. What actually comes out from the dynamo, depends on the stator field strength (as given by the current in the field windings) and the armature speed (RPM). The regulation is done by the regulator, by controlling the field current. The regulator is governed by the voltage of the system as primary factor, and by the output current (omitted in some systems). The regulator is set to keep the field current at a level which gives a suitable system voltage (13,7 - 14,4), irrespective of engine speed. In actual practice, the regulator "feels" the system voltage and adjusts the field current to keep the system voltage stable in all circumstances. Some regulators also have a sensing coil for output current, and "downshifts" on the field current if the output current is getting too high for the dynamo. In addition to this, some regulators also have a unit for reverse-current switch-off, that is getting active when engine stops to prevent battery current feeding an idle dynamo backwards.

What is important to keep in mind, is that measurements at one point in the circuitry may be very inconclusive, if the point in itself is not properly identified and related the general picture. A totally unregulated 6 V dynamo might well produce 13 V at the output if it were not connected to a consumer, or if the regulator is not working.

Your course of action will depend on what you want to do with the tractor. Full restoration - go for original parts and a 6 V system, even if it means getting another dynamo + regulator. If you just want a working tractor - try to find an alternator with built-in regulation (or another dynamo...) and fit it. Some seem to accept 12 V drive of 6 V starters, so your starter could be left as is (it doesn't mind a polarity change anyway). Don't use too heavy wires, though; losing some of the oomph from an overvoltage battery might keep the starter working longer before having damage. Usually this is not a problem with engines that are good starters, but if you often have to keep grinding to get the engine going, the starter may eventually develop signs of abuse.

ddclutch
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Location: nr. Kendal, English Lake District

Re: Dynamo and regulator wiring

Post by ddclutch » Wed Apr 17, 2019 8:51 pm

Thanks for that explanation. Helpful to get a grasp of how it works. Though I still don't really understand how it might produce a steady 13.8 v on that cable, if the windings and armature are designed to supply 6v. I do still wonder if it has been modified for a higher voltage at some time.

As things stand I am pretty sure that although the previous owner only used the tractor intermittently, the regulator that is attached to the dynamo well pre-dates his ownership and was professionally set up that way with those components at a time when it was a proper daily working tractor. Therefore the components themselves must have been compatible and functional. Even if the regulator is not a DB item it must have been configured to work correctly. And as things stand I haven't given up on the idea of getting this arrangement to work again, with these components. I just need to work out how to reconnect it to the tractor wiring.

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db2d
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Re: Dynamo and regulator wiring

Post by db2d » Wed Apr 17, 2019 9:19 pm

rid54. This is a seventy year old tractor with a gear driven CAV dynamo with engine governors attached. Without major modifications the fitting of alternative equipment is not a viable option.

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rid54
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Re: Dynamo and regulator wiring

Post by rid54 » Wed Apr 17, 2019 9:26 pm

I think your ideas are all sound. What you need to do is to find the proper relationship between the connections from the dynamo itself and the regulator. It may indeed be worth while to take the unit off of the tractor and examine it thoroughly, or take it to an electrician with the required knowledge of old equipment.... Look inside, check brushes and commutator etc and see how it is all wired up. What is needed is proper common "earth" and then the proper connections to the regulator, as seen from the dynamo.

On the regulator:
There must be a connection from/to the battery. Often this is labelled B+ on the regulator. Routed perhaps via fuse to the ammeter or directly to battery or starter system connector. Thick wire required, as it should be able to carry full dynamo output current.

There must be a connection from one of the brushes (dynamo output). Label is often D or D+. Routed from dynamo to regulator. Thick wire required, see above.

There must be a connection to feed the field, normally labelled DF, or F. Routed from dynamo. Not very thick wire required, as the field doesn't take very high current.

There may be a connection from regulator to a charge warning light or to the ignition switch. Thin wire. Other end should normally be "system" (that means "+" or "-" according to polarity of vehicle system.

In your situation, I'd remove the dynamo and go through it and the regulator carefully, noting any kinds of labelling on conectors etc and work from there.

It has been pointed out above, that fitment of newer components will be difficult due to the construction of dynamo drive. I cannot argue with that. It merely amplifies the ideas I would advocate about restoring the dynamo + regulator system that is already in place.

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cobbadog
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Re: Dynamo and regulator wiring

Post by cobbadog » Thu Apr 18, 2019 7:57 am

Here is a schematic diagram for a 6v +earth wired David Brown. It shows 2 wires only from the dynamo, both going directly to a separate regulator using an unidentified terminal and "D". Ammeter is wired between terminal "A" on the regulator and - on the battery. It also shows a lighting schematic. Hope it helps.

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cobbadog
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Re: Dynamo and regulator wiring

Post by cobbadog » Thu Apr 18, 2019 7:59 am

Finally got it attached.
Attachments
6v Electrics.jpg
6v Electrics.jpg (53.96 KiB) Viewed 50 times

ddclutch
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Location: nr. Kendal, English Lake District

Re: Dynamo and regulator wiring

Post by ddclutch » Thu Apr 18, 2019 10:01 am

Thanks Rid54 and Cobbadog, both helpfull replies which now give me something to go on.
The wiring diagram page is particularly good to see and instantly I learn some answers like:
Is my tractor supposed to have these multi-coloured plug leads? - Yes
Have I got the actuating bar on the starter the right way round? - No

But the main thing is it shows the connections between dynamo and regulator and I can now dismantle mine to compare. My dynamo definately has 3 wires exiting, but that diagram shows 2 plus a small wire ending in an arrow - does this mean to earth? It appears to be inside the dynamo on the drawing, and connects to a brush and the remote end of the field coils, so probably to earth. Perhaps my third wire is this one, only external. Next task is certainly to remove the dynamo to inspect where each wire originates.

Whilst I am asking questions though, were the cables going forwards to the lights and the dynamo secured, wrapped or protected in some way? I cannot see any obvious route or securing tags and they seem vulnerable if just as wires strung past the side of the block.

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rid54
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Re: Dynamo and regulator wiring

Post by rid54 » Thu Apr 18, 2019 11:01 am

ddclutch wrote:
Thu Apr 18, 2019 10:01 am

...But the main thing is it shows the connections between dynamo and regulator and I can now dismantle mine to compare. My dynamo definately has 3 wires exiting, but that diagram shows 2 plus a small wire ending in an arrow - does this mean to earth? It appears to be inside the dynamo on the drawing, and connects to a brush and the remote end of the field coils, so probably to earth. Perhaps my third wire is this one, only external. Next task is certainly to remove the dynamo to inspect where each wire originates.
The wire inside ending in an arrow, is very probably meant to show an internal connection to chassis earth. The diagram is very neat and gives much detail - very good. I hope you get it all sorted out!

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cobbadog
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Re: Dynamo and regulator wiring

Post by cobbadog » Fri Apr 19, 2019 7:16 am

On any schematic diagram the "arrow" looking icon is always the earth wire, the only thing that changes is whether it is positive or negative earth but always is the earth wire. I would use a multi meter to check the terminals to confirm which is your earth if it is not stamped somewhere near or on the terminal of the regulator. Some regulators do earth themselves and some must have a dedicated earth wire.
On my later model 30C the headlight wires run down the starter and dynamo side of the tractor and they use metal clips from one of the battery box bolts to old them in place. Then they follow the radiator blind operating tube forward then split to go to each head light. On the same side my temperature gauge line, horn wire and distributor wire runs along the top of the engine block or bottom of the head and are held in place by simple plates with a kink in them to wrap over the wires and temp line using some small screws to lock them in place. When I re-assemble my 30C I am fitting up stop/tail and number plate lights so will be running them under the tractor in some tubing to protect them. Exactly where is yet to be determined.

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