DEL 1929 dynamo

[JonE]

I know the DEL has the internal resistance for the half charge wrapped round the field windings. Does the unit have qualities over the later 35 A/M dynamos because of its dual bearing for the armature, or is its value (for use) only in originality to 1929 cars? 

Can I assume that it can be used with later control boxes, but that if one did, the resistance might be a little higher IF the original internal system was still functional?

It looks like the DEL may have already been converted for 2 brush use, as it is paired with a Dauphine regulator. But i'm just trying to work out what is the sensible thing, i.e. pass this onto a 1929 owner, or work on it because it is there.

[Parazine]

Jon, I don't know whether the CAV DEL in either long or short armature form has any significant advantages over the later C35A/M, other than being a nicer engineering answer due to the better bearings. The CAV is a four pole machine, the Lucas is a two pole but I can't see any practical advantages there.
Most of the internal resistances on CAV DEL dynamos are open circuit; I usually wire an external  7.5 or 10 ohm wire wound ceramic resistor between F and D to give 1/2 charge.

I've got a DEL short armature on my '29 RK saloon and it works very well at 7.5A/3A charge rate and has done for a few years now.

[JonE]

That's helpful, thanks. The 'Charging Refresher' series of wiring diagrams doesn't actually mention the short and long armature differences - how would one tell... and what did they relate to - is one later than the other?

Can I also be thick over the "Most of the internal resistances on CAV DEL dynamos are open circuit" bit? I realise that means the circuit is not activated if its open, but what does that mean in practice vis a vis checking if the original resistance still operates and how you deal with that? I presume that your 7.5 Ohm is brought in to play when the SM switch activates the F-D bridge?

---

The Charging refresher article says:
"Repairing these windings can be a real pain, which is why (according to Harry Hale, the expert,) many of the DEL types are simply used with the resistor open circuit, or replaced for later machines. Again, there has to be some appropriate modification of the circuit – they might fit mechanically but need some other changes electrically"
I waas uncertain whether Open Circuit meant "not functioning", or whether one needed to detach something.

[Bob Culver]

The long ones are interchangeable with the 35A and 35M with any wiring changes as per the Refresher article. Note the main brushes are 90 deg to each other. If no 3rd brush the user would have to be aware of precautions necessary to limit the field current, unless it has been rewound, which, with 4 coils, seems less likely. Some claim slightly less capacity than the 35M. With 3rd brush lifted there should be no connection between the field terminal and anything else if the internal resistor is out of action. The armatures are wound different and fault tracing with a meter is different and much more confusing! Excellent diagram in Woodrow. My RP has had all 3 over the ages; it is only recently I grasped all the differences.

[JonE]

that is enlightening. I hadn't properly realised that means 4 field coils when 'poles' had been discussed. So plainly, the DEL is probably best kept standard for sheer practical reasons.

[Parazine]

That's helpful, thanks. The 'Charging Refresher' series of wiring diagrams doesn't actually mention the short and long armature differences - how would one tell... and what did they relate to - is one later than the other?

Can I also be thick over the "Most of the internal resistances on CAV DEL dynamos are open circuit" bit? I realise that means the circuit is not activated if its open, but what does that mean in practice vis a vis checking if the original resistance still operates and how you deal with that? I presume that your 7.5 Ohm is brought in to play when the SM switch activates the F-D bridge?

---

The Charging refresher article says:
"Repairing these windings can be a real pain, which is why (according to Harry Hale, the expert,) many of the DEL types are simply used with the resistor open circuit, or replaced for later machines. Again, there has to be some appropriate modification of the circuit – they might fit mechanically but need some other changes electrically"
I waas uncertain whether Open Circuit meant "not functioning", or whether one needed to detach something.

Jon,

The term "long" and "short" refer to the physical length of the armature, the later dynamos being the long variety. The two can be differentiated by the fact that the short armature DEL has a fabricated distributor end cover, whereas the long armature machine has a one piece cast aluminium end cover. The changeover was December 1929 at around engine number 99900. The drive gear also changed from the extremely fragile bell gear to the solid gear familiar to the later cars.
The term "open circuit" means just that, not connected, no current can flow, disconnected.
On full charge, the dashboard switch places a short circuit (N.B. "short circuit" is the opposite of open circuit and implies that two parts of the wiring are connected together with 0 ohms resistance between them) between F and D. On 1/2 or "summer" charge, this short is removed and that's when the current can flow from D to F, through the internal resistance if it's still operational or through an external resistor if connected between F and D.

[JonE]

Just something else to add under this topic re how to find the third brush.
Harry Hale's Austin Electric book and Green companion page 205 both feature the 3rd brush position and how to access it on DEL. Looking from O/S wing, it is on the right hand side with the cover removed, and the 3rd brush securing screw is at 4/5 o clock position if you were looking from the end plate inwards. It is thinner in form as per later dynamos.
My maximum charge comes with the right hand (third) brush right up next to the left hand one, and I needed to push it down, clockwise when viewed from the end, to reduce charge.
Questions:
Can the DEL 3rd brush be left so it has the same easy-to-adjust friction movement as later dynamos, or is this a bad idea?
When in 'maximum' position, ammeter action smooth and higher than I would expect. When moved to restrict, the ammeter needle is very jerky although it does reduce overall. It is moving through a wide range. What can be causing the jerkiness?

Would a DEL owner check my first statements and check you agree please? I am a little wary as Hale's text implies the two main, (thicker) brushes can be moved too - mine do not appear to be at 90 degrees to each other as in his theoretical diagram. I'd also like the clarify the position of large and smaller dynamo terminals and which is which. All the references to them are slightly ambiguous depending on how you view them.

[AustinWood]

The 3rd brush is the thin one.
Moving it in the direction of rotation of the armature increases the charge & vice versa.
There is no means of moving the 2 thick brushes.

[Parazine]

Hi Jon,

The third brush should be clamped, the later dynamos have  a spring to add stiffness to the system, allowing the brush holder to be run unclamped but this doesn't exist on the DEL.
Ammeter jerkiness - don't know, could be that the ammeter has some internal friction, causing problems or there could be intermittent current flowing. Do you know someone who has a reliable moving coil meter such as an AVO8? This are the best way of checking and setting the system up. The Lucas ammeter is a bit Michael Edward Mouse.

The main brushes shouldn't move but, depending on the skills of the last person to disassemble/reassemble the dynamo, anything is possible!

Large terminal (1/4 BSF I believe) is D, smaller (2BA or 5/32 WW) is F. 3rd brush nearer main brush = max output. Run at 8A absolute maximum, I use LED lamps so run at 5A/2A. Set it up on an Avo, the Lucas ammeter lies without shame.

Regards

Tim R

[JonE]

brilliant thankyou both. For info, the Hales text is below. Do you both have the 90 degree arrangement? It feels to me (without removal - I'll go and scrutinise with a mirror after reading this) that the main brushes are at 12 o' clock and possibly 6 ' clock (180 degrees) with the third moving between 1 until 5 looking from distributor end! 
My present ammeter is a 60's monstrosity so I'll revert to Austin first and then find the decent meter. Can I put it series to test both, or will that half the reading?

  Screenshot 2021-04-06 at 10.12.42.png (Size: 169.38 KB / Downloads: 365)