potentiometers for manual dynamo control

[JonE]

Dave Mann, Malcolm Watts and others have all discussed potentiometers in old threads on the old forum allowing full manual control of the dynamo. Cornwall Club members mentioned the 'simmerstat procedure'; Dave has mentioned mini fan rheostats. I'd just like to bump the topic to find out exactly what items have been used - as cooker ring switches, the fan rheostat and Malcolm's 150W 0-5 Ohm potentiometer all seem to be different in spec.
Is anyone else using such a thing still?

[Bob Culver]

Adjustable resistances are always a bit tricky as the watt rating is generally for the whole or most of the resistor not just part of it, for which it is more or less proportional.
Adjustment of the 3rd brush is preferable as there is no associated power loss.
To manipulate really need a voltmeter; a zener necessary to expand the scale. Very cheap LED indicators are available.
For most now a modest Summer rate used in conjunction with a smart bench float charger is probably the ideal, esp if the battery is CaCa. For 400 mile day trips on the later cars the field fuse can be removed to stop charging for periods.

[Mark McKibbin]

I have a CAV generator on my Chummy with an open circuit resistor in the field coil, so to give me some "Summer" charging I have put a 3 ohm 20w resistor in the summer circuit and I get about 1-2 amps going into the battery so fine for long trips. I have the third brush set for about 8 amps for winter setting. I like the idea of the pot however but I also like simple.

The only trouble with my solution is that it only works when cruising as in traffic it will be negative so a pot maybe the answer.

Lastly I have purchased one of these single multicoloured LED voltage indicators that can be programmed for 6, 12 or 24v that I will hide to tell me what really is going on.

https://www.ebay.com.au/itm/6v-12v-24v-P...0843083721

[andrew34ruby]

As a temporary measure until I splash out on an electronic regulator I am using a stop/tail bulb and two switches. With the 'tail' filament switched to supply current to the field windings I get a bit of charge. With the 'stop' switched to supply current instead, I get more charge. With both switches on I get even more charge.

Crude, but it works.

I am on 12 volts with 12 volt field coils, original armature windings, and the 3rd brush removed.

And I'm thinking there is little point in getting the electronic regulator.

[JonE]

That's lovely! Just a spare bulb to carry rather than a spare solid state regulator!

[Bob Culver]

Without a rewound field, nothing is electrically more efficient than the 3rd brush picking off a reduced voltage for the field. Lamps and resistors absorb precious watts, undesirable at full output. Very inexpensive multi LED dipslays are available with voltage range adjustable. Often used for monitoring oxygen sensors.
Cannot see the justification for a variable resistor.

[JonE]

Very inexpensive multi LED displays are available with voltage range adjustable. Often used for monitoring oxygen sensors.

Bob - are you saying these are a potential efficient theoretical replacement for the potentiometer idea?

[Mark McKibbin]

As a temporary measure until I splash out on an electronic regulator I am using a stop/tail bulb and two switches. With the 'tail' filament switched to supply current to the field windings I get a bit of charge. With the 'stop' switched to supply current instead, I get more charge. With both switches on I get even more charge.

Crude, but it works.

I am on 12 volts with  12 volt field coils, original armature windings, and the 3rd brush removed.

And I'm thinking there is little point in getting the electronic regulator.

The system on my special is the same as your but with 6v field coils, I use one of the regulators from A.O. Services, price list here http://www.aoservices.co.uk/prices(V29).pdf they were designed for motorcycles but they make an uprated one for cars, works flawlessly. 

I am thinking of getting a 12v field to improve low speed output, where did you get yours?

[Bob Culver]

Hi Mark
It might pay to check with someone using the same regulator. Might not make much difference. If the regulator controls field current in theory only about 1.5amps at 12v instead of 3 amps need be supplied to the field so at present the field can presumably be fully magnetised when the output is only about 5 volts as from the original 3rd brush.

---

Hi Jon E
Nope. Just inexpensive voltage monitors if 12v supply available. I use one calibrated to monitor my battery charger. Can be observed at a glance. (many chargers have built in) Seem to recall about L4 equiv here.
Particulalrly without a regulator, max output is most efficently limited by the 3rd brush. There is seldom cause to alter the summer rate but the fixed resistor can be substituted or augmented by an external one to suit. For traffic driving use Winter.

[andrew34ruby]

As a temporary measure until I splash out on an electronic regulator I am using a stop/tail bulb and two switches. With the 'tail' filament switched to supply current to the field windings I get a bit of charge. With the 'stop' switched to supply current instead, I get more charge. With both switches on I get even more charge.

Crude, but it works.

I am on 12 volts with  12 volt field coils, original armature windings, and the 3rd brush removed.

And I'm thinking there is little point in getting the electronic regulator.

The system on my special is the same as your but with 6v field coils, I use one of the regulators from A.O. Services, price list here http://www.aoservices.co.uk/prices(V29).pdf they were designed for motorcycles but they make an uprated one for cars, works flawlessly. 

I am thinking of getting a 12v field to improve low speed output, where did you get yours?

My 12v field coils were from here...    https://www.eics-products.co.uk/shop/classic-and-vintage-parts/c35-dynamo-12-volt-field-coils/

They need heating to help them to be fitted, and it's still tricky. Low speed output is still low.