I have read that a miller maglita should not be mounted to an iron or steel base, presumably it upsets the magnetic flux..
B.T.H Magneto-Generator Series 'A' Comet
- Thread starter Michel
- Start date
Hi Simon
I've just been reading this old post as today I received a BTH Dynamag which was purported to be from a pre-war HRD single. It looked right but it turns anti clockwise. Luckily it has tight wire advance so all I need to do is to change the points and I should have a clockwise mag with slack wire advance. I have 6v LED lights which are now readily available on Aliexpress. There are even 6-12v ones. Do you know if Brian managed to get a suitable regulator? If not I'll use the original setup with resistors.
Regards Bill
Hi Bill
I never heard anything else about an electronic regulator for a BTH magdyno, but Brian is on this forum under the name @A Nut . These are a strange dynamo as they are permanent magnet field and very difficult to control as they have no field winding to switch in and out.
The BTH was used by other manufacturers. I know Rudge used them and also Scott and theirs were strange because the mag ran at twice the usual speed been a 2 stroke so the internal gearing between mag and dynamo was different to slow down the dynamo part.
Simon
Thanks Simon
I believe that Douglas used them too.
As I always ride with my headlight on I’ll select bulbs and perhaps a resistor to leave a small charge available to keep the battery topped up. I’ll use a diode for the cutout. At the moment I run led bulbs with total loss which is fine for day rides but not for touring.
Simon is quite correct in that there is no way to regulate a BTH dynamo. The way a dynamo is normally regulated is by switching the field windings in and out. I once asked AO Sevices if it was possible to regulate it electronically. It was going to be expensive and still not sure if it would work so I didn't pursue it.
Brian
Brian
Not quite right: You don´t regulate the alternator, be it permanent magnet or other, you convert high voltage up to 50 V to 13.8 V or whatever with this electronic box in my link. You just get a rectifier that is connected to the alternator and next stage is the converter for 13.8 V - or 7 V as you like. I tested this setup some years ago and had mentioned this several times here and no excessive heat is generated neither in the alternator nor in the converter. It does not matter if you got single phase or three phase, as the rectifier is first stage - and that will not care about this.
Vic
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Vic
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Vic, I think you may have missed the point, this is a DC generator, not an AC alternator. Think Tesla, not Edison Or am I wrong?Not quite right: You don´t regulate the alternator, be it permanent magnet or other, you convert high voltage up to 50 V to 13.8 V or whatever with this electronic box in my link. You just get a rectifier that is connected to the alternator and next stage is the converter for 13.8 V - or 7 V as you like. I tested this setup some years ago and had mentioned this several times here and no excessive heat is generated neither in the alternator nor in the converter. It does not matter if you got single phase or three phase, as the rectifier is first stage - and that will not care about this.
Vic
7.89US $ |Xwst Dc Dc 36v 48v To 13.8v Step Down Voltage Converter 13.8 Volt Buck Voltage Transformer Waterproof Dc Power Supply - Inverters & Converters - AliExpress
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Robert, no troubles from that, so you can bin the rectifier. We agree that we deal with permanent magnets in the dynamo , so there is some sort of commutator and brushes contained - no ? Even so, for the converter it does not matter what supplies the power into it. It just brings down excessive voltage to 13.8 V or 7 V , just get the desired converter for your bike.
Vic
Vic
Robert you are correct.
The BTH mag-dyno in question is a 6V DC dynamo generator that has no field winding and it is built as a permanent fixture into the top of the magneto and you cannot remove the dynamo from the magneto and fit a different dynamo or generator. It was designed in the late 1920's and generates a max 24 watts at 6V which doesn't even keep up with the lights unless you use LED bulbs.
I was worried that it would overcharge the battery on my bike when the lights were not on as the regulation is basically just a load resistor on the back of the headlight switch which cuts the charge in 1/2 when no lights are used. When measured, the dynamo will reach 8.5V to 9V max unregulated so there is no way you can let it run up to 13.8V and then convert it back to 7V with a DC-DC converter as the dynamo is incapable of reaching 13V.
Rather amazingly the system works as designed and I have never boiled or overcharged the battery.
