Joined: Aug 2017 Posts: 2,748 Threads: 31
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Location: Auckland, NZ
Hi Zeto
The terminolgy can get tricky. Whiist not all diodes are used primarily as rectifiers, the 4 in one diode as the second posting, of which two are used in parallel, is intended primarily as a rectifier so the term is not unreasonable, even if it is not so functioning with a dc dynamo!
At 30 ohms the cutout absorbs a watt plus a tad in the heavy winding whereas a conventional diode absorbing .6v at 10 amps soaks 6 watts......
Joined: Aug 2017 Posts: 3,329 Threads: 372
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Steve Marks at Magnetoguys sent me this which I thought would be good to post here just as another debating point:
"The Conrad Direct device is a very standard bridge rectifier which contains four rectifier diodes. If wired up the way it is suggested, there will be two rectifier diodes in parallel between the dynamo and battery. Nowadays, rectifier diodes are a poor choice for this application - too much volts drop for one thing. When Schottky diodes came along, they were a better choice. Time (and technology) moves on and neither of these options are as good as our Smart Diode Cut Out (but I guess I would say that wouldn't I! ?) but don't take my word for it - compare the performance figures for it listed on the website compared to the figures for Rectifier and Schottky diodes! No doubt the time will come when the Smart Diode becomes obsolete because something better has been developed.
It is interesting to see that many still look on electronics with suspicion and are convinced that they will fail. Nothing is perfect but modern electronics is much more reliable than early mechanical or electromechanical options - and they don't require maintenance and adjustment either! Personally, for me it's a no-brainer. Vehicles I have which originally had three brush dynamos have all been converted to two brush operation and use an electronic regulator. The AO and DVR ones are good. The only time we fit our Smart Diode Cut Out is if the owner wants to keep things as original as possible or if the dynamo in question has the field provided by permanent magnet(s) in which case there is no way to regulate the output by adjusting the field strength so an electronic regulator is not suitable."
It is interesting, as it still puts the onus on carrying a spare being the crucial thing for roadside fixers. The cheapest AO device (now not really recommended by AO for car use), is about 50 quid which is just about in range for doing that - not a lot more than what people are doing with electronic points systems.
...
Zeto - the reason I started looked at this again was as the Speedex has a need for a water pump and also has no original PLC switch or cutout. Ian had suggested that the Davies Craig pumps would still work 'out of range' on 6V, but I'd started to look at 12V and all the options just because it's a non-original car. I still want to aim for simplicity (in the longer term beyond running an auxiliary battery and a cheap 12V-only aux pump) and being able to be in control/fix things!
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Is anyone actually using the Magnetoguys smart chip and able to give feedback on whether it is stable in Austin 7 terms?
I presume it is essentially supplying one function of AO and DVR regulators, but not sure...
Joined: May 2018 Posts: 2,098 Threads: 110
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Location: Llandrindod Wells
Car type: 29 Special, 30 RK, 28 C Cab
Hi Jon
I’m using one on the special and it seems to work well but I’ve not done enough miles to give reliable feedback.
Cheers
Howard
Joined: Aug 2017 Posts: 1,014 Threads: 53
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Location: The delightful town of Knaresborough, North Yorkshire
I'm using a diode from the rectifier pack out of a 1980s Lucas alternator. It works.
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More on the TI chip, being sold on ebay for a fiver...
"You could connect them any way as long as your method can take the rated current. As follows.
1/ As you say soldered directly to a purpose made PCB
2/ Connect wires by soldering to the leads and then to the tags.
3/ Use crimp connectors straight onto the leads. Make sure they are well crimped (ie. No sign of movement on the lead). A poor crimp can lead to hotspots and failure/fire/damage to surroundings.
Note. In all circumstances:
1/ Be careful not to exert pressure on the lead/package interface during connection. This could damage the device.
2/ Do not overheat the leads during soldering, this could permanently damage the internal circuit.
3/ Use a connecting method that can handle the very high forward current.
IPC-620 regulations describe electrical interface methods that should be employed.
Regarding your intended use I really can't advise whether it will work or whether it work or whether it could cause damage. Please read the Texas Instruments data sheet"https://www.ti.com/lit/ds/symlink/sm74611.pdf" online
Remember that internally, these are not actually built as a Recifier diode. They are a hybrid equivalent and as such they do have an inate instability. This is because when passing current, the internal circuitry turns off for a very short period, about 2 to 3 ms. During this period, the forward voltage drop increases to to about 0.6V due to the internal parallel Schottky rectifier. Whether or not your car could be affected by this I don't know, since they were designed for Solar cell and power supply purposes. So any other use is carried out at your own risk.
And additionally. These can probably not be used as a Back EMF clamping diode, since the reverse voltage may be too high.
As I suggested, please read the manufacturer's data sheet to decide if these are suitable for your intended use".
Joined: Aug 2017 Posts: 5 Threads: 1
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Hi JonE
I've just ordered one of these, hopefully it will help me to resolve the charging issue I'm having with my Mk1 Ruby
I'll let you know whether it 'does what it says on the tin' once I've fit it
Peter
Joined: Aug 2017 Posts: 2,748 Threads: 31
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Location: Auckland, NZ
I have some electronics background but would rather grapple with a cutout any day. Resistant to reverse battery, igniton hash etc Stand alone cutouts may now be uncommon, but the cutout part of old regulator units can be utilised. simple bobbin windings can be redone
