Davenset battery charger

[ppppenguin]

Oh what a lovely glow. It actually looks slightly better in the photo than in real life. I need to choose a suitable load resistor to leave permanently connected for demo pruposes.

You can also see the new (actually rather old) mains cable I fitted to replace the horrible, perished and not even original one.

Shame that the previous owner painted the transformer cover plate blue rather than the correct crackle black but I'm not planning to change that. The transformer has clearly been removed from the basebaord at some point by cutting all the wires. They were reconencted using choc block.

I reckon I bought this charger at Harpenden something like 20 years ago and have finally got round to making it at least partially work.

[Torchie]

I know this is an older thread but I happened accross it whislt doing some research. I also have one of these Davenset GC battery chargers which I too am trying to restore back to working condition - My charger is missing the rectifier valve, barretters and lamp.

I believe the main rectifier valve is a Phillips 367 or equivalent, but I am having a bit of a job trying to identify the barretters (I believe Davenset called them resistance tubes).

I did see a different charger of a similar vintage on another forum. This other charger had the same Phillips 367 valve accompanied by Phillips 1130 Barretters but these have a B4 base rather than the Edision Screw type that is on my charger.

Would anyone know which type of barretter would have been used?

Any help would be greatly appreicated.

[ppppenguin]

Hi Torchie and welcome. I think I have a spare 367 rectifier so I may be able to help there. No idea about what the resistance tubes are. In terms of appearance I suppose you could stick anything with an ES cap in there for now and hope that something turns up. There are LED "fake filament" lamps of all shapes and sizes. The little BC lamp on mine is unlikely to be original. It's a blue golfball size lamp. There is no marked rating nor have I tried to establish it with a variable power supply.

I note you're in Lincolnshire. I know it's a big county but are you anywhere near Hemswell Cliff where we have the Broadcast Engineering Museum? www.becg.tv

[Ed_Dinning]

Hi There is an identical charging board in the Arc& Sparks collection at Newcastle Discovery museum. Not restored and display only I'm afraid.

This board is quite an advanced piece of kit , using Barretters. Mist simpler ones used the likes of car lamps as limiters

If no success with the search for the bits PM me with specs and I'll see what can be found

Ed

[Mike Watterson]

A barretter is usually iron wire in hydrogen. The closest off the shelf may be a tungsten lamp of suitable resistance, though halogen types have a better characteristic. Few thermistors are suitable and most have the opposite characteristic. The barretter is usually an approximation to a current limiter as resistance rises sharply with increasing current. Most thermistors are designed to be the reverse to limit power on inrush current on either series filaments or SMPSUs. A halogen lamp is a bit more than double resistance from cold to full power and a regular tungsten lamp (nitrogen filled not vacuum) maybe a bit less than double, I forget. Maybe some low power festoon lamps use a vacuum and will be more like a direct valve filament in resistance change.

[joebog1]

Very interesting thread. I have never seen a charger like this one .
In fact I didnt think a mercury rectifier would supply the sorts of current this charger claims.
Live and learn I guess.

Joe

[Torchie]

Hi all,

Thank you very much for all the information.

I think I am going to first trace the circuit so I can see exactly how the barretters were connected, that may give me an idea as to what rating they may have been then I can stick a roughly appropriate filament lamp in. The small lamp is probably just an off / on indicator so may not be an issue.

Normally a barretter is used in a radio to protect the valve heater filaments. As there were two barretters in this set up I am thinking they were most likely there to limit the charging current and protect the Rectifier valve itself and would be switched in or out depending on the charging circuit employed.

Its odd how the Internet has so much information about pretty much everything, and yet there are still plenty of things such as this and a few other bit of kit I have where they are almost absent from the web!



PPPPenguin - Yes I am in south Lincolnshire, about a 1 1/2 hour drive from Hemswell Cliff. The museum looks very interesting, I am currently perusing the pages, The P5 1952 Bedford is particularly nice.