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Old 28th Feb 2023, 10:42 am   #1
Keith956
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Default B126 sized box

Mods, please move if there is a more appropriate section for this.

I'm making a 90v battery replacement for a valve portable. It's basically a 7.2v Li battery and a flyback converter to step up to 90v. The idea came from the following, but with a more modern PIC the 12LF1572:

https://www.dos4ever.com/battery/battery.html

The nice thing about this circuit is it senses the valve set's on/off switch to switch itself on; when off it consumes only 7uA.

I'm looking for a plastic or diecast box the size of a B126 so I can fit the battery and PCB into it, and ideally cover it with a print of a B126 cover to make it look like the real thing! It's a bit chicken and egg as I can't finalise the PCB until i know what box it should fit into.

So has anyone an idea on where I might find such a box? Also the plug/socket that was used with a B126? I think it was a 3 pin one to prevent inadvertently connecting the wrong way...
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Old 28th Feb 2023, 11:09 am   #2
Dave Moll
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Default Re: B126 sized box

Unfortunately, my go-to site for battery scans appears to have gone away - clicking on a link to it gives a "server not found" error - but I do still have a scan downloaded from that site, which I attach below, along with a scan of the end of a B126 showing the connector.

Measuring an actual B126 gives W=65mm, D=45mm and H=95mm. The + and - terminals are 10mm apart, with the third hole about 4mm above the centre.

I hope this is of some help.
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Old 28th Feb 2023, 12:09 pm   #3
Keith956
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Default Re: B126 sized box

THanks Dave for the scan, now all I need is to find a suitable box!
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Old 28th Feb 2023, 12:12 pm   #4
Superscope
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Default Re: B126 sized box

With a Battery Box the size of what you want, I would be
inclined to make the Box yourself from Acrylic Sheet.

Do a search on Ebay, but you will have to trawl through all
the building material stuff.
You need to be looking for 2mm or 3mm thickness Sheets.

That way, you could make an exact sized replica.
You can also decide for yourself the best place for an Access
hole or Door if needed.

I have had good results on other projects with making Boxes
myself.



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Old 28th Feb 2023, 12:25 pm   #5
radiomobile
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Default Re: B126 sized box

A plastic box is likely to allow horrendous interference from a flyback/switch mode converter in close proximity to a ferrite rod or frame aerial
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Old 28th Feb 2023, 12:30 pm   #6
TonyDuell
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Default Re: B126 sized box

What about making it from unetched copper clad board with the seams soldered? Would that provide enough screening?
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Old 28th Feb 2023, 12:32 pm   #7
Superscope
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Default Re: B126 sized box

A nice lining of Kitchen Foil works wonders
if shielding is required.




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Old 28th Feb 2023, 12:52 pm   #8
Keith956
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Default Re: B126 sized box

The converter runs at 100Hz (it uses a standard 9-0-9v mains transformer, the 'wrong' way round) and doesn't seem to give any interference when on an open breadboard to a LW/MW radio a foot away. But if it can be screened, it will be.

I'm struggling more with how to get the board and battery in the space available, though. The board measures 93mm long x 58mm wide by 38mm high - this could be squuezed down to 50mm wide. Then the width and height are dictated by the mains transformer.

An AA battery is 14mm wide by 50mm high, 6 of them make 84mm long. So I could just about squeeze everything into 95mm x 65mm x 50mm by putting the batteries to one side of the PCB. That's not allowing for box thickness though.

I think it might be time to look for a smaller transformer, the Myrra 44272 I happenned to have is rated 5+5VA, given the converter needs to be 90v at 10mA max i.e. just under a watt, and the efficiency is about 50-60%, a smaller transformer should be adequate - and might fit!
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