Homebrew Battery Eliminator
 

I mentioned a few days ago in my "Old Tag Boards" thread - that I needed to repair a useful old one for a Batt. El. project. Well its now fitted fine - just the ticket.
Got plenty of PSU's & voltages for connecting up my two 1920's TRF's, but what a lot of fannying about with banana plug leads & crock-clip leads, etc. Voltages needed :- 2 or 4V for Filaments, a range of -ve Vg's up to 7.2V, & 4 HT's - - 60, 90, 120 & 150V. I've an excellent two channel modern digital LV DC PSU for heater/filament voltages(PSM 3/2A), but the rest I wanted to place inside a handy sized sloping spare cabinet. So - 60V from a rechargeable battery pack(made up with PP3's), a -7.2V GB rechargeable pack made up with AA's, and the other three HT's made up from three mains T/F's - - FWR's, Chokes & Electrolytics. Now done, next stage is to cut out a cardboard template for the front top panel - meter, switches, fuses, indicator lights, etc. Bit of jiggery-pokery I expect to get everything to fit. (Some wits or wags might say that all ex RAF guys are good at jiggering & pokering).

Regards, David

Re: Homebrew Battery Eliminator
 

More Pictures. D

Re: Homebrew Battery Eliminator
 

You can't beat a wholly unnecessary number of meters on a panel. Otherwise they get lost and unloved, saves a switch too. I wonder why some volts are coming from batteries and others from mains?

Re: Homebrew Battery Eliminator
 

Well, 1920's TRF's don't usually draw very much valve Ia, and if an SG valve is used then Is would be negligible. Likewise Ig should be negligible. My two TRF's only require 60V Vs, and the other HT's are near enough 90,120 & 150V. So three wee mains T/F which will handle approx. 10mA Isec. & their associated chokes & capacitors take up a fair portion of space available. For all the use they'll get, the two rechargeable battery packs could soldier on for years, if regularly checked & charged.
2V Filament supply could actually come from an original working glass Exide 2V accumulator. But my digital LV PSU is jolly handy & reliable for all my heater/filament requirements.
Meters - I've plenty just now. So will monitor all the HT currents & voltages. So once the panel layout is decided, and a hinged paxolin or aluminium panel cut, drilled & polished - then I'll get round to calculating multipliers, shunts & so on. Then fit rotary yaxley type selection switches, and other ON/OFF toggle switches etc. Plus Pots to fine adjust HT voltages.
Isn't electronicing fun ?

Regards, David

PS.Have you seen the cost of those modern digital Battery Eliminators from the States - a couple of hundred quid at least. My costs for all the above - NOWT ! Plus hours & hours of work in my wee office/workshop on frosty January & February days - I'll just have to force myself.

Re: Homebrew Battery Eliminator
 

David.
Outstanding work , You need to move down to South Yorkshire so we both could work on all these Projects in the same workshop Kevin. Ps will phone you later.

Re: Homebrew Battery Eliminator
 

Thanks for the kind words, Kevin. Folks - some might say - where does that guy get his drive & energy to fanny about building fanciful homebrew projects ? The answer is in the pictures, (& other pictures in the past), - - you'll often see in the background - empty Ferrero Rocher clear plastic boxes. Of course, I'm forced to eat all the contents so that the boxes can be used to hold all sorts of bits & bobs which I need for these projects.

Regards, David

Re: Homebrew Battery Eliminator
 

Well, that's it finished. Lot of fannying about to get everything fitted inside, and had to raise the top panel height slightly with some wee hardwood lengths so that there was sufficient clearance between the meters & switches, and the chokes & capacitors beneath.
60, 90, 120 & 150V HT's(HT's 1, 2, 3 & 4) can be monitored current & voltage wise. And, HT's 2,3 & 4 can be adjusted by their 3 variable resistors, according to loading. Filament & Vg voltages can also be monitored. The 60V & Vg rechargeable battery packs can charged externally, if needed. But their functions within TRF's(Screen Volts & Grid Bias) should draw very little current, if any. All voltages fused. Just the Filament supply(2 or 4V) is sourced from an external modern digital LV PSU.
Cost - just about nowt ! What I didn't source from my junk shelves & boxes, I scrounged from kind local Forum/VMARS chums up here(thanks guys). Rechargeable PP3 & AA batteries were new, but Birthday/Xmas vouchers for a local DIY store, took care of that.
Must get back to finishing sorting a chum's Taylor 47A now. Then heaps of gardening jobs beckon.

Regards, David

Re: Homebrew Battery Eliminator
 

More pictures

Re: Homebrew Battery Eliminator
 

David, considering the many used parts used (eg various transformers, when 1x custom one might suffice) that is just lovely. You really know how to use lacing cord, together with a very nice layout, inside and out.
Now, you just need to find time to put it to use!
Well done indeed!
Rob

Re: Homebrew Battery Eliminator
 

Thanks Rob for your kind words. Looming & Lacing eh ? I try, from time to time, to keep my hand in. As it was once a big part of RAF workshop training, (just like effing tagboards & Plessey plugs). Eventually, for my sins, I ended up teaching it on a monthly basis for nigh-on two & a half years, back in the early 70's.
Choice of cabinet size, design & circuitry :-
a) Nice empty JJ Electronics sloping cabinet, which fits neatly under a protruding window ledge in my wee workshop. Leaving me with approx. 12" x 40" work space on lower workbench.
b) Need to maximize workspace on that lower workbench due to two heffing big ex Marconi TF995A cabinets which house a big HV HT PSU with my DC Valve Tester sat on top.
c) That leaves approx. 46" x 16" of workspace on higher workbench.
Drilling, filing, sawing, painting, etc. - just done outside in un-heated passageway on two 35" x 14" benches.
This battery eliminator can also be used for more modern portable battery Rx's, such as a couple of 1950's BEME Loop Marine Rx's which I have.
Reason for initiating this thread post - merely to encourage folk to utilise spare old test equipment cabinets, gash but working meters, gash but usable components, etc.

Regards, David

Re: Homebrew Battery Eliminator
 

David,is circuit schematic for your design posted somewhere? Les

Re: Homebrew Battery Eliminator
 

David, I like your workshop. Looks nice and cosy. Personally, I like just a small bench area. However, it has become a necessity. Inside shack, one is about 18" x 12", other is about 36" x 18". Outside workshop, I have abot 36" x 22". Just big enough (but plenty strong enough, as a kitchen worktop board) to manoeuvre a RA17 on!
When (IF!) I get mine tidy I will post a photo or two. I am too ashamed at the moment though. It is above the kitchen and there is a visible sag in the ceiling! I reckon about 700kg in my workshop upstairs and 1000kg in my outside 8ft x 12ft shed.
Rob

Re: Homebrew Battery Eliminator
 

Aye Rob, either sod's law or a mathematical law dictates that a vintage radio enthusiast's storage of equipment & stuff expands exponentially in relation to the size of his shack/workshop. Seriously though, I'm sure that Forum guys would enjoy seeing a picture or two of your set-up. In fact, I think there is another thread running somewhere on forum folk's workshops.
OK Les, I'll rustle up a diagram or two. Just sketches at the moment, plus a number of "suck it and see" thoughts in my head as I went along. As a hint to folk who contemplate similar projects - always make up a template for placement of meters, switches, pots, etc. Try & adopt a simple colour code for wiring separate sub-circuits. Get all cutting, filing, drilling of metalwork, paxolin, etc. done before fitment of components. Keep intended meters safely well away from everything, until the circuitry is ready for them. I have a wee car hoover which works off 12V DC - ideal for removing debris. Also a decent set of tweezers. Sods law dictates that occasionally nuts, bolts, washers, etc., sometimes fall behind transformers & chokes, & so on.
Yep, a bit of maths is involved(Ohms Law) when it comes to working out meter shunts & multipliers. But, if some folk aren't too sure - contact an experienced Forum guy or two who live nearby, and ask them to help. A cuppa, packet of Hobnobs, & a chance to yap. Time well spent.

Regards, David

PS. Off to watch "Death in Paradise" on the telly soon. Scenery-wise, brings back fond memories of a short electrical/building contract I was on in the SW of Jamaica, back in the 80's. Well away from the tourist hot-spots. And the local folk were great.