Hi,
I have a salvaged EI transformer from old boombox. AC voltage details are as follows
My questions are
1) Can I buck the transformer by using one of the isolated secondary winding of lower voltages (A or B) ?
2) What if I discard the center tap of winding B shown in middle (10.7/13 v ) and short two 10.7 v points to use as center tap ? See pic below ... What voltage I will be getting ?
thanks and regards.
I have a salvaged EI transformer from old boombox. AC voltage details are as follows
- 235 AC input at primary
- There are three isolated secondary windings (0-5 v) (13/10.7 -0- 10.7/13 v) (40.7-0-40.7 v)
- The middle one has multiple voltage with common center tap
- I need approx 25-0-25 or any range between 20 to 30 v center taped for example 30-0-30 will also do.
- When I measure secondary voltage by connecting multimeter prongs to output shown in two cyan color dots I get 0-23.7 v
My questions are
1) Can I buck the transformer by using one of the isolated secondary winding of lower voltages (A or B) ?
2) What if I discard the center tap of winding B shown in middle (10.7/13 v ) and short two 10.7 v points to use as center tap ? See pic below ... What voltage I will be getting ?
thanks and regards.
I don't understand question 1. Connecting a secondary winding in series with the primary will probably lead to insufficient insulation from the mains, as the insulation between the secondary windings will not be designed to handle full mains voltage (including the voltage peaks that can occur on the mains).
2) will blow out the mains fuse (if any) or overheat the transformer.
2) will blow out the mains fuse (if any) or overheat the transformer.
OK. So secondary windings can handle current but not high voltages. If so I can drop the idea.
I suppose by insulation the varnish the copper wire has ? or some isolation between windings ?
I suppose by insulation the varnish the copper wire has ? or some isolation between windings ?
A solution to lower voltages is to use LC filtering instead of just C. The costs will be higher than buying the right transformer (in general). IMHO you have the bad luck most of us have when finding a beautifully made multiwinding transformer: is just is not the right one for your application. Never throw such transformers away as there will come a day they can be used.
Or do the brave thing, change your project to the transformer you have. You haven't mentioned what currents the windings can deliver but it seems a good candidate for a chipamp of normal output power with a tube input stage. 2 x 13V AC so +/- 16V for the chipamp, 80V AC so 110V DC for the tube and 5V AC so about 6V DC for its filament (test this). If the boombox used that 2 x 40V and 5V for a VFD display it is wise to first check/test maximum output current (or its service manual).
Or do the brave thing, change your project to the transformer you have. You haven't mentioned what currents the windings can deliver but it seems a good candidate for a chipamp of normal output power with a tube input stage. 2 x 13V AC so +/- 16V for the chipamp, 80V AC so 110V DC for the tube and 5V AC so about 6V DC for its filament (test this). If the boombox used that 2 x 40V and 5V for a VFD display it is wise to first check/test maximum output current (or its service manual).
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I'm no expert on transformer construction but as far as I know, there is normally an extra layer of insulating material between the primary and the rest. It has to withstand over 2 kV of peak voltage because of possible peaks on the mains (lightning strikes, inductive effects when large loads are switched off), or over 4 kV of peak voltage when it is meant for equipment without protective earth.
Hampering that when not experienced/qualified is not the best of ideas. It can be done, certainly in India but then by a transformer winder.
If the project as it is needs a 2 x 20....30V center tapped transformer the shortest path to success would be finding a 2 x 20...30V one of the right ( = overdimensioned) VA rating.
If the project as it is needs a 2 x 20....30V center tapped transformer the shortest path to success would be finding a 2 x 20...30V one of the right ( = overdimensioned) VA rating.
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Hi. If you can access to individual wires of center tap, you can split that winding to two separate 0-10,7-13V and then use that to buck down 40v windings. But question is what current these windings can supply and how much current you need. You may test current by trying to load a winding with resistor and see how much voltage drops. I think 10 percent voltage drop means winding can handle the current you loading with resistor now, but don't increase it more. Current handling also can be determined visually , by wire diameter, coming from secondary windings. Again, if you see a enamelled wires coming from winding, not bare flexible wites, soldered inside transformer and hidden under insulation.
Thanks everyone. I understand the safety required. All points noted. Will see what can be done safely.
I can see the wires coming out of secondary. I will measure diameter. And safely proceed for any action.
Common the two centre taps, then use 40.7V, 13V and 13V, with one of the 13V being you new notional centre-tap. That gives a somewhat asymmetrical 27.7--0--26
However you'll have to determine the phasing as it matters! And the two original windings are likely very different wire-thickness so you are limited to the lower of the current ratings.
Its hacky but I can't see a closer match to what you want without re-winding secondaries.
However you'll have to determine the phasing as it matters! And the two original windings are likely very different wire-thickness so you are limited to the lower of the current ratings.
Its hacky but I can't see a closer match to what you want without re-winding secondaries.
Visually guessing the copper wire diameter of secondary windings, they are as follows.
1) Winding A (0-5v) Thinnest of all around ~0.4mm may be less.
2) Winding B (10.7-0-10.7 v) around ~0.5 mm But has two wire parallel connected making effective diameter 1mm
Winding B (13-0-13 v) around ~0.6 mm
3) Winding C (40.7-0-40.7 v) around ~1.2 mm
1) Winding A (0-5v) Thinnest of all around ~0.4mm may be less.
2) Winding B (10.7-0-10.7 v) around ~0.5 mm But has two wire parallel connected making effective diameter 1mm
Winding B (13-0-13 v) around ~0.6 mm
3) Winding C (40.7-0-40.7 v) around ~1.2 mm
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@Mark Tillotson
Thanks! That looks like clever and excellent solution. Do you mean like this ?
I can use 10.7 windings and get 21.4 as wires on those are double the thickness. (Picture in above post)
Looking at photo, 40v windings looks strongest , and if other weak , much weaker winding is connected in series, with required polarity, voltage without load will reduce , but what happens with strong loads, like capacitor bank charging ? Weakest winding may hurn, easily overloaded, so i think ypu should cancel the buck down idea. It looks like 40,7V was used for power amplifier itself, and another center tapped winding for preamplifier probably, so current handling is very different. If things would be reversed, 10,7 or 13V windings stronger than 40,7 , then you buck down will work ok. Now you have to use full voltage, matbe build some special switchmode stepdown regulator, or linear regulator (much easier) with big heatsink, and reduce voltage with that. As was mentioned before, using one of secondaries in series with primary is bad idea, because of insulation loss. Some transformers use two bobbins construction, secodaries have it's own bobbin, primary its own, and they are placed inside one. As i remember, primary placed inside secondary, so windings have great insulation. I don't know if there's exist a way to linearly reduce primary voltage .... Halogen lamps dimmer not suitable here, because it will just delay phase and you still get voltage peak, but transformer will buzz loudly and will dislike that. Maybe solution is to use small trafo , 230/24 , and buck down mains voltage to 200V roughly. Just guessing.