So I was kinda uneducated to the fact that when you buy a transformer what you order and what you get dont match.
All I knew is that your asking for a/c and to convert it to d/c you need to multiply it by 1.4.
What I did not know was that without a load the voltage would be nowhere near what you wanted.
So say I placed an order for a 26-0-26 or a 15-0-15 with zero load I am getting 10-15 volts higher than the number asked for.
Anybody else had this issue. i.e. higher or too high zero load voltage.
Is it an issue that I need to worry about ?.When will it drop to the right voltage under full load / some load.
Is there anyway for me to drop this voltage.
My audio guides tell me you cant regulate transformer output this.
Would just adding a few bridge rectifiers or diodes like 4-5 help like each one would drop my voltage by a volt.
This is a 15 amp supposed to be 26-0-26 but in fact giving 38-0-38 Its to drive 4 chan lm3886 or 4 chan tda7294.
(38x1.4=53.2 DC).
As per datasheet both are supposed to be able to handle 53v fine but guys in my group say you will blow it. Heat sink heat will be monitored and power cut if it goes too high. With a cheap 2$ circuit
Just curious how people handle such an issue.
All I knew is that your asking for a/c and to convert it to d/c you need to multiply it by 1.4.
What I did not know was that without a load the voltage would be nowhere near what you wanted.
So say I placed an order for a 26-0-26 or a 15-0-15 with zero load I am getting 10-15 volts higher than the number asked for.
Anybody else had this issue. i.e. higher or too high zero load voltage.
Is it an issue that I need to worry about ?.When will it drop to the right voltage under full load / some load.
Is there anyway for me to drop this voltage.
My audio guides tell me you cant regulate transformer output this.
Would just adding a few bridge rectifiers or diodes like 4-5 help like each one would drop my voltage by a volt.
This is a 15 amp supposed to be 26-0-26 but in fact giving 38-0-38 Its to drive 4 chan lm3886 or 4 chan tda7294.
(38x1.4=53.2 DC).
As per datasheet both are supposed to be able to handle 53v fine but guys in my group say you will blow it. Heat sink heat will be monitored and power cut if it goes too high. With a cheap 2$ circuit
Just curious how people handle such an issue.
The best you can get from an article about LM3886 Power Supply is from Neurochorme by Tom Christiansen
https://neurochrome.com/pages/power-supply-design
https://neurochrome.com/pages/power-supply-design
26-0-26 volts 15 AMPs.
Primary 230 volts
Made by a pretty reputed local company. They have been doing this for 30+ years. Machine wound. Very neat and looks good.
Secondary regulation ? Not sure what that means. But to convert it to DC I plan to use this power section.
http://diyaudioprojects.com/Chip/LM3886_CA/lm3886-manual.pdf
There is another TI reference design for Audio Im considering.But there is no regulation here. That is my question can you even regulate your amps power.?
The tone control board has a 7815 7915 pair this works fine.
Reason for the post was to even ask can the power to an amp be regulated and how.
I have seen son of zen or daughter of zen board where they some regulation for a pre amp using Zener diodes and a tip IC. But I was told this would not work for my amps. And the tip would heat up like crazy. And it was a bad idea.
The AC voltage should only be a couple of percent higher for a big transformer with no load compared to its nominal rating. So something is very wrong somewhere. Are you sure your primary voltage is correctly specified? and is the meter reading correctly?
These show typical rated on load voltages and off load voltages. The bigger the transformer and the better the regulation factor (on load vs off load voltage)
These show typical rated on load voltages and off load voltages. The bigger the transformer and the better the regulation factor (on load vs off load voltage)
52 volt transformer @ 15amps ??
sounds close to 750 to 800 VA
in general regulation should be very good
with large transformer
if transformer is rated for 52 volt @ 15 amps
then voltage would be that with 15 amp load.
Assuming max power needed from lm3886
is 40 watts. each amp needs around double VA
rating 80VA. 120VA more overhead
4x amplifier need around
320 to 480VA
Assume primary wound for 230volt
not sure if your electrical provider
is closer to 240volt
With 240 volt assume voltage be around 5 to 8 volt higher
and unloaded 8 to 12 volt higher
sounds close to 750 to 800 VA
in general regulation should be very good
with large transformer
if transformer is rated for 52 volt @ 15 amps
then voltage would be that with 15 amp load.
Assuming max power needed from lm3886
is 40 watts. each amp needs around double VA
rating 80VA. 120VA more overhead
4x amplifier need around
320 to 480VA
Assume primary wound for 230volt
not sure if your electrical provider
is closer to 240volt
With 240 volt assume voltage be around 5 to 8 volt higher
and unloaded 8 to 12 volt higher
Ok let me put it under some load and see what happens.
The guy did ask me what my input voltage was this is a tricky kind of question to answer in my country. As based on which city you live in. Is it summer or winter. The voltage can vary from 200 volts to 240 volts. So I told him I dont know. Just use a value that you give to others. So he said your city 230v and I said ok.
It was a good guess when doing the no load tests the input voltage was 238 I have seen it go down to 200 volts some days.
This was my first go. I can just order another one from another vendor. And use this with a circuit which would be happy to work with these voltages. All part of the learning process. This time Ill be better educated.
Ps: White Dragon I think you nailed it. Voltage was higher than designed voltage.
I just had an idea. Fix this the same way Akai did. i.e. have two input options 220 and 240.
I was getting too much voltage on the Aka and I changed the fuse form 240 to 220 and it worked fine.
Next transformer I should do this. Have two input voltages.
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750 to 800 VA
very strong transformer.
Will support current project
and even more powerful future projects.
Some regions have very well
regulated electrical providers.
Some not.
200 to 238 volt very wide swing
you have no control of electrical provider.
Main concern really if using large smoothing
capacitors for typical unregulated supply.
Surge current very high at startup.
With 700 to 800 VA transformer
and large capacitor bank.
Important to have soft start circuit.
You noted National Semi
Data sheet / Paper for high power
supply.
they use softstart.
Also use dual, full bridge rectifier
for both secondary.
full bridge not necessary.
for both secondary.
but At least in your case it will have
slightly more voltage drop.
and current will be distributed among 2 bridge rectifiers
not just 1
very strong transformer.
Will support current project
and even more powerful future projects.
Some regions have very well
regulated electrical providers.
Some not.
200 to 238 volt very wide swing
you have no control of electrical provider.
Main concern really if using large smoothing
capacitors for typical unregulated supply.
Surge current very high at startup.
With 700 to 800 VA transformer
and large capacitor bank.
Important to have soft start circuit.
You noted National Semi
Data sheet / Paper for high power
supply.
they use softstart.
Also use dual, full bridge rectifier
for both secondary.
full bridge not necessary.
for both secondary.
but At least in your case it will have
slightly more voltage drop.
and current will be distributed among 2 bridge rectifiers
not just 1
Can you be trusted to measure wall voltage? Be careful!
And yes: it costs a few bucks more to specify 200-210-220-230-240V taps. Much cheaper than making several transformers.
I am running a pair of 3886 amps at +/- 38 volts for many years. No issues.
The transformer is 28-0-28 volts, Load 8 ohms speakers.
Maximum voltage it can take is +/- 45 volts. So even if supply voltage fluctuate, no issues here.
Just do not run more than specified power output for 8 ohms load.
If your transformer ac out is 38-0-38 volts, means, you bought a wrong transformer.
Either return or buy new one or change to discrete transistor amp
Regards.
The transformer is 28-0-28 volts, Load 8 ohms speakers.
Maximum voltage it can take is +/- 45 volts. So even if supply voltage fluctuate, no issues here.
Just do not run more than specified power output for 8 ohms load.
If your transformer ac out is 38-0-38 volts, means, you bought a wrong transformer.
Either return or buy new one or change to discrete transistor amp
Regards.
7294 will work, I think.
Just check the weight...
And tell the vendor load and DC volts for the new one.
He might have mixed them up in dispatch, with those intended for another customer.
I have on old Nokia charger from the time they used transformers, it says 9V, but no load volts is about 14.5...
If you want to risk it, try.
You can use NTC based soft start circuit if you want protection.
Just check the weight...
And tell the vendor load and DC volts for the new one.
He might have mixed them up in dispatch, with those intended for another customer.
I have on old Nokia charger from the time they used transformers, it says 9V, but no load volts is about 14.5...
If you want to risk it, try.
You can use NTC based soft start circuit if you want protection.
Use one 0-26 winding for each channel.
You will be fine.
Just bear in mind TI voltage recommendations for 4 and 8 ohm loads.
And do check on load.
Though I think 15A is too much, but here many 200mA transformers are labelled 500mA. So may not be really 15A, but you say supplier is reputed.
Soft start circuit is easy. Put a Zener based high voltage (DC side) protection circuit as well.
If in doubt, @tomchr has done a great amount of work on the 3886, look up his site.
You will be fine.
Just bear in mind TI voltage recommendations for 4 and 8 ohm loads.
And do check on load.
Though I think 15A is too much, but here many 200mA transformers are labelled 500mA. So may not be really 15A, but you say supplier is reputed.
Soft start circuit is easy. Put a Zener based high voltage (DC side) protection circuit as well.
If in doubt, @tomchr has done a great amount of work on the 3886, look up his site.
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Expensive method here, most winders will freak unless you give design specs, and it is your fault if something goes wrong.
Can use a Variac, but it is a make shift method.
Best try on load, or change the transformer, or change the circuit to suit the transformer.
Can use a Variac, but it is a make shift method.
Best try on load, or change the transformer, or change the circuit to suit the transformer.
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Reduced primary voltage will increase the amps on the secondary?
And 800 VA step down will cost about the same as the original transformer.
Not practical.
And 800 VA step down will cost about the same as the original transformer.
Not practical.
Not so. if the 800 VA transformer is rated at 4 amps primary, the bucking transformer as in the above example has to be rated at 20 volts at 4 amps, 80 VA.
Regards
hi,
why not rewind it to give required voltages ? That is less than 26-0-26v.
Another option would be to sell this transformer to local DIYers (as shipping would be expensive for heavy transformer) and make new one.
I had measured voltage fluctuation for a single whole day here in my town and maximum was I think 245v so you will have to take that in to account as chips will be vulnerable to it. Best would be to have little less voltages than required to be safe. As I think few volts will not make significant output power increase if we take in to account normal listening levels.
regards
why not rewind it to give required voltages ? That is less than 26-0-26v.
Another option would be to sell this transformer to local DIYers (as shipping would be expensive for heavy transformer) and make new one.
I had measured voltage fluctuation for a single whole day here in my town and maximum was I think 245v so you will have to take that in to account as chips will be vulnerable to it. Best would be to have little less voltages than required to be safe. As I think few volts will not make significant output power increase if we take in to account normal listening levels.
regards
Yes I can be trusted. As an 8 year old I would spend my summer vacation re-wiring peoples tube lights to work by adding a 2nd choke.
Part of the process was measuring their voltage and showing them it was only 180 Volts. This was in Hyderabad Shapur Baug back in the 70s.
I have a speaker protection board with delayed start. I wonder if I can use that or just buy one more and use that. After I beef up the relay.
Its no a big issue as I have some Transistor amps that can handle this voltage.
Somebody asked for the weight its over 8 Kgs. Yes not asking for multiple input taps was the only real mistake made. Thanks for all the posts. I see I have some reading to be done.
Hiten you know how it is here in India. What wall voltage you get is anybody's guess. It depends on how far you are from the last transformer.
In our building the builder skimped and did not install a transformer. So in summer when everybody switches on their A/c sthe voltage really dips.
The vendors recommendation of 230 was pretty good. We pretty much have to run voltage stabilizers on everything from a/c to tv.
Looking into these links.
https://www.google.com/search?q=usi...7j33i160l3.13901j0j9&sourceid=chrome&ie=UTF-8
https://www.google.com/search?q=usi...7j33i160l3.13901j0j9&sourceid=chrome&ie=UTF-8
The obvious thing to do in DIY audio) is to rectify and capacitor and hang a representaticve load on it and see how the actual under-load output is. You may be pleasantly surprised! Beats trying to find a solution for an issue you don't even know is there.
Jan