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Classic Chargers - Alberto Fenini - 01-17-2011

ciao a tutti,

I have few chargers that need the transformator replaced,

I digged a while on the forum and on some more sites, like Jacque's one but I'm a little confused

what the specs exactly are ? primary 220 V, secondary 16 V and VA ???
thanks for help, Alberto

Re: Classic Chargers - Kees van der Sanden - 01-18-2011

Hi Alberto,

The secondary voltage of the transformer must be between 6V and 9 V.
The 16 V given on the site of Jacque is too high. I expect this is a typo. A secondary voltage of 16 Volt will destroy the 400uF/15V capacitor.
A 6 or 8 VA transformer will do the job.



Re: Classic Chargers - Alberto Fenini - 01-18-2011

ciao Kees

thanks for the information, I'll give it a tr.

I have purchased two transformers that will perfectly fit
into the case but the specs are 6V 2.4VA

In a way the 16 V made sense, it would be slightly dropped by
the four diodes and will properly charge the condenser,

I'm afraid that a lower secondary will not work, but since
I have two of them I'll try soon.

Thanks again, I'll let everybody know if it will work

take care Alberto

Re: Classic Chargers - sylvandb - 01-18-2011

In a way the 16 V made sense, it would be slightly dropped by
the four diodes and will properly charge the condenser,

The condenser will charge to the peak voltage (RMS * sqrt(2)). Yes, the diodes will drop the voltage about 0.7v each. (If using a full-wave bridge rectifier, about 1.4v.)

Your 220v:6v transformer might be close enough. 6v would be about 8.4v before the diode drop. So a full-wave bridge would provide about 7vdc. If you supply it with 240v on the primary you would get about 0.5v more on the secondary. Or if you use a half-wave rectifier you could get another 0.7vdc but might need more capacitance.

Re: Classic Chargers - Alberto Fenini - 01-19-2011

I think I will desolder a transformer from a good working classic power supply and see how much is the secondary value
thanks again Alberto

Re: Classic Chargers - Jacques Laporte - 01-21-2011

Ciao Alberto,

Yes, in the past (2007 i think) I have done measures on the Classics transformer 82002A.
I wrote on my site that the output voltage of the constant current circuit is @ 15V DC (unloaded).

You can easily confirm that with a multimeter.
See photo below.
With the calc attached (the load) the voltage drops.

That's it !

I will open a working adapter this WE for you and measure the voltage at the Xformer's secondary.

That said, my HP calc site has become too huge (too much data) : errors are certain.

Thank you all to help me correct them!

Edited: 21 Jan 2011, 9:21 a.m. after one or more responses were posted

Re: Classic Chargers - Bart (UK) - 01-21-2011

In Tony Duell's article on classic chargers he shows the rectified output to be 16V (I think this is open circuit voltage, as the cap is rated 15V). Therefore I would guess a transformer with a secondary voltage of ~10V AC would suffice. HOWEVER, in another thread Tony warns "The output voltage of this transformer is designed to fall under load, in a specified way" (I would hazard a guess that this is to reduce the stress on the power transistors as the load increases). So a standard transformer may not be the best solution.

Re: Classic Chargers - Jacques Laporte - 01-21-2011

Alberto, I have done (at the risk of my life ....) a video of the measure.

Took a 82011A which is safer : I have only 2 hands (with the 82002A, it's not easy to keep the 110-220 slider in place !!)

Result is : 12,5 V AC at the secondary (unloaded).

See : checking a 82011 battery charger

Edited: 21 Jan 2011, 9:27 a.m.

Re: Classic Chargers - Alberto Fenini - 01-21-2011

Thank you very much !!!!

Boy this was cool, even my name on the video,

I'll stop by the shop tomorrow morning and see what they have

Take care and thanks again, Alberto