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HP Forum Archive 20

 Classic ChargersMessage #1 Posted by Alberto Fenini on 17 Jan 2011, 9:15 a.m. 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 ChargersMessage #2 Posted by Kees van der Sanden on 18 Jan 2011, 3:13 p.m.,in response to message #1 by Alberto Fenini 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. Regards, Kees

 Re: Classic ChargersMessage #3 Posted by Alberto Fenini on 18 Jan 2011, 4:42 p.m.,in response to message #2 by Kees van der Sanden 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 ChargersMessage #4 Posted by sylvandb on 18 Jan 2011, 10:04 p.m.,in response to message #3 by Alberto Fenini Quote: 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 ChargersMessage #5 Posted by Alberto Fenini on 19 Jan 2011, 3:52 a.m.,in response to message #4 by sylvandb I think I will desolder a transformer from a good working classic power supply and see how much is the secondary valuethanks again Alberto

 Re: Classic ChargersMessage #6 Posted by Jacques Laporte on 21 Jan 2011, 4:40 a.m.,in response to message #1 by Alberto Fenini 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 ChargersMessage #7 Posted by Jacques Laporte on 21 Jan 2011, 9:17 a.m.,in response to message #6 by Jacques Laporte 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). Edited: 21 Jan 2011, 9:27 a.m.

 Re: Classic ChargersMessage #8 Posted by Alberto Fenini on 21 Jan 2011, 11:26 a.m.,in response to message #7 by Jacques Laporte 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

 Re: Classic ChargersMessage #9 Posted by Bart (UK) on 21 Jan 2011, 9:02 a.m.,in response to message #1 by Alberto Fenini 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.

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