PSU alternative?

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Cristian
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Re: PSU alternative?

Postby Cristian » Wed Sep 19, 2018 8:37 pm

Thank you very much Tofro and Nasta for your important and useful information. I'ts always a pleasure for me.


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Re: PSU alternative?

Postby Cristian » Mon Feb 11, 2019 9:50 am

tofro wrote:This is not so easy to answer - it depends a lot on the "stiffness" of your power supply under load.
Power supplies are typically reted at a voltage that can be maintained under a typical load - Note, what you would measure on an unknown PSU is the open circuit voltage which is typically much higher than under nomainal load.

And what about the risks concerning the alternate current overvoltage? I have an unmarked AC transformer without specs, and without load the multimeter reads 21V. To make a comparison, I tested a marked 15V AC transformer: 21V without load, and actually 15V under load. But the unknown transformer is bigger, so its "stiffness" may be greater... So, what is the QL tolerance for AC input?


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tofro
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Re: PSU alternative?

Postby tofro » Mon Feb 11, 2019 11:32 am

#one question: How did you measure the AC? RMS? If yes, the voltage that goes into the +-12V circuit after rectifying is ~1.4 times higher than what you measured.

The +- 12V circuitry which is fed by the AC input is actually not so extensive that it would draw a lot of current. I would rate that at 200-300 mA. Here, the maximum input voltage is limited by the same linear voltage regulators, only in their +- 12V incarnation. (7812/7912). Those are rated at 18-22V input, so your transformator should in no case exceed 44V Vpp. And, because the current draw is so low, I would really make sure the 44V Vpp is not even exceeded with an open circuit. (With 44V Vpp, you're also getting close to the maximum voltage of the input capacitors, which is 25Volts, so I'd rather stay beyond 20V (with "close", here I don't mean "dangerously close", but rather "long-term inappropriately close").

Tobias


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Cristian
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Re: PSU alternative?

Postby Cristian » Mon Feb 11, 2019 5:32 pm

First of all, thank you very much for your reply. Since I joined this forum, my so poor electrical knowledge has improved. But it's still considerably limited, so please forgive me for my rough explanations and questions.
I measured the AC with a simple digital multimeter (model dt-9205a) set to 200V AC, and I didn't even know the existence of Vpp and Veff currents.
Also I forgot to say that the unknown transformer has 3 output pins: at diametrically external pins I get 21V, while at central pin / external pin(s) I get 10V. So, what can I do?


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Re: PSU alternative?

Postby nikosdoykas » Mon Feb 11, 2019 7:43 pm

nice thread.... so i have a 15 vac /1 amp from a psu from a charger i measure it an tis 15.2-3 vac its actually very close to ql psu ac 15.6-8 and its small to fit in the (secret.... hehehe) progect i made ... so one 9vac charger(switching)2 amps will be fine for the 9 vdc?


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Re: PSU alternative?

Postby Cristian » Tue Feb 12, 2019 12:09 pm

nikosdoykas wrote:nice thread.... so i have a 15 vac /1 amp from a psu from a charger i measure it an tis 15.2-3 vac its actually very close to ql psu ac 15.6-8 and its small to fit in the (secret.... hehehe) progect i made ... so one 9vac charger(switching)2 amps will be fine for the 9 vdc?

Please refer to Nasta's comment at the bottom of the previous page


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Re: PSU alternative?

Postby nikosdoykas » Wed Feb 13, 2019 6:53 pm

ITS THE SAME....
THE PROBLEM ITS ON THE FEMALE CONECTOR OF THE PSU.... CAN WE FIND THE 3D PRINT???


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Cristian
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Re: PSU alternative?

Postby Cristian » Wed Feb 13, 2019 7:22 pm

nikosdoykas wrote:CAN WE FIND THE 3D PRINT???


Try to ask dex, who prepared some 3D prints for the connector. Please read his posts in the previous pages (page 5)


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Cristian
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Re: PSU alternative?

Postby Cristian » Wed Feb 13, 2019 8:00 pm

tofro wrote:(With 44V Vpp, you're also getting close to the maximum voltage of the input capacitors, which is 25Volts, so I'd rather stay beyond 20V (with "close", here I don't mean "dangerously close", but rather "long-term inappropriately close").


The original QL PSU is rated 15,6V AC
RMS-Vpp.jpg

so, the 44Vpp max voltage is exceeded... Sorry, I must have misunderstood something crucial, but what?


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Re: PSU alternative?

Postby Andrew » Wed Feb 13, 2019 11:38 pm

Cristian wrote:Try to ask dex, who prepared some 3D prints for the connector. Please read his posts in the previous pages (page 5)

Martin J Dean has a post on FB, in group "Sinclair QL For Everyone" , describing his PSU replacement.
For the power connector he used a molex connector from the link below and cut it into shape.
https://ro.mouser.com/ProductDetail/Mol ... OEo_lKCzA8

Link to the FB post (Martin's description is in the comments): https://www.facebook.com/groups/3069939 ... 164192075/
Attachments
QLconnector.jpg



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