Practical Electronics. Battery Valve Radio Power Supply.
Hi.
Just picked up January 2022 issue of Practical Electronics magazine from Smiths and noticed an interesting project that might interest you. It's a battery valve power supply using Li-ion batteries. The circuit will provide the valve heater supply as well as the HT. Quite a useful circuit where no mains supply is required, ie it is truely portable. Regards, Symon |
Re: P.E. Battery Valve Radio Power Supply
This is exactly the same project published by Silicon chip magazine in the December 2020 issue.
Peter |
Re: P.E. Battery Valve Radio Power Supply
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https://www.siliconchip.com.au/Issue/2020/December Peter |
Re: Practical Electronics. Battery Valve Radio Power Supply.
Cheaper to buy PE.
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Re: Practical Electronics. Battery Valve Radio Power Supply.
So , tempt me... (nearest PE will be in Barnstaple, 20 miles away): Is there an efficiency figure quoted? And are LT and HT both derived by switching techniques or is the LT just a linear regulator straight from the battery?
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Re: Practical Electronics. Battery Valve Radio Power Supply.
Is it using four 18650 cells? Seems a lot.
B |
Re: Practical Electronics. Battery Valve Radio Power Supply.
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The HT uses a normal mains transformer "I chose a 5W PCB mounting mains transformer which I used backwards" so the switching frequency must be between 50 and a few hundred hertz. Peter |
Re: Practical Electronics. Battery Valve Radio Power Supply.
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David |
Re: Practical Electronics. Battery Valve Radio Power Supply.
i prefer the ancient method of using a transformer of wwhich there are plent of designs. why build a sophisticated noise machine when old systems work well EI7KA
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Re: Practical Electronics. Battery Valve Radio Power Supply.
Hi.
The LT supply is derived via a linear voltage regulator whereas the HT supply is switch mode with a typical center frequency of 72kHz. It seems to use readily available components and no special wound parts, just a standard iron core mains transformer To quote a few points from the Features and Specifications: Runs from two or four Li-ion, LiPo or LiFePo4 batteries HT output 24 to 135V DC at 2W LT output 1.2 to 2.5V at up to 3A (with a heatsink) Low EMI. Variable drive frequency and duty cycle. Battery over discharge protection Regards, Symon |
Re: Practical Electronics. Battery Valve Radio Power Supply.
Some time ago, Joebog1 pointed out the availability of some ready-made DC-DC modules 8-32 V in, 45-390 V out, online for £1-74 (they've gone up to £2.03 now) https://www.aliexpress.com/item/3295...4d1f4c4dv69dFH
Not sure how much time and money the PE projects will absorb :shrug:. B |
Re: Practical Electronics. Battery Valve Radio Power Supply.
There's a really nice article for a 90V battery replacement from Ronald Dekker here: https://www.dos4ever.com/battery/battery.html with full explanation of the circuit and at the end he shows a quite simple but very nice design.
I haven't compared Ronald's design to the article but I have experimented with Ronald's design and found it very useful. |
Re: Practical Electronics. Battery Valve Radio Power Supply.
Unless the PSU can fit where the original battery did I find these types to be of no more use than any transformer-derived supply kept in a box.
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Re: Practical Electronics. Battery Valve Radio Power Supply.
The PE/Siliconchip design also uses some esoteric bits as opposed to more garden variety components and is not small - as in no chance of fitting in a battery space.
There are better designs out there. Re the 18650 cells - the LT side has two cells in parallel (design flaw no1) and HT side uses two in series. |
Re: Practical Electronics. Battery Valve Radio Power Supply.
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I made a converter this year providing HT, LT, and GB- operating from a 12V SLA battery. Overall efficiency is around 80% (it's based on a flyback converter running at 25kHz), but I needed 3-stage LC filtering on the HT output, the LT output, and the 12V input (and 3-stage RC filtering on the GB output) to keep it quiet. Working at low frequencies does offer the opportunity to use slow switching devices, keeping RFI right down, while not hurting efficiency by much because there are fewer switching events per second. The down side is that the size of the transformer increases. But, it's still not going to be massive, at a few watts only if power, and I can see the attraction of using an off-the-shelf transformer. |
Re: Practical Electronics. Battery Valve Radio Power Supply.
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Thanks B |
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Re: Practical Electronics. Battery Valve Radio Power Supply.
Because when used in parallel packs, either they have circuitry to prevent one or other of them being over discharged or they are very carefully matched.
There is no such provision for or mention of this in the article. |
Re: Practical Electronics. Battery Valve Radio Power Supply.
Paralleling cells is common in laptop battery packs.
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Re: Practical Electronics. Battery Valve Radio Power Supply.
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Circuit diagrams might follow later! It's not at all an optimum filter, use of 25V capacitors on the 1.2V LT line is vast overkill, but they were to hand... The chokes are hand-wound on little toroidal cores. You can see a few. The whole thing is wrapped in bubble wrap and Bacofoil (hence the foil grounding lead). It's a lab demo setup, but it does work well. |
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