Bugle PS Blowing Fuses After Testing LED In Circuit

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addaz

Re: Bugle PS Blowing Fuses After Testing LED In Circuit
« Reply #20 on: 15 Aug 2011, 07:42 pm »
For me - the decision is rather expensive for the nature of the problem, but if you are happy with it - then all is OK.

I'd agree, but I felt the circuit was starting to resemble the Ship of Theseus paradox. Jim and I got the heat problem solved but the voltage on the big caps was still 29v. I didn't want to gamble on running them at that voltage indefinitely.   :)

poty

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Re: Bugle PS Blowing Fuses After Testing LED In Circuit
« Reply #21 on: 16 Aug 2011, 11:34 am »
Is it possible to know the way Jim suggested to solve the heat problem?
Actually all voltages after the regulators doesn't have to be tuned - they are ok with the existing parts. Before the regulators you have 3-4 more volts  than usually which should be eliminated. The goal can be achieved by adding 4 diodes in each polarity circuit in place of the existing serial resistors. That is all. The expenses on this change is around 10 cents.

addaz

Re: Bugle PS Blowing Fuses After Testing LED In Circuit
« Reply #22 on: 16 Aug 2011, 06:09 pm »
Hi, poty. Thanks for reminding me as I meant to post the remedy I was given for the hot resistors.

I removed the hot resistors (R4 and R7) and I replaced R1 and R11 with 10 ohm resistors. Jim mentioned that this was to get more headroom and share the heat load between them and the regulators. That worked great for the heat problem and he suggested I either leave R4 and R7 out, or change them to 4.7k or 10k as they provide a minor snub to the tranny when the diodes turn off.

Jim did say the caps were fine, but something really irked me about those voltages on C1,2,4,5. If the new tranny doesn't help with those then I'll give that diode trick a try.

poty

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Re: Bugle PS Blowing Fuses After Testing LED In Circuit
« Reply #23 on: 16 Aug 2011, 07:56 pm »
The voltages on the capacitors depends on the load current. The current forces some voltage drop on the combined resistance of the second (and partly primary) coil of the transformer and the serial resistors in each polarity halve. You measured the voltages with the iddle current which is very small so the voltage drops are small too. More than that - you have eliminated the R4 and R7 resistors, which have lowered the iddle current even more. In the real life you will use the power supply with some device which will significantly raise the current. The voltage drop will increase and so - it's lower the voltage on the capacitors. So, the device will work correctly "as is".
My "trick" with diodes (which is not mine and not trick at all :) ) is based on almost constant voltage drop on a diode regardless the current (as you know - the voltage drop on the resistor is a linear function of the current: U=I*R). So even with small iddle current you will have the nessesary voltage drop on the diodes to keep the capacitors' voltage in safe margins.
« Last Edit: 17 Aug 2011, 07:27 am by poty »

hagtech

Re: Bugle PS Blowing Fuses After Testing LED In Circuit
« Reply #24 on: 20 Aug 2011, 05:53 am »
Someone found the "TE2236-ND" as a much better transformer alternative.  That gets around the other issues.

jh