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Old 3rd August 2019, 08:58 AM   #281
CallMeMike is offline CallMeMike  United Kingdom
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Quote:
Originally Posted by dtses View Post
thanks for helping
it's 5.9vdc across 1n4007. Ambient C is about 25-27c. The trafo is pretty warm I would say, but not hot. Unfotunately do not have any other to test with. Might it be less hotrod with 30VA toroid, for instance?
You've mentioned earlier << 50VA trafo (14vac 3.57A), configured to 12vdc to feed Mytek Brooklyn Bridge >>... A proper heatsink is needed anyway (and it would help if the trafo would supply, say, 12 Vac). The 50VA spec is fine but the trafo should not get that 'pretty warm'... maybe there is something not quite right about the trafo build IMHO...

Last edited by CallMeMike; 3rd August 2019 at 09:05 AM. Reason: misspelling
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Old 3rd August 2019, 09:41 AM   #282
Salas is offline Salas  Greece
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5.9V * 1.75A makes 10.325W dissipation on Q2. So its not weird a down facing medium size mounting plate reaches about 65C after all. Based on your temp numbers the plate's heating rate is roughly 4C/W right now. If the voltage drop was 3V the dissipation would halve. Something near 45C would be expected.

Otherwise if the 10x12xcm 1cm thick plate grew twice in surface area it should behave much better with the original dissipation.

(1.75A load I presume because Mytek Brooklyn Bridge's manual says 21W @ 12V DC so 21/12=1.75. It also says 23-28VA consumption from 230V AC, so your original question of why 33VA from the wall with the L-Adapter finds a clearer answer from your Tx warm up report. I.e. its not too great a difference in apparent consumption from an SMPS adapter considering the linear losses. Only the toroid's warm up loss should account for the best part of the difference. Thus nothing untoward about the 33VA your wall meter displayed).
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Old 3rd August 2019, 10:49 AM   #283
Salas is offline Salas  Greece
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Quote:
Originally Posted by CallMeMike View Post
You've mentioned earlier << 50VA trafo (14vac 3.57A), configured to 12vdc to feed Mytek Brooklyn Bridge >>... A proper heatsink is needed anyway (and it would help if the trafo would supply, say, 12 Vac). The 50VA spec is fine but the trafo should not get that 'pretty warm'... maybe there is something not quite right about the trafo build IMHO...
The Brooklyn seems not to ever ask for less than 1.25A DC so its not too little constant for a relatively high regulation 50VA core ordinary component. The wall meter says 33VA and the Tx is 50VA, thus "pretty warm" ain't that an unexpected description when we think about it again. If below 45C it will have a descent life.

@dtses
Is there a chance its a dual secondary trafo that that hasn't been yet paralleled? Such a scenario would have it behaving like a 25VA and get too warm indeed.
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Old 4th August 2019, 04:45 PM   #284
dtses is offline dtses
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Originally Posted by Salas View Post
@dtses
Is there a chance its a dual secondary trafo that that hasn't been yet paralleled? Such a scenario would have it behaving like a 25VA and get too warm indeed.
nope, it's only one secondary. Actually it's a new trafo I bought specially for L adapter. Nothing should be wrong here. I will try to get another heatsink and see how it will cope with the heat.

My idea was to fit everything in this case (218*115*50mm), however now I see that even with a solid plate attached to the top of the case with Q2, it still might be not enough...
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Old 4th August 2019, 04:51 PM   #285
Salas is offline Salas  Greece
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When you will double or triple the plate's surface area, plus it will be bolted to the chassis, the temperature should moderate a lot. Be generous with the plate's size. Because there are no fins.

There is a threshold in the sinking solutions after it they become saturated. When below that saturation threshold the temperature loses 10-15C kind of abruptly. Watch to have some top and bottom ventilation slots or holes in the final assembly.
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Old 5th August 2019, 06:47 AM   #286
dtses is offline dtses
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thanks!
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Old 7th August 2019, 07:06 PM   #287
jimk04 is offline jimk04  United Kingdom
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Default L-Ad > 3 x Lt1963 > Rpi

Having taken inspiration from here

3x powersupply for rpi : Raspberry Pi - Page 5 • RuneAudio Forum

I thought I may do something similar.....in powering the 1.8v......3.3v.....and 5 volt requirement of the Rpi (not the dac) from 3 regulators of LT1963 fed from the L-Ad running as pre reg .

Does this sound a good idea......I'm not causing noise by using a lesser reg (Lt1963) after the beautiful Salas item?
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Old 7th August 2019, 07:10 PM   #288
Salas is offline Salas  Greece
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Technically such chips have great characteristics, also the separation of rails and the pre-reg stage are always important. Sometimes less is more though, so try and see.
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Old 11th August 2019, 12:58 AM   #289
DRONE7 is offline DRONE7  New Zealand
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I'm building a couple of L-adapters (and have to say the boards are magnificent!)
The first is for a Raspberry Pi using the standard BOM. Though I do have some electrolytics in the spares box.
They're 5600mF rather than the 6800 on the BOM and not 105c rated.
So, presume capacity is fine for the Pi and as I have a rather large case I thought to mount them from the underside of the board and thus away from the heating.... sound workable ?
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Old 11th August 2019, 03:32 AM   #290
Salas is offline Salas  Greece
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Workable
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