Bottlehead Forum
General Category => Technical topics => Topic started by: ashbrook.m on April 09, 2015, 06:58:45 AM
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Hi guys, I am doing some redesign work on my Crack's power side. I was wondering if somone could validate my assumptions on the source and load. Note that I have an out to pasture mechanical engineer's understanding of EE.
PT-3: The labeled coil output is in peak voltage, not RMS. Also, does anyone know the spec coil resistance? I suppose I could just measure myself
Crack+Speedball Load: I am modeling this as a constant current load assuming 33 mA based on the assumption of 10V 300 ohm. This seems kind of kludgey, is it accurate?
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PJ likely has the pertinent numbers for the PT-3 in PSUD. If you double click on the transformer, then double click each box that looks like [...], you can fill in some of those values.
The coil label is RMS. It's rare to see peak-to-peak labels, as your multimeter won't measure that.
There's an option in PSUD to measure constant current, I prefer that myself. A Speedballed Crack will draw something like 80mA from the HV winding.
Since you know the current draw and the RMS voltage of the power transformer, you can set up a model of the current power supply, then tweak it a bit until it lines up in terms of voltages with what you are measuring in the real world.
-PB
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This should be roughly it - data copied from other members, notably JamieMcC.
I hope it's OK to post parts of Crack schematics.
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi84.photobucket.com%2Falbums%2Fk26%2FBwaze%2FPSUD%2520Crack%2520Stock_zpsvvnff0ft.jpg&hash=677a0c01e7afc2e2fc46bfab6e4931c9abbd3119)
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I would like to mention the kind assistance I received from Mark to help use this as a base for modelling different Choke and capacitor configuration really for the final capacitor. I believe there was a good amount of reverse engineering and searching of past posts for snippets of info to arrive at the input data used for the model.
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Thanks for the help! From the screen shot, the transformer has an 8 ohm resistance and the caps 67 mOhm correct?
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What I have is design notes. These are not measurements, they are the predicted measurements of the final design, made before the transformer was first built.
These notes say the "160v" winding can be modeled in PSUD as 173.5vRMS and 66.7 ohms. The resistance includes the effect of the primary DCR.
In the real world, current consumed from the heater winding will cause increased losses in the primary, effectively giving you less voltage than PSUD predicts. It's not usually a huge effect, but don't let it surprise you!