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Old 1st June 2012, 08:44 AM   #1
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Default PSUD help - 26 heater

Hi all,

Getting to grips with PSUD but I am getting some odd results - I am obviously doing something wrong and after a little guidance please.

Attached is the supply, copied from Rod Colemans notes on building a heater supply for 26 DHT.

I keep getting the "current pulled voltage below zero" alert, so I tried a stepped load 50mA - 1A after 2 seconds - Noticed that the voltage slowly rise as expected, but then plummets when it draws 1A.

Any input would be hugely appreciated. Was talking with Mogliaa last night and he is a big fan of PSUD so it would be good to use it more in my builds.

Many thanks

Charlie
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Old 1st June 2012, 10:52 AM   #2
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OK so found the transformer rating settings, getting better results but still a lot of ripple.

Baby steps
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Old 1st June 2012, 06:21 PM   #3
jamesdb is offline jamesdb  United States
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Sorry but the 450 milli Ohms for the transformer does not sound realistic. Also the choke is way too low, 1 milli Henry is too small. Do you have that choke already, or can you select a different one?
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Old 1st June 2012, 06:24 PM   #4
jamesdb is offline jamesdb  United States
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PS don't do a stepped load, 50mA to 1mA, just leave it at 1A.
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Old 1st June 2012, 11:24 PM   #5
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2 ohm ESR for 10000uF cap isn't right. Should be on the order of 0.1 ohms or less.
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Old 1st June 2012, 11:55 PM   #6
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I measured the unloaded transformer voltage and resistance to get the figures. I corrected the capacitor resistance, which lowered the ripple to about 0.3v. As for the choke, it was part of the design set up for the Rod Coleman DHT boards, it's a common mode choke, and I also have 2 0.2ohm resistors on each rail after the choke that can not be simulated on PSUD.

I was playing around with stepped loads to see when the voltage dropped, but adjusted the transformer ratings so no problem there.

Thanks for the help - Learning a lot.

Charlie
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