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Hi Russ,
As mentioned in the diyAudio forum, I was wondering if the Placid HD can provide ~890mA out. I will be using 2.5" tall heatsinks. However, why do I need to use a 35-50VA transformer as you stated? It seems kind of big to me.
If I have a Placid HD BP providing 450mA out, will a 15V 25VA transformer be enough?
Thank you
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Don't take this the wrong way, I am really trying to help. Do you understand What VA is a measure of? If not, then just spend a few minutes on google.
You need to source ~890 ma, but your supply is going to be drawing something like 1.25 x that.
I like to spec my trafos so they don't sag much. You could probably use 25VA in both spots. The choice is yours, just do the math.
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I did indeed spend some time reading about the VA measure. I just can't understand how I determine the VA rating for a transformer based on my current draw from the connected boards. Is there a specific formula I can use? Since I am powering 5x IVY boards with two Placid HD BPs, can both of those share a transformer? Would a 35VA 2x15V transformer be adequate, or would I need a 50VA one? Edit: I did find a formula, but it does not give me an answer that makes sense. If I'm pulling a total of ~750mA from the 5x IVY III boards, then the formula should be .75 x 15 = 11.25VA, which seems really low. Even with rounding up to an amp, the VA is still only 15. Am I missing something? Edited by user Saturday, September 3, 2011 9:12:36 PM(UTC)
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A single transformer can be used. The amperage conversion factor from DC to AC across those bridges is 1.6. The round up to 1 amp to compensate for the shunt current seems reasonable. So, the current draw on the transformer is 1.6 amps, and in the BP configuration, two 15V windings essentially gives a 30V transformer. The result is 48VA. I wouldn't run less than a 75VA unit, because in this situation a non-stressed transformer is good. Edited by user Sunday, September 4, 2011 9:53:07 AM(UTC)
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Both those transformers would work. These all come with two separate 15V windings. So, you would not prewire the windings in series or parallel, just land each on the Placid board, keeping track of polarity. I would get the Hammond before the Triad, but what about a Plitron 80VA, can't you get those cheap in Canada? Edited by user Monday, September 5, 2011 8:06:11 AM(UTC)
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I wasn't aware of Plitron... I'll definitely go with a Canadian company before others! Thanks for the suggestion. I'm not sure what you were referring to about being cheap, they seem to be expensive transformers! Maybe the shipping won't be so bad. When using these transformers, do I wire the primaries in parallel since I'm using them on 115V AC? Edited by user Sunday, September 4, 2011 4:24:31 PM(UTC)
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There is some debate on whether or not two Placid HD BPs can be connected to the same transformer. Russ, could you please confirm this? My plan is to use two Placid HD BPs on one 80VA transformer. Leon's BIII guide states not to combine them on the same transformer, and when I asked Leon he said I should check with you.
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Yes, you can connect two Placid HD-BP to the same dual secondary transformer, just make sure you use the same secondary in the same phase relation for each supply.
Example:
PS1+ S1 PS2+ S1
PS2- S2 PS2- S2
Just remember to wire the secondaries on each supply identically.
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Thank you very much for the information! :)
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Toroid Corporation of Maryland if not Plitron. Edited by user Wednesday, September 7, 2011 9:18:58 AM(UTC)
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Or Avel Lindberg, our faithful and totally awesome supplier. http://avellindberg.com/Give them a call... they are always very helpful. Edited by user Wednesday, September 7, 2011 9:46:38 AM(UTC)
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