From: Alan Neel [neel@edgetech.com] Sent: Wednesday, July 02, 2008 4:30 PM To: Massion, Gene Cc: John Spruance; Mohammed Sanhaji Subject: RE: PS data sheets Gene, Sorry for the delay, I was out of town. The ESR is unimportant for the cap bank. The amp has its own low ESR caps to filter the high frequencies. Alan -------------------------------------------------------------------------------- From: Massion, Gene [mailto:magene@mbari.org] Sent: Thursday, June 26, 2008 6:09 PM To: neel@edgetech.com Cc: John Spruance; Mohammed Sanhaji Subject: RE: PS data sheets Alan Thanks for the equations. One more question. Can you estimate how low the ESR of the capacitors should be? Does it make sense to build up the 32,000 uF with a bunch of smaller caps in parallel to get the ESR down? Regards Gene Massion Monterey Bay Aquarium Research Institute 7700 Sandholdt Road Moss Landing, California 95039 831 7751922 (tel) 831 7751646 (fax) -------------------------------------------------------------------------------- From: Alan Neel [mailto:neel@edgetech.com] Sent: Wednesday, June 25, 2008 4:55 PM To: Massion, Gene Cc: John Spruance; Mohammed Sanhaji Subject: RE: PS data sheets Gene, These calculations have several simplifying approximations which are not stated: The numbers are from the assumptions given below. Power supply energy to cap during pulse: I = 6V / 1 ohm / 2 = 3 Amps average, E = .05 sec * 3 A * (52V + 46V) / 2 = 7.35 Joules Energy supplied to amp during pulse = 200W * 1 / .6 (percent eff) * .05 sec = 16.65 J Cap = 2 * E / ( Vi ^ 2 - Vf ^ 2 ) = 2 * ( 16.65 - 7.35) / (52 ^ 2 - 46 ^ 2 ) = 31,000 uf Average power dissipated in resistor = approx (6V / 1 ohm) ^ 2 * 1 ohm * .05 duty cycle = 1.8 Watts ( or 10% duty = 3.6 Watts) Alan -------------------------------------------------------------------------------- From: Massion, Gene [mailto:magene@mbari.org] Sent: Wednesday, June 25, 2008 7:27 PM To: neel@edgetech.com Cc: John Spruance; Mohammed Sanhaji Subject: RE: PS data sheets Many thanks Alan, this is a big help. Would you be willing to pass on the calculations you did that gave you the 32,000 uF? Thanks again Gene Massion Monterey Bay Aquarium Research Institute 7700 Sandholdt Road Moss Landing, California 95039 831 7751922 (tel) 831 7751646 (fax) -------------------------------------------------------------------------------- From: Alan Neel [mailto:neel@edgetech.com] Sent: Wednesday, June 25, 2008 4:14 PM To: Massion, Gene Cc: John Spruance; Mohammed Sanhaji Subject: RE: PS data sheets Gene, I should have added a schematic, see attached. Alan -------------------------------------------------------------------------------- From: Alan Neel [mailto:neel@edgetech.com] Sent: Wednesday, June 25, 2008 6:47 PM To: 'Massion, Gene' Cc: John Spruance; Mohammed Sanhaji Subject: RE: PS data sheets Gene, I have done some calculations with the following assumptions: Output power = 200W Input voltage = 52V ( this will affect your power supply selection or you will have to adjust the voltage up) Max duty cycle = 5%, 10% is probably ok but you will have to heat sink the amp well in both cases. Capacitor droop = 6V (during pulse, see comment below) Series resistor = 1 ohm, 5 watt (if needed for stability as we discussed) Pulse width = 50 ms You will need about 32,000 UF of capacitance for energy storage (63 Volt caps is a good choice). The droop will not affect your pulse fidelity if the peak to peak output voltage (between each output pin and the minus power rail (usually ground)) is about 42 Volts maximum. This will give you a total peak to peak output voltage of 84 volts. There are many ways to do this but going with a larger droop makes the cap bank much smaller (by factor of about 4 over a 3 volt droop and a 48 V power supply). A power supply of at least 200 watts also makes life easier. The amp should have a heat sink that doesn't let the aluminum bar get any hotter than about 80 degrees C. This will be directly proportional to duty cycle. The heat sink will need to dissipate about 400 watts * .05 (duty cycle) = 20 watts in the worst case where the load is highly reactive. A more reasonable value may be more like 10 watts. Good Luck, Alan Neel -------------------------------------------------------------------------------- From: Massion, Gene [mailto:magene@mbari.org] Sent: Wednesday, June 25, 2008 4:13 PM To: neel@edgetech.com Subject: PS data sheets Neel Sorry I forget these in the initial e-mail. I’m looking at the Vicor VI-MU or the Lambda PFE500. Thanks for your help Gene Massion Monterey Bay Aquarium Research Institute 7700 Sandholdt Road Moss Landing, California 95039 831 7751922 (tel) 831 7751646 (fax)