Archive of the former Yahoo!Groups mailing list: MOTM

OK, there is one other thing to consider: NEVER run these Power One's "harder" than 80% of
current rating. This is to keep the transistor junction temperatures low enough so that they are
warm to the touch, but don't give you the infamous "Batwing Tatoo" (old timers will know what
this means).

As a rule: assume every modules will draw 40ma off each supply EXCEPT the EGs, use 10ma. Add up
the current (don't worry about + and - current). Then, divide by 0.8 and that is what the current
(1 side) of the supply needs to be AS A MINIMUM.

Example:

50 modules x 0.040A = 2.0A + 8EGs = 2.08A. Then 2.08A/0.8 = 2.6A, buy a 3A supply.

Going "backwards":

an 800ma supply will power about (800ma)(.8)/0.040) = 16 modules (actually about 20)

a 1.5A supply will power about 30 - 35 modules
a 3A supply will power about 65 - 70 modules
a 5A supply will power about 120 - 130 modules

This is on the 'conservative' side, but the #1 failure mechanism in the power supply will be
power transistor junction temperature, which is proportional to the current draw. Also, the
ripple current in the big rectifier caps will cause heat in the caps themselves.

Paul S.