dgilbert
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1 edit | reply to DocWonder
Re: Cayman 3220-H running hot with stock Power Ada
just because the PS is RATED at 1.5 or 2A, does NOT mean it is delivering that much. it will only deliver the rated voltage up to that amount of current, draw more current and the voltage starts to drop. in this case, we don't need to figure on resistance, since resistance is not the only factor in the equation. we need to look at POWER, P=V*I. so, using your examples, and keeping in mind that POWER is our constant, we get:
9V*1.5A=13.5VA or Watts since this is DC.
now, by taking a 6V supply, we must adjust current to equal the same power.
13.5/6=2.25A
therefore a 2 amp power supply will not cut it, IF all power is used for running the unit, and none is lost due to heat. in reality, there is significant heat lost due to the inefficiency of the unit. Regardless, the unit is still going to consume the same amount of power to run the circuits and is still going to lose close to the same amount to heat. the regulator WILL work when fed by at least 6 volts, but the problem comes in when your power supply dips below the minimum 6 volts the regulator delivers to the rest of the circuitry. if your borderline rated (6V-2A) power supply dips to 5.5 volts, then the regulator can no longer put out 6 volts. it will try, but it can't do it. therefore, vital circuits run on low voltage which INCREASES their current draw and causes them to fail sooner or to corrupt data. this is why units not run on UPS often have corrupt firmware, the brown outs lower the voltage to a point that the unit goes stupid and corrupts NVRAM.
so, my point is why would you knowingly put yourself right at that threshold? a good rule of thumb is to always use a power supply that is rated so that current draw is only about 60%-70% of the PS max to keep it from failing or dropping voltage under load. keeping that in mind, assume the cayman only draws about an amp. that means that it is using 9VA to run or about 1amp of draw, with some lost to heat. with a 6v power supply, you would DRAW 1.5 amps. either way you figure it, you draw more current with lower voltage. more current in the same circuit=more HEAT to lose!
to summarize, the lower your voltage the more current you draw. the more current you draw in a FIXED circuit, the more power is lost to heat and the less efficient the circuit becomes, as the heat leads to MORE resistance in the circuits.
keep in mind that as long as the supply voltage stays above 6 volts, the internal 6V regulator is going to be what takes the abuse. but let it drop below 6v and EVERYTHING takes the abuse.
it just does not make good sense to go with a lower voltage supply. regulators are designed to regulate a minimum input voltage to a set output voltage. excess power is blown off via heat loss, but this is figured into the rating of the regulator.
best bet is to use a fan or two, or if you a comfortable with electronics you can put a heat sink in on the regulator to disipate the heat more evenly and quicker. either way makes for a cooler running device.
EDIT:
and yes, these temps are well within specs. i have approximately 40 3220 units in service, and they all run fine with factory PS. i don't even try to cool them. i just set thin in areas that they will get good air flow.
BTW, if you search back a ways you will run across threads referencing bad power supplies for the 3220. those were replaced with 9v 1.5a PS. the old PS was 1.4A. this PS got hot and delivered low voltage and caused the 3220's to fail. again, this is due to the POWER the 3220 draws is a constant. the 1.4A was barely above the needed supply and therefore failed early. the same thing applies on the voltage side, so a 6V supply will run too hot and cause failure unless it is rated to at least 2.25A, preferably more.
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