Another elementary question, but certainly leads to debate.
During a pm of equipment, I was told by some that motor amperage should be as close , or adjusted to (if possible) to Full Load Amps. In this way, the motor is running as efficiantly as possible. Or in other words "optimized"
Others , however, say that that is not true and I should back off the amperage draw by adjusting the sheive, that FLA is the MAXIMUM acceptable amount of amperage draw for the motor and I will be shortening the life expectancy of the motor if I keep it at that range. I have been adjusting the sheive to about 80% of FLA to stay in the safe area. Am I wrong?
Should I be trying to "optimize" the motor and bring it to FLA?
You need to go by your operating conditions (meaning evap. temps and condensing temps) that are called for by your compressor manufacturer. Copeland has the performance calculator Bristol has the efficiency sheets. I'm sure almost every manufacturer has info like this about their compressors. RLA is what the amperage draw is at test conditions if you are below these your draw will be less.
are you speaking of air flow?
if so, the sheave size should be adjusted to supply the proper amount of air flow only. we do not have an infinite number of motors with every horsepower ever needed. therefore, you need to use a motor that will allow you to reach your required air flow. if that means you need 0.9 HP then you will need a 1.0 HP motor. if you need 1.1 HP then you will need a 1.5 HP motor. you may be able to get away on the 1.1 HP requirement with a 1.0 HP motor if you had at least 1.10 SF (service factor). while running a 1.0 HP motor on a 1.1 HP requirement does give you more electrical effeciency...you also have no safety room at start up or brown out conditions or temporary overloads or lots of cycling. the FLA rating (Full Load Amperage), is a number indicating the amps expected at that HP and voltage and hertz listed on the nameplate. you may or may not have these conditions...esp. voltage.
so stop adjusting sheaves because of amp draw. i would only adjust them if my motor were tripping due to some unknown cause and i needed it to run in order to troubleshoot. the only other reason to adjust them is because the balance report said so or conditions changed that required more or less air flow.
Be careful on what you start adjusting during pm s
Talking about Test and Balance
Depending on what you're adjusting you may be throwing off the balance of the store or resturant ...ie. exhaust, maf, blowers.
and cause more trouble than you are looking for...
Isn't sanity just a one-trick pony anyway? I mean, all you get is that one trick, rational thinking, but when you're good and crazy, well, the sky's the limit!
OOPS, so much for that expensive air balance, FLA is a max, there is no minimum, kick the guy in the ass that told you to that.
Yes, your actual amp draw should be close to rated load amps RLA (FLA). Electric motors have a service factor (SF on name plate) usually 1.15. This means you can take the SF X the RLA and look at your actual amps this will be the maximum amp draw. I am assuming that this is an indoor fan on a RTU or air handler. Hope this helps
Originally Posted by mickyj
Sic Semper Tyrannis.
stay away from adjusting for rla, when design conditions are meet, like a properly charge compressor circuit your not looking always at fla to be meet, this is asking for trouble.... and usally 3 phase gets a sf, you better look for a name plate data if there is a sf to play into.. not all motors have a sf..go for what is needed only. i know your asking about air handler but think about it first,, don't cause more problems.
i think all the RLA, FLA, LRA on the name plate are got in labs or ideal condition. so what we get on field always have some difference from it. we cant judge the system only by the amps.
keep in mind readings should be taken with a true rms amprobe or else you will have additional problems
Can you qualify that statement?
Originally Posted by superfittertech
An averaging meter is all many service people will ever need. Unless the load has non-linear elements in it such as a VFD or neutral harmonics, the true rms and averaging meter will read the same.
"Why True -RMS?"
"Why Tru-RMS matters for HVAC technicians?"
good post, Wolfie.....
[QUOTE=wolfdog;1526591]Can you qualify that statement?
An averaging meter is all many service people will ever need. Unless the load has non-linear elements in it such as a VFD or neutral harmonics[QUOTE]
exactly...ever have a bad drive "echo" throughout the building? i have heard of one building without drives have lots of problems because of the building next door. if you are in commercial...just get a true rms meter. most do not cost much more.