Measuring Amps on Variable Speed Blower Motors

[jmsmars1]

As a part of our PM's we measure the amps that the blower motors are pulling. When you pull the door off of a variable speed unit the motor ramps down and any measurement taken then is not true to conditions. Just wondering how everyone else is handling this. I have tried a few different ways but none seem very easy or accurate for that matter. Is there a meter out there that will hold the peak value so I can recall the amperage after shutting it up inside the unit?

[ckartson]

Quite a few meters with min max. I use an inexpensive amprobe digital mainly because it is small (to small, what a mistake) but it does min max

[Elfshadow]

As a part of our PM's we measure the amps that the blower motors are pulling. When you pull the door off of a variable speed unit the motor ramps down and any measurement taken then is not true to conditions. Just wondering how everyone else is handling this. I have tried a few different ways but none seem very easy or accurate for that matter. Is there a meter out there that will hold the peak value so I can recall the amperage after shutting it up inside the unit?

Fieldpiece wireless handle with a wireless receiver? The units that I tend to work on have the vfd mounted in a control panel so you could take the measurement at the vfd without opening the blower door. Also some vfds can be programmed to display the motors amp draw.

[SBKold]

Open the disconnect?

[mark beiser]

When you pull the door off of a variable speed unit the motor ramps down and any measurement taken then is not true to conditions.

Even with PSC motors, if you measure the blower amps with the panel off, you are not getting the true reading of what it is pulling under normal conditions with the panel on because the motor loads up, causing the amps to go up, when the panel is removed.

For measuring the amps on ECM motors you need a true RMS meter, so if you did something wireless, you would need something like the the Fieldpiece SC57, or the Fluke 381 or CNX setup. The Fieldpiece clamp accessory head is not true RMS, so wouldn't work.

[ECtofix]

Open the disconnect?

What he said...

Leave the doors/panels intact. Go to the disconnect or gain access to motor supply wires at a breaker in a distribution panel. Read your amps from there. Your airflow will be unaffected. You're getting your reading while maintaining the exact conditions under which the motor operates.

[jmsmars1]

I have done that on the occasions where they have 1) installed a disconnect and 2) it had enough wire/room in it for me to get the clamp around. Unfortunately in my area that adds up to about 1/4 of the time

[m singer]

Even with PSC motors, if you measure the blower amps with the panel off, you are not getting the true reading of what it is pulling under normal conditions with the panel on because the motor loads up, causing the amps to go up, when the panel is removed.

For measuring the amps on ECM motors you need a true RMS meter, so if you did something wireless, you would need something like the the Fieldpiece SC57, or the Fluke 381 or CNX setup. The Fieldpiece clamp accessory head is not true RMS, so wouldn't work.

doesn't "true RMS" refer to the way that voltage is measured? What difference would it make in Amp mode?

[WhoIsThat?]

doesn't "true RMS" refer to the way that voltage is measured? What difference would it make in Amp mode?

Voltmeters and ammeters can respond to average or RMS
values.

Early on they responded to average values but read out in RMS values for a sine wave because sine waves were common.
Now with all the weird waveforms seen, an RMS meter is better and a scope is even better.

http://www.google.com/search?client=...Gba44AOWjoCACQ

[jbarron4]

the amps with a VFD drive are relatively meaningless. The power is the amps X volts X Powerfactor X efficiency.
The standard VFD varies the voltage and the current in the F to V ratio. This means that at low power and RPM settings the current may be high, but the voltage low and therefore the power is low.
We often see currents fairly high at low RPM (low voltage as well). If you just look at amps you would think that the power is relatively low instead.
Most VFDs will read out power as well as amps and this is the best way to measure the actual power to a vfd.
This is not necessarially the case with an ECM that might also be variable speed. In this case the input power to the motor SYSTEM might relate to the power to the motor.
Also in this case the amps to the motor might not be indicative of the actual power unless you also know the voltage applied. IF we are talking a DC motor then the power formula would be Volts X amps and power factor would not be a factor.

[simclardy]

I just bought this ideal Ideal 61-775 1000A AC-DC TightSight-amp;reg; Clamp Meter with TRMS
It works well. I have used amprobe for years but I don't think they make a good clamp meter that does Ac and dc amps, Hz, and capacitance. Anyway this Ideal product has a min max button. good luck.

[simclardy]

Sorry just realized this thread is dead. I am new to threads and blogs and chats and .......

[TBrazin]

I just bought this ideal Ideal 61-775 1000A AC-DC TightSight-amp;reg; Clamp Meter with TRMS
It works well. I have used amprobe for years but I don't think they make a good clamp meter that does Ac and dc amps, Hz, and capacitance. Anyway this Ideal product has a min max button. good luck.

that's more a meter ill ever use. Nice meter man! Hats tightsight?