Measuring Inrush Current

[@Kevin-ib4gv]

I understand that a meter needs an "inrush current" capability that most meters don't have. The reason being that the inrush current only lasts 3 or 4 cycles (10ms) and goes by too quickly for regular meters to measure. If you put the meter on "max" you are measuring current draw not only on the first 10 ms of inrush, but also on the next 990ms of startup current which is less current draw as the motor gets to full speed and therefore a lower reading than the inrush current value as the two are combined over the 1 second start up. I just installed a new 3 ton condenser, coil, and furnace with a LRA of 77 and I measure 85 amps of inrush consistently using the inrush capability of my meter.

[@ianrosal1235]

buy UNI-T 208b it has inrush current😊

[@PH-md8xp]

This is not an accurate way to measure inrush current. You need a clamp meter with an Inrush button on it that is specifically designed to measure Inrush current which occurs during the first 100 ms of startup. I’ve tested this on my compressor with a Klein CL900 that has both and Inrush button and a Max/Min button. Consistently, I get a reading of 98A for Inrush and for MAX, I get a reading of 76A. It’s not the same thing.

[@flex20144]

378 fc best Meter for that

[@russelldelorey7348]

The 374 FC has proprietary inrush measurement capabilities, the 378 FC is just the Cadillac of clamp meters, the Fieldsense tech is a game changer.

[@ncooty]

Shouldn't the max (peak) be higher than the in-rush (average of the first 5 cycles on a Fluke)?

[@jlg3315]

66 is close to 82?

Fantastic✔Sent this to my HVAC folks since they didn’t know how to use their clamp on meter etc. I want to run my AC on a portable generator so need the new surge amps after the soft start installation. If it’s below 30 amps, I’m good.

[@brentjohnson6654]

New subscriber here. As a home owner I am trying to add up all my inductive loads for the house and am measuring surge or startup current on the heavy hitters such as my HVAC, Well Pump, and machine tools such as table saw and welder. Thanks again for your video.

[@andyapple9]

If inrush measures the maximum current drawn by the compressor, what does the MAX button on the meter do? Thanks.

[@JPTinioMedia]

The max button could do it but its not accurate as the max button isn't fast enough to measure the inrush amps which is why newer or fancier meters have a dedicated inrush

[@dantronics1682]

The max button stores the max current or voltage measure by the meter in the timeframe that you are measuring, it doesnt measure the inrush current since its an average. If you was to use a storage scope on motor switch on you would see a massive spike, thats the inrush currrent of v/r when there is no back emf

[@johnthomas5786]

what model number fluke meter you are using?

[@qiangzheng821]

Fluke 902 FC True RMS HVAC Clamp Meter

[@das250250]

Quite incredible 10x the avg current

[@rcinfla9017]

Most clamp on meters on inrush/surge current mode require 0.3 to 0.4 seconds duration for time averaging of current to make an accurate startup surge current measurement. A hardstart kit may reduce startup time to less than 0.3 seconds causing meter to report an erroneously low startup surge current number. This is the reason many techs incorrectly believe hardstart kits reduces compressor startup surge current. Hardstart capacitor decreases startup time. It does not reduce peak surge current, only shortens its duration. Hardstart capacitor gets the start winding to run winding current closer to 90 degree AC phase shift which improves startup torque of single phase AC induction motor. The amount of additional start winding current is very small, it is the AC phase improvement due to larger capacitor value that improves the startup torque, reducing the spin up time of motor. LRA is set by motor design and does not change unless voltage on motor changes. What changes is the length of time the motor takes to spin up to operating speed. As a compressor approaches 0.7 to 1 second of time to spin up due to whatever issue inside compressor (copper plating on bearings, liquid flood back in off mode. etc.) the internal thermal cutout breaker inside compressor will likely trip due to LRA current for the long period of time. Bad wiring, connections, bad contactor, can also cause additional voltage drop during high startup surge current, therefore longer spin-up time, causing compressor internal breaker to trip after 0.7 to 1 seconds.

[@kdcarver]

It may be beneficial to inform folks about the difference between a hard start kit and a soft start kit. A hard start kit actually will not change the inrush current, it will simply decrease the duration of this spike. A soft-start kit, on the other hand, should decrease that spike peak.

[@smokey3829]

RLA = Rated Load Amps. Measured amps while compressor is running. LRA = Locked Rotor Amps. A locked rotor is the worst possible case for impedance that leads to the highest measured amp reading.

[@deang5622]

Incorrect. Impedance doesn't change. It's a function of design of the motor. What changes is the magnitude of the back EMF. When the motor is not rotating, there is no back EMF, and the circuit is simply the DC resistance of the coils and the voltage across them. The coil resistance is low and hence the locked current is high I am surprised how many people are making statements on how motors operate and do not understand basic motor theory. It's shocking

[@juanitaharris4320]

SHOCKING indeed :)@@deang5622

[@bernardocisneros4402]

@@deang5622 Besides the inductance of the motor, frequency also effects impedance.

[@johnconnor7501]

Are all inrush clamp meters huge?

[@CM-bq9fp]

I am wondering which breaker you were using for this 66 Amp ?

[@james10739]

I mean probably just whatever it's calling for like a 20 or 30 since it only pulls like 6 while running I assume there is also the fan but a breaker can handle it for this couple milliseconds

[@Adrianyoutubing]

My guess, here in the UK a 20A type C or D type MCB.

[@tommaxwell429]

I'm confused! As the inrush current goes down, that's a problem? I would think as long as the inrush current is less than LRA that would be a good thing. Less current, less heat. No?

[@bernardocisneros4402]

The lower the inrush current the better because it's easier on the compressor windings. A little more longevity for the compressor.

[@tommaxwell429]

@@bernardocisneros4402 Yes I agree. At least I would think so. They may be negative to too little inrush current as well, but I can't think of what that might be as long as there is enough current to get it moving.

[@bernardocisneros4402]

@@tommaxwell429 The ideal scenario would be for the current to gradually ramp from zero to rated RLA. That is what a compressor that has an EasyStart installed does and it does it in about 3/4 of a second. Whereas a new compressor without EasyStart or a hard start kit installed, experiences an inrush current spike lasting about 100 milliseconds and the compressor reaches rated speed in about 250 ms.

[@Editronone]

Awesome video, very clear, visually and technically. Thank You!

[@theackid7887]

I like to see the compressor at 75% of the RLA rating. I take running conditions and refrigerant charge into consideration when checking amps to deciding the health on the compressor I’m working on because amps will fluctuate in different situations

[@johnconnor7501]

I agree

[@p200]

What model fluke meter is that?

[@b-2466]

Looks life 902fc which is what I use and it does not measure inrush current.

[@toloulafaumuina3068]

Great video helpful

[@nvg57]

This video is absolutely misleading. Inrush current measurement can only be performed using meters that have an inrush capability and equipped with inrush button. This guy did the test with the tool, which does not have an inrush option and not measured correctly.

[@PH-md8xp]

That is correct. Using the Max button is not the same thing as Inrush.

[@BastrdMcQueen]

Show the difference with a hard start.

[@dantronics1682]

I heard him saying hard start but I thought it was soft start

[@saulurena7681]

Mine just says OL, ALWAYS doesn't matter which wire I put it at, it's annoying

[@dantronics1682]

thats what it should do, ol means over load. thats why you need a meter with inrush current reading

[@Rinconmaniac]

Thanks for the info!

[@JB-bb1zw]

The problem with trying to diagnose using Inrush Amperage measurements is and I'll quote Fluke Instruments "Inrush amperage can be 4x to 10x RLA" so with out a substrate or baseline amperage, you can't judge wear and tear.

[@JPTinioMedia]

The LRA number is what the engineers have designed for that specific unit to pull when the unit is locked or trying to start up, if your inrush is below that number its using less to start up, if you ever come across seized motors the amp draw is usually a lot higher and stuck at the LRA rating if the motor has an lra rating. From what I was told and taught at least

[@Artificialturflover]

Missing the most important piece of info "which wire are you clamping your meter to?" Thanks!

[@joshflynn9388]

Common

[@Editronone]

Not trying to be mean, but if you don't know what wire it goes on don't even take the cover off.

[@PH-md8xp]

@@Editronone Lots of people are learning here, there are no bad questions. Better to ask and gain knowledge than not to.

[@bernardocisneros4402]

@@PH-md8xp @Editronone never said not to ask questions.

[@dfigueroa903]

Does this meter have DC my... yes,no.....¿¿

[@CuongNguyen-xv2cm]

Can it measure Inrush DC ?

[@rbhndrsn14]

The reason why I viewed the video is to see what wire you're measuring for inrush amps. The video had no information

[@armandmelch8110]

Too much guessing for an educational video

[@hounddoggzgaming6970]

Armand Melch its called a system diagnostic real tech have to test multiple components before we replace a part. We call this trouble shooting i know this is brand new to you.

[@ameen3372]

yes, indeed

[@bigdaddybk8817]

"66 is close to 82". Wow.

[@tmacgee1234]

Yea max is similar but not inrush. Inrush is a spike, max is over a duration

[@bernardocisneros4402]

Spike is also over a 100ms duration. Which is too much time. 1 to 5 ms would be ideal.

[@beretta0222]

You are not measuring an inrush current .

[@james10739]

I bet the in rush current on a new unit is probably real close to 3X the running amps

[@UnbornWarrior123]

Hi, I am also surprised to see the inrush currents are 10 times the steady state currents and he is counter verifying with the name plate details.

[@dantronics1682]

it can be up to 50 * running amps but last only 0.5 seconds which is why the fuse doesnt blow, most fuses are antisurge.