problem with peak current

[wigglies]

I'm trying to fault find on a 3 phase warehouse lift that keeps blowing 32A bs88 fuses on L1 & L2 but may go a few days without fault, the motor is a 5.5 KW and when measured has a start up of around 11A and normal running of 7A however when measured on peak it returns a reading of 80 to 90 odd amps , which has me a little confused! any ideas would be greatly appreciated.

 

[NozSpark]

If you are not a lift engineer then you shouldn't be working on it I'm afraid

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An electricians job ends at the local isolator

 

[wigglies]

Thank you but as a Maintenance Electrician i keep getting called out to the problem. I just cant understand the high peak current.

 

[Riggy]

Sticking brake perhaps? Just about has to be something mechanical/system related I'd have thought.

 

[Technician]

Yes; Lift engineer problem; But the brake may not be releasing

completely.

What do you mean by "peak" current? Is this taken on a peak

reading meter?

 

[wigglies]

Yes the peak was taken on a meter and the results suprised me, everything looks normal by meter until you take a peak reading its only a small goods lift between two levels but the brake being slow to release would explain it! Think i'll get them to get the supplier of the lift in.

Thank you for all the expert guidance its great knowing help and advice is at hand

 

[ProDave]

I sometimes find for things like this, digging out my old analogue (moving coil meter) clamp meter gives you a better indication of the peak current and how long it lasts for, much more "real time" reading than many digial meters.

That might show the peak demand lasts a fraction of a second and goes suddenly (rather than slowly decaying) which might well point to a sticking brake.

 

[Evans Electric]

Did the peaks appear when the lift was fully or overloaded ?

 

[wigglies]

Both fully loaded and also empty as soon as it started to move from one floor to the other

 

[Sidewinder]

Another Q.

Is the control 400V across those 2 phases?

Could be an intermittent control fault?

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Another Q are the fuses gG or gM?

 

[Technician]

I like Pro Dave's point about the analogue meter. Not all that is digital

is good for troubleshooting. I still use my old clamp meter for looking at

troublesome loads aside from the digital one that can read and store

maximum demand.

Thanks, Msr. d'Arsonval!

 

[Sidewinder]

Yes good point wrt analogue meter, I carry an AVO9 around for fault finding, but have not yet managed to get my hands on a moving coil clamp meter, but the Fluke I have has a bar graph at the bottom of the screen which is a bit nearer real time.

I do have a 1ph power analyser though which will graph current and voltage against time which is also useful for fault finding.

Apparently the Fluke clamp outputs a voltage proportional to the current, so perhaps I can link this to the AVO & see currents real time from that...

I feel an experiment coming on!

Goodness knows when mind!

 

[Technician]

Maplin tried (hard) to sell me a pocket oscilloscope.

Given that this is one of the most versatile diagnostic

tools around, it must be adaptable to alternating

current measurement.