3 phase compressor contactor failures

[marc5180]

What causes compressor contractor failure more than once.

We've inherited a few old Daikin units ERC5EB and when we arrived on site we found the 3 phase compressors down to earth on both units and the compressor contactors on both units only letting through 2 of the 3 phases which has most probably caused the compressor failure.

However the contactors have been in 2 weeks and they have failed again causing only 2 phases to be supplied to the compressors rater than the 3.

The guy on site thinks these contactors have been changed several times in the past but what can be causing them to fail so often.

I've checked all the obvious things electrically;

The supply voltage and neutral has been checked (by our electrician) and proved to be ok.*
The contactors are fitted with overloads.
The contactors are the correct ones and the coil is the correct voltage.
All terminals are tight.
The compressors are brand new and so are not at fault (acid test was carried out on old ones)
The compressors both pull around 9amps per phase with the overload set at 15amps.

This ones a head scratcher for sure.

[monkey spanners]

A chattering pressure switch or similar in the feed to the coil will cause the contractor to pull In and drop out rapidly resulting in burnt contacts, if this is the case a time delay in the feed my help though it won't fix the original problem.

im sure others will know of a more daikin specific problem that could be the cause also.

[marc5180]

Hi Monkey,
I originally thought this may be the cause but whenever I'm on site and with the units in question the feeds to the coils are constant and never drop or lose the signal.
The refrigeration side is okay as well as both pressure switches.

It may well be worthwhile to fit a start limit timer for say no more than 12 start per hour.

[frank]

Hi Marc

What is protecting the mains supply to the unit. Is it fuses or MCB? I would suspect it's fuses, as a large imbalance like 2 phasing should take out an MCB.

I've only got details for the old ERC5 C series which shows the compressor contactor circuit fed from the indoor unit on wire terminal 5 which goes through the overload (95 - 96) and a delay on timer K2T (3 minutes)

Is the current draw equal on all 3 phases?

[chemi-cool]

When you say "contactor failed", do you mean main contacts burnt? coil burnt?
What is the amp peak start?
What is the run amp draw?
What is the contactor amp rating?
What is the contactor make?

[Grizzly]

A remote location can cause issues, as due to the distance from the grid, which we get a lot down here in the s.west.
Can play havoc with the incoming voltages. Which in turn will cause all sorts problem. If this is related to just one set of kit then I think the others have it sussed.
Grizzly

[install monkey]

stick a 3 phase controller on it which detects 3 ph and will open circuit ur comms to the contactor- at least this will react quicker than the overload and prevent 2 phasing

[monkey spanners]

If its got a seperate delay timer (as opposed to built into circuit board) then i'd change it, have had these go bad and case contactor chattering.

[glenn1340]

Install monkey`s got the right idea a phase failure relay drop the compressor out before any damage occurs. Also try a low voltage trip relay, if it trips on that you know you`ve got voltage supply problems.

[monkey spanners]

Overloads should trip if it loses a phase if they are set correctly, check they are not set to auto reset.

As said above though a phase failure doodad would be extra insurance.

[install monkey]

overloads would trip, but not instantly- thus by fitting the moniter


3 wire 3phase under voltage relay,500Vac

Enlarge
Image representative of range only

Technical Reference UL/CUL E111187 M3PR Phase Sequence / Failure & Under Voltage Relay Statement of conformity RS Components Statement of conformity RS Stock No. 342-944 Description 3 wire 3phase under voltage relay,500Vac Manufacturer/Brand: Broyce Control Mfr Part No. M3PR 300-500VAC Contact Configuration NO/NC Electrical Phase Three Height 89mm Length 59mm Monitoring Application Phase, Voltage Phase Sensitivity Phase Loss, Phase Sequence Supply Voltage 300 → 500 V ac Time Delay 1 s Voltage Sensing Range 300 → 500 V ac Voltage Sensitivity Undervoltage Width 35mm

Three-Phase Sequence/Failure & Under Voltage Relay Detects under-voltage condition Detects phase loss (and neutral loss on 4-wire) Detects incorrect phase sequence Adjustable trip level Monitors own supply DIN rail or surface mount Phase Sequence/Failure Relays Monitoring of 3 phase supplies

Overloads should trip if it loses a phase if they are set correctly, check they are not set to auto reset.

As said above though a phase failure doodad would be extra insurance.

[marc5180]

Guys I'm away from home and I'm having issues replying to this thread and have been having since Friday. The site lets me log in but won't let me reply, it just times out.
I'm back home tomorrow and so will reply to all the comments made, thanks for all the replies.

[Magoo]

Had similar problem with failing contactors, ended up being induced voltages screwing up contactor coils releasing quickly, fitted snubber resistors across contactor coil terminals, no further problems.

[mikeref]

Contactor leg open circuits. Same phase as last time?
If so, see if your control circuit is fed off that phase.
Measure your full load amps and corresponding supply voltage. Your overload should have tripped before the burn-out happened.
If the contactor is too closely rated to the running amps of the compressor, any leg is likely to burn first.

BTW, Magoo. should your comment read " contactor coil not ​releasing quickly?

[marc5180]

Hi Marc

What is protecting the mains supply to the unit. Is it fuses or MCB? I would suspect it's fuses, as a large imbalance like 2 phasing should take out an MCB.

I've only got details for the old ERC5 C series which shows the compressor contactor circuit fed from the indoor unit on wire terminal 5 which goes through the overload (95 - 96) and a delay on timer K2T (3 minutes)

Is the current draw equal on all 3 phases?

Hi Frank, the unit in question is an ERC8 C not an ERC5...sorry, meaning there is no delay on timer.
It has MCBs protecting the mains supply rather than fuses and the current draw is equal on all phases.

When you say "contactor failed", do you mean main contacts burnt? coil burnt?
What is the amp peak start?
What is the run amp draw?
What is the contactor amp rating?
What is the contactor make?

Hi Chemi, when I say contactors failed I meant 1 of the main contacts were burnt out of the 3.
The overload is set to 15a and the run amp is around 9amps and balanced.

The contactors is a Siemens type although I don't have the model at the min.

[marc5180]

stick a 3 phase controller on it which detects 3 ph and will open circuit ur comms to the contactor- at least this will react quicker than the overload and prevent 2 phasing

Yeah that's another idea install, good suggestion, I'll look into this.

[marc5180]

Had similar problem with failing contactors, ended up being induced voltages screwing up contactor coils releasing quickly, fitted snubber resistors across contactor coil terminals, no further problems.

How did you figure out that it was induced voltage that was causing the issue Magoo?

[marc5180]

Contactor leg open circuits. Same phase as last time?
If so, see if your control circuit is fed off that phase.
Measure your full load amps and corresponding supply voltage. Your overload should have tripped before the burn-out happened.
If the contactor is too closely rated to the running amps of the compressor, any leg is likely to burn first.

BTW, Magoo. should your comment read " contactor coil not ​releasing quickly?

Hi Mike,
I think it may be the same phase as last time although I can't be certain.
The control circuit doesn't come from a live in the condensing unit but a switched live from the time clock in the HVAC panel.
Full load amps were 9.5a and supply voltage 235.

The overload never trips but instead the main MCB in the fuse board trips.

[chillerman2006]

Hi Marc

just a thought, what else is drawing power off that same phase

looked at a condensing unit the other day, that had a new contactor fitted recently and went down again

was at a petrol filling station and there was a fault with the single phase petrol price sign

that was some how fed from the same L1 as the condensing unit

R's chillerman

[install monkey]

try higher rated contactors- inertia on start up could be causing contacts to wear- were the previous contactors the correct rating?
used to go to 3 ph fujitsus aoy36's where muppets had fitted danfoss cI9 contactors- used to last about 6 months until starting current used to weld the contacts or frazzle em

[Magoo]

Basically sat there and watch system stop, the contactor spluttered. So when stopped checked contactor coil terminals with an electronic multimeter, read 80 odd volts, no potential with a dusspol check. Fitted bleed resistors to drain induced voltage. Came across the problem decades ago with early genertion Allen Bradley PLCs, all outputs to contactors etc., had to have bleed resistors at contactors.

[chemi-cool]

One more thing that comes to my mind after replacing compressor overload relay today.
make sure that the screws which hold the wires, will be tight, very tight, as tight as you can.

Copper wires behave like water pipes, when the amps are high, you can see them move and try to be straight, the same with high pressure in water pipes.