Is this WEG SSW05+ shorted out?

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moonshineJ

Member
Location
USA
In WEG SSW05 Plus I have R to U about 1 MΩ, S to V about 1 MΩ, T to W less than 1 Ω. When 480 VAC is applied to R, S, T, I immediately have power available at U, V, W even though there is no start signal order. No load connected to the output, by the way.
There is voltage drop of about 25 VAC across R-U and S-V, and almost zero across T-W.
IF I do apply the starting command, I have red LED Phase Loss on, which is understandable, since I have no motor connected.

The two identical controllers were installed to control two small (7.5 kW) water pumps (which was strange to begin with to use a softstart for a small size pump motor, which can be cycling on and off frequently). The project was never finished, and different people have been working on it in last 3-4 years.

I took the ohmic readings (no voltage checks!) on the second controller, and they are exactly the same.
It looks like T-W is somehow dead shorted inside, but why it's only between T and W on both controllers?
I saw at least one similar thread on this forum (though a different brand) and several other instances on other websites when electricians run into the same scenario.

Is this softstart busted? There should be no way to read between T and W in de-energized state, not to mention to observe full voltage output on U, V, W without starting command. If the softstart is bad, what potentially could cause such damage? IF IT ISN'T bad, isn't it weird and dangerous that a softstart having no starting command has a full output voltage across it?
 

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petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Many soft starts only have semiconductors on two of the three phases. The third phase just passes thru from the input.

I don't think your readings are especially meaningful, but they suggest nothing wrong to me.

When the semiconductors are off they are at a high impedance but not open so they should show line voltage when not connected to a motor.
 
M

moonshineJ

Member
Location
USA
petersonra said:
Many soft starts only have semiconductors on two of the three phases. The third phase just passes thru from the input.

I don't think your readings are especially meaningful, but they suggest nothing wrong to me.

When the semiconductors are off they are at a high impedance but not open so they should show line voltage when not connected to a motor.
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This is a good explanation, thank you! While reading all those threads of folks who ran into similar symptoms, I see that there is a lot of confusion about it. Many believe, that bypass contacts of their softstarts are stuck together in one phase or another. This is what I thought myself when I saw it, but then I asked "Why both softstarts would have the same zero ohms just between T and W?"

I've seen people are talking about the third phase passing directly from the input, especially for cheap brands. What kinda concerns me that the manufacturers say nothing about it in documentation supplied for these models. Someone can be zapped one day dealing with this stuff in a way they deal with old starters/ contactors.
 
M

moonshineJ

Member
Location
USA
ptonsparky said:
Note the little green light that indicates ready?
Click to expand...
Well, originally there was on the red Phase Loss LED, because before I turned it on, the motor was not even hooked up to the output cable (I taped conductors, of course). I had to debug the PLC ladder logic first, because the PLC was getting "Start" command at all times, because someone used the wrong latching type coil + some other errors. At the end, I would have just green Ready LED. Yet, 480 VAC power was still sitting at the output of soft starter, command or no command. I just replaced this softstart with a regular electromechanical Fujitsu contactor; it runs like a champ. I am just uncomfortable with the idea that high voltage power is fed to the motor when its softstart is in OFF condition. What a garbage...
 
P

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
moonshineJ said:
Well, originally there was on the red Phase Loss LED, because before I turned it on, the motor was not even hooked up to the output cable (I taped conductors, of course). I had to debug the PLC ladder logic first, because the PLC was getting "Start" command at all times, because someone used the wrong latching type coil + some other errors. At the end, I would have just green Ready LED. Yet, 480 VAC power was still sitting at the output of soft starter, command or no command. I just replaced this softstart with a regular electromechanical Fujitsu contactor; it runs like a champ. I am just uncomfortable with the idea that high voltage power is fed to the motor when its softstart is in OFF condition. What a garbage...
Click to expand...
Basically all soft starts and vfds will have output voltage when the drive is off. It is not a safety issue because if the cabinet is energized no one who is unqualified is allowed in the cabinet. If they are qualified they would know to wear their gloves when inside an energized cabinet, in the very few cases this is allowed.
 
ptonsparky

ptonsparky

Tom
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
petersonra said:
Basically all soft starts and vfds will have output voltage when the drive is off. It is not a safety issue because if the cabinet is energized no one who is unqualified is allowed in the cabinet. If they are qualified they would know to wear their gloves when inside an energized cabinet, in the very few cases this is allowed.
Click to expand...
I’ve never put a meter on the output of a drive when energized with no motor. Never thought of it. I’ll have to try it,
 
kwired

kwired

Electron manager
Location
NE Nebraska
moonshineJ said:
In WEG SSW05 Plus I have R to U about 1 MΩ, S to V about 1 MΩ, T to W less than 1 Ω. When 480 VAC is applied to R, S, T, I immediately have power available at U, V, W even though there is no start signal order. No load connected to the output, by the way.
There is voltage drop of about 25 VAC across R-U and S-V, and almost zero across T-W.
IF I do apply the starting command, I have red LED Phase Loss on, which is understandable, since I have no motor connected.

The two identical controllers were installed to control two small (7.5 kW) water pumps (which was strange to begin with to use a softstart for a small size pump motor, which can be cycling on and off frequently). The project was never finished, and different people have been working on it in last 3-4 years.

I took the ohmic readings (no voltage checks!) on the second controller, and they are exactly the same.
It looks like T-W is somehow dead shorted inside, but why it's only between T and W on both controllers?
I saw at least one similar thread on this forum (though a different brand) and several other instances on other websites when electricians run into the same scenario.

Is this softstart busted? There should be no way to read between T and W in de-energized state, not to mention to observe full voltage output on U, V, W without starting command. If the softstart is bad, what potentially could cause such damage? IF IT ISN'T bad, isn't it weird and dangerous that a softstart having no starting command has a full output voltage across it?
Click to expand...
Mechanical shock to driven load components is one reason to use soft starters, it will make those items last longer, especially if frequently started.

In fact mechanical reasons is the main reason for soft starting a lot of lower horsepower units as starting surge current isn't as much of a problem to the electrical system like it can be for large motors.
 
M

moonshineJ

Member
Location
USA
kwired said:
Mechanical shock to driven load components is one reason to use soft starters, it will make those items last longer, especially if frequently started.

In fact mechanical reasons is the main reason for soft starting a lot of lower horsepower units as starting surge current isn't as much of a problem to the electrical system like it can be for large motors.
Click to expand...
That is very true, and for bigger motors softstarting offers significant benefits. But, let's say, the 7.5 HP motor/pump (I typed above "7.5 kW"; so it's 7.5 HP/ 5.6 kW) starts, comes to speed in 10 sec, then shuts down. During peak water demand, the pump would kick on and off every 1-2 minutes. Looking at ACCEL TIME, which was set at about 10 sec, I am wondering if the 7.5 HP motor will be stressed unnecessarily due to frequently going thru long acceleration cycles? Looking thru the SSW05+ manual, I think 10 sec is just the factory default (it marked by a red dot).
Put it in other words, would a longer acceleration time create more heat within a motor? I don't think this is the case with a VFD, but what about a softstart?
What would be the ideal acceleration type for a 7.5 HP motor which starts/stops frequently?
 

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petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Starting and stopping the motor every few minutes regardless of whether you have a soft start or not is going to put extra stress on the motor. The soft start will reduce the stress, but can't eliminate it. But a lot of motors are run this way and last a long time. I would not be real worried about it with a small motor like this.
 
kwired

kwired

Electron manager
Location
NE Nebraska
moonshineJ said:
That is very true, and for bigger motors softstarting offers significant benefits. But, let's say, the 7.5 HP motor/pump (I typed above "7.5 kW"; so it's 7.5 HP/ 5.6 kW) starts, comes to speed in 10 sec, then shuts down. During peak water demand, the pump would kick on and off every 1-2 minutes. Looking at ACCEL TIME, which was set at about 10 sec, I am wondering if the 7.5 HP motor will be stressed unnecessarily due to frequently going thru long acceleration cycles? Looking thru the SSW05+ manual, I think 10 sec is just the factory default (it marked by a red dot).
Put it in other words, would a longer acceleration time create more heat within a motor? I don't think this is the case with a VFD, but what about a softstart?
What would be the ideal acceleration type for a 7.5 HP motor which starts/stops frequently?
Click to expand...
ptonsparky said:
Not your question, but a VFD would be more suitable.
Click to expand...
VFD maybe would be best, and instead of stopping and starting frequently you vary the speed as demand changes.

10 seconds is a long acceleration time for other than high inertia loads.

With a soft starter you are still applying full Hertz but varying volts as you ramp up to speed. Though this ultimately does limit current as well compared to across the line starting it still draws more current than running current during the acceleration so you still have added heating to motor windings if you start and stop frequently and whether using soft start or not possibly need to derate the motor because of frequent starting.

A VFD will vary frequency and voltage as the intended output speed changes. There is parameters to tweak those settings to gain more torque during acceleration but too much tweaking will put you in similar situation of overheating the motor windings if this is done for too long or too often. A 10 hp 460 volt 60 Hz motor running on a VFD at 50% speed will generally be seeing 230 volts and 30 Hz and will only be able to produce 5 hp before it will be drawing too much current in this condition and is why it can run indefinitely at this volts and frequency as long as not expected to do more than 5 hp of work.

Centrifugal fans and pumps are loaded by speed, actually by volume of media moved but that typically increases with speed unless gates, valves, etc. are in the media flow to control that, so during acceleration they initially have low torque requirements that rises as speed increases
 
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