Bravheart
"Tomorrow will be a good day"captain Tom1920-2021
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- Thread starter Bravheart
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daleyd
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Are there any controls (eg relays) associated with this motor? If so then you need to make sure the control voltage is suitable for these as well, a vsd typically won’t be suitable for these.
For that motor it looks like you need a 230-380v vsd unless there is some links inside the terminal box to change voltage.
For that motor it looks like you need a 230-380v vsd unless there is some links inside the terminal box to change voltage.
Bravheart
"Tomorrow will be a good day"captain Tom1920-2021
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Inside of control box just power off/on and stop start buttons on the front. thanks.
ajlelectronics
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If I can hijack the thread for a moment please...
I was surprised to see that the realistically priced VFDs claim that they can't be used with compressors, which is what I need. £3k for a rotary converter is not an option, I can replace my three phase with two single phase compressors for less than that.
I was surprised to see that the realistically priced VFDs claim that they can't be used with compressors, which is what I need. £3k for a rotary converter is not an option, I can replace my three phase with two single phase compressors for less than that.
Smouser
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Buy a Chinese VFD with minimal documentation. They won't mention that it is not suitable for an compressor
The big issue with ramps (and compressors) is the startup.
When connected to the mains, the motors spin up quickly which means they're pretty much at speed before the pump starts loading the motor.
A typically sized VFD can't supply the same surge current as the mains, and rely on accelerating the motor relatively slowly, which means the pump will often stall the motor before it gets upto speed.
To get around that, you either need to oversize the VFD, or remove the pump load until the motor is at normal speed.
When connected to the mains, the motors spin up quickly which means they're pretty much at speed before the pump starts loading the motor.
A typically sized VFD can't supply the same surge current as the mains, and rely on accelerating the motor relatively slowly, which means the pump will often stall the motor before it gets upto speed.
To get around that, you either need to oversize the VFD, or remove the pump load until the motor is at normal speed.
Guineafowl
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Keep an eye out for secondhand rotaries - there’s an 11 kW one near(ish) me for £1100 at the moment.
ajlelectronics
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Thank you. The compressor is this one: 3 phase compressor... And I have been starting it remotely with a power switch for convenience; the motor never stalls under the load.
Guineafowl
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I see your semicolon
That looks about the same size as mine, which runs quite happily with a TEC 2.2 kW single phase, two-cap motor. Might be an option.
Agroshield
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I was under the impression that something called an 'unloader valve' is available for a similar situation. It allows the motor and compressing bit to spin up to full speed before it starts squirting air into the tank. I guess it is similar in principle to a decompressor on a hand start diesel engine.
I wonder if something as simple as a solenoid valve on a timer would work. Vent the comporessor to atmosphere for five seconds after power is applied and then let the valve close.
I wonder if something as simple as a solenoid valve on a timer would work. Vent the comporessor to atmosphere for five seconds after power is applied and then let the valve close.
daleyd
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On a normal run of the mill compressor the unloader valve is usually part of the pressure cut out switch (i think) - and simply vents to atmosphere when the pressure switch kicks in (it’s the hiss you hear when the compressor cuts out on reaching pressure) but it only allows a very short start up time so probably not enough for a vfd to ramp up.
You could of course stick a solenoid in there and have it close only when the motor is up to speed, driven by a contact on the vfd, but that would be a bit more work than using the “standard” unloader valve.
The motor label states "thermal protect". If the motor overheats and activates the thermal reset, this could be an issue for the VFD as it would be seen as a disconnection of the running load. Maybe you'd need to disconnect the thermal reset mechanism and replace with a thermistor connected to the VFD?
Agroshield
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Your observation is good but perhaps the suggested 'replace' solution may not be required. The OP should examine exactly what the thermal protect actually does and how it is wired. If its normal state and its activated state are compatible with the VFD control logic, it can be plumbed directly into the VFD.
A pure guess is that the thermal protect would show continuity in normal operation and then would go open circuit on overheat. That would be a mode of operation compatible with a standard contactor.
If that is so, the thermal device can be wired in series with the VFD's stop circuit. It would act the same as a microswitch on a machine access door.
