Thermal Protection for Inverter duty motor

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jdub63

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I'm wiring a 5 HP 3 phase Black Max motor to a Hitachi WJ-200. The Black Max has two wires for Thermo-Protectors (P1 and P2). Based on my research, I think I can connect those leads to Terminal 5 (PTC) and Terminal P24 and once I update the option code to 19, the VFD will shutdown if the motor overheats.

Are my assumptions correct? I can't find any Black Max documentation on the Thermo-Protectors but when I check the ohms they are currently closed.
 
I don't have time to look up your motor datasheet and drive manual but I can say this: thermal protection in a motor can be a thermostat (thermal switch), PTC thermistor, or NTC thermistor. VFD input might be a digital input for thermostat, or an analog input for thermistor. You need to confirm what thermal device is in the motor and what kind of input the VFD has, and if they're compatible. You said it was "closed" according to DMM but was it just "low resistance?"
 
That's why I love this place, good job. :encourage:
 
The motor thermal switches are NC, they can either be wired to a VFD input to trigger a fault or through a low voltage relay that can act like an E-Stop. Some are thermistors (PTC) change resistance based on temperature. The VFD input terminal [5] has the ability to be a logical input, and to be an analog input for a thermistor device when PTC function (option code 19) is assigned to that terminal. That being the case, there is no need to use it for a manual lathe or mill, you will never come close to exceeding the thermal limits of the motor. If running in a continuous mode at high load like a CNC application then it would be warranted.

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mksj said:
There is no need to use it for a manual lathe or mill, you will never come close to exceeding the thermal limits of the motor. If running in a continuous mode at high load like a CNC application then it would be warranted.
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I don't think it's impossible to over-stress a motor on a manual machine but even if it is, that's not IMO a good reason to forego using provided Thermostats. An honest-to-goodness prolonged overexertion of the motor in the course of making chips isn't the only thing that can cause overheating. Ever seen how fast they let the smoke out when the rotor is locked or they get single phased?

Besides, black max is a TENV (totally enclosed, non-ventilated) motor. It has no cooling fan, so it plays by different rules. The I²R calculation is different for it. Some drives allow you to specify this in the parameters and it uses a different algorithm but I don't know if this hitachi is one of them. That's probably why they stuffed 3 Thermostats in it. Wouldn't hurt to utilize them.
 
If you speak to anybody that has used these types of motors in a manual machine in particular in a hobbyist setting, they never get past luke warm even under hard use and repeated stopping +/- DC injection. TENV motors are less prone to low speed cooling issues, and the level of DC injection is minimal if used. When is the last time you saw a factory installed VFD system on a 5 Hp and under mill or lathe have motors that use PTC's wired to the VFD? Sure you can possibly damage a motor from idiotic VFD settings, but I still feel It is not necessary in this application, basically wasted effort.
 
Since it seems I have both motor and VFD compatible, I'll take the suspenders and belt approach. But, if not, would the P1 and P2 leads just get taped off within the pecker head?

Thanks for the informative discussion.

Jdub
 
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