Initial Sanity Check
As a sanity check, I verified the connectivity of all 9 leads (as they are labelled on the wires themselves, T1
-T9
):
$$\begin{array}{c|cccccccccc|}
& T1 & T2 & T3 & T4 & T5 & T6 & T7 & T8 & T9 \\ \hline
T1 & - \\
T2 & 0 & - \\
T3 & 0 & 0 & - \\
T4 & 1 & 0 & 0 & - \\
T5 & 0 & 1 & 0 & 0 & - \\
T6 & 0 & 0 & 1 & 0 & 0 & - \\
T7 & 0 & 0 & 0 & 0 & 0 & 0 & - \\
T8 & 0 & 0 & 0 & 0 & 0 & 0 & 1 & - \\
T9 & 0 & 0 & 0 & 0 & 0 & 0 & 1 & 1 & -\\
\end{array}$$
This is expected for a Y-configuration motor: 3 pairs with exclusive connectivity, and one group of 3 with exclusive connectivity. That means T7
, T8
, and T9
can keep their existing labels (i.e. no matter what combination is used, those 3 labels belong on those 3 leads so we might as well leave them alone).
Preparing for Trial and Error
The next thing I needed to work out was the polarity of the other 3 windings. Lacking an analog voltmeter to attempt the method described here (listed under "I have lost track of the leads of a nine lead three phase motor. How can I re-identify these leads?"), I decided to puzzle it out through trial and error.
Note: all indications found online suggest this is a bad idea, and can cause you to burn out your motor. I relied on the current-limiting feature of the VFD to protect my equipment, and this may not be appropriate for your application.
The first step of trial and error is to get a baseline understanding of what the motor would sound like with only 3 windings working properly -- because that would indicate success.
The T7
, T8
, and T9
leads are perfect for this. I simply lowered the maximum current on the VFD to 1.6A (half the rated current for low voltage mode, presumably the rated current for each individual winding) and connected the VFD's 1
, 2
, and 3
terminals to T7
, T8
, and T9
(all other leads were disconnected and isolated). With the VFD at 5Hz, the motor ran with a slight amount of bumpiness but did not trigger the over-current protection and did not allow its rotation to be reversed.
Trial and Error part 1
The next step was to sort out the polarities of the 3 individual windings. This method can group the polarities of the T1
-T6
wires into 2 groups of 3, although it won't tell you which group was positive or negative.
Essentially, I am recreating the configuration that I used in my baseline test, but with the other 3 windings. I took one wire from each of the T1
/T4
, T2/T5
and T3/T6
pairs and shorted them together (e.g. T1
, T5
, T3
) and connected the other 3 leads to the VFD's terminals. I turned on the motor at 5Hz on the VFD; if it ran more roughly than the baseline (or had one of the obvious symptoms noted earlier), I turned it off and wired up the next combination of positive and negative leads.
Note: if the motor runs in reverse, but seems fine in every other respect, you are ready to go on to the next section.
At the end of this experimentation, I was left with a configuration where the motor ran like it did in the baseline test. This gave me 2 groups of 3 leads (the shorted ones, and the ones connected to the VFD).
Trial and Error part 2
There are now only 12 possibilities left to check. The 3 windings need to be properly matched to their T7
, T8
, and T9
counterparts (6 combinations), but the groupings discovered in the previous section might be reversed.
I left group of 3 shorted leads alone, connected T7
, T8
, and T9
to the VFD's terminals, and disconnected all the T1
-T6
leads. Then I chose one of the disconnected leads and connected it to T7
. If the motor appeared to fight itself, I connected the lead to T8
, and so on. I connected the remaining loose wires in this way.
If there appears to be no solution, then it's time to disconnect all of the T1
-T6
leads from the VFD, swap that entire group with the group of 3 shorted T1
-T6
leads, and start this section over again.
But for me, I found a solution and the motor started running smoothly.
Finishing up
Fix your labels and raise the current limit on the VFD back to what it should be.