Legacy Elevator VFD upgrade with KEB F5 Inverter
In the elevator industry the implementation of variable frequency drives for the control of AC motors didn’t really begin until the late 1980’s, but over the course of the next 20 or so years AC motors as well as VVVF drives began to rapidly replace their DC counterparts. Generally, these drives have a usable life of about 10 to 15 years before they require replacement.
Unfortunately, direct replacement of the original drive is sometimes not possible because companies that previously manufactured the drives have either gone out of business or ceased production of that particular unit. Older elevator drive manufacturers Baldor, SWEO, and Unico come to mind.
This can be a serious problem because changing drives often introduces a hefty cost to engineer the controller to accommodate a different layout of inputs. Luckily, with the new v3.21 US Lift software for the KEB F5 it is possible to completely customize the input layout of the drive to allow it to match the operation of many older generation drives such as the Baldor/SWEO 18H or Yaskawa F7.
This can be done by using the Li16 parameter. It allows a custom input logic table to be defined for binary speed control mode, US04 Control Type = Binary Speed Selection (1). To select this function, set Li03 Speed Input Decoding = Decode with Li16.
Speeds are assigned the following values:
Li16 is 7 digits, populated one digit at a time with the above values to create the decoding. The first, right-most digit corresponds to binary 001 and the seventh, left-most digit corresponds to binary 111 where I8>…>I1. Zero speed is fixed with binary 000.
As an example we can imagine a three input, binary encoded drive setup that allows 5 speeds (5 speeds is generally all that is required for a drive crossover, however the F5 is capable of up to 7 total speeds). These speeds correspond to the input conditions that can be seen in the table below.
These inputs do not correspond to the encoding normally used by the F5 but using Li16 we are able to match it so a direct replacement of the outdated drive can be made.
Assuming we will be mapping I3, I2, and I1 to I4, I3, and I2 respectively on the F5 then we would configure Li16 as follows:
|I4||I3||I2||Speed||Li16 Digit||Li16 Value|
The table shows that entering a value of 0x0028CA6 into Li16 would give us the proper binary input logic table to make a direct crossover from the old drive to a new KEB F5.
The F5 is also capable of using both PNP and NPN input logic. While this is irrelevant if the inputs are switched using the drive supply, it is very useful if an external supply is used for input switching.
Although conversion kits for these types of crossovers can be found, they usually cost a premium. Luckily the same thing can be accomplished by simply adjusting Li16. This can save you money and also much of the headache that comes with having to upgrade an obsolete drive.
Do you want to discuss retrofitting an old elevator drive? Talk to a KEB elevator application engineer and they can help you find a way to make the F5 work for you.
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