PowerFlex 40 and Relay Logic

I need some advice on a problem I have. I will like to know if this is even possible.

I have a motor that I will like to control the speed on it, with three different preset speeds using a PowerFlex40.

The kicker is that I want to use relay logic to do this task. I don't want to put any PLC controls on this machine because due to its age, the chances of getting the equipment replace are fairly high.

I was looking at parameters A50, A51, and A52 to be the three 24Vdc inputs that will trigger the three preset speeds.

I'm planning on using switches to set each of the three digital inputs to change the speed on the motor.

I don't see why not I am not sure on the actual inputs you need to use or their coresponding parameters, but the vfd souldn't care where the signal comes from whether a plc or relay logic.

If you're talking about manual switches, I would recommend using a single three-position switch. No relays required. This would eliminate the possibility of someone flipping on two or all three of the inputs at once. Not sure what the PF40 would do in that case.

cbuysse said:

If you're talking about manual switches, I would recommend using a single three-position switch. No relays required. This would eliminate the possibility of someone flipping on two or all three of the inputs at once. Not sure what the PF40 would do in that case.

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That's right,The highest speed maybe executed when more than one speed control teminal is activated.

Note the table for parameters A70 through A77. The three input points select from up to 8 preset speeds depending on the combination of inputs which are on.

This motor drives an assembly that performs a swepping motion. The switches I'm refering to are going to be "Limit Switches" to hopefully set various speeds for forward and reverse.

JoseM said:

This motor drives an assembly that performs a swepping motion. The switches I'm refering to are going to be "Limit Switches" to hopefully set various speeds for forward and reverse.

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You may need to have some relay logic to seal in those inputs when the sweeper moves off the end limits.

The preset inputs will create a bcd word, which will select your preset. Two inputs will give you 4 speeds. Normally 0 is your default referance (HIM/Analog Input) I would set this up as your fast speed adjustment. If both inputs are on, then you will be running on preset 3. Even if you do not plan on using this, you may want to copy your slowest referance to this address, in case a switch or relay sticks. I've been caught before on a drive that would not run, and it had a zero speed reference. This should be fairly simple to do with relays (or directly from the switches); However, if you get very many relays or too much wiring, it may be more cost effective with a small PLC / smart relay. Not to mention easier if you need to modify it in the future, for more speeds.

Brijm said:

However, if you get very many relays or too much wiring, it may be more cost effective with a small PLC / smart relay. Not to mention easier if you need to modify it in the future, for more speeds.

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i agree. when i was younger in the trade, and didnt know much about plcs, and thus i stuck to relays. then when they changed things i had to rewire or add more relays, etc. long story short, i realize now that i would have been better off with a smart relay/ microplc

JoseM said:

The kicker is that I want to use relay logic to do this task. I don't want to put any PLC controls on this machine because due to its age, the chances of getting the equipment replace are fairly high.

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if you are refering to replacing the drive with a new one, well then a microplc/ smart relay would be better for you, to adapt to the new drive. if however you are refering to the equipment that it drives being replaced, well how are you going to control the new equipment? the microplc saves the day again? possibly.

of course, convincing your boss to spend the extra money isnt always as easy as that. haha. good luck.

Since there are three inputs to control, and three speeds desired, it seems a natural to use the switches directly. That's assuming that no latching is required, as OkiePC mentions.

To avoid some of the problems with multiple switches creating higher dangerous speeds, set speed 1 as the slowest speed, set speed 2 as the middle speed, set speed 3 (the combination of 1 and 2) at the same speed as speed 2, set speed 4 and all higher numbered speeds for the fastest speed. That way, you cannot get any combination of switch closures that will exceed the highest speed setting.