Relay Timing Circuit

[Sparkz]

1.) Power is applied.
2.) Relay A energized for 1 min. then drops.
3.) 5 sec. delay.
4.) Relay B energized for 30 sec. then drops.
5.) 5 sec. delay.
6.) Back to line 2.
The cycle repeats until power is removed from the circuit.
All three time periods are independantly adjustable.
Perhaps this might reduce the number of components required

Hi Ralph,

So my guess is you want to 'do something else' during the 5 second delays besides decelerating, right?

You would need 4 timers (edit: all "delay on operate"), all cascaded, where timer #4 (= '5.) 5 sec. delay') deenergizes timer #1 (= '2.) 1 min.').

Use a NC contact of timer #1 to activate the FWD input.

edit: DISREGARD the following:
Use a NO contact of timers #1, #2 and #3, all in series with a NC contact of timer #4 to activate the REV input.

edit: NEW INFO:
Use a NO contact of timers #1, #2 in series with a NC contact of timer #3 to activate the REV input.

 

[Sparkz]

OK, so now I missed your post!

Sparkz,
Thanks for the suggestions. I didn't see your post until after I made my last one.
Again, for requirements not previously listed, I need this discrete timer circuit.
I'm using the drive's only built-in relay contacts to signal when the motor is at the commanded speed.
Another one of my reasons for the 5 sec. delay period is to prevent drive shut down when FWD/REV commands might appear at the same time.
Best regards

But that's exactly the beauty of a VFD! You can have both inputs FWD & REV activated without the VFD tripping! So it's definitely OK to deactivate the FWD input and at the same time activate the REV input without ANY issues. Like I mentioned before, the VFD WILL perform a deceleration FIRST before reversing.

 

[krk]

Here's a quick sketch of a relay circuit that will function as you described.

You'll need timer relays with both delay-on & instantaneous contacts.

Sorry about the euro symbols, I'm not that familiar with the US versions...


Kevin H

 

[kittydog42]

A lot of drives have programmable relays. If you were creative, you could use two of those relays with the on/off dealy functions to control the direction continuously. I usually control those relays vis modbus to control the start/stop of the drive, because that way I can use the N.C. pole and have a fail to run situation when the communication is severed.

 

[Sparkz]

You could try this one if you really need the extra 5 second intervals:

Set timers: KT1 = 60s / KT2 = 5s / KT3 = 30s / KT4 = 5s

Can I make a small suggestion? Use 24Vdc timers in stead of the 120Vac types. Nearly all available VFDs are equipped with 24Vdc inputs. This way you can connect KT1-16 and KT3-16 directly to the VFDs FWD & REV inputs, without the need of auxiliary contacts!

BTW, please don't tell me I just made your homework assignment!

 

[krk]

Sparkz,

Your circuit will cascade & cycle OK...but Ralph wanted the 60s & 30s timed elements to 'drop out' after their time had elapsed.

The circuit I posted isn't that great either...I ommitted to use 'early make' & 'late break' contact symbols on the instantaneous contacts of KA3 & KA4 to prevent a 'race' (without this the circuit may 'chatter' depending on the relay characteristics)

This kind of thing makes me realise how much we take PLC's for granted nowadays.....

 

[Sparkz]

...but Ralph wanted the 60s & 30s timed elements to 'drop out' after their time had elapsed.

Hi Krk,

Not really sure what you mean by 'drop out'...

Contact KT1-16 is active (= carrying 24Vdc) ONLY while KT1 has not elapsed;
Contact KT3-16 is active ONLY while KT1 & KT2 have elapsed AND while KT3 has not elapsed.
As soon as KT4 has elapsed all timers are reset by momentarily opening KT4-18, so the entire cycle starts all over again.

Or do you mean (old) mechanical timers that HAVE to be deenergized if their time has elapsed?

 

[rmarotta]

> "This kind of thing makes me realise how much we take PLC's for granted nowadays....."

KRK,
I totally agree.

Guys,
Let me put a few other concerns to rest:
The VFD (AB Cat.# 160BA) being used is to replace a failed reversing contactor & soft starter. Relays & timers are also older Allen Bradley components that are on hand.
(Plenty of 700-HA32A1's, 2 HRM12AT17's & 2 FEA1SU22's.)
My customer lost the original PLC program, so now wants something he can work on to fall back on......
Sparkz, see, it's not homework....

Thanks again for looking at my mess.
Ralph

 

[Lancie1]

Ralph,

If you must stay with relay-type timers, then you can replace your whole she-bang with one Eagle Signal Type MP Stepswitch. This is a timer with built-in cam-operated switch contacts. You would need to select a 60 to 180 second timer range, with at least 4 outputs. These cam switches come in a variety of configurations with different numbers of switches and different timer ranges. The switch contacts can be made to go on/off at any point in the cycle by adjusting the cams. Eagle Signal also has other cheaper options. See this link:

http://www.eagle-signal.com/accessories.aspx?sPartNumber=MP&sType=Partial

 

[Sparkz]

...The VFD (AB Cat.# 160BA) being used is to replace a failed reversing contactor & soft starter. Relays & timers are also older Allen Bradley components that are on hand.
(Plenty of 700-HA32A1's, 2 HRM12AT17's & 2 FEA1SU22's.)...

Bummer!

According to the specs, the 160BA only has START, STOP & FWD/REV inputs! And they expect you to buy an optional 24V interface module if you want to get rid of the silly 12V interface! What a load of ****! Sorry, but I had no idea these VFDs were still available.

There are also some issues with the available timers:
1. The mechanical, motorized HRM12AT17 timer relays will need more than a momentarily power interrupt to fully reset. Now I see why krk suggested the rather complicated sketch: It can deal with the shortcomings of this type of timers. My apologies, krk!
2. A 700-FEA1SU22 timer relay only has a NO contact; you would have to add an extra 700-HA32A1 to get the same output, so try to get a hold on the 700-FEA3TU23 type. It has an SPDT contact instead.

But I'm still wondering what would happen if the FWD/REV input changes while the START input is active... I couldn't find any detailed specs...

No offense, but after checking your available material, the other suggestions posted here start to make sense...

 

[CaseyK]

Poll anyone?


Relays and Timers vs. PLC!

 

[Lancie1]

I vote for using a small cheap programmable relay, but that probably won't hold any sway over Ralph's customer....