post flow for mig

[bearracecars]

has anyone modified a miller mig for post flow? if so how was it done and how was it wired in and on what machine?
thanks william haywood

[pulser]

Assuming your MIG has a gas solenoid valve that is activated by torch switch, you would just need to add a "delay-on-break" timed relay in the solenoid circuit so that when you turn off the gun, the relay to the solenoid remains latched for whatever time you have set. Relays are available in either 120VAC or 24VAC.

[awright]

Pulser is exactly correct.

Check out relay manufacturers SSAC, Potter and Brumfield, IDEC, Omron, and others. If your machine has contacts that drop out at the instant of release of the foot pedal or hand switch, you may be able to use one of the least expensive off-delay timer modules, the Dayton stock number 6A857 for $23.27 in the Grainger catalog (www.grainger.com).. Since this needs an external contact opening to initiate it's delay, you will have to check your machine's controls and be careful of creating an inadvertent short circuit.

The easiest function to use is the "Power Off Delay" (Function 10 in Grainger's), which senses shutting off of power to the controlled device and keeps power on for the set time. You don't need an external control contact for this device, but you do have to wire constant power to it. The devices mentioned above are 115 VAC. You can find 24 VAC devices easily, but will have to shop around.

Wiring is not complex. You will get wiring instructions with the relay.

One thing you might want to look for is remote time delay setting capability using an external potentiometer. The alternative is to mount the timer with built-in adjustment in an accessible location on the control panel so you can access the delay time adjustment pot or just resign yourself to having to open up the case to adjust the delay.

Since the valve solenoid is an inductor, you should put arc suppression across the valve wires to protect the relay contacts. Note that the relays are usually rated for resistive loads that do not produce voltage spikes when power is cut. Relays will typically work for a while, or even a long time, without suppression, but sooner or later will fail due to the high voltage spikes produced when the current through a coil is interrupted. The Grainger items 1A609 ($5.32 for 24 VAC) or the 1A610 ($4.81 for 120 VAC) look appropriate, but ask Grainger.

Have fun.

awright

[smithboy]

I have two dohickies wired in with a dial to adjust both pre and post flow on my old hobart hefty wire feeder. I got it that way, so I am not the one who wired it, but it doesnt look that complicated. It is a Very nice feature to have.

[bearracecars]

thanks guys
that is some awesome advice
william haywood:drinkup:

[smithboy]

If you are interested, I can take a snapshot or two to show how it's wired in my feeder...It may not help you directly, but it might make you more comfortable about the procedure.

[halbritt]

I'd be interested in a schematic for a pre and post flow meter. Though I suppose I could probably design one if I put my mind to it.

[bearracecars]

a snap shot would be great then i could have a visual in my head
thanks so much

[smithboy]

Here are some pictures of what are in one of my feeders. The base makes it look more complicated than it really is. I think there are only about 8 or 9 wires going to both the pre and post flow. I was going to trace the wires, but he installation prevents easy access to the board behind the plastic divider. The picture of the two timers have a phone number that you might call to get more info. You might even use the model number and ask if there is any documentation. These timers are varible...I think the pre and post are adjustable from a fraction of a second to about 4-5 seconds.

[bearracecars]

thanks for the photos those are the style that i was actually looking at thanks for your time also
william haywood