Re: [CAD_CAM_EDM_DRO] I need a latching relay...or do I?

Yes, there is a much simpler way. All you need is a relay with two sets of
contacts..one N.O. & one N.C., the foot switch and two N.C. limit switches.

Wire the foot switch and one limit switch in series with the relay.

Wire the N.O. set of relay contacts in series with the Fwd solenoid.
Wire the N.C. set of contacts and the other limit switch in series with the Rev.
solenoid.

The system will operate as follows:
Depress the foot switch and the relay will energize. The N.O. contacts will
close energizing the Fwd solenoid while the N.C. contacts will open ensuring the
Rev. soleniod remains de-energized. When the ram stroke reaches its forward
limit, the limit switch will open and de-energize the relay. The Fwd solenoid
will de-energize while the Rev solenoid energizes causing the required reverse
motion.

When the ram reaches the reverse home postion , the extra limit switch will open
and cause the system to stop.

During any forward motion, the foot switch must be held down...a good safety
precaution in case you need an "instant reverse"

You can also put in an emergency stop button to cause all motion...forward and
reverse to cease.

Smoke

Smoke

> Group,
>
> I think I need a dual coil latching relay. Checked with Grainger and
> they don't have the 120V model I'd like so I need another source.
>
> Here's the project...I want to advance and retract a hydraulic ram
> with the motion initiated by momentary contact of a foot switch. My
> hydraulic pump has a 120V solenoid valve with two solenoids. Call
> them A for advance and R for retract.
>
> Hook the latching relay to A so it's latched on foot switch contact.
> The ram advances until it hits a limit switch which will un-latch
> coil and de-energize A, then ram motion will stop. The limit switch
> will be ganged with another one which will simultaneousy latch the
> the other relay coil controlling R which will cause the ram to begin
> retracting. When the ram retracts to it's start position it'll hit
> another limit switch which will un-latch the relay's R coil.
>
> Make sense? Seems simple enough or has anyone got a better idea?
> Part numbers for dual coil latching relays? Grainger has their own
> brand relays (around $12) so it may be less expensive to buy two of
> their single coil units instead of trying to get a more expensive one
> from someone like Potter-Brumfield.
>
> Thoughts?
>
> thanks,
>
> Doug
>
>
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