Posted by NCWayne on June 11, 2013 at 10:29:41 from (173.188.169.54):
Just read the posts so far, and thanks for the ideas. That said, unfortunately what I've read so far won't work in this application. So, here's a little more info for ya'll on what I'm dealing with.
The way I have it wired, the control circuit, (ie-power to all of the hydraulic solenoids, that control the functions) passes, in series, through several standard, red, labled, mushroom type emergency shutdown switchs. That being the case pushing any one of the switches immediately cuts power to the control circuit causing all of the solenoid valves to close and everything to stop immediately. Now even with all of the valves back in their neutral position, and the converyors, ripper tines, fluffer tines, etc all stopped, the engine is still running and powering the bailer. With the solenoid working the engine is also shutdown, when any of the buttons are hit causing EVERTHING to stop dead. Unfortunately, when they burn up the solenoid, the engine keeps on running and the only way to shut if down is to pull the shutdown lever manually.
As with most older diesels, the engine runs with absolutely no external electrical source applied. Granted I do have a 'engine safety system' on it that activates an alarm and lights for low oil, high water temp, etc. Other than the alternator, the starter, and power to the A/C compressor clutch, that's it as far as the engine itself goes in the way of electrical wiring.
That said, many engines have a fuel solenoid valve that powers up to either allow or stop the flow of fuel to the engine, but not an old two stroke Detroit. Some also have, push or pull type solenoids that are powered up to allow the engine to run or to stop it. Usually with those it's moving a lever on the injection pump and it doesn't take much force to do it. With an older Detroit you have to pull the shutdown lever, which is spring loaded. In turn it acts against the force of the governor, and pulls the rack to the no fuel position to shut it down. Once the solenoid is denergized the spring on the shutdown lever moves the rack back into the run position. The strength needed by the solenoid to overcome the forces of the governor and the spring on the lever, etc is high enough that there are solenoids designed specially for the Detroits. I tried the strongest, 'off the shelf' solenoid I could find (was nearly $150) and it burned up in about 10 days of normal use (ie no accidental button hits). The only ones I've found that will do the job reliably, and consistently, are those made specifically for the Detroits, so that is the solenoid I'm using. In fact a Detroit uses the same shutdown solenoid for the regular fuel shutoff as it does for the true Emergency shutdown that pulls the lock that allows the air intake flap to close. In either case the solenoid has to be energized to pull for the engine to shutdown. Due to the way it's wound to obtain the strengh needed to do the job, the duty cycle on them is extreemly low.
In this application the engine is shutdown by activating the solenoid to pull the rack and shut off the fuel. Regardless of wether the operator does it from the cab or wether a worker does it from the end of the prep table 30 feet away, or the head of the baler 15 feet away, the end result is the same. The only difference is when the operator does it from the cab, with the regular 'off switch' the control circuit isn't cut first shutting off hydaulic solenoids. However the operator also has a mushroom style Emergency stop switch that shuts off everything just as all of the others do, just in case he sees someone in an unsafe situation and they can't hit a button themselves.
To go a bit more in depth, the control circuit is wired using standard NC emergency stop switches to break the control circuit. With the button is pressed, and the circuit broken, everything hydraulically driven stops. Along with shutting down the hydraulic solenoids, a continuious duty, NC relay, that is being held in the open position by power from the control circuit then returns to it's NC state. Upon closing, the contacts supply non-switched battery power to the shutdown solenoid on the engine. The way it's wired, even if the operator turned the key switch off (it does nothing but supply power to start the engine), the solenoid on the engine would still energize by pushing any of the Emergency stop buttons, or the regular stop switch in the cab. I did this as a fail safe because even thoug shutting down the engine doesn't cause any of the hydraulic solenoids to close, but it does stop the hydraulic pump stopping the flow, and equipment operation that way. With the baler and pump both pulling on the engine shutdown from wide open to stop doesn't take but a few seconds. So, even in a worst case, everything screws up scenerio the whole machine will stop by stopping the engine.
This whole deal wasn't really that bad getting everything to work together like it needed to, and it actually works as designed. The only thing I didn't anticipate, and should have given the operational conditions, was the solenoid burning up because of 'operator error'. Now if it was just a matter of a true emergency happening and the solenoid burning up because it was used, that would be perfectly acceptible. The way I see it, the cost of a solenoid is small compared to the cost of an injury. Unfortunately the only way to really keep it safe and be able to shut down the engine when something happens is to install some sort of timing device to keep the solenoid from being toasted by someone being careless and hitting an emergency stop switch when it's not a true emergency. As it is everything in the system is shutting down perfectly, except the engine, which powers the baler through a pto. Now I've got to make it as safe as humanly possible by getting the engine to shutdown at the same time as everything else...without toasting a $100 solenoid every time one of the guys accidentally leans his pitch fork against one of the buttons, shuts things down, and then takes ten minutes to figue out that his pitchfork was what caused things to come to a screaching halt and reset the button.
I've been researching things a little more and I think what I need is an interval timer. The way I read it, signal power is supplied, the contacts shift sending power to the load (the solenoid) for a set period of time. The contacts then time out and reset to their origional positions, regardless of wether the signal is removed or not. Once the signal is removed the cycle resets and application of a signal shifts the contacts sending power to the load until they time out.....and on, and on. I think this is what I need to mak this work. Once again, any ideas or advice would be greatly appreciated.
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