Can I use two temp guages on one engine temp sensor?

[happycamperbrat]

Sean I intend on wiring my coach almost identical to yours and using your many informative articles, posts, pictures, drawings on your website, etc. as my instructions and plans. However, I really dont like the automatic shut down of anything (other then if I am going to blow up my engine because of overheating and even then I want the option to override that if need be). John's idea of the alarm and lights is right on as far as I am concerned because I only use the gages for mostly troubleshooting or monitering if I know there is a problem, otherwise I am just blissfully driving along happy as a lark but keeping a closer eye on my speedometer "especially" if I see a black and white

[Sean]

... I really dont like the automatic shut down of anything ...

Well, generator manufacturers have been using safety shutdowns for years for good reason.

The day WILL come when you are running the generator out of sight and earshot of any sort of alarm, or out of reach of the kill switch.  Perhaps you'll be sound asleep, with the air conditioner running.  Or you'll be outside, gathering firewood, checking out the swimming hole, or even driving back to the park entrance to pay for your site.  Maybe you'll be working on the roof with a power tool.

Generators are (and should be) designed to run unattended.  By contrast, a main engine is far less likely to be running when you are out of the driver's seat and away from the kill switch.  Even then, most heavy diesels have safety shutdowns, which must be deliberately over-ridden with a dead-man switch to keep the engine running.

If I turn the cooling fan off on my generator while it's under load, it will shut down within 30 seconds.  The time between when an alarm could sound and the engine would be damaged would be even less -- maybe 15 seconds or so.  To keep a generator safe with an alarm-only system, you'd have to be within 5-10 seconds of the kill switch at all times.  For low oil pressure, you'd have even less time, perhaps a second at most.

I do not know of any reputable genset manufacturer that does not included these two basic shutdowns.  But many of us are getting used generators that may have been subject to amateur modifications, and some folks are putting one together from component parts, and these safety shutdowns are a critical part of any generator that needs to be paid attention to.

FWIW.

-Sean
http://OurOdyssey.BlogSpot.com

[Sean]

Sorry, missed this one while I was off line (long story):

... I now think I over reacted and extend the apology you deserve.  ...

Not necessary, really.  I recognize that this is a flat medium -- tone and inflection do not come across -- and it is all too easy to misinterpret the tone of written words.  One of my faults is that I write in the technical style of an engineering manual, and I tend not to "hear" all the ways in which the inflection might be misconstrued.

... I have always used a single wire sender where the sender was NO and went to ground.  That design, one that predominates in the industry, is deficient in that a broken wire defeats the alarm. a ground, on the other hand, will alert you to the circuit failure.  I incorporated a Bosh 30 amp relay(for overkill) into my circuit so I got the two wire system but only ran one wire into the engine bay. ...

The reason why grounding-type senders should not be used for the safety shutdown circuit is that they can not be made fail-safe.  By this I mean a loss of electrical power to the sender circuit or a broken wire should cause an immediate shutdown.  You might be able to do this with an oil pressure switch, if you got one that was NO, and it was the final completion of the Run circuit.  But a temperature switch is more problematic, because you now need to open the circuit in the middle.  So you need at least one two-wire sender.

While I agree with you in principle that an alarm/light circuit is nice to have, in practice, the set-point of the alarm circuit would either have to be so far from the set-points of the safety shutdowns as to be a source of nuisance alarms, or else they'd be so close together that the delta between alarm and shutdown would be milliseconds, rending the alarm circuit useless.

The more important issue, though, is the limited placement of temperature senders.  While oil pressure can simply be manifolded from the existing pressure sender port and will work fine, proper temperature senders actually protrude into the coolant flow.  You can't simply extend an existing sender location with a tee and gang more than one sender, because they will not be getting the correct readings.

If your engine has a single temperature sender port, my advice would be to use that port for the safety shutdown sender, which will be two-wire NC.  And if it has two ports, then the second one would be used for the gauge(s) that started this whole thread.   If two gauges are needed, then a dual sender is called for, again because there is no good way to add another sender.

If two gauges are not needed, there are senders that have dual terminals, one for a gauge, and one for a grounding-type alarm circuit.  These senders are commonly sold for applications where a simple idiot light is being replaced by a gauge/light combination, or where the user wants a gauge but the ECM requires the switch.  This could be used to implement a tell-tale alarm, but, again, the setpoint would likely be so close to that of the safety as to be nearly useless.

I have never seen a sender that has both a two-wire NC switch as well as a gauge output.  Nor have I ever seen a sender that has both a dual gauge output and a grounding switch.  Not that those things could not exist, but the market would be very small, and these are mass-quantity items.

FWIW, and speaking as I was about "amateur modifications," when I got my bus the generator in it had been modified either by the PO or by the crappy outfit that converted it (long since defunct, for good reason) with a tee into which the original safety sender and a gauge sender had been threaded.  As a consequence, neither sender was in the coolant flow and they were both getting lower temperature than actual.  They had two different gauges with two senders which never agreed, and lord knows whether the shutdown switch could even have been effective if needed.  To make matters worse, the shutdown mechanism they had cobbled together was power-to-shutdown, meaning that an electrical failure would prevent the generator from being shut down at all (whether with the control switch or by the safety shutdowns).  We ended up putting all new safeties and gauges on it, rewiring everything, and putting a proper power-to-hold run solenoid in.

I hope that clarifies a bit more why I recommend focusing on a properly configured (and tested) safety shutdown system rather than adding a tell-tale alarm.  Doing both correctly may be difficult if not impossible depending on engine configuration.

-Sean
http://OurOdyssey.BlogSpot.com

[JohnEd]

Brat,

I remember a lot of discussion about auto shutdown here.  Must be an hour or so of speed reading.  Lots of different opinions and a host of options.

We are kindred spirits on the issue of getting a gauge in front of you for everything.  They are most applicable for troubleshooting and for spotting trends.  To expand on that I think you need a gauge at the device and in the cockpit.  Solely because you "troubleshoot" at the device, also.  Back in the day, we Triumph pilots were well aware that there was no incident in recorded history of anyone looking at a gauge when it went to peg.  We all installed idiot light senders and audibles.  Race cars have this feature.  What  are we talking....water temp, oil pressure, volts and current.  I don't think the alarm circuit is as justified at the gen cause you are in there.  BUT, all of these are just the addition of a wire mainly.  I wouldn't mess with the OEM protection circuits unless you are driven to that and even then I would get a lot of advice.  I have no difficultywith imagining myself looking at the temp gauge and pondering ..."that is 10 degrees hotter than it usually runs....hummmmmm".

I don't like the auto shutdown except to protective from an idiot that is running my engine independent of my supervision.  And you can dream up any circumstance you wish.  An "over ride"....certainly...as long as it isn't labeled as such.

I remember hearing that the DDEC III had a auto shutdown AND a alarm that "sounded" a few degrees from shutdown.  Also, that the shutdown came 20 seconds after the shutdown alarm, not the "caution-hi temp"alarm, sounded.  That sounded a bit much to me but why not,  if you have the computer and sensors do everything you can to make life safe and easy.  Admittedly, I don't have all the facts, or even a portion, but that was discussed as a reality of some ECU or a possibility.  And just what flexibility does Silver Leaf give you in the alarm dept?  

If you get an alarm before b"terminal" temp is reached you can reduce speed and drop a ear to see if you an maintain.  You get some time from a well designed system.  Normal is 180 to 185 on a hill.  205(?) is getting to the damage temp and 212(?) equals cracked heads and other stuff.  A couple thousand pounds of cast iron doesn't go up 8 degrees instantly or in 30 seconds so a alarm before shut down is use full and allows you time to take action and analyze the results.  Whether the alarm is selected for 190 or 195 or 200 is a choice that will be driven by the normals for your particular system.

John