Engine/Transmission (1998.5 - 2002) Grid Heater, ideas for meltdown protection?

[David_VT]

(before you might get put off by my long winded post, please scroll down and look at the photos from another rig on this first page..... )

Hello,

It looks like I just lost one of my Intake manifold heater relays. (aka grid heater). The one relay failed closed, thereby sending the entire dual battery current to that one heater. I was lucky enough to be standing there so as to be able to disconnect it manually.



I was starting the truck this am and in mid crank the truck just died. I turned the key again and it acted like the dual battery pack was instantly dead... . For once I had the right train of thought and went directly to the intake heater assy first. Yep, hot and getting hotter by the second... . I could not remember where the power came from and wasted some time pulling the fuse box open and reading the inside cover... I quickly gave up there and unscrewed the very hot nuts and wires from the firewall side of the grid heaters... . The boot on one was already melting... .



As my wife was standing there to run errands, I just wrapped up the wires and had to put too tiny portable battery packs on to get the truck started. No shortage of warm air inside the intake manifold so it started quickly...



While waiting at a store for my wife I put the volt meter to the relays and discovered one was shorted closed with the truck off Again, full current power available at the heater end of that one cable with the truck 100% turned off, key in my pocket! I decided to reconnect the 'good' relay and it's one heater lead for now. When starting and driving, the amp gauge shows the correct pattern of cycle drains as expected.



After coming home I did the old TDR search and see some great ideas for how to control the heaters but did not find anything regarding how to 'safe' the shorting / overheating potential in this heater circuit.



Am I correct that there is no fusing or protection anywhere on the power side of this and thus no way to halt a runaway like mine?



So, I am looking for more ideas on how to make this a bit safer and to prevent me from being stranded somewhere.

I have a few ideas:

1. A fuse would be too simple but I suspect that sizing it large enough to allow the heaters to work normally would likely prevent it from protecting the circuit.
   
2. A simple battery disconnect switch in the feed side of the relays could halt the problem if one knows it is going on. The con is that you have to know the problem exists..... Surely you could use it seasonally but... .
   
3. A high current thermal snap switch that can carry the current that these heaters demand and would open if the horn is getting too hot. Does such a high current snap switch exist?
   
4. What about a large constant duty relay in the feed side before the oem relay pack that has a simple low current thermal snap switch mounted on the horn and is powered by the ignition...
   

Have any of our trucks actually been destroyed by a grid heater runaway?



I think that at 140K miles and being a 99, I'd be hard pressed to replace this truck on what my insurance company might come up with for a total loss fire. Besides I am kind of fond of the aging beast. .



Thanks for any ideas from the forum!



David



This thread is to inquire about how to make the high current grid heaters more protected from one or both of the power relays sticking closed. This thread is not meant to debate the pros and cons of the heaters or discuss oil switches , thermal controls or toggle switches which are all seemingly on the low current control side of things. I've done some thread searches this am and see some great stuff for the control side and some wonderful debates about the heaters themselves. Now please help me find what is out there for protecting the high current power side of things... thank you!!

 

[JTCash]

David,



Have you looked at the heaters to be sure they didn't melt into your intake?



R/



Jim

 

[David_VT]

I have not yet inspected them.



My feeling is that I got real lucky and broke the chain of destruction before the melting started. I found at least one thread that spoke of dramatic color changes to the horn from the run away. I did not see any of that but then again, at the worst point, it would have been a real challenge to hold my hand on that intake horn for very long.



Due to your input, I will make a point of taking the heater apart before putting power back to the element that overheated.



Thanks for the input!

 

[JTCash]

Cool, But I was thinking it would have been a good idea to look before starting the truck... Too late for that, but I'd check it before starting it again... I expect the grids are fine, but if even one piece goes through your engine it'll cost ya.



R/Jim

 

[Bob Wagner]

it also happened to a member of the nw bombers, the relay welded



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[David_VT]

HOLY COW! I would call that a dramatic color change... .

Thanks for the photos. This puts a little more meat to my curiousity regarding finding a safety device(s) to prevent this.



My damage is totally insignficant compared to that. I have one small gauge wire slightly melted which was laying an inch back from the terminal, across the heater power lead. I have one boot melted on the effected heater lead where it joined the heater terminal that I unscrewed to stop the melt down.

 

[David_VT]

Perhaps I should just find out how much the relay combo is and if affordable, wire in two sets in series as kind of a failsafe???

Anyone else?

 

[foolkiller]

holy cr@poly... ... . those pics scared me so bad i immediately diconected power from my grids!!!



thanks for the heads up guys.



is there a fix for this issue?



jeff

 

[David_VT]

I found a manual type high current switch for one of the ideas:

http://www.12voltguy.com/e-commerce-solutions-catalog.0.html5.0.html



Better yet,

I found a heavy duty relay which seems to fit the need.

http://www.12voltguy.com/catalog.0.html41.0.html



I would wire this relay between the battery and the grid heater ECM controlled relays. I would wire it constant on with ignition but would include some way to break the control side when runaway overtemp or manually desired... .

(work in progress, and still looking for ideas from the forum. . )

 

[Rman]

I've got delay switches here at work that I found. Varibale up to 10 seconds. If this switch sees certain voltage for up to 10 seconds it automatically disconnects. We use them as protection on certain circuits here. I think this would work well... However, the ones we use are rated for 10 amps. If you could find a 200A I think you got the problem solved. Do you know exactly how much these heaters draw? I've always heard in the hundreds, but never seen a proven number.

 

[David_VT]

I see the challenge as trying to put some protection in this circuit while trying to keep it simple, cost effective and reliable.



I believe I read in the 99 service manual that each heater gets fed with 95amps.



Your timer switch idea might work well on the control side of an additional relay installed before the OEM pair. Rather than sensing for thermal runaway, we just decide how long the high current should safely be available to the heaters and break the circuit after that time.

 

[Rman]

I agree, I counted this morning the heaters are only on for maybe 4 seconds a time while idling... . however, on cold days they do run for quite some time. Just an idea I had while thinking of a solution. If it's only 95 amps (which is a BOATLOAD in its on right) then it's much more managable. When you start talking high current 12V batteries you start talking welding steel real fast. Car batteries are designed to supply infinite current for short periods.



And to think years ago they were bickering about which voltage system to run... can you imagine DC in your house, truly a safety hazard. I still think they should switch to 220V circuits, I think 110 is run at too high of current... . another battle though.



I think a timed relay controlling the high current relay would work well.

 

[David_VT]

At -40F, I run the wait to start cycle twice before turning the engine over. It has never let me down. To that end, I know I have to have both heaters operational before next winter.

As long as the timer circuit resets when I cycle the ignition key, I imagine that something like 2x to 3x the wait to start cycle time will be enough to allow starting in severe cold weather. Naturally experimenting will tell if that is enough to prevent engine codes.....



Still looking for any other ideas for this protection device... . ???



ps: i see what you mean about battery current and welding:

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[David_VT]

I am now considering making something with some logic that will see the ECM signal to the heater relays and compare it to the high current output of the heater relays. When both the ECM signals says 'no heat' but at least one of the heater relays (in the OEM pack) is still outputing voltage, then interrupt the high current line.



if not(ECM1 and ECM2) and (RELAY1 or RELAY2) then interrupt...



The interrupt side is easy with a big constant duty relay on the ignition circuit. However making a cost effective and reliable detect circuit that will stand up to environmental issues is a bigger challenge...



To get started, I will likely get the 200amp relay installed before a new relay pack and fire the new relay off the ignition on circuit so that I can be more confident that there is no way the heaters can stay on if the truck is turned off. This is similiar to how some have protected their trailer power lead from draining the truck batteries when the truck is off.



Currently with one heater still connected, I am not getting any codes set and I am getting the benefit of a smooth start in the 20's(F).

 

[Rman]

Logic circuits are simple. If you just got a standard bread board and hard wired on the back, you could dip this in protective coating. Heat becomes an issue under the hood, maybe run it into the cab and just have the relays under hood? Are you still seeing 20F in the mornings? Must be colder in VT then I thought!

 

[nps]

I am now considering making something with some logic that will see the ECM signal to the heater relays and compare it to the high current output of the heater relays. When both the ECM signals says 'no heat' but at least one of the heater relays (in the OEM pack) is still outputing voltage, then interrupt the high current line.



if not(ECM1 and ECM2) and (RELAY1 or RELAY2) then interrupt...



The interrupt side is easy with a big constant duty relay on the ignition circuit. However making a cost effective and reliable detect circuit that will stand up to environmental issues is a bigger challenge...



To get started, I will likely get the 200amp relay installed before a new relay pack and fire the new relay off the ignition on circuit so that I can be more confident that there is no way the heaters can stay on if the truck is turned off. This is similiar to how some have protected their trailer power lead from draining the truck batteries when the truck is off.



Currently with one heater still connected, I am not getting any codes set and I am getting the benefit of a smooth start in the 20's(F).

Sounds kind of complicated, and at the end of the day you are still using a relay to protect the circuit - the same type of component that gave you the trouble in the first place.



If you are comfortable with relay protection, a simpler approach would be to put a second pair of factory relays in series with the current relays, and run the control wires in parallel. That way two relays would both have to fail in order to cause a problem.



You could check them every so often with a multimeter to see if the relays are stuck on, or alternately put a led under the hood or in the cab that illuminates when they are powered up.



Just a thought.

 

[David_VT]

I agree about using one relay to protect a second as not being a perfect solution.

I also have considered running dual OEM relay packs as you suggest and have not ruled that out as a KISS solution.

The logic idea kind of appeals to me simply as I am a gadget nut. However, the reliability and KISS thing keeps me from making a commitment thus far in that direction.

Please keep the ideas coming... .



While the run away heat issue is real, I can't ignore that the OEM pack did not fail me until recently (at 140K miles). These heaters have worked hard on this truck and cold winters have been a reality since the day I bought it. If the next OEM relay pack will get me to 280K, who am I to question the DC engineers... .



But then again, there is that cost of replacement vehicle vs cost of some electrical insurance so to speak... .



Oh well, I can just pull the power to the heaters for the summer and think about it while the weather is good... .



I remain interested in any other idea which are out there,

Thanks all!



It seemed to have fired the heaters while cranking, but perhaps it was just a fluke timing thing that is hardly repeatable.

 

[Vaughn MacKenzie]

David, seems I haven't seen ya posting on TDR in like forever, great to see you here



Another idea . . . might use a blade switch like used on batteries for the grid heater supply wiring which you could manually throw if all else fails. It would at least give you a bulletproof and reasonably fast way to definite current interruption.