Hot plate problems.

One thing that I have found before is the fuse holder if it is not clipped tight to the fuse. The loose end heats up and instead of actually blowing the fuse it melts the solder that retains it. Pull a blown fuse apart and check that its blown from over current.

Another thought is the power company maybe dropping the voltage intermittently to handle the load in hot weather that may be causing it. You did not say how long this has going on.

The problem started occurring around the end of April. We only use the device about once to three time a month and it usually runs for about 1-3 days at a time for about 18-20 hours a day when in use.

The last time we used it was about 2 weeks ago and it ran up until Friday of last week. When it got started up today the same thing happened. The examination of the last fuse was that it was blown that was a tr30 fuse. I have checked out the holders and they have a pretty good grip on the fuse. Very difficult to remove and the fuse shows no signs of arcing.

The fuse was however very hot as if it was running that way for an extended period of time which may have fatigued it.

It may be possible that one of the heating elements is shorting to ground somewhere close to the middle of the element. This could cause one leg to draw more current than the other, which normally would not be the case. It is possible that the short exists while the machine is in a cooler state. I read that you checked the resistance of the elements, but did you check for resistance to ground through the elements while the machine is cool, then again when hot?

It sounds like the overload is such that it takes a bit of time before it blows the fuse. The only other thing I could suggest is monitoring the current through the fuse as you start the machine (or any other condition that leads to the fuse blowing). Another way to check for possible ground faulting conditions is to measure both of the incoming power lines with a clamp-on amp meter at the same time. Under normal conditions, the currents would cancel showing a zero reading. A reading of anything beyond that would indicate the current is finding a ground path.

Swapping out the loads on the solid state switches to see if the fuse blowing will change location will eliminate a faulting switch.

Are these cartridge heaters?

There are 4 cartridge heater that are made into the plate yes.

I have just completed testing on all the heaters per the OEM tech's instructions and they are all confirmed to be good.

I have however just completed a test on the supply transformer that may prove to be the problem. I get a .9 ΜΩ reading from line to earth and a 1.0 Ω from line to line.

I don't know if this is where the problem is for sure or not but as it is getting out of my realm I have done as suggested to many other in the past and called the electrician to have him check it out. Best to have someone more informed to look at it than risk my own skin.

I will update you when I have more information.

Here are a few possibilities:

The heater coil is dirty, or operating slightly out of specifications. Clean the coil, compare the resistance to the other coils. If the resistance is lower by 20% or more replace the coil.

The biggest problem that I have seen with time delay fuses is that they typically get replaced with a fuse with a different time delay. Try swapping the fuse to a working leg. If the problem moves, replace the fuse with one exactly the same as the working leg.

After a fuse blows, it will always be hot.

I swapped the legs and the same leg continued to blow.

The heaters ar of a cartridge type and are sealed in the hot plate.

The fuses are the ones that the manufacturer suggests to use.

The manufacturer is as confused about this as I am.

I am getting ready to do a est on the individual heaters to check and see if they are reading the same as they were when they left the manufacturer.

Could be the relays. Can you check the peak current when turned on for all legs. Are they SCR or hard contact.

The relays are solid state.

Have you been monitoring the voltage? Perhaps it is seeing over voltage. If it is fused on the edge of what it can handle and sees over voltage then you will be blowing fuses.

I design heating elements for presses so I often see these sorts of questions.

If you have measured the resistance of the element and it seems ok that does not neccesarily mean that all is ok with the element. Have you measured resistance on the element when both hot and cold. The resistance should be slightly higher at temperature.

Have you used any thermal imaging on the press on heat up to determine where the cold areas are? On a manufacturing press that is on most of the day or all day you will eventually see some equalization in temperature even with a partially failed element.

Does the platen have insert elements or a blanket type element? Edit: sorry i see you have cartridges. The comments bleow have no bearing.

Typically blanket type silicone elements will have more then just one coil in it and it is often possible for the element to continue functioning at a reduced capacity even with 1 of its legs not working properly. I have also seen blanket elements give resistance readings that were close enough to their designed spec that we did not assume there was anything wrong with them ... until they were removed and upon visual inspection found an area burned out. Some how the carbon trail left behind as the element consumed itself was giving a resistance close to what was expected.

Is the resistance values across all legs similar? Perhaps it is unbalanced?

Good luck in figuring it out.

I appreciate the input. I have not seen any over voltage situation on the plate as yet.

I read that you switched legs and it is following the leg?

If it is the same leg that continues to blow and everything else looks good, I'd trace back and look for corroded connections, damaged wiring or anything else that could be adding that extra bit of resistance. Any of the hook up wire looking heat stressed?

Do you have seperate controllers for the cartridges, or are they ran off of a single controller? Is the RTD probe (or whatever you are using to relay temperature to the controller) reading correctly?

GL.

Good morning!

I would check and verify the power relays/contactors are not cycling on and off too quickly as the extended "in-rush" current during these conditions can cause the fuse(s) to fail.

Make sure the time delay curve on the fuse element you are using matches the load demand requirements per OEM specs.(direct replacement)

Verify the magnitude of the supply voltage is not greater than the machine rating.

If your heater elements are immersion type and are of the calcium filled composition, you may have a rupture in the element wall or a bad seal at the connection end allowing moisture impingement and accumulation inside of the element. This can create a high-resistance parallel path for the voltage to flow to ground with enough force to fail the fuse feeding that element. As the calcium drys out due to the moisture being evaporated, the leakage current is reduced and the total current demand is lowered. This is common with equipment that is only occasionally used. Some sites apply reduced voltage during off-line periods of time to keep this from happening but in my opinion it is best to replace the element if this condition exists.

If you are only using a meter to check/take resistance readings to ground, you are only applying a maximum of 9 volts DC to the device which is not enough to properly detect and identify a high resistance gound in a 240/480 or higher voltage rated circuit. Instead use a 500 volt (meggar) insulation resistance test meter and apply the rated voltage for your test.

On the transformer readings: A .9 MegOhms to ground on a 600 volt rated device is acceptable especially in high-moisture environments. The 1 ohm reading betwen the phases is also normal as you are reading the transformer winding impedance which is dynamic (changes with load). Checking a transformer or motor with a VOM is useful but not very accurate or dependable. It will detect "solid" low-resistance grounds but the VOM cannot check for phase-to-phase faults with any accuracy. Instead you need a TTR (Turn-to-Turn Ratio) meter/tester to properly test a transformer and/or a DOBLE type machine.

Good luck!

Thanks for all the good ad vice and information. I have recently had the transformer and system looked at by an electrician.

Now there are 2 of us here scratching our heads and wondering what the heck is going on.

I am not completely sure of the specific type of heater I will try to get that information. However the plate itself is not being immersed in any type of liquid and it operates at about 360° in a climate controlled environment where we maintain the humidity at about 36% at a temp of 72°

I will look at the settings for the control to see if there is an inrush problem. I did not see it or notice it when I was monitoring the current for flux but again not sure if it is indicative of the problem.

I am using a Fluke 26III true rms multimeter to do the testing currently. If you have any suggestions on specific settings that might help point out the problem with it please let me know. I am looking for a place near me that might rent a trending meter to hook up to it and look for faults. I will also see if they can rent a Meggar there as well.

For now I guess it's back to the OEM for more information on the system itself.

I will get back to you with more info as it comes available. If a solution presents itself I will post it here.

Macarroonii! All advicements do make a lot of senses and after reading all such great ones is do impressive all this wisely here is, so I dont know what the he... more to contribute with these troubleshooting except to add that it will be great to install like an stages sequencer to avoid inrushing current into these puppys all at once plus keep an eye on all of those wirings and wires nuts connectors just in case there are some of those neutral or returns getting too loose at some points, Heeyyy.. we never know. But so far with all of these guys advicements I'm sure you'll be getting out of the woods sooner than later, I believe. CR-4 Techno Mall are super definetly. Way to Go Buddies...Heeheehaa!

Lock and Tag,

MC

The great thing about CR4 is that you learn stuff by looking at other peoples problems. So first I need to say that I have no experience or knowledge in this field, and, I'm really only asking these questions for my own education whilst "pretending" to try to help!

Is this approximately the setup:-

1.) Are the heaters purely resistive? If so you should be able to work out the current needed from the resistance and voltage.

2.) The transformer can only supply 32 Amps, so I'm assuming that the two legs are rated at 15 Amps each (and take just over 12). What rating are the actual fuses?

3.) Have I got the fuse and the solid state relay in the right order?

4.) Have I "tapped off" the power for the control card in the right place? It's unlikely that it will take enough power to make a difference, but: if it's tapped off one of the legs, and, if there's a fault (or something odd) in the power supply it might be pushing that leg over the edge.

You are basically correct with the diagram there is a thermocouple in ther somewhere but that is the gist of it.

Answering the q's as posed:

1) unknown but I believe they are as ther are a cartridge or barrel type heater.

2) Not sure of the individual leg rating but the fuses are rated at 30amp, this is a step-down transformer and it is set up as is required to produce 2 legs at 120 v or for 240 v 1ph operation from 2 legs of 480v 1ph on the primary side.

3) They are in the correct order.

4) Yes all is as the manufacturer built it. legs seem balanced and I had the transformer tested and it appears to be well within tolerance.

Look at the fuse arrangement in the diagram. It makes sense if the transformer has one leg grounded (the non-fused leg). However, if the transformer has a 120/240V secondary, then it may be center grounded. If that is the case, then each leg would have a fuse. Do you have a schematic you can post?

Unfortunately I do not have a schematic which is art of the problem.

The center windings are bonded to earth and non fused.

I have recently discovered that the fuse holder however after the last incident seemed a bit loose. it was fine as far as the fuse snapped it rather tightly but you could spin the fuse once it was in the hold with very little difficulty. I have tightened the clamps on the fuse holder and it holds the fuse nicely now.

I will not be able to do further testing on the machine for a couple of days now but it will be back in operation Monday for the opportunity to see if all the suggestions have had any effect.

I will keep you advised. Thank you all again for you excellent advise.

Agree I dont going arguing this one with no one but I did learn a lot just by reading and really is like reading a real time book this what is real cool here at CR-4 Techno Mall and I do enjoy it here definetly being around these Master from all over. No doubth about it you have a better clue than myself I have to say it. I did noticed that in some other inrush equipment some of them have like a 'sequencing stages controller' with some 'time delays' in between as well to avoid so much juice at once into it, but I dont know! That's what I can tell so far with this one. I did noted that so far all the Buddies here really know the stuff obviously. The Man of the Moment...

You have the Tech...

MC

Is there an actual overcurrent? In other words, have you physically checked the current when the fuse blows? Fuses are thermal elements, and the trip rating is based on a certain ambient temperature. During normal operation, the fuse link will generate heat due to I²R losses, but that heat is radiated and/or convected away to keep the link temperature below its melting point.

Check the air flow (ventilation filters, cooling fan (if one exists), etc. around the fuse holders. If there is any blockage, clear it. Reduced air flow would allow the heat to build up around the fuses, causing improper operation.

If the unit continues to blow fuses:

1. Use a recording ammeter to determine the characteristic of the current when the fuse blows. Is it a spike, a gradual rise, or does it remain the same (the fuse blows below its setpoint). There is are several clamp-on accessories available for your Fluke, and I believe your model has max/min recording capability. If you have or can get one of the clamps, it will make your life a lot easier, now and in the future.
2. If an overcurrent occurs, use the ammeter on the leads going to each element to isolate the problem.
3. If an overcurrent does not occur, check all electrical connections near the fuse holder, including the fuse clips themselves. Any loose or dirty connection will have a higher resistance and cause localized heating.

If you need to rent test equipment, RC Ramsey in Tulsa has instruments which would work; It looks like Davis Instruments (also in Tulsa) sells the clamp-on for your Fluke, but I don't know if they rent.

Thanks for the links!

And the tips

I have not been able to see an overcurrent situation. every time I have tested the plate and controls the current has been virtually the same within .2-.4 amps. I am using a clamp on meter with my fluke meter and all batteries on both are new. I don't believe it has the ability to record but does have a hold button.

I did however find the clips to be somewhat loose (hadn't thought to look there) and had already tightened all the connections before i even posted. electrical 101. LOL

There is no blockage and air flow seems good.

After working on food equipment for the last 30 years, i can say that you have a bad connection on that paticular leg. If the manufacturer used any solid wire, get rid of it (you need high temp. stranded wire & connectors). The element could also be partially shorted, but look good. Take a reliable Ohm Meter @ higest resistance setting (with all connectors unhooked) & read from lead or connection to body of element (outside). Any reading whatsoever will indicate a bad element, causing the amperage to very slowly raise to the point of fuse failure. Also, TR fuses are for motor starting, etc. You should be using a fuse designed for Resistance Heating.

Have fun & good Luck!

Ok after all the fine information I received on this site I believe i have finally sorted the problem out.

I am not 100% sure of it but I think it is solved.

Turns out I should have double check the fuse holder as suggested in the first post.

Thinking that it was snapping pretty tight or to put it another way, it was difficult to put in the holder but once in there is spun around with relative ease. Upon re-examination of the fuse holder, and listening to all the information, re-crimping the fuse holder to provide a tighter connection appears to have been the solution.

Sometimes you gotta feel like a complete dolt before you can fix a problem.

Thanks again for all the great suggestions guys. Now if I could just get the blamed thing to recover a bit faster i would be in great shape.

Good to hear you solved it!

Thanks for updating us with the soloution

Glad you found the problem. In the years of working on electro-motive equipment that problem was the first one that got my head to spinning. Everything just checks out right. It was one problem that I would see over and over again. Especially on electric lift trucks that had clip type fuses.

Thanks for the solution. I just wish I hadn't been so thick as to think I had that part solved in the first place.

Ahh well ya live and ya learn. Other wise ya just live......... or not.