Rational Blues

[fixbear]

Sounds like you have a bit of a challenge ahead of you.  Is the fuse snap in and open, or enclosed?  If open you can take a blown fuse and solder wires to it to install a ammeter and fuse in series to monitor and measure the actual current.  It should be no more than 80% of fuse rating.  60 is better. Then tracking it down can be a bit challenging.  Transformers are always suspect as well as MOV’s on a board.  MOV’s are a clamping device for over voltage and get shorted if the circuit had a spike in the past.

 

Ectofix is sure to have good input on this one.

[ectofix]

rico wrote:

 

I have a question for all those Rational sluggos out there.

I have an SCC202G. Bout every other month or so it dies. Upon inspection, I find the 2.5 amp control/transformer fuse blown. I also find that the boiler hi limit has tripped. I replace both and its off to the races again. The boiler set temp is set for 214deg. I called Rational here in Chicago and I can here them shrug their shoulders, over the phone. I have five other units that run ok. My question is, has anyone else experenced this and how can I turn the boiler temp down to 212/213. ? 

I can answer your questions, but can’t give you much guidance on why those things occurred.  Not enough info provided.

 

Question #1: Has anyone else experienced this?

   I don’t know about anyone else, but I haven’t.

 

Question #2: How can I turn the boiler temp down to 212/213?

   The operator’s manual explains that.  However, in a nutshell:

Select STEAM cooking mode. Press the TEMPERATURE button.  It will begin flashing. Use the CENTRAL DIAL to adjust to desired temperature. Push in the central dial in or press the temperature button to save it.

 

Now.  Some other things I’ll comment on:

 

Firstly –

The boiler hi-limit trips at 314°F.  I SERIOUSLY doubt that the moist heat set-point is the problem.  In Illinois (where you’re located) – the peak temperature for boiling water is around 212°F or slightly lower (sea level is 212° -versus- Denver CO is 203°F).  So although Rational’s designed MOIST HEAT temperature is as high as 266°F, anything above the boiler’s 212°F limitations is additional heat introduced by the AIR elements being cycled on and off. 

 

Besides, the boiler hi-limit doesn’t monitor the AIR element heat output.

 

So if the boiler hi-limit is tripping, then the boiler is dry-firing.  Therefore, I HIGHLY recommend that you thoroughly descale it. 

Why? Because scale can possibly bridge the water probe to ground – thereby causing the water controls to see a boiler full of water when it’s actually empty.

 

If that doesn’t do it, then there’s another problem – such as a SSR that’s shorted closed or a boiler element that’s grounding out.

 

Secondly –

I can’t find a 2.5a fuse for the control transformer on my SCC202G schematic.  Mine shows a 1.6a one on the control transformer.

 

Can you offer a bit more clarity on the components you’re speaking of?  For instance, a transformer on a schematic is generally identified by an alpha-numeric designator of a “T”…with a number.  A fuse is a “F”…with a number.

 

Thirdly –

Based upon how you’d written your statement, I had surmised that every couple of months you find the hi-limit tripped AND the control transformer fuse blown.

So, do they INDEED both occur simultaneously?

My guess would be NO…and that you have two separate problems to deal with.

[fixbear]

Rico, hope to hear how you made out on this.

 

Ectofix,  Think you nailed the over pressure limit problem as being a water sensor problem.  Wish I had a wiring diagram for this machine. Like to figure out how it overloads and blows a oversize fuse.

[ectofix]

There’s no over-pressure limit situation here since that oven technically doesn’t have a boiler.  It has an atmospheric steam generator.  Just a tank which boils water and is directly ported to direct the steam into the atmospheric cooking compartment.  Therefore there’s no pressure switch to monitor any of that.

 

The term “boiler” is commonly used loosely.  Rico did it in this post.  I do it.  Many techs do it.  However, a true boiler actually builds up steam pressure.  Steam generators do NOT.

 

As you well know fixbear, pressure raises the boiling point.  The higher the pressure, the higher the boiling point.  So…the higher the temperature of the steam which exits the boiler and into the cooking compartment. 

 

There ARE steamers that are boiler-based.  Usually institutional type places like hospitals, prisons, some large hotels use them.  Sometimes those units will have what I loosely call a “PTO” (power take-off).  My farmer’s term for auxiliary steam connections to supply steam into something else…like a nearby steam-jacketed kettle or two. 

 

Amongst the boiler-based steamer family, there are some which actually COOK at a higher pressure.  Those steamers will have cooking compartment doors that lock shut – with the door actually resembling a small “vault” door. 

 

Boiler-based steamers were only about 10% of my repairs on steamers, so I didn’t get to see many of them.  Even far less of the ones featuring a pressurized cooking compartment.  Either way,they ARE a different animal to work on…and (as you well know) whosoever works on them most CERTAINLY better know what they’re doing.

 

MOST floor-type steamers, generally ALL counter-top steamers and ALL combi-ovens only employ an atmospheric steam generator.  Not a true boiler.

 

The truly exceptional deviation to all that are the counter-top steamers which operate in a VACUUM (a whole ‘nother topic).

 

SO…my point is that the maximum boiling point of the water in that Rational SCC-202G combi-oven depends upon the geographic elevation of the venue.  The best you’ll get is 212°F.  Unless the restaurant is located below sea level.

 

A casino on the river in Illinois doesn’t have anyplace like that. 

[rico]

Gentleman, Thank you for all your replies.

I purposley did not give you too much info because I did not want to steer you in a particular direction, of my own choosing.

So to elaborate and reply, in no particular order; its a 202G, so solid state relays are not an issue. I am at the bottom of Lake Michigan (pun intended) so we run about 8 grains of hardness here. Howeber we are using the marvelous Slecto Flash 5000 filter systems, recommended by Rational. After the filter units, we run 1.0 to 1.5 grains of hardness for the boiler feed. I wish they were boilerless. You are correct in stating that the fuse is a 1.5a. I had my head up my a– when I asked the orginal question. I descale all the boilers based on gallons used, we have a meter at each unit. There doesn’t seem to be a set pattern as to when this problem occurs. It can be after a descale or 500 gallons before it is due to be cleaned. Its always the same. I arrive to find the unit is dead. I open it up to find the 1.5 amp transformer fuse is dead. I will find that the boiler hi limit has tripped.

I have four of these units in a row, all four have their own filter unit. All have accumilated about the same run hours. Yet this is the only unit that this happens to. When this occurs I will inspect the boiler for scale. I have had it happenen four days after a boiler descale.

My conclusion was that it was also a dry-fire situtation but sometimes the water probes are somewhat dirty and sometimes not. I pull them every time it happens. Awhile back, Rational changed their boiler limit from a 273deg. part to the current 314deg. unit. The 273 was for gas and the 314 was for electric boilers (two different part numbers). I tried them both with no difference. 

If they all were doing this, I could look for something in common, but its just this one. I thought about replacing the boiler, in case there was some sort of mfg. defect (it was replaced three years ago). I don’t want to try this unless I have exhausted all other possibilties. I’m already exhausted, myself.

Is there any other information you could use, that I may have missed?

Thank you again for all your responses, Rico  

[fixbear]

Yes I realize that they are a open system and just a steam generator. I used to maintain a boiler, steam cabinet, steam kettle system that ran off a 15 lb boiler. One little door leak and cooking times jumped drastically in the steam cabinet.  Like having a instant pressure cooker. They have gone out of favor due to the high maintenance cost and extra regulations and annual inspections that not only cost a lot to do, but also require several days of down time. If you just build a steam generator you avoid a lot of certifications and testing. But as always, there are some municipalities that like to make their own rules without a proper definition of a boiler.  And we all seem to call steam generators boilers.  Wonder where they got that.

 

It’s just like I refereed to the rational safety as a pressure problem.  Sorry about that, but I seem to have in my head the steam – pressure charts from way back. Like if I wanted 265 F, I needed 125 psi. for saturated steam.  Dry steam can go a lot higher.temperature wise.  I realize that they use a temp safety.  Most expesso machines run 1.1 to 1.3 bar.  That’s 14.7 to 18.9 psi.  Yet they avoid testing due to low volume.  Note that the bigger machines use multiple small boilers to avoid regulation.  Problem is that any restriction to a steam generator now becomes a boiler.  With the inherent dangers.

 

You refereed to PTO’s.  Funny, I still remember working with a thresher and Case traction engine. Harrowing with a steel wheeled Fordson,  Haying with horses,  Rolling over a Ferguson 30, and numerous days harvesting and plowing. Some of my fondest memories are of farming.  One learns a lot on a farm of all types of fields. The worst memory is of course peeing on a electric fence. Not something one forgets.  Same with getting hit with lightening. That one can generate a instant steam that can blow holes in anything.

 

The Rational’s must really cook different in Denver then. I think water boils about 198F there.

[fixbear]

Have you tested the steam generator thermocouples?  Being a gas unit it has to be firing above the designed temperature to trip the overtemp limit. Something causing the burner to continually fire over the needed temp or a heated mass causing overrun.  If the boiler was replaced, make sure to check the wiring routing for the controls and damage. Perhaps a miss wire.

[ectofix]

Well PH-TH-PH-TH-PH-P!

I’m a bonehead for suggesting faulty SSRs or elements in a gas unit.  I have more electric (21) than gas (7) Rationals, so without my standing there looking at it, my feeble mind reverted to the former.

 

Certainly an odd problem.  I’ll put some thought towards it for any ideas.

[ectofix]

I knew that you knew that.  Just thought that could be informative for others.  Your post is more so…

[ectofix]

fixbear, I’d share the schematic with you, but I don’t see a way to do that here without making it public.  Rational wouldn’t want that and specifically states not to in their manuals and their service partner portal.  I could share so much more without my conscience (and the possible repercussions) observing those restrictions.