Odd occurences with my Convotherm 4 oven.

Odd occurences with my Convotherm 4 oven.

Odd occurences with my Convotherm 4 oven.

Posted by guest on May 7, 2017 at 12:00 am

I had an interesting problem last week with my Convotherm, C4ET 20.20 GS oven.

Its not all that old yet so I believe experience with these is pretty limited but let me try and explain what I got.

The unit has a touch screen, looks like its all it is and the brains of the operation or the main control board is directly behind it. when you take the service cover off, you can see the front of the board where everything plugs in, my particular problem was the bottom combustion blower wouldn’t run, I tried reading their wiring diagram and its, well, confusing and not that easy to understand unless you really try.

So I went ahead and tried a couple of things, I tried finding where the power came into it, it has 2 plugs on it, both of which have 3 wires on them, its a 220V 50 hz blower…… 50hz… german….. grr..

So I looked for power on both, saw none but didn’t think it was the right place regardless so I checked the top one and sure enough, 1 of the 2 did have 230 V on it so I checked the bottom one and there was no power, so I pulled the connector off the board and ohmed out the wires, all came through clean. I tried swapping the top blower to the bottom as well as the ignition module and still, no life.

Called Cleveland, said it might be the board, I had figured it might be a relay on the board supposed to switch power over but after spending some time figuring their wiring diagram, that didn’t really make sense either so I was kind of lost. Figured the only way to really know was to check on the board with the unit running, tried removing the board and it didn’t budge so I figured maybe I could get to it by removing the touch screen, turns out that’s the way to do it. Popped the screen off and what do I see? Fuses…… They mounted fuses on the opposite side of the board………. oh boy.. 5 hours of troubleshooting back and forth on the phone with Cleveland with 0 mention of this.

Checked the fuse matching the connectors location and sure as rain, it was blown. It was a 2 A, slow blow, ceramic, 250 V mini fuse. Drove down to radio shack, they had 1.6 A fast acting ones, figured it couldn’t hurt. Put 1 in, ran the unit for 20-30 minutes, no problem.

Next day, chefs use it, cook for 45 minutes and it triggers the same error code, same problem, same fuse. Figured okay, I checked the A draw on that fan, it was less than 1 A so its gotta be the inrush, drove to some random speaker store, picked up the original type and put it in, ran it for 3 hours, no problem. Chefs ran it the next day for over 8 hours straight, no problems.

2 days later (today) same error code triggers, well that’s embarrassing, check the unit again, figured okay its gotta be a wire problem or something dumb, ohm out the wires again, one of them no longer is showing a connection, trace the wire through and find a black cylinder on the wire, another fuse…. This time its a 1 A slow blow, 250 V in a littelfuse black cylinder. Its blown, great. back to Radioshack to get their 1 A fuse, picked up both the fast and slow, planning on putting in the fast acting one first after checking everything and see what happens, that way I am safe in case something slips me in the troubleshooting.

That’s where I am at now, my first thought is when the first fuse blew (2A one) that it might have weakened the 1 A one since they are on the same line. OR the internal blower wheel is somehow compromised in a way that its messing things up. Have to take the blower off and disassemble the venturi to get to that wheel but I will if it comes to it. I am going to check the top fans A draw and see if its any lower or higher, maybe it will tell me something.

I could use some help on this, don’t want to miss something this time so if you guys have any advice, please, do share it.

You guys got any input on this?

olivero replied 6 years, 12 months ago 1 Member · 13 Replies
13 Replies

olivero

Member
May 7, 2017 at 7:51 pm

Just checked both fans, top one “in rush” is 0.20 A, runs at max speed at 0.16 A

Bottom one is 0.25 A, runs max speed at 0.18A

Put the fast acting in the lower one, runs just fine now, once again, im stumped.
fixbear

Member
May 8, 2017 at 7:02 am

Is this motor 3 wire 3 phase variable frequency, variable speed? Just curious.-

Sounds like you may have a Compressor (Regen air pump) intermittent load problem. If sleeve bearing, oil. If roller bearing, replace. Regen’s are normally roller bearing due to the tight side clearances that have to be maintained. Usually about .006 in. After all, they are a form of turbine. And we all know how small of particle in a ball bearing can cause a problem. Like putting a small wedge in front of a wheel.

Or, the scroll clearance in the blower as some interference/clearance problem. One small particle will gall the impeller to housing causing a high spot and increase load that will vary as it gets knocked off and reforms. The aluminum expands and contracts a lot with heat fluctuations.

Or, A build up of grease, dirt in the intake that breaks off and hits the impeller. Again causing more load that comes and goes.

You may want to megger the winding’s if you don’t find a rotational resistance problem.
olivero

Member
May 8, 2017 at 9:05 am

Fixbear,

Its got 2 wires coming in and a ground wire. I don’t think its 3 phase, not variable speed. The other fans in the oven, the actual convection fans in the oven itself are 3 phase and run by VFD’s

I checked some of the things you mentioned, its an odd combustion fan really, the exterior has a circuit board and an induction coil mounted on the frame of the blower and the blower wheel is encased. The casing that holds the blower wheel has one side where it sticks out, not the shaft itself but the casing is made that way and that is what the coil sits on which makes the blower wheel itself turn.

The fan spins freely, I checked the inlet, there are no particles, very very little grease build up

If I were to oil the blower wheel I would have to take apart the venturi housing as its on the inside of that.
fixbear

Member
May 8, 2017 at 9:42 am

What conponets do you see on the circuit board?
ectofix

Member
May 8, 2017 at 4:36 pm

Is this the blower?
olivero

Member
May 8, 2017 at 5:12 pm
olivero

Member
May 8, 2017 at 5:13 pm

Looks just like that, yeah.
fixbear

Member
May 8, 2017 at 5:33 pm

You should also consider that with a regen blower like that, the load will get higher with more air flow. Like a leak to the burner area. It is a form of pump. More flow equals more load. Not like a squirrel cage blower. I’ve worked on Regens that produced 40 psi. They are also common today in the aquarium industry to supply air stones in deep multiple tanks.
olivero

Member
May 9, 2017 at 1:27 pm

Interesting, okay. I will look for that.

i think the board has problems, the lighting circuit transistor burnt up as well so I think the board might be having issues.

Going to get it replaced, hopefully that handles it.
ectofix

Member
May 9, 2017 at 6:07 pm

Not much help from me olivero, but I’ll try. I have NO experience on those ovens and extremely limit experiece of the preceeding, now-defunct Convotherm oven models that were actually made in Ohio.

Although made in Germany (now) like my Rational ovens, Convotherm’s controls are layed out differently from Rational’s. For instance, the VFDs in Rationals are completely integrated into their circuit board design. There’s no separate, off-the-shelf, boxy-looking thingie with its own LCD display to run a motor in a Rational.

However, it’s funny how their gas systems appear so similar.

You’d mentioned several fuses had blown. Pretty much anything downstream of those fuses could be the culprit. Seems that a burner blower would have a more robust circuit to need just a 1a or 2a fuse to protect it. So, those are probably a control circuit fuses and a controlling component (or wiring) is the problem…like that board.

Interesting setup – these German ovens. They’re built in a country where 230v line-to-neutral is the standard. Then, each oven is tailor-made for the country it’s going to. SO…our USA gas ovens are received to run on our 115v 60hz, but a gigantic toroidal transformer in there steps that voltage right back up to Europe’s standard 230v right away. Then THAT voltage is divvied up to the respective oven components…and to step-down transformers where needed. Kinda hilariously ingenious. Well HEY! They’re successfully selling ’em!

From what I can tell (from the little study I’ve put to this for my own reasons), the burner blower motor in my Rational gas ovens are brush-less DC motor with a built-in inverter.

Here’s a silly little video on brushless DC motors:

Brushless DC Motor, How it works

I think the main convection blower motors in my relatively new Rationals (since 2004) use brushless DC motors as well. So happens that I have some ovens that were made as far back as 1993, so the design differences between old and new are significant…which is a whole other topic I might share someday.

Whether it’s the main blower motors or the burner blowers, that 230v plug supplied to the motor ASSEMBLY is the main power to its built-in board…and ultimately the motor. The control signal is supplied separately.

So in the burner blower, 230v is always there at rest. A separate plug supplies a signal from the ignition control module which, once IT’S told to by the computer (through a bus connection), tells the the burner blower’s board to ramp the motor up to a pre-programmed speed. Of course, the gas valve and ignition will follow suite in the next stage of operation. A Hall Effect sensor senses motor RPM…which can ultimately be read on the oven’s touchscreen in the technician’s level of programming.

So that’s my newer Rational ovens in a nutshell. Maybe your Convotherm…and AltoShaam’s Combitherm – do it the same way.

Whatever is blowing those fuses is probably in the control side of things instead of a faulty motor. B-U-T…I’ve wrong before. Just can’t remember when that was.

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