Ravelli RV80 - Problem: Air Flow Meter

[Blstr88]

This issue is getting completely ridiculous...every year for 3 years now I've had to replace this. Now this is my 4th year.

When I pull the sensor from my stove it literally looks black and charred. There must just be too much heat radiating that close to the pipe for that sensitive little electronic to handle? Mine can't be cleaned, its actually burned up.

I can't find one now either - they seem to be out of stock everywhere. Ridiculous such an expensive stove that otherwise would be great is out of service from a dumb little part like this.

Has anyone successfully bypassed the flow meter from the menu? I plan to look into that tomorrow when I'm home.

Another option I considered is when I get a new one (IF I can even find one) I'm going to actually drill a few small holes as needed in my cold air intake pipe further back from the stove and try installing the meter further down the intake pipe. I'm thinking maybe if it's further from the stove the heat won't break it down so quickly?

Anyone ever try contacting Ravelli about this?

 

[Monica in France]

That sounds very interesting.
Could you share more information with us ?
Is the 'charred' bit inside the inlet tube ( on the actual sensor ) or on the outside / connector side ?
What is your usual setting for the stove ? P5 at a guess !
If this is happening I am surprised that the fuel hopper is not getting overheated as well.
My stove is pre RDS by a number of years but if the inlet pipe got that hot I would be very worried.
I've just touched the inlet tube on my stove where the sensor would be - nearly as cold as the outside air - not surprising when you think about it !

 

[Ssyko]

that sensitive little electronic to handle

its not t he air or tube it is probably the the electrical current flowing through the device that is burning it. it looks like it is a thermister type resistor that changes resistace as air flows through it(temp change). this is a guess, i have never had my hands on one to test and there are none in my area that i have worked on.

 

[Monica in France]

The other possibility is the direct radiation from the burn pot which is not so far away.
In my stove there is a straight tube between the two. Obstructed by the igniter perhaps.
But if this was the case , surely the MAF would not work at all ?

 

[Ssyko]

Well if the stove is in operation it will be drawing cooler air through the tube into the burn pot. And if it is getting that hot, there is a more serious issue going on thats way beyond my pay grade

 

[Blstr88]

Yeah it's drawing very cold air in from outside so I would have thought that would keep it cool. Maybe as Ssyko mentioned its not actually radiant heat, but electrical current? I'll post a picture of it.

I found in the settings where the air flow meter is set to auto but I can't seem to actually change it to off, do I need to enter that RDS key before I can make that change? If so, any idea what the key is? Or does it vary by stove?

 

[Pelleting In NJ]

The code is 11 to disable the "debimeter" (airflow meter).
Private message me your email address and I can send you the Tech Manuals for Ravelli RDS stoves.

 

[donedeploying]

So... I followed most, if not all suggested cleaning of both the vacuum system & airflow sensor/"debimeter" without success... Until I reset the stove to factory default settings (user code "11"). No longer in modulation mode, pumping out the heat in working mode. I'll advise if that changes.

 

[waltonb]

replaced the air flow meter on mine twice over the years before finding out about this setting.

 

[Manly]

replaced the air flow meter on mine twice over the years before finding out about this setting.

I’ve just Installed my fourth replacement in five years. Unfortunately my Francesca firmware does not have the option to turn the flow meter off. My stove dates to 2010 and apparently is an early version of the RDS implementation. I recently traveled to western MA to purchase new debimeters. When I explained my ongoing issue he immediately asked if I have outside air piped into the stove. I do. He said thats what causes the failure. He has found once the cold outside air is removed the failures go away. Made sense. I’ll try running without the outside intake connected. Rather be able to turn it off in the software but not possible on my version.

 

[waltonb]

I don't have an external air supply duct on mine, it just pulls air from the room.

This is all making me wonder what exactly the air flow meter is trying to measure for the RDS. Is it only that the air supply is not blocked? Or does a debimiter failure indicate the combustion/exhaust fan may be underpowered, thus making the air flow inadequate.

 

[Pelleting In NJ]

The airflow sensor measures the amount of intake air. The RDS system uses this info to maintain a constant amount of airflow through the combustion chamber, with the goal of keeping the air-fuel ratio of the burn constant. It is like an automatic damper adjuster.

As the exhaust path restriction increases (from ash build-up), the RDS "sees" the reduced airflow from the airflow sensor, and then increases the RPM of the exhaust fan to get the actual airflow back to the original value, thereby maintaining the same air-fuel ratio. Eventually, when the ash restricts the burn-pot / exhaust passages enough, to the point that it can't increase the fan RPM any more to maintain a constant airflow, the clean the burn-pot alarm is triggered.

The set-up of the RDS system, where it "learns" the baseline airflow amount, of a clean, low restriction burn-pot and exhaust pipe configuration, is the RDS setup routine that is supposed to be performed when the stove is first installed.

The airflow sensor works as follows: There are two main parts, an air temperature sensor (thermistor), and a heater (fixed) resistor. These are the two chip parts soldered to the ends of the two "fingers" of the sensor board. The control board sends current through the heater resistor, and the downstream thermistor measures the air heated by the heater resistor. The control circuit adjusts the heater power so that the thermistor measured temperature rise is constant. So, if you connect the outside air to draw cold air from the outside, the heater power is cranked up to compensate for the much colder outside air. Maybe that's why the airflow meters fail more often if you use cold outside air, the design of the heater resistor is not able to withstand the higher power dissipation, and gets brown, or burns out completely. Probably needs a higher power rated resistor.

 

[Manly]

The airflow sensor measures the amount of intake air. The RDS system uses this info to maintain a constant amount of airflow through the combustion chamber, with the goal of keeping the air-fuel ratio of the burn constant. It is like an automatic damper adjuster.

As the exhaust path restriction increases (from ash build-up), the RDS "sees" the reduced airflow from the airflow sensor, and then increases the RPM of the exhaust fan to get the actual airflow back to the original value, thereby maintaining the same air-fuel ratio. Eventually, when the ash restricts the burn-pot / exhaust passages enough, to the point that it can't increase the fan RPM any more to maintain a constant airflow, the clean the burn-pot alarm is triggered.

The set-up of the RDS system, where it "learns" the baseline airflow amount, of a clean, low restriction burn-pot and exhaust pipe configuration, is the RDS setup routine that is supposed to be performed when the stove is first installed.

The airflow sensor works as follows: There are two main parts, an air temperature sensor (thermistor), and a heater (fixed) resistor. These are the two chip parts soldered to the ends of the two "fingers" of the sensor board. The control board sends current through the heater resistor, and the downstream thermistor measures the air heated by the heater resistor. The control circuit adjusts the heater power so that the thermistor measured temperature rise is constant. So, if you connect the outside air to draw cold air from the outside, the heater power is cranked up to compensate for the much colder outside air. Maybe that's why the airflow meters fail more often if you use cold outside air, the design of the heater resistor is not able to withstand the higher power dissipation, and gets brown, or burns out completely. Probably needs a higher power rated resistor.

This sounds like a very plausible explanation to these component failures. I’ve been dealing with this issue four years running. I would prefer to have outside combustion air but I will leave it disconnected and see how many seasons I get in this mode. Really wish I could disable the debimeter in the software but I’m 97% certain that option was not in the early version I have. It’s not seemingly possible to talk to a Ravelli rep that can give definitive answers on technical issues.

 

[Mt Bob]

The airflow sensor measures the amount of intake air. The RDS system uses this info to maintain a constant amount of airflow through the combustion chamber, with the goal of keeping the air-fuel ratio of the burn constant. It is like an automatic damper adjuster.

As the exhaust path restriction increases (from ash build-up), the RDS "sees" the reduced airflow from the airflow sensor, and then increases the RPM of the exhaust fan to get the actual airflow back to the original value, thereby maintaining the same air-fuel ratio. Eventually, when the ash restricts the burn-pot / exhaust passages enough, to the point that it can't increase the fan RPM any more to maintain a constant airflow, the clean the burn-pot alarm is triggered.

The set-up of the RDS system, where it "learns" the baseline airflow amount, of a clean, low restriction burn-pot and exhaust pipe configuration, is the RDS setup routine that is supposed to be performed when the stove is first installed.

The airflow sensor works as follows: There are two main parts, an air temperature sensor (thermistor), and a heater (fixed) resistor. These are the two chip parts soldered to the ends of the two "fingers" of the sensor board. The control board sends current through the heater resistor, and the downstream thermistor measures the air heated by the heater resistor. The control circuit adjusts the heater power so that the thermistor measured temperature rise is constant. So, if you connect the outside air to draw cold air from the outside, the heater power is cranked up to compensate for the much colder outside air. Maybe that's why the airflow meters fail more often if you use cold outside air, the design of the heater resistor is not able to withstand the higher power dissipation, and gets brown, or burns out completely. Probably needs a higher power rated resistor.

"The control board sends current through the heater resistor, and the downstream thermistor measures the air heated by the heater resistor"

I find this highly illogical, but if true, would be very inefficient, nor accurate, unless it was closed down in a very small air channel. Is it?
The way MAF (mass air flow) sensors work-- one of the "sensors" measures the temperature of the incoming air. The other (hot wire,hot film,etc) has constant voltage to it, and, as incoming air flow "steals" it's heat, the amount of current used goes up. The computer programming takes over from there,using this information. Unless Ravelli has some screwed up system.
The amount of failures seems amazing to me, Integras had this system, and many MAF sensors are original,still running, and ones that have been replaced,were not the problem with the stove.
BTY, the Integra ones were made from some parts from BMW sensors.

 

[Mt Bob]

OK, did some research. These are made by MicroNova (Italy). Seeing better pictures,and pictures of their other products, these are simply 2 sensors, and 1 resistor. No programming chips or other items. IF you could get the specs on the sensors,they would be very easily repaired,even duplicated.
From reviews, these also have a very high failure rate in Europe.
And you can buy them for about 20 bucks,over there.
The manufacturers # is PK063.

 

[Monica in France]

I was looking at a MAF in a car the other day.
There must be millions of them all round the world working without a problem .
So why does the Ravelli one screw up with such regularity ?
The automobile version looked somewhat less delicate. And complete with electronics cost the same as the Ravelli's two thermistors and restistor.
I'm inclined to agree with Pelleting in NJ : the Ravelli implementation compensates for seriously cold air by frying the resistor.

 

[Pelleting In NJ]

If people are willing to mail me their broken air-flow sensors, I will attempt to figure out if they can be repaired, with better quality parts. If they can also send me a new sensor, that would also help me investigate this. I will return both sensors to you when I am done with my investigation. I am an Electrical Engineer with a well equipped lab bench.

Send me a message through the "Conversation" feature of this forum (envelope icon next to your user name, upper right of the page), and I will send you my mailing address.

 

[Mt Bob]

If people are willing to mail me their broken air-flow sensors, I will attempt to figure out if they can be repaired, with better quality parts. If they can also send me a new sensor, that would also help me investigate this. I will return both sensors to you when I am done with my investigation. I am an Electrical Engineer with a well equipped lab bench.

Send me a message through the "Conversation" feature of this forum (envelope icon next to your user name, upper right of the page), and I will send you my mailing address.

GM. Long time,life has kept me busy.
Yes,if it is usually the resistor failing,all you would need is for someone to measure a new one. And, as you know,traces can be fixed. I contacted the manufacturer, and they basically lied, I aske for the specs on the thermistor chips, and they said that is the property of the stove manufacturer. Well, that same part number is used interchangeably in other stoves and devices,even BBQ's! Over in Europe,anyway. I have found them as cheap as 23 bucks, over there(on the net). As it is a simple board,with 3 smt devices, they probably cost less than 2 bucks to mass produce. I see the price now for places in USA that have them is 90 bucks. Is there a way to identify the thermistors? I do not think they are marked like other SMT devices.

 

[Pelleting In NJ]

I should be able to identify the thermistors by measuring their temp-versus-resistance curve, and then matching that curve up with an available substitue part.

 

[Mt Bob]

I should be able to identify the thermistors by measuring their temp-versus-resistance curve, and then matching that curve up with an available substitue part.

Ah, but with a new functioning part,I assume? Will se if I can find a cheap one for you, as the ones I have found in the USA are 90 bucks. BUT, do those stoves function OK when people put them in the mode to bypass the sensor?

 

[Pelleting In NJ]

If the RDS function is disabled in the menu, the stove operates fine, like the older non-RDS models do. The stove just will not try to maintain a constant air-fuel ratio as the burn pot and exhaust passages get more restrictive due to ash build-up. The bottom line is that a non-RDS stove will require cleaning more often than if RDS is functioning.

 

[Mt Bob]

If the RDS function is disabled in the menu, the stove operates fine, like the older non-RDS models do. The stove just will not try to maintain a constant air-fuel ratio as the burn pot and exhaust passages get more restrictive due to ash build-up. The bottom line is that a non-RDS stove will require cleaning more often than if RDS is functioning.

AH so there is great benefit to it working, much like having the latest prom in an Integra.

 

[Mt Bob]

If the RDS function is disabled in the menu, the stove operates fine, like the older non-RDS models do. The stove just will not try to maintain a constant air-fuel ratio as the burn pot and exhaust passages get more restrictive due to ash build-up. The bottom line is that a non-RDS stove will require cleaning more often than if RDS is functioning.

Got a sensor coming from Europe, but looks like will be 3-4 weeks to get here.Can send to you for testing when it arrives. Was 40 bucks,including delivery, cheapest I could find,delivered to USA.

 

[Pelleting In NJ]

I received two failed airflow sensors, sent to me by Manly...thanks!!
One sensor was his original that came with the stove (#1), which was later replaced by sensor #2.

Here are my observations so far:

Sensor#1
- Sensor #1 has minimal, to no, "browning" ("burnt") areas from high temperature exposure.
- No cracked solder joints were observed.
- The Heater resistor R1 measures correctly at 750 Ohms.
- Thermistor RT1 (airflow outlet) measures a correct 10K at room temperature.
- Thermistor RT2 (airflow inlet) measures an incorrect 15.5K Ohms at room temperature.

Sensor #2
- Sensor #2 has significant "browning" ("burnt") areas from high temperature exposure, on the edges of the finger PCB. It is not browning of the the electronic components, but of the PC board itself. As it is only on the edge of the board fingers that face the airflow outlet, that indicates that somehow, hot combustion air from the firebox must have flowed backwards through the intake tube, and cooked the edges of the board. The only way that can happen is if there is a wind gust that drives air backwards through the flue, overcoming the combustion blower, and then out the cold air intake.
- No cracked solder joints were observed.
- The Heater resistor R1 measures correctly at 750 Ohms.
- Thermistor RT1 (airflow outlet) measures a correct 10K at room temperature.
- Thermistor RT2 (airflow inlet) measures an incorrect 13.2K Ohms at room temperature.

Thoughts so far:
- The airflow meters seem to fail when the two identical thermistors drift apart too far. I think the stove, when it is first turned on, checks the two thermistors, and if the resistance values don't match (they should match when they are both at the same temperature), the stove flags the "Bad Airflow Sensor" alarm. I am not sure what is the root-cause of the value drift of one of the thermistors (RT2 in both units I tested).
- I don't think the overheat browning issue is the cause of the RT2 value drift, as the brownest finger is where RT1 is located, and it's value is still correct.
- I think I found the manufacturer of the thermistor parts used by Ravelli/Ecoteck (really MicroNova, the maker of the airflow sensor and stove control board). I need to do some more testing to then be able to select a suitable equivalent replacement part, to repair these boards. Stay tuned.....

 

[Pelleting In NJ]

Blster88: Please post a close-up picture of your "burnt" airflow sensor.