Quieting the Suburban furnace model NT-16SE, same as the NT-20SE

[DavidSo]

Well, I have found a candidate for the room air fan. It is 7.5 inches diameter, produces 166cfm (24cfm over stock), draws just .7 amps, 1300 rpm, rated life expectancy 40,000 hours. Operating temp up to 200 degrees. Just 37 Db-A

I don't want the thread full of conflicting info so I'm withholding the model info till I confirm compatibility. The fan has speed modulation capability. Not sure I'll use that. There is a Youtube video of the fan, recording the noise level. Very Quiet! I'll share all this later so I don't run people down blind alleys!

The crazy thing is this. You buy an "RV" fan motor that draws a ton of power, has a limited life, and is noisey, for well over $100. You buy a computer type fan like this for $12 + shipping. I bought 3 and got free shipping! The market is so huge that the end pricing is low. I figure I'll use them for cooling fans around the coach since they draw so little and move so much air. I'll also have ready replacements for the furnace fan if one does fail.

My only real concern is whether the heat is high enough at shut down to affect the fan. During operation the fan is self cooling since it is a pusher. At shutdown it will have to sit next to the cooling combustion chambers. The fan is very thin so it can be moved to the rear of the case away from the burner section. There is about 4-5 inches of separation. The factory fan is so long that it runs about an inch from the combustion chambers. A short shutdown delay of maybe 1 minute would remedy the problem if it comes up.

Finding this fan is a major step forward if it works out.
David

[David Morgan]

I picked up a New all-be-it older 1200SE Model and I believe that it is slightly quieter than the 1600 + units.

One thing I noticed was one time my battery was just about depleted and I had exactly 12V on it, the furnace seamed to run fine but significantly quieter. That gave me an idea to try something. I had a universal laptop power supply for a car 12V plug that supplies up to about ~4 amps at 12V and i ran that in between the battery and the furnace, the difference in sound its very noticeable. I figure that the furnace is designed with the possibility of running on a discharged battery system, and 12V is not quite a dead battery. If your plugged into shore power your line voltage at night to your furnace is probably going to be closer to 14V or so. Anyway ran it that way for a couple of trips without any issues. I needed my power charger so I pulled it back out since then. I figure that the manufacture designed it so that as long as you are pulling the sail switch open you're in the clear for undervolt. Allthouh it could reduce the life of the motor the electronics themselves are most likely ran on much lower voltages with MOSFETs to regulate the voltages. Ill leave that to you engineering people to debate.

[floyd]

Originally Posted by David Morgan

I picked up a New all-be-it older 1200SE Model and I believe that it is slightly quieter than the 1600 + units.

One thing I noticed was one time my battery was just about depleted and I had exactly 12V on it, the furnace seamed to run fine but significantly quieter. That gave me an idea to try something. I had a universal laptop power supply for a car 12V plug that supplies up to about ~4 amps at 12V and i ran that in between the battery and the furnace, the difference in sound its very noticeable. I figure that the furnace is designed with the possibility of running on a discharged battery system, and 12V is not quite a dead battery. If your plugged into shore power your line voltage at night to your furnace is probably going to be closer to 14V or so. Anyway ran it that way for a couple of trips without any issues. I needed my power charger so I pulled it back out since then. I figure that the manufacture designed it so that as long as you are pulling the sail switch open you're in the clear for undervolt. Allthouh it could reduce the life of the motor the electronics themselves are most likely ran on much lower voltages with MOSFETs to regulate the voltages. Ill leave that to you engineering people to debate.

Good post!

[Gene L]

Originally Posted by David Morgan

I picked up a New all-be-it older 1200SE Model and I believe that it is slightly quieter than the 1600 + units.

One thing I noticed was one time my battery was just about depleted and I had exactly 12V on it, the furnace seamed to run fine but significantly quieter. That gave me an idea to try something. I had a universal laptop power supply for a car 12V plug that supplies up to about ~4 amps at 12V and i ran that in between the battery and the furnace, the difference in sound its very noticeable. I figure that the furnace is designed with the possibility of running on a discharged battery system, and 12V is not quite a dead battery. If your plugged into shore power your line voltage at night to your furnace is probably going to be closer to 14V or so. Anyway ran it that way for a couple of trips without any issues. I needed my power charger so I pulled it back out since then. I figure that the manufacture designed it so that as long as you are pulling the sail switch open you're in the clear for undervolt. Allthouh it could reduce the life of the motor the electronics themselves are most likely ran on much lower voltages with MOSFETs to regulate the voltages. Ill leave that to you engineering people to debate.

I just tried this same concept. I have a 12v motorcycle battery that has been sitting around for about 2 years on a shelf. I checked the voltage of it and it was 10.5 volts so I used some alligator clip test wires and connected it to my Casita and turned the furnace on and it ran it just fine and sooooooooooooo much quieter. It did try to ignite the burner but I have the propane off so assume it will function just fine. The battery was so weak it quickly went down to 7 volts and the furnace was still running just fine! The only issue I see which at some point I will test further is how long the burner will run before it activates the hi-limit switch because of the reduced air flow.
I am going to try using a PWM (pulse width modulator) speed control assembly which I just ordered from Hong Kong for $12.69 which is good for up to 10amps and will see where that needs to be set for the best/quietest performance.
I realize this will not reduce any battery drain but so far I have never had that problem anyway as we run the generator a "little" each day to re-charge the battery when boondocking.

[David Morgan]

Originally Posted by Gene L

I am going to try using a PWM (pulse width modulator) speed control assembly which I just ordered from Hong Kong for $12.69 which is good for up to 10amps and will see where that needs to be set for the best/quietest performance.
I realize this will not reduce any battery drain but so far I have never had that problem anyway as we run the generator a "little" each day to re-charge the battery when boondocking.

Gene. A PWM is a pulse wave modulator, if you attach that to you're furnace I think it will burn out you're electronics. Unless you have the ability to disable the "pulse" and simply adjust the voltage. Unless I am mistaken PWM pulses Voltage In a manner similar to AC but in a DC square wave. That will blow up the control board, and the motor.

I may be off base, but please double check this before hooking it up.

[Gene L]

Originally Posted by David Morgan

.

Gene. A PWM is a pulse wave modulator, if you attach that to you're furnace I think it will burn out you're electronics. Unless you have the ability to disable the "pulse" and simply adjust the voltage. Unless I am mistaken PWM pulses Voltage In a manner similar to AC but in a DC square wave. That will blow up the control board, and the motor.

I may be off base, but please double check this before hooking it up.

David,
I am not going to run the PWM to control the whole furnace, just the motor itself which is what the PWM is designed to do (slow down a 12v dc motor that has brushes). I also just found a 3.2 amp one which I ordered which is much closer to the 2.8 amp draw of the Suburban motor so according to the "experts" you should have a PWM as close to the rated amps as possible.
So in theory the furnace calls for heat which in turn then turns on the PWM only and the PWM then sends the lower voltage to the motor which causes the motor to run slower and much quieter which will then activate the sail switch (full 12v+) which will then cause the gas to flow and ignite the burner. So the PWM will be installed between the board and the motor only.
Gene

[DavidSo]

A PWM does not supply a lower voltage, it supplies a pulsed full voltage. A lower voltage can be supplied by a simple rheostat resistor. A PWM varies the time that the power is on and off, allowing the motor to coast in between power pulses. The pwoer pulses are whatever the PWM is set for. 12V motor gets 12V The shorter the power cycle and longer the coast cycle, the slower the motor turns. If it is wired as Gene describes it should not harm the electronics. Motors draw more current at start-up so you don't want one rated too low to handle the start-up current. A PWM is better at starting a motor because it supplies full voltage. Resistors are best used where the motor is started on "high" and then turned down. That's why most fan switches are off>high>med>low instead of off>low>med>high.

David

[David Morgan]

Originally Posted by DavidSo

A PWM does not supply a lower voltage, it supplies a pulsed full voltage. A lower voltage can be supplied by a simple rheostat resistor. A PWM varies the time that the power is on and off, allowing the motor to coast in between power pulses. The pwoer pulses are whatever the PWM is set for. 12V motor gets 12V The shorter the power cycle and longer the coast cycle, the slower the motor turns. If it is wired as Gene describes it should not harm the electronics. Motors draw more current at start-up so you don't want one rated too low to handle the start-up current. A PWM is better at starting a motor because it supplies full voltage. Resistors are best used where the motor is started on "high"

and then turned down. That's why most fan switches are off>high>med>low instead of off>low>med>high.

David

The only problem I see with using a PWM or variable resisters are that the voltage is proportional to the input, always. That means that if you're taking an input off a charged battery or almost 14V and you shave that to 10, either by RMS variation or or direct resistance, when you're battery voltage drops to 11V at nearly discharged, you will have an output voltage of 7V which I believe would be dangerous. This would be ok for testing when you have a steady input voltage. But not really useable in the real world from my opinion.

You need a voltage regulator, that includes some kind of switch mode power supply with step-up down regulation. The power supply I was using is designed to give good clean regulated power. If the car battery is putting out 10v and has enough amps left in it the supply would step it back to the exact set output voltage. If the input drops below a safe threshold it shuts off completely.

Any modifications that involves "man in the middle" with the fan motor circuit would be best using a dry contact relay. As a PWM is going to cause noise back to the control board. And a variable resister could potentially over, over current the circuit board in motor start, I think any way.

I'm not an engineer but I have burned up a lot of equipment over the years.

[DavidSo]

Originally Posted by David Morgan

The only problem I see with using a PWM or variable resisters are that the voltage is proportional to the input, always. That means that if you're taking an input off a charged battery or almost 14V and you shave that to 10, either by RMS variation or or direct resistance, when you're battery voltage drops to 11V at nearly discharged, you will have an output voltage of 7V which I believe would be dangerous. This would be ok for testing when you have a steady input voltage. But not really useable in the real world from my opinion.

You need a voltage regulator, that includes some kind of switch mode power supply with step-up down regulation. The power supply I was using is designed to give good clean regulated power. If the car battery is putting out 10v and has enough amps left in it the supply would step it back to the exact set output voltage. If the input drops below a safe threshold it shuts off completely.

Any modifications that involves "man in the middle" with the fan motor circuit would be best using a dry contact relay. As a PWM is going to cause noise back to the control board. And a variable resister could potentially over, over current the circuit board in motor start, I think any way.

I'm not an engineer but I have burned up a lot of equipment over the years.

Good points David. I think the one message to take away is that to do the voltage/speed control thing, you need to go through the whole circuit and comprehend all the angles. Putting together piecemeal information leaves you open to trouble. I'm not going that route, so I'm not doing it. I'm sure there are people around who could work it out in a complete form. The other approach is just to keep burning stuff up till something works

David

[DavidSo]

Originally Posted by David Morgan

I picked up a New all-be-it older 1200SE Model and I believe that it is slightly quieter than the 1600 + units.

.

David,
How would you rate the heating from the 12K unit? It seems to me the 16 is overkill. Lowering the BTU makes everything else a little easier, if it can be done without sacrificing cold weather performance. What trailer is yours in?
David

[Gene L]

David,
My 17' Casita has a NT-12SE in it originally from the factory and it is more than enough to keep it toasty warm even in below freezing weather. The NT-16SE had to be used in later years because Suburban stopped making the NT-12SE.
Gene

[DavidSo]

Originally Posted by Gene L

David,
My 17' Casita has a NT-12SE in it originally from the factory and it is more than enough to keep it toasty warm even in below freezing weather. The NT-16SE had to be used in later years because Suburban stopped making the NT-12SE.
Gene

That's what I figured Gene. Actually, I think the 16k works against itself to be honest. It raises the air temp so quickly that it shuts off the thermostat before any of the structure warms. Then the temp drops like a rock and the cycle repeats. If the thing warmed more slowly, the heat would be absorbed and the cycles would be smoother, at least in theory
David

[David Morgan]

Originally Posted by DavidSo

That's what I figured Gene. Actually, I think the 16k works against itself to be honest. It raises the air temp so quickly that it shuts off the thermostat before any of the structure warms. Then the temp drops like a rock and the cycle repeats. If the thing warmed more slowly, the heat would be absorbed and the cycles would be smoother, at least in theory
David

Honestly, the 1200 is still too much if you ask me. It gets too hot to quick, and causes the extreme "hot & cold" swings. Should note that I have an ensolite unit with no insulation like the newer rigs.

I have the standard cheap thermostat.

Is there one with better duty cycle control? I really think this is where we could all get some benefit!

[DavidSo]

David,
Lots of people have switched to digital thermostats. It is a cheap and very good fix to the wild temp swings. I do think a smaller heater would actually match the space better too.
David

[David Morgan]

Originally Posted by DavidSo

David,
Lots of people have switched to digital thermostats. It is a cheap and very good fix to the wild temp swings. I do think a smaller heater would actually match the space better too.
David

I wondered if the digital ones worked better! Learn something everyday

That is what I love about the catalytic styles. You find a balance point on the dial... And you're comfy all night! I think an 800 -900 BTU furnace would be more appropriate for a 13' trailer.

Anyone know the rating on the wave 3 catalytic off the top of their heads?

I couldn't take the condensation with smooth walls. That is why I switched to the furnace to begin with. The noise is a fair trade off from the inside rain!

[DavidSo]

Originally Posted by David Morgan

I wondered if the digital ones worked better! Learn something everyday

That is what I love about the catalytic styles. You find a balance point on the dial... And you're comfy all night! I think an 800 -900 BTU furnace would be more appropriate for a 13' trailer.

Anyone know the rating on the wave 3 catalytic off the top of their heads?

I couldn't take the condensation with smooth walls. That is why I switched to the furnace to begin with. The noise is a fair trade off from the inside rain!

David,
People have been using the cheap digital thermostats from Walmart, and that is what I plan to do. Don't buy an RV digital because they cost way too much! I've used cats before too and I like them. I especially like the quiet. I designed an exhaust hood for mine that eliminated most of the moisture. It came down over the top of the cat slightly and served as a heat exchanger as well as an exhaust. It was all made from aluminum sheet. My trailer came with the furnace but if I can't successfully quiet it, I will probably go back to using a cat.
David

[GeorgeR]

Originally Posted by DavidSo

David,
People have been using the cheap digital thermostats from Walmart, and that is what I plan to do. Don't buy an RV digital because they cost way too much! I've used cats before too and I like them. I especially like the quiet. I designed an exhaust hood for mine that eliminated most of the moisture. It came down over the top of the cat slightly and served as a heat exchanger as well as an exhaust. It was all made from aluminum sheet. My trailer came with the furnace but if I can't successfully quiet it, I will probably go back to using a cat.
David

I installed this thermostat - http://www.fiberglassrv.com/forums/f...t-40903-2.html - post 17. It runs on 2 AA batteries which are installed in the swinging door. To disconnect the batteries I just swing the door out.

George

[GeorgeR]

I found these two 3A and 6A 12VDC regulators. Waterproof feature is nice. Fan RPM at 12V could be reduced by approximately 13% from 13.6V or 17% from 14V. In noise level this reduction could be more significant. I am contemplating getting one of these and measure the sound at 12V and 13.6V. Furnace noise is very annoying. Additional RPM reduction could be easily done by a resistor in series.

George.

DC-DC Stable Converter Voltage Regulator 8V-40V Step Down 12V 6A 72W waterproof | eBay
DC-DC Converter Regulator 8V-40V Step Down 12V 3A 36W Voltage Stabilizer | eBay

[Herb Sutton]

In the installation manual for NT 16 SE furnace that I installed last year it tells how to adjust the thermostat for longer or shorter cycles. The adjustment is called the "anticipator"

[David Morgan]

Originally Posted by Herb Sutton

In the installation manual for NT 16 SE furnace that I installed last year it tells how to adjust the thermostat for longer or shorter cycles. The adjustment is called the "anticipator"

Yes that is correct, I have tried Various combinations with the little dials, and it does change to cycling times, but not in a seemingly beneficial way. I am going to give the digital house Tstat a try. And see what happens. It should be noted that while I was running on the reduced power, the cycle times were more appropriate. And the unit ran slightly longer but without the huge extremes in temperatures.