Suburban SF-30 Furnace - Current draw

Chris

Again thanks for the info - sure appreciate your comments over the years

No time delay relay on mine - not sure what serial # they changed over - mines a 2009 model year. Fan starts instant and stays on after the fire goes out for (best guess)60 to 90 seconds.

I heard from Suburban - My 2009 unit is considered old and obsolete

"As to the manufacturer this motor is no longer used in current production we still maintain replacement motors for the older SF series that used the 3 inch diameter motors.

I know the old manufacturer was Telco"

Have to guess my 5 year old unit is considered old & obsolete
Wonder why they no longer use this supplier?????

FWIW, if your furnace uses the standard time delay relay (there is a ~30-45 second delay on startup and shutdown) instead of the fan control circuit boards (no delay on start, delay on shutdown), you can replace the board with a fan control board and eliminate the time delay relay, which consumes a bit over 1/2 amp by itself (it uses a small heater for the time delay). This would require a bit of rewiring.

ktmrfs

Will let you know
Not sure if many others would be interested looks like $350 or so for the motor but not totally sure just yet. The price of about a tank and 1/2 of gasoline for the rig. Most of the custom motor manufacturers will not talk to me unless I have a volume purchase being directed to the Grainger's of the world. The search continues .............

KJINTF:

If you find a motor that works, let us know. I have the same furnace, and even a couple amp drop would make a difference. In the fall and spring the furnace draw really adds up and we dry camp a lot. One hour of furnace run time = 8 hours of living area LED lighting in our trailer. And in the "cool" seasons, the furnace runs WAY more than 1 hour/day. 1-2 hours in the morning is VERY common, then cycling during the day. And as the days get cooler, it gets worse fast. And like you I have a programable thermostat and also have set the allowed temp swing at 3 degrees.

Huntindog

Yes - the goal is to reduce current draw from the house battery, which is simply two 6Vdc GC batteries - no plans or space to make any changes there.
This motor exchange is one of the last currently planned modifications (to date completed about 150 modifications to the rig, with maybe 30 or 40 of them related to the DC power systems). I hope the motor exchange works as planned but if not I learned something along the way. Yes I plan on furnace air flow and power consumption measurements both before and after.

Yes I have 100% LED's no incandescent or florescent lamps anywhere inside the rig. Yes I have an accumulator tank on the water pump, low draw Fantastic fans, 550 watts of solar power, proactive alarm/warning system which drives LED's and sonalerts for both high and low temps/voltages, 2025RV Trimetric, Sure sine 300 inverter, etc.........

This last camping session the furnace had to run all day for two full days evening/night temps in the low 20's and day time in the low 40's. I use a 3 degree offset programmable digital thermostat to reduce the furnace cycling. Say 48 hours of furnace "on" with a running time of say 20 hours I hope to save 60 to 80 amp/hours again if not, O' well I tried and it did not work but I learned something along the way and the project kept me busy. I GREATLY enjoy this kind of challenge and have a shop with very impressive fabrication capabilities as well as the tools and experience required.


Chris

Thanks - I was not aware the other items of the furnace drew as much as a full amp of current. However the motor remains the power hog. Guess that's the reason I see 7.5 to 8amp draw when running. My Norcold 621 frig gas valve draws <400ma so I assumed the furnace valve would be about the same.

mena661 wrote:
Not all RV furnaces draw 6.5 amps. My MH's and my last 5er both draw 9 amps. Don't know the make though.

Yep- Suburban makes models that draw anywhere from 2.8 amps to 11.5 amps- Hydroflame is similar (though they have one that draws 1.8 amps).
The differences are all in the cfm rating of the blower motors (though the new models do use about 1/2 amp less than old ones, due to no klixon blower relay, which drew ~.5 amps).

Look at it this way- a cubic foot of air weighs ~.08 pounds. Moving 300 of them per minute is 24 pounds of air every minute. It adds up.

Not all RV furnaces draw 6.5 amps. My MH's and my last 5er both draw 9 amps. Don't know the make though.

KJINTF wrote:
Chris

"That" much as in 1/2 reduction? I hope so but am not holding my breath
The motor is rated at 6.5amps - Data from the Suburban web site
My 2025RV reads it taking 7 or 8 amps to do the job
Agreed its moving combustion air as well as room air
For me it's worth a few $$ to take a chance
Sure hope the manufacturer comes through with a nice motor
My Fan-Tastic fan motors are way more efficient that the cheap motors in the Suburban furnaces

Ken

I hope to - but am not setting my expectations too high - even a two amp current reduction would be nice and well worth the effort

The whole furnace is rated at 6.5 amps, but fully 1 amp of that is electronics and gas valve. The fact that yours is drawing above that does mean your motor is failing. The issue is amount of air moved- you can lower the current draw by blocking off some of the air flow, but that really isn't a good idea.

I'm sure you can lower the current draw, but I think only in the 10-15% range, or a half to one amp.

Chris

"That" much as in 1/2 reduction? I hope so but am not holding my breath
The motor is rated at 6.5amps - Data from the Suburban web site
My 2025RV reads it taking 7 or 8 amps to do the job
Agreed its moving combustion air as well as room air
For me it's worth a few $$ to take a chance
Sure hope the manufacturer comes through with a nice motor
My Fan-Tastic fan motors are way more efficient that the cheap motors in the Suburban furnaces

Ken

I hope to - but am not setting my expectations too high - even a two amp current reduction would be nice and well worth the effort