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Topic: Suburban Furnace Model SF-35 Battery Drain

Posted By: StonePony on 01/17/09 03:09am

From what I can Figure out ,the furnace operates on 12V. When I use the Furnace, it draines my generator starting batteries even when I am hooked up to shore power.

Does anyone reccomend a fix for this problem?

Posted By: past-MIdirector on 01/17/09 06:10am

Check your battery first. Then check your converter since it runs the 12 volt power threw the battery on shore power. It's sounds like it's going to be either the battery or converter is bad.

Posted By: MNtundraRet on 01/17/09 06:33am

If you haven't done it already, check the circuit breaker for the converter/charger. Also check for blown fuse for unit.


Mark & Jan "Old age & treachery win over youth & enthusiasm"
2003 Fleetwood Jamboree 29

Posted By: ronfisherman on 01/17/09 06:35am

Many converts have a set of fuses at the out put side of converter. check these fuses.

2004 Gulf Stream Endura 6340 D/A SOLD
TST tire pressure monitor system
2012 Chevy Captiva Toad

Super C Group Forum

Posted By: MELM on 01/17/09 09:01pm

What RV?

What power converter do you have? Make and model?

Your problem may be the result of the manufacturer's choice of connection point for the furnace power.


Posted By: StonePony on 01/18/09 07:34pm

I just bought this RV. I will start at the converter. It is connected to a 110 AC outlet in the rear of the unit. I can hear it buzzing, so I know it must be getting power... I will chect output voltage, and make sure it is connected to my Batteries..


Posted By: MELM on 01/18/09 08:25pm

I guess I wasn't clear...

We need the make and model number of the converter - there are not all created equal, and it would be helpful to know what RV you have - year and model info.


Posted By: StonePony on 01/18/09 09:29pm

1992 Safar Kenya.
454 Chev.

I will take a look at the Charger / inverter in the AM and post the brand / info.


inverter is a Magna-Tek 50 Amp Series 900 Model 950-2

* This post was edited 01/19/09 07:53am by StonePony *

Posted By: Triker33 on 01/19/09 04:56pm

Hummmm! MELM must be busy today. Looks like you gave him the information he wanted.

Posted By: MELM on 01/19/09 09:23pm

I looked early this morning, and the converter model hadn't been posted yet...

The converter model makes a big difference.

MagnaTek became Parallax, and Parallax discontinued the 900 line over 5 years ago. It is a ferroresonant converter, and Parallax has the information on them on their website: Ferroresonant Converters. You can download an owners manual and a FAQ document, and click on the Technical Documents Link at the top of the page, you can get a schematic for it on that page.

The current Suburban listing shows the SF-35 furnace draws about 9 amps.

The converter is connected directly to the batteries, and all 50 amps should be available to power the furnace and any other loads and charge the battery when you are on shorepower or generator. So, the batteries should not be discharging when the furnace is on.

The converter does have a couple of unique requirements. It requires a good battery, or a battery simulator, to have the correct output voltage. And, particularly when on generator, the generator AC output frequency must be 60 Hz or higher or the output of the converter drops rapidly.

Some things to check:

1. It is common for the generator to start off the house batteries, but some use the chassis battery. So, you need to determine which yours uses. Disconnect shore power. Disconnect the house batteries. Try to start the generator - and/or check the voltage at the generator with a meter.

If it still starts, it gets its voltage from the chassis battery.

2. If the generator started, shut it off. Try the furnace. If it runs OK, it has been rewired to the chassis battery.

If it doesn't run, connect the house batteries, turn on a light and try the furnace again while watching the light. The light should only dim slightly with the added load of the furnace. If it gets real dim and/or the furnace fan does not come up to speed and the burner light, the battery needs to be recharged, or possibly replaced. If there is a good battery shop near you, they usually will test batteries for free.

If you have a voltmeter, you can check the output of the converter and at the battery. The converter output is about 13.8 volts when it is correct and the battery is at least partially charged.

With the converter output being 13.8 volts, it will take at least 3 days for that converter to fully charge deeply discharged batteries. (The initial charge rate is high, but falls very rapidly.) And, in hot weather, that voltage will cause the battery to need a lot of water.

Make the checks to determine which battery your generator is connected to, and on the furnace performance running on battery only.


Posted By: StonePony on 01/20/09 01:41am

Thank you Mel...

I havent had time yet to really get into it, but I will try in the morning..
This is what I know so far...

Although the batteries die faster with the furnace running, I have noticed that even the flourescent lighting on, the generator starting batteries will drain...

When the batteries get run down, the battery monitor inside the cabin above the frige reads low battery, and the generator wont turn over...(there are 3 Brand New Marine Deep Cycle batteries mounted in the generator box...)

There is a momentary on switch on the dash. (with a picture of a battery on it, and it looks worn, like it was used alot) When I push it, the cabin lights get brighter... So I tried having someone push this switch while at the same time I pushed the starter button on the generator. This allows the generator starter to spin rapidly, and start...

I have noticed that after using the switch on the dash to "jump start" the Generator, The Generator will re-charge its starting batteries, (because after a few minutes, I can shut the generator off, and re-start it without issue..)

However even with the generator running, the monitor inside the cabin (Above the refrigerator) will not show a charging condition....(only when the RV engine is running will the inside monitor show charging)

Also when the cabin monitor above the frige shows low batteries, and the generator will not spin, I am able to start the engine on the RV with no problem. With the RV engine running, the cabin monitor above the frige will now show that the the batteries being monitored are charging..

I dont know which group of batteries are being monitored by the cabin monitor though... I will assume that There is an isolator somewhere that will allow the alternator on the RV engine to charge the cabin monitored batteries and prevent current drain to the starting battery. (the starting battery is monitored by a seperate guage on the dash)

So far I have located 2 battery groups... one single battery up front near the RV engine, (I assume for starting), and one group of 3 on the generator.

I have noticed something in the rear compartment next to the Charger / inverter that may be part of the problem:

If I look in the rear compartment of the RV, where the Charger / inverter is located, I can see that there was a battery or maybe batteries... next to the inverter at one time because there are battery cables just dangling that are routed to and look like they were connected to the group of 3 on the generator at one time... The cables are very thick (look like#2) and in good condition, and just sitting there with both ends taped up, and not connected to anything...

I just purchased this RV, and I am starting to think that maybe the dealers mechanic removed this rear battery because if I look at the pictures of the RV on the internet, The 3 batteries in the picture are older, and therfore I know that he replaced them because all 3 are spanking new now...

I think there is reason to believe that the Charger / Inverter may not even be attached to the generator batteries.... It is possible that he didnt make this connection when he replaced these batteries...

Posted By: StonePony on 01/20/09 07:23am

Thank you for your time, your link to the manual let me better understand the system, I didnt realize how simple the wiring is, and I was able to trace the wires back and found 2 bad connections.

Problem solved....

Thanks Again...


Posted By: MELM on 01/20/09 08:59pm

I'm glad you found it. You made had acquired and provided some good information. But you found the problem and posted it before I saw it.

I'll make some comments on things you said.

Your dash switch should cause a relay to pull in connecting the house batteries (the ones by your generator) and the chassis battery for Emergency Start. That relay (sometimes called a solenoid) should be near the chassis battery with the heavy positive chassis battery going to one large terminal, and a similar size cable from the house batteries going to the other large terminal. The small terminals are for control of the relay.

When the engine is running, that relay should engage so the alternator charges the house batteries. And that relay is called the battery isolator - one relay usually is used to do both isolation and emergency starting.

The wiring in the compartment where the converter is located was possibly used for a large inverter (changes the 12 volts DC to 120 volts AC for TV's, kitchen appliances, etc.) or inverter/charger. (It is not good to install batteries and electronics in the same area - the gasses from the batteries are corrosive to the electronics.) If it was an inverter/charger, there may be an AC power cable in that area, too. If it was an inverter/charger, they may have just left the converter installed and unplugged the AC power to it. They removed the inverter/charger before selling it, and didn't recheck that it was working correctly.

If you didn't get manuals for the appliances with the RV, find the make and model information on them as many of the manuals are available online.


Posted By: StonePony on 01/21/09 07:19am

I do have a ton of manuals and records.. the original owner documented everything.. including hand written instructions on how to operate a few things... they are in a large file box, and categorized...

Although it is an older coach(1992 Safari Kenya), It seems to be very well maintained. It only has 40,000 miles on it and there is hardly a screw hole in the wall that shouldnt be there. The cabintery appears to be solid maple and is in perfect condition...
a new onan 6.6 generator delivers enough electric power for all the appliances, including a washer / drywe, and both AC units.. The 454 delivers plenty of power, with the banks powerpack, and there are a few suspension upgrades as well..

You seem to know alot about these coaches, and this is my first.
If you dont mind, I would like to ask you a few questions please.

1. There is an air compressor on the underside of the coach that has lines leading to a set of airbags and the electrical connection has been disconnected, but there is also an air fitting mounted on a fender...... Should I check for and maintain a certain pressure in the rear airbags, or is this supposed to be an automatic system..

2. There are 2 air fittings in the front of the Coach that lead to airbags on the front suspension... how much airpressure should be maintained ?

3. I am in the process of Replacing the suburban Hot water heater... it looks like someone installed a manual shut off valve on the inlet side of the heater.. shoud I reinstall it with the new heater, and when would I need to use other than if I had a leak in the water heater?

4. I noticed at many of the races, people sit on thier roofs to watch.... is it safe for the roof? and are there railings that I can buy to make it safer for the people up there?

Posted By: MELM on 01/22/09 09:55am

Much of my "knowledge" is from the various manufacturers and other credible sources that have printed or put their info on the Internet. And much of that is from other forum members' posts. But your MH is a couple of years newer than mine, so a lot of what I have for it also fits yours.

I'm a little tardy on the reply, but my links didn't work and both websites listed below have been redone since my last visit. (That's my excuse, and I'm sticking to it.)

Your airbags are probably Firestone Ride-Rite's: Ride-Rite Air Helper Springs. You can "wander around" that site and learn more about them. The rear springs for your '92 Chevy motorhome are probably an earlier version of these:2080 Kit. In the Air Accessory Kits, you can see different kits that they have for control of the compressor. At the end of the Installation Manual, they have information on adjusting the pressure and recommended minimum and maximum pressure. Basically, they are used to get the motorhome level under varying rear axle loads.

The front airbags may be these: 4100 Kit.

When the front airbags fail, they are often replaced with these: Air Lift. They are available from a number of online sources.

The front airbags are an integral part of the front suspension, and need to be at the correct pressure as they affect the alignment, and hence, the ride and handling.

From the Chevrolet motor home chassis service guide:
"Inflation pressures should be maintained at 10 psi minimum to avoid chafing.
Under load, 40-50 psi is recommended for a 4,300-lb. suspension, 50 psi for a 5,000-lb. suspension, 80-90 psi is recommended for the 5,500-lb. suspension."

You can also do measurements of the suspension components to determine that they are properly inflated; and they need to be properly inflated if you have a front end alignment done.

There also higher rated springs that can by used to replace the existing springs and the airbags, but they are more expensive than the bags.

I hope that helps.

In the future, I recommend that you start a new topic when you make a major topic change. In this case, I know there are members that have some experience with the airbags. If you do a Search on airbags or air bags, you'll find a ton of posts in Tech Issues and Class A, too.


* This post was edited 01/22/09 10:04am by MELM *

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