12 Volt Gremlins

[Radshooter]

I just put in a new deep cycle battery a few months ago. Now when the furnace is running, the 12v lights are dim. When we shut off the lights, the furnace spins faster. When the furnace shuts off, the lights come back up. I pulled a bulb out of a fixture last night and checked the voltage without the furnace running and only that fixture on. I got 12. 3 volts from the fixture. We are full-timers and hooked into shore power. We have not experienced any problems on the 110 circuit, just the 12v. The trailer is a '99 Travel Supreme 36RLTSO. We are the original owners.

We had a new fan put in the furnace last month, and the problems seem to have started since then. Could the repairman have re-wired the furnace incorrectly so that it pulls too much voltage? Before the furnace repair, all the 12v lights were dim, but the new battery fixed that. The old battery was fried and would not hold a charge.

Any ideas? Where do I start checking?

Thanks

 

[fest3er]

Look for a poor connection (B+ or ground). Using a simple volt meter, measure the voltage across the connection while there's a load (lights and furnace, for example). You shouldn't see more than a few millivolts. If you see . 1 volt or more, fix the connection (jiggle it, clean it, et al).

Remember P=IV (power = current * voltage). Suppose the furnace and lights draw 40A. A . 5VDC drop across a connection generates 20W of heat right there. Even . 1VDC generates 4W of heat.

Start with the usual suspects. First check the battery connections. Then check around the furnace, then expand from there. I'll bet someone didn't get a connection tight.

 

[jelag]

The lights dim from low voltage... I'd do that voltage check when the furnace starts and see what the real voltage is as the furnace starts... .

I'm going to guess that the voltage drops below 10. 5 to 11... . you might need a metered volt meter to see the drop... or a high end digital that will respond quickly... .

Now its time to find the cause... . The most common problem would be a bad connection, than a low battery... .

If your hooked to shore power when this occurs than you don't have a fully charged battery... . you should see 13. 5 or so with the voltmeter when the shore power is connected...

Its common to find loose connections because the connection itself is hot... any loose connection will increase the resistance of the circuit, thus increase the current draw and the voltage drop... that's why the connection is hot...

Do the simple checks and post your results...

 

[NIsaacs]

Since the problem seemed to surface after the new blower motor install, I would say the new motor is not the same. Maybe a higher amp draw unit or possibly even a 24 volt motor.



Nick

 

[Mikey-KE7LBB]

Another possibility is that one (or more) of the batteries isn't pulling it's weight anymore...



Disconnect and load test each battery by itself and check it with a load tester. Unfortunately, even new batteries can show 12v on a meter and be complete junk when subjected to a load test. FACT is that a battery may have a broken plate or two and still be able to show full voltage, but fail miserably when any significant amp draw is needed: ie... Water heater, furnace, inverter powering TV, starting generator, opening/closing slide outs... You get the hint???



Feel lucky that you have voltage at all cause I couldn't even get a single light to glow after a month in bitter cold. I had switched the isolator switch off to avoid this exact problem from happening and evidently, I too have a gremlin of some sort!!!



I will have to wait until spring or early summer to even try to figure it out :-laf

 

[Hoefler]

Check your connections at the battery, also check your convertor, it could be weak or bad.

 

[Radshooter]

Thanks everyone. Hopefully it will warm up a bit this afternoon and I can get out and check things.

The motor is a direct replacement, at least the numbers on the new motor matched the numbers on the old motor. We checked it before we put it in.

I just checked the light fixture with the furnace running... . 10. 3v. I did not check it as the furnace came on. The furnace and that light fixture were the only thing drawing power.

The lights do not dim and recover... they stay dim until the furnace shuts off.

I only have one battery in this trailer. How do I do a load test? Does it take a special tool or meter?

I will check the connections later today. I can disconnect the battery and get that voltage reading. If I put the tester on the cables while not connected to battery, will that tell me what the converter is doing?

I will also check the ground connections.

Thanks. I think I am fairly mechanical, but have never messed with electricity that much.

 

[B.G. Smith]

Could be a bad cannection as stated above. For the converter to keep the battery charged the voltage has to be above 13 volts. The converter should be of sufficient output to run your 12 volt equipment without a battery. It takes a special meter to load test the battery, and yes, you should be able to see what voltage the converter is maintaining with the battery disconnected but with some 12 volt load on the converter.

Good luck. bg

 

[CAPTPHIL]

Remember that BLACK WIRE IS POSITIVE in RV wiring. Make sure that you didn`t hook the black wire from converter to batt. to the Neg. post. Also if old batt. had a short in it, it could have taken out your converter. Been there done that on both.
Good Luck Capt Phil

 

[Radshooter]

OK... here is what I found:

All connections at the battery end are tight, no corrosion.

Battery unhooked from cables = 14. 8v
Measured across cables unhooked from battery = 15. 3v
Battery with cables hooked to it = 16. 9v

After my fingers thaw out I will check out the connections at the furnace.

Ideas???

 

[HBarlow]

I'm surprised your Travel Supreme has only one battery. The Travel Supreme I owned had two and the HitchHiker I own now also has two. A large fifth wheel, particularly a luxury fifth wheel like the Travel Supreme, has far too many lamps and other circuits using 12 volt power to power them all with only one battery.

The voltages you reported above suggest the ac-dc converter is working fine so I would have the battery load tested and then, if it is good and a very recently new battery, install a second one identical to the battery you already have. Two batteries in parallel will avoid the voltage drop and dimming lights when the furnace runs.

 

[Radshooter]

Thanks everyone. I just checked the connections at the furnace, and they appear OK. I undid the wire nuts on each connection, re-twisted the wire and put the nuts back on. It made no change after I turned the furnace back on.

I guess it is time to call an electrician.

I have thought many times about adding a second battery. Maybe now is the time. HBarlow... . when you say to install in parallel, do you mean positive to positive and negative to negative? I get parallel and series confused because I don't work with it enough.

Thanks all.

 

[Mikey-KE7LBB]

How do I do a load test? Does it take a special tool or meter?

A load tester is a very simple tool that can be purchased or rented from just about any auto parts store. It is basically just a heating element (like in a toaster), a couple of clamps to hook to a battery, a switch to apply the load, and a meter.



The tester is connected to the battery leads and when the switch is held in the "test" position, it will get hot while measuring the ability for the battery to supply the amperage needed.



It sounds like you have a decent battery, but with only one, it is being worked to death with trying to take care of ALL the 12v systems.



My RV has two, but the battery tray will hold six of them.



Multiple batteries connected in parallel are needed to supply enough current (amps) to power everything in the system and also maintain 12v.

 

[Mikey-KE7LBB]

Parallel would be all of the +'s hooked together with a strap and all of the -'s the same way and connected to ground... This will give you 12v with DOUBLE the amps and is what you need. ie, two 600 amp batteries in parallel would yield 1200 amps and 12v

If they are + to - with the same two batteries, it would give you 24v and 600 amps.

 

[HBarlow]

Thanks everyone. I just checked the connections at the furnace, and they appear OK. I undid the wire nuts on each connection, re-twisted the wire and put the nuts back on. It made no change after I turned the furnace back on.

I guess it is time to call an electrician.

I have thought many times about adding a second battery. Maybe now is the time. HBarlow... . when you say to install in parallel, do you mean positive to positive and negative to negative? I get parallel and series confused because I don't work with it enough.

Thanks all.

Yes, + to + and - to - as Mikey above already explained.

Be aware that if you install another fresh new battery in parallel with an older, weaker battery the new one will be limited by the weak one it is paired with. It is usally imperative to replace both at the same time. You should be okay if the current battery was recently purchased.

My Travel Supreme was a '95 and had a battery tray large enough for two batteries as original factory equipment. I'm surprised you can even run your slide-outs in and out using only one battery. The slide motors probably draw a lot of current.

 

[jelag]

You have another problem... if your connected to shore power and you only have 10. 3 volts with the furnace running, your power supply (converter) is not working as it should supply enough current to power all the items(12 volt) in the trailer at once...

If you had excessive current draw to the furnace... . it should trip either a fuse or a circuit breaker... I'd also look to be sure that you have something close to a 10 or 12 gauge wire from the circuit panel to the furnace...

There also might be another connection someplace in the circuit between the furnace and the circuit panel... . BTW - I don't remember seeing if you checked the connections at the circuit panel??

 

[Radshooter]

Thanks everyone... ... Well, 2 days and $700 later, we are fixed. The converter was fried, (it was 12 years old... things don't last anymore :-laf) and so was the battery. Failed the load test. Bought and installed a new converter. The battery got replaced under warranty. The other casualty (that we have found so far) was the circuit board in the fridge. Replaced that this morning, and now everything seems to be working fine.

Thanks again.

 

[jelag]

This might help prevent issues in the future... I put a digital volt meter in the trailer where I can walk by and read it, it's connected to 12+ at the batteries and has a push to test switch (momentary).

Sometimes when I'm hooked to the truck I push the button, verifies that the batteries are charging, and sometimes when connected to shore power, I do the same... . sort of a safety factor especially when we're parked and know that the temperature will drop and we'll need extra 12 volt power for heated mattress pad...

We have 3 12 volt batteries... and we installed a full sine wave inverter (square wave won't work), the inverter is 400 watts... which will power the flat screen, DVD player, other electronics, my cpap machine and of course the wife's heated mattress pad...

The heated mattress pad uses about 40% of a heating blanket as the heat rises, on at full it draws 90 watts, but with the dwell cycle it has, its average use is something like 30 watts an hour... . More than enough to allow the trailer to be a few degrees cooler, save on propane and keep the wife happy... . and theirs nothing like crawling into a warm bed. .

I could go on and on about the quality of the connections in a modern 5er... . needless to say I've changed out all the ones that I can find and pitched the scotch loc type for HD butt connectors and shrink tubing with adhesive in the tube for a water tight connection... .