Battery drain only while towing

[CampbellMcCa]

Each time I tow my 76 Argosy 24, the trailer battery is dead on arrival.

When connected back to shore power, the battery charges normally and holds its charge until the next time I tow.

This happens when towing during the day as well as at night, so the running lights would not seem to be the source of the battery drain.

My theory is that I have some kind of grounding problem that is causing the trailer brake circuit to drain the trailer battery in preference to drawing current from the TV. I say that because the trailer brakes seem to work normally right to the end of the trip, so I'm thinking the TV provides current once the trailer battery is drained.

Has anyone else seen this problem?

[azflycaster]

The trailer brakes and trailer lighting (running, brake and turn lights) run independently from the battery on the trailer. The only tie together they have is the break away switch in the trailer, but you would know if that was activated.

My guess is that the line that provides 12 volts to the trailer battery from your TV is somehow grounded. You should be able to meter the lines from your TV to verify this.

[CampbellMcCa]

Thanks for the suggestions, Richard. Any advice on where to put the probes would be welcome or maybe I need one of those 7 way breakout boxes?

One followup question I have is that if the drain is being caused by the TV, then I'd expect the TV to be blowing its own fuses ? The charge line is (AFAIK) connected direct to the TV's 12v line, so a short to ground there would be pretty catastrophic as far as the TV was concerned. I have not seen any strange behavior from the TV or its battery.

As you say, the only common point of potential failure is the breakaway switch. The breakaway switch is indeed old, its in my list of things to replace. However if that were the source of the problem, I think the drain would be independent of whether I was towing or not.

[azflycaster]

Maybe the 12 volt line has blown it's fuse and you do not know it. It is most likely a seperate fuse that only provides power to the trailer. In some TVs they are not installed by the manufacturer and need to be added when you go to tow. The other lines to the trailer would not be on the same circut. I would meter the end of the cable that plugs into the trailer (disconnected) first to see what you are getting from the TV. If that is good, check that the lines from the trailer (12 volt and ground) are correct also.

[overlander63]

It is possible the 12v feed line for the trailer is connected to something else when towing, instead of the charge line. Maybe the backup lights on the tow vehicle, or the backup lights to the trailer, etc. Does your fridge require 12v? It's possible if you have a 3 way fridge, it is switching to 12v, and your charge line can't keep up with the demand, thus draining the trailer battery.

[richinny]

Originally Posted by azflycaster

Maybe the 12 volt line has blown it's fuse and you do not know it. It is most likely a seperate fuse that only provides power to the trailer. In some TVs they are not installed by the manufacturer and need to be added when you go to tow. The other lines to the trailer would not be on the same circut. I would meter the end of the cable that plugs into the trailer (disconnected) first to see what you are getting from the TV. If that is good, check that the lines from the trailer (12 volt and ground) are correct also.

the wiring shown seems to be different from the "flashing trailer lights while parked" thread.

it would seem to be either a break in the 12v + feed from the TV due to either a blown fuse, broken wire or bad connection.

[ve3czn]

The TV should not be connected when you are in transit. Perhaps (if you have and electric fridge) a current drain maybe there. The fridge would drawn a considerable current.
I would have a suspicion that ther blocking diodes. that feed FROM THE CAR TO THE TRAILER ONLY could be suspect. There should be no current from the trailer battery to the car. If so then removing the 12 plus line from the battery and measure it with an OHM meter to chassis (ground) should show if that was a leakage. This is done with the supply line disconnected from the car.
You did not mention how long you would run before the battery is exausted.

Rae

[Inland RV Center, In]

Originally Posted by CampbellMcCa

Each time I tow my 76 Argosy 24, the trailer battery is dead on arrival.

When connected back to shore power, the battery charges normally and holds its charge until the next time I tow.

This happens when towing during the day as well as at night, so the running lights would not seem to be the source of the battery drain.

My theory is that I have some kind of grounding problem that is causing the trailer brake circuit to drain the trailer battery in preference to drawing current from the TV. I say that because the trailer brakes seem to work normally right to the end of the trip, so I'm thinking the TV provides current once the trailer battery is drained.

Has anyone else seen this problem?

There should be two 50 amp fuses in the Univolt.

One goes to the trailer battery, and the other goes to the charge line.

Disconnect the trailer battery, then plug the trailer into the tow vehicle. If nothing works, the charge line fuse is bad.

Or, if you have a DC voltmeter, see if you have 12 volts DC at the trailer connector. Again, if not, then the charge line fuse is open.

Andy

[TomW]

Originally Posted by overlander63

It is possible the 12v feed line for the trailer is connected to something else when towing, instead of the charge line. ...

I think Terry's on to something here.

Tom

[CampbellMcCa]

I can't say for sure how long it was before the trailer battery was drained, I noticed after a 200 mile trip and again after a 1500 mile trip.

I have had a few blown fuses here and there in the trailer systems but I had thought I had resolved them all. I did not think to check the TV 12v fuse.

Thank you all for your suggestions.

I will try them all and report back.

[CampbellMcCa]

In reply to Terry's suggestions;

I'm pretty sure the 7 way connector wiring is OK. The TV end was done professionally and I carefully rewired the trailer end myself. I tested it all with a meter before connecting up and it all worked perfectly first time (apart of course from the anomaly under discussion). I am aware of the common backup light issue and confirmed during initial hookup that it isn't happening here.

BTW, our fridge is currently off. It needs to be replaced.

I also confirmed that there is no drain on the trailer battery when it is at rest.

[CampbellMcCa]

Richard,

That diagram is the back of the TV plug, right?

If so, TV voltages look good.

[overlander63]

Hmm...Maybe you are leaving the water pump on? Maybe the furnace fan is coming on (the mercury switch is being engaged by road shock--AKA bumps)
Try unplugging the fan motor on the furnace, and make sure the water pump switch is off. There's gotta be something...
Do you still have the original Univolt? I tossed ours when it started discharging the battery when not plugged in. It was a pretty hefty drain, too, about 10 amps.

[Zeppelinium]

Originally Posted by overlander63

Hmm...Maybe you are leaving the water pump on? ...

If it's the water pump, you should hear it when you enter the trailer. This happens to me frequently because I'm too damn dumb to remember to turn it off. What happens is an air bubble gets bounced up into the impellor and the pump starts running due to some pressure fluctuation. It can't prime itself due to all the faucets being closed and the back pressure. So it sits there and runs.

But your TV charging line should prevent the pump from running the battery down. You have a real mystery.

Zep

[overlander63]

Originally Posted by Zeppelinium

If it's the water pump, you should hear it when you enter the trailer. This happens to me frequently because I'm too damn dumb to remember to turn it off. What happens is an air bubble gets bounced up into the impellor and the pump starts running due to some pressure fluctuation. It can't prime itself due to all the faucets being closed and the back pressure. So it sits there and runs.

But your TV charging line should prevent the pump from running the battery down. You have a real mystery.

Zep

But if the Univolt had an internal short, it could charge the battery when plugged in, and discharge it just as quickly when unplugged. I am only dwelling on this, because it happened to us with our Sovereign. It would charge, then I would unplug it, and return to the storage lot, and a day or two later, the battery was dead.

[overlander63]

Now, here is how to check for a draw:
1- Make sure the battery is fully charged to begin with, then unplug the main power.
2-Remove the negative battery terminal, and place a test light between the terminal, and the negative post of the battery. If there is a draw, the test light will light.
3-If the test light does not light, hook the umbilical to the tow vehicle, and retest, with the tow vehicle both running, and off.
4-With the test light lit, disconnect fuses one at a time until the light goes out. That circuit contains the draw. If you remove all the 20 amp fuses, and the test light is still lit, the problem is probably in the Univolt. Disconnect it from the system, and the light goes out, you have narrowed the problem to the Univolt, and can replace it.
5-If the test light remains lit, check for non-stock items that are wired directly to the battery, such as a radio amp, or TV antenna booster.
6-If the test light never comes on when performing this test, remove the battery and take it to be checked, it may have a problem that causes it to drain itself.

[CampbellMcCa]

Good suggestion on the water pump, but no. I've been towing dry and the water pump has been switched off throughout.

Unless this problem has appeared in the last month, I can say that the Univolt is not discharging the battery, because it was holding the charge fine when disconnected before that.

Terry, that test sequence is great, guaranteed to isolate the problem one way or another. I will carry out this test and report back (the trailer is in storage and this test will have to wait until I next visit it).