Battery Drain When Travelling - Power Converter Issue?

[SirDrake]

On the last couple trips we took we have arrived at the campground with a drained TM battery and a not so cold refrigerator (about 5/6 hours on the road).

We tow the TM with a fully charged battery with the refrigerator on DC and the refrigerator fan running.
We also have an electric cooler plugged into one of the 12 volt outlets inside the TM.
We have traveled like this in the past with no issues.
Since our last trip I have done extensive troubleshooting and I am stumped.
Perhaps someone can help me find the culprit.

Here is some history:
We have a 2004 2720SL Trailmanor. We have owned it for 5 years now.
We tow the TM with a 2002 Chevy Avalanche Z71.
I replaced the battery in the TM in 2011 with a DieHard Deep Cycle Group 27 battery (the previous battery was a Group 24).
I replaced the alternator in the Avalanche in 2012 because it failed. It is a 105amp alternator (same output as the original).
I had the option to upgrade to a 130amp alternator, but I decided to stay with the same kind (never was a problem before).
When the TM is parked at home, I keep it plugged into shore power to keep the battery charged.
Over the winter I bring the battery inside and keep a trickle charger on it.
I clean the connections on the TM tow cable and on the Avalanche tow connector every year and make sure lights, etc are all working.

Since the battery drain incident I did some testing with my volt meter and here are the results:
With a fully charged TM battery the reading at the battery is 13.76 volts (right after being plugged into shore power).
With a fully charged TM battery, the reading at the TM Tow Cable is 13.66 volts
With the Avalanche running, reading at the Tow Plug on the back of the truck is approx 13.60 volts
With the TM plugged into the Avalanche and the Avalanche running, reading at the TM battery is approx 13.56.
If I let the truck run and plugged into the TM (nothing else drawing power - no fridge or anything) the voltage will drop about .01 volts every 5 mins or so.
If I turn on the TM Fridge & Fan, voltage drops more rapidly. If I plug the Electric Cooler in voltage drops even more.
At one point I checked the voltage at the TM battery before I plugged everything in and I got 13.05 volts.
Then I turned on the Fridge & Fan and the reading went to 12.69 volts
I added the Cooler and reading went to 12.49 volts
The reading will continue to drop at a good clip if I leave it all running like this.

Here is where it gets interesting...
I decided to turn everything off and disconnect the cables on the TM Battery.
With the truck running and plugged into the TM I took a reading at the TM Battery Cables (not connected to the battery), the volt meter reading was 1.5 volts!
I was shocked, I thought I should get the same reading as if I were taking it right at the truck tow plug (somewhere around 13.5 volts).
I expected that the voltage from the truck should be passing directly to the TM Battery.

So I decided to take a few more readings.
I went inside the TM with my volt meter and took a reading at the positive & negative cables inside the Converter.
With the truck running and plugged into the TM I get 1.5 volts!!

Next, I disconnected the Tow Cable from the TM (I opened the side compartment on the TM and untwisted the wire nuts connecting the Tow Cable's positive and negative lines).
With the truck running and plugged into the TM tow cable, the reading at the ends of the cable (bare wires) I get approx 13.5 volts. So voltage is passing through the Tow Cable from the truck no problem.

If I connect the positive cable from the Tow Cable to the positive cable that goes to the on board Power Converter, the reading drops to 1.5 volts!!!.
So the power coming from the Avalanche, through the Tow Cable apparently passes through the TM's Power Converter and then into the TM battery.
I'm getting the full 13.5 or so volts through the truck, and through the tow cable, but as soon as I introduce the power converter, it drops to 1.5 volts.

My question is, shouldn't it pass the full voltage to the battery (13.5 or so volts)? Dropping to 1.5 volts seems to be ridiculously low.
Is the Power Converter defective?
It works fine when I have shore power plugged in (it powers the TM and charges the battery).
The converter in my TM is a Parallax 7345.

I was ready to start replacing the tow cable or the truck alternator, but I think there is something wrong with the power converter.
Anyone have any ideas?

~ John

[Bill]

Nice job of troubleshooting. You've already eliminated most of the things I was thinking could be wrong.

Let me be sure I understand. In the past, with this TM and this tow vehicle, you have been able to travel with the TM refrig running, and at the same time a separate thermo-electric cooler running? That is an impressive electrical load - most rigs won't handle it.

So the TM battery is connected to all the TM loads, and these loads are sucking the TM battery down. And power from the tow vehicle reaches the converter, but doesn't pass through, to power the loads and keep the TM battery charged? This should be a direct metallic connection - to my knowledge, there is nothing inside the converter that could affect or disconnect the pass-through of the truck power. So that is where you should start looking.

First step. With everything hooked up as it should be, tow vehicle running, use you meter to measure the voltage between the converter's 12-volt in (from the tow vehicle) terminal, and the converter's 12-volt out (to the TM battery) terminal. There should be no voltage there, but it sounds like you will find almost 12 volts there, indicating an open or almost open circuit within the converter. Assuming you find a big voltage there, next step would be to shut everything down (disconnect TM battery, disconnect Bargman connector, no shore power), disconnect from the converter terminals the two 12-volt wires mentioned above, and connect them together to bypass the converter (be sure they don't short to anything else, including ground). Start the tow vehicle, plug in the Bargman, and see if the situation is now normal, or still has an error. If you can do it, the best check is to measure the charge current into the TM battery with the tow vehicle running. It should be a couple amps with no loads turned on and the TM battery charged.

Bill

[SirDrake]

Thanks for the reply Bill.

Let me be sure I understand. In the past, with this TM and this tow vehicle, you have been able to travel with the TM refrig running, and at the same time a separate thermo-electric cooler running? That is an impressive electrical load - most rigs won't handle it.

That is correct. The first couple years we just used the TM fridge while traveling - no issues. Then we added the small electric cooler.
Most of our trips have been between 4-6 hours long.
Always arrive at campsite and able to use electric tongue jack and fridge is reasonably cold.
We also start the fridge and cooler a day or so in advance and load them with items to get a head start.

First step. With everything hooked up as it should be, tow vehicle running, use you meter to measure the voltage between the converter's 12-volt in (from the tow vehicle) terminal, and the converter's 12-volt out (to the TM battery) terminal. There should be no voltage there, but it sounds like you will find almost 12 volts there, indicating an open or almost open circuit within the converter.

I think I understand what you mean here.
I disconnected the positive and negative wires from the converter board.
I twisted them together with wire nuts (positive on one nut, neg on the other).
I connected the truck to the TM and started it. I am reading 14 volts at the wire nuts I just made.
Also reading 14 volts at the battery end (disconnected from TM battery).
If I connect the positive leads and negative leads back to the converter board and put the volt meter on the connection block, I get 1.5 volts.
So it looks like there is something drawing down the voltage through the converter. How do I proceed from here?
I am not an expert with electrical systems by any means - I know enough to get by (or get in trouble, he he).
What do you think?

[Padgett]

First: is anything other than the back of the fridge or the cooler getting hot ?
Seccond, while voltage can tell you something, I'd also want to look at the current draw at each point particularly at the Bargman. (am building a male-female bargman jumper to be able to test such easily.

ps with the TV running my thought is that the 1.5v is the difference between the 13.6 alternator output and a 12.1v battery.

Enclosed is information I've comllected on the WFCO from several sources. Hopefully it will help put together what goes where. How do you submit things for the library or do we have copyright issues ? (generally if for purposes of education collections are OK.)

[ZekenSpider]

My thoughts are:

In any TrailManor that I have worked on, the 12 volt side of the TM, tow vehicle(if plugged into the TM) and converter output are all tied directly to each other. All of the positive wires are connected to each other (some through plugs and through fuses) and all of the negative wires and frame grounds are tied to each other. Look upon the DC system as consisting of a positive Buss and a negative Buss (Buss is just a fancy word for a common connection. There is a positive buss and a negative buss). Weird things can happen if any single wire becomes disconnected it's appropriate buss.

The most common malfunction occurs when a ground (negative) wire gets loose or corroded and is no longer connected to the negative buss. The TM frame is the primary negative buss.

A converter malfunction should have no effect on what I call this TM 12 volt Buss unless the converter malfunction (if any) is drawing current from the 12 volt Buss. It is clear from your tasting that the converter charges the battery so that means both the positive and negative wires from the converter to the battery are connected.

Your test also showed only 1.5 volts DC at the disconnected battery leads with the tow vehicle connected and running. This tells me that, at least, one of the battery leads is not connected to the part of it's DC buss (probably the negative and the frame). I suspect the TV negative is not grounded.

I would look carefully at all TM frame connections. The converter negative output should be tied to the frame and the tow vehicle cable negative should also be tied to the TV and TM frames. Do not use the hitch ball as a negative (ground) connection.

These are tough problems to track down but a serious clue is that "it used to work but now it doesn't". Frame connections very often become loose or corroded. First use your voltmeter to check for voltage from all positive test points to the frame. I think you will find the tow vehicle negative cable is not connected to the frame somewhere. I found mine in a loose wire nut inside the refrigerator outside lower access door.

Hope this helps,

Jerry

[mjlaupp]

Originally Posted by SirDrake

....Next, I disconnected the Tow Cable from the TM (I opened the side compartment on the TM and untwisted the wire nuts connecting the Tow Cable's positive and negative lines).
With the truck running and plugged into the TM tow cable, the reading at the ends of the cable (bare wires) I get approx 13.5 volts. So voltage is passing through the Tow Cable from the truck no problem.....

13.5 volts is a normal reading with no load on the circuit. Add a load (converter) and you get:

....If I connect the positive cable from the Tow Cable to the positive cable that goes to the on board Power Converter, the reading drops to 1.5 volts!!!.....

You have a bad connection or corrosion on the 12 volt line between the TV battery and the point where you are measuring voltage. Does your Avalanche have a battery isolation device? My first suspect area would be at the 7 pin connector.

[mjlaupp]

Originally Posted by mjlaupp

....You have a bad connection or corrosion on the 12 volt line between the TV battery and the point where you are measuring voltage.....

Try connecting the TV battery to the converter wires at the fridge connection using battery jumper cables to test for this.

[SirDrake]

OK. I think I have solved the problem.
I am now getting 13.5 volts at the connection on the Power Converter (where I was getting 1.5 volts previously).

After reading all the advice you guys posted, I started looking into those areas you pointed out.
I had replaced the connector on the back of the truck so I know that is good.
I also cleaned and tested the end of tow cable on the TM - so I know that is good.
While troubleshooting this issue this weekend I also opened all the wire nuts in the refrigerator compartment on the side of the TM.
They were all in good shape - no corrosion etc (I replaced all wire nuts here a few years ago anyway).

So then I started looking at all the ground points on the Avalanche.
I found a broken ground strap between the hood and the firewall - I cleaned and repaired it.
Cleaned the ends of the ground cable from the engine block to firewall.
The underside of the truck is very rusty, so I located all the ground points I could find - about four in all.
I used PB Blaster on all ground points then I removed the bolts and scrubbed everything with a wire brush, then I reconnected them.
After that I began to look for ground points under the TM.
The only connection that looked suspect was one of the gray water tank probes - it was rusty and corroded.
I disconnected it and scrubbed it with a wire brush and replaced.
That was it.

I left the TM battery disconnected, plugged in the Tow Cable and started the truck.
Put the meter on the positive and negative block on the Converter and to my surprise it now reads 13.5 volts!
I reconnected the TM Battery and tested again - 13.5 volts and holding.

In addition, I managed to fix another important issue while investigating all this.
I found that the power lead to the safety breakaway cable for the brakes had been severed at one point along the frame!
Not sure how that happened, perhaps it has been like that since I bought it, but in any event I reconnected the line so all is well.
I suppose I should test it. Another day....

Thank you to everyone who helped out with advice. It is much appreciated.
Our next trip is in August to the Thousand Island region in upstate NY - about a 4-5 hour trip.
I will post here the results of running the fridge and cooler.
Hopefully it goes well.

~ John

[TM Pilot]

That the grounding points on your TV were corroded and causing the low voltage instead of the grounding points on the TM makes sense since the TM battery didn't charge via the TV but did charge when connected to shore power.

Low voltage is often caused by a corroded ground, therefore it is a good place to start the troubleshooting process. My electric tongue jack stopped working because of low voltage due to a corroded ground through my swing hitch. Once I cleaned it, it worked great.

Good work, John! Glad your TM issues have been resolved. And nice catch on the breakaway cable power lead. Having a fully charged battery while towing wouldn't mean a thing during a breakaway if the power lead is disconnected! Looks like your charging issue was a blessing in disguise.

[SirDrake]

Yeah, I think it was Jerry who pointed out the positive and negative buss and that everything grounds to the frame on the TM and TV.
Started to make sense that if there was a bad ground it would cause the low voltage, but was not obvious to me at first; especially that it would be the TV.
Not sure which ground it was on the Avalanche, but I think I fixed them all (including the broken strap to the hood).
It was pretty rusty on the underside, not surprised if there was a bad contact there.
And like you said, I found the broken breakaway cable so I guess it was all worth it.
Thanks again for all the help guys.

~ John