I thought I would post this here as it isn't really specific to my '99 SD.

I'm pretty sure I already know what the issue is, but wanted to run it past a few of you smart people before I run out and grab a new battery for my 350.

This weekend we took our TT out for the first time but were on full hookups and did not use batteries other than an hour two where power went out in the entire valley due to a wind storm. Upon returning home I parked in the driveway temporarily and while cleaning up I was checking my tanks to see if the tank sensors were reading properly as empty yet (separate issue) and pushed the battery button to find that it was only reading 2/3 which surprised me as they should have been fully charged after the 90 minute drive home and the converter being on all weekend. I checked the voltage manually and sure enough they were only 12.4 volts (50% I believe). I was starting to wonder if there is something wrong with my converter or my batteries. The batteries are two fairly new (less than 1 year) 12V Interstates. I checked the converter and it seemed to be working once I parked the TT and plugged it into the house.

Then I had a thought. I've noticed my battery voltage before I start my 350 is running around 12.1 to 12.2 which I know is a bit low, but the truck has been firing up just fine. I went and checked the truck's battery and sure enough it was only reading 11.9. So do you think it's possible that even though my alternator was putting out close to 14V the whole trip home (according to my SG2) that sitting in the driveway for a little while with the TT plugged in that it drained my TT batteries down trying to charge the truck battery? I'm sure I need a new battery in the truck, but I'm hoping that caused my charging issues on the TT too.

On a separate note, should I trust the converter that came with my Jayco to maintain my batteries or should I use my battery tender instead, at least until I get solar?

 

I've heard of the TT draining the TV battery, but not the other way around. I would imagine the converter's circuits would prevent that kind of back flow to the current.
If the TT batteries are in physically good shape (plenty of water, etc), I'd recheck them after being on shore power over night.
Normally your truck runs all electrical from the battery as you drive, then when the voltage reaches a certain point the alternator kicks in to recharge it. I imagine if your battery is bad then the alternator might be trying to constantly charge it and there is nothing available for the TT batteries.

 

I would disconnect the batteries & charge & test separately first,then clean connections before connecting to known good batteries,check any grounds as well.

 

I've actually had that happen about a year and half ago. My TT battery died on me (old TT) and I almost ended up stranded in an empty campground during the winter. I didn't notice until I tried to do dishes in the morning when I turned on the water pump as we had LED lighting and the furnace didn't have a blower. I had left the truck plugged in as it was a quick overnight stop. Luckily I was able to unplug the trailer and barely get it started, I don't know how it started considering how slow it was turning over and it was only 35 outside. Fortunately we were only 10 miles from a NAPA in a town of a few hundred so it didn't ruin the weekend and we were able to dry camp for two more nights with the new battery.

Anyhow, based on the advice here and elsewhere I think I'll check the water levels, charge them separately with the battery tender, and then see how they behave with a load, I've got at least two weeks before our next outing. But the truck is getting a new battery for sure. Don't want to have to use the TT to jump start the 350 on our next trip .

 

Pardon my ignorance, but shouldn't there be power at the 7 pin plug only when the ignition is on? That's how it works on my current truck, which isn't a Super Duty.

 

That's what I thought as well. I'm wondering if that true based on my experiences. That is another thing I definitely need to look into. My camper shell lights (bought by the PO and installed by the camper shell dealer) are tapped into the 7-way and always have power now that I think about it. I think some re-wiring is needed to remedy that. After my experience a while back running the truck battery down I usually unplug the trailer once we stop somewhere for more than an hour or two.

 

If things are happening as you suggest there is a problem with your truck. The charge line should only go hot with the ignition on, as there should be a relay that closes when the ignition is turned on.

Using your power converter to charge your trailer batteries is not the problem or a problem.

Your alternator should easily handle your loads, but the numbers you want to verify that are amp outputs and draws, not voltage.

As suggested, get everything charged up, so you have valid baselines. All stuff that is very easy to check.

Steve

 

We have a work van that has an aftermarket install of the 7 pin and hitch. When the person wired it, the 12 volt pin is live and hot. When the trailer new or old is hooked up to the truck, we have to be cognizant the trailer's internal dome lights are not on when we park for the night. Both my boss and I have walked in at work to a van with a dead battery. All because something like a pallet jack handle turned on the dome light in the trailer.

When my parents had the motorhome years ago, the chassis was wired to use an on board battery plus the engine compartment battery. Over the years, my father installed and extra 2 batteries and a switch to isolate the engine compartment so the van would turn over. It was standard practice to turn over the motorhome once every 2 days for 30 minutes to give the batteries a charge. This was also when we were into NASCAR years ago (late 80s and thru 90s) and before generators were fairly affordable. WE also dry camped a number of times at different places too. Eventually the motor home did get a generator installed in the 2000's it actually helped sell the motorhome a little easier since the install was done in early 2000s. We had A/C during the summer racing. LOL

Northwind, I think you found your problem is the truck and trailer are hooked up and the truck battery is feeding power to the trailer when parked at a camp ground.

 

It is easy enough to verify whether the charge line is always hot and certainly a simple thing to wire so that it is not.

Steve

 

I keep messing around with my trailer batteries every time I go camping. I guess it's good to have a hobby? While I'm having no problems, I have some indications that the trailer converter is charging at a lower amperage than my portable 15A "smart" battery charger, which has an amperage display, and shows the full 15.0A or close to it most of the time.

So, Steve, I agree, the best thing to do is to check the amperages. Stupid question maybe, but how do I do that? I don't own a clamp meter, and the one I was looking at buying says it only works for AC amps. I tried to figure out why that might be, and things got technical too fast. I'm lost.

Volts seem so easy, and all my cheapo multimeters will measure AC and DC volts just fine.

It's been a lot of years since I took my circuits class in school, and to be honest, I think I've killed those brain cells off since then.

Kind of a related question, but how would one test a converter?

 

In rereading the initial post, we really need to nail down some amperages and the only way to really do that is with an amp meter. I know very few folks own one because of the expense, but I think it is an essential if one want to avoid throwing parts at things. Owning one means having the ability to test multiple things on both the truck and the trailer in seconds and answer a multitude of questions.

The thing about alternators and power converters is they are not supposed to put out full amperage as they respond to the level of the battery charge and throttle back. A "dumb" battery charger will put out its full 15 amps all the time, so you can not compare a smart to a dumb charger. Your alternator and converter will still read voltage, but will be putting out almost no amps. A smart power converter like those found in all RVs will read about 13.5 volts, but will only be putting out about 1 amp or less with a fully charged battery.

If you don't want to invest in a meter, pay for an hour's worth of a tech's time. You will still save money over buying parts you don't need.

Steve

 

if you want and willing.. go to an automobile swap meet... and look for used aftermarket AMP meter... 60 amp or more.... the type you mount below the dashboard.

make up a couple of cables. and with your Trailer battery disconnected.. insert wires from amp meter. while NOT real accurate... will give you an idea of amp draw..

Also.. you could also find used automotive test meters that measure RPM/voltage/Amps/Starter Amps..
I know mine, I have owned for 20 plus years. and still works fine.. will read 100 amp and 500 amps. possible you could fine one for less the 50 dollars.

but if you plan to do stuff for years. its worth the money for a descent one.
and direct reading is better than clamp one... my opinion.

 

I have found the cheap clamp meters are almost worthless. The $300+ Fluke I use reads factory new parts at exact factory spec new. Have never compared to direct read, but it is awfully hard to use direct read in many situations. I think with meters, you get what you pay for.

Steve

 

I ended up putting one of these on my TT, both for monitoring charging from the converter and my suitcase solar kit.




It's one of these from a certain giant online retailer that begins with an A.





I mounted it in a project box with a DPTP switch to allow monitoring of both charge and discharge. I have a quick connect for it in the battery box (the shunt is permanently installed) and it's on a 8 foot cord so I can set it near the solar setup or out of the weather and remove it easily when I don't need it. The AMP reading seems very accurate, at least down to .05 from what I can tell.

Additionally since the original post I have figured out that my SG2 isn't reading the full voltage from the battery with the ignition off. I checked with my Fluke and I'm getting closer to 12.8 from the truck battery with the ignition off so I do not have an issue after all.

 

I use one of these: https://amzn.com/B00SWGWILI . I plug it into a 12v power outlet in the cabin. It cycles between voltage and temp. The usb outputs are useful.