Best way to tell if TV is charging battery in camper

[sreston]

I'm eagerly awaiting the delivery of my Casita in the next couple of days. One of the things I've been unable to confirm about my tow vehicle is whether it's supplying voltage through the 7-pin connector to charge the battery in my camper. I can't use an LED tester or a multimeter directly on the 7-pin because my vehicle senses when a trailer is connected.

What's the easiest way to tell if my TV is charging the battery in my camper?

[Jon Vermilye]

If you don't have the trailer power cord plugged into a power pedestal, the only thing charging the battery would be the tow vehicle (unless you have solar). Check the trailer battery voltage before plugging the 7 pin connector to the tow vehicle (use a plug in 12V meter in a 12V receptacles in the trailer, or a meter on the battery if you don't have a 12V receptacle).

With no load on the trailer, the voltage should go up a bit when you plug in the tow vehicle. With modern tow vehicle electronics if might not stay up long, but a plug in volt meter is useful & should show the difference.

[AC0GV]

Originally Posted by Jon Vermilye

With no load on the trailer, the voltage should go up a bit when you plug in the tow vehicle. With modern tow vehicle electronics if might not stay up long, but a plug in volt meter is useful & should show the difference.

And if wired to do so, the tow vehicle may need to be running. Note that some vehicles (my f-150) do not have a very high voltage. It maintains the battery better than it charges it.

[gordon2]

Voltage is not power... 1,000,000 volts at 0 amps = zero watts and no power (and zero charging).

So the BEST way is to use a ammeter (amp meter) on the charge line near or at the camper. A clamp on DC ammeter such as https://www.amazon.com/Klein-Tools-C.../dp/B08DTDCG7T works well.

With that said, checking for an increase on voltage as described above is much easier, usually cheaper, and almost just as good a method to use. If the voltage is higher than you can assume the battery is getting some charge, but you cannot easily tell how much. The ammeter will tell you how much (assuming other loads are off and battery charging is the only thing happening).

[ThomasC]

Originally Posted by AC0GV

And if wired to do so, the tow vehicle may need to be running. Note that some vehicles (my f-150) do not have a very high voltage. It maintains the battery better than it charges it.

All vehicles vary. My 2019 F-150 has to be started and running and put into drive to activate the charging wire. Every time you turn off the ignition you have to go through the whole cycle again.

[sreston]

Thanks for all the great advice, y'all. IIRC, Casita now provides a 12V meter with campers. I see that this'll only give me an indicator of whether or not my TV is charging the battery, but not the actual voltage. I'll check around to see if I've got a friend with an ammeter...

[gordon2]

Keep in mind if the battery is fully charged the current will be low but the voltage still above 13 (hopefully). So to tell if the charging is effective, you want to see higher current when the battery is somewhat discharged.

[Bruce H]

Midtronics PDF-40

Very accurate low voltage/amperage multi-meter
down to 1/10th volt or 1/10th amp.

I have had one for over 10 years and highly recommend one for every RVer.
$200+. Price shop the internet.

[Borden]

Originally Posted by Bruce H

Midtronics PDF-40

Very accurate low voltage/amperage multi-meter
down to 1/10th volt or 1/10th amp.

I have had one for over 10 years and highly recommend one for every RVer.
$200+. Price shop the internet.

Have never carried a meter on trips. Have different ones and the pocket unit is small will have to add it to the tool kit.

Did not think of it.

[Raz]

A new trailer will have a new battery that may or may not be charged. Go to the local hardware or autoparts store and buy a Digital Multimeter (DMM). $20 You want one with a digital read out not a needle. There should be instructions on how to read voltage. With the scale set to 20 volts DC, and the battery connected to the trailer, measure the terminals. A charged battery that has been at rest for a while will read about 12.6 volts. Now plug in and start your tow vehicle. Remeasure the battery terminals. If it's being charged the voltage will increase. The amount of increase will depend on how close to full charge the battery is. On a fully charged battery I see about 12.9 volts.

The plug in meter is fine but the DMM has several advantages one being a continuity tester for checking wires. While the meter will have a way to measure current I don't recommend it with out instruction. Back in my teaching days I saw many meters destroyed by beginners.

[gordon2]

Originally Posted by Raz

... Back in my teaching days I saw many meters destroyed by beginners.

Which is why I suggested a DC clamp on meter if you want to measure current. Its much eaiser than trying to use a DVM (multimeter) in series to measure current. For voltage and ohms a cheap DVM is fine.

[Dan Meyer]

What is the best way to tell if your tow vehicle is charging the battery in the camper? In my experience, it is best to just assume it is not charging.

Unless everything is perfect, including all connections from the alternator to the camper battery (there are several other than the 7 pin connector between the trailer and tow vehicle), and wiring is adequately sized all the way also (unlikely in any factory tow vehicle installation), there will not be enough current to adequately charge the battery on your camper.


--Dan Meyer

[Raz]

Originally Posted by gordon2

Which is why I suggested a DC clamp on meter if you want to measure current. Its much eaiser than trying to use a DVM (multimeter) in series to measure current. For voltage and ohms a cheap DVM is fine.

Easier? With a motivated student, learning how to use an ammeter takes about 5 minutes. But in my opinion not necessary. The op asked how to tell if the battery was charging from the tow vehicle. A simple voltage measurement will answer that question. As you know, over time you get to know your system, how much energy you use overnight and how long it takes to recharge. But that was not the question asked.

[sreston]

My Casita arrived yesterday evening. I was able to successfully test that my TV is sending power over the 7-pin connector using the 12V plugin-meter that Casita sent with my new camper.

[Raz]

Good for you. It was years ago but I remember when I got mine. Christmas. Enjoy, Raz

[Johnsonbrits]

Hi,

I have an older HiLo travel trailer and when on the road the refrigerator is switched to 12 volt battery which can draw the RV battery down in a few hours if the TV is not charging (found out too many times over the years).

Earlier this year I purchased a Bluetooth battery monitor (around $30 on Amazon, even less expensive on Aliexpress) and installed it across the RV battery. This allows me through an App loaded on my Android smartphone to monitor the RV battery voltage continuously in real time.

Before setting off on a road trip I reset the device, fire up the phone app and connect it via bluetooth, then note the starting voltage (typically low to mid 12 volts in my case due to the heavy refrigerator draw), then after starting my Ford Expedition which then activates charging to the TV I verify the voltage increases on the phone monitoring app to the high 12/ low 13 volts with the refrigerator turned on. I also installed another App on the Android phone (stay alive) which allows me to monitor the RV battery voltage in real time over the entire duration of the trip.

Hope this helps!
Peter

https://www.amazon.com/s?k=battery+m..._ts-doa-p_5_15

[leecyrille]

If you see higher voltage, like above 13V at the trailer battery, you should be charging. Check with meter right at the battery terminals if you can.

[Defenestrator]

Originally Posted by Bruce H

Midtronics PDF-40

Very accurate low voltage/amperage multi-meter
down to 1/10th volt or 1/10th amp.

I have had one for over 10 years and highly recommend one for every RVer.
$200+. Price shop the internet.

That's a very nice multimeter, but honestly for 99% of RV applications a $60 generic like https://www.amazon.com/dp/B07W3C6DTX/ will probably be fine. For that matter, 90% of the time a <$25 generic without the clamp will do.