Truck not charging trailer battery

[Lorraine Pittsburgh]

I recently picked up my 5.0 in Sumas, & figured out most of the appliances & systems on the long drive back to Pittsburgh. As this is my first trailer, the learning curve was steep. The many notes I'd taken while perusing this forum along with the ETI tutorials allowed me to figure out most things. One item is still a mystery.

On the display in the truck, a message appears that says that the truck is not charging the trailer battery. The DC to DC charger is there in the little compartment with the power jacks. The Ford dealer confirmed that the charging line from the alternator to the 7-pin is in place. Any suggestions as to what I should look for next? I will really appreciate it if you can put any suggestion in VERY simple terms as all of this electrical stuff is completely new to me; I've just sorted out 12V vs 120V, & AC vs DC.

You folks on this forum are a wealth of info & thoughtful suggestions. I'd have never figured out enough of this to have the confidence to get into trailering without you - you are much appreciated.

[Iowa Dave]

Will the shop at the Ford dealer check the seven pin receptacle on the truck and make sure there is power at the back of the truck. If there isn’t power, there’s a fuse or breaker that’s open. He could figure out why and fix that.

If there is power then you’ll need a multimeter. Once hooked up, see if there’s power coming to your converter. And next on the other side from the converter on into the trailer. That would tell you if the converter is working.

That’s where I would start. The multimeter, if you don’t have one, is not expensive. One that will do about everything you’d ever need to do on the trailers is less than $30.
Hope this helps
Iowa Dave

[alanmalk]

Originally Posted by Lorraine Pittsburgh

...
I will really appreciate it if you can put any suggestion in VERY simple terms as all of this electrical stuff is completely new to me; I've just sorted out 12V vs 120V, & AC vs DC.
...

Sorry, no suggestions, just some questions.

First, are you sure your trailer batteries even need a charge? By this, I mean, are you camping every night in a full-hookup campground with your trailer plugged in and charging all night long? Or conversely, are you boondocking every night, running the furnace to keep warm and using the water pump a lot? In that case you can assume your batteries need a good charge the next day. But even then, your solar might be doing the job.

Second, are you certain the DC-DC converter/charger is not doing what it is supposed to? Do you finish a days drive with weak trailer batteries that have less power than you started with? Your "full-medium-low-dead" lights might be of some help with that question. Or better, use that brand new multi-meter directly on the batteries in the morning before starting the truck, and again at the lunch stop. Again, the solar might complicate this answer - a cloudy day might be your friend in this rare instance.

The point is - your truck may be giving you false information and it is possible that nothing is wrong.

But that said, a multi-meter might become your best friend when trying to diagnose problems.

[Centex]

Lorraine - you mention having a Ford but not the model (F150?) or year(?).

IF yours is a 2021+ F150 there are several things one should be aware of which may affect testing the bumper-socket output with the trailer disconnected using a multimeter as some have suggested. FYI clipped verbatim from the Workshop Manual for the 2021+ F150:

Trailer Battery Charging

NOTE: For vehicles equipped with push-button start, the trailer battery charging output is disabled when the drivers door is ajar.

The TRM provides voltage to the trailer tow connector for trailer battery charging when all the following are true:

• The TRM detects that a trailer is connected.
• The ignition is in ACC or ON.
• The BCM load shed strategy is not active (a message is displayed in the instrument cluster, such as Low Battery Features Temporarily Turned Off or Turn Power Off To Save Battery, to indicate that BCM load shed strategy is active).

"TRM" is the "Trailer Module", and not all F150's with trailer tow capability have that module. Trucks without the TRM may behave differently.

It is possible that some or all of the above applies to F150's prior to model year 2021 and/or to F250+; I'm referring to the 2021+ F150 because that's the Workshop Manual I have.

The point - Later model Ford pickups may not indicate ~12VDC on the 'aux 12volt / battery charging pin 3' when tested with a multimeter with the trailer disconnected. Absence of ~12VDC at the open trailer bumper connector tested in that manner may not indicate a vehicle fault at all.

The Workshop Manual provides trouble-shooting procedures for testing the trailer connector output without a trailer connected, but that requires use of the dealer diagnostic tool to 'force' a 'trailer connected' signal when a trailer is not actually connected.

As an alternate, one could employ several 'tricks' to check for ~12VDC at the bumper socket with the trailer connected but without any trailer devices possibly interfering with that test. The procedure I envision would require un-hooking a wire in the umbilical-cord junction box under the front of your 5.0. IF inclined to do that, drop me an email for more detailed instructions.

Personally, admitting no real basis for the thought, I'm inclined to think your issue, if you have one, resides on the trailer-side of things relating to the DC>DC charger, possibly its configuration.

Good Luck!

(All of this is much simpler on my much less 'sophisticated' 2005 F150 which shows ~12VDC at the bumper connecter whenever the ignition is on)

[DanK]

My ford f150 with max tow package did not have the fuse in place when I purchased it. Check that first

[Lorraine Pittsburgh]

Wow, should be used to this by now, but y'all came up with so much more than I could have hoped for.

Dave, I'll pick up a multimeter this morning & see what I can do with it tomorrow with the trailer (parked a distance away). The Ford folks did check the 7-pin receptacle on the truck, which I should have mentioned. Since my outlets (both 12V & 120V) work with the trailer on both shore power & on battery power, I'm thinking that both the converter & inverter are working. Is this a good assumption?

Alanmalk, Good questions. The trailer batteries do not need a charge as they have been kept charged by shore power or solar; I'm just assuming that the notification on the truck screen about the truck not charging the trailer battery is correct - hadn't considered the possibility that the truck might be giving me false info...hmmm. I'm really just trying to confirm that things are working as they should, not actually needing the truck to charge the trailer battery at this point.

Alan/Centex, The truck is a 2022 F-150 V-8. I THINK I followed all of what you wrote about the TRM. Since I got the tow package, & the truck is giving me all kinds of info relating to towing & the trailer (like keeping track of mileage & such for multiple trailers), I'm assuming that I have this TRM. Is this a safe assumption? So sorry not to have mentioned that the Ford folks did check the 7-pin receptacle on the truck. With all of the electrical stuff in the trailer seeming to work fine, your thought that the issue is with the DC to DC charger (or related wiring) feels right to me. I looked at & felt around on the charger itself looking for something obvious like an on/off switch or loose wire, but no luck. Guessing that this might be an issue for a professional.

[JohnK]

Some DC-DC chargers also incorporate MPPT solar controllers which, when the trailer batteries are fully charged, allow the solar array to charge the tow vehicle battery, thereby unloading the tow vehicle's alternator so as to save a smidgeon of fuel. I installed one of these units on our previous trailer.

If you have one of these DC-DC charger/solar controller units installed, this may be what is happening. If this is the case your tow vehicle is not lying to you and your solar array is doing the entire battery charging task, tow vehicle battery and all.

John

[Lorraine Pittsburgh]

Originally Posted by JohnK

Some DC-DC chargers also incorporate MPPT solar controllers which, when the trailer batteries are fully charged, allow the solar array to charge the tow vehicle battery, thereby unloading the tow vehicle's alternator so as to save a smidgeon of fuel. I installed one of these units on our previous trailer.

If you have one of these DC-DC charger/solar controller units installed, this may be what is happening. If this is the case your tow vehicle is not lying to you and your solar array is doing the entire battery charging task, tow vehicle battery and all.

John

Ooo, another good thought. I'll have to notice when this notification occurs & see if the timing could fit this theory.

Also, I'll be right up the road from you in McPherson for Christmas - small world.

[Centex]

Originally Posted by Lorraine Pittsburgh

....The truck is a 2022 F-150 V-8 ..... Since I got the tow package, & the truck is giving me all kinds of info relating to towing & the trailer (like keeping track of mileage & such for multiple trailers), I'm assuming that I have this TRM. Is this a safe assumption? ....

Yes, most likely yours has the TRM as does my 2022 Lariat with similar trailer info display information.

In any case it seems all of my exposition is moot, seems you've eliminated questions about the 'vehicle-side' of this equation (which is good)

Good luck figuring out the 'trailer-side' of the equation; I don't have a DC>DC charger so can't contribute to that effort, others seem to be doing a good job with that.

[SRS]

Originally Posted by Lorraine Pittsburgh

I recently picked up my 5.0 in Sumas, & figured out most of the appliances & systems on the long drive back to Pittsburgh. As this is my first trailer, the learning curve was steep. The many notes I'd taken while perusing this forum along with the ETI tutorials allowed me to figure out most things. One item is still a mystery.

On the display in the truck, a message appears that says that the truck is not charging the trailer battery. The DC to DC charger is there in the little compartment with the power jacks. The Ford dealer confirmed that the charging line from the alternator to the 7-pin is in place. Any suggestions as to what I should look for next? I will really appreciate it if you can put any suggestion in VERY simple terms as all of this electrical stuff is completely new to me; I've just sorted out 12V vs 120V, & AC vs DC.

You folks on this forum are a wealth of info & thoughtful suggestions. I'd have never figured out enough of this to have the confidence to get into trailering without you - you are much appreciated.

I have a 2021 F-150 and my 2022 17A has the Victron DC-DC charger. Like you I initially couldn't tell if the truck was charging the trailer batteries. Periodically I would also get the same message that the truck isn't charger the trailer. I found using the Victron App on my phone helped me see what was going on. What I do is drive down the road a little ways or stop after several hours and check my phone before I turn off the engine. The DC-DC charge is always present on the app and charging the batteries. Yours is likely working as well but it is a little mysterious.

[oldwave]

Right use the victron app to check the status of the charging.

[edlynnrich]

We occasionally get that same message on our 2021 F150 but it appears to only display when the battery is fully charged. I believe that since the battery is topped up the charging from the truck shuts down and you get that message.

[MD-Escape]

Our DC/DC charger was set to "Power Supply" mode when we first received our trailer in October. You may need to switch it to "Charge" mode. Honestly I'm glad they defaulted to power supply mode because getting charge mode setup can be a little trial-and-error. Also I don't think our F150's wiring is suitable to provide 20A of power. I now have mine set to power supply mode until I can run a beefier wire from the batter along with a relay.

Download the Victron app to see what's going on and make changes. Much easier.

Note: unlike the over Victron devices onboard, the dc/dc device won't show up in your bluetooth until it gets power which means 7-pin connect connected and truck powered up.

Hope this helps.

[splitting_lanes]

The DC/DC converter on my 2022 trailer was “off” by default. Have you installed the Victron app on your smartphone?

There are a number of settings you can tweak to make the converter do what you want.

For me, I found that it’s too much load for the truck wiring, so I’m installing an additional power and ground wire.

[Lorraine Pittsburgh]

Thanks all for the thoughtful & helpful responses. I'll get the app & see what I can do with that. Will be towing the trailer about 8 hours on Monday, so will noodle a bit with it then & try out a few things. Seems like the easiest thing to test is if the notice about the truck not charging the trailer battery comes on when the trailer battery gets fully charged by the solar panels, so will try that first (run the battery down a bit, then allow it to recharge). The folks on this forum are the best - so much appreciated!

[TahoeJoe]

Originally Posted by DanK

My ford f150 with max tow package did not have the fuse in place when I purchased it. Check that first

Agreed that you should try this first. This once happened to me as well, a Ford F150 I had didn't have the fuse installed...it was in a little baggy in the glove box, and I used the manual to find out which slot to put it, and then it worked!

[SRS]

Originally Posted by Lorraine Pittsburgh

Thanks all for the thoughtful & helpful responses. I'll get the app & see what I can do with that. Will be towing the trailer about 8 hours on Monday, so will noodle a bit with it then & try out a few things. Seems like the easiest thing to test is if the notice about the truck not charging the trailer battery comes on when the trailer battery gets fully charged by the solar panels, so will try that first (run the battery down a bit, then allow it to recharge). The folks on this forum are the best - so much appreciated!

While there may be other issues in your situation, my 2021 F-150 will give me that message and a mile or so down the road, the app shows the charging is working and if I stop but leave the truck running, I can look at the DC-DC charger and it's light is on which means its getting power from the truck. I only occasionally get the "trailer not charging message" and I never get one afterwords telling me the "trailer is charging" so that's why the app is so helpful. If you always get that message when the trailer is connected and you start the truck, then yes, I would be concerned that something else is wrong like a blown or missing fuse. IMO, downloading the app to your phone, iPad or similar device will give you better information almost instantly. It will also allow you check the chargers setting. Good luck.