Shore power charging truck battery

MA

Marblehead

Advanced Member
Joined
Aug 30, 2020
Messages
39
Location
Quincy IL
Greetings,

My 2018 Grandby Flatbed in storage is hooked up to 120V power for battery (2-6V) maintenance and my truck battery goes on a tender.

After my last trip, I noticed the tender for the truck battery would not enter the float stage. Scratched my head and check the voltage a couple of days later and it was ~13.5V which didn't seem right to me.

Removed the 120V power from the camper and the truck battery started dropping voltage as of course my house batteries did.

It appears to me that power is coming from the camper when plugged in and charging my truck battery.

This is recent development and I've had no other issues, electrical or other wise with my rig.

I'm not sure where to start looking for the cause. I emailed FWC service about 10 days ago but have not heard back. Flatbed and Grandby installed in Denver.

Any comments, suggestions would be most appreciated. If I've missed something really obvious, you can give me grief instead :D

Thanks in advance.

Steve
 
If you don’t have a circuit breaker or switch in the positive truck to camper wire, the easiest thing to do may be to disconnect the truck to camper connector when you want to store the rig with both chargers on.
 
Thank you Jon for your replies.

I thought maybe something was going on with the isolator but not sure what. When the camper was installed, a "thermal fuse" was used inline from the truck battery to the camper. I seem to remember being told it was a resetable fuse.

I unplugged the camper from the truck yesterday and am headed over to check voltages, etc.

I can disconnect the 2 when in storage but am concerned if I am camping off grid that my solar system will try to keep my truck battery charged which I don't want. AND, being a starting battery, it might not like the charging profile set up for my house batteries.

Thanks again, off to learn more.
 
Jon R said:
If your isolator is working correctly you shouldn’t have that problem when not using the tender on the truck battery. Testing it will tell you for sure.
Click to expand...
I checked voltage at the truck/camper connection plug. The plug from the truck battery is showing the truck battery voltage and the plug from the camper is showing the maintenance voltage of the batteries.

Admittedly, I'm a bit fuzzy on the workings of the isolator other than it is to prevent the camper from drawing power from the truck battery. Is voltage at the camper plug indicative of a problem with the isolator?

I may have a wonky truck battery. After unplugging the camper from the truck, I put the truck battery on a tender but it never went into float mode. And I did have an "issue" with battery about the time this problem came to light.

Will have the truck battery checked out today and look into trouble shooting the isolator.
 
Vic Harder said:
Then again, some of us LIKE having the solar charging both battery banks!
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With different battery types, wouldn't you need different profiles?

Again, I've not gone that far down the "rabbit hole" of the various aspects of solar. But from my reading on this site, I know you and several others have. I've much to learn.
 
Vic Harder said:
Then again, some of us LIKE having the solar charging both battery banks!
Click to expand...
That would be me. I also like that when I plug the camper into shore power the charger that I installed in the camper will eventually also charge the truck's batteries.

I have the charger set for the AGM's in the camper and don't worry too much about it matching the inexpensive FLA starting batteries. Before one of the DieHard Platinum starting batteries shorted a cell (just before a planned trip of course!) it wasn't a concern at all. The solar controller that our camper came with looks to be stupid enough to not have different charge settings. It's next on my list to upgrade.
 
Marblehead said:
With different battery types, wouldn't you need different profiles?

Again, I've not gone that far down the "rabbit hole" of the various aspects of solar. But from my reading on this site, I know you and several others have. I've much to learn.
Click to expand...
Yes, the different battery types mean that the charging profiles are not ideal.

And to clarify, the battery separator is designed to prevent either the camper or the truck from discharging the other. Meaning if you left your truck lights on, the separator would disconnect the camper battery once the truck battery got too low, and vice versa, if you are using too much power in the camper, the separator disconnect the truck battery so you can start it and go home.

AND, it is designed to allow a charging source to charge both battery banks, regardless of where that charge originates.
 
I tried to edit my first post to correct what I said about only the truck side voltage closing the Blue Sea ACR, but accidentally hit the delete post button. Vic is correct (as usual) that sufficient voltage on either side of the ACR closes the relay. The voltage specs are on the Blue Sea web site. That explains the behavior seen by the original poster.
 
Vic Harder said:
Yes, the different battery types mean that the charging profiles are not ideal.

And to clarify, the battery separator is designed to prevent either the camper or the truck from discharging the other. Meaning if you left your truck lights on, the separator would disconnect the camper battery once the truck battery got too low, and vice versa, if you are using too much power in the camper, the separator disconnect the truck battery so you can start it and go home.

AND, it is designed to allow a charging source to charge both battery banks, regardless of where that charge originates.
Click to expand...
Thanks Vic, I didn't know the separator would work in both directions and that appears to be what's happening.

My separator must have detected low voltage in my truck battery and sent power to it in addition to my camper batteries. It sounds as though it is working correctly and would explain why my truck battery tender would not go into float mode with the battery showing 13+V

I am now suspecting my truck battery is having issues. The trickle charge is good as I checked it on another vehicle and it does go into float mode. The folks at Interstate Battery told me my truck battery was at 12.4V and suggested my battery needed a proper charging/reconditioning. The Vector Battery charger I used at home indicated the battery was full and would not accept any charge or reconditioning.

More sleuthing today....
 
Marblehead said:
...
My separator must have detected low voltage in my truck battery and sent power to it in addition to my camper batteries. It sounds as though it is working correctly and would explain why my truck battery tender would not go into float mode with the battery showing 13+V

...
Click to expand...
That’s not really how the Blue Sea ACR is triggered. Here is a good discussion from the Blue Sea web site:
https://www.bluesea.com/resources/58
 
When my camper batteries reach a high enough voltage, and I can’t remember the exact number, the BlueSea closes and connects to the truck, thus charging the truck batteries. I have solar so my truck batteries and camper batteries are usually always topped off.
 
Outnabout said:
When my camper batteries reach a high enough voltage, and I can’t remember the exact number, the BlueSea closes and connects to the truck, thus charging the truck batteries. I have solar so my truck batteries and camper batteries are usually always topped off.
Click to expand...
The spec page for the Blue Sea ACR says it will close the relay when it senses at least 13.6 volts for 30 seconds or 13.0 volts for 90 seconds. It will open the relay when voltage drops below 12.35 volts for 10 seconds or 12.75 volts for 30 seconds.

https://www.bluesea.com/products/7610/SI-ACR_Automatic_Charging_Relay_-_12_24V_DC_120A
 
Marblehead said:
you're bride is a keeper!
Click to expand...
Thanks! I kinda think so too. Kind of ironic that the most important test that I've made with it was her car's battery after the Dealership said it was fine and after it stranded her and our 4 yo grand-daughter 50+ miles from home.
 
Thank you all again for the input. It's obvious to me I need more than a bit of education on the ACR and how it works.

I was just thrown a curve ball by not being able to get my truck battery to float. All the while everything was operating as it should.

I believe I will spend more time in this forum reading and increasing my knowledge of all things electronic on my rig.

Steve
 
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