Battery on or off when on shore power

TerryV6

My wife saw this discussed on FB.  When you connect to shore power, do you need to have your battery disconnect switched on?  You have power to the camper and I assume the battery is still being charged...

Sharon_is_SAM

To charge or use the battery, the switch must be on.  If turned off, the battery is isolated from charge or discharge.

You aren’t required to keep your switch on, but I imagine that most folks want to charge their battery while they can.  

TerryV6

Ahhh... thanks, that makes sense.  It was intimated that you could cause problems if you weren’t connected... ( you just won’t charge.. slight difference)

Sharon_is_SAM

@TerryV6, we sometimes plug in, isolate the battery, then charge the battery via smart charger.  

TerryV6

So, if you are shore power connected and battery on, are you using the battery and the converter is charging it (albeit slowly).  This is what is causing questions btw..

Cbusguy

I would like to think that keeping the battery on would help "buffer" the surge loading on the dc power supply as well.  Other than when in a long term storage situation,  I leave mine battery on when using the trailer.

gspdx

Terry - I think the comment about the battery always running the DC circuits and the converter just keeping the battery charged is a little misleading.

In my T@B 400 I only have two wires connected to the batteries: one for positive and one for negative.  That completes a single circuit.  That set of wires will carry current into the battery and out of the battery.  So the same wires will provide power to the DC circuits when shore power is disconnected and receive power from the converter to charge the battery while connected to shore power.  That also explains why the DC circuits still operate when the battery disconnect switch is set to off - the converter is powering the fuse panel for the DC circuits.

Anyway - the battery cutoff switch will isolate the battery from shore power and the DC circuits. 

I also have the factory solar panel and the inverter.  Both of these devices are connected directly to the battery without going through the battery cutoff switch.  So the solar panel can charge the battery and the Sine inverter can be used with the battery cutoff switch set to off. 

I agree with Cbusguy about leaving the switch on unless in long term storage.  Everything works as designed when it is on, and turning it off in long term storage eliminates the parasitic loss from any little items using power when storing the camper. 

Sharon_is_SAM

The battery only runs the TaB appliances when not on shorepower.  The converter steps down the power from 120 v AC to 12 v DC which allows the 12 v appliances to operate on shorepower.  Paul Thomas on FB is incorrect.

davel4wa

Interesting conversation here. Your converter is basically a switch mode power supply. These modern converters tend to have very ripple free outputs and can supply the trailer's 12 volt requirements without problems. I don't have experience with the particular converter being used by NuCamp and I haven't checked the specs concerning output ripple. Suffice it to say that when the battery is connected to the output of the converter it acts like a large filter to smooth out any irregularities on the converter output and as a bonus it keeps the battery nicely topped up. If there are substantial loads on the 12 volt system the converter is going to stay in its bulk charge mode and not drop into float mode. Once you are done doing whatever it is that is loading the system, say in the morning and you are showering, making breakfast, charging your portable electronics, whatever, the converter will likely be supplying a fair amount of current. Once you start your adventures and you leave the trailer with most of those loads turned off the converter will be supplying small currents for devices that are always on and it will be recharging your battery. A test for converter output ripple is to turn on your radio. If the radio sound is normal then output ripple is low but if you get a buzzing then not so much. Keep your battery connected while using the trailer. That is how the system is designed to operate.

jameskuzman

The T@B 400 manual from NuCamp has this to say (page 15 for reference). The bold text is mine to highlight specific information relative to the OP's specific question.

• "The battery disconnect switch is used to separate the batteries from the 12-volt distribution panel and converter charging system. When the switch is turned to ON and the trailer is plugged into a 120-volt shoreline, the 12-volt distribution panel will receive power from the converter and the batteries will be charged through the converter charging system. When the switch is turned to OFF and the trailer is plugged into a 120-volt shoreline, the 12-volt distribution panel will still receive power from the converter, but the batteries are disconnected from the system. The batteries will not be drained with the switch in the OFF position. The converter will not charge the batteries with the switch in this position." 

Put another way, the 12-volt converter takes the 120-volt shore power, converts it to 12 volts, and then supplies DC power to everything in the camper irrespective of the battery disconnect switch. The difference is that when the switch is turned "on", the converter charges the batteries; when it's turned "off" it does not charge the batteries. 

Things are slightly different when connected to the tow vehicle through the 7-way power cable or when using solar, however: 

• "The charge in the 12-volt batteries can be replenished, depending on the tow vehicle, from the tow vehicle alternator through the 7-way cord. This charge will flow to the batteries regardless of the battery disconnect switch position. Likewise, if on or off, the solar panel is still charging the batteries."

gspdx

I do wish there was a comprehensive electrical schematic in the manual.  

Sharon_is_SAM

@jameskuzman, we believe that the charging via the 7 pin with the battery switch off is a typo. No charging occurs if the battery switch is off because the switch breaks the circuit to the battery.  Same thing is true with operation of the break away brakes.  If the battery switch is off (battery circuit disconnected) your break away brakes will not receive power from the TaB battery.

jameskuzman

@Sharon_is_SAM - You know, I’m glad you said that. In my head I was trying to figure out exactly how that would work but in the absence of a diagram, I was just trusting the manual to be accurate but the theory that this is a typo makes more sense to me. I assume the claim about solar is correct though as the charger itself bypasses the switch? 

And hey, I see you’re In Cleveland Heights - not too far north from me at all in the Youngstown area :-) 

Cbusguy

You mean the manual that hasn't been updated since when?

The manual is wrong in regards to charging while towing and the battery disconnect switch. Both fused wires go through the switch to my battery.  



The systems on these trailers are super simplistic no relays or auto transfer switches.    

The battery is simply charged because it is in the 12 volt circuit and the circuit voltage exceeds the voltage if the battery.    

No special battery charger.

Sharon_is_SAM

@jameskuzman, we are building our NE Ohio fan base!

gspdx

jameskuzman said:

@Sharon_is_SAM - You know, I’m glad you said that. In my head I was trying to figure out exactly how that would work but in the absence of a diagram, I was just trusting the manual to be accurate but the theory that this is a typo makes more sense to me. I assume the claim about solar is correct though as the charger itself bypasses the switch? 

And hey, I see you’er In Cleveland Heights - not too far north from me at all in the Youngstown area :-) 

I can confirm in my T@B 400 the solar charger connects to the battery and not through the battery cutoff switch.  The solar panel does still charge the battery with the battery cutoff set to off. 

jameskuzman

Sharon_is_SAM said:

The battery only runs the TaB appliances when not on shorepower.  The converter steps down the power from 120 v AC to 12 v DC which allows the 12 v appliances to operate on shorepower.  Paul Thomas on FB is incorrect.

I went back and re-read this comment, then looked again at what Paul Thomas said on Facebook.

What he is (incorrectly) suggesting is that the batteries in the camper work as most UPS (un-interruptible power supplies) do - and I'm talking about continuous UPS's here, not stand-by designs.

In continuous systems, the incoming 120VAC charges the batteries, and the 12VDC output of the batteries feeds a DC-to-AC inverter which then powers any 120VAC device plugged into the load side outlets. Put another way, the batteries - albeit by way of the inverter - are actually powering anything plugged into it. 

That is not what's happening in our campers. 

pthomas745

@Sharon_is_SAM I had a further comment in there pointing out another user had a better explanation than I did.

Sharon_is_SAM

@pthomas745, you had a comment on FB?

Sharon_is_SAM

@gspdx, yes, anything directly connected to the battery is not impacted by the battery switch.  

pthomas745

@Sharon_is_SAM the comment mentioned as "incorrect" is mine.

klenger

gspdx said:

I do wish there was a comprehensive electrical schematic in the manual.  

Click on the link in my signature, hover over the Modifications tab on the top menu, and then select Wiring Diagrams, nuCamp Original.  This is for the 320S.  It's not very complicated.

Sharon_is_SAM

@pthomas745, I did not make the connection.  So, what is the better explanation from FB?  It’s always good to hear another approach.

gspdx

@klenger Thanks!

pthomas745

@Sharon_is_SAM I probably should have said the "correct" explanation!    (At least it seems to be....)

"The converter is what provides all this power when shore power is available. When no AC power is available, the converter just acts as a fuse panel for the DC circuits and the battery provides all the DC power at 12-13 volts to run everything. The converter's power supply does nothing when there's no AC power coming in. It doesn't provide 120 volts to the plugs - that's what an INverter does, not a CONverter, so don't get these two devices mixed up. T@B's (except for the 400 with solar) don't come with inverters; only converters."

gspdx

klenger said:

gspdx said:

I do wish there was a comprehensive electrical schematic in the manual.  

Click on the link in my signature, hover over the Modifications tab on the top menu, and then select Wiring Diagrams, nuCamp Original.  This is for the 320S.  It's not very complicated.

This is exactly what I want for the T@B 400.  Do you have a few minutes to draw it up? 

klenger

I have no information on the 400 to work from.  My drawing was essentially reverse engineered. 

gspdx

That is what I am starting - but it will take some time.  You did a great job.

TerryV6

So, in the past I had the battery on when boondocking and off when I was parked at home, or on Shore power at the park.  Now after reading all of this, I will have the battery on when the camper is in use regardless, and turn it off when I am parked at home.  Or charging....
(Three years ago, I purchased our camper and didn't have a disconnect,  only a fuse to pull out.  I was green on this and didn't know about the fuse, and when we went to go on a trip, I had a dead battery.  I then did some more reading here and put in a disconnect switch, which now I hear comes standard)

wooper

After reading through all this I'm still a little confused.  Please tell me if I'm wrong.

1.  When on shore power, the battery will charge if turned on and will not charge when turned off.
2.  When on shore power with the battery turned on, the battery continues to run 12v items but remains charged because it is on shore power.  If the battery is off shore power runs the 12v items.

If the above is correct, and your battery is charged, should you just leave the battery off when connecting to shore power and only turn it on to charge or when you don't have shore power but need power for the 12v items?

pthomas745

#2:  On shore power, the converter (not the battery) provides power to the 12V items and the 120v items.  It charges the battery if the battery needs charging, if you have the battery switch on.