Fuse keeps burning out

Freespirit · March 2021

I have replace my 15 amp fuse in slot F3 three times now and cannot figure out why it burns out. I am not hooked up to any shore power. I have tried all 15 amp devices (I can think of) and they all are working, radio, lights, fan [Alde, air conditioner(shore power)], TV, I cannot find anything that is not working. I have not tried the water pump as fresh water tank is dry. The T@B is not connected to the T/V.

Suggestions appreciated as I am electricity challenged.

Sharon_is_SAM · March 2021

There should be a label inside the converter box indicating what appliances are on the F3 fuse circuit. That is where you should start.

Freespirit · March 2021

This is what is inside the converter box:

DelZMan · March 2021

From the Pre-2021 manual on nuCamp documents site: https://nucamprv.com/app/uploads/sites/5/2017/03/2017-T@B-MANUAL.pdf

Looking at the picture on page 16; tough to read but maybe the porch light?

Sharon_is_SAM · March 2021

This is from @BrianZ:

Looks like the porch light, all inside lights, and the 12v and USB ports. Check the USB ports - known weak link, but not known to trip fuses.

Freespirit · March 2021

@DelZMan thanks for the link, we did have the printed version of the user manual but could nor read the labeling
@Sharon_is_SAM, @BrianZthank you for the clear picture of the labeling of the fuses. Porch light and all inside lights work and the 12 v plug is working. I am off to check the USB plugs.
I will keep you updated.
Thank again.

Sharon_is_SAM · March 2021

Now that you know what devices are supported by that fuse, maybe you can correlate use and then blowing the fuse.

Freespirit · March 2021

@Sharon_is_SAM ,Like I mentioned earlier I am electricity challenged, if the fuse is burned out why does the porch light, inside lights and 12 v outlet continue to work. I removed the fuse and all of the above continued to work. I even remove the other 15 A fuse and as you would expect all of the above continued to work.

The 2 USB ports next to the 12 V outlet however do not work.

MuttonChops · March 2021

Freespirit said:

@Sharon_is_SAM ,Like I mentioned earlier I am electricity challenged, if the fuse is burned out why does the porch light, inside lights and 12 v outlet continue to work. I removed the fuse and all of the above continued to work. I even remove the other 15 A fuse and as you would expect all of the above continued to work.

The 2 USB ports next to the 12 V outlet however do not work.

Interesting. USB Ports have no voltage but everything else seems OK.

Is there a specific action that causes F3 to blow . . . like plugging something in to the USB port?

And 'everything' else works . . before a specific action blows F3 or everything else works when F3 blown LED is on?

Is F3 really blown; can you see broken wire or have ohm meter confirmed it is open?

In general NüCamp has not changed the DCV Fuse number to function wiring in many years. Good chance the your 2020 is nearly identical to this 2019 wiring:

Image: https://us.v-cdn.net/5021717/uploads/editor/ze/mtmjrjd4q2cm.png

The USB could fail without causing the Fuse to fail.

But difficult to see how Porch Light works if fuse is really blown.

Freespirit · March 2021

@MuttonChops, I have not been able to isolate an action that causes the fuse to blow. Replaced the fuse 3 days ago and the T@B has been parked with no activity at all do not even use the USB ports in the back. The USB port in the Jensen worked. Today noticed the red light in the converter box and pulled the fuse and it was definitely burned, element was visibly broken.

Everything works before blown F 3 ( not sure if the back USB ports worked before the blown fuse because I was not using them )and everything continues to work after blown F 3 fuse except the 2 rear USB ports.

My fuse box is identical to this 2019 wiring except:
#1 is 7.5 amp, #2 and #3 are 15 amp, #4 is 20 amp, #5 is 7.5 amp and #6 is 30 amp.

I just replaced the blown fuse and the only difference before blown fuse and after blown fuse is now the 2 rear USB ports work. I can only theorize that fuse F3 only protects the two rear USB ports? Still do not know what causes it to break.

MuttonChops · March 2021

Freespirit said:

@MuttonChops, I have not been able to isolate an action that causes the fuse to blow.
. . . replaced the blown fuse and the only difference before blown fuse and after blown fuse is now the 2 rear USB ports work. I can only theorize that fuse F3 only protects the two rear USB ports?

Okay, thanks.
For now I guess you just continue on and see what happens.

If possible check the Power Center Fuse status frequently to establish 'what happened' just before F3 failed (assuming it continues to fail).

If you have an afternoon to spare, you might consider trying to confirm which 12VDC Fuses control what.

Remove all fuses Except F6 and F7 . . . confirm everything won't 'power-on'
Install F1 . . . again try every switch, what did turn-on
continue with F2**, etc (it is helpful to remove F1 when testing F2, etc only one fuse in per test)

Typical 320S Wiring:

Image: https://us.v-cdn.net/5021717/uploads/editor/sp/1qzy5u72m1it.png

Good Luck, let us know what you find . . . . . .

** to reduce sparks and possible problems, disconnect the battery when inserting fuses
(use battery cut-off switch for this)

P.S. As others have noted.
The USB ports are very poor. They fail frequently.
So your having possible issues with them is not surprising

Bayliss · March 2021

@Freespirit, @MuttonChops provides a good procedure for troubleshooting the issue.

To add to this discussion, I have learned over time that the nuCamp 12V fuse label at the converter panel is, at times, either non-existent or inaccurate (which is what I discovered on my label.) nuCamp seems to change the circuits with different year models.

For example, on my 2019 320 S, F3 is 15A and protects the USB and 12V sockets; F4 is 20A and protects the ceiling and porch lights and the refrigerator. The only way to figure out what fuse protects a particular circuit is to go through the troubleshooting process described above and prepare a new label for your converter. It will be time well spent for you to do that, because it will come in handy for quickly diagnosing future electrical issues.

Regardless, since you stated that the two rear USB ports are not working after the F3 blew, I'm guessing that is where the issue is. The USB port(s) may be shorting out, or need to be replaced.

Sharon_is_SAM · March 2021

Anybody with a 2020 320 that can chime in regarding their fuse assignments?

Freespirit · March 2021

I took the advice of @MuttonChops and confirmed which 12VDC Fuses control what. Below is what I discovered:

Fuse 1 (7.5 amp): lights(rear reading, kitchen, porch, ceiling), ALDE
Fuse 2 (15 amp): TV, radio, USB in radio
Fuse 3 ( 15 amp): rear USB
Fuse 4 ( 20 amp): fridge
Fuse 5 ( 7.5 amp) water pump, ceiling fan, CO2 detector

The rear 12 VDC works with each fuse.

This exercise was well worth the 20 minutes it took to complete, just needed a push to do it, (thanks to everyone).

It looks like now I need to monitor the rear USB port and if I continue to experience a blown F 3 fuse just replace it

One last thing, I discovered the red blown fuse light does not work on the circuit board for F 4, is this of any concern other than I do not have a visual for a blown fuse.

Cheers

ScottG · March 2021

Good sleuthing, @Freespirit. It looks like some changes have been made over the years with regard to which devices are served by which 12V circuits.

I doubt the dysfunctional indicator light in F4 will cause you any problems. I find it's usually the dysfunctional devices that tip me off when a fuse has blown. :-)

MuttonChops · March 2021

Freespirit said:

Fuse 1 (7.5 amp): lights(rear reading, kitchen, porch, ceiling), ALDE
Fuse 2 (15 amp): TV, radio, USB in radio
Fuse 3 ( 15 amp): rear USB
Fuse 4 ( 20 amp): fridge
Fuse 5 ( 7.5 amp) water pump, ceiling fan, CO2 detector

The rear 12 VDC works with each fuse.

Nice work.
Am not sure what your "rear 12 VDC works with each fuse" means.

Assuming the 12VDC (lighter style plug) and the USB are in the same housing they should be on the same Power Center Fuse. The 12VDC outlets should only function on one fuse, F3.
If the 12VDC function when any fuse F1 - F5 is installed then something seems wrong.

Freespirit · March 2021

@MuttonChops, “something must be wrong” my 12VDC(lighter style plug) works when any fuse 1-5 is installed, but the rear USB only works when fuse F 3 is a “good” fuse.

The 12VDC (lighter style plug) and the USB are in the same housing.

Any suggestions?

Freespirit · March 2021

@MuttonChops, @ScottG, trying to put this fuse puzzle together and as I mentioned earlier I am NOT an electrician, could there be a connection to not having a red fuse light on F 4 and the 12VDC(lighter style plug) works when any fuse 1-5 is installed.

ScottG · March 2021

Just to make sure I understand correctly...

Are you saying that if you remove all the fuses 1-5, the 12VDC "lighter style" plugs DO NOT work. However, if you replace any single fuse 1-5 those plugs DO work?

Freespirit · March 2021

@ScottG, that is correct, with all fuses removed (1 thru 5 ) the 12VDC “lighter style” plug in back where the USB plugs are housed DOES NOT WORK. If I PUT any fuse in (1 thru 5 ) the 12 VDC “ lighter style” plug will work. It is only when I put in fuse F 3 that the USB PORTS WORK AND THE 12 VDC “ lighter style” plug works. The only time the USB ports work is when fuse F 3 is in and not burned out.

When I was testing fuses 1 thru 5 they were tested one at a time individually.

ScottG · March 2021

Weird. That--combined with your other issues--suggests a short somewhere in the 12V system. I'm just taking a wild guess here--unfortunately I have no bright ideas how to go about trouble shooting that. :-/

Bayliss · March 2021

@Freespirit, re your statement:

"One last thing, I discovered the red blown fuse light does not work on the circuit board for F4, is this of any concern other than I do not have a visual for a blown fuse."

Back in 2019, I had a similar issue and was confused as to why that was happening. @BrianZ set me straight on it by providing the following explanation (I underlined and bolded the most important part of his information):

"Try turning on an appliance on that circuit before pulling the fuse & see if it comes on. My kill switch on the Alde causes the same behavior when I pull the fuse. The fuse panel red LED needs current flowing through the circuit to light up, so if everything on the circuit is turned off, it won't light."

I keep forgetting to go back and try that out, but it makes sense. However, to see what is happening, go to the below WFCO link and watch the short video for the question, “Why is there voltage on both sides of the 12V fuse board?”

https://wfcoelectronics.com/product-support-videos/

As best I can recall, it was also my F4 LED that was not lighting up. Therefore, since your F4 is for the refrigerator circuit (same as mine), turn the refrigerator "ON" (i.e., 12V/battery power) and then pull out the F4 fuse. The red LED should illuminate when you do that. I recommend that you turn the refrigerator "OFF" before replacing the fuse, just to avoid the possibility of that act alone blowing the 20A fuse. Better yet, follow @MuttonChops suggestion and cut the 12V power to the entire trailer by turning off the battery cut-off switch before replacing any fuse - - - better safe than sorry.

Simply stated, as long as the refrigerator is turned "off," there is no voltage available to light up the red LED, which makes it appear that the red LED is not functioning. By turning the refrigerator "ON", the circuit is completed, thus providing the power/voltage necessary to illuminate the LED when the fuse is either manually removed, or blows. Pretty simple, yet tricky at the same time.

Finally, for a basic understanding of why a fuse may blow, while you are on the WFCO site you should also take a look at the short video for the question, “Why do fuses keep blowing on my 12V fuse board?”

Hope this helps. Please let us know how the F4 "test" described above works out. Thanks for the post. It has been interesting reading and will be helpful for others in the future.

Freespirit · March 2021

@Bayliss, you are an life saver, did as you suggested and fuse F4 worked as you indicated it should. All is well with fuse F4!,

Thanks @BrianZ for your explanation back in 2019.

Bayliss · March 2021

Cool, @Freespirit! And I echo the thanks to @BrianZ.

rfuss928 · March 2021

The same circuit characteristic that is the root of the F4 LED operation described above will make measurable voltage appear at the "rear 12VDC" even with the fuse removed. Similar to turning on the refrigerator made the LED light come on, plugging something into the outlet (that draws current) should show which fuse is controlling its supply when pulled.

MuttonChops · March 2021

rfuss928 said:

The same circuit characteristic that is the root of the F4 LED operation described above will make measurable voltage appear at the "rear 12VDC" even with the fuse removed.

Yes !
Just before falling asleep last night the (mental) light turned-on.
Thanks to @Bayliss for reminding us about the Bad Fuse LED Operation.

@Freespirit is "seeing" an indication of the 12VDC Outlet being on but there is no usable current.

Image: https://us.v-cdn.net/5021717/uploads/editor/9k/rj569k09lqhh.png

Freespirit · March 2021

A BIG thank you @Bayliss, @MuttonChops, @rfuss928 and everyone’s effort for explaining why my 12VDC socket is always working no matter if I have a good fuse or not.

Cheers

Fuse keeps burning out

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