Inline fuse from battery to converter overheating / blowing

[jpich0001]

Originally Posted by craigav

If any cable was reversed momentarily, would that cause the fuse to blow immediately?


Normally the answer is yes, but the more in-depth answer is that the reverse polarity fuse(s) would only blow immediately if there was a direct reversal short circuit that exceeded the amperage of the fuses (and the battery had enough capacity left in it to exceed the amp rating of those fuses). So if you had for example 3 connections to the battery and 2 of them were correct but the 3rd connection resulted in a reverse connection (for that circuit) but that circuits resistance was more than that of a direct short (less current flowing) then you would experience what you are experiencing which is a high amp load that overheats the wires and may or may not blow the fuse(s). High resistance is similar to the 12v electric cigarette lighters where the element can get extremely hot but not enough current flows to blows its fuse. Somewhere in your system is a short as that is the only way these wires and fuses would overheat, and the only way the reverse polarity fuses can blow is with a true reverse connection. A reverse connection is similar to a short circuit in cases like this. The reason for the reverse connection that I believe you have is that there are diodes in the converter that act as a one-way valve that would only pass the current and blow the fuses if the current was\is reversed (otherwise the diodes block the flow of power in a non-reversed connection). I have discussed this point with others quite (different website) a while back and added that the only other possibility which would be extremely rare would be that the converter itself is shorted internally and in the reverse polarity circuit itself. You would have smelled smoke most likely if that was the case, and again, I have never seen that happen but I am familiar with electronics and understand that scenario could happen. Even if it did happen though, the overload would be internal to the converter and would not overheat any of the wires like you have occurring.

The battery isn't the issue at this point either (whether or not it is still good is a different concern). The reason it isn't an issue at this point is because the converter is limited in its design to how much output it has so even if the battery was completely bad, the converters output still would not exceed the amperage of the reverse polarity fuses, only the battery could do that (or perhaps jumper cables to another battery that is reversed).

I have extremely high confidence that you have a reversed connection still yet. Some thoughts of what I would check and if you could take a few pictures of the connections on the battery that may\would help. Keep in mind that at the battery many manufactures and many times use black for the ground and still yet for other connections they use back for the positive which adds to this type of issue. Usually with white and black connections the white is the negative (ground) and black the positive, however certain connections to the battery may not be that way and the black could be used as the negative connection.

I would suggest to take a photo(s) of the battery connections for reference if nothing else and then disconnect all the cables except the two largest ones and then test for issues (hot wires or fuses blowing, etc.), then add another pair of cables and retest, and then another (depending on how many you have). If any connection results in a decent size spark and the wires start overheating then that would be the connection causing the issue.

To re-emphasize, this type of issue isn't caused by a bad battery, and isn't caused by the converter, and can only be caused by one or more connections reversed. When I say "this type of issue" I am specifically speaking to an issue where the wires, cables, fuses, etc. overheat along with blowing the "reverse" polarity fuses on the converter fuse panel output side (one or more times).

Feel free to share more pictures if you like as that may provide me with enough information to be more specific. Do you also have a clamp style dc amp meter? That could be of value as well.

~CA

See attached pictures. I do not have a DC amp-meter, just a DMM. My battery is currently at about 11.1V.

There is a diagram I provided in one of my first posts that explains the wiring in the battery. I have since removed the splice that required butt connectors and made it a continuous wire. The positive terminal is connected directly to the fuse and the runaway trailer brake via ring connector. the other side of the fuse goes into the wire nut which also contains the main trailer wire and the power jack wire.

The box seems fine to me but I'm not an expert.

[RoadrunnerII]

Ok
Lots of info in this post.
Have you taken the battery in and had it load tested yet? Not just tested with a volt meter. 11 volts is still telling the converter to bulk charge ie high current.

If the battery was bad from the get go you are going to chase ghosts.
Eliminate the obvious.
A bad cell in the battery will draw current forever from the converter because it never gets charged up enough to tell the charge wizard in the converter to lower the current level.


RoadrunnerII

[craigav]

I agree with RoadrunnerII that it would be good to have the battery tested, however even if the battery was a very bad battery, that would not blow the reverse polarity fuses. That entire reverse polarity circuit is protected with (diodes) that act as one way valves so to speak and they will not allow the the positive to positive current to blow those fuses as they block the current unless the polarity is reversed then the diodes pass the current which results in a short (by design) which then blows the fuses.

I was re-reading the original post again and wonder if being this is the first time out if the previous owner changed anything, or if you changed anything when installing the new battery? I was expecting that there would or could be other wires attached directly to the battery but seeing they are all joined together in the electric box makes things a little bit more challenging as what needs to occur at this point which is to trace (follow) the wires and make sure none of the positive cables (red or black or otherwise) have a connection to the ground. You can set your DMM for ohms with no power on the RV (battery or shore power) and then check the resistance of each wire under each "power wire" wire cap (those cables directly attached to the battery) between the wire and the ground and any one that measures 0 or close to 0 resistance should be going to the ground, and if one is at 0 that is supposed to be a positive cable then it needs to be checked further to see where it is going. The box you show in the last image, I suspect most of that wiring is for the trailer lights perhaps? If so then you need to trace the black hot wire down further to see where it goes and what ties into it further past the box.

Just some quick questions (and a repeat of one above), did you make any wiring changes when you installed the battery? Do you know if perhaps before you got the RV if someone else did? Was there any changes made elsewhere such as at the converter panel or with an inverter installation, or anything you can think of that changed?

In the meantime, I would still suggest to disconnect the battery and have it charged, that would be needed for any test as well.

~CA

[craigav]

For another test, as possibly the reverse polarity fuses were blown prior to your current issues. Recharge the battery while it is disconnected, make sure the reverse polarity fuses are in place and good, reconnect the battery (after it is fully charged) and see if the reverse polarity fuses blow again. ~CA

[jpich0001]

Originally Posted by craigav

I agree with RoadrunnerII that it would be good to have the battery tested, however even if the battery was a very bad battery, that would not blow the reverse polarity fuses. That entire reverse polarity circuit is protected with (diodes) that act as one way valves so to speak and they will not allow the the positive to positive current to blow those fuses as they block the current unless the polarity is reversed then the diodes pass the current which results in a short (by design) which then blows the fuses.

I was re-reading the original post again and wonder if being this is the first time out if the previous owner changed anything, or if you changed anything when installing the new battery? I was expecting that there would or could be other wires attached directly to the battery but seeing they are all joined together in the electric box makes things a little bit more challenging as what needs to occur at this point which is to trace (follow) the wires and make sure none of the positive cables (red or black or otherwise) have a connection to the ground. You can set your DMM for ohms with no power on the RV (battery or shore power) and then check the resistance of each wire under each "power wire" wire cap (those cables directly attached to the battery) between the wire and the ground and any one that measures 0 or close to 0 resistance should be going to the ground, and if one is at 0 that is supposed to be a positive cable then it needs to be checked further to see where it is going. The box you show in the last image, I suspect most of that wiring is for the trailer lights perhaps? If so then you need to trace the black hot wire down further to see where it goes and what ties into it further past the box.

Just some quick questions (and a repeat of one above), did you make any wiring changes when you installed the battery? Do you know if perhaps before you got the RV if someone else did? Was there any changes made elsewhere such as at the converter panel or with an inverter installation, or anything you can think of that changed?

In the meantime, I would still suggest to disconnect the battery and have it charged, that would be needed for any test as well.

~CA

Ok, sorry it's been a while but I had a busy weekend, Happy Easter everyone!

I have not nor did the previous owner (my sister and her husband) make any wiring changes to the trailer.

Today, I performed some continuity tests to see if anything is short circuited. You can see the junction box with the screws circled in one of the pictures. This is what I had to use as my ground since just touching the trailer frame wasn't enough. I confirmed that both the positive and negative wires are grounded to the frame. I went inside to the fuse panel and confirmed that all of the wires with green + are in circuit with the ground and all of the red X are not(used gas connection as ground). I find it weird that the white wires were not grounded, is that how it should be? Also, the copper wires with no color were all grounded, is that normal as well?

I need to do additional tests but I think that the continuity test confirms what you guys have been saying all along that there is a short somewhere. I will check back to see if you have any input while I continue to investigate.

Also, I will have the battery checked soon and do the recharge test to see if it causes the fuse to blow when the battery is already full.

[jpich0001]

Originally Posted by jpich0001

Ok, sorry it's been a while but I had a busy weekend, Happy Easter everyone!

I have not nor did the previous owner (my sister and her husband) make any wiring changes to the trailer.

Today, I performed some continuity tests to see if anything is short circuited. You can see the junction box with the screws circled in one of the pictures. This is what I had to use as my ground since just touching the trailer frame wasn't enough. I confirmed that both the positive and negative wires are grounded to the frame. I went inside to the fuse panel and confirmed that all of the wires with green + are in circuit with the ground and all of the red X are not(used gas connection as ground). I find it weird that the white wires were not grounded, is that how it should be? Also, the copper wires with no color were all grounded, is that normal as well?

I need to do additional tests but I think that the continuity test confirms what you guys have been saying all along that there is a short somewhere. I will check back to see if you have any input while I continue to investigate.

Also, I will have the battery checked soon and do the recharge test to see if it causes the fuse to blow when the battery is already full.

Newest update: I took the wires to the positive terminal apart and it appears that the short is only with the breakaway trailer wire. I will work on figuring out what exactly is wrong with it. Quick question, if the pin for the breakaway brake is out, would it cause this issue?

[craigav]

When you have issues as you have had, then certainly you should fix what you find when you find it as one problem can be the cause of other problems or add confusion to other problems.

Regarding the brakeaway switch, I have had the pin pulled on mine (previous TT) without my knowledge many years back and that will certainly drain the battery fairly quickly and could even overheat the wires and blow the in-line fuse with time (but shouldn't blow them, or at least not quickly otherwise the brake away wouldn't work very well). Unless I missed something earlier, or something else isn't working I don't understand though how you could have brought the RV home though if the brakes were engaged like that, in any case, a short there certainly could pull a lot of amps from the battery and needs to be corrected first and then re-check everything further.

Also, under the circuit breakers (pics 3 and 4), those cables and connections are the 120v connections and would not be related to the issues with the 12v battery voltage wiring. However, it is always good to check everything while you are there checking other things.

In picture 3 where the 12v fuses are and the green 30a fuses (reverse polarity), is it the green 30a fuses that blew out on you? Did both blow at one time and only one time? Did any other fuses in that panel also blow? Sounds like you are on the right track in any case.

I would highly suggest to pickup one of these or one very similar. If you do purchase one, be sure it states that it is for both AC and DC current. This type of meter would help you by showing you how much current is flowing through each wire you clamp the clamps around. ~CA

Be sure to click the 15% coupon if you purchase this one.

https://www.amazon.com/dp/B07Z398YWF...lig_dp_it&th=1

[jpich0001]

Originally Posted by craigav

When you have issues as you have had, then certainly you should fix what you find when you find it as one problem can be the cause of other problems or add confusion to other problems.

Regarding the brakeaway switch, I have had the pin pulled on mine (previous TT) without my knowledge many years back and that will certainly drain the battery fairly quickly and could even overheat the wires and blow the in-line fuse with time (but shouldn't blow them, or at least not quickly otherwise the brake away wouldn't work very well). Unless I missed something earlier, or something else isn't working I don't understand though how you could have brought the RV home though if the brakes were engaged like that, in any case, a short there certainly could pull a lot of amps from the battery and needs to be corrected first and then re-check everything further.

Also, under the circuit breakers (pics 3 and 4), those cables and connections are the 120v connections and would not be related to the issues with the 12v battery voltage wiring. However, it is always good to check everything while you are there checking other things.

In picture 3 where the 12v fuses are and the green 30a fuses (reverse polarity), is it the green 30a fuses that blew out on you? Did both blow at one time and only one time? Did any other fuses in that panel also blow? Sounds like you are on the right track in any case.

I would highly suggest to pickup one of these or one very similar. If you do purchase one, be sure it states that it is for both AC and DC current. This type of meter would help you by showing you how much current is flowing through each wire you clamp the clamps around. ~CA

https://www.amazon.com/dp/B07Z398YWF...lig_dp_it&th=1

So, the breakaway trailer brake was in while driving but I pulled it out for storage. I'll throw it back in.

The only fuse that blows is the 30A fuse on the left (and the battery inline fuse). This fuse has blown multiple times. In fact, it seems like the battery fuse and the reverse polarity fuse take turns blowing, but the battery fuse blows more often, maybe 4:1. It seems that the trailer wire wasn't the only issue because I took it off the battery terminal and experienced the same problem.

I actually just bought the Uni-T 203 and should receive it by Thursday.
https://www.amazon.com/UNI-T-Digital...21&sr=1-4&th=1

[RoadrunnerII]

Originally Posted by jpich0001

So, the breakaway trailer brake was in while driving but I pulled it out for storage. I'll throw it back in.



The only fuse that blows is the 30A fuse on the left (and the battery inline fuse). This fuse has blown multiple times. In fact, it seems like the battery fuse and the reverse polarity fuse take turns blowing, but the battery fuse blows more often, maybe 4:1. It seems that the trailer wire wasn't the only issue because I took it off the battery terminal and experienced the same problem.



I actually just bought the Uni-T 203 and should receive it by Thursday.

https://www.amazon.com/UNI-T-Digital...21&sr=1-4&th=1

Bingo!
You are not suppose to remove it Ever!! Its for applying brakes if the trailer becomes disconnected from the tow vehicle
What you have done is applied the current to the brake magnets continuously at full power which will kill the magnets and wires eventually.
You still need to test your battery and have someone check each wheel brake and magnet

RoadrunnerII

[craigav]

Originally Posted by jpich0001

So, the breakaway trailer brake was in while driving but I pulled it out for storage. I'll throw it back in.

The only fuse that blows is the 30A fuse on the left (and the battery inline fuse). This fuse has blown multiple times. In fact, it seems like the battery fuse and the reverse polarity fuse take turns blowing, but the battery fuse blows more often, maybe 4:1. It seems that the trailer wire wasn't the only issue because I took it off the battery terminal and experienced the same problem.

I actually just bought the Uni-T 203 and should receive it by Thursday.
https://www.amazon.com/UNI-T-Digital...21&sr=1-4&th=1

The Uni-T 203 should work well for you.

Interesting observation with only blowing one of the 30a rp fuses. What I suspect is that you have a 40 or 50a converter (do you know which converter and its amperage output?), in any case, those two fuses are in parallel and together support 60 amps of current, which is why I was saying that the converter itself should never blow those fuses as the converters output capability is less than the "2" fuse combined rating. With that in mind the reverse current from the battery could easily output more than the 60a capacity of the 2 fuses.

When you have two 30a fuses in parallel, that pair of fuses would support up to 60a. Any time the first fuse blows the second one blows as well (should blow as well if it is connected into the same circuit) because the current load with the first blown fuse is more than the double the remaining fuse's capacity. What this would mean is that even though there are two fuses there, the right one is either no good to start with or it has a bad connection at the fuse or on the board itself and if so that would explain why the only the left fuse blows as if the right one isn't carrying its load, then all you have left is the one at 30a which would be less than the converters output capacity.

For a test, remove the left fuse, and with your voltage meter check that you have power on both sides of the right side fuse.

As RoadrunnerII shared concerns, just as in the same manner the wires overheated, if the brake wires also overheated (or the electro magnet in the drum) then that could damage them. Very soon, perhaps after fixing your electrical issues (or along with if you find brake wiring damage), I would take the wheels off and re-pack the bearings while you are there (if they haven't been repacked recently) and carefully inspect the brakes, wiring, shoes, etc. as well as the brake wiring to each wheel. I would have to look it up as it has been a while, but I believe that you can measure the resistance of the brake's electro magnet to help determine the health of it, certainly you could tell if there was infinite resistance that would indicate an open circuit. ~CA

[jpich0001]

Originally Posted by RoadrunnerII

Bingo!
You are not suppose to remove it Ever!! Its for applying brakes if the trailer becomes disconnected from the tow vehicle
What you have done is applied the current to the brake magnets continuously at full power which will kill the magnets and wires eventually.
You still need to test your battery and have someone check each wheel brake and magnet

RoadrunnerII

Hmm that might be why the breakaway trailer switch seems to be badly damaged also. In my ignorance I was using it to keep the trailer from moving while it was being stored, but I see why that's a bad idea. Lesson learned there.

[RoadrunnerII]

Originally Posted by jpich0001

Hmm that might be why the breakaway trailer switch seems to be badly damaged also. In my ignorance I was using it to keep the trailer from moving while it was being stored, but I see why that's a bad idea. Lesson learned there.

So.....
Disconnect the breakaway switch asap. That should fix the high current draw immediately.
Get a new one. Get it installed and wired up properly.
Then the brakes and wires need to be inspected and replaced.
Given the load on your battery and discharge to so low voltages you are looking at another battery almost a guarantee at this point.

RoadrunnerII

[jpich0001]

Originally Posted by RoadrunnerII

So.....
Disconnect the breakaway switch asap. That should fix the high current draw immediately.
Get a new one. Get it installed and wired up properly.
Then the brakes and wires need to be inspected and replaced.
Given the load on your battery and discharge to so low voltages you are looking at another battery almost a guarantee at this point.

RoadrunnerII

Installed the new switch today. See attached for what happens when you pull the breakaway pin indefinitely. Because I don't want to test this I wonder if anyone knows offhand, if I had not plugged my trailer into shore power, would this damage still have happened? I know the battery would have drained quickly but it seems like it shouldn't have caused this damage to the switch if it was just the battery power. Thoughts?

After installing the new switch I put the same battery back in line and plugged in shore power. Both fuses remained intact. Inline fuse holder got warm but not burning hot. Battery was at 11.4V before I put it on and I charged it up to 12.53V. Also, the battery gauge showed something other than empty for the first time. It went from 1/3 to 2/3 to full throughout the charge. I bought a battery tester so when it arrives I will still test both batteries to make sure they're good (I have been doing all my testing with only one battery to remove one bit of complexity).

Once my clamp on AC/DC ammeter arrives I will check the breakaway trailer brakes on all 4 tires as you guys have advised previously. Hopefully I haven't damaged anything else in my ignorance.

I appreciate all your responses, you've helped me learn a lot! Thank you

[RoadrunnerII]

So you need to think a little different on battery empty vs full.
A battery below 12 volts is empty and likely incurred damage to the internal plates. The only real way to validate the battery is with a load tester.
Since you have two batteries assuming same age and size if it was mine I would get both load tested.
Then you know what you got.
If one is lower than the other on the load test.... in use it will pull the better battery down to its state of charge level
In terms of use the bad battery will kill both prematurely.
If you have multiply batteries it best and more economical to replace together

As for the brake magnets
Internally when left on this long they have overheated in all likelihood you will need 4 new ones.
Its your families safety on the road.
Don't cheap out.
If you want buy 1 new one to measure the resistance on.
Compare your 4 to that new one
You can do it by disconnecting each magnet at the backer plate connections under the trailer. If they all measure the same verify your brake wires to each backer plate from 7 pin embilical cord
Make sure none of the wires is shorted to ground.
If you are unsure how to test
Find someone knowledgeable on troubleshooting electrical wiring to help you.
Again this is you and your families safety

RoadrunnerII

[lthistle]

Jpich0001, did you resolve that battery fuse getting hot issue ? I am having exactly the same thing happen. My battery fuse melted and I am not getting charge from the converter, only 12.2 volts with the battery installed. It's a new battery.

[jpich0001]

Originally Posted by lthistle

Jpich0001, did you resolve that battery fuse getting hot issue ? I am having exactly the same thing happen. My battery fuse melted and I am not getting charge from the converter, only 12.2 volts with the battery installed. It's a new battery.

If you're not getting any charge from the converter when connected to shore power, check the reverse polarity fuses in the fuse panel. You may need to replace the fuse(s). They could be old a replacement could solve the problem or you could have a short circuit somewhere.

I believe my issue is resolved. I had pulled the pin out of the breakaway trailer brake and was using that function as a parking brake while in storage. Do not use the breakaway pin that way. It will ruin your battery and when you are hooked up to shore power it will continue to draw full power and send it to the trailer brakes. If it goes on long enough it could ruin the brakes as well as the breakaway switch. The current draw can also blow the fuse to the battery and melt it if it gets hot enough.

If you read through this entire thread RoadrunnerII and Craigav provide a lot of good information. What ultimately led me to figuring out the issue was their explanation of the presence of a short somewhere, which they explain as being the likely (or only) reason for the reverse polarity fuses to blow. I think when the breakaway switch circuit is closed it causes a short (I could be wrong here) because when I used my multimeter to perform a continuity test, it beeped when I tested it against the brake line and a grounded bolt on the trailer. Check out the video below on how to perform the test.

https://www.youtube.com/watch?v=m-rLnWqRMbs