Fuse Fire

[Lee R]

Hello,

This is my first boat that has a solar charger and an Inverter setup. I started using the boat in May of this year. The Inverter is original from 2000 and the Solar Panels have probably been on the boat for 10 years or so but not 100%. Anyway this weekend when we had a heavy load on the inverter I smelled something burning. I quickly climbed into the engine room and had smoke coming from the battery box. When I opened the cover the inline fuse from the solar charger was melted and glowing red. It charred the top of the fiberglass battery box which was close to igniting. Luckily I caught it in time but now I am looking for some help on the why?

The solar charging unit is the Sun Duo SSD-25 by MorningStar. The system is connected to the house battery bank as well as the starting battery. The Inverter that runs on the house side is the Xantrex SW3000.

The incident happened when my wife was preparing breakfast. She used the toaster oven for a few minutes and then when that was done kicked on the microwave for a few minuts so there was a heavy load on the inverter. I am assuming the inverter load somehow was pulling amps through the solar wire and over heated it? The charging wire from the solar charger with the inline fuse is only a 12 gauge wire with a 25amp fuse. I believe there should be a 10gauge wire for a 25amp fuse so that may be part of the overheat / melting point on the fuse assembly. Not sure if putting that kind of load on this setup is not good. Looking for some help on how to determine why this turned to a near fire instead of just blowing a fuse. Any help would be appreciated.

 

[BlueFox]

I would suspect a loose or corroded connection on the fuse or fuse holder, 12AWG wire will get warm at 25A but otherwise should be completely fine.

It sounds like the heavy load meant the charge controller was charging the batteries at full current, which could have caused a bad connection to heat up.

Or it just was unrelated to the high inverter load and the bad connection happened to fail then.

 

[Bob B]

I agree with BlueFox

A bad connection usually won't fail all at once. It will heat and cool which will cause the connection to get worse and worse til it finally goes over the cliff like it did.

It's a good idea to periodically check the system by putting it under a moderate to high load and check the temperature of the connection points ..... Just feeling them with your had is probably sufficient or you can get more sophisticated with thermal imaging.

 

[BlueFox]

I agree with BlueFox

A bad connection usually won't fail all at once. It will heat and cool which will cause the connection to get worse and worse til it finally goes over the cliff like it did.

It's a good idea to periodically check the system by putting it under a moderate to high load and check the temperature of the connection points ..... Just feeling them with your had is probably sufficient or you can get more sophisticated with thermal imaging.

Good advice! You'll also usually see some discoloration on terminals and the wire nearby if they are getting too hot.

 

[mikefitz]

As he said.

There is an outside chance the PWM controller has failed and excess current was going to the controller.

A picture of the fuse damage would be interesting. Anything over 20 A is a bit much for a standard blade fuse and many of the fuse holders make poor contact. For a 25 amp controller I suggest a 30 A midi link fuse and fuse holder with ring cable terminations. On a 25 A controller I would have used 10 or 8 gauge to reduce volt drops.

Electrical stuff on a boat has a hard time. This failure may be an indication that electrical systen needs a compressive examination. Look for volt drops on cable runs.

Mike

 

[Bud Martin]

The inverter should be pulling the current through a big fuse that is connected to the battery banks for 3000 Watts inverter, the bulk of the current draw by inverter will be from the battery banks, the 25A from charger to the battery banks is for handling the charging current.
You should check out the wiring and verify that the inverter is connected to the battery with large fuse, and the charger is wired to to the battery with its own fuse.
As other said, it sounds like poor connection.
Pictures of the setup?

 

[Zwy]

Hello,

This is my first boat that has a solar charger and an Inverter setup. I started using the boat in May of this year. The Inverter is original from 2000 and the Solar Panels have probably been on the boat for 10 years or so but not 100%. Anyway this weekend when we had a heavy load on the inverter I smelled something burning. I quickly climbed into the engine room and had smoke coming from the battery box. When I opened the cover the inline fuse from the solar charger was melted and glowing red. It charred the top of the fiberglass battery box which was close to igniting. Luckily I caught it in time but now I am looking for some help on the why?

The solar charging unit is the Sun Duo SSD-25 by MorningStar. The system is connected to the house battery bank as well as the starting battery. The Inverter that runs on the house side is the Xantrex SW3000.

The incident happened when my wife was preparing breakfast. She used the toaster oven for a few minutes and then when that was done kicked on the microwave for a few minuts so there was a heavy load on the inverter. I am assuming the inverter load somehow was pulling amps through the solar wire and over heated it? The charging wire from the solar charger with the inline fuse is only a 12 gauge wire with a 25amp fuse. I believe there should be a 10gauge wire for a 25amp fuse so that may be part of the overheat / melting point on the fuse assembly. Not sure if putting that kind of load on this setup is not good. Looking for some help on how to determine why this turned to a near fire instead of just blowing a fuse. Any help would be appreciated.

I would disconnect the charge controller from the batteries and run the inverter under heavy load. I'd check for voltage drops in the feed to the inverter from the battery and look for any hot spots. Note amp draw under load and voltage.

 

[sunshine]

Unsure if the Sun Duo SSD-25 by MorningStar shares the positive common feature of most PWMs out of China and if the + from the pv has been connected elsewhere (as in common + "earth") and then onto the pwm there is only a minimal switching current in the B+ lead out of the PWM.
Rather pointless putting a fuse on the B+ lead out of a common + pwm if wired in such a way as it would only blow when there is a failure somewhere else in the system and where a fuse should have been located....probably, as in the posts above, there is a loose connection and the electrons have found another path!

 

[Lee R]

Thanks for the responses. Great to find a spot with knowledge of these systems. I am on the boat now so attached are some photos.

One thing to note is I replaced the batteries in the boat probably 3 or 4 weeks ago. I do not remember where the fuse holder was placed exactly before I undid the connections and changed the battery but where it was when it burned up is right over the top of the battery service / fill caps with the battery box cover snug against it. I am wondering if off gassing of the battery could of corroded the fuse? The fuse holder was an anchor marine brand and is pretty well sealed with a gasket but it is something that popped into my mind.

The wire from the solar controller turns out to be 10 gauge but then they butt spliced it to a 12gauge wire fuse holder with the 25amp fuse.

In the pictures the good fuse holder is the one for the starting battery. I also attached a picture of the solar remote meter showing the max amps from solar charge which was 27.21. I am not sure when that max amp was hit. When the melted fuse situation happened it was partly to mostly cloudy. Not to say there were not some holes with sun but it was on and off.

The inverter is pulling power through much larger wire and has a 300amp fuse. The charge wires from the solar charger are run separate directly to the house battery and then the starting battery and each run has its own fuse though as mentioned it is a 12gauge wire with a 25 amp fuse. The length of the wire on the fuse is 4 or 5 " on each side. One side was directly to the battery terminal and the other side is spliced to the 10 gauge wire that runs about 3ft to the solar control.

 

[rhino]

27A would have been above the 25A fuse rating. Fuses should not be run anywhere near 100% as they will normally not blow at exactly that rating and will cause excessive heat running at 100% over an extended period and could start melting the fuse/fuseholder .. especially with a blade style which has a lot of surface area and potential for corrosion to increase that resistance and therefore more heat. I also believe the AIC rating for an ATC style fuse is too low for connecting directly to house battery so it shouldn't be used in that location to begin with. One possible solution is to upgrade the cable to larger size and switch to a ANR style fuse.

 

[rhino]

The sunsaver duo manual also states it should have a 30A fuse, not a 25A fuse.

 

[Hedges]

I assume it was resistive connections.
Corrosive battery vapors could do that; fuses and electronics shouldn't be exposed to it. Or just the environment. Consider dielectric grease.

If overloaded, the wires and holder should never burn. Supposed to carry sufficient current to blow the fuse.
Failed SCC could overload fuse, but again should have blown not burned.

House wiring, we're not supposed to put more than 20A through 12 awg. But ampacity is 30A, so that isn't the problem. 12 awg may be too much resistance and voltage drop, affecting measurement of battery voltage by SCC.

Was that an automotive style fuse? It is between battery and SCC, which could short out.
What voltage, 12V? 24V?
Whatever current the battery can put into a short, the fuse should have AIC rating that high. Maybe you have CCA rating (current at 8.5V per 12V, in cold weather). Multiply CCA by 3x to get an estimate of short circuit current. Fuse AIC rating should be at least that current, at battery voltage.

 

[mmtech]

Possible fuse overheated but not enough to blow. When you replace the holder if you re locate it remember that it is to be located within 18 inches of the power source by cost guard and apba regulations

 

[Lee R]

Hedges, The boat is set up for 12V. The house side uses 6V batteries tied together to produce 12V. Their is a bank of four 6V batteries on the port side and another two on the starboard side all. The starting battery is a single 12V on the starboard side.

From all of the feed back and looking at how the fuse burned I am thinking the connection at the fuse was compromised, either loose or corroded. My question is since I was running the inverter with a heavy load powering the microwave and there was a solar charge coming into the house battery, would the current draw on the battery create a situation where the current coming in from the solar was trying to come in faster creating the extra resistance that over heated the fuse? I am wondering if the fuse had been compromised for some time and had heavier resistance than normal. Under conditions of standard battery draw it was not enough resistance to melt the fuse but with the heavy draw from the inverter it created such a draw and imbalance on the battery side that it increased the resistance through the fuse and was the final trigger point? I guess I am comparing the inverter to a vacuum almost and trying to pull the charging amps from the solar panel in faster but not sure if that is how it works. I am just trying to understand the final trigger point if anyone has info on this theory.

Moving forward I like the suggestion on the Midi style fuse. I am going to switch both solar feed wires over to that setup in a 30amp and increase the wire size to 8awg. I will mount the fuses just outside of the battery box on the bulkhead. I do see in the SunDuo manual where they suggest a 30amp fuse. I talked to them yesterday and they sent me a test guide to go through for their unit. They said if the unit malfunctioned it is possible it could back feed current from the staring battery to the house batteries on the heavy inverter draw but said if that was the case the fuse on the starting battery would have heated up as well so they do not think think took place. Once I get everything hooked up I will run the inverter with a heavy load and check amps on different areas of the system.

 

[Supervstech]

Setup looks great, do you have any before pictures?

 

[Lee R]

Attached are the pictures showing the fuse before it burned up. This is also before I replaced the batteries. The new batteries only had the single threaded post so I had to move the one wire in this picture that was on the other post to the stud with all of the others. Is there any issues with all of the wires going to the 1 stud? I would like to find a better copper plate to spread out the connections.

 

[Hedges]

My question is since I was running the inverter with a heavy load powering the microwave and there was a solar charge coming into the house battery, would the current draw on the battery create a situation where the current coming in from the solar was trying to come in faster creating the extra resistance that over heated the fuse?

Basically, yeah. With light use, there would have been a small charge current for a shorter time. With a heavy load, or if battery was more deeply drained overnight, then charge controller has to deliver more current longer. Improperly sized, fuse and wire should have been able to carry any current until fuse blows without other damage. Could just be corrosion or normal oxidation.

Actually, if partially drained overnight then as sun comes up it would start to recharge slowly. So heavy draw in middle of day when PV can deliver lots of power could be what produced the highest current.

How long are wires from charge controller to battery? You can look up resistance per unit length and multiply by max current rating, see how much voltage drop. Should be a very small percentage of 12V, like 0.1V or less. Could be good to use 8 awg.

You have a large fuse for inverter. The small fuse for charge controller could tap off from other side of large fuse. Although sometimes extra voltage drop/bounce from high inverter current confuses charge controller. Could use higher quality fuse (or whatever is approved for for boat use by ABYC).

In a car, there is or used to be a "fusible link", a length of wire in a tube which served as a fuse able to interrupt even the 3000A short circuit current a starting battery could put out. That was between fuse box and battery. Now there may just be a larger fuse. Only starter goes direct to battery. So the various automotive fuses aren't wired directly to battery.

 

[Daddy Tanuki]

better cabling and a better fuse... that and a lot of Oxguard or its equivalent. corrosion in a salt air or even freshwater environment is a sneaky thing on wires. I bet if you strip the wires back on that fuse holder you will find corrosion running the length of the wires as well.

I work as a contractor taking care of gear on the local military bases including at the local SRF. i find that wires that are not prepared for the moisture in the air (especially if salt water) really messes the wiring and fusible links up.

A little corrosion causes a rise in temperature at the corroded location, which as the temp rises so does your resistance.... its a viscous cycle which can rapidly lead to overheated wiring and fused connections.

Good luck!

B Break
O out
A another
T thousand

 

[Lee R]

The inverter was being used around 9:30 am or so and was after a draining on the batteries overnight running lights, stereo, refrigerator etc.. so battery bank was down to about 71% capacity on the meter. The wire length from battery to solar controller is around 3ft.

I will peal back the sheeting on the wire close to the burned fuse area to see if it looks corroded.

And Yeah B.O.A.T. holds very true. They should make a $1000.00 bill that has a picture of a boat on it instead of a president.

 

[Daddy Tanuki]

you could also just take a accurate multimeter set it for resistance and then probe at the junction of the inverter and wire to the junction of the fuse and wire. look up the expected resistance for the wire on line and compare. I bet you find its at the bonkers end. easier than stripping and will give you a good idea of your resistance.