HELP - Melted Main 12v Fuse - Fiberglass RV


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Old 08-13-2018, 07:11 PM   #1
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HELP - Melted Main 12v Fuse

Setup:
(2) 6v Trojan T105's only 17 months old and always kept full and charged.
TM-2030-RV Battery monitor (and handheld meter that verified readings).
Progressive Dynamics 9130 Converter with added Charge Wizard Pendant.

Recent issues with appliances and cause was a melted main fuse. Its the 30A 12V fuse right at the battery. It was melted but not fully blown so it was causing a voltage drop from 12.7 at battery to 11.98 at appliances. Once I cleaned up fuse holder and installed a new fuse - all is well. No voltage drop any more. Problem fixed. But WHY??

So I thought, what have I done differently lately? Well 2 weeks back I boondocked and for the first time ever we used our new Honda EU2000. We used it for water heater, make coffee, electric skillet, etc. Maybe ran it for 2 hours total over 2 days. It would scream full blast when the 1450w water heater would be in use.

So for the life of me, why would the use of a generator overheat a main 30A 12v fuse? I'm stumped. Is it just coincidence the fuse melted same time frame as using generator? Id have to guess its related. Any help thoughts would be greatly appreciated!!

THANK YOU!!!! Joe
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Old 08-13-2018, 08:36 PM   #2
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Joe, I think its a fluke. The generator has nothing to do with your 12v, the 120 only goes to the converter and that takes care of the 12v.
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Old 08-13-2018, 09:05 PM   #3
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There's a couple things I believe going on here. 1. The fuse inside the battery compartment needs to taken out and put back in every couple years to control corrosion. 2. You charging system may be over charging, easy to tell if the liquid is going down in the batteries.



Now for bit on fuses and fuse rating. Most fuses do NOT blow the instant the current reaches the marked current. The fuse is heat device and blows the rated current is reached or exceeded AND there's been some time pass at the elevated current rate.

EXAMPLE.. A few years ago we wanted to know how well a 1amp fuse protected a consumer device. We connected a fuse is such a manner that the fuse had 2amps of current. NOTE is a 1 amp rated fuse. After over an hour the fuse was still allowing current to flow through it.
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Old 08-13-2018, 09:48 PM   #4
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Quote:
Originally Posted by Joe & Cherie View Post
Setup:
(2) 6v Trojan T105's only 17 months old and always kept full and charged.
TM-2030-RV Battery monitor (and handheld meter that verified readings).
Progressive Dynamics 9130 Converter with added Charge Wizard Pendant.

Recent issues with appliances and cause was a melted main fuse. Its the 30A 12V fuse right at the battery. It was melted but not fully blown so it was causing a voltage drop from 12.7 at battery to 11.98 at appliances. Once I cleaned up fuse holder and installed a new fuse - all is well. No voltage drop any more. Problem fixed. But WHY??

So I thought, what have I done differently lately? Well 2 weeks back I boondocked and for the first time ever we used our new Honda EU2000. We used it for water heater, make coffee, electric skillet, etc. Maybe ran it for 2 hours total over 2 days. It would scream full blast when the 1450w water heater would be in use.

So for the life of me, why would the use of a generator overheat a main 30A 12v fuse? I'm stumped. Is it just coincidence the fuse melted same time frame as using generator? Id have to guess its related. Any help thoughts would be greatly appreciated!!

THANK YOU!!!! Joe
One potential cause might be undersized or improperly crimped connections on the wiring coming out of the battery, at the ends of the fuse or at the end going into the converter. Faulty connections, undersized wires, etc can create excess heat. So do a careful inspection and/or replace those wires and connections. Better to spend money on some new wires and fittings than end up with more expensive repairs. If I saw that happen on my trailer I would be taking a very careful look at the wiring sizes and checking the crimps on the connectors. You did not say what type of fuse holder you have. Perhaps you need a more robust one from a marine supply source as the fuse holder itself could be the issue.
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Old 08-14-2018, 05:36 AM   #5
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Joe,

Agree with above comments. Getting more specific, you didn't say whether the appliances you were running were AC or DC. Measure the peak amperage at battery, both when charging and with peak loads. If you are using an inverter (e.g., 300 watt or more), the amperage draw can easily exceed 30 amp at 12 vdc. A 300 watt inverter typically can produce much higher wattages for short periods.

- John
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Old 08-14-2018, 05:39 AM   #6
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Thank You!

I think you guys are spot on! That's what I love about this site, everybody is awesome and super helpful! I thought I was on the right track, and happy I found the fuse, but was wrong in thinking the genny did it. After thinking about what you guys say - I fully agree the genny cannot be suspect and it was coincidence (that's what makes electrical fun! ).

My appliances running were a 12v water pump, a few LED 12v lights, and the 12v (compressor) fridge that draws 4.5A when running. That's it. I do not have/use an inverter. How I noticed the issue was the water pump sounded weak, and the fridge was shutting on/off every 30 seconds (it does that when it gets too low of a voltage supply).

So anyway, fuse holder is now clean. Next I will check the wires and crimps. That's great advise! I believe the main wire is sized at 10ga - and the battery is only 5 ft from the converter. Should be ok there but again I will check!

So you mentioned overcharging. I'm starting to think that is the issue. I did have a little wetness on top of the batteries. Also I filled them a few weeks back to the bottom of the plastic necks (a tad too full I realize now), and in 2 weeks time they are now about 1/8" below the necks (proper level). So they have lowered.

When I bought the egg it had a PD9130 in it. I added the charge wizard pendant to make it a smart charger last spring when I added the new batteries. I'm going to monitor the charging rates. I believe it goes on 14.4v boost up to 80 or 90%, then 13.6v up to 100%, then 13.2v storage. What I think is happening is it is staying on 13.6 normal charge well after the battery is fully charged. I have noticed the meter reading 100%, or even 102%, and the wizard still going at 13.6v and on normal charge mode. If this is true, I have a converter/wizard not doing its job properly. I'll do some more monitoring for a few days and report back.

If this is the issue I may just shut off the battery at the main switch when plugged into shore power and charge it separately with a CTEC 7002 I recently purchased. Its a shame to have to do that, but I assume its a much better/accurate charger than the PD.

Thanks again for all the help! I'll reply back with findings!
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Old 08-14-2018, 09:57 AM   #7
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Perhaps vaguely related, I treated myself to a sweet-looking set of heavy-gauge jumper cables at a famous big-box store some years back. One of the two conductors checks out OK for continuity, but doesn't transmit any amperage to speak of. The other is fine.

It's some sort of manufacturing defect. The clamps look to be well-connected, based on a cursory inspection, but something is not right about the one conductor.

To date, it remains an unexplored "project" as I still have the cheesy set of cables I had intended to replace. Somewhere under all that insulation lies a very poorly-made connection which was fouled up at the factory. As everything visible looks so skookum, I've even wondered if it was the end of a reel and the strands got tugged apart somewhere under the insulation.

My point being that sometimes electrical stuff just isn't well-joined when manufactured. We just had a thread which apparently involved a brand-new wiring harness which was faulty.
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Old 08-14-2018, 10:23 AM   #8
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A lose or bad connection causes that kind of heat. Clean the connections and make sure they are tight. Also use a die electric grease on the connections to stop any corrosion. The die electric grease is available at auto parts stores.
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Old 08-14-2018, 10:30 AM   #9
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"When I bought the egg it had a PD9130 in it. I added the charge wizard pendant to make it a smart charger last spring when I added the new batteries. I'm going to monitor the charging rates. I believe it goes on 14.4v boost up to 80 or 90%, then 13.6v up to 100%, then 13.2v storage. What I think is happening is it is staying on 13.6 normal charge well after the battery is fully charged. I have noticed the meter reading 100%, or even 102%, and the wizard still going at 13.6v and on normal charge mode. If this is true, I have a converter/wizard not doing its job properly. I'll do some more monitoring for a few days and report back."

Joe, the suggestion was that your melting 30 amp fuse might be due to the charger applying current in excess of 30 amps. The charging amperage can be checked with a multi-meter or ammeter.
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Old 08-14-2018, 12:42 PM   #10
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Originally Posted by John in Michigan View Post
Joe, the suggestion was that your melting 30 amp fuse might be due to the charger applying current in excess of 30 amps. The charging amperage can be checked with a multi-meter or ammeter.
See, this is where I think I'm doing ok on electrical but miss a lot! Its a lot to learn! So if I understand correctly, the batteries being "overcharged" or the charger supplying 13.6v for too long would not hurt the fuse. It would only hurt the battery.

So the only way the fuse will melt is either higher than 30A going thru it, or a bad connection. I googled how to measure Amps with a multimeter and it shows most go up to 10A. I believe my hand held also only goes up to 10A. Therefore I would need a 30A meter to test this. BUT, since I have the TM-2030 battery monitor, it also reads amps in and out of battery. I should be able to easily see the charging amps by shutting everything off and letting the charger go on boost and see what the amps says. Sounds easy enough. But I have to admit I don't ever think I have ever seen amps that high going into the battery while charging. I will recheck tho.

That leads me to a bad connection, and as stated above - that bad or dirty connection could have been the fuse holder itself! Hopefully I'll find something.

Thanks again so much and please correct me if I'm still misunderstanding!
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Old 08-14-2018, 01:29 PM   #11
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Joe,

Reasons for the fuse melting in the way you described are:

- exceeding 30 amp current
- poor (dirty, corroded) connection in the fuse socket
- cheaply constructed or faulty fuse socket
- EDIT: also, cheaply constructed or faulty fuse

Concerning the charging voltages that you mentioned, it seems to me it wouldn't be bad if the charger continued charging to 102%. A wet lead acid battery is fully charged at 12.7 to 12.8 volts. Also, while the battery is charging the voltage will read somewhat higher, and while the battery is discharging the voltage will read somewhat lower. So +2% is well within normal range.

-John
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Old 08-14-2018, 01:42 PM   #12
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to narrow down the problem with those jumper cables, connect them between a power source and a heavy current load like a car headlight, and measure the voltages at the clamps, and at the wires right next to the clamps.
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Old 08-14-2018, 01:44 PM   #13
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exceeding 30 amps would have blown the fuse. fuse holder melt downs are far more likely from resistance in the connections...
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Old 08-14-2018, 01:50 PM   #14
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John in SC, Joe is reporting that the fuse melted. What do you make of that? Still a faulty connection? Or out of spec fuse, or ...
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