Blew a 250 amp fuse the other day. How to avoid this

[Skwidward]

I'm a bit confused about the 250 amp fuse blowing.

RV air conditioners usually draw about 10-12 amps AC which would be about 120 amps at 12 V, so why did the fuse blow?

I'd check all the connections around the fuse block to make sure they're sound. Some of the heat could have been caused by a bad connection at the fuse block and the excess heat caused the fuse to fail.

Do have a low voltage alarm and disconnect to save your batteries?

I’m a bit confused myself, to be honest, by your post.

Air conditioners have a starting surge—for a second or so when the compressor first kicks on they use way more power than they do when just running normally. This is something of which you should be aware and for which you should account, especially when sizing a generator you plan to use to power your air conditioner.

No, the connections at the fuse block are not bad. They’re sound.

Yes, I do have both a battery disconnect and a low voltage alarm.

[Driggs-Dave]

I'm a bit confused about the 250 amp fuse blowing.

RV air conditioners usually draw about 10-12 amps AC which would be about 120 amps at 12 V, so why did the fuse blow?

I'd check all the connections around the fuse block to make sure they're sound. Some of the heat could have been caused by a bad connection at the fuse block and the excess heat caused the fuse to fail.

Do have a low voltage alarm and disconnect to save your batteries?

[Skwidward]

... I am now, as I type, in the process of ensuring this does not happen again...

Just to clarify, I am not in the process of ensuring my failsafes do not work again.

I am, instead, in the process of ensuring that they do work and work faster at less of a current/draw and without a scary burning smell and very small but still very heart-stopping amount of smoke.

[Skwidward]

as a motorcoach owner, with a Magnum Inverter/Charger, and a small amount of solar, I'm really curious as to WHY you would change the RV's built capacity and move the Shore cord to the Inverter's input, directly, when the Inverter/Charger ALREADY is designed and installed to handle battery Charging with it's original installation(i.e., thru the breaker which feeds it from the Main Panel)...

As a non-motorcoach owner without a Magnum Inverter/Charger, and a large (relatively speaking) amount of solar, I did this because:

1.) I want to live unplugged.

2.) I replaced my TT’s factory lead acid battery with $3,000’s worth of LiFePO4 batteries, and I want to control how they are charged; the battery manufacturer is very specific about how these batteries are to be charged. The factory converter in the TT does not allow me to do this.

3.) The factory converter in my TT charges the batteries when it is receiving 120V AC. Since the 120V AC it receives comes from my battery bank (when I am unplugged..see 1.)), I do not want to charge my batteries in this unmonitored and unadjustable manner with their own power.

what you've done is exactly what you've done - you've created a scenario where when you loose Shore or Generator power, whether intentional or not, your INVERTER is now going to be trying to power EVERYTHING that is on/running in your coach, i.e., the 120v Air Condtioners, which it is NOT designed to do, but also quickly depleting your Battery Bank, which is your precious power Storage for the solar power you spent so much money to install.

Yes, this is the scenario I have created. However, my TT is 19ft long. I never intended to run my air conditioner off my battery bank. In fact, I never really planned to ever run the air conditioner. It’s just at this moment in time I am confined to south Florida for a while, and since I now live full time in my TT, I do use the air conditioner now and then. Besides the air conditioner, there are no appliances in my TT that pull more power, ac or dc, than my batteries can supply.

When designing this solar system I did not account for being plugged in with an air conditioner running, losing shore power, and the inverter trying to run the air conditioner off the batteries. However, I did install a number of failsafes to protect my wife and myself and the system. The other night one of those failsafes worked. I am now, as I type, in the process of ensuring this does not happen again.

I did use the bluesea chart when designing my system. I guess I looked elsewhere for the max current of 2/0 wire and evidently misinterpreted the information.

But yeah, 2/0 wire from battery positive to positive bus bar with now a 200 amp ANL fuse, and 2/0 wire from positive bus bar to the inverter with now a 150 amp breaker. This will protect everything while I work on installing a sub panel to isolate the shore power and the air conditioner like jflorey2 mentioned above. This will kill the air conditioner when shore power is lost. Thanks again, jflorey2! I knew there had to be a way to isolate that thing.

Also, thanks to everyone on this site who’s helped me along my way.

[Skwidward]

What kind of fuse are you using? A high quality fuse will not burn up when it blows.

It was a 250 amp ANL fuse by Baomain.

https://m.youtube.com/watch?v=pP_Yv5rgfwc

I apologize for my sensational use of the English language in my OP. What I see in this YouTube video would have caused the issue I had the other night.

[NCmountainsOffgrid]

as a motorcoach owner, with a Magnum Inverter/Charger, and a small amount of solar, I'm really curious as to WHY you would change the RV's built capacity and move the Shore cord to the Inverter's input, directly, when the Inverter/Charger ALREADY is designed and installed to handle battery Charging with it's original installation(i.e., thru the breaker which feeds it from the Main Panel)...

what you've done is exactly what you've done - you've created a scenario where when you loose Shore or Generator power, whether intentional or not, your INVERTER is now going to be trying to power EVERYTHING that is on/running in your coach, i.e., the 120v Air Condtioners, which it is NOT designed to do, but also quickly depleting your Battery Bank, which is your precious power Storage for the solar power you spent so much money to install.

[emartin00]

I'm gonna guess the fuse? The fuse cover, which is clear plastic, now looks like someone held a flame to for a short while.

What kind of fuse are you using? A high quality fuse will not burn up when it blows.

[Skwidward]

If the wires didn't start to smoke, what caused the smoke / smell that disturbed your sleep ?

> In no time at all my wife and I were lifting the bed (my solar components are located under the bed) fire extinguisher in hand to inspect the burning smell and smoke!

I'm gonna guess the fuse? The fuse cover, which is clear plastic, now looks like someone held a flame to for a short while.

[Mike90250]

If the wires didn't start to smoke, what caused the smoke / smell that disturbed your sleep ?

> In no time at all my wife and I were lifting the bed (my solar components are located under the bed) fire extinguisher in hand to inspect the burning smell and smoke!

[Skwidward]

...An even easier method is to use a separate subpanel for shore power in. There would be two outputs from this panel - A/C and inverter. That way the A/C is depowered when shore power goes away.

This is an excellent idea! Thank you. This is absolutely what I was looking for. It won't be easy, as I used 10/2 UF wire to run from shore power to the inverter, but it's doable and will totally ensure the air conditioner ONLY runs on shore power. I think I'll add the fridge to this too (with its own breaker, of course), so I can run it on shore power too without worrying, when plugged in.

As as for the fuses, I'm gonna replace the 250 amp fuse that blew, between the inverter and the positive bus bar, with a 150 amp circuit breaker. I'm also gonna replace the 250 amp fuse I have between battery positive and the positive bus bar with a 200 amp fuse--this will be my reserve 'chute in case the breaker fails. All 2/0 wire.

[inetdog]

Just 1 week into full time RVing and still at a park with hookups to iron out kinks, of which there are many (don

EDIT: continued in next post

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[jflorey2]

I don't know. A flipped breaker just seems a bit less dramatic and scary when compared to a burnt out fuse.

If your inverter and battery bank can handle 250 amps, then it would be wise (IMO) to design the wiring and protection to handle that level of current. Replacing the fuse with a 250 amp breaker would also work. Nothing should burn or smoke at that level; people often design for such power levels. You can replace it with a smaller breaker if you like without any additional risk, but that will lead to more nuisance trips (during motor startup for example.)

If you want to run the A/C only when shore power is present, you might consider a 120VAC relay connected to shore power that enables the air conditioner. Easiest way to do that is via the thermostat line (if you have a separate thermostat.) You can also switch the power to the A/C itself.

An even easier method is to use a separate subpanel for shore power in. There would be two outputs from this panel - A/C and inverter. That way the A/C is depowered when shore power goes away.

[PNW_Steve]

Perhaps making some adjustments to your inverter install may prevent you from having future close calls?

It is not too tough to set the inverter up so that it only runs the loads that you select..


I really encouraging folks to take this seriously. I've been to one funeral as a result of failed DIY electrical. Don't want to see any of you in the obits.

[Skwidward]

I have 2/0 wire and a 2000 Watt inverter. The smoke was from the fuse. The wires were fine just super hot.

I like the idea of replacing the 250 amp fuse with a 150 amp breaker. Do you see a problem with that?

[Skwidward]

With proper wiring and fuses, even extreme conditions should not smoke wires. I'm glad you were not hurt.

A 250A fuse is to protect 4/O wire. That's big wire, and very unusual to find in an RV

1/O wire is roughly rated to handle 150A, That's still pretty big wire. You need to review the wire gauge used in your system and use the right size fuses. Fuses/breakers are
there to protect the wires. Nothing else. Some DC breakers are rated for "switch duty" and can be used for daily on - off usage.

This is one of the reasons 12V systems with 3000w inverters are dangerous. Inadequate wiring "works" for a long time, and then something bad happens and you get smoke.

styles of fuses in this chart here: https://www.bluesea.com/support/arti...t_Installation

https://lugsdirect.com/WireCurrentAm...ble-301-16.htm or https://www.bluesea.com/resources/1437

I have 2/0 wire and no wires we're smoking just very hot to the touch. I have a 2000 Watt inverter.

I like the idea of the 150 amp breaker in place of the 250 amp fuse. Do you see any problems with that?