DC fuses for an inverter?

[John in Santa Cruz]

So I installed a Renogy 2000W Pure Sine inverter... I used the two short dual-AWG4 cables it came with to tie it directly to my 250A rated DC positive and negative bus bars... the 2 x 206AH LFP batteries each have a 150W ANL style fuse on their own AWG 4 short cables, paralleled at the same bus bars (which is also where the solar controller, orion dc-dc charger, and main power panel all tie in too).

That should be sufficient fusing for this setup, eh?

[BobG]

John,

Here is a link to PYS where they talk about fusing a 2000w Magnum inverter. They recommend a T fuse for the inverter.

https://www.pysystems.ca/resources/b...k/robert-fuse/

Here is link to Blue Seas T fuse discussion.

https://www.bluesea.com/products/cat...ss%20T%20Fuses

I have never quite understood how to fuse dual cables to the inverter although Victron discusses it in one of their manuals I read a long time ago. They also recommended a T fuse.

As far as the cabling, I don't suppose the size really matters if the fusing is matched to the cables. I don't know if your fusing is matched to the cables but it should be. Then either the inverter will work for your loads or it won't. I think your double AWG4 if very short will work for running your loads including the AC. If the fuse blows then you can up size the cable and fuse. Connections or cables may get warm if running the inverter to capacity.

I assume the battery manufacturer sized the battery fuses to protect the batteries. I am thinking that if one of your battery fuses blows then the other will quickly follow since they are in parallel.

The following link gives access to a Victron manual for their 2000VA inverter installation. They specify cables be 70mm2 which is a 2/0 cable. You are somewhat shy of this so don't run at max load and make sure your cables are fused correctly. If one of your dual cables from the bus bar to the inverter goes down, the other cable is going to be carrying a large current. It seems like it should have its own fuse. I am not an electrician so I may be off base here.

https://www.victronenergy.com/invert...000-va#manuals

[Perry Butler]

With the high power available from lithium batteries an ANL fuse can melt and become a solid conductor when using an inverter. You should have a T fuse directly (within 7" from the battery, in theory) when using lithium batteries. Even though I don't have lithium batteries (I chose SiO2) I used a 250 T fuse for our 1500 watt inverter when installing the inverter last June, just in case I was wrong using the SiO2 batteries. So far the SiO2 batteries work exactly as claimed, but the T fuse is there if they fail and I install lithium.

Enjoy,

Perry

[BobG]

I used a 300 amp T fuse for my MultiPlus 3000AV inverter/charger. The inverter is 24 volts. Victron specified a 300 amp T fuse on 1/0 cable.


Bob

[John in Santa Cruz]

FWIW, my ANL fuses are mounted on a viertical board, so I'm not sure how they could melt and bpuddle and short themslves, wouldn't be much of a fuse if they did.

not running the A/C on the inverter, just plug-in stuff, short intervals like wife's hair dryer, and such.

the dual AWG 4 cables *came* from Victron with the inverter, hey are 3 feet long which was just about optimal for my install. My calculations said short runs of 165A should be on AWG 2 at least, and 2 AWG 4's is equiv to AWG 2.

I may get around to upgrading the battery primary circuit and the inverter circuit to AWG 1. More than that would be overkill. I'm using pure copper fine strand welding wire exclusively.

[Vermilye]

Originally Posted by John in Santa Cruz

FWIW, my ANL fuses are mounted on a viertical board, so I'm not sure how they could melt and bpuddle and short themslves, wouldn't be much of a fuse if they did.

not running the A/C on the inverter, just plug-in stuff, short intervals like wife's hair dryer, and such.

the dual AWG 4 cables *came* from Victron with the inverter, hey are 3 feet long which was just about optimal for my install. My calculations said short runs of 165A should be on AWG 2 at least, and 2 AWG 4's is equiv to AWG 2.

I may get around to upgrading the battery primary circuit and the inverter circuit to AWG 1. More than that would be overkill. I'm using pure copper fine strand welding wire exclusively.

It isn't so much "puddling" as it is the arcing that takes place as the fuse opens. Under very high currents, the arc can form a plasma that will maintain the current even after the fuse element opens. Unlikely, but that is the main reason for going to the Class "T" fuse. Another reason is they are faster opening fuses than an ANL and offer a bit more protection for electronics.

[Perry Butler]

Originally Posted by John in Santa Cruz

FWIW, my ANL fuses are mounted on a viertical board, so I'm not sure how they could melt and bpuddle and short themslves, wouldn't be much of a fuse if they did.

I didn't save any links last summer, but here are a couple I quickly found:

Fuses

Fuse Types? Why is it a big deal?

I investigated many inverters (GoPower, Renogy, Victron, etc), called if possible, and at least a couple recommended a T fuse with lithium batteries to protect our camper. I do know when I talked to AM Solar last summer about adding an inverter one of the first questions they had was "Do you have lithium batteries?" They explained about the massive power lithium can provide if there is an inverter short. Aside from the cost there is better protection using a T fuse, so that's what I installed.

I realize there are many opinions on forums, but when AM Solar told me about a T fuse I said, "Why not." I'm sure if you search well enough you can find documented instances where an ANL fuse did not prevent component loss or runaway lithium fires.

I chose a GoWise 1500 pure sine wave inverter, recommended by Will Prowse at the time, and it has worked perfectly for our needs, mainly a toaster.

I spent hours and hours investigating inverters and fusing, so I'm comfortable with my choice. I just know from that research last year I would definitely have a T fuse protecting my camper investment, and do, especially if I had lithium.

Enjoy,

Perry

[Centex]

Originally Posted by Perry Butler

.... I investigated many inverters (GoPower, Renogy, Victron, etc), called if possible, and at least a couple recommended a T fuse ...

Add xantrex to the list of inverter manufacturers which explicitly recommend a Class T fuse on the DC input (it's in the installation manual).

[John in Santa Cruz]

yeah, i see that ANL fuses are intentionally not a fast blow, that with currents just over their rating, they take about a second to blow.

well, if I ever rewire this with #0 or whatever, I'll also upgrade the fuses. The batteries BMS should kick in if the draw is over 150A anyways.

[John in Santa Cruz]

so I got a class T 200A fuse and fuse holder, only, wtf, the fuse doesn't fit. both are Blue Sea brand, which has been pretty good. I got them from Amazon, so I can return them, but I wanna know why they don't? are there different physical size class T fuses?




and, OOOOH. the fuse block says "225-400A" while the fuse says its a 110A-200A class T. so they are different physical sizes? ugh. and the only 200A sized class T blocks I can find are 'ignition protected' (whatever that means, and cost twice as much ($100 instead of $50, yeouch!)

gopower makes a 200A class T fuse block, but it uses crappy wire clamps (I want to use ring terminals) and gets crummy reviews.

What about Mega/AMG fuses? or do they have the same problem as ANL ? Edit: google says, yes, Mega/AMG are also slow blow. good for short circuit protection, not good for inverter protection. so good to know.

that T fuse holder is freekin' huge. but I'm replacing two ANL fuses with it, so I guess it will fit.

[John in Santa Cruz]

oh, and I got 10 feet each of red and black 1/0 for this rewire. gonna go back to paralleling the batteries directly, and using a single fuse on a 1/0

I think it will be easier to get a 225A fuse than to find a 200A 'T' fuse block to my liking.

[Perry Butler]

I had trouble finding a 250a T fuse in stock. Last summer, after a few hours searching, I got my first one from West Marine, the website was out, but I found one at the Minnetonka store. I then ordered a spare from Blue Seas and a couple of months later they contacted me and I bought the spare.

I wonder if supply chain issues will ever go away.

Enjoy,

Perry

[Centex]

Just FYI from this Blue Sea Class T fuse FAQ page
https://www.bluesea.com/products/511..._T_200_Amp/FAQ

Frequently Asked Questions
Q: Are there different sizes of Class T fuses?

A:Yes, The 110- 200 amp are smaller than the 225-400 amp

The 110-200 need the 5007100 fuse holder.

The 225-400 need the 5502 or 5502100 fuse holder.

Hope that helps

Aside, I've had good results ordering these fuses (and other Blue Sea items) from https://shop.pkys.com/Class-T-Fuses_c_113.html; not always in stock but their "Put me on the waiting list" system for email notification when out-of-stock items are available has been effective for me.

[BobG]

I have had the same experience with PKYS as Centex. I like dealing with them. They also have decent technical support on the phone for questions. At least that has been my experience.

[John in Santa Cruz]

yes, and that 5007100 fuse block is $85+ while the 225-400A one I got is $48.

[BobG]

Can you change to 225 amp fuse and use the fuse block you received? It is a frustrating situation you have. A year ago I had to use the wait list to get a fuse.

[John in Santa Cruz]

yeah, I ordered a 225A. paying $100 for a single fuse holder seems outrageous to me.

[Mike Lewis]

Originally Posted by Vermilye

Under very high currents, the arc can form a plasma that will maintain the current even after the fuse element opens.

Yikes! Now that would make me puddle. I'd better install a "T" fuse on the line to my inverter as well. Thanks for that info.

[hugh]

Yeah, those class T fuses are expensive. I know you're supposed to use them because "Lithium" and the bigger the AIC the better. But it's not like the AIC is an order of magnitude larger than other fuse options. It's only 2x higher than MRBF, for example.



So Class T would only help if a short circuit current happened to fall between where MRBF would fail (>10,000A) but class T would function (<20,000A) _and_ nothing else (like the BMS) interrupted the short circuit.



Theoretically, the short circuit current on my Lithium batteries is 120,000 amps so it seems even a class T won't protect against all possible shorts.


I'm not an EE, so maybe in practice, many short circuits currents are in the 10kA - 20kA range. But, it's also possible that the overall risk reduction from class T is so small, that you'd be better off investing the safety dollars elsewhere.

[hugh]

Maybe one of these would be appropriate?


https://www.amazon.com/dp/B01MAWEDCR


It's a bit big (12 inches long, 4 pounds), but it almost meets the AIC of my lithium bank.