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Old 13-06-2024, 21:43   #1
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t class, anl, mega or mbrf

I have 3 280 AH batteries each with their own 150 Amp fuse (MEGA), and each has a rotating on/off switch.

I can and will go further into the rest of my install if needed or desired by anyone.

When I powered about 1500 WH I blew two fuses shutting off 2 batteries. Didn't realize this at 1st then messed my back up so just getting back into this again.

I don't fully understand the difference between these fuses. The ANL's as I understand it can handle higher voltages and the blow slower than the Mega's. MBRF and T Class I don't know about.

Interested in which fuse I should use and why.

BTW- I have overkill BMS (not very happy with) and they are rated for 120 Amps.

Thanks,

Mark
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Old 13-06-2024, 21:47   #2
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Re: t class, anl, mega or mbrf

Lithium or flooded?

What was the 1500 Watt load?
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Old 14-06-2024, 04:41   #3
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Re: t class, anl, mega or mbrf

What about the Overkill BMS in these batteries are you not happy with?

No idea why 2 fuses of any variety would blow with that load.
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Old 14-06-2024, 06:06   #4
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Re: t class, anl, mega or mbrf

Cheap Chinese fuses or legit fuses from a marine dealer?
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Old 14-06-2024, 06:33   #5
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Re: t class, anl, mega or mbrf

The differences in fuses are more in interrupting capacity. A 150A fuse should not blow below 150A. You should be able to pull 150A 24/7/365 for decades and it never blow.

I agree with the other poster in that you may have Chinese trash fuses in which case a "150A" fuse could blow at 50A or not blow at 500A.

Beyond that more details are needed. Did you have all 3 batteries on and in parallel at the time the fuse(s) blow? What type of load was it? What type of batteries?

The last one is more to determine what type of fuse would be apropriate not to determine why it blew.
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Old 14-06-2024, 06:53   #6
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Re: t class, anl, mega or mbrf

You are not trying to start a big aircon unit or big diesel? Start up or locked rotor currents can be 400- 500A at 12V.
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Old 14-06-2024, 07:31   #7
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Re: t class, anl, mega or mbrf

Inrush to discharged capacitors of an inverter could possibly blow fuses, especially if the battery switches were all off initially and you turned them on one at a time, blowing each batteries fuse in turn. Caps got a bit of charge from each one so the last one could finish the job without blowing the fuse?

There are inverter precharge circuits available specifically to address this.

MEGA fuses are rated to clear 2000A fault at 32VDC
ANL fuses are rated to clear 6000A at 32VDC. (They were the original "cheap" battery fuse, not very precise in their trip curve.)
Class T fuses are rated to clear 20,000A at 125VDC.

Trip curves for each are attached. ANLs are not as precise as the other two. Class T are VERY reliable, but also expensive, and voltage rating is higher than it needs to be on a 12V system.

You should (must) have a fuse with a rated interrupt capacity (AIC) higher than the amount of current your battery can supply into a short circuit, otherwise they arc instead of breaking the circuit and are a serious fire risk.

As mentioned in previous replies, there are lots of counterfeit knockoffs of legitimate fuses flooding the market through Amazon and Ebay. No need to buy them from a marine store, but you should buy only legit brand Bussmann or Littelfuse (Blue Sea private labels fuses from them and are good) and get them from a legitimate distributor. (I prefer Digikey or Mouser for things like this).
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Old 14-06-2024, 07:54   #8
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Re: t class, anl, mega or mbrf

When you say you "powered about 1500WH" I assume that means you were pulling 125 Amps at a nominal 12 Volts for a total of 1500 Watts. Even allowing for your batteries running a bit above 12V, that is getting really close to your BMS capacity. Especially when you use the word "about" in there. Or maybe when you typed 1500WH you really did mean "Watt-hours" in which case we have no idea of the actual current flow...

It also doesn't sound like you really know WHEN the fuses failed.

Without detail about what the system looks like, how it is set up, and what is connected to what, we are all just guessing about what's wrong. Of course some people can take almost no data, make a guess, and be 1000% confident they are right...

I think you can safely dismiss the idea that charging capacitors in the system caused your fuses to blow. ANL fuses will handle HUGE loads (>500% of rated capacity) for the time frame it takes to charge a capacitor.
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Old 14-06-2024, 09:40   #9
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Re: t class, anl, mega or mbrf

Quote:
Originally Posted by Bellinghamster View Post
Inrush to discharged capacitors of an inverter could possibly blow fuses, especially if the battery switches were all off initially and you turned them on one at a time, blowing each batteries fuse in turn. Caps got a bit of charge from each one so the last one could finish the job without blowing the fuse?
MEGA, ANL, and MBRF are all relatively slow blow. While I’m a proponent of precharge circuits, that shouldn’t have blown a proper quality fuse. Now a Class T? Those are deliberately fast blow.
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Old 14-06-2024, 09:58   #10
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Re: t class, anl, mega or mbrf

Quote:
Originally Posted by hjohnson View Post
MEGA, ANL, and MBRF are all relatively slow blow. While I’m a proponent of precharge circuits, that shouldn’t have blown a proper quality fuse. Now a Class T? Those are deliberately fast blow.
Even fast is all relative here. A quality class T should be around 3x rated capacity for 1 second and 2x rated capacity for a minute.
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Old 14-06-2024, 12:27   #11
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Re: t class, anl, mega or mbrf

Quote:
Originally Posted by Cpt Mark View Post
I have 3 280 AH batteries each with their own 150 Amp fuse (MEGA), and each has a rotating on/off switch.

I can and will go further into the rest of my install if needed or desired by anyone.

When I powered about 1500 WH I blew two fuses shutting off 2 batteries. Didn't realize this at 1st then messed my back up so just getting back into this again.

I don't fully understand the difference between these fuses. The ANL's as I understand it can handle higher voltages and the blow slower than the Mega's. MBRF and T Class I don't know about.

Interested in which fuse I should use and why.

BTW- I have overkill BMS (not very happy with) and they are rated for 120 Amps.

Thanks,

Mark
Since you mention a BMS, you have lithium chemistry. That means use Class T due to the IC capacity. Lithium batteries can push enormous currents when shorted. The other fuse types run the risk of melting down but keeping the circuit closed and still burning down your boat.
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Old 14-06-2024, 13:08   #12
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Re: t class, anl, mega or mbrf

Hi all,

Thank you so much for your inputs.

Yes. It is a Lifipo4 battery system. I have 3 separate batteries each with it's own BMS, Fuse and ON/Off switch. All Negs go to a central neg busbar. That busbar then feeds the DC Main distribution which also has connected the windlass and electric winch. Moving those 2 cables would be a nightmare so I installed a heavy duty busbar.

On the positive side, all cables go to a very heavy duty busbar and from there to a 500 amp fuse which then goes to the main Positive distribution busbar.

Positive cables are all 1/0 ga. Neg cables from BMS to busbar are 2 pairs of 6 AWG cables. From Neg busbar to distribution is 1/0 cable.

Original design for dc distribution was a single post. With so many cables going into them I installed appropriate sized bus bars to handle the loads.

What was running was a 1500 watt electric heater. That shouldn't have popped any fuses but 2 did.

Fuses were bought at West marine, Blue Seas.

Re: Overkill. What I can't stand is their absolute lack of service after the sale. After a couple of years I finally had 1 tech reach out to me regarding settings. It has been hit and miss, mostly miss. If anyone out here understands these settings I'd love to talk with you. Currently, even tho they shouldn't, when the battery gets very close to full I get a cell over volt fault and the FET that controls the charging gets turned off. This over volt must happen in terms of microseconds as I've not seen it as it happens and the cell voltages are all where they are suppose to be for a full battery which is below the trip point.

And their display of battery full etc. Batteries full, 100%. Switch to invert only and 1 immediately goes to 59% even tho the voltage is the same for the other batteries which are in the high 90's.

You might be wondering why it has taken me so long to get here considering I built this sytem a couple of years ago. I just installed 1080 watts of solar. i need to be able to go offgrid. 1. I'm going cruising 2. my marina picks out a number to charge for electricity. Pretty sure it's based on whatever extra money they need that month. Last year I had a bill and when I asked about it was given the excuse and blah blah blah. I pointed out I was gone for 5 weeks so, no, that can't be right.

I had a 2000 watt inverter connected to a Sterling Pro 50 amp charger. Their Ultra Pro might be fine for lead acid but not for Lifipo4 batteries.

Including my rants, sorry about that, I hope this provides the additional info requested.

Thanks again
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Old 14-06-2024, 13:18   #13
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Re: t class, anl, mega or mbrf

Quote:
Originally Posted by Bellinghamster View Post
Inrush to discharged capacitors of an inverter could possibly blow fuses, especially if the battery switches were all off initially and you turned them on one at a time, blowing each batteries fuse in turn. Caps got a bit of charge from each one so the last one could finish the job without blowing the fuse?

There are inverter precharge circuits available specifically to address this.

MEGA fuses are rated to clear 2000A fault at 32VDC
ANL fuses are rated to clear 6000A at 32VDC. (They were the original "cheap" battery fuse, not very precise in their trip curve.)
Class T fuses are rated to clear 20,000A at 125VDC.

Trip curves for each are attached. ANLs are not as precise as the other two. Class T are VERY reliable, but also expensive, and voltage rating is higher than it needs to be on a 12V system.

You should (must) have a fuse with a rated interrupt capacity (AIC) higher than the amount of current your battery can supply into a short circuit, otherwise they arc instead of breaking the circuit and are a serious fire risk.

As mentioned in previous replies, there are lots of counterfeit knockoffs of legitimate fuses flooding the market through Amazon and Ebay. No need to buy them from a marine store, but you should buy only legit brand Bussmann or Littelfuse (Blue Sea private labels fuses from them and are good) and get them from a legitimate distributor. (I prefer Digikey or Mouser for things like this).
Thank you for this. Looking at the MEGA graph I see that they have a 100-300 amp range. My AIC is 2000 amps. Do their fuses come in different amp ranges which is why the 100-300 etc? For sure I could have blown them at 100.
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Old 14-06-2024, 13:33   #14
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Re: t class, anl, mega or mbrf

Quote:
Originally Posted by Cpt Mark View Post
Hi all,


On the positive side, all cables go to a very heavy duty busbar and from there to a 500 amp fuse which then goes to the main Positive distribution busbar.

Positive cables are all 1/0 ga. Neg cables from BMS to busbar are 2 pairs of 6 AWG cables. From Neg busbar to distribution is 1/0 cable.
This fuse size is too large to protect the cable.
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Old 14-06-2024, 13:47   #15
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Re: t class, anl, mega or mbrf

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Originally Posted by noelex 77 View Post
This fuse size is too large to protect the cable.
That busbar connects all 3, 280AH batteries together . So there is a potential for a lot of current to hit if there was a surge from all 3 batteries is the thinking. Am I wrong?
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