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Class T fuses

CarlN

.
Jan 4, 2009
560
Ketch 55 Bristol, RI
I'm planning to install a new house bank (Lithium) and was planning to use Class T fuses. There will be a large inverter, But the biggest class T fuse that BlueSea offers is 400amp while their ANL fuses go up to 750 amps.

While I realize that the Class T fuses have a higher interrupt rating, the ANL are supposed to meet ABYC ratings. Am I OK using ANL or is it very important to seek out a big enough Class T fuse?
 
Nov 14, 2013
196
Catalina 50 Seattle
Class T fuses are fast-blow and generally recommended for inverters and other sensitive equipment that can be damaged with even a brief overcurrent spike. ANL fuses are fine for the load bus of a battery bank.
 
Feb 6, 1998
11,353
Canadian Sailcraft 36T Casco Bay, ME
LiFePO4 should use Class T. It's all about the AIC rating...
 
Nov 14, 2013
196
Catalina 50 Seattle
I'm curious about this. The manufacturer of my LiFePO4 batteries makes no specific recommendation or requirement for a minimum AIC rating. Blue Sea says their ANL fuses are good for 5,000A, their MRBF fuses are rated for 10,000A, and their class T fuses are rated for 20,000A.

The BMS in my system will trip the contactor long before even the ANL limit is reached, so what is the use case or failure mode where a 20,000A rating is necessary but a 10,000A or 5,000A rating is insufficient?
 
Feb 6, 1998
11,353
Canadian Sailcraft 36T Casco Bay, ME
I'm curious about this. The manufacturer of my LiFePO4 batteries makes no specific recommendation or requirement for a minimum AIC rating. Blue Sea says their ANL fuses are good for 5,000A, their MRBF fuses are rated for 10,000A, and their class T fuses are rated for 20,000A.

The BMS in my system will trip the contactor long before even the ANL limit is reached, so what is the use case or failure mode where a 20,000A rating is necessary but a 10,000A or 5,000A rating is insufficient?
Your battery manufacturer is not the ABYC and I have had long discussions with Valence, now Lithiumwerkz about marine applications.. These batteries were designed for industry not the marine market though some marine systems were deisgned, but for commercial applications. They do not have an internal BMS switch and the contactors are external to the battery if you can find one of their external BMS controllers. We've seen numerous folks destroy these batteries by not realizing they don't have any internal BMS protection switch. We have one sitting in the shop now ruined by an RVer after purchasing them on the advise of Will Prowse where he claimed they had an internal BMS for "protection", which was not correct..

Even FET based LiFePO4 batteries can allow an inrush that can exceeds the lower AIC requirements. We've now seen at least two marine breakers welded shut with "drop-in" LFP batteries. For committee work a single FET based 100Ah LFP battery exceeded 13,000A of in-rush when shorted. This is why the Class T is advised and subdivided.

Class T is currently recommended for subdivided LiFePO4, under ABYC TE-13, will become a requirement when TE-13 becomes a full blown standard. Subdivided means the individual batteries each get a fuse so as not to exceed AIC of a single bank fuse.. LiFePO4 batteries also require external communication to warn of an impending shut down and the vast majority of drop-in LFP batteries do not meet this requirement either. We are already hearing of surveyors flagging vessels for AIC fuse violations as well as no external communication even though TE-13 is not yet full standard and the insurers are agreeing with them..
 
Nov 14, 2013
196
Catalina 50 Seattle
Thanks, Maine. Valence/Lithiumwerks/Lithion are pretty strident in their warnings not to run their XP modules without their external BMS and a contactor. I guess I shouldn't be surprised that people try it anyway, especially when "influencers" are spreading misinformation.

Per Valence's recommendation, I'm currently running a 100A MRBF fuse (equal to 1C) for each of the three modules in my 1S3P configuration. Will TE-13's Class T requirement distinguish between BMS/contactor protected systems and "drop in" systems or will Class T be required across the board for any LiFePO installation?
 
Feb 6, 1998
11,353
Canadian Sailcraft 36T Casco Bay, ME
Thanks, Maine. Valence/Lithiumwerks/Lithion are pretty strident in their warnings not to run their XP modules without their external BMS and a contactor. I guess I shouldn't be surprised that people try it anyway, especially when "influencers" are spreading misinformation.

Per Valence's recommendation, I'm currently running a 100A MRBF fuse (equal to 1C) for each of the three modules in my 1S3P configuration. Will TE-13's Class T requirement distinguish between BMS/contactor protected systems and "drop in" systems or will Class T be required across the board for any LiFePO installation?
No it will not. Contractors are even worse as they can carry immense current for short duration's, even more than a FET BMS can. I too have a contactor based system, with a 500A constant duty rated contactor. It is protected by a Class T fuse. Will you ever have any issues with an MRBF, likely not, but they ABYC is not about "likely not" instances. Ask Valence what the short circuit current rating of each module is.. I can guess they likely cannot produce this data for you as the places that can accurately test for this are slim.
 
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Johann

.
Jun 3, 2004
247
Leopard 39 Pensacola
Looks like I have some rewiring and fuses to do. Thanks for the info.
 
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