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More Class T fuse questions

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richard cabesa

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Mar 16, 2021
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OK , I‘m a dummy so tread lightly.

I have a 600AH battery pack and a 2000 watt inverter. 250 A class t fuse and all wiring should handle 300A plus. So unless I manage to somehow pull beyond 250A for some period of time, I should be covered?

But. . .

What else is this class T fuse protecting?

Drop a pipe wrench across the main battery terminals?

Positive wire fall out of the inverter and land on the negative buss bar?

Dead short from what to what?
 
Class T fuse is a fast acting hi-amperage interrupt. Used to protect against a dead short.
 
12vDC said:
Class T fuse is a fast acting hi-amperage interrupt. Used to protect against a dead short.
Click to expand...
That is how I would describe it too, but what conditions would make it blow?

What would have to happen to create that short?
 
The cable vibration rubs a hole in the positive cable and that touches either a rubbed hole in the negative or the metal of a grounded piece of equipment.

That will make a spectacular short!
 
Rocketman said:
The cable vibration rubs a hole in the positive cable and that touches either a rubbed hole in the negative or the metal of a grounded piece of equipment.

That will make a spectacular short!
Click to expand...
Thanks. I’m pretty good on this one. I’m a bit of a nut on strain relief and cable retention.

What else?
 
Dropping a “tool” on an exposed positive lug, or working around that lug and either a tool slips or the back end of tool gets pushed into the lug.

The fuse protects the wire…. It’s your choice at what level of protection you want.
 
Very possible to have a simple install with short protected wire and skip the fuse.
200 amp should be plenty for 12v into 2000w inverter.
 
time2roll said:
Very possible to have a simple install with short protected wire and skip the fuse.
200 amp should be plenty for 12v into 2000w inverter.
Click to expand...
a blue sea thermal breaker works well too.

my 125A thermal popped when the microwave and keurig were run at the same time (without my knowledge).
 
Or consider an MRBF mounted to the battery post to capture virtually all possibility of a random fault.
 
MRBF with the class T is the way to go. The class T are fast blowing an extinguish and the MRBF on the battery post in parallel battery setup will keep one battery from freaking and ruining another. The MRBF are 10kamps and the class T are 25k amps for killing arcs... I dunno if they add in series or if they blow one before the other...
 
richard cabesa said:
OK , I‘m a dummy so tread lightly.

I have a 600AH battery pack and a 2000 watt inverter. 250 A class t fuse and all wiring should handle 300A plus. So unless I manage to somehow pull beyond 250A for some period of time, I should be covered?

But. . .

What else is this class T fuse protecting?

Drop a pipe wrench across the main battery terminals?

Positive wire fall out of the inverter and land on the negative buss bar?

Dead short from what to what?
Click to expand...
How is your 600Ah battery setup?

In my bank, I have 4 batteries. Each battery gets a 175A T fuse. The purpose is if one battery has a short internally, the other batteries could deliver unlimited current to the shorted battery. You can see each T fuse on far sidewall.

Battery bank finished2.jpg

Thanks for bringing up the topic. I'm building another bank like this plus 2 more batteries and needed to order some T fuses. I quick checked Don Rowe to see if they finally had the 175A back in stock. $59.99, that is a deal. https://www.donrowe.com/TFB1-175-175A-Class-T-Fuse-Kit-p/tfb1-175.htm
 
KITROBASKIN said:
donrowe link says 'in stock late April-get in line.'
Click to expand...
I must have bought all they had. I ordered 6.

Edit: checked email and yes, they did backorder my order. They will charge the CC when they ship unless I cancel the order. April/May works for me, I won't see cells for 60 days.
 
I will go against the grain of the class T fuse concept, except for very large packs.

IMHO, you are better off using a 187 type breaker and running the setup as (individual parallel battery) - ( breaker ) - ( bus bar.)

This provides an easy safe way to cut off power and do maintenance.

If your battery pack is Li, it provides a way to shut off each individual battery to re-set the BMS.

Yes, I know it is not the popular opinion, but think through what it will take to re-set the BMS of a Li battery that you have in that system. Now imagine your wife being out with the vehicle on her own and needing to do that?

Are you really going to want to tell her over the phone to get out some tools, in the dark and rain to pull live wires, or just flip a breaker off and on?
 
HarryN said:
Are you really going to want to tell her over the phone to get out some tools, in the dark and rain to pull live wires, or just flip a breaker off and on?
Click to expand...
If something severe enough has happened to blow a class T fuse, do you really want her messing with anything? I have breakers for convenience but fuses for safety.
 
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