Single vs. Multiple Class-T Fuses

[AHTrimble]

The lynx power in has to be modified to accept fuses.
Also, batteries should be fused as close to the positive terminal.
This minimizes the chance of an un-protected short.

I have already modified a couple of PowerIn's...really simple. I am using one in my upgrade as a distributor (inverters & charge controlers) without all the fancy LEDs and computer board of a Lynx Distributor, didn't need those features.
Yeah, I as afraid you would bring up with the "...close to the positive terminal..." thing. But, given the mission of the fuses, protecting batteries from each other, I was hoping it would be ok.

But what do you think of the 250a version for battery-battery protection?

 

[AHTrimble]

Also I'm guessing that the breaking capacity is ~5000 amps at 60VDC.

Yeah, I get it. And the math indicates you would be right.
I am just trying to get something affordable to do the battery-to-battery protection.
The battery bank is protected right after the busbar (PowerIn) with a Class-T but after having read the posts in this thread I am think more might be better.

 

[Danke]

Yeah, I get it. And the math indicates you would be right.
I am just trying to get something affordable to do the battery-to-battery protection.
The battery bank is protected right after the busbar (PowerIn) with a Class-T but after having read the posts in this thread I am think more might be better.

I’m modifying my Victron Power In to take class T fuses (three) . My plan is to connect two batteries in parallel for each class T fuse on the Victron busbar. So six batteries per Power In.

 

[John Frum]

But, given the mission of the fuses, protecting batteries from each other, I was hoping it would be ok.

That is only part of the mission.
The other mission is to protect the wire which means the fuse must be at the battery.
The most important mission is protect the battery from a dead short.
Nobody wants an electrolyte volcano.

But what do you think of the 250a version for battery-battery protection?

Should be fine.
Requires 1/0 awg wire or better for ABYC rules.

 

[John Frum]

Yeah, I get it. And the math indicates you would be right.
I am just trying to get something affordable to do the battery-to-battery protection.
The battery bank is protected right after the busbar (PowerIn) with a Class-T but after having read the posts in this thread I am think more might be better.

IMO that is a waste of a class t fuse.
It seems to me, this whole thread and many others like it is about people trying to save money.
IMO over-current protection is the last place to try and save money.

 

[AHTrimble]

I’m modifying my Victron Power In to take class T fuses (three) . My plan is to connect two batteries in parallel for each class T fuse on the Victron busbar. So six batteries per Power In.

Very cool !
Pictures?????

 

[AHTrimble]

IMO that is a waste of a class t fuse.

What part?
I see most folks, including Will, put a Class-T after their busbar.
What are you suggesting?

 

[John Frum]

What part?
I see most folks, including Will, put a Class-T after their busbar.
What are you suggesting?

The class t fuse between the busbars.
Just join the backplanes of the lynx components.

 

[John Frum]

@AHTrimble please post your updated topology and I will critique it.
As I said before the whole topology has to be considered.

 

[AHTrimble]

The class t fuse between the busbars.
Just join the backplanes of the lynx components.

Between the battery busbar (PowerIn) and the Lynx Shunt is where the Class-T is...as close the battery bank as I can get it.

 

[AHTrimble]

@AHTrimble please post your updated topology and I will critique it.
As I said before the whole topology has to be considered.

 

[John Frum]

View attachment 139159

Get rid of the circuit breaker box between the lynx power-in and the batteries.

Use a 250 amp class t fuse as close as possible to each battery positive terminal

Get rid of the class t fuse between the power in and the shunt
Connect the the backplane of the lynx power-in to the lynx_shunt

Use this fuse in the lynx shunt

Littelfuse 0CNN800E.V CNNE Series, Very Fast Acting Fuse, 800A | Waytek

Littelfuse 0CNN800E.V CNNE Series, Very Fast Acting Fuse, 800A, 80VDC is in stock and ready to ship. Order today!

www.waytekwire.com

If you have specific questions I will do my best to answer them.

 

[AHTrimble]

That is only part of the mission.
The other mission is to protect the wire which means the fuse must be at the battery.
The most important mission is protect the battery from a dead short.
Nobody wants an electrolyte volcano.

I hear ya! As a retired firefighter...well, you can guess it from there.
Problem is...I have no way to connect a fuse at the battery terminal. I was leaning towards the MRBF but you pointed out that its AIC isn't good enough. So I am trying to find something.
You can see in the topo I have a 125a CB but I would rather have a fuse...or a fuse in addition to the CB.
And I still haven't seen a system yet with a fuse right on the battery terminal. I also still haven't seen an explanation yet why a Class-T at each of two inverters vs a single Class-T at the busbar.
I am no brainiac, by far, but I can understand things...just no one is giving a clear answer or showing pictures.
Yeah, you can tell I am frustrated. I just want to get this right...and understand what I am doing.

 

[Danke]

Very cool !
Pictures?????

this should give you an idea what it will look like:

 

[John Frum]

Kirchhoff's circuit laws - Wikipedia

en.wikipedia.org

The summary of this article is, current in = current out.

I hear ya! As a retired firefighter...well, you can guess it from there.

Nope I can't.
Just assume I'm not from this planet.

Problem is...I have no way to connect a fuse at the battery terminal. I was leaning towards the MRBF but you pointed out that its AIC isn't good enough. So I am trying to find something.

Use a small wire try for <8 inches.

You can see in the topo I have a 125a CB but I would rather have a fuse...or a fuse in addition to the CB.

I already told you to get rid of them.

And I still haven't seen a system yet with a fuse right on the battery terminal.

I don't care what you have seen.

I also still haven't seen an explanation yet why a Class-T at each of two inverters vs a single Class-T at the busbar.

Its been discussed at length in this very thread.
re-read all my posts and all by @upnorthandpersonal

I am no brainiac, by far, but I can understand things...just no one is giving a clear answer or showing pictures.

Yes they have repeatedly.
Help us help you by asking questions about the words and concepts that you don't understand.

Yeah, you can tell I am frustrated. I just want to get this right...and understand what I am doing.

Do you trust my advice on the matter?

 

[LithiumSolar]

I’m ordering longer bolts, but this should give you an idea what it will look like:

View attachment 139160

Please keep in mind those fuses can get pretty warm/hot under normal operation.

 

[John Frum]

@the overall topology concept is called feeder and branch.
The lynx components are made to work with this topology.
The batteries connect to the power-in, which doesn't have fuses because the batteries are supposed to be fused at source.

The optional shunt tracks all current in and out of the batteries.

The distributor is for all the branch circuits which are fused at the busbar.

 

[AHTrimble]

Get rid of the circuit breaker box between the lynx power-in and the batteries.

Use a 250 amp class t fuse as close as possible to each battery positive terminal

Get rid of the class t fuse between the power in and the shunt
Connect the the backplane of the lynx power-in to the lynx_shunt

Use this fuse in the lynx shunt

Littelfuse 0CNN800E.V CNNE Series, Very Fast Acting Fuse, 800A | Waytek

Littelfuse 0CNN800E.V CNNE Series, Very Fast Acting Fuse, 800A, 80VDC is in stock and ready to ship. Order today!

www.waytekwire.com

If you have specific questions I will do my best to answer them.

First off...THANK YOU !!!! I am not a dummy, but I don't know the deep technical stuff like what we are talking about. You taking the time to help me out, and educate me, is incredibly kind of you.

I am using the CB box as a battery disconnect since 2 of the 3 batteries don't have a CB of their own. I wanted to be able to isolate each battery in the start up process. Can you tell me what I gain by getting rid of the CB box?

You have me convinced on the Class-T for each battery. I will have to figure out a mounting scheme to get it as close as possible to each battery. I hate to just "hang" the fuse holder off the cable. Not real professional, probably not safe either.

And it makes sense now to connect all the Lynx components since getting rid of the Class-T downstream of the PowerIn.

Right now, I already upgraded the 325a to a 400a CNN fuse. What is the benefit to an 800a? The 325a/400a was to protect the 4/0 cable. I know I wouldn't need that amp rated fuse now since the 4/0 is eliminated, but why 800a? Because the Lynx busbars are rated to 1000a? And since each battery would now have a 250a fuse...ok, my head hurts.

 

[AHTrimble]

I’m ordering longer bolts, but this should give you an idea what it will look like:

View attachment 139160

So basically you are just substituting a Class-T where the MEGA would go. Did you have to modify the class-t holes, etc?
Where did you source your fuses?

 

[AHTrimble]

Nope I can't.
Just assume I'm not from this planet.

I already told you to get rid of them.

I don't care what you have seen.

Its been discussed at length in this very thread.
re-read all my posts and all by @upnorthandpersonal

Yes they have repeatedly.

Do you trust my advice on the matter?

Sorry to have bothered you.

And FWIW...I do trust your advice, I hope you didn't think otherwise. If I offended you, I apologize.

 

[John Frum]

First off...THANK YOU !!!! I am not a dummy, but I don't know the deep technical stuff like what we are talking about. You taking the time to help me out, and educate me, is incredibly kind of you.

I am using the CB box as a battery disconnect since 2 of the 3 batteries don't have a CB of their own. I wanted to be able to isolate each battery in the start up process. Can you tell me what I gain by getting rid of the CB box?

The batteries have smart BMSs which you can use for administrative disconnect.
The circuit breakers add significant resistance, significant expense and just add clutter.
This guy said it best

A quote from Airman's Odyssey

Perfection is achieved, not when there is nothing more to add, but when there is nothing left to take away.

www.goodreads.com

Right now, I already upgraded the 325a to a 400a CNN fuse. What is the benefit to an 800a?

It stops that fuse from getting in the way.
The backplane is rated for 1000 amps continuous.
A 400 amp fuse is a potential bottleneck for no good reason.
Blowing that fuse would be a pain in the ass.
The lower the fuse rating the higher the resistance.

The 325a/400a was to protect the 4/0 cable.

Understood.

I know I wouldn't need that amp rated fuse now since the 4/0 is eliminated, but why 800a?

see above ^

Because the Lynx busbars are rated to 1000a?

Yes.

And since each battery would now have a 250a fuse...ok, my head hurts.

4 batteries each with 250 amp fuse is 1000 aggregate fault amps.
The busbar is good for 1250 fault amps.
We hope the 800 amp fuse never gets in the way.
BTW we can go back and forth between continuous amps and fault amps by using the .8 reciprocal.

continuous amps / .8 = fault amps
fault amps * .8 = continuous amps

 

[Danke]

Please keep in mind those fuses can get pretty warm/hot under normal operation.

Using 2/0 in from batteries and 4/0 out to inverters. Most the fuse should see is less that .4C (40 amps)
Do they get any hotter than MEGA fuses?

 

[Danke]

So basically you are just substituting a Class-T where the MEGA would go. Did you have to modify the class-t holes, etc?
Where did you source your fuses?

Had to drill those center holes. Easy, soft metal. Didn’t touch other holes.

I bought fuses last year when they were hard to find and expensive. Got some from Alibaba. KingSun Microelectronics CO., LIMITED

I am thinking of buying more to have some spares.

 

[John Frum]

@AHTrimble are your batteries made by trophy?
They have a different breaker in them.
If yes, I suggest you talk to the owner of trophy and finding out breaking capacity of those breakers.
Remember breaking capacity is voltage specific.
We are looking for > 4000 amps at > 60 volts.
Ideally > 10,000 amps at > 60 volts.

 

[John Frum]

@AHTrimble what does you being a firefighter have to do with anything?