EG4 18kPV - Proper T Fuse between Battery Rack and 2 x 18kPVs in Parallel

WattAboutThat · May 3, 2023

I have zero understanding about T Fuses, but noticed Will had one in his review of the 18kPV.

I am intending to have 2 x 18kPV inverters in parallel, and connected to a rack of 6 EG4 LL V2 batteries.

Please explain how to calculate the appropriate size of T class fuse, that needs to be between the battery rack and each inverter’s battery input? (so i will understand how to calculate in the future) (but also what size you would recommend that will be safe)

Also could you provide links on where to purchase a good quality reliable T Fuse of the recommended size, and holder, along with a battery disconnect.

Any assistance is appreciated.

thx

Quattrohead · May 3, 2023

1. That is not much battery for that amount of inverter....what is your useage model ?
2. The fuse protects the cables, not the inverters or batteries. The manual suggest's 4 battery cable options.
3. The inverter has battery CB, the batteries have CB, do you really need any other protection ?
4. Battery disconnects as above.
5. Victron Energy Lynx Distributor is a good busbar/fuse system, available from SS.

WattAboutThat · May 3, 2023

I intend to ad more racks of batteries and more inverters in the future. This is just a starting point.

I need to know what size T Fuse to use for the entire rack to the busbar then to the inverters.

And would like to know how to properly calculate that fuse size, so i will have a better understanding as I ad more batteries in the future.

niktak11 · May 3, 2023

WattAboutThat said:
I intend to ad more racks of batteries and more inverters in the future. This is just a starting point.

I need to know what size T Fuse to use for the entire rack to the busbar then to the inverters.

And would like to know how to properly calculate that fuse size, so i will have a better understanding as I ad more batteries in the future.

The 18k already has a breaker for both battery inputs so a fuse isn't really required

SignatureSolarJames · May 7, 2023

the built-in breaker is all you need IMO

clockenessmnstr · May 8, 2023

If you use 2x sets of 2/0 battery cables from one battery bank mentioned you could use 4x fuses close to the bus bars to protect all four conductors just to be paranoid in case one conductor comes loose.

If you have separate bus bars / battery banks on each 2/0 circuit you'd want 1 fuse per circuit so you don't disconnect/service a bank and overload a 2/0 circuit with ~200+ amps on accident.

Inverter Breaker should protect the inverter. battery breaker (if present) should protect the battery unit.

cs1234 · May 8, 2023

SignatureSolarJames said:
the built-in breaker is all you need IMO

Do you happen to know the AIC rating of the built in breakers? How does it compare to a t-class fuse?

Will Prowse · Jun 5, 2023

I use t class fuses to isolate each tower of batteries in my system. It's more for protecting the batteries, than the unit. I have a video about current sharing that covers this.

But in some of my systems there is a recommendation in the manual to have a fuse for each parallel inverter. For example the LV 6548. So in that instance I will always put some type of ocpd there.

I like to follow the recommendations in the manual so there is no argument.

Farm Boy · Jun 8, 2023

Will Prowse said:
I use t class fuses to isolate each tower of batteries in my system. It's more for protecting the batteries, than the unit. I have a video about current sharing that covers this.

But in some of my systems there is a recommendation in the manual to have a fuse for each parallel inverter. For example the LV 6548. So in that instance I will always put some type of ocpd there.

I like to follow the recommendations in the manual so there is no argument.

I'm sorry this isn't exactly on topic but you sure have been help full to all of us in the solar world and in making this forum. I just want to say thanks and also to all your videos.

Will Prowse · Jun 8, 2023

Farm Boy said:
I'm sorry this isn't exactly on topic but you sure have been help full to all of us in the solar world and in making this forum. I just want to say thanks and also to all your videos.

Thanks

glad I can help

Shimmy · Jun 8, 2023

SignatureSolarJames said:
the built-in breaker is all you need IMO

It really depends. For 6 batteries and one inverter it is fine, but if you go for 12 batteries and two inverters you should be fusing each group of 6 batteries at a minimum. If the cables from the common bus bar to the inverter are under 6' you are fine with the internal protection.

The 6-disconnect limitation really makes me wonder why EG4 has not gotten into the 300Ah battery class to better support larger inverters. The 18kpv really should have a minimum of a 40kW battery IMO and you are lacking a good solution today to pull it off.

WattAboutThat · Jun 9, 2023

Shimmy said:
It really depends. For 6 batteries and one inverter it is fine, but if you go for 12 batteries and two inverters you should be fusing each group of 6 batteries at a minimum. If the cables from the common bus bar to the inverter are under 6' you are fine with the internal protection.

The 6-disconnect limitation really makes me wonder why EG4 has not gotten into the 300Ah battery class to better support larger inverters. The 18kpv really should have a minimum of a 40kW battery IMO and you are lacking a good solution today to pull it off.

Can you recommend a dc breaker, disconnect, etc that should be considered.

thx

Shimmy · Jun 9, 2023

WattAboutThat said:
Can you recommend a dc breaker, disconnect, etc that should be considered.

thx

That starts to get into the awkward "it depends" realm. If you are sizing your system to never exceed 30A/module (on a 100Ah unit) then I would stick to Class-T fuses generally. If you have more than 5-6 cabinets (of 6 modules) you really should have a breaker to isolate them into groups, but how that is done becomes very system-specific (and expensive).

On a system designed for a worst-case load of 100A per module then maybe you want to split your protection down into smaller groups--400A fuses are kind of a sweet spot for wiring complexity.

The only time you really need a breaker is if the inverter doesn't have one internally and you have more than 6 modules in parallel.

rafaelrivas69 · Jun 10, 2023

Will Prowse said:
Thanks glad I can help

How did you do the firmware updates in the 18k pvs? Every time I try, it tell me that I have to verify a code, but I don’t have a code.

Will Prowse said:
Thanks glad I can help

I too second Farm Boy coment.
Will, how did you updated the firmware in the 18kpv? Every time I try, it tell me that I have to verify a code, but I don’t have any code.

Will Prowse · Jun 10, 2023

Remote firmware update

EG4 18kPV - Proper T Fuse between Battery Rack and 2 x 18kPVs in Parallel

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