Battery bank fuse

[Ucatchmydrift]

Hi, ive decided to go ahead and build a diy battery bank, initially using 8 of these cells:

https://www.fogstar.co.uk/collections/lifepo4/products/eve-lifepo4-280ah-prismatic-cell
They will be placed in series to make 24v. At a later ish stage i will get another 8 and add in parallel.

Ive been reading up about types of fuses etc so i can fuse the bank safely.
I already have a 200amp dc breaker and a dc isolator installed ready and waiting. (which i have rigged up to a couple of old car batteries just to test the inverter and get used to playing with the custom settings etc, and alls good.)

It seems that to be safe, i will need a rather expensive fuse called a class T fuse that containes sand inside to stop any arcing if there is a short circuit.

Problem is, to spec the fuse, i need to know the short circuit current for one of the above cells to work out the interrupt capacity of the fuse. At a guess, something in excess of a crazy 10,000 amps!

Something like this: (there are cheaper versions!) :

https://www.raptorsupplies.co.uk/se...VDP5LPqCxXbXyU0EMwigz881gMWi9eIwaAu3mEALw_wcB
Anyone any ideas?

Thanks

 

[Ucatchmydrift]

And just as i post that, fogstar batteries have just gotten back to me and said they always spec 20,000amps! Crazy.

Now im wondering, with 8 in series, would that still be 20,000amps?
And when adding another bank in parallel, that would then be 40,000 amps?

 

[johnb2713]

And just as i post that, fogstar batteries have just gotten back to me and said they always spec 20,000amps! Crazy.

Now im wondering, with 8 in series, would that still be 20,000amps?
And when adding another bank in parallel, that would then be 40,000 amps?

Yes and yes.

I've used automotive 200A Fuse on my system with the exact same cells from Fogstar. Have you purchased your cells yet?

Ive assembled mine into modules of 4 cells for easy handling, youre supposed to apply compression to them to stop them bulging. What BMS are you going to use?



The small wires are individually fused BMS wiring for each cell. There is also a temperature sensor included in the BMS wiring for each module. The Anderson connector being the main connection from the module.

 

[Ucatchmydrift]

Yes and yes.

I've used automotive 200A Fuse on my system with the exact same cells from Fogstar. Have you purchased your cells yet?

Ive assembled mine into modules of 4 cells for easy handling, youre supposed to apply compression to them to stop them bulging. What BMS are you going to use?

View attachment 14193

The small wires are individually fused BMS wiring for each cell. There is also a temperature sensor included in the BMS wiring for each module. The Anderson connector being the main connection from the module.

Thanks .
All looks very nice and professional .. (mine will be very similar ) Im ordering them in 2 weeks, but thats on pre order to be delivered in november from fogstar. I ordered the bms yesterday:

￡6.30 26%OFF | Jikong Active Balance BMS Battery Protection Board 7S ~ 24S 100A 300A CAN RS485 APP LCD Lifepo4 li-ion LTO 48V 8S 16S 20S 72V
https://a.aliexpress.com/_EwRTA1z
Its the Jk-b2a24s20p model, so, 200amp, 8s-24s, 2 amp balancing, bluetooth, temp sensors. Seem to be rated highly, and balance well supposedly, so hopefully it will be good, and will future proof the battery bank incase i want to change to 48v one day too.

Just figuring out the final bits like fuses and fuse holders, battery bank parts etc.

 

[johnb2713]

Thanks .
All looks very nice and professional .. (mine will be very similar )

If you want any of the case/module parts making, I've been known to vapourise MDF on a regular basis with my laser cutter, I'd be happy to make some for your for the cost of materials and post.
Note whatever you do, the batteries need to kept in compression.

Im ordering them in 2 weeks, but thats on pre order to be delivered in november from fogstar.

Mine too were a pre order, I was more than slightly concerned but I needn't have worried, Fogstar have been great. A couple of suggestions:

1) Look around for discount codes, I found one that gave me 20% off
2) I'd Loaded them into my basket having setup a user account and left them there with the discount applied, after 2 days I received an email from Fogstar with more discount offered.

I dont know if either of the above are still working but worth a shot to save ££££

I ordered the bms yesterday:

￡6.30 26%OFF | Jikong Active Balance BMS Battery Protection Board 7S ~ 24S 100A 300A CAN RS485 APP LCD Lifepo4 li-ion LTO 48V 8S 16S 20S 72V
https://a.aliexpress.com/_EwRTA1z
Its the Jk-b2a24s20p model, so, 200amp, 8s-24s, 2 amp balancing, bluetooth, temp sensors. Seem to be rated highly, and balance well supposedly, so hopefully it will be good, and will future proof the battery bank incase i want to change to 48v one day too.

BMS's are a minefield LOL, I settled on SEPLOS purely for it's comms capability with my Victron Inverter.

Just figuring out the final bits like fuses and fuse holders, battery bank parts etc.

I used one of these isolators:
https://www.ebay.co.uk/itm/195238325062
This fuseholder
https://www.ebay.co.uk/itm/284985766329?
This cable for interconnections - (nice and flexible)
https://www.ebay.co.uk/itm/142796139227?var=441802778486
and about a million other minor items.

Good luck, keep us posted on your progress.

 

[Ucatchmydrift]

If you want any of the case/module parts making, I've been known to vapourise MDF on a regular basis with my laser cutter, I'd be happy to make some for your for the cost of materials and post.
Note whatever you do, the batteries need to kept in compression.


Mine too were a pre order, I was more than slightly concerned but I needn't have worried, Fogstar have been great. A couple of suggestions:

1) Look around for discount codes, I found one that gave me 20% off
2) I'd Loaded them into my basket having setup a user account and left them there with the discount applied, after 2 days I received an email from Fogstar with more discount offered.

I dont know if either of the above are still working but worth a shot to save ££££


BMS's are a minefield LOL, I settled on SEPLOS purely for it's comms capability with my Victron Inverter.



I used one of these isolators:
https://www.ebay.co.uk/itm/195238325062
This fuseholder
https://www.ebay.co.uk/itm/284985766329?
This cable for interconnections - (nice and flexible)
https://www.ebay.co.uk/itm/142796139227?var=441802778486
and about a million other minor items.

Good luck, keep us posted on your progress.

Thanks for the offer
I have the 15% off discount code ready to go (fogstar dont do the 20% anymore )
I have the 200a version of that breaker:

(ill double up the wires on the negative & pos once i build the bank.. The isolator is a blue sea systems good for 300a contiuous, might get another one for the negative.. )

This video is what made me want to go for a class t fuse:


The rest of the setup so far: (i have an armoured cable running into the loft into a metal consumer unit containing a type b rcbo and mains switch, then going to double sockets in each room and 2 in the kitchen - seperate system to the grid. Buying a multi oven (850w and an air fryer to do the cooking so dont need to use the cooker. Only thing i will ever take from the grid will be for the shower). The inverter has a pass through ability so will switch to take feed from the grid when no solar or battery. Will charge the battery bank in the winter via ocopus go 7.5pkw/h EV tarrif from 12:00-4:00am when needed. (3kw of panels on two shed roofs - 3kw all in one inverter))


Ill keep you posted when i receive the batteries and start to put them together
Is a great project

 

[johnb2713]

Thanks for the offer
I have the 15% off discount code ready to go (fogstar dont do the 20% anymore )
I have the 200a version of that breaker:
View attachment 14194
(ill double up the wires on the negative & pos once i build the bank.. The isolator is a blue sea systems good for 300a contiuous, might get another one for the negative.. )

This video is what made me want to go for a class t fuse:


The rest of the setup so far: (i have an armoured cable running into the loft into a metal consumer unit containing a type b rcbo and mains switch, then going to double sockets in each room and 2 in the kitchen - seperate system to the grid. Buying a multi oven (850w and an air fryer to do the cooking so dont need to use the cooker. Only thing i will ever take from the grid will be for the shower). The inverter has a pass through ability so will switch to take feed from the grid when no solar or battery. Will charge the battery bank in the winter via ocopus go 7.5pkw/h EV tarrif from 12:00-4:00am when needed. (3kw of panels on two shed roofs - 3kw all in one inverter))

View attachment 14195
Ill keep you posted when i receive the batteries and start to put them together
Is a great project

Looks really good, nice space you have there.

I did look around a lot at fuses, I hadnt seen the video you liked. I did however blow two sample fuses with no issues so I intend to carry on, the BMS has it's own fuse to protect the batteries and will allegedly successfully switch off on overload including dead short.

We shall see (hopefully not LOL).

 

[ruggedscot]

DC is formidable - And it has to have properly rated switchgear. not just for breaking a fault, but for switching duties.


below demonstration.



A 2.5kw load on ac and then dc.... you can see why you really need to have the correct specification.

You also need to take into consideration the fault levels that would be present. DC batteries are well known for the potential to provide several thousand amps. And in some farms where you have series and parallel combinations then you can run a risk fault currents that could obliterate a poorly designed installation.

 

[johnb2713]

DC is formidable - And it has to have properly rated switchgear. not just for breaking a fault, but for switching duties.


below demonstration.



A 2.5kw load on ac and then dc.... you can see why you really need to have the correct specification.

You also need to take into consideration the fault levels that would be present. DC batteries are well known for the potential to provide several thousand amps. And in some farms where you have series and parallel combinations then you can run a risk fault currents that could obliterate a poorly designed installation.

A good demonstration and certainly food for thought. I can understand the arc as demonstrated with an inductive load / supply and in fact it does sound like an inductive supply. My first 20 years of working life was in the steelworks, loads of DC stuff in there, huge mercury-arc rectifiers and the like, inductive loads often had airblast circuit breakers to blow the arc out.

For peace of mind though I'll obtain a suitable fuse and carrier.

Thank you.

 

[ruggedscot]

A good demonstration and certainly food for thought. I can understand the arc as demonstrated with an inductive load / supply and in fact it does sound like an inductive supply. My first 20 years of working life was in the steelworks, loads of DC stuff in there, huge mercury-arc rectifiers and the like, inductive loads often had airblast circuit breakers to blow the arc out.

For peace of mind though I'll obtain a suitable fuse and carrier.

Thank you.

Load was just over 2kw of resistive element... so not inductive. DC is very hard to break.

 

[johnb2713]

Load was just over 2kw of resistive element... so not inductive. DC is very hard to break.

The load may have been resistive but from the sound, the power supply was inductive. I find it hard to believe you can maintain an arc without a voltage high enough to ionise the air, I dont believe 50v will sustain an arc like that. That said, I'm not willing stick my neck out either so I have ordered the recommended DC rated fuses and holder.

 

[johnb2713]

Hi, ive decided to go ahead and build a diy battery bank, initially using 8 of these cells:

https://www.fogstar.co.uk/collections/lifepo4/products/eve-lifepo4-280ah-prismatic-cell

I've finished assembling my battery modules but I've been unhappy with the terminals on the batteries. The adapters fitted are aluminium with M6 Helicoil inserts. Fogstar say to torque to 4NM but in my view that's not tight enough. There's considerable drag from the flanged nuts supplied and I feel this is misleading ending up with an incorrect pressure applied to terminals and busbars.
I have replaced all of the supplied nuts with M6 washer, spring washer and nut, cost a grand total of £5 from a local fastening supplier. Looking at the Helicoil site they can be tightened to 12NM. I have tightened them to 6NM and even though there is additional torque applied there's was also way more clamping pressure due to the reduced friction between the nut and the busbar or terminal.

 

[Ucatchmydrift]

I've finished assembling my battery modules but I've been unhappy with the terminals on the batteries. The adapters fitted are aluminium with M6 Helicoil inserts. Fogstar say to torque to 4NM but in my view that's not tight enough. There's considerable drag from the flanged nuts supplied and I feel this is misleading ending up with an incorrect pressure applied to terminals and busbars.
I have replaced all of the supplied nuts with M6 washer, spring washer and nut, cost a grand total of £5 from a local fastening supplier. Looking at the Helicoil site they can be tightened to 12NM. I have tightened them to 6NM and even though there is additional torque applied there's was also way more clamping pressure due to the reduced friction between the nut and the busbar or terminal.

Thanks for the update.... Do you mean that fogstar actually supply m6 helicoil inserts? - or you had to buy them to replace studs that they supplied?
They dont just supply the cells with studs that screw in? You have to actually tap the thread? Not sure how it all works... Thank you..

 

[johnb2713]

Thanks for the update.... Do you mean that fogstar actually supply m6 helicoil inserts? - or you had to buy them to replace studs that they supplied?
They dont just supply the cells with studs that screw in? You have to actually tap the thread? Not sure how it all works... Thank you..

No, the aluminium terminals have helicoils in them already, Fogstar supply small threaded rods and some flange nuts which cause a lot of drag when tightening. Just replacing the flange nuts with M6 nuts / spring washers and washers has resulted in a much better connection.

 

[Ucatchmydrift]

No, the aluminium terminals have helicoils in them already, Fogstar supply small threaded rods and some flange nuts which cause a lot of drag when tightening. Just replacing the flange nuts with M6 nuts / spring washers and washers has resulted in a much better connection.

Ok great, i expect ill end up doing the same..

 

[johnb2713]

Ok great, i expect ill end up doing the same..

B&Q have the bulk supplies, you pay £5 and grab handfuls of nuts / washers etc to fill up the bag if you dont have trade access to a fastener supplier.
M6 BZP Nuts, washers and spring washers is what you need.

 

[Ucatchmydrift]

If you want any of the case/module parts making, I've been known to vapourise MDF on a regular basis with my laser cutter, I'd be happy to make some for your for the cost of materials and post.
Note whatever you do, the batteries need to kept in compression.


Mine too were a pre order, I was more than slightly concerned but I needn't have worried, Fogstar have been great. A couple of suggestions:

1) Look around for discount codes, I found one that gave me 20% off
2) I'd Loaded them into my basket having setup a user account and left them there with the discount applied, after 2 days I received an email from Fogstar with more discount offered.

I dont know if either of the above are still working but worth a shot to save ££££


BMS's are a minefield LOL, I settled on SEPLOS purely for it's comms capability with my Victron Inverter.



I used one of these isolators:
https://www.ebay.co.uk/itm/195238325062
This fuseholder
https://www.ebay.co.uk/itm/284985766329?
This cable for interconnections - (nice and flexible)
https://www.ebay.co.uk/itm/142796139227?var=441802778486
and about a million other minor items.

Good luck, keep us posted on your progress.

Well, just in case you or anyone is interested, thought id make a quick update as to how its getting on..
Received the cells from fogstar, all good, top balanced them to 3.65v in parallel, then compressed them as shown below. Got a class t lawson fuse 355amp with a 80,000 amp interrupt current! ( £15 from ebay! - bargain, and made my own fuse holder - £3 pice of perspex which i heated and bent).



Built a box to put it all in (made from an old wardrobe! (not finished yet!)) with a 20w heating pad, as its in a metal workshop outside. its been in use the last couple of days (heating pad), and working well. Controlled via a £12 gadget from ebay.

https://www.ebay.co.uk/itm/22412471...sv1MPSPSK-&var=&widget_ver=artemis&media=COPY
https://www.ebay.co.uk/itm/16571823...sv1MPSPSK-&var=&widget_ver=artemis&media=COPY




Attached a 200amp jk bms to keep the battery bank safe, used off grid garage on youtube to setup all the settings, very handy. Very small cell deviation of about 0.002mv at a current draw of about 20 amps, so very pleased with that.
Also bought a junctek 400amp shunt with bluetooth so i can now see whats going on in the house! - jk bms doesnt reach inside, and inverter doesnt have bluetooth or wifi .






Now setting up a set of contactors that i can use to switch the inverter grid supply on and off automatically via a wifi socket, so i can activate grid charging remotely from inside the house using a shedule or whatever i like via the wifi socket app

Been all up and running now for a couple of weeks, just doing the finishing touches. All working well, and very pleased with it all. - as its a 3000w inverter, ive bought a multi cooker (600watt) and a air fryer (1200w). Which i can easily run at the same time to cook my dinner instead of using the 4kw oven attached to the grid. I am also replacing the 3kw element in the emersion heater to a 1 kw on a timer with a shower attached to the bath so i dont have tobuse the 8kw power shower any more! - basically off grid in the summer, and using only cheap rate elec in the winter (12p kw/h currently)! Amazing!

 

[johnb2713]

Looking good there, have you found the cells ok capacity wise?

I'm just waiting for delivery of my last bit of heatshrink and battery cable and I'm then good to go with mine.

 

[Ucatchmydrift]

Looking good there, have you found the cells ok capacity wise?

I'm just waiting for delivery of my last bit of heatshrink and battery cable and I'm then good to go with mine.

Ive not done a proper capacity test, and probably wont bother doing one, just trusting fogstar, but they all arrived at exactly the same voltage, and due to the low cell deviation on the bms id guess that they are all similar, so either they are all no good, or all good . They seem about right from the total watts beig drawn from them based on me using about 90% of their capacity (charging to about 99% - 3.45v per cell, and charging when they reach about 10% or 3.00v per cell), which is about 6.5kw. Doing some quick maths tells me im getting about 6.5kw due to what ive pulled from them, so im happy with that..

 

[roys]

Enjoyed reading this thread from the both of you, very interesting and good builds.