Fuse Sizing

Sunnytheskoolie

New Member
Joined
Feb 12, 2021
Messages
25
Hello there,

Would you have a moment to answer my questions, I'm a little confused with fuse sizing.

I have a 16s2p battery (51.2v 560ah) bank and am looking for a battery disconnect/fuse. I actually purchased the BlueSea M series but I didn't see that it was max rated for 48v and has a 300a rating. Do you know of a better manual disconnect that also has a fuse? I have been trying to find a Bussmann Tyco EV disconnect with a fuse but hard to come by.

My system doesn't have a fuse between my battery and my Lynx Distributor at the moment it only has the Contactor from my REC BMS and that Bluesea switch. Also, how would I calculate the fuse size to put in my Lynx Distributor? I have a 120v panel 100amp Square D panel(8 15 amp breakers and 2 20amp breakers), a 12v breaker box, and my MPPT hooked up to the Lynx Distributor and need fuses for each.

My solar array will be 9 400w panels 3s3p that will run through a Midnight solar Baby Box and a Victron Mppt.

Thanks for your help.
Derek

ps. my system is not connected I just have all the components.
 

smoothJoey

Its a hot one!
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Nov 30, 2019
Messages
9,341
Hello there,

Would you have a moment to answer my questions, I'm a little confused with fuse sizing.

I have a 16s2p battery (51.2v 560ah) bank and am looking for a battery disconnect/fuse.
Over-current protection sizing is based on the planned maximum continuous load.
Typically that is the continuous rating of the inverter.
Example:
2000 ac watts / .85 conversion factor / 10 volts low cutoff = 235.294117647 service amps.
235.294117647 service amps / .8 fuse headroom = 294.117647059 fault amps.

That means the main current path requires a 300 amp fuse and wire rated for in excess of 300 amps.

Each battery should be fused separately.

I actually purchased the BlueSea M series but I didn't see that it was max rated for 48v and has a 300a rating.
You mean this product https://www.bluesea.com/products/category/11/37/Manual_Battery_Switches/m-Series ?

Do you know of a better manual disconnect that also has a fuse?
You mean a breaker?
I have no experience with these but @MurphyGuy says they are ok.
Looks like they top out at 250 amps.
My system doesn't have a fuse between my battery and my Lynx Distributor at the moment it only has the Contactor from my REC BMS and that Bluesea switch.
Please put a class-t fuse as close as possible to the master positive terminal of the battery and before the contactor.
This minimizes the risk of an un-protected short upstream.
This fuse protects the wire and the battery.
These batteries contain a metric fork ton of energy so care must be taken.
Also, how would I calculate the fuse size to put in my Lynx Distributor?
The lynx has 4 fused positions.
Sounds like you have 2 items to fuse.
The fuse on branch circuits are meant to protect the wire, I suggest you use the same size fuse and wire for both items if possible.
That way you can cut down on the number of spares you have to keep on hand.
I'm guessing that 6 awg and a 100 amp fuse will cover both.
Check the specs though and apply the formula to make sure that exceeds the minimums.

Since you have 2 open fusible positions you could connect each battery to a fused position.
Still use a fuse as close as possible to the battery terminal in addition to the one on the busbar.

I have a 120v panel 100amp Square D panel(8 15 amp breakers and 2 20amp breakers), a 12v breaker box, and my MPPT hooked up to the Lynx Distributor and need fuses for each.
 

Sunnytheskoolie

New Member
Joined
Feb 12, 2021
Messages
25
Over-current protection sizing is based on the planned maximum continuous load.
Typically that is the continuous rating of the inverter.
Example:
2000 ac watts / .85 conversion factor / 10 volts low cutoff = 235.294117647 service amps.
235.294117647 service amps / .8 fuse headroom = 294.117647059 fault amps.

That means the main current path requires a 300 amp fuse and wire rated for in excess of 300 amps.

Each battery should be fused separately.
Ok so I have a Quattro 48v 5000w inverter. So you are suggesting that I would need a 730amp fuse? Is this the Class T fuse that you are mentioning adding right by the battery?
yes, that's what I have. I was thinking of putting it before my contactor actually and then putting the fuse on the contactor.
I am thinking of sticking with the switch and then putting a Class T fuse on the Contactor after the switch
Please put a class-t fuse as close as possible to the master positive terminal of the battery and before the contactor.
This minimizes the risk of an un-protected short upstream.
This fuse protects the wire and the battery.
These batteries contain a metric fork ton of energy so care must be taken.
Yes, this is what I was also reading this morning. I am going to do that. Thanks.
The lynx has 4 fused positions.
Sounds like you have 2 items to fuse.
The fuse on branch circuits are meant to protect the wire, I suggest you use the same size fuse and wire for both items if possible.
That way you can cut down on the number of spares you have to keep on hand.
I'm guessing that 6 awg and a 100 amp fuse will cover both.
Check the specs though and apply the formula to make sure that exceeds the minimums.
I am going to have my 120v 100amp panel(125amp fuse on the lynx), 12v 30amp panel(40amp fuse), and my MPPT connected to the Lynx(100-125 amp fuse). I am also going to add another 12v 30amp converter with fuse for a car stereo amp to the lynx(another 40amp fuse)
Since you have 2 open fusible positions you could connect each battery to a fused position.
Still use a fuse as close as possible to the battery terminal in addition to the one on the busbar.
I was going to run the battery into the main lugs on the Lynx. It will be one + and one - cable coming from the battery, not two separate batteries.
 

smoothJoey

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Ok so I have a Quattro 48v 5000w inverter. So you are suggesting that I would need a 730amp fuse? Is this the Class T fuse that you are mentioning adding right by the battery?
5000 ac watts / .85 conversion factor / 40 volts low cutoff = 147.058823529 service amps
147.058823529 service amps / .8 fuse headroom = 183.823529412 fault amps.
You want a 200 amp fuse with 2 awg wire or better.

yes, that's what I have. I was thinking of putting it before my contactor actually and then putting the fuse on the contactor.
Fuse is the first item off of the positive terminal.
I am thinking of sticking with the switch and then putting a Class T fuse on the Contactor after the switch
The fuse goes closest to the positive terminal to minimze the chance of a short upstream.

I was going to run the battery into the main lugs on the Lynx. It will be one + and one - cable coming from the battery, not two separate batteries.
16s2p is 2 batteries each with its own bms.
I stand by my suggestion to put each on its own fused position even though you will fuse them at the positive terminal.
That way you can connect/disconnect them independently.
My advice stands.
You don't have to take it though.
 

smoothJoey

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Do these batteries have smart bms that do current accounting?
If not perhaps you do want to run them off the main busbars with a shunt in-line.
 

Sunnytheskoolie

New Member
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Feb 12, 2021
Messages
25
5000 ac watts / .85 conversion factor / 40 volts low cutoff = 147.058823529 service amps
147.058823529 service amps / .8 fuse headroom = 183.823529412 fault amps.
You want a 200 amp fuse with 2 awg wire or better.
Thanks for clarifying that. I was planning on a 300amp fuse but maybe I'll look for a 200-250amp fuse. I will put the fuse right off the bus bar and connect it to the wire going to the switch. If the fuse blows then I will not be able to shut off the power when replacing it though. This was my thought on having the fuse after the switch. My initial plan was to have a 6" wire between my battery and fuse, just to go around the corner of a 3/4 sheet of plywood to where my fuse and switch are mounted.
Fuse is the first item off of the positive terminal.

The fuse goes closest to the positive terminal to minimze the chance of a short upstream.
Just read the RV fire thread with the metal battery box.... I have no issues putting the fuse as close as possible. Also, I was not planning on bonding the ground to the frame...thoughts on this?
16s2p is 2 batteries each with its own bms.
I stand by my suggestion to put each on its own fused position even though you will fuse them at the positive terminal.
That way you can connect/disconnect them independently.
My advice stands.
You don't have to take it though.
My mistake, I am doing a 2p16s setup. One BMS. I have the REC Q1 BMS. I have their contactor, precharge, and shunt.
 

smoothJoey

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Just read the RV fire thread with the metal battery box.... I have no issues putting the fuse as close as possible. Also, I was not planning on bonding the ground to the frame...thoughts on this?
If you are using the big blue prismatic cells its a good idea to have some thin insulation between them and around them.
The pvc wrap is pretty thin and the aluminum underneath is positive or negative, can't remember which.
The lynx distributor should be bonded to the chassis.
Not for chassis return but to keep the system at the same reference potential as the rest of the vehicle.

My mistake, I am doing a 2p16s setup. One BMS. I have the REC Q1 BMS. I have their contactor, precharge, and shunt.
Since its one battery with 1 bms including shunt you can put it off the main busbars.
Saves the resistance of the 2nd fuse.
 

Sunnytheskoolie

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Messages
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If you are using the big blue prismatic cells its a good idea to have some thin insulation between them and around them.
The pvc wrap is pretty thin and the aluminum underneath is positive or negative, can't remember which.
I have a material called Puck Board. I used to use it for practicing stick handling. It's the type of material they use on the side of hockey rink boards. You can rub the crap out of it and it hardly damages it. I am going to put this in between each cell and on the outside edge as well. I have threaded rods holding the pack together with plate steel on the ends. Check the pic. There is a7/16th threaded rod on the top with a 1/2 pex pipe around it. It's not squeezing the batteries down but just holding them in place so they don't bounce up. The rack with be hanging from the chassis and floor of the bus and will also have two 1/2 bolts holding it to the bottom of the storage floor.
The lynx distributor should be bonded to the chassis.
Not for chassis return but to keep the system at the same reference potential as the rest of the vehicle.
How do you bond it to the chassis? Suggestions or pics would be great.
Since its one battery with 1 bms including shunt you can put it off the main busbars.
Saves the resistance of the 2nd fuse.
so if it does blow then I will not have a switch to kill the power when changing it....😅

The image attached is only half of the pack. I will have the two endplates welded to the metal angle iron and a small plate in the middle of the two halves that one rod will pass through. This will help hold the batteries to the rack and the middle plate of each 16 cells will float so that I can compress the cells a bit. They sit on a sheet of 3/4 plywood but I could put a 1/16 sheet of rubber mat down but it would reduce the airflow a bit. I have some holes drilled in the ply
 

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smoothJoey

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I have a material called Puck Board. I used to use it for practicing stick handling. It's the type of material they use on the side of hockey rink boards. You can rub the crap out of it and it hardly damages it. I am going to put this in between each cell and on the outside edge as well. I have threaded rods holding the pack together with plate steel on the ends. Check the pic. There is a7/16th threaded rod on the top with a 1/2 pex pipe around it. It's not squeezing the batteries down but just holding them in place so they don't bounce up. The rack with be hanging from the chassis and floor of the bus and will also have two 1/2 bolts holding it to the bottom of the storage floor.

How do you bond it to the chassis? Suggestions or pics would be great.
Just attach a wire to the lynx negative busbar.
The wire as thick as your thickest equipment ground wire.
Find a bolt that is well anchored to the frame.
Clean the metal for good contact and connect.
Spray rust paint over any exposed metal.

so if it does blow then I will not have a switch to kill the power when changing it....😅
Sorry I don't get what you are saying here.
 

Sunnytheskoolie

New Member
Joined
Feb 12, 2021
Messages
25
Hi, I just finished the grounding paper. It was interesting and also confusing.

Everything is mounted right beside the frame and there are multiple bolt holes in my frame so it will be easy to do this.

Thanks for your help.
 

bhavin66

Solar Enthusiast
Joined
Sep 24, 2019
Messages
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Location
Edison NJ
Don't want to hijack this discussion.
Anyone use ANM-H3 mega fuse available on AliExpress on battery?
US $1.24 13%OFF | ANM/MEGA Bolt-on Fuse 40A 50A 60A 70A 80A 100A 125A 150A 200A 225A 250A 275A 300A...500A / Flat Type Fuse/auto fuse/ Blade Fuse

Looks very similar to littlefuse mega 70v HP fuse.

My point of reference here is 48v battery system and class T fuses.
 
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