Fuse between batteries

[Notty1975]

Hi all I’m in the process of upgrading my solar set up to 2x 260w panels with a 40a mppt tracer
I’ve just bought a 2000w(4000w peak) inverter which will be running off my 2 120ah leisure batteries connected in parallel using 70mm2 cable fused at 350a
But my question should the fuse between the batteries also need to be 350a
Thanks all

 

[telectrix]

350A seems a tad high for 70mm cable.

 

[Deleted member 26818]

Are the batteries in series or parallel?

 

[PEG]

350A seems a tad high for 70mm cable.

You better be careful when you turn that ignition key,then...

 

[Notty1975]

The batteries are in parallel
I took the wattage of the inverter and made my calculations
4000w/12v= 333.33amp
According to the site I got the cable from
PVC70 888/0.30 70 485 15.5 Black, Red
It can carry 485a
So my thoughts were the inverter is internally fused so just had to protect the cable what size fuses would you recommend then to go from
1, battery bank to inverter
2, in between the 2 batteries connected in parallel

 

[telectrix]

that cable is, as you say, capable of 485A. it's not a type that we use generally, so our bible does not list it. however, your batteries will last about 30 minutes running at that. if batteries are in parallel, you need a fuse in the +ve going out to the inverter. no need for additional fusing on the battery side as the 350A fuse will blow under overload/short circuit.

you also need to calculate the load on the inverter. that's what will determine your battery current, not the max. load the inverter will supply.

 

[Notty1975]

So what if there was a problem in one or both of the batteries you recommend not having a fuse between the 2? For my peace of mind in case there was a problem (dead short etc) I would rather have protection between the 2 and not risk damaging both and/or the wiring there will be a fuse between the batterie bank to the inverter as stated in my original question there will be a fuse between the batteries my question is should it be the same size as the one going to the inverter
Thanks all

 

[telectrix]

can't see any reason for a fuse between the batteries. how can a + to a + short unless the batteries are in a metal enclosure and trhe insulation of the link cable wears through and shorts on the metal enclosure.

 

[Notty1975]

So you can’t see that a dead short on one battery couldn’t damage the second battery by using the cable to transfer the short if there was a fuse in between it would blow thus protecting the second battery and the cable? Or am I really missing something here?

 

[Deleted member 26818]

The extra fuse would protect either battery from a dead short on the other.
Thing you gotta ask, is why would you have a dead short on one of the batteries.
Do you run around dropping metal objects across the battery terminals much?

 

[Notty1975]

The extra fuse would protect either battery from a dead short on the other.
Thing you gotta ask, is why would you have a dead short on one of the batteries.
Do you run around dropping metal objects across the battery terminals much?

Why have an rcb then do you do installs expecting things to break
It’s there for safety in case the unexpected happens

 

[Deleted member 26818]

Why have an rcb then do you do installs expecting things to break
It’s there for safety in case the unexpected happens

RCDs are primarily used in case someone plugs in a defective appliance, drills though a cable concealed in a wall or to add an extra bit of safety for someone having a bath or taking a shower.
Your proposal is to protect the batteries against a metal object either falling or deliberately being placed across the terminals of the other battery.
With vehicle batteries, the common practice is to place a piece of plastic across the live terminal or to use a rubber boot over the connector.

 

[Notty1975]

RCDs are primarily used in case someone plugs in a defective appliance, drills though a cable concealed in a wall or to add an extra bit of safety for someone having a bath or taking a shower.
Your proposal is to protect the batteries against a metal object either falling or deliberately being placed across the terminals of the other battery.
With vehicle batteries, the common practice is to place a piece of plastic across the live terminal or to use a rubber boot over the connector.

Ok well thanks for the advice but after gathering information from a dedicated solar forum I’ve found that not only is it recommend but in some countries it’s law so the fuse will be fitted as would rather be safe than sorry and I’m not one to cut corners even though it’s highly unlikely it can still happen