Mega fuse size

[Chanchan168]

Hi there,

I am installing a new bluesea add a battery kit and as part of that kit I need to install the split charge relay. It’s the 120a version.

I’m installing mega fuse holders in between the relay and batteries, and have 35 and 50mm tinned cable, but I’m not entirely sure in fuse size.

I’m running a yam 150 hpdi and both my batteries are 110amp. The instructions say 80amp for 2awg cable but as my cable is 35 to the electrics and 50mm from the batteries should I go for 150amp?

Any advice would be greatly appreciated.

T.i.a.

[GuyC]

The cables to the relay are based on the charging rate of the alternator. I'm not sure which ACR you have but in the instructions it talks about the charging amps. I imagine your alternator is only kicking out 25A or so. As a result 10mm cable will be OK.

The ACR isn't meant to carry any starting loads - it's just there to manage the charging of the two batteries. It's no issue to use bigger cable though. The fuse is really to protect the cable so you could go for a bigger fuse. 35mm cable has a rating of 240A so a 150A fuse would be more than fine.

[Chanchan168]

Thanks Guy, makes sense. The Acr comes in the kit with the battery isolator from Bluesea.

The diagram just shows a mega fuse link between the Acr and both batteries. In the pic it shows 80amp with 2awg cable and then a 150amp fuse between the isolator and the main fuse block.

I’ve attached a pic.

Thanks again

[Chanchan168]

Here’s a pic

[GuyC]

The two lower fuses in the picture are related to the charging and can be sized either on the charging rate of the alternator or the size of the cable you've used. If you've used 35mm cable between the ACR and the house and starter batteries, then either a 75A or a 150A will be fine.

For the main fuse block, it's dependent on the cable size which in turn is dependent on the electrical load from the consumers. I'm guessing that the consumer load won't be more than about 20A - VHF, chartplotter, bilge pump etc. As a result you can get away with quite a small wire feeding the fuse block - 6mm with a 40A fuse for example. It is all dependent on what you are running.

[Chanchan168]

Cheers Guy, thanks

[breezeblock]

ive got the same set up and the 2 fuses at the charge relay are 80amp and the one feeding the aux electrics is a 40amp

[Chanchan168]

Brilliant thanks.

[Chanchan168]

Originally Posted by breezeblock

ive got the same set up and the 2 fuses at the charge relay are 80amp and the one feeding the aux electrics is a 40amp

Hi Breezeblock,

What size cable have you run from the batts to the relay?

Would 25mm or 4awg be ok with an 80amp fuse?

T.i.a.

[breezeblock]

big enough I can't remember what size it was just a short bit that was underneath the bench

[Manolism]

You can find the appropriate fuse size based on your wire according to this table. Itx very useful this table.

https://www.bluesea.com/products/200...9QEwAnoECAAQBQ