Battery switch installation

[Dirtyfuzz]

Thoughts on battery switch position, I want to install the bep twin outboard combo switch with vsrs so both start batteries charge the house battery, is a bit of overkill but my thoughts are if it’s available just do it, only concern I have is the cable run to the location up the front in front of passenger seat is approximately 6m, cable price doesn’t concern me just the voltage drop across the distance and will the cable be too large to go into the motor. Switch and location attached


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[scottar]

So if understand correctly, you want to put the switches in front of the passenger seat but leave your batteries where they are - I assume at the stern or at the rear of the side pockets like most cats. Not what I would do. The voltage drop will be significant for starting. Do you have an existing start / parallel switch assembly down the back? If you do the addition of two VSR's - one from each battery and a house battery switch will give you everything the switch cluster is without creating any possible starting / cable gauge issues.

[Islander77]

There is a good voltage drop calculator in the middle of the page here
https://www.12voltplanet.co.uk/cable...selection.html

I've recently built an off-grid container house and used that calculator exclusively for all the cable runs. Good luck

[Dignity]

Also when you upgrade your motors (I thought there were murmurs about that happening) you'll have auxiliary charging circuits on each motor that can be used to charge the house battery separately.

[Dirtyfuzz]

I should have been a bit clearer, I want to put the switches in the enclosed compartment in front of the passenger seat so they are out of the weather, the two start batteries are at the stern on each side and the house battery is in the battery box up the front on the port side, there currently is no isolator switches of any sort installed, I was hoping to offset the the voltage drop by just going larger cables! Trying to find a conversion of 4/0 cable size to an Australian equivalent


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[Dirtyfuzz]

Also when you upgrade your motors (I thought there were murmurs about that happening) you'll have auxiliary charging circuits on each motor that can be used to charge the house battery separately.

Yeah I think I read about the new mercs increase the rpm to keep batteries at correct voltage so maybe vsr are not required on modern motors


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[Islander77]

... I was hoping to offset the the voltage drop by just going larger cables! Trying to find a conversion of 4/0 cable size to an Australian equivalent

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The question is how much current draw is required to start the engine? Not sure but think it can be up to 500amp at peak?

The largest cable you can easily get is AWG-0, which is equivallent to 50sq.mm (pain to work with due to size, but still...)

The calculator that I posted above tells that by using that cable for 6m length, with max voltage drop of 3%, maximum current draw it would handle is only about 90amps.
Also the AWG0 cable is about $20 a meter

[Dirtyfuzz]

The question is how much current draw is required to start the engine? Not sure but think it can be up to 500amp at peak?

The largest cable you can easily get is AWG-0, which is equivallent to 50sq.mm (pain to work with due to size, but still...)

The calculator that I posted above tells that by using that cable for 6m length, with max voltage drop of 3%, maximum current draw it would handle is only about 90amps.
Also the AWG0 cable is about $20 a meter

Thanks for that, I might have to position the switches at the back going off those numbers then


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[Fed]

It's doable with your V4s but computerised Mercs are not happy with a compromised power supply.
Starter motors usually pull about 150A but Mercury computers can be finicky.
Short cable runs are best.

[Dignity]

As your starter batteries are at the stern there shouldn't be too much of an issue provided you keep your switches down there as well, you could install a vinyl flap at the transom to prevent most water ingress, also the vsr should be waterproof. The house battery won't need as heavy cable as you think, just have a look at the size of cable your battery charger is using and at least double it or treble it, do use tinned cable, it will last longer.

Forgot to add if you can get hold of welding cable then it has far less voltage drop due to the number of strands giving a much higher surface area for the current to flow, unfortunately finding tinned cable like this is very difficult but this where getting good lugs and dual wall heatshrink plans a vital role.

[TheRealAndy]

Just a heads up, if you have not yet bought the BEP switches, then I would suggest blueseas instead. The BEP switches are rubbish, to the point where I am sick of replacing them. I decided to keep the last one I changed (just last week) with the intention of taking a photo and posting it up here. I'll grab the dud one off the boat tomorrow and take a photo.

BTW, I have more or less the exact same setup on my boat. Currently uses BEP switches (the last on I replaced with a BluesSeas switch) and 2 Enerdrive Dual ) VSR's. I installed it about 12 months ago, and its still going strong.


Last but not least, for cable tried Cameron's Electrical Cable at Geebung. You will be pushing to find a cheaper source of tinned cable in Brisbane, and he normally has stock as well.

[Dirtyfuzz]

Just a heads up, if you have not yet bought the BEP switches, then I would suggest blueseas instead. The BEP switches are rubbish, to the point where I am sick of replacing them. I decided to keep the last one I changed (just last week) with the intention of taking a photo and posting it up here. I'll grab the dud one off the boat tomorrow and take a photo.

BTW, I have more or less the exact same setup on my boat. Currently uses BEP switches (the last on I replaced with a BluesSeas switch) and 2 Enerdrive Dual ) VSR's. I installed it about 12 months ago, and its still going strong.


Last but not least, for cable tried Cameron's Electrical Cable at Geebung. You will be pushing to find a cheaper source of tinned cable in Brisbane, and he normally has stock as well.

Cheers mate! Was just going to go the bep just for the convenience of them coming as a unit but will look at other alternatives now!


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[ranmar850]

The all in one units are convenient, and compact, but the cheap ones are unreliable, and the quality ones are expensive. I made my own using all Narva components for about $170 ,iirc. 3 switches and a vsr. I covered the access protection side of things by mounting it on a hinged dropdown, although this will be totally dependent on transom layout. Mine was really awkward, no obvious place to mount them, Caribbean need to address this on the Reefrunner. I'm on my phone, see if I can post a pic.

[ranmar850]

Attachment 117830Attachment 117830
Pita doing this on a phone, no matter how good it is Anyway, that panel is hinged at the back, so it folds forward and up, ends up in the void in front of the well, secured by an over centre catch. edited to insert photo