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everyone this is jeff cote and we are

filming

on location at votingtechtalk.com

all right so we've got the next question

we have is from a fellow voter

and this fellow boarder says jeff i've

just started

the renovation of a vintage sailboat

congratulations even old sailboats

deserve a lot of love

the boat has four 100 amp hour house

battery bank and an 85

amp power engine battery okay so a 400

amp hour battery bank for house and an

85

amp hour for engine okay thanks to your

diagrams and learned

to fuse between the battery bank and the

switch what is the recommendation

of the fuse on my configuration and

which one is the best to buy

good setup but difficult question fusing

from a battery bank to a switch really

depends on multiple things

first of all you've got to ask yourself

is my house battery bank

ever going to be part of my starting

circuit

right and a lot of battery switches

including

off one two both switch or off on

combined switch

will give ourselves the boaters the

ability of putting

our batteries in parallel and or even

selecting the house battery to start

the engine so in those situations

fusing the house circuit is not just

fusing the house circuit

because the house can play a backup role

for also

starting the engine so what you've got

to do at that point is you've got to ask

yourself what am i going to be doing

with the house is my house ever and

only ever going to be running households

or will it also be running my engine

loads

so generally what you want to do is if

you're going to be starting

also the engine from the house battery

you want to make sure that if you put a

fuse on that circuit

that fuse is rated to handle the maximum

amperage that you expect your

engine to be requiring from the battery

bank

and that's something that honestly i

don't think if a lot of

engine manufacturers are going to say

what the amperage exactly is going to be

they're going to rate

maybe saying what they want is coal

pranking amps cca

or marine cranking amps mca what we

normally do

is we actually put a clamp on meter on

the cable to try to assess

what is the basically realistic amperage

that that starter would draw

and if that's the case then we would

size the fuse to be at least

1.25 or even 1.5

that maximum current so you never get

nuisance tripping

and then furthermore and i know there's

a lot of ends but this is a boat it's

not supposed to be easy and if it was

easy

it wouldn't be boating then basically

what you do is maybe one and a half

times your sort of anticipated amperage

for that starter circuit and make sure

also that your wiring can handle

that average as well so your house loads

might never

see more than maybe 30 40 50 okay 100

amps 200 amps

but it's not uncommon for a starter to

draw way more than 200 amps

so make sure that both your wiring and

the fusing are

paired married well right so you want to

make sure that you don't have a fuse

that's too big for the wire size

you could certainly have a fuse much

smaller than the wire size that doesn't

that's not a big concern and now if your

circuit in this instance your house

battery is

not going to start the engine battery

then it makes it easier so you think

about okay well what are the maximum

amount of

concurrent loads that i can have at any

given time right so maybe it's going to

be my windlass

uh maybe my panel my navigation you know

on most sailboats you know assuming

again not the starter and no thruster

and just a windlass um then maybe you're

going to be drawing 150 at

max amperage ever at one time and then

you would take that number

and again you want to give yourself a

little bit of sort of

room to maneuver and you might multiply

that times one and a half

and then you're gonna size both the wire

to be able to handle one and a half

times

150 which would be 225 i think i did the

math right

so a 225 amp fuse on a circuit that you

expect to draw 150 and then you need to

make sure that the wire size is able to

handle that

and that's how you go about sizing a

fuse

for a wire and for a battery bank note

i get this question quite a lot recently

over

the youtube and people are always asking

me and they're taking they're saying how

do i go about sizing

my fuse do i consider the battery bank

or do i consider the loads

and the answer is it's irrelevant the

battery bank could be 100 batteries

could be a thousand batteries there

could be one battery

realistically where it matters is how

much current you expect to draw from

that battery bank and what is that max

current

and so you're actually when you're

selecting a fuse you're actually basing

it on the size of the loads that you

anticipate to run concurrently at one

given time if you expect all of them to

load

to run at one time then you're going to

have to do all the math give yourself

again

maybe a ratio of 1.25 1.5 size the wire

accordingly

and remember always always

carry a spare fuse for those circuits

because if you're in the middle of

paradise it's unlikely that in paradise

you're going to be finding that fuse

that you need

because it accidentally blew so that's

my

my advice on that question great

question by the way thanks for asking

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