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hi everyone

jeff cote here with boatingtechtalk.com

we have a question from a fellow voter

mel mel says jeff

my boat has two motors two engines i

haven't really investigated

a mel adds my alternator situation but i

was wondering

if the alternator on one motor charges

the house batteries and the other

engine charges the engine batteries

okay what's normal what to expect

well unfortunately nothing is really

normal on a boat

because all of us eventually modify

boats

so if your boat is again from the

factory

most installs and again this is sort of

like these generalities that don't apply

to anyone but

since you know we're putting context

here in an ideal world and certainly

what i advise many boaters to do i'll

remember there's always real exceptions

to every rule

but what i advise is that each engine

should have its own dedicated engine

battery

that's my advice so if you have two

engines

two engine batteries and i know some of

us

will have one engine battery do two

engines but i'm

we could take a whole one hour spiel on

why

my advice is an engine battery is not

that expensive have a dedicated engine

battery per engine

now in this instance this boarder mal

talks about

not multiple battery banks he's talking

about only two battery banks so he's got

two engines two alternators one house

battery

one engine battery generally

generally the starter is connected

to the alternator and i mean the starter

solenoid

so when you buy an engine straight out

of the factory

any factory any car if you wire

either two engines to one battery both

alternators are going to be recharging

that single engine battery that's how it

would come from the factory now

over time and certainly boat builders

and technicians like ourselves

will what they'll do is they'll

intercept one of the alternators and

instead of that alternator recharging

and connected to the starter solar

on the engine they're going to intercept

that power and they're going to run it

to the house batteries so it is possible

now that on your boat you have literally

two engines and each engine

is connected to its respective

battery bank and they're separate the

best way of testing this by the way

is not actually following the wiring the

best way is to

confirm behavior so here's how you would

confirm mel

and this applies to all of us how would

you confirm what is going on in your

boat

the first thing is disconnect shore

power from your boat

if you've got solar panels cover them up

i want

no charging voltage at all on your boat

so it can the only charging voltage

you're going to get is from your

alternators you've got a methanol fuel

cell disconnected if you've got a wind

turbine disconnected

solar panels cover them up disconnect

them but on most cases most of us don't

have all those things we either have a

battery charger and alternators so

that's for most of us

all right so now that we're

disconnecting from shore power you want

to measure the voltage at each battery

so whatever it is it doesn't really

matter absolutely what it is you just

want to know what it is

at the meter and what you're looking for

is change

so what you would do is you would start

let's say for example the starboard

engine

you look at the voltage prior to

starting you start the engine

and now you look at the battery voltage

at both the

engine battery and the house battery one

of them

or potentially both the voltage should

rise

if it does then you've confirmed that

some way

either your that engine is recharging

two batteries one battery or none

no batteries so that's one thing you

want to confirm because it's possible

that you have a battery isolator on this

boat and if you do have a battery

isolator each engine could be recharging

two battery banks

but you don't know that and that's what

you're confirming so you start you look

at the voltage prior to starting

the engine and once you start the engine

and by the way some of these alternators

don't output at low rpm so you might

have to rev up to maybe 13 1400 rpm in

idle

just enough so that the alternate

outputs

and measure and now notice did the

battery voltage at

either battery increase one of them is

going to drop down of course

the one that started the engine so

that's the other thing too you're going

to confirm

because as you're starting the engine

you're going to see a battery voltage

drop

that battery voltage is dropping before

the engine actually

ends up running as you're trying to

crank it over

that tells you that that engine battery

or battery is what's connected to the

starter

check next do it on the port side

again now you do it on the port side

with the starboard side not running

because what you want is isolation right

you're looking for

if you're creating change and you're

looking for

outcomes right so now you do the port

side again

so in this instance mel is supposing

that one engine is connected

to the engine battery and another engine

is connected to the house in this

instance

one engine should only recharge the

engine battery and the other engine

should only recharge the house battery

and now should be able to notice

those voltages going up and that would

be a way for mel to confirm

his assumption but it's a great way and

you don't even need a voltmeter

i mean like a multimeter you just need a

voltmeter on your panel and

obviously all engines should have a

voltmeter

on the dash and your house battery has

to have a voltmeter if you don't you got

to get one

and then just simply even without a

multimeter look for behavior

do a change and look for a consequence

right and that's how you're able to

confirm and this is how i confirm on a

lot of our boats when we do electrical

audits that's how i confirm

what does what not even by looking at

the wire because ultimately

sometimes it's pretty complicated

looking at behavior looking at changes

so that's a great question from mel and

it's not a simple answer because

over time boats have been modified

adapted to meet different needs

but it's good to be curious and good on

one to melt again if you have stories

about your boat and how crazy or great

it was on your boat and why you like

your boat or don't like your boat set up

in terms of

charging from alternators post it down

below share

we all learn from that and this is the

purpose of this boating tech talk

channel

thanks for watching everyone i

appreciate it thank you for watching

this pys video

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again for watching

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