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hi everyone jeff gotti here

with boatingtechtalk.com

so we've got a fellow boater with

lithium batteries

asking uh some questions about what's

gonna happen

when my bms disconnects my batteries so

let's go through the question and this

question is from gary gary thanks for

submitting your question by the way i'm

installing four 170

amp hour 12 volt lithium

house batteries in parallel that are

combined with a 4d

agm start battery via a blue seize

automatic charging relay

so in this instance this boater has four

lithium batteries 170 amp hours each

and also has a 4d agm battery

each battery has its own bms which you

would expect

my concern is for a scenario where all

the bms is shut

off charging input will the agm

absorb the load without a momentary

disconnect from the alternator

causing the alternator to run without a

blow

a load blowing the diodes

by the way the regulator is externally

controlled with a

via balmar 614 any other red flags on my

install

well first of all gary very good

questions and you've been doing your

homework

clearly you've been reading online and

educating so

learn first and then do okay

so when you have doesn't matter that you

have one battery four batteries or ten

either way if one battery

potentially they could all behave the

same way so let's take

the confusion of having four batteries

out

and let's just have one lithium battery

and one agm battery

having four or ten is really the same so

when you've got a lithium

battery and an agm battery the question

is

how are you and where are you going to

connect your alternator to

because your bms on your battery might

at one day especially if you're motoring

for a long time and you don't have a lot

of loads

might say you know what enough that's it

not a mass it's my little spanish here

meaning

i can't do it enough can't do no more

so what happens in those situations well

when the bms disconnects the battery and

especially if it's a

sort of nominal battery that lithium

battery doesn't have a

charging post and a load post you're

going to

basically lose it all so your battery's

going dark

when that happens an alternator can

never

be disconnected when running ie when

turning

and now you when your engine is engaged

and turning

either at doesn't matter if you're in

idle or not as long as the engine is

actually turning your alternator is most

likely outputting

in this case this alternator is

controlled by an external regulator

and we have by the way love external

regulators

like i'm not joking love them pretty

neat perfect device

or close to it we've got lots of

articles on external regulators on our

website

again probably over a hundred if you

wanna geek out you can geek out on

external regulators i'm pretty

passionate about them

so this fellow has an external regulator

on his alternator

and he's worried and rightly so by the

way what's gonna happen if his lithium

battery

bank of four battery says enough well

what you want to do in this situation

is either you can do two things either

you can have your alternator be

connected directly to your engine

agm battery right and then you could

share

the alternator charging voltage to the

lithium bank

via one of these this is a battery

combiner

it's a device that basically puts two

battery banks in parallel whenever

there's a charging voltage

so that could be one option and so even

if your

lithium battery bank said no more that's

okay

basically the parallel link would lose a

battery but the alternator is always

connected to the engine battery so

that's one way

another way is if you're having your

alternator directly connected to your

house battery bank in this case a

lithium battery bank

well this is where it gets interesting

if you have a battery combiner again

connected between your engine and your

house battery

right what's going to happen if your

alternator loses its connection to

your house battery well it's very

possible in that moment when the bms

blocks off

you're hoping that this is going to stay

engaged but you know there's no promises

if this for whatever reason disengages

then you're hooked your alternator is

going to have no more connection to your

lithium bank and your alternator will

blow up

so instead of putting a battery combiner

another alternative would be to put a

battery isolator

battery isolator is sort of one input

going to two outputs

okay it's like a y right it is so the

alternator comes in

goes to two places lithium is here agm

starter batteries here the good news in

this situation is

even though the lithium battery might go

dark

and simply disconnect the battery

isolator will still

give a path to the agm starter battery

and your

alternator won't blow up because there's

still an alternative path

so really there's two ways to slice and

dice you have your alternator

go directly to your engine battery bank

and then have a battery combiner go to

your lithium

or you have your alternator go to a

battery isolator which in turn is

connected to both the lithium

and the atm battery so that's how i

would tackle this problem and

uh gary honestly your question seems

like you're doing a lot of your homework

and i bet this project is going to go

well for you yeah those were really good

questions and thanks for asking

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