Dual battery system

[Ted]

Hi all,

I've been in the process of installing a a dual battery system. I didn't see the need to be able to link the batteries so I went for 8 gauge power cable and 40amp breakers.

I had assumed that the isolator would disconnect the link as soon as the engine stops running but it appears that it stays linked for some time after. The documentation states to turn the lights on while testing to drop the battery voltage enough to disconnect the link.

My question is if the engine is stopped and restarted shortly after, before the isolator has disconnected the battery, will that blow the 40 amp fuse or circuit breaker?

Thanks for reading!

[Mayhem2015]

I don't think it will blow it. I can't remember the specs on mine as far as cable amps etc but the isolator keeps feeding the aux battery till the main battery drops to 12.8 or something. So it is normal for the isolator light to stay on once parked and for a period of time.

The isolator should also limit the power heading to the aux and therefore not blow anything.

That is my take on it assuming I have understood your post correctly.

[ag9111]

No
It will not blow

[kitemanwest aussie]

Providing your start battery is well charged....no.
But it might if the aux battery is flat and the alternator tries to pump 100amps into it on recharge. But realistically that may not happen either as 8 gauge will current limit thanks to voltage drop and not properly charge the aux battery.

[snakesoup]

other way round I think, if your start battery is low, it will try and suck more amps from the aux and blow it, maybe it's hard to say

[Ted]

Thanks guys, I might need to reconsider the cabling size.

[irwazza]

other way round I think, if your start battery is low, it will try and suck more amps from the aux and blow it, maybe it's hard to say

Ahh, No. If the starter battery is low then the isolator won't allow current to the aux battery....

[ag9111]

I run that size fusing and cabling on my last vehicle for 155,000km.
Not a problem.

[Ted]

I run that size fusing and cabling on my last vehicle for 155,000km.
Not a problem.

Thanks, that's good to know. I figure that as soon as the starter motor starts cranking, the voltage on the starter battery will drop and the VSR will un-link the batteries, so it would only be a second or less that they are connected. I just wasn't sure if that would be enough to blow a fuse, or circuit breaker.

[snakesoup]

other way round I think, if your start battery is low, it will try and suck more amps from the aux and blow it, maybe it's hard to say

Ahh, No. If the starter battery is low then the isolator won't allow current to the aux battery....

ahh yes, you would be right on that front, my bad

[Maxiy]

HI ALL

Looking for some advice (i know jack about electrics)

Can anyone tell me if the below will work.

[kitemanwest aussie]

yes it will work if you want nothing to work and want to let the smoke out of the cabling.

[Maxiy]

yes it will work if you want nothing to work and want to let the smoke out of the cabling.

hahah very helpful kiteman

so what is wrong with the proposed ??

As i said, i know nothing about electrics so need all the help i need.

[NowForThe5th]

so what is wrong with the proposed ??

Nothing, if you want to let the smoke out.

What you'll need is something like this:

2nd-batt.jpg

Is your "isolator" some kind of management system or just a switch? You really should have something in there to stop the 2nd battery draining the starting battery. Even if it's just a simple VSR.

Note you'll need to modify that battery box to fit leads to an Anderson plug. Those systems are not really ideal for permanent connection in a vehicle, particularly if you use a lead/acid battery that could give off fumes while charging. So, you'll likely need an AGM battery.

[Maxiy]

Thanks 5th

appreciate the input.

Yes it is a simple VSR, and i will be using an AGM battery so fully sealed.

I have been reading that newer model trucks will not have enough charge rate off the alternator, 13.8 or something, while to get the best battery life you should be charging your battery upto 14.8. So thats why people use a DC/DC charger in the dual battery setup.

Is that right?? or will i be fine with charging the battery off the alternator through a simple VSR ?

[NowForThe5th]

No worries.

Batteries don't charge off volts, they charge on amps. So, as long as the voltage is within the range and the battery/alternator can supply the amps then the battery will charge.

Volts are used as an indication of remaining charge in a battery so the VSR will stop charging the 2nd battery when voltage at the main battery falls to a predetermined level, thus saving your main battery so you can start the engine the next morning.

There are about a thousand different opinions on this whole subject but what I have is basically a VSR with some "smarts", feeding into an AGM in the back. Works perfectly and I think that, to some degree, keeping it simple has lots of benefits in terms of reliability.

[Atmce]

Im new to all this so if i want to run a dual battery set up in my tub with a drawer sytem fitted. To run a fridge and camp lights. Csn i run a setup using vsr isolator from main battery to dual in the tub or is the distance going to be a problem.

[darreljourgenson]

Im new to all this so if i want to run a dual battery set up in my tub with a drawer sytem fitted. To run a fridge and camp lights. Csn i run a setup using vsr isolator from main battery to dual in the tub or is the distance going to be a problem.

I'm in the same position as you but having scoured this forum, I think it will be fine as long as you use big cable (6b&s) to keep voltage drop to a minimum and have a circuit breaker at the starter battery and the auxiliary battery ends. Someone please correct me if I'm wrong!

Sent from my SM-N910G using Tapatalk

[jamielaw]

hi all
has any one used this?
https://www.ebay.com.au/itm/Mitsubishi- ... Sw-EJZ3eCE



just looking for some advice seems small

thanks

jamie

[har05l]

Im new to all this so if i want to run a dual battery set up in my tub with a drawer sytem fitted. To run a fridge and camp lights. Csn i run a setup using vsr isolator from main battery to dual in the tub or is the distance going to be a problem.

I'm in the same position as you but having scoured this forum, I think it will be fine as long as you use big cable (6b&s) to keep voltage drop to a minimum and have a circuit breaker at the starter battery and the auxiliary battery ends. Someone please correct me if I'm wrong!

Sent from my SM-N910G using Tapatalk

This is correct


Sent from my iPhone using Tapatalk

[Quinny]

So ... this morning I get a waft of rotten eggs - "far out, that stinks", I thought I go get on with my day ...

This afternoon, I park the car in the garage at home - fffeeeuuuwww Then I realised what it was ... aux battery is cooking

Missus is real happy with me too, as it's stunk out the house ...

Until I can get the thing to a shop to get it replaced, I'm thinking I'll remove the negative lead to stop it from charging. I don't want the positive lead flapping around in the engine bay live (via the VSR).


How does that sound for an idea ?

[ag9111]

Sounds good

[Quinny]

I just wanted to confirm it's a negative earth ...

Thanks mate ...


Q

[Quinny]

Damn thing looks ok ... Less than two years old Damn batteries ...

[ag9111]

Get the charging system checked out. You never know, the battery may not be the cause of the problem, only the symptom.