Anyone 'always starting from both batteries' Redarc SBI12?

[MyGU8]

Hello All,

Has anyone using https://www.redarc.com.au/handy-hints/wiring_guides/always_start_from_both_batteries/
to always use both batteries to start.

I currently have this setup in my Patrol, but contacted RedArc and they advised that Inrush current is for less than about 2secs, I haven't cranked more than 2 secs to start.

But just wondering anyone else is using the same setup.

Regards,

[BigRAWesty]

You gotta remember that your niw drawing off 2 batteries.
So if it takes 300A to turn it over each battery is only needing to produce 150A.

[MyGU8]

Ah.. why I didn't think of that....

Thank you Kallen. From memory (tech manual) the starting current is only 140A, so the cranking battery can go as low as 40% of the aux battery before the SBI12 overloaded.

Cheers,

[Cuppa]

Whilst it is possible - what is the point? I can’t see any benefit. Being able to parallel both batteries for emergency jump starting yes, but why the need for a relay & starting from both as the norm?

[MyGU8]

Hello cuppa,
Although I have dual battery setup I don't run anything off from aux battery, my purpose of dual batteries is to make sure there is always a good battery available for starting. I also don't have any major battery draining equipment other than audio amp. My plan is to replace my cranking battery with a dual purpose cranking + deep cycle battery later on.

I can also regularly monitor how long it is taking for SBI12 to kick in to start charging the aux battery so to manage the cranking battery condition.

[the evil twin]

snip...
I can also regularly monitor how long it is taking for SBI12 to kick in to start charging the aux battery so to manage the cranking battery condition.


That won't give you an idea of the Cranker condition.

VSR's like the Redarc SBI12 will NOT priority charge a low Cranker.
What they will do very effectively is isolate a battery so a downstream battery/load doesn't drain the upstream battery

Typically an Alternator can put out more current than your Cranker will accept (Charge Acceptance Rate or C.A.R.).
As an example, assuming no other loads like headlamps etc, if you have a 90 amp Alternator and a 105 AH battery the Battery has to have a C.A.R. over 90 Amps before the Alternator voltage will fail to reach the pull in voltage of the VSR

The C.A.R. of a 105 AH Lead Acid that is deeply discharged, lets say 50% ish is much less than 90 Amps

So, normally, no matter what the 'condition' of the Cranker as soon as the Alternator voltage rises above 13.5 (typically for most VSR) then the VSR will pull in regardless of the Cranker condition

[the evil twin]

Hello All,

Has anyone using https://www.redarc.com.au/handy-hints/wiring_guides/always_start_from_both_batteries/
to always use both batteries to start.

I currently have this setup in my Patrol, but contacted RedArc and they advised that Inrush current is for less than about 2secs, I haven't cranked more than 2 secs to start.

But just wondering anyone else is using the same setup.

Regards,

Well, that is an absolutely shit page from Redarc because of the lack of an explanation.
IMHO the idea has merit in some applications but not most others and they don't explain the difference.

If the Aux is a similar or higher rated Battery AND up to capacity then OK.
If the Aux is depleted then it is a shit idea as the Cranker will try and equalise the charge between batteries AND start the engine.
If the Aux is significantly smaller or is an exotic with low discharge rating then it is a shit idea as it will load the Aux

Like Cuppa I also don't see the point of the relay.
The blue wire is a relay input anyway so you may as well just connect it to 'start' without a relay
In a 'normal' installation the blue is connected direct to 12 volts via a switch to parallel the batteries

Bottom line is I am either missing something or why would you want to do it?
Only relevant application would be if both batteries are dedicated to SLA IE the Aux isn't running Camping Gear, Fridges etc.

[threedogs]

Joining the two your motor would spin like a top.
On my other 4x4 I had a toggle switch in case the
Main starter failed, flick the switch the 2 are joined.
I never left them joined though.
You may be better off with a starter jump pack or those small
hi CCC battery starters

[MyGU8]

ET / TD,

Point(s) noted, but in MY case, my intention is to consider aux battery as the cranker, as I mentioned in my post above, I am also planning to convert the start battery to a dual type (cranker + deep cycle).

My current setup doesn't have any aux items connected to it, so it is a standalone battery used only for startups (Marine Pro 730).

In simple terms, it doesn't really matter which battery is dead as long as both batteries are connected when starting ( which is the idea of SBI12 anyway).
In usual setups the only advantage is that the starter battery has the priority when charging, so in my setup if I can make sure (monitor through red LED) that the aux battery charging period is equal or very closer to the period of that of the start battery, then I can be confident that the aux battery will be in good nick when I need starting, of course given both batteries have a same or close enough AH rating.

[MyGU8]

but why the need for a relay?

I think I didn't answer this question;

reason: the main advantage of the SBI12 - Isolation.
Because I am using the main battery for all my power usage when the batteries voltage reduced to a certain level then the aux battery will be disconnected, this ensures that the aux battery will be available to start, and why always? because I am using the main battery for my power usage it gives a slight advantage in not overloading the start battery when cranking after some time of usage of my main battery. And again I don;t have any major power hungry aux equipment in my trol, it's just the radio and amp and internal/external lights.

[the evil twin]

snip...

think I didn't answer this question;

reason: the main advantage of the SBI12 - Isolation.


The relay that Cuppa and I are talking about is the 'extra' one in the circuit not the SBI12.

There is no point that we can see for it.
All it means is you will be using a relay to switch a relay

[MyGU8]

The relay is to connect the blue wire to the aux battery positive not the start battery positive, and I am not entirely sure how the Redarc internal electronic system works to see whether I can connect this to start battery positive.

And it needs isolation for the red LED too...!

[the evil twin]

The relay is to connect the blue wire to the aux battery positive not the start battery positive, and I am not entirely sure how the Redarc internal electronic system works to see whether I can connect this to start battery positive.

And it needs isolation for the red LED too...!

The 2nd relay is switched by 'start' voltage at the starter solenoid
That voltage is from the Starter Battery via Ign switch
If the voltage is sufficient to pull the 2nd relay then it will be sufficient to pull the SBI12
If the voltage is not sufficient then it won't pull the SBI12 anyway.
If the voltage drops below the SBI12 low voltage cutout under cranking load the SBI12 will drop out anyway.

The vast majority of users will be running accessory loads off the 2nd battery not the Cranker such as you are doing.
Nothing wrong with that, I'm just saying your setup isn't in the majority.

As for the LED isolation I don't quite understand what you mean

Bottom line... it isn't any different to a switched system ergo the comment of I don't quite get why the relay is there

[MyGU8]

it isn't any different to a switched system

The switch system connects the blue wire to the aux battery not the start battery, as I said before I am not sure whether this is because the start battery may not have enough voltage to trigger the solonoid so need to connect to aux battery or for any other reason.

I am not trying to defend Redarc's circuit, but only trying to be a bit extra careful on things that I don't know fully yet.




As for the LED isolation I don't quite understand what you mean


Please ignore..




If the voltage drops below the SBI12 low voltage cutout under cranking load the SBI12 will drop out anyway.


I believe, this won't happen in overriding mode



The vast majority of users will be running accessory loads off the 2nd battery not the Cranker such as you are doing.
Nothing wrong with that, I'm just saying your setup isn't in the majority.


I totally understand that, you can think this as a setup where all the ACC connections are moved to an aux battery and you are using the start battery just for cranking.
Rather than doing this, I use my aux battery for starting only, the only difference is I use both batteries for starting which may put a slight additional load on the aux battery if the start battery is drained too much.
And again i don't have any accessories which will drain either battery too much.

The reason for my dual battery setup is, once my battery went flat when the hood light was left on overnight and I also turned on the radio in the morning before cranking (this was in my ex CRV). So I had to push start the car with very helpful neighbor campers. But I can't imagine doing a push start of my manual patrol.

May not happened to anyone yet, but I believe in 'NORMAL' connection there's always a chance that even with the isolator installed you can drain both batteries as there are still several things connected to the start battery, which if not careful will drain the start battery.

Thanks for this informative discussion.

[Rossco]

I've got mine hooked up to a manual switch in the car with the idea of using it for winching and starting if the cranker is down a bit for whatever reason. Haven't really had the chance to user it yet but happy with the setup / idea of it. You can run the blue wire through the ignition so it's powered every time it's in the start position, but don't know if i really like that idea much- would rather have manual control over it.

[Winnie]

I've got mine hooked up to a manual switch in the car with the idea of using it for winching and starting if the cranker is down a bit for whatever reason. Haven't really had the chance to user it yet but happy with the setup / idea of it. You can run the blue wire through the ignition so it's powered every time it's in the start position, but don't know if i really like that idea much- would rather have manual control over it.

Quick question for ET or anybody else who knows.
I've been wanting to do the same setup as Rossco and run a 25mm cable between the batteries (redarc inbetween) for winching. Is this going to be pointless if my winch has 70mm cable going to it? Is the winch going to be able to draw enough power from the 2nd battery?
My thinking is it will take the majority of its power from the main battery and maybe some dregs from the 2nd battery through the 25mm cable, making it seem kinda pointless.
At the moment I have 8B&S cable and the blue override cable is not connected.

[MyGU8]

Winnie, when two batteries are connected in parallel, it is hard to know how much current will be drawn from each battery as it depends on several factors.

If you are using 25mm wire between batteries and the winch is drawing more current from aux battery most likely the wire will burn.

The wire size does not limit how much power can be drawn from a supply. If the battery is capable of supplying the current required regardless of the wire size the current will be drawn, but it will overload the wire and possibly burn as said before.

[the evil twin]

Hiya Escix, I totally understand where you are coming from and I'll try another way to explain.

Hypothetical situation - your Cranker won't start the Car or is really lazy

With Jumper Leads - first thing you do is jumper in a good battery (your Aux or another vehicle) to the Cranker and wait before attempting a start.
The reason is you want the Batteries to equalise at least a little so the good battery doesn't have to try and crank the engine and equalise the low battery all at the same time

With a Redarc wired as per their normal configuration - first thing you do is flick a switch and that connects a good battery (your Aux) to the Cranker and wait before attempting a start.

With a Redarc wired as per their hint - it won't pull in until you try and crank then the Aux and the Redarc is under a much higher load trying to crank the starter and equalise the Cranker which isn't a real good idea.

Personally (I am guessing here) they have included that tip sheet for the rare configuation of auto switching dedicated twin cranking SLA batteries
IMHO if you were running your accessory load off your second battery go for it but as you are running down your Cranker I wouldn't.

I would, in your case however, seriously consider running the Redarc trigger from "Ign On" instead of "Start".
Why?
That way the second battery will assist with the Glow Plug current and equalise the Cranker at least a little bit before you start cranking

[MyGU8]

Hey ET,

A real good one.

Thanks for taking the time on this discussion. I highly appreciate it and hope this will help someone down the track with the same thoughts.

I will reconfigure my setup with a switch when I get a chance.

In saying that, is equalize required/possible in dual batteries (without an engine running like in jump start)
Sorry.., Point noted, when the crank battery voltage is lower...!

[Cuppa]

The reason for my dual battery setup is, once my battery went flat when the hood light was left on overnight and I also turned on the radio in the morning before cranking (this was in my ex CRV). So I had to push start the car with very helpful neighbor campers. But I can't imagine doing a push start of my manual patrol.



Fitting a VSR like the SBI12 is precisely to avoid this sort of problem. In normal configuration it prevents draining of the crank battery by aux accessories which you don’t have. I understand you having a second battery as a back up, but must still be missing something. I cannot understand why you would want to use the aux as the primary cranker & the primary cranker as the aux. If you fitted the SBI12 conventionally then in the situation as you have described you would be able to jump start your car from the aux battery simply by flicking a switch. That switch would connect the blue SBI12 wire to earth, which operates the SBI12, paralleling the two batteries. Using the relay will parallel the two batteries every time you start the motor ..... what is the benefit & if no benefit you are only adding a component into the system which is unnecessary, & just something extra to fail.
If the relay is activated by the accessories position of the ignition switch, although you will have double the the battery capacity, you could still find yourself with a flat battery unable to start the car.

I have posted the following on Redarc’s forum.

I am involved in a forum discussion about the SBI12 setup as shown on your website link below.

https://www.redarc.com.au/handy-hints/wiring_guides/always_start_from_both_batteries/

Please can you explain the purpose of this setup & in what circumstances it would be used? I’m struggling to see the point.

Thanks

[MyGU8]

Thanks for taking this with Redarc cuppa,

The reason for using the aux for every start is basically I don't want to 'have' something and not using it. Every battery has a lifetime regardless whether used or not, so no point having an aux battery and not using it.

I may put an override switch, but what if I ever not needing to use it...? (Hope it is correct English)

And by using it, I believe I am at least doubling the lifetime of the cranking battery.

Or is this not right

[the evil twin]

The biggest single factor of many in determining a standard lead acid battery life is time spent at full state of charge where hard sulfation is minimised.
In the real world keeping the battery above 95% SOC is about the best you can hope for.
So, yes, you will probably extend the life but no where near double.

[Cuppa]

Thanks for taking this with Redarc cuppa,

The reason for using the aux for every start is basically I don't want to 'have' something and not using it. Every battery has a lifetime regardless whether used or not, so no point having an aux battery and not using it.

I may put an override switch, but what if I ever not needing to use it...? (Hope it is correct English)

And by using it, I believe I am at least doubling the lifetime of the cranking battery.

Or is this not right


I guess you are talking about ‘exercising’ a battery to prolong it’s life.

If that is the case the same could be achieved by powering something off the aux now & again. Those who believe the ‘exercising’ myth for lead acid batteries generally agree that they need to be be placed under moderate loads & discharged to around 50% now & then. Paralleling your batteries to start the vehicle will not do this but permanently paralleling them & powering everything off them both might, but it would be pointless having an isolator if that is what you were doing.

In my experience & from most of my reading batteries will last longest if kept fully charged/floated. Some deep cycle batteries kept floated for standby use can have lives exceeding 20 years. This is why the ex telco batteries are often bargains for folk setting up stand alone solar systems. The deep cycle batteries in my bus were over 8 years old when I sold it last year & still performing faultlessly. I expect them to have a number of years life left in them still. They were used daily for 18 months, but never discharged below 12.3V & fully recharged every 24 hours. The rest of their life was spent being floated (fully charged) except during occasional short trips away.

To prolong the life of your aux battery the best treatment is to keep it fully charged & when used to minimise the discharge & to recharge it asap.

The problem with using a VSR like the SBI12 is that both batteries are being charged direct from the alternator & will not reach much more than 70% to 80% charge, which is fine for starting a car, but not ideal for long battery life, hence the average crank battery life of around 4 years. You can expect the same from an aux battery which is used, & charged via the SBI12. If the aux battery is an AGM type rather than ‘wet’ battery you could expect a better life span as the aux, if unused, would charge a bit each time you drive, & because of it’s lower self discharge rate would gradually get closer to 100% charge. If driven *very* regularly & for long periods the same could be achieved with a wet aux battery, but it would also require regularly topping up as charging a wet battery to these levels causes them to bubble & gas, which will see fluid levels drop.
To *fully* charge an aux battery to ensure max lifespan generally requires a smart charger particularly if the battery is used or if it is a wet battery with it’s higher self discharge rate. The smart charger is generally one of three types. A mains charger connected & plugged in on a regular basis (weekly at least), a solar regulator if solar input is available, or a dc to dc charger between the crank battery & the aux battery, in which case it also provides the isolating function currently provided by the SBI12.

Of course if the aim is just to prolong the life of your existing aux battery it may not be worth spending the price of a replacement battery on a smart charger in the short term. In the longer term it’s a different story. If wanting to simply get the best aux battery life possible with what you already have my choice would be to connect the aux ‘conventionally’, & not use it unless needed for emergency jump starting.

If you plan on buying a deep cycle battery in the future to power your audio, I would choose to have it as the aux & would fit a dc to dc charger. Their are arguments for having a wet deep cycle if mounted under the bonnet, but this will require regular maintenance. My preference would be a AGM. Although some claim they are less tolerant to heat, they charge more quickly, self discharge less & importantly don’t require you to top them up regularly. If you can remember the weekly check/top up, (most people don’t) then a wet deep cycle may suit better.

[MyGU8]

@ET, sorry 'extending lifetime' is actually what I wanted to mean, but wrote double instead.

@cuppa, thanks for the helpful post, what I really meant was extending the 'cranking battery' not the aux battery.
In my case both batteries are given minimal attention (just look and add water as required, and it is done by the service people) so by using both batteries I believe I can extend the cranking battery lifetime, not significantly, but worth compare to not using the aux at all.

[Cuppa]

by using both batteries I believe I can extend the cranking battery lifetime, not significantly, but worth compare to not using the aux at all.

I think we may need to agree to differ on that, although I’d be happy to read anything which supports your belief.

[the evil twin]

I think we may need to agree to differ on that, although I’d be happy to read anything which supports your belief.

Hiya Cuppa,
He may, assuming all other factors are equal, get a slightly longer life as the batteries may spend less time at lower SOC.
Be really hard to quantify it tho.
Like you I don't hold to the 'exercising' school of battery management for Lead Acids myself but pffft no biggee.
Agree, the best way to get long life is to keep a good SOC and zap 'em with a smart charger every 3 to 6 months or so.