Dual battery install help

[YRPsycho2 Lurker Find all posts View Profile Close YRPsycho2]

G'day all,

If this as been answered somewhere before, please forgive me. I have looked, but the answers seem to allude me.

Some very brief details....
2000 model Diesel, and not much done to it just yet The dual battery was installed by me, so I could have made a beautiful mess of the whole thing.

In short, this is a charging question. So, I will ask without the detail, as someone may know the answer without having to go into it all. Is there a voltage sense wire that controls a switching circuit for the alternator? And which wire is it?

In long. I installed a dual battery system (according to the diagrams supplied with the solenoid), and all appears to be working correctly (which may sound odd, but will hopefully make more sense as I go on). The crank battery and auxiliary are isolated, and remain that way until the crank battery reaches the voltage to close the solenoid. I know this all works, and I know the alternator is no dead because when I connect the accessories back on to the crank battery, the alternator starts charging, and after the voltage is reached, the solenoid closes connecting the auxiliary battery. This leads me to believe I need to connect a sense wire to the cranking battery.

The only thing that I can think of is that I need to flatten the new auxiliary battery so that it reaches the point where the charging circuit is started. I only see this could defeat the purpose of having an auxiliary battery, as if I do a lot of starting/stopping in a short period, then I have he potential to flatten the cranking battery before the auxiliary is at a point needing charging.

I hope that all makes sense, as I am off work with lots of pills floating around my head to try and make it a little clearer. Anyway, here are some pictures if people are interested. And before someone says "That box isn't waterproof because you have put holes in it", well I wasn't going for a waterproof box, I just needed a barrier to stop the risk of someone (most likely myself) shorting the cables to ground. I don't like vaporising tools, or setting vehicles on fire.




Thanks for looking, and helping.

[Schaffer Addicted PP Member Find all posts View Profile Close Schaffer]

Re: Dual battery install help

So you are saying that normally the alternator isn't charging the battery because it's detecting that the primary is fully charged? That is normal as a means of prevent overcharging of the battery.

If you have concerns about the auxillary battery not being fully charged then place this onto a good multi stage battery charger. I can't think of anybody who would not recommend doing this to ensure that your battery is fully charged. If you don't then you are shortening the amount of power that can be pulled and potentially shortening the life of your battery.

[YRPsycho2 Lurker Find all posts View Profile Close YRPsycho2]

Re: Dual battery install help

Hello again,

Nothing like a good first post to highlight how dumb I am.....

I was concerned about the cranking battery not being charged (which it wasn't). But then my brain decided to work and I realised that it charges through the same lead that the auxilaries run off (I will change this one day, but not today). I just changed the side the solenoid senses so that it closes. Not ideal, as it means the Aux gets chrged first, then the crank (but it will work for the short term).

I would have put in a better system, but I was limited to a budget that the Minister had approved.

Thanks.

[Guest Close Guest]

Re: Dual battery install help

Mate,

I think you must have way too much time on your hands to worry about stuff. If you have fitted the system as it was intended then it should all work fine. The alternator will detect when charge is required to the starting battery first then the auxillary.

The only way the auxillary battery's life is shortened is if the starting battery's capacity drops and the auxillary begins to take up the slack. My starting battery was dying and I didn't even realise until I tried to use the auxillary battery to start the truck and nothing.

If in doubt I suggest you contact an auto electrician or 12 V specialist.

[drivesafe Senior Member Find all posts View Profile Close drivesafe]

Re: Dual battery install help

Hi YR, do you by any chance have a multi meter, if not, it would be a good idea to go buy one of those $10 jobs, it will probably be one of the best investments you can make.

If you have a multi meter, before starting your vehicle, measure the voltage at both batteries then start the motor and let it idle for a minute or two then measure the two batteries again.

Post up what you find once you have done that and we will see if we can help sort it out for you.

Cheers.

[YRPsycho2 Lurker Find all posts View Profile Close YRPsycho2]

Re: Dual battery install help

Hi All,

I have figured it out. The alternator connects back to the battery via the fuse box, where is bussed on the auxiliary circuit. And unless I break out the circuit from the box, the crank battery will not charge first (I would be curious to know if others that are using a solenoid to do this job have had the charge circuit separated out of the fuse box).

Unfortunately, after already having a car fire due to dodgy electrics, I prefer to be sure (so worry is fine with me).



This is a very rough drawing of what I found going on. The only way to get the crank battery charging first is to separate out the alternator fuse in the box and run a new cable to the cranking battery. I am pretty certain this drawing is correct, as I buzzed it out.

[Corigator Avid PP Poster! Find all posts View Profile Close Corigator]

Re: Dual battery install help

Hi YRP,

I'm no expert, but it seems to me that the cranking battery is in the wrong position in that circuit. If you want the cranking battery to charge first it needs to be on the alternator side of the soleniod/relay/isolator.

Cheers
Greg

[LeighW Avid PP Poster! Find all posts View Profile Close LeighW]

Re: Dual battery install help

Generally the Alternator will wire back to the fuse box then via the Alternator fuse to the bus bar then
to the positive terminal on the cranking battery. ie there will be a heavy cable going from the positive
terminal of the cranking battery to the starter motor, and a smaller gauge wire about 100A
going back to the fuse box bus bar.

To install the isolater all you need to do is run a heavy cable from the positive terminal of
the cranking battery to the isolator then to the positive terminal of the aux.

Then run a heavy cable from the negative terminal of the cranking battery to the negative
terminal of the aux. And possibly some other minor wiring to pick up ignition etc depending
on the isolator being installed.

Cheers
LeighW

[tinkera Member Find all posts View Profile Close tinkera]

Re: Dual battery install help

Ditto LeighW.I cannot see why you would be playing around in the fuse box to install a simple solinoid :? or am I missing something. TINKERA.

[YRPsycho2 Lurker Find all posts View Profile Close YRPsycho2]

Re: Dual battery install help

Um........

Lets see...... The original configuration:

1 Battery (which has 1 +ve and one -ve terminal)
One heavy gauge cable from -ve terminal to engine block
One smaller gauge cable from the -ve terminal to the chassis
One heave gauge cable from +ve terminal to starter - This has one purpose, and it is to supply power to the starter, there is no return on this cable (ie charging).
One smaller gauge cable from +ve terminal to fuse box - This supplies power to the accessories, but also has the return from the alternator charging circuit
No other cables are going to the battery.

Now, the cable and interest point is the smaller gauge cable coming from the fuse box. The alternator charges via here so that the accessories are getting power straight from the alternator before going into the battery. The "left over" charge is then absorbed by the battery (in the original configuration). In order to move where the charger connects into the system, I need to break a bus bar, and run a new cable from the fused side of the charge circuit to the crank battery.

If I had 3 cables going to the +ve terminal i.e. crank/acc/charge, there would not have been any question. But there is only two. If you have a 90 series, and a dual system, have a look if the fused side of the charge circuit has been moved from the bus bar in the fuse box and placed onto the crank battery.

Simple way to check this would be, place a meter on the crank battery and start the vehicle. Is the charge voltage present there to start with? If you are lucky enough to have 2 meters, place one on each battery to see where the charging voltage is when you initially start the vehicle. If anyone is in or near Canberra, I could do this, and it would help me see what has been done.

Perhaps I should note that I am using a Redarc SBI212 as the solenoid. So it waits until Batt 1 is charged (or at least within a certain voltage range) before connecting Batt 2 to the system.

I am happy with how my system is set up, and as I said, it is not ideal but it is working for the moment. It will cause a problem should the Aux battery start to die, but I will bomb that bridge when I get to it.
Anyway, here is a picture of the bus bar. You will notice that it connects to a cable, and this is the accessory cable that returns to the battery. In order to make the crank the first battery charged, this bus bar needs to be broken, and a new connection from the 100A fuse to the crank battery needs to be made.



P.S. If I am wrong, can someone please show me pictures of how they did it (or how someone they paid did it). I am suspecting that if it is a paid for system, that the installer has said how it should run, but this is different to how it is running.

[LeighW Avid PP Poster! Find all posts View Profile Close LeighW]

Re: Dual battery install help

Hi YRPsycho2,

I see what your trying to do but it will be a lot of effort for little gain.

The way these systems usually work is the cranking battery is charged first
to around 13.5V. The isolator then connects the Aux for charging in parallel
with the cranking battery.

As the cranking battery is usually fully charged and only used to start the car
it should only be a matter of seconds before the isolator connects the Aux for
charging.

As a general rule you always want to charge the cranking battery first to make
sure you can start the car.

The danger in wiring the way you have is as you have written in that if the AUX is always
down unless you run the car for very long periods the cranking battery might get little charge and
you could end up with both batteries flat and going nowhere.

Hence why it is better to give some charge to the cranking battery first before
connecting the Aux for charging.

Far better and simpler to use the normal config and just connect all new accessories to the AUX.

If you want to get maximum charge into the aux in the shortest time I would suggest
you take a look at the Rotronics independent charging system. It charges
the cranking battery to a certain point then connects the aux for charging.
Once it has determined the cranking battery is charged it then isolates the cranking battery
and all spare charging current is sent to the aux. This can speed up the
charging of the aux considerably.


Cheers
Leigh W

[Schaffer Addicted PP Member Find all posts View Profile Close Schaffer]

Re: Dual battery install help

Hey YR, I have pretty much the same Redarc solenoid that you have. What I have done is run a 16mm2 cable from the positive terminal on the crank battery to the input terminal on the solenoid. On the way it it passes through a fuse (100A from memory). The auxillary terminal of the solenoid is also connected to a 16mm2 cable that runs to the positive terminal of the auxillary battery. I have then also run a 16mm2 cable between the negative terminals of both batteries and a 16mm2 from the negative terminal of the auxillary to ground.

The way it works is the alternator is feeding power directly to the primary battery. The solenoid is also monitoring the primary battery through the 16mm2 cable between the +ve of the primary and the input terminal of the solenoid. When the primary battery voltage rises above 13.2v then the solenoid allows power to flow to the aux battery charging this as well. When the primary volts or flow through the solenoid drops below 12.7 then the solenoid disconnets the link and the aux is no longer being charged. This is how it should work as advised in the installation instructions supplied with the isolator:
Instructions Sheet
Product Flyer (Refer SmartStart standard installation diagram)
Basic SBI install

1 SBI with 2 auxiliary batteries.

Redarc Wiring Guides

I have also run additional 6mm2 runs from the auxillary terminal of the solendoid to a 4 fuse Narva fuse block mounted next to the solenoid. From here I then power the indervidual ciruits such as fridge, spotties, UHF, etc...

[drivesafe Senior Member Find all posts View Profile Close drivesafe]

Re: Dual battery install help

Hi YR, while your system is working then it’s probably not worth the time but you system does leave you open to a greater potential problem of ending up with a flat cranking battery then would be the case with a standard wiring set up.

Perhaps I should note that I am using a Redarc SBI212 as the solenoid. So it waits until Batt 1 is charged (or at least within a certain voltage range) before connecting Batt 2 to the system.

Another point, I know a lot of isolator suppliers state that their isolators will not connect the auxiliary battery until the cranking battery is fully charged.

Unless your vehicle is fitted with an alternator that is no bigger than about 40 amps, this is just not the case. Unless the dual battery system actually separates the cranking battery from the vehicle’s electrical system ( and some of the very expensive systems do ), no isolator can have the foggiest idea of whether the cranking battery is fully charged or just had enough to start the vehicle and is then flat.

Nearly all isolators work by simply monitoring the input terminal’s voltage and when this voltage rises above 13.2v ( on newer isolators ) the isolator cuts in and connects the auxiliary battery(s) to the vehicle’s cranking battery.

No matter how low the cranking battery is, once the motor is started, the alternator’s voltage will take no more than about 60 seconds to rise above 13.2v

It’s that simple and because an alternator can easily charge two or more batteries at once, there is absolutely no reason for not connecting all the batteries as soon as the alternator voltage is up to 13.2v.

YR, one suggestion to improve your set up, run a new thicker alternator the cranking battery cable. Most vehicle makers, while installing large capacity alternators, they are not using 80+ amp alternators to give you all that power, the are fitting large alternators so that when the motor is idling and the alternator is not running at optimum revs, it will still be putting out a reasonable current, but this current might only be around 30 amps and this is all the manufacturers need to cater for.

Replace the alternator to cranking battery cable and you can give your whole system an improved current supply.

[YRPsycho2 Lurker Find all posts View Profile Close YRPsycho2]

Re: Dual battery install help

Replace the alternator to cranking battery cable and you can give your whole system an improved current supply.

Ultimately, that is what I intend to do, which will also cover the questions that I asked.

Oh well......

[drivesafe Senior Member Find all posts View Profile Close drivesafe]

Re: Dual battery install help

Ultimately, that is what I intend to do, which will also cover the questions that I asked.

Hi YR, the suggestion is to go directly from the alternator to the cranking battery, and don’t go via any fuses or the solenoid.

This will give you the shortest cable run, which means less voltage drop and that all equates to fast battery charging.