dual battery with isolator or second alternator ?

[stockhorse]

This stuff is definately not my strong point.
I am wanting to run 6x 100watt lights (plus normal headlights etc) plus my 40ltr fridge and I don't think my standard alt. will handle it.

Second battery with own alt.(possible 100 amp) seems like a good idea. I would run all driving lights fridge etc from this battery/alt combination. I am thinking that this would mean starting is standard system and second battery/alt combination should be able to handle the demand and stay charged.

Would this be better than using and isolator and upgrading original alternator? I have a 60 series cruiser with H3 motor.

Thanks.

[drivesafe]

Hi stockhorse, before you do anything, what is the current output of your existing alternator?

[stockhorse]

It currently has a nippon denso 55 amp altrenator fitted.

[drivesafe]

Hi again stockhorse,Your 55a alternator is a tad small and it would be far simpler to just install a bigger alternator and an isolator. Leave all your lights powered from the cranking battery and run your fridge and any other accessories off the auxiliary battery.

The fitting of a second alternator can be a major job, just to mount the alternator, but you also need a to do some non standard wiring to keep the two alternator’s power outputs separated.

[stockhorse]

Thanks Drivesafe, I actually thought two alternators might be easier (the ambition of the uneducated hey!). A bigger alt and isolator it is then.Thanks for the help.

[its aford not a nissan]

why do you need to keep the alts output seperate ?

[-Scott-]

why do you need to keep the alts output seperate ?

How do you regulate both alternators if they both sense the same battery voltage? Best case I can see, one alternator will do all the work until it's maxed out, then the second will kick in.

[its aford not a nissan]

just thought i would ask as i fitted a 2nd alt on saturday and just hooked it up to the main battery same as the original alt , the alternaters are shareing the load with anything more than 5 amps running
the factory alt is regulated to 14.13 volts and the 2nd one runs at 14.1 volts , 5 amps seems enough to to bring down the volts (0.03 volts) of the main alt to get the 2nd one working
i got a bit worried as i could smell something burning when running all the lights , a/c , boss compressor, wipers etc , to see if it could keep up .
turned out to be a dry joint in the fuse for the headlights ( melted the fuse plug )
but so far everything seems to be working fine and i have 140 amps to play with , just need some more gadgets to connect

[suggy126]

The only reason i can see for Drivesafe wanting to keep the circuits seperate is so the standard alt runs the vehicle and the second alt runs all the gadgets, which would also work, and all it would mean is running a 8mm wire from the back of the second alt to the second batt instead of the start batt.

[MightyMouse]

Bosch state that its Ok to parallel alternators if ......

Quote from Bosch Alternator Catalogue......

Operation of alternators in parallel

If demanded by power requirements, alternators with the same power rating can be connected in parallel.
Special balancing is not necessary, although the voltage regulators concerned must have the same characteristics, and their characteristic curves must be identical.


I suppose what does it matter if they "stage" themselves depending on battery voltage. At the days end a high load will drop terminal voltage and so bring the alternators in as required.

[Hobzee]

Hi guys - I have similar situation and would welcome your thoughts.

I used to have race GU with 120 amp alt - issues with failing regs and not charging at idle - not sure I want to go there again.

Now got cheaper to own GQ wagon with std 4.2 carby pet engine and std alt - have to say that unit is much happier than the old race GU set up. This rig has no air con and so I have the space for a second alt. I have 3 batteries under bonnet. Purpose of rig is to set up events (Cliffhanger, pursuit, etc so lots of winching). My thoughts are to get a second standard alt. It would charge the 2 x aux batteries and those 2 need to be separated by some kind of dual battery system capable of big current draw (winch). When I do winch or need extra starting power I hit a solenoid switch that joins main battery to the 2 aux batteries. That solenoid could be powered by the winch overide button that runs the fan that keeps the winch cool and that same system could be turned on if I need starting assistance.

Bearing in mind it is not racing and winch speed is not essential. Does this sound like a plan? What sort of isolation should I run between the 2 aux batteries? Should the second alternator be std and have charge at idle?

[suggy126]

It does sound like a good working setup, but why not run the winch off the second pair, rather than the start battery and therefore having to have a big issolator?

With regards to the issolator though, you can get 200amp costant work solenoids for around $100.

For charging i'd definately recomend that the Alt charges at idol if you can, purely because when you're finished winching and are spooling cable or picking the parts you used the vehicle will be prepping itself for the next assault without you having the sit there with revs up to make it charge.

[Patroler]

similar situation and thoughts are welcome, i'm looking at running a second alt on a gq td42 under the power steer pump to charge a second battery...
My second battery would be a marine and would be used for a fridge, hf radio and some lighting at night - no big current draw.
The alt would just be an ultra common bosch from a holden 6 with internal reg at somewhere around 40-60 amps

My reasons for doing this are:
Keeps both batteries and charging systems totally seperate, negating the problem of dual battery controllers charging aux batteries not enough due to internal resistance differences
Handy if the main alternator dies miles from nowhere
Cheaper than a dual battery controller - if i forked out for the controller i'd still only have a 60a standard alt (not that i'd need much more but if i did, upgrading the standard alt with vac pump is pretty dear!)

Anyone think of any reason why this is a bad idea - given i can make the brackets up and get an alt for well under $100???

[fool_injected]

Just to throw a spanner in works
Why not run both set ups but with a manually switched solenoid
If one alt ever fails, manually operate the solenoid to keep charging both batteries

I run duals with a single alternator and solenoid. Basic set up no voltages sensing just a solenoid
I have hooked up a switch to manually operate the solenoid.
After starting and running for a bit switch it start charging the second.

If the main is running a little flat at starting I switch the solenoid to give a boost (effectively a jump start)
Not the best for Deep cycle batteries but it has saved me when I had a dodgey main battery

[drivesafe]

negating the problem of dual battery controllers charging aux batteries not enough due to internal resistance differences

Sorry Patroler but thats nothing more than a myth, if your main battery is being fully charged then your electrical system is working properly and therefore there is no reason why an auxiliary battery would not be fully charged, if installed and using your existing set up.

The only thing you would have to keep an eye on would be how much power you needed for other devices while you were driving, like driving lights and so on.

[Patroler]

negating the problem of dual battery controllers charging aux batteries not enough due to internal resistance differences

Sorry Patroler but thats nothing more than a myth, if your main battery is being fully charged then your electrical system is working properly and therefore there is no reason why an auxiliary battery would not be fully charged, if installed and using your existing set up.

The only thing you would have to keep an eye on would be how much power you needed for other devices while you were driving, like driving lights and so on.

Thanks for the reply, i see what you are saying, ive heard both stories about wether the aux battery will or won't fully charge, either way i'm sure that would be ok. As it is now both batteries (two cranking) are just wired in parallel, there is no controller - i want to run a marine battery and a cranking and as such don't want them parralled all the time, really it just comes down to if there is any negatives with running two alternators apart from the obvious extra load on a belt?

Talked to the mate who said no good to charge batteries in parallel and discussed why, his answer is that the different batteries have different float voltages, the crank battery may be lower and when it runs parallel that means the system will run at the lower voltage and not fully charge the aux battery
- my answer was that the alt is regulated to 14volts and the float voltages he's talking about are like 14.3 and 14.6 volts so regardless it will only run at 14 volts max
The other problem he suggested is that if the main battery starts to get stuffed it may start gassing - and stop charging before it gets to the voltage at which the isolator switches to charge the aux battery - causing the aux battery not to charge - this sounds a little reasonable considering it came from a guy with a tjm shop who often got people come in with dual batteries and complaining of stuffed aux batteries when the above thing was happening...
You pointed this out in you reply

if your main battery is being fully charged.

[suggy126]

One thing in defence of patrolers setup that drivesafe didn't mention, is that if one of your batteries fails with only one alt, the failed battery will suck all the charge even though it never actually properly charges.
When a battery fails by dropping a cell or getting old it's internal resistence doesn't rise as it charges, so if both batteries are new it's fine, but if one drops out the good battery will never get a good charge, this also happens when one gets old, so if say your deepcycle is on it's way out, it'll take all the charge and you start battery will suffer the concequences.
So at least by putting in 2 alternators you don't run that risk as both setups are on their own charge circuit.

So yes to Drivesafe, if we lived in perfect world, a second alt would be a waste of time, but we know we don't live in a perfect world, and if your alt is gonna fail, it's gonna do it where you can't get spares, so a second alt would definately be a better idea, especially if you can do it relatively cheaply.


Michael

[drivesafe]

Hi patroler, your mate wants to stick to being a salesman.

For a starter, float charge is not available on normal alternator equipped vehicles and the only vehicles that have intelligent charging are new Land Rovers and Jags.

Next, even with high tech batteries, a float charge would be 13.2 to 13.7 at the highest.

For any vehicle to be able to fully charge ANY automotive battery, the operating voltage must be 13.8 or higher.

So if your vehicle is running at 14 volts, your will have no problem fully charging any automotive battery.

The one thing that governs whether a battery is going to be fully charged and is the one thing the self proclaimed experts fail to grasp, is the amount of driving time.

Depending on how low your battery is when you start driving, if you don’t drive long enough, sure your battery is not going to be fully charged.

It’s not that your set up can’t fully charge all your batteries, it’s whether you give your set up enough driving time to allow it to fully charge them.

[drivesafe]

Hi suggy126, if a battery cell collapses in such a way that it draws the sort of current that you are talking about, then the likely hood that the vehicle could actually be started in the first place is very remote and even if this type of failure were to occur after the vehicle was started, the problem would be realised very quickly as the vehicle’s electrics would start to fail through lack of power.

[chimpboy]

Basically no system is any good if you don't take care of your batteries and replace them when they are on the way out.

[suggy126]

I agree they would, assuming you have a vehicle relying heavily on it's electronics.

I should have been more clear though, if one battery has failed it won't kill the vehicle instantly, but say you second batt (deep cycle or otherwise) has failed, the vehicle will still start but it will shorten the life expectincy of your start battery.
Also the big plus to having twin alts which i obviously didn't press home is in the case where your alt fails in the middle of no where.

My alt recently failed (turned out to be the regulator not functioning correctly), the problem was as it was still trying to charge, the warning light didn't come on and the first i knew of it was when my vehicle wouldn't start (first assumption was stuffet battery) but i jumpstarted it and when i disconnected the chump battery the vehcle died, if i'd been out bush with mates this would have been a tow home job, but if i'd had twin alternators i could've connected the two batteries and gotten home.

The benefit in a twin alt setup is more in the get home safe option they provide.

P.S. Drivesafe, i'm not a salesman or a 'self-proclaimed' expert, but i do understand vehicle electronics and batteries, and if in future you have information proving i have made a mistake or am slightly off coarse with my information, i'd appreciate not spoken down too as a lower being, but i will happely accept being wrong if someone has information showing otherwise.
This is a public forum where people ask questions when they don't know the answer, not a bunch of professionals brain storming, if it sounded like i was trying to prove you wrong then i appologise, but it was my opinion to the setup as i have seen both used effectively and a second alt is always a good backstop.

[drivesafe]

I agree they would, assuming you have a vehicle relying heavily on it's electronics.

I should have been more clear though, if one battery has failed it won't kill the vehicle instantly, but say you second batt (deep cycle or otherwise) has failed, the vehicle will still start but it will shorten the life expectincy of your start battery.
Also the big plus to having twin alts which i obviously didn't press home is in the case where your alt fails in the middle of no where.

Hi suggy126, first, why would one battey's failure have any effect on the other.

P.S. Drivesafe, i'm not a salesman or a 'self-proclaimed' expert, but i do understand vehicle electronics and batteries, and if in future you have information proving i have made a mistake or am slightly off coarse with my information, i'd appreciate not spoken down too as a lower being, but i will happely accept being wrong if someone has information showing otherwise.
This is a public forum where people ask questions when they don't know the answer, not a bunch of professionals brain storming, if it sounded like i was trying to prove you wrong then i appologise, but it was my opinion to the setup as i have seen both used effectively and a second alt is always a good backstop.

I think it’s time you took a chill pill, my inference to a salesman or self proclaimed expert was not aimed at you or anybody else on the site. If you care to read back through the thread you will see I was clearly aiming it at Patroler’s MATE.

Cheers

[-Scott-]

In an ideal world I would prefer to have a dual alternator setup, but my engine bay simply doesn't allow it. So I'm stuck with a battery management system, and I'm not particularly upset about that.

On "salesmen": many of them are knowledgeable, and do their job well. The problem starts when uneducated opinions are stated as fact, or a customer mis-understands what's happened, and (unintentionally) spreads misinformation. (I'm not suggesting that has happened in this thread.)

The other problem he suggested is that if the main battery starts to get stuffed it may ... stop charging before it gets to the voltage at which the isolator switches to charge the aux battery

The solution to this problem is to install a voltmeter, not a second alternator.

No system is foolproof. To talk down a robust, reliable, well-proven solution because the wrong set of circumstances can cause an engine to stop is silly. There are a whole host of single points of failure which can cause an engine failure in a modern 4wd. Try crank angle sensors, ignition module, fuel pump.

For the record, if I was out bush with my usual travelling companions, and had a regulator fail, there would be options other than towing. And I'm not talking about a spare regulator.

Scott

[UNJUST]

so in a nut shell is a twin alternator setup good or bad? I could see its benifits for myself, a twin setup that is. Just with all the posts in this topic, there doesnt seem to be a definate yay or nay?

As someone basically stated, keep one Alternator/battery setup dedicated for the motor, I.e. Cranking, computer, gauges etc

And have the second setup for all the Aux items. Therefor the systems are completly seperate with no confusion. And if one alternator were to die out the bush, atleast you still had a second one to get you somewhere to safety (pub)

And im sure you could work the setup to have the option of linking them for a jumpstart or winching?

Jlowe

P.s for those of us with old trucks i see it being a pretty foolproof setup

[-Scott-]

Yes, a twin alternator setup is good. However, the "value" of it depends on what you're doing with your 4by, so that determines whether or not the benefits are worth the hassle - because, for some vehicles, installing a second alternator is quite a hassle.

For most people, a decent battery management system is all they need. If you're really worried about redundancy you could also carry a few more spares - depending on your vehicle, this is probably simpler than a second alternator.

[UNJUST]

cool, thanks for that

Now come to think of it, a mate has an ex ambo F-250. It has a twin alternator twin battery setup, im sure an ambo has a few more bells and whistles run so to speak but i still found it quite interesting that they had gone down that path.

I think id be going a twin alternator/battery set up

Jlowe