Dual battery setup, one main and 2 aux batteries???

[osidepunker]

What I think:
you must keep batteries in the bank the same age, size and type.
When you combine everything with the solenoid you have one big bank.
Starter batteries are crappy deep cycle batteries, deep cycle batteries are crappy starter batteries. What are you going to use in your combined bank? To charge both starter and house with the same voltage (solenoid combined) is inefficient at best damaging batteries at worst.
Solenoid charging systems are cheap inefficient and shorten battery life. I would strongly suggest you look at alternatives first. Check out the Stirling web site.

I appreciate the suggestions

I looked at the sterling system. They recommend AGAINST AGM batteries so that will not work for me.

Can you expand on why the National Luna or IBS systems would be inefficient and/or damage batteries?

As for my "combined bank", they will be two identical group 31 sears platinum marine batteries. One battery was purchased last spring and is rarely used. I hook up a battery maintenance charger about once a month for a day or two. The other battery will be purchased next spring. I doubt age of the batteries will be a concern.

 

[Joe917]

Your combined bank when charging is your two group 31 batteries(HB) and your starter battery(SB), so you will be charging a small charged starter battery and a larger depleted pair of batteries. All 3 will be charged by the alternator for the same period at the same voltage. The SB will be overcharged the combined system voltage will appear charged before the HB come up to full charge. The bigger the difference between SB and HB the bigger the problem.
Stirling recommend against AGM as a waste of money, their systems will work with any battery type including AGM. The chemistry of AGM batteries is exactly the same as flooded, the difference is the absorbed glass matt that holds the electrolyte between the plates. The advantage of main advantage of AGM is no maintenance and, as you noted, increased durability. Flooded battery levels must be checked regularly. AGMs can be inverted, great for Jeep guys who park upside down. Flooded batteries can be charged at higher voltages, can be equalized and have a longer life span when maintained.
The best system charges SB and HB at the correct voltage for each bank, combining works, but not well.

 

[osidepunker]

Your combined bank when charging is your two group 31 batteries(HB) and your starter battery(SB), so you will be charging a small charged starter battery and a larger depleted pair of batteries. All 3 will be charged by the alternator for the same period at the same voltage. The SB will be overcharged the combined system voltage will appear charged before the HB come up to full charge. The bigger the difference between SB and HB the bigger the problem.
Stirling recommend against AGM as a waste of money, their systems will work with any battery type including AGM. The chemistry of AGM batteries is exactly the same as flooded, the difference is the absorbed glass matt that holds the electrolyte between the plates. The advantage of main advantage of AGM is no maintenance and, as you noted, increased durability. Flooded battery levels must be checked regularly. AGMs can be inverted, great for Jeep guys who park upside down. Flooded batteries can be charged at higher voltages, can be equalized and have a longer life span when maintained.
The best system charges SB and HB at the correct voltage for each bank, combining works, but not well.

Thanks. I think the newer battery management systems take all this into consideration. For one thing, I will rarely deplete the house batteries all the way. Like I said, the fridge is the only round the clock draw. And if I do deplete them, or the starter battery for that matter, I think the battery manager can handle it. Looks like the IBS can handle more current. Here is a couple faqs from their website that address your points:

"Q. A fully charged and an empty battery are linked in parallel, a massive current flows from the good battery into the discharged battery?

A. First at all the charge voltage has to be above 13V that the battery starts taking charge. In both batteries there are inner resistances, cable resistance, terminal resistance what are in the sum at least 0.01 ohms (resistance of the good battery, the discharged battery and wiring). A voltage difference of 0.6V divided by 0.01 ohms creates a current of roughly 60 Amps; this is only during a very short time. If a battery is shortened, currents above 500Amps are possible.

Q. In the set-up of an IBS Dual Battery System a good and a discharged battery are linked in parallel for a “linked” start, the discharged battery immediately discharges also the good battery?

A. This is correct that if a good and discharged battery are wired in parallel for a long time, the discharged battery starts to discharge the good battery, but this happens over hours or even days. In short term only the new system voltage will be somewhere between the voltage from the two batteries before they have been linked. The reserve capacity is still available and can be used for a proper link start. For this kind of situation it is recommended to have the optionally available RBM (Relay Booster Module) installed, that guaranties to have access to the auxiliary battery capacity if the starter battery has failed totally.

Q. The alternator only sees the well charged starter battery and does not properly charge the discharged auxiliary battery?

A. The alternator is a constant voltage charging device with temperature compensation and delivers up to its maximum rating charge current. The IBS Dual Battery System links the batteries as soon the charge voltage exceeds 13.1V this happens within a few seconds up to 3 minutes depending on the car. When the batteries are linked, the current flows according to the internal resistance of the batteries. The starter battery, in most cases, only takes a little current and the rest of the alternator capacity is available to recharge the auxiliary battery and to run auxiliary electrics and electronics."

 

[osidepunker]

IBS lists the IBS-DBS Dual Battery System with Microprocessor as:

Relay load current (max.) 200A/500A

I think I am more than good to transfer current between the SB and HB

 

[RubiconGeoff]

I ran one primary AGM battery under the hood and two auxiliary AGM batteries (in parallel) mounted underneath the bed of my 1st-gen 4Runner off a standard 12v high-amp solenoid for years, never once had a problem. This was controlled by the setup from Wrangler Northwest.

I currently have one primary AGM battery under the hood and one auxiliary Group 31 AGM battery mounted underneath the rear seat of my JK off a standard 12v high-amp solenoid. Rather than buy an expensive kit again like the one from Wrangler Northwest, I just manually control the solenoid with my sPOD. I keep the two batteries isolated until I'm actually drawing power from the auxiliary battery or needing to charge it; otherwise I keep the solenoid turned off.

As mentioned in this thread this doesn't optimally charge the batteries, but for the weekend warrier who just runs LED lights and a freezer/fridge off the auxiliary battery and charges it back up once under way, it's more than adequate. If I'm going to be camped stationary for more than a couple days I'll hook up a small solar charger to the auxiliary battery to buy me some more time before the fridge's low-voltage cutoff shuts it down. Whenever I get home from a trip in which I've used the auxiliary battery, I'll plug in my battery charger/maintainer to make sure the battery is back in top health.

If I was living out of my Jeep for extended periods of time I would get a much fancier setup, but for my needs this has proven for 12 or 13 years to be a perfect setup and it keeps the cost and complexity down.

 

[4x4junkie]

Marine batteries will not stand up to as many deep cycles as a true deep cycle battery. A true deep cycle battery has much thicker plates and consequently cannot supply the high cranking amps for starting. I stand by the statement. If you want the best value over the life of a deep cycle battery golf cart or true deep cycle is the way to go.
Starting batteries have thin plates to give a large surface for a rapid discharge and recharge, deep cycles are the opposite. There is no "dual purpose battery" that can do both jobs well.

Apparently you have different definitions for batteries than the industry as a whole does.

"Marine" simply means a battery that has wingnut terminals on it for attaching accessories to it as is common in boats (infact that is literally the only difference between the DHMP battery the OP has and it's non-marine DHP equivalent... well, and a somewhat-shorter warranty also).
"Deep-cycle" means the battery is designed to tolerate deep-discharges (and yes, they do have much thicker plates than "starting" batteries).

As for "Dual-Purpose" batteries not doing anything well... I guess it would depend on what exactly you need out of it. Obviously you have no need for a dual-purpose battery, but others may.



To the OP:
I don't see a problem with your planned setup. There could be some concern with the age difference of the two DHMP batteries you plan to put together, however if the one you have now has been properly stored and has little use, I don't see it being an issue (this is much more likely to cause problems if you were to string it in series with another (brand new) battery for a 24V setup, but with them in parallel (12V), not quite as much).

I also agree fully with the statements quoted from IBS's site, the alternator will not overcharge any battery no matter how discharged another battery in the system is. The alternator's voltage output is preset and will not vary either way (that is unless a deeply-discharged house battery is drawing a very heavy current (preventing the alt from reaching it's voltage set-point), this can actually delay to some extent charging of the starting battery until the house battery's voltage rises up to that of the alternator's set-point, at which point charging of both batteries will commence).

Big thing is to be sure you're using large enough gauge cables so that you will have good availability of charge current coming in from your alternator (#0 is the minimum I'd use if the batteries are not located under the hood, #00 would be better still IMO). Be sure to also fuse it at both ends, being that you have a power source (battery) at each end of the line.

 

[pappawheely]

I have a similar set-up with an odyssey group 65 agm under the hood and dual group 31's mounted where the back seat used to be. I use a CTEK D250S. It takes a charge from my powermaster 200 amp alternator, isolates the starting battery and controls the voltage from my solar panels. :sunny:

 

[zelatore]

Apparently you have different definitions for batteries than the industry as a whole does.

"Marine" simply means a battery that has wingnut terminals on it for attaching accessories to it as is common in boats

Well, if one wants to be technically correct, wing nuts are verboten in the marine world per USCG standards. Any NAMS/SAMS surveyor will ding you every time if you have wing nuts instead of regular nuts.

But I'm being needlessly picky here. I know you simply mean it has threaded studs for securing the cables instead of the common automotive posts.

Carry on.

 

[dwh]

[Yawn. The problem with being a "napper", is sometimes you wake up in the middle of the night and don't feel like going back to bed.]


That's a clean setup pappawheely - nicely done!



To the OP...

Batteries must be same size, age, type, manufacturer, etc. when tied into a full-time bank. I.e., charged *and discharged* together.

So your dual battery bank in the rear DOES need to have a matched set of batteries (and cables).

But when batteries are tied ONLY during charging - not discharging - they don't need to be a matched set. (If they are rigged in parallel anyway, series rigging always requires a matched set.)


The alternator knows and sees nothing. The voltage regulator sees only the bus voltage and knows only if the bus is at full voltage or is low. The smart isolator knows and sees nothing except the voltage on either side (call it the main bus and aux bus). When conditions meet what the isolator is programmed for, it connects the aux bus to the main bus thereby creating one big bus.


So then the bus is held to a certain voltage by the voltage regulator switching the alternator on and off to hold the bus voltage wherever it's supposed to be. The batteries are connected to the bus, and when charging, they are a load on the bus, not a supply. Whatever the voltage of the bus is (think of it as pressure), versus whatever the resistance of the battery (or bank) is (think of it as a choke point), will determine how much amperage flows through the battery (or bank).

The chassis battery will absorb however much it can, and the aux bank will absorb however much it can. They don't affect each other, because they are both just sucking (most of the time, sipping) power from the bus.



In other words, the reason the chassis and house batteries don't have to match is that your chassis battery and house battery (bank) DON'T get drawn down together. They are isolated when the engine is off. They also DON'T get charged together - each one charges independently by drawing whatever it can from the bus.

In other, other words...it's convenient to say, "batteries tied" and we all do it, but the truth is - they are NOT tied. At no time are your chassis and house batteries actually tied into a "bank". They are each an independent load on the bus, or an independent supply to the bus, but not a bank. (The two in the back, are of course a bank.)

The main and aux bus are what actually get tied by the smart isolator. (Or dumb solenoid which is what I have. A smart isolator is just a dumb solenoid with a little brain to decide when to turn it on and off.)



Someone asked a question the other day, and it got me to thinking about smart isolators. The other guy has a Painless, and after reading the manual about how it works, I saw that you have to connect the winch to the main battery - not the aux - because the way the Painless works, if the main bus voltage drops below a certain level, the Painless ties in the aux bus to double the available battery power, but if the aux bus voltage drops, the Painless isolates the main and aux buses.


But a different smart isolator could operate differently and require it the other way around. Lemme see if I can work out the logic on this...I'll use the National Luna for an example. The manual is here:

http://www.nationalluna.com/Datasheets/Intel Solenoid Instructions.pdf

The manual says that it has a 5 minute timer. So no matter what, it won't tie the aux bus to the main bus until 5 minutes after the engine is started.
The manual also says that is won't tie the aux bus to the main bus until the main bus reaches 13.2v.

So far, so good.

The manual also says that it will disconnect the aux bus if the main bus falls below 12.7v.
That might be the gotcha! Let's see...

So say the winch is on the main bus and you really load it up. If the two batteries plus the alternator cannot supply enough current to hold the bus at 12.7v, then when the bus voltage (total, main+aux) drops to less than 12.7v, the aux bus will be disconnected - thereby removing the aux battery (or bank) from the bus and now the loaded winch has to operate from ONLY the main battery plus alternator. Which just compounded the problem.

But if the winch were connected to the aux battery, then if the bus voltage drops below 12.7v, the main and aux will be disconnected and the winch is running only from the aux battery - without help from the main battery OR the alternator.

So it's sucky either way you go. But less sucky to have the winch connected to the main battery, so that if the buses get isolated, at least the main battery has help from the alternator.


Fortunately, the NL has a way to deal with that - the optional Dual Controller, which will allow you to over-ride the automatic disconnect and force a connection even if the bus voltage is below 12.7v. The manual even says:

'This is useful for "jump-starting" the main battery or providing extra power from the auxiliary battery during winching applications.'

So with the over-ride, it's all good. Can hook the winch to either main or aux, doesn't matter.



Of course, the dumb solenoid doesn't have that problem. Both buses are tied whenever the ignition is on.

 

[osidepunker]

You guys are making some good points! Keep em coming!

I think I have settled on the IBS-DBS Dual Battery System. I dont see the age difference of the two batteries being an issue. Like I said, about a one year difference and the older battery is used maybe a dozen times total for the year.

I will wire it up exactly like this. I have a 170 amp alternator. Winch and aux driving lights will be wired to the main battery. Rear and side lights to the aux batt. The winch and forward lights will normally only be run when the engine is running. I can always connect the aux battery if I need more. For example, in a winching situation I will open the pipes and have 3 batteries and a 170amp alternator behind a 10k winch. Plenty.

If the starter battery takes a dump, the two aux are more than enough to take over.

I have a similar set-up with an odyssey group 65 agm under the hood and dual group 31's mounted where the back seat used to be. I use a CTEK D250S. It takes a charge from my powermaster 200 amp alternator, isolates the starting battery and controls the voltage from my solar panels. :sunny:

^^ Thats exactly what Im going for. Nice setup

 

[dwh]

That IBS is a nice setup. Wire it like the diagram and you're golden.



But the IBS is certainly a different beast than pappawheely's CTEK, which is a DC-DC charger that draws power from the main bus in order to do a proper multi-stage charge on the aux. It's also got a built-in MPPT solar charge controller.

The IBS is a smart isolator - in other words, a "split-charge relay" with a computer brain to switch the solenoid on and off. It's NOT a DC to DC charger. Also with the IBS you'll have to supply your own solar charge controller.


Different strokes - they both get the job done.

 

[osidepunker]

That IBS is a nice setup. Wire it like the diagram and you're golden.



But the IBS is certainly a different beast than pappawheely's CTEK, which is a DC-DC charger that draws power from the main bus in order to do a proper multi-stage charge on the aux. It's also got a built-in MPPT solar charge controller.

The IBS is a smart isolator - in other words, a "split-charge relay" with a computer brain to switch the solenoid on and off. It's NOT a DC to DC charger. Also with the IBS you'll have to supply your own solar charge controller.


Different strokes - they both get the job done.

Please correct me if I am wrong, but the CTEK is just a charger. I need something capable of transferring (in either direction) a full current load in case I need to connect the aux batt to the main for high current use. For example, I need to winch with lights on and engine is dead. In this case, I will be transferring HEAVY current from the aux to the main batts. The IBS is rated for 200 amps. I read the description for the CTEK D250S DUAL, but it appears as if that is just a charger for two batteries.

EDIT: I reread what you said and I guess we are both saying the same thing. But in my situation, I need the IBS or something similar. I suppose I could look into a smart charger after the IBS, but that seems like over kill to me

 

[pappawheely]

Please correct me if I am wrong, but the CTEK is just a charger.

The CTEK D250S is an isolator, charger and solar controller in one unit. It determines where the stronger voltage input is coming from. When the truck is parked, it draws from the solar panels. When the truck is running it switches to alternator power to charge the batteries. If I understand correctly, it will also send voltage to the starting battery if the house bank is topped off; I'm still learning about it's features. I have had great success getting technical support from Matt @ CTEK. I'm very happy with the odyssey AGM batteries too.

 

[DiploStrat]

Good Company!

Some comments on CTEK

-- Lifeline recommends CTEK products.

-- The D250S is a nice Battery to Battery charger at 40A with an integrated solar controller. http://smartercharger.com/battery-chargers/#CTEK D250S DUAL N.B. It is a charger for one battery, not two. As dwh noted, it can boost voltage and add a multi-stage charger to your system. Very nice if your vehicle alternator lacks these features.

-- If you need more, the SmartPass is an intelligent relay rated at 80A designed to be used with the D250S for faster charging during the bulk/boost state. Had to read the manual a dozen times to get it all. http://smartercharger.com/battery-chargers/#CTEK SmartPass

The dreaded manuals: http://smartercharger.com/wp-content/uploads/2010/11/manual-d250s-dual-and-smartpass.pdf

Friend of mine installed the pair, D2450S and SmartPass on his Tiger and is VERY happy. The more you read about the SmartPass, the more you will like it.


For the odd time that you need to winch, you might consider a simple manual switch.

 

[pappawheely]

Had to read the manual a dozen times to get it all. http://smartercharger.com/battery-chargers/#CTEK

If you had to read it multiple times, I don't feel so stupid now.