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

[dwh]

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

You won't need the CTEK with the IBS. In fact, you can't - if you rig both, you'll create a loop and defeat the CTEK.

You might still want a smart charger that is shore powered though, to top up the batteries when the truck is parked and shore power is available.

 

[dwh]

-- The D250S is a nice Battery to Battery charger at 40A

Typo alert - it's a 20a charger, not a 40a.

 

[osidepunker]

Great discussion! Im soaking it up

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.

The CTEK sounds like a great way to integrate solar and keep your batteries healthy, but I don't think it was designed to transfer full current between the batteries.

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
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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.

I am looking at a TJM 10k winch. Max current is listed as 405 amps. I understand that winch situations are going to be rare and winching with a dead engine even more unlikely. However, I am attempting to build out a fully prepped vehicle and I think it is important to be able to fully utilize the aux batteries in ANY situation. This means being able to transfer a full current load.

The smart pass is cool, but not rated for 405 amps.

You won't need the CTEK with the IBS. In fact, you can't - if you rig both, you'll create a loop and defeat the CTEK.

You might still want a smart charger that is shore powered though, to top up the batteries when the truck is parked and shore power is available.

Typo alert - it's a 20a charger, not a 40a.

Yeah Im with ya, no need to do both systems. As for shore power, Im not planning for it. I believe in using as little electricity as possible. The fridge will be the largest draw while boondocking. Other draws include cell phones/tablets, 12v water pump and maybe a coffee maker (other coffee solutions dont seem to taste good to me). I feel that the solar panels will be all I need. In the event that the solar is not enough, I can always crank the engine for a while. In any case, we very rarely camp where there is shore power so its not really an option.

Let me know if you guys think I am asking too much of solar. I haven't researched panels yet so not sure how many watts I need...

 

[osidepunker]

Also, isnt my alternator going to charge my batteries "smartly"???

 

[DiploStrat]

OOOPs!

Typo alert - it's a 20a charger, not a 40a.

OOOPS! Tanx!

To the point - the low output of the 250 is exactly why they created the SmartPass. It basically adds an intelligent relay rated at 80A into the mix. When the batteries are low, e.g. bulk charge, the relay closes. When the charge rate drops below 20A, then the relay opens and the 250 takes over to assure proper voltage (and float) as needed. If I read correctly, the relay will also close when the solar kit is active, to tend your starter batteries.

This is basically what I do on my truck, except that I do not include a secondary regulator like the 250 and my relay has a higher rating at 200A. But, as you have noted, the charge rate falls off after an hour or two, so it it hard to keep it up over 150A for very long. The pair of CTEK devices make a very attractive package.

 

[dwh]

Also, isnt my alternator going to charge my batteries "smartly"???

Nope. Alternators are dumb. But they're controlled by voltage regulators, and some of them are smart. Diplo has probably the "smartest" voltage regulator I've seen, but it still just basically turns on the alternator when the bus voltage is low, and turns it off when the bus voltage reaches the set point.

It can read temp on battery and IIRC alternator(s), and make some smart decisions about its voltage set points and how much to load the alternator.


But ultimately, it's still a constant voltage charging system. [EDIT: As is yours - even with the IBS. The IBS FAQ page even says that.]

The CTEK (and other DC-DC multi-stage chargers)(and all shore powered multi-stage smart chargers) charges with both constant current and constant voltage. Constant current for bulk stage, constant voltage for absorb.

Here's a good video for understanding the difference:

 

[dwh]

HAHAAH!

Okay, I was screwing with you.

I'm an electrician and a welder, so I understand what he's saying, but if anyone else is able to follow that guy's presentation I'd be surprised.


Here's a better vid that explains it:

 

[dwh]

Here's the quote from the IBS FAQ page (rumors section - 2/3 down the page):

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

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."


http://ibs-tech.ch/en/products/dual-battery-system/faqs-for-ibs-dbsdbi.html

 

[dwh]

Hrmm.

That quote is a bit deceptive. When he says temperature compensation, he's not using that term the way it would normally be understood. Smart chargers with temp compensation will read the temp of the battery and adjust the charging voltage so as to maximize what goes into the battery, without overheating it.

What he's talking about is just that the alternator puts out less when it's hot.

 

[DiploStrat]

Been there, Do that, Everyday.

OPunker,

You may find this an interesting read: http://diplostrat.org/about/

Some of us have trod the path you seek to follow. Basically, my truck has no genset and uses all electric appliances and air conditioning. To make this work, I use:

-- A 600AH battery bank

-- A factory dual alternator set up (2x125A) with a rather good voltage regulator.

-- 500w of solar with a good controller.

-- A 2800w inverter/charger.

-- An intelligent relay to link the camper batteries to the starter batteries.

Truck has run since December 2013 without use of shore power.

Some roolz:

-- First you must have enough battery to run your load for the length of time you require. (Without A/C I use 125Ah for dinner/overnight/breakfast.)

-- Then you must have enough charge source and time to recover.

-- Typically an engine alternator makes a great bulk charger (i.e. lots of amps) but you will rarely run it long enough to complete the charge process.

-- Typically, solar or shore power will be necessary to complete the acceptance charge stage.

Hope this is helpful.

 

[osidepunker]

The CTEK (and other DC-DC multi-stage chargers)(and all shore powered multi-stage smart chargers) charges with both constant current and constant voltage. Constant current for bulk stage, constant voltage for absorb.

Ok, I understand the difference

But honestly, none of that matters if I cant xfer several hundred amps between batteries...

OPunker,

You may find this an interesting read: http://diplostrat.org/about/

Some of us have trod the path you seek to follow. Basically, my truck has no genset and uses all electric appliances and air conditioning. To make this work, I use:

-- A 600AH battery bank

-- A factory dual alternator set up (2x125A) with a rather good voltage regulator.

-- 500w of solar with a good controller.

-- A 2800w inverter/charger.

-- An intelligent relay to link the camper batteries to the starter batteries.

Truck has run since December 2013 without use of shore power.

Some roolz:

-- First you must have enough battery to run your load for the length of time you require. (Without A/C I use 125Ah for dinner/overnight/breakfast.)

-- Then you must have enough charge source and time to recover.

-- Typically an engine alternator makes a great bulk charger (i.e. lots of amps) but you will rarely run it long enough to complete the charge process.

-- Typically, solar or shore power will be necessary to complete the acceptance charge stage.

Hope this is helpful.

Thank you! That is exactly what I was looking for. Ok, so I wont be running AC or anything heavy like that. So I doubt I will need as many amp hours as you. Diehard lists the specs for a group 31 platinum marine as:

Amp Hours at 20 Hour Rate: 100
Capacity Amp Hours at 10 Hour Rating: 92
Cold Cranking Amps (CCA at 0 deg.F): 1150
Reserve Capacity (RC): 205 min.

So does that mean I have "200Ah" with two batteries in parallel?? You think that will be enough?

and if I have a battery bank 1/3rd as big as yours, could I get away with less than 500 watts solar? Just wondering where best to spend my money. I would like to have enough solar so that I do not have to rely on the engine, but I also dont want to spend a ton of $$$ on panels if I dont need the watts.

I thought about dual alternators, but mine is 170 amps. You think that will be enough?

 

[DiploStrat]

It Depends

PM sent.

Basically:

-- Looking to add a second battery, same size as your starting battery? Stick it under the hood and use a key controlled relay.

-- Looking for real camper power? You are looking at about 200 - 400 AH - that is, 100 - 200 AH usable. This is probably too big to go under the hood and EVERYTHING gets harder. Not impossible, just harder.

A lot depends on your load and duty cycle. A small load for many days is as hard as a big load overnight. Only you can decide.

Winching is actually easy; just need a force combine. (I could do this with a simple dash switch.)

Finally, really need a moderator to move this to the 12v forum.

 

[dwh]

Ok, I understand the difference

But honestly, none of that matters if I cant xfer several hundred amps between batteries...

There ya go. Define the needs, you define the solution.

So does that mean I have "200Ah" with two batteries in parallel??

Yes. Rig in series, you double the voltage, but amp*hours stays the same. Rig in parallel, you double the amp*hours, but voltage stays the same.

You think that will be enough?

We'll know when you report back.

and if I have a battery bank 1/3rd as big as yours, could I get away with less than 500 watts solar? Just wondering where best to spend my money. I would like to have enough solar so that I do not have to rely on the engine, but I also dont want to spend a ton of $$$ on panels if I dont need the watts.

If you take a 200ah battery bank down 50% (don't want to go below 50% as that shortens the battery life a lot), then you have to put back 100ah. But you'll need more because the system, and especially the batteries are not 100% efficient. So figure you'll need to supply 120ah to get the battery bank full again.

How many hours a day will you get full direct sunlight (in the solar racket they call that, "good sun") on the solar panels? Most solar installers use 4 hours/day when estimating. But depending on where you are, they might use 5 hours/day.

Let's say 5 hours/day of good sun. So you need a solar array that can supply 120 / 5 = 24 amps.

24 amps * 12v = 288w.

But again, not 100% efficient, so add another 20%..

288w * .2 = 57.6w
288w + 58w = 346w


So if you can count on 5 hours a day of good sun on the panels, you'll need a 350w array. If you only count on 4 hours a day of good sun, redo the math.

That's to run the whole thing from solar only. If you figure out how much you drive a day, and how much that puts into the batteries, then you can subtract that from the solar you need.


(Or, you could do what I do. Park in the shade and carry a small generator and forget solar. I like shade.)

I thought about dual alternators, but mine is 170 amps. You think that will be enough?

Plenty. As the voltage of the battery rises, the amps flowing will go down.

By the time the battery is almost full, very few amps will be flowing. Your alternator probably won't be putting out 170a except for a short while. 90% of the time, it'll almost certainly be putting out 100a or less. 50% of the time, probably 30a or less.

 

[pappawheely]

FYI, If you look at the stats on the battery you plan on using, the group 31 allows about 100 AH. Their info states that in actuality it can range from 85-100 AH.

 

[osidepunker]

Thank you all for your help. I think I have most of this pinned down. I will look for solar that is between 200 and 300 watts and an appropriate controller. Most of the time we will be driving during the day so the batteries will be topped off. Boondocking in one place for extended periods will be rare; I doubt we will go longer than 7 days. Since our only real draw will be the fridge I think we will be ok with that amount of solar. Most of our camping will be desert (plenty of sun) as we live in SoCal, but I do plan on wandering all over North America so we have to be flexible.

Going with the IBS-DBS controller. Dual group 31 diehard platinum marine batteries for 200Ah capacity for the aux bank. I will keep my current diehard Gold AGM group 31 for my starter battery for now. I may upgrade to a group 34 if I find the 31 is not cutting it.

I forgot to mention that one of my primary concerns with my truck build is weight savings. I am trying to keep everything as light as possible. With this setup, I will have about 150lbs of batteries. I will try to make this work as I do not want to add more battery weight. To that end, I will also install a propane tank for our hot water system and stove.

I will put this together over the winter and keep you guys updated. Thanks again!