Dual battery for Africa expedition

[zsuzsiestekergo]

Dear All,

I would like to have advice on my possible dual battery set up for my expedition HZJ 75. I will not prepare the system myself but I would like to understand it well for possible future troubleshooting and to be able to choose what would be best for me. Currently I have no experience on car electrics.

My constraints are the followings:
- For simplicity, I would like to have a dual battery system entirely under bonnet where I have around 70 cm of space for batteries.
- Sufficient power to start 1HZ engine by the second battery, even if starting battery fails is a must, I would not want to get stranded.
- I would like to run a ~30l fridge, extra lightning, a waterpump, laptops, etc. Overall, my possible daily consumption will be somewhere between 40Ah and 65Ah.
- Reliability is important so both batteries should be shock resistant.
- Use will be continuous so many cycles.
- Replacement of one battery without significant problem should be possible, so generic solutions preferred (in any case being in Hungary I have no access to many specific brands)
I have an OEM alternator and planning to complement the system with a ~130watt Solar Cell fixed to top.

I was thinking in buying either
- 2 92 Ah capacity AGM starting batteries (such as Banner Running Bull)
- 2 75 Ah capacity Optima Yellowtops, or
- 1 92 Ah capacity AGM starting battery and a dual purpose battery (such as Varta Professional dual purpose, but this may not be available)

I will connect these batteries with a CTEK D250S gadget which has a nice schematics for how the system would function.
What I do not fully understand yet is how the consumers should be connected. I guess there are two circuits one with the existing consumers on the starter battery, the other is all new consumers on the working battery and the two are connected via the CTEK. However, it would be best to allow giving access to the starter battery's capacity to improve the lifespan of the working battery. At the same time it would be important that neither battery's voltage drops below what is necessary for starting.
Finally, I cannot figure out how the CTEK is affecting the charging of the starter battery, i.e. whether the alternator will manage to charge it the way required for AGMs.

Thanks for any comments and suggestions.
Csaba

 

[DiploStrat]

Some thoughts

You will find much more discussion of this subject here: http://www.expeditionportal.com/forum/forums/48-Power-Systems-12v-Solar-Gen

(Some of us post on this subject a lot. I have several documents on the subject on my website, under "Documents")

Your situation is similar to this one: http://www.expeditionportal.com/forum/threads/145696-Aux-Battery-Set-up-with-Ram-EcoDiesel

Assuming that your power consumption estimate is correct, that is 60Ah overnight, then you need a camper/house/domestic battery of about 100-150Ah if you are using lead acid. None of the options that you listed are big enough. But, assuming a typical trans-Africa travel routine of driving almost every day, things may not be that bad, as you can assume that your alternator will carry the load while driving. In any case, if using lead acid batteries, your battery bank needs to be about twice the size of your maximum load.

While CTEK makes nice equipment, a D250S doesn't get you much as it has a maximum charge rate of 20A. You will get better performance with a simple relay. The D250 DOES make sense if:

-- It is your solar controller as well, and,

-- You pair it with the SmartPass.

In this case you will get a much faster charge and the D250 will do double duty as your solar controller.

N.B. The D250S has no impact on charging the starter battery. Before you do anything, you have to be sure that your Land Cruiser's electrical system is properly set up to charge your starter battery. Grossly, that means at least 50A at 14.4v at 20C or as close to that as you can get. If the vehicle's system does not charge at over 14v you will need to fix that first. (Here is a link to one way to do this: http://www.smartgauge.co.uk/alt_mod.html)

N.B.2 The CTEK products do not offer an self-jump option, but if both batteries are under the hood, simply use a jumper cable if required.

Don't go with a pair of starter batteries; you want a true deep cycle, not a starter or dual purpose battery to handle the refrigerator.

While distances under the hood are not great, do make sure that all of your wiring is large enough.

Hope this is helpful.

 

[zsuzsiestekergo]

Dear Diplo,

Thank you very much for your comprehensive response which gave me enough material to learn more on this, which I clearly need.

To be honest I am somewhat puzzled because it seems that there is no simple (and relatively cheap) solution for my problem, even with compromises. Having a real deep cycle battery as service battery would not allow me to have a starting backup independent from the starter battery. Having 3 batteries (2 starter + 1 service) would be complicated and would take a lot of space.

The only alternative I see now would be to connect two identical AGM starter-type batteries together so that they are used in parallel and set a safety for too low a voltage.
As regards the CTEK, indeed I imagined D250s indeed as a solar controller. According to its manual it is sufficient for a starter battery + "small" service battery + solar power + alternator combo.

Thanks again for your helpful reactions, I will continue my research.

 

[DiploStrat]

To be honest I am somewhat puzzled because it seems that there is no simple (and relatively cheap) solution for my problem, even with compromises. Having a real deep cycle battery as service battery would not allow me to have a starting backup independent from the starter battery. Having 3 batteries (2 starter + 1 service) would be complicated and would take a lot of space.

Actually, there is a simple answer; just use two deep cycle batteries. In fact, if they are the same size/age/etc. you don't even have to worry about an isolator. A pair of 100Ah deep cycle batteries will have more than enough power to start your truck and still give you about 100Ah to use over night. I would still add a solar charger.

You just don't want to use two starter batteries.

 

[zsuzsiestekergo]

Actually, there is a simple answer; just use two deep cycle batteries. In fact, if they are the same size/age/etc. you don't even have to worry about an isolator. A pair of 100Ah deep cycle batteries will have more than enough power to start your truck and still give you about 100Ah to use over night. I would still add a solar charger.

You just don't want to use two starter batteries.

Thanks for the creative idea, but it would still leave me without starting in case one of the batteries dies. What if I take a starter as first battery. As second battery I will have a deep cycle as you proposed and an antigravity microstart to help it start the car, would it be sufficient? It is very difficult to get info on a concrete deep cycle battery's cranking possibilities!

 

[DiploStrat]

Don't Overthink This

Amps are amps. Starting batteries usually have a second specification, often called "Cold Cranking Amps" which is a kind of peak output, but you can ignore that. (My Delco starting batteries are rated at something like 700 CCA, but they are, in the end, simply 75Ah batteries. Either one of them would be more than enough to start my six litre diesel.

Lead Acid batteries are simply not that sophisticated. More and thinner plates give you more CCA, fewer and thicker plates give you longer life and greater resistance to discharge. Manufacturers like high CCA starting batteries because they are physically smaller and lighter. (And probably less expensive.)

There are two reasons to isolate your batteries, one bad and one good:

-- BAD reason: I need to be sure that I can start the car in the morning. Wrong issue. The real issue here is that your battery bank is too small for the load and you plan to run it down past the point at which it can recover. There may be some logic to this - "I'll buy a cheap battery and replace it when it dies." But this is not the way I would plan for a trans-Africa trip.

-- GOOD reason: I have two dissimilar batteries and I don't want to deeply discharge a starter battery.

If your battery bank is large enough to handle your load (and you can properly recharge it each day) then there is no particular reason to have a separate starter battery. The key thing is to be sure that the camper/house/domestic battery is large enough.

My case is a bit extreme; I have 600Ah of camper battery and 150 Ah of starter; even discharged 50%, my camper battery is twice the size of my starter battery.

In your case the essential number is the amp draw per hour and the number of hours you need between recharges. Make sure that your camper, or your combined batteries, are twice that size and you are done.

The next big thing, of course, is to be sure that your alternator produces a high enough voltage, and a reasonable number of amps, to recharge the whole mess. Solar is invaluable for finishing the charge.

 

[Hilldweller]

Everything that Diplostrat is telling you is spot-on.

I have similar energy demands to you and I handle it with two flooded/sealed house batteries @ 122 ah each and one AGM under the bonnet @ 75 ah. They are separated at night but in parallel while traveling.
I use solar during the day to recharge the house batteries when needed.

 

[zsuzsiestekergo]

Everything that Diplostrat is telling you is spot-on.

I have similar energy demands to you and I handle it with two flooded/sealed house batteries @ 122 ah each and one AGM under the bonnet @ 75 ah. They are separated at night but in parallel while traveling.
I use solar during the day to recharge the house batteries when needed.

Thanks, I had no doubts about it! Now the question is whether I can limit my consumption to work it out with a single 105 Ah. Having the solar+alternator during the day, I am somewhat optimist.

 

[Hilldweller]

Thanks, I had no doubts about it! Now the question is whether I can limit my consumption to work it out with a single 105 Ah. Having the solar+alternator during the day, I am somewhat optimist.

The problem you'll have is that the battery will be deeply discharged in the morning. Most chargers and all alternators can't deal with that.
Many chargers require you to parallel a healthy battery to the discharged one to begin the charge; better ones won't but you'll still need an a/c source or solar.

Look at batteries for home solar or cel tower use. They can handle deep cycling better than auto batteries. My boat batteries certainly are better than standard auto batteries but I still consider them disposable at 3 years of abuse.


Some of my Optima buddies have put together some informative videos
https://www.youtube.com/user/OptimaBatteries

 

[DiploStrat]

... What if I take a starter as first battery. As second battery I will have a deep cycle as you proposed and an antigravity microstart to help it start the car, would it be sufficient? It is very difficult to get info on a concrete deep cycle battery's cranking possibilities!

Again, don't overthink this. You don't need a "starter" battery if you have enough deep cycle battery power. And if your two deep cycle batteries have enough amperage, say greater than 200Ah, and you only use 100Ah a night, then you will still have more than enough cranking power to start the truck in the morning. As a reference, I only use 125Ah overnight and I run a refrigerator, furnace, and cook all electrically. I doubt that you will use much more than 75Ah.

Key Points:

-- You do want to isolate a starter battery from deep discharges as they can be damaged.

-- You can certainly use a deep cycle battery as a starter battery.

-- By putting 100Ah in each of your two battery trays you will have much more amperage for both starting and camping than you would have with one 100Ah starter battery and only 100Ah of camper battery.

Ideally, you would leave your starter battery alone and simply add enough camper battery to carry the load, but you imposed the additional requirement that everything be under the hood, hence my recommendation.

 

[Hilldweller]

Putting extra emphasis on what 'Strat is saying about deep cycle batteries. Not the same as the batteries in the autoparts store but, like he said, two of them will work for you.

 

[rayra]

Go one further and get 3 of the same, like the AGM Optima yellow-top, works as both start and 'house' battery, 1 as your main / start battery, the other pair as your 'house' system in parallel. And if your start batter dies you pull one house battery to replace it and keep on trucking. I'd think such interchangeability would be a very desirable thing for an African expedition vehicle. Weight be damned. I'd consider it 'essential equipment', second only to water storage.

 

[Hilldweller]

Go one further and get 3 of the same, like the AGM Optima yellow-top, works as both start and 'house' battery, 1 as your main / start battery, the other pair as your 'house' system in parallel. And if your start batter dies you pull one house battery to replace it and keep on trucking. I'd think such interchangeability would be a very desirable thing for an African expedition vehicle. Weight be damned. I'd consider it 'essential equipment', second only to water storage.

A YellowTop string wouldn't work well for what he's planning.
They are not designed to cycle that low on a daily basis. They're a tough battery that can handle abuse but not constant deep discharging. And his alternator would not recover them.

 

[rayra]

shrug. He's talking about solar too, and it's worth amending the usage pattern to maintain the vehicle starting ability. Likewise upgrade the vehicle alternator output.
It's also possible in most cases to fit larger deep cells to supplant the typical auto starting battery to have a rough equivalance in cold-cranking amps - which is the primary concern of what sort of battery you use in a vehicle config.

The Optima D34/78 is listed as having 55Ah. A 3 battery bank would put him at about a 40% daily discharge rate. And that's about 20mins at a moderate idle on my Suburban's stock alternator. If I'm doing the math correctly.

peak output on a well positioned solar panel is max 9A? 10A? at 12v. 2 panels or 3, flat on the roof, OUGHT to meet his anticipated daily power consumption. Again I might be screwing up the amp hour math.

Anyway, my point is the problem is flexible and adjustable during the design. Figure which criteria are most important, without arbitrarily ruling anything out or being irrevocably wed to one aspect, be it size, weight, capacity, redundancy, cost and prioritize those concerns and meld the solution to fit. Redundancy and fault tolerance would be top of my list for heading for the middle of nowhere. I'd design my system for that and optimize the other factors however I could. That's all I'm talking about.


The point of a deep cycle battery is its ability to be more deeply discharged without long-term damage, it doesn't mean that you MUST deeply discharge it.
That's also the point of multiple batteries - as well as the redundancy - so the draw on each battery is far less for the same total draw / system output.
Besides all that, there are alternators available which produce far more power at low RPMs, so a daily period of idling could supplement the recharge without using much fuel.

All of these expedition vehicle systems are a sum of goals and compromises. Choose and set your priorities and make your configuration choices based on them. Don't let a single aspect or shortcoming rule something out. It's a total system, with tradeoffs.

And quite frankly, a true expedition vehicle, I'd want the battery out of the hot engine compartment anyway. And since the rest of the vehicle is likely being reworked I'd just go with a multiple battery array that powers everything, sizing each individual battery to have sufficient cranking amps to stat the vehicle and on the 'house' side of things using a quality inverter that has a settable low-voltage cutoff. Then how deep the discharge might be doesn't matter, your system is protected.

 

[zsuzsiestekergo]

Indeed, the point on having two identical batteries is taken. The reason why I have not considered two Deep Cycle batteries is that I understood regular use for starting does not make them any good. I have to say this is so counterintuitive that to Dual purpose batteries would give me more peace of mind.

Interestingly I have seen Exide Dual AGM's specs now: http://www.exide.com/Media/files/Do...xide_Multifit Leaflet 2015_Europe_EN_copy.pdf
They claim over 500 cycles which should be sufficient. This would make it better for the purpose than YellowTops.

So 2*75 Ah with the daily use of Solar+Alternator would cover my 60 Ah overnight, probably without dischargin below 60%.