Dual battery system - WITHOUT solar - DC only questions

[king]

2007 chevy express 1500

Hi. Looking for help setting up dual battery system. No solar, no generator, only charging off alternator.  And shore power when available.

Originally planned to have only an isolator, after research now I'm thinking a DCDC charger instead.

Planning to boondock, not driving much, will it really take over 2 hours to fully charge, even if down to 75%? I know not to take a AGM deep cycle down below 50%.  

Planning to get:
one 12 volt (100-125ah)
DCDC charger
4awg cable and fuses

Would appreciate any simple diagrams or a list of components needed. My needs are minimal/basic - fan, light, phone charger and laptop charger.  Any suggestions on a DC adapter for laptop?

I don't want to buy an inverter, so will not use any AC.

I have been researching for months and am frustrated/confused and about to give up on electric all together.

Any help would be great. Thank you

 

[John61CT]

If your House bank is lead-based, it will take 5+ hours to 100% Fully charge.

It needs to get there a few times per week for good longevity, 98% is not enough.

Most of that time the bank is only able to accept small amps current.

So if you really can't have any solar (why?) then your choices are, get to shore power every other day or so, or

accept you'll need to replace your bank much more frequently.

Since a 200+AH true deep cycle bank of reasonable quality (pair of FLA Duracell 6V GCs) can be purchased for a couple hundred bucks, maybe that last approach is NBD for you.

Some people scam big box retailers on their warranty year after year, but I don't recommend that.

Or go to a LFP chemistry, no need to get to Full, but lots more expensive, and solid research and very precise infrastructure is needed to get that investment back in longevity.

 

[highdesertranger]

yes it really takes over 2 hours to charge your house battery. if discharged close to 50% it could take 8 hours of driving at highway speed, not idling. this is why solar is so attractive. highdesertranger

 

[Reducto]

Here's a thread on laptop adapters. The one I linked has been working flawlessly for some time. You just need to find a tip to fit your laptop or cut it off your 110 adapter.

https://vanlivingforum.com/showthread.php?tid=27333&highlight=laptop

As for whether you can get away without solar it just depends on how much power you use. You can burn a LOT of juice playing games on a laptop or almost none of you just surf 20 minutes a day. Get a cheap battery gauge off Amazon and watch it. Don't let your battery go too low. If you find you can't use your laptop as much as you want then get some solar.

 

[king]

Thank you for your replies. To be clear, I have nothing against solar, and am in fact in favor of more solar power as a society at large. I am very concerned about energy consumption and the ecosystem destruction it causes. I have not owned a car in 20 years and didn't want to buy this van because I don't like using gasoline and contributing to the problem, but I can't afford an electric vehicle, or other sustainable option right now. 

My personal circumstance is that I am going to be out living in the van in two weeks, otherwise homeless, been staying with family but have overstayed my welcome while trying to convert the van into a camper. I want to choose rural van life over the city shelter and social service dependence which I have done in the past, even though that is far easier.  With not a lot of money, I am trying to do what I can that is simple and cheap - though I understand cheap and easy will not last long.  Perhaps I should just return the fan I bought and learn to live without the comfort of electric altogether. I will not be driving 5 hours every other day, that is for sure.

My main question was about whether a DCDC charger is worth the investment. I quess not if it will still take 5-8 hours of driving to charge a battery

 

[Trebor English]

If your electrical use is light, just a phone recharge and a low current fan, 5 hours isn't necessary.  20 minutes is likely to put back most of what you used.  

A dc to dc charger should make it better but those are expensive.  Amazon has a Ctek for $250.  That seems too high for your need.

What I have is a 12 volt flooded deep cycle battery for the engine and phone charging.  I needed a new battery so I bought the largest battery that would fit in the original location.  It's a group size 24, 75 amp hour.  The battery was $80.  

What I have done is to add solar so that I can stay put as long as I want.  You can do that for $110.  Home Depot has panels for $89 and Amazon has PWM controllers as cheap as $12.  A portable installation where you park facing south and lean the panel against the windshield will need two 10 foot pieces if #8 wire.  Then you could leave the panel inside on a driving day, pop the hood and clip on to the bsttery and deploy the panel on non driving days.

 

[MrAlvinDude]

I have been researching for months and am frustrated/confused and about to give up on electric all together.

Sorry to hear that, but please don't give up, because it does not have to be perfect (or super optimized) in order to give you some power rather than no power while you are boondocking.

It is possible to use gradients between "no power" and  "super optimized way to have power"

I suggest that you use the advice you get here, to simply try to avoid the biggest (or most costly mistakes), but other than that, just go for it, and find something that will work for you!

Originally planned to have only an isolator, after research now I'm thinking a DCDC charger instead.

Anything specific that made you think that you need (or want) a DC-DC charger rather than a big solenoid (isolator)?

Planning to boondock, not driving much, will it really take over 2 hours to fully charge

Like other people have said, yes it does take a long time to charge a lead acid battery.
When being charged, then at first it is possible to charge at a high amperage, but after a while, it is only possible to charge at a lower amperage, and that takes time (hours), but greatly benefits the longevity of a lead acid battery.

One option could be to combine charging by engine and charging by solar.

Meaning, the main charge can be done by running the engine for some time (you could simply choose to let that be 30 minutes or an hour), then the rest (hopefully the natural slow charge, the low amperage charge) can be done by the solar.

This may not be an ideal way, but it would cut down on the use of the engine.


Another option is, to simply not use more power than what you can get from running your engine for a decided upon, short time.


When you run the engine you could possibly also be charging your phone battery, your laptop battery and one of those usb power banks.

However long you choose to run your engine might not get them fully charged, but at least those batteries don't need to be fully charged to live a long life, unlike lead acid batteries where their longevity greatly benefits from regularly getting fully charged.

Planning to get:
one 12 volt (100-125ah)
DCDC charger
4awg cable and fuses

Sounds like an okay plan. But I still think that a big solenoid could do you just as well, especially if you are on a budget.

My needs are minimal/basic - fan, light, phone charger and laptop charger. 

One option could also be to only use those items running on their own power/batteries. And just focus on getting those batteries charged.

The fan might be able to run off one of those usb power banks.

For light you might choose those luci lights (shop), that have solar charger and battery built in.


But I still think you will get more light (and more versatile power) for your dollars, if you get a 100W solar panel.

And if you combine a small solar panel with your original plan, of an isolator and a battery, you get to use power even when the internal batteries of your devices are used up.
And you get some more power, rather than just what you can get from your engine.

 

[tx2sturgis]

It won't take 5 hours, or even 2 hours, of driving to replace the energy used to charge a normal laptop and phone, and run a small fan and a couple of small LED lights for a few hours....that's just crazy talk...

As Trebor said above in post #6, 20 minutes could do it. 

Now if it's a high-power gaming laptop, used all day....well that is in a different category. And yes, you will need significant solar to run one of those all day, or fast idle the engine during its use.

 

[tx2sturgis]

My main question was about whether a DCDC charger is worth the investment. I quess not if it will still take 5-8 hours of driving to charge a battery

For the price of a good DC-DC battery charger, you could spend less $$$ and buy a 100w portable panel and a water-proof charge controller which would be mounted under the hood, with a pigtail to plug in that panel when parked.

Then buy a $25 laptop car-charger and have at it.

 

[John61CT]

Think of this like a Choose your Own Adventure game.

If you go back and read my response you can see an unavoidable set choices laid out.

That first hour of charging, with enough amps at the right voltage, might get your SoC back to say 80% or higher.

Getting to mains power even *once* a week may allow your bank to last years, not 5-8 but maybe 3-5.

The question of whether you need a DC-DC charger was not yet addressed.

But for every AH you take out of the bank, you have to find a source of energy to put 1.2AH or so back in. Hours of heavy gaming uses a lot of juice.

Those are just harsh Physics reality and unavoidable. But depending on the size of your bank, you can buy longer cycles, maybe doesn't have to be every 24 hours.

Try to clarify and understand, ask questions and you will climb the learning curve, about amps, watts voltage of proper charging, spend some money on the various components,

make decisions that will optimize your setup best we can within your situation's limitations.

Perfect is enemy of the good, just because the ideal situation is not realistic for you now, doesn't mean a workable compromise won't be "good enough", until you get to being able to improve it.

 

[Weight]

You are talking about a minimal house battery. Rather than a DC/DC I would use this. https://shop.marinehowto.com/products/blue-sea-7610-automatic-combining-relay

Spend more on a quality 120 volt charger.

 

[Trebor English]

You are talking about a minimal house battery. Rather than a DC/DC I would use this.  https://shop.marinehowto.com/products/blue-sea-7610-automatic-combining-relay

Spend more on a quality 120 volt charger.

That combining relay is $87.  Home Depot Grape Solar 100 watt panel is $89.  You could get a $5 Harbor Freight multimeter, sometimes free with a coupon, and you could be the controller.  Connect the panel direct to the battery, start up all the chargers, watch the voltage.  When it gets to 15 volts disconnect the panel and put it away.  Next day, repeat.  When you get some extra cash, get a cheap PWM controller.  If amazon won't work, Home Depot has a Renogy for $40.

 

[Trebor English]

Upon further review, Home Depot Grape solar 100 watt panel is back up to $146. Amazon has several 100 watt panels in the $99 to $110 range.

 

[DLTooley]

Solenoids have the reputation for making a durable alternator-house battery connection. A small solar panel will help with that long, low power, charge 'tail' required to get a battery up to snuff. I recently upgraded from a 50 watt panel to a 100 watt panel and use the above windshield trick when camped as supplemental power.

I've been told a 15 watt panel doesn't even need a controller - it just acts like a full time trickle charger. Estimating, and tracking your actual, power usage is important. The Victron 75/15 does this, as well as your solar input. It's $120.

I still have my first warranty replacement Walmart deep cycle. I do my laptop charging while I'm in that 'long tail', so it puts no drain on the house battery at all. I am also able to run a 12v freezer on 100-150 watts of panel during the day only, albeit somewhat marginally.

 

[tx2sturgis]

When I first posted about hooking up a small panel to a battery directly, there was some disbelief and ridicule. 

I have been there, done that, got the t-shirt. It can be done, but YOU become the controller.

Do I recommend it for long term use to actually power anything? No.

But a very small panel, 5-15 watts or so, can be connected directly to maintain a normal FLA starter or deep cycle battery. The user must monitor the battery for voltage, and water levels, but it does work. You do need a blocking diode inline. 

But panels and controllers are so cheap now, that it makes little sense to try to make do without a controller. 

BTW, dont forget that Walmart.com sells solar panels too...

https://www.walmart.com/search/?query=solar panel&cat_id=0

 

[king]

This is the kind of answer I was hoping for, but getting such radically different responses (5 hrs vs 20 minutes charging tine) is what led to my initial frustration and not knowing who to believe.  Guess I will just have to put in the money and figure it out as I go.  

I will not be playing games or using much electricity at all, I have a small chromebook, an old flip phone, a maxxair 5 amp fan, and that is it, I dont even have lights yet, only battery powered lights and a luci light.  So I feel your answer is likely more correct for my situation. Thanks, it is more encouraging.

 

[John61CT]

There was no disagreement between us, just your limited understanding of how charging works.

The 5+ hours is about getting back to 100% Full.

20min may be enough to replace a certain amount of power used, but the batt may only be 75% full at that point.

The former is only required for bank longevity, and 2-3 times a week may be sufficient for that, rarely do we achieve ideals in real life.

 

[king]

Sorry to hear that, but please don't give up, because it does not have to be perfect (or super optimized) in order to give you some power rather than no power while you are boondocking.

Thank you for your encouragement. I installed the fan yesterday, so no going back now : )  I'm also thinking of getting 200 watt solar power now, since that seems to be the consensus.  


Anything specific that made you think that you need (or want) a DC-DC charger rather than a big solenoid (isolator)?

My research suggests that it will charge more (full 100% rather than 80% with isolator) and faster, they also have a solar hookup. I have watched many videos like this one which made me change my mind:



 

 

[king]

I was avoiding solar in an attempt to keep things simple, but now I see that a dual battery system is not a good idea unless one plans to drive a lot, which I do not. I'm following Bob's recommendation here, and ordering:

12 volt AGM battery (100-125)
solar charge controller MPPT
solar panel (kit with fuses and cables)


Is there anything else that is required?
I am buying all the components and having someone else do all the wiring, so I need to make sure he has everything he needs to do it.

 

[Trebor English]

If you get a flooded battery you can test the state of charge using a $10 hydrometer.  Particularly with a first battery, it is good to be able to tell exactly what is going on.  Checking and refilling with distilled water takes 5 minutes per month.