Duel battery system in car

[lightseeker2009]

Hi guys. I know this is not flashlight related, but it is battery and light related:thumbsup:
I've read that people doing a lot of camping do not use generators, in order to cut down on noise. They merely use lead acid car batteries, or deep cycle batteries. Some even install the second, or third battery permanently in their cars.
So I thought about taking my car in and get it done. BUT, I was charged over $500.00 for a converter between the batteries. Why are such a ''converter even needed at all? I thought it was simply a matter of coupling the batteries in parallel?
My idea is to have the cars battery, and the extra battery coupled 100% of the time. So then the two batteries will supply the power needed in my campsite. I've worked out that the max usage, if I use all the lights etc, will be less than 70 amps. Normal usage will almost allways be under 50 amps per night. I want to couple the second battery permanently to my cars battery, as doing so it will also charge everytime I drive and will always be 100% fully charged and ready.
I don't want to carry around a single loose battery and would very much like my idea to work...
Is it possible at all?
Thanks

 

[billy_gr]

Hi,

You will need a way to be sure that you will be able to start you car/caravan in any case

Search for National Luna - Dual Battery Controller. It charges both automatically without overcharging and you can switch to primary/secondary.

Common setup for 4x4 winch

Hope that help

Bill

 

[Fird]

i'd look around for a "battery isolator" equal to the full capacity of your alternator. its a very simple device that puts a power diode in line with each battery, completely passive. when the alternator is running, both batteries will charge. when the car is off, you can draw power from one battery without draining the other. I wouldn't parallel a deep cycle directly with your current starting battery because they will likely "fight" as their charge/discharge curves may differ. if you use a battery isolator, you're free to deep discharge the deep cycle without killing your start battery. I used to have such a setup in my car. deep cycle and 1kw inverter along with ham radio gear, all "isolated" from the start battery when the engine was off

 

[SilverFox]

Hello Lightseeker2009,

There are two ways to do what you want to do.

One involves simply hooking another battery in parallel. The other involves using an isolator to preserve one battery and run everything else off an additional battery or set of batteries.

The first method is simple but has the drawback of not having a reserve. If you run the battery bank down, you don't start your vehicle.

The second method involves having two systems. One battery is isolated and only runs your vehicle. The additional batteries run your additional needs but do not tap into the vehicle battery. Since it is difficult to know your needs ahead of time this allows you to still start your vehicle should to run you additional loads longer then you thought you would.

Additional circuits cost more money. If you decide to go the simple way be sure to have a set of jumper cables packed along with you. Eventually you will find them very useful.

Tom

 

[lightseeker2009]

Hello Lightseeker2009,

There are two ways to do what you want to do.

One involves simply hooking another battery in parallel. The other involves using an isolator to preserve one battery and run everything else off an additional battery or set of batteries.

That is why I thought why a converter of $500.00..... The installation guy was adamant that the system will never work without this part. I don't even know what it does. He also said the second battery will never charge if you just connect them in parallel in a car. I have a hard time accepting that. But I simply did not have the energy to argue with a supposedly ''expert'' I have multiple modified spotlights (flashlights) running batteries in parallel, problem free. One that does this in standard form is my TK40. I don't see a converter between the sets of batteries in it.

 

[SilverFox]

Hello Lightseeker2009,

If I were in your shoes...

I would go back and ask to have the $500 converter removed and refunded. Tell them you want to try it just wired in parallel to see how that works to start with and will consider a more complex option if that doesn't work out.

I would let them know that if the battery gets ruined in the process of the experiment you won't hold them responsible but expect the wiring to be done properly with + going to + and - going to -.

Tom

 

[cland72]

I used a Blue Sea Automatic Charging relay ($100) to connect my batteries. Here is a link explaining how it works, but the short version is the ACR only connects the two batteries when the alternator is charging (car is running). When the car is off, it disconnects the batteries so you can use your AUX battery until it is depleted without the danger of depleting your primary (starting) battery.

http://www.bluesea.com/resources/1366

How does an ACR work?
An ACR senses when the voltage of either of the batteries rises to a level indicating that a charge source is active (13.0V for 2 minutes). The ACR′s contacts then connect and the ACR applies the charge to both batteries. If the voltage on both of the batteries subsequently drops to 12.75V for 30 seconds, the ACR will disconnect, isolating the batteries.

Basically, your factory battery is unaltered, save for an additional cable that is added from the positive post to one side of the ACR. Then, another positive cable from the other side of the ACR to the positive terminal of the auxiliary battery. Then, ground the negative post of the AUX battery to the frame/body/motor, and you're done.

 

[WalkIntoTheLight]

That is why I thought why a converter of $500.00..... The installation guy was adamant that the system will never work without this part. I don't even know what it does. He also said the second battery will never charge if you just connect them in parallel in a car. I have a hard time accepting that. But I simply did not have the energy to argue with a supposedly ''expert'' I have multiple modified spotlights (flashlights) running batteries in parallel, problem free. One that does this in standard form is my TK40. I don't see a converter between the sets of batteries in it.

Remember that a car mechanic (or whomever is installing this) is not an electrical engineer. He probably has been taught one way of doing something, and he doesn't understand how anything works. So he's only going to install it one way, the only way he knows. Attempts to get him to explain why will just get him flustered and he'll use the old "expert" clause to end the conversation.

Either that, or he's just trying to rip you off for another $500.

Either way, I'd take it somewhere else, where the "expert" is more relaxed, and understands how to hook batteries in parallel. Yes, you run the risk of draining both batteries if you drain them too much, but is sounds like you understand that. Also, I wouldn't use it in winter, because you risk draining your starter battery (that gives you the high cold-cranking-amps), and the deep-cycle battery may not have enough CCA to start your car if it's really cold (even though it may still have plenty of remaining capacity).

Isolating them is better, but may not be worth $500 if this is just for occasional use.

 

[lightseeker2009]

Remember that a car mechanic (or whomever is installing this) is not an electrical engineer. He probably has been taught one way of doing something, and he doesn't understand how anything works. So he's only going to install it one way, the only way he knows. Attempts to get him to explain why will just get him flustered and he'll use the old "expert" clause to end the conversation.

My thoughts exactly. How do I know maybe he just started working there and must still gain experience.

Either that, or he's just trying to rip you off for another $500.

Either way, I'd take it somewhere else, where the "expert" is more relaxed, and understands how to hook batteries in parallel. Yes, you run the risk of draining both batteries if you drain them too much, but is sounds like you understand that. Also, I wouldn't use it in winter, because you risk draining your starter battery (that gives you the high cold-cranking-amps), and the deep-cycle battery may not have enough CCA to start your car if it's really cold (even though it may still have plenty of remaining capacity).

Isolating them is better, but may not be worth $500 if this is just for occasional use.

I thought about getting the exact same battery that is in the car, so it wont be a deep cycle.
I just think to draw somethink like 50 amps, 25Amps from each, will not really cause any issues with starting the car and its altenator. But then again, I just might be wrong?

 

[Samy]

Voltage drop is a big issue as are modern vehicle alternators which often can't provide enough voltage to charge two batteries in a dual battery systems. It sounds like you have a DC-DC charger installed to ensure a full charge in the second battery. They are very popular here in Australia. Take a look at this: https://www.youtube.com/watch/?v=kfp0vE7teNg

cheers

 

[lightseeker2009]

Voltage drop is a big issue as are modern vehicle alternators which often can't provide enough voltage to charge two batteries in a dual battery systems. It sounds like you have a DC-DC charger installed to ensure a full charge in the second battery. They are very popular here in Australia. Take a look at this: https://www.youtube.com/watch/?v=kfp0vE7teNg

cheers

No, I don't have a DC-DC charger. I was hoping the altenator can take care of things.

 

[WalkIntoTheLight]

Voltage drop is a big issue as are modern vehicle alternators which often can't provide enough voltage to charge two batteries in a dual battery systems.

I don't understand. Why would an alternator not be able to provide enough voltage to charge 2 batteries (in parallel)?

I get that it may put a heavier load on the alternator, and that voltage may be temporarily depressed while providing that load. But any voltage higher than the voltage of the batteries will charge them, and of course the alternator will be providing charge. As the batteries become charged, the alternator should see no difference between 1 or 2 batteries.

The risk I see is that the alternator may be put under more stress than it was designed for. But that will be the case for anyone who regularly depletes his car battery.

 

[WalkIntoTheLight]

I thought about getting the exact same battery that is in the car, so it wont be a deep cycle.
I just think to draw somethink like 50 amps, 25Amps from each, will not really cause any issues with starting the car and its altenator. But then again, I just might be wrong?

If you're planning on depleting those batteries, it's probably better to use a deep-cycle battery. The regular flooded batteries are designed for high current but little capacity drain. Regularly draining a starter car battery will likely result in its death fairly soon.

What about just using a stand-alone deep cycle battery, and charging it from the cigarette lighter (with a charger)? I think you get about 10 amps from those sockets, which should charge a deep-cycle battery in 8 hours or so. Yes, that's a lot longer than from an alternator, but it's simple and no risk. Just plug it in whenever you're driving. Or charge it at home when you can.

And since it's portable, you don't need to use long extension cords out to your car when using the battery.

 

[lightseeker2009]

I think I will just get a deep cycle and charge it seperately. This seems like the best, and safest option after all.
Thanks everyone.

 

[mvyrmnd]

I have my secondary battery (150Ah VRLA) wired in behind the ignition so that I can run it independently (ignition off) Run in parallel (Ignition On) and it will charge in parallel with the engine running.

The secondary battery is isolated while cranking to only use the car battery to crank, but if the car battery goes flat I can leave it in ACC for a while to equalise the batteries and get enough power to crank.

 

[Samy]

Apparently it's an issue if you have a temperature compensating or ecu controlled alternator. Take a look at this PDF: http://www.redarc.com.au/images/uploads/files/tech_tip_-_bcdc1220_vs_alternator_charging.pdf

cheers

 

[mvyrmnd]

I am aware my setup will only charge my aux battery to 80%. I think the 60% figure they give in the PDF is a bit of scaremongering to drive sales. (I'm satisfied from using a watt meter when discharging that mine charges to 80%)

I use a mains powered battery charger to top it off on a regular basis - it's not hard to plug it in and leave it overnight