How can i add a second battery?

Hi. I am wanting to add a second battery so when im at a show i can run my install without running the power down on my main battery. 

I have seen it before where the person who owned the car had a battery under the back of the car and just plugged it up somewhere using jump leads. I was wondering if there is an easy way of doing it without draining the main battery or spending a lot of time and money installing a second battery with a cut off switch?

It will only be used for a few hours so the second battery doesnt have to last too long and i can just plug it upto a charger in the garage when i get home.

Any help would be appreciated, Thanks i advance mark.

p.s - This might have been explained somewhere already but i could not find it, If so i apologise. 

first i recommend that the battries be identical we just finished a threed about this https://www.the12volt.com/installbay/forum_posts.asp?tid=80238&PN=0&tpn=1

next check out this site there is a nav on the right of the page you want #118 this will help u deside which kind of set up to usehttps://www.bcae1.com/

Thanks a lot.

That makes it a bit easier to understand. I thought it would have been asked before but i couldnt find it.

I think i will go for the diode type isolator as it looks easiest to set up. The car is only used at 6 shows a year so it isnt a big deal if i lose .6 v on the set up.

Thaks for your help.     Mark.

so lemme get this right from what that thread said, you are supposed to use the SAME EXACT Batts.? And if so under that rule, you shouldnt use a Red Top under the hood and Yellows as secondary? if i read that right i would say i would have to disagree with that too. i have seen many setups that come through the shop that have done that setup and everything works fine, and have yet to see problems.

From what i have read, If im understanding this right, they mean you cannot use a battery that has been on the car 5 years and then throw a brand new one on as your second.

You can use different types but they have to be the same age.

jvillefinest wrote:

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so lemme get this right from what that thread said, you are supposed to use the SAME EXACT Batts.? And if so under that rule, you shouldnt use a Red Top under the hood and Yellows as secondary? if i read that right i would say i would have to disagree with that too. i have seen many setups that come through the shop that have done that setup and everything works fine, and have yet to see problems.

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and i have seen many cars with 4awg power wire,10awg ground, wire ive seen phone cable for speaker wire, radios ing wires hooked up so that the radio only turn on when the parking light are on, but thay work with no real negative consequeence. the question to ask is it the right way to do it? are these people getting the most out of there equiptment? should any self respecting installer tell a custome that its right just beacuse it works and the car is not on fire? the answer is no. so next question are any of us batt. experts? probly not ,do the batt. experts say  that your battires should be identical in type, CCA ,and age, yes so why do we argue that fact?   

Just for another data point, there is another application that uses a battery for 'engine off' use, and an 'engine start' battery.  RVs.. motor homes and campers.

Here's an application where the engine start battery is a standard starting battery.. probably something like 12v 100ah. The battery bank for 'engine off' use is often something like (4) 6v 220ah deep cycle golf cart batteries wired in series parallel. An isolator is used, and while battery matching is *strongly* recommended for the battery bank itself, the age/size/usage level comparison between the battery bank and engine start battery really isn't a concern.

Personally, if you're not using an isolator of some sort then match the batteries. If you're using an isolator (correctly), then I'm not too awfully concerned about battery matching. The RV industry has been doing it this way for decades.. on hundreds of thousands (if not millions) of vehicles. 

In short, it all depends on what you're trying to do, and what you want to accomplish.

Jim

nouseforaname wrote:

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great thread, huh josh?

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ya it seams like we just did this.

Mad Scientists wrote:

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Just for another data point, there is another application that uses a battery for 'engine off' use, and an 'engine start' battery.  RVs.. motor homes and campers.

Here's an application where the engine start battery is a standard starting battery.. probably something like 12v 100ah. The battery bank for 'engine off' use is often something like (4) 6v 220ah deep cycle golf cart batteries wired in series parallel. An isolator is used, and while battery matching is *strongly* recommended for the battery bank itself, the age/size/usage level comparison between the battery bank and engine start battery really isn't a concern.

Personally, if you're not using an isolator of some sort then match the batteries. If you're using an isolator (correctly), then I'm not too awfully concerned about battery matching. The RV industry has been doing it this way for decades.. on hundreds of thousands (if not millions) of vehicles. 

In short, it all depends on what you're trying to do, and what you want to accomplish.

Jim

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good point. but the main diffrence in rvs are that the battries when in use are compleatly isolated under no circumstance will thay ever power the same load. in a car with most isolator set up the battries are only disconected when the car is off therefore thay power the same load and charge at the same time .that will not happen in a rv.

Using the link you posted (https://www.bcae1.com/) and example #118..

Most RV circuits that use a solenoid look like the 'Dual batteries without an isolator' with the addition of a single solenoid connected near the left fuse (off the front battery). They aren't nearly as complicated as the 'solenoid type isolator' circuit with its two solenoids and switches. The RV solenoid is trigger by ign+12; when you turn on the ignition the front and rear batteries are hooked together in parallel.

We took our RV out over the July 4th weekend.. while driving, the alternator died. At that point we were running on battery power; both the engine battery and the house batteries.

You said;

"in a car with most isolator set up the battries are only disconected when the car is off therefore thay power the same load and charge at the same time .that will not happen in a rv.."

That is **exactly** how it works in an RV with a solenoid based isolator system. When the solenoid is energized all the batteries are hooked together and power the same load and charge at the same time.

Answer this for me.. how much power is coming _out_ of a battery when the system voltage is 13.6vdc?

ok maby i spoke too soon on rv"s i have no hard proof but  i will do my research

Answer this for me.. how much power is coming _out_ of a battery when the system voltage is 13.6vdc?

ok if your asking me how much power you can get at 13.6vdc  that depends on the load. with out you giveing me your amperes or  the resistance of a load i can not tell you how many watts you batt. is putting out

When system voltage is 13.6v, the battery is being charged and nothing is coming out of it. I can take a 12v 7ah battery and plug it into the power port on the dashboard (of my work truck) and charge the battery. The fact that it's in parallel with a 12v 105ah battery isn't important.. because they are both being charged.

Discharging is a different matter entirely.

As I mentioned earlier in the thread, how you hook up two (or more) batteries depends on what you are attempting to do. Ford uses two 12v batteries in parallel in their diesel pickups; they need the cranking amps. These do not use an isolator, and they need to be matched batteries. Military equipment is often 24vdc; they use two 12v batteries in series, no isolator. These also need to be a matched set of batteries. Early Porsche 911/912 used dual batteries.. again, matched set.

If you want a second battery to run your stereo/ham radio/inverter/whatever with the engine off (and you don't want to kill the starting battery) then use an isolator and a deep cycle battery. Discharging two paralleled batteries of different capacities just isn't a good idea. Deep discharging a non-deep cycle battery (like a starting battery) isn't a good idea either.

Jim

Did the RV tech mention anything about the different sized batteries being charged?..  Solid state isolaters are nice (and expensive) but did he really say that they switch the alternator output from battery to battery? Isolators divide the charging output.. not switch it from battery to battery.

There are some isolators/combiners that will delay charging the coach battery bank if they detect that the starting battery voltage is low.. but once the starting battery is charged the isolator/combiner goes back to charging both at once.

Jim

i cut this from https://www.hellroaring.com/rv.htm

For motorhome types with high output alternators and large house loads while operating, consider the RV starting battery isolation technique as a simple solution to multiple use batteries.  With this setup, a high output alternator can supply maximum charge current to large house battery banks.  All batteries receive proper alternator voltage from an internally sensed alternator due to the very low ON resistance of the BIC-75150A (less than 0.008 ohms).  Since there is no diode drop, the starting battery stays fully charged.  Electrical loads on either battery will not draw from the other.  If you choose this method, we recommend that you contact our technical support staff for assistance.

For most applications, (i.e. slide-in camper, trailer, RV's with required continuous loads under 50 amps on the auxiliary side during engine operation, etc...) consider the basic deep cycle application.   Your primary objective is to prevent your  starting battery from draining while you consume power from your house (deep cycle) battery.   (Don't be fooled by low cost battery disconnect devices as a solution.  If you try to use these, your starting battery will get deep cycled and will result in early failure.)    You also want your house battery to obtain full charge as quickly as practical while operating your vehicle.   With the BIC-75150A installed as shown below, you will obtain those two objectives!   The BIC-75150A has very little resistance (less than 0.008 ohms) when ON during charging and it automatically isolates the two batteries when charge voltage stops, even if your alternator fails.   If desired, you will have the ability to combine the batteries manually for a starting boost (the main battery must still supply substantial cranking current).   It has no mechanical moving parts to degrade or wear out!  For those on a budget and who want the simplest installation, the BIC-75150A basic Auxiliary setup makes an excellent choice for full charging without the voltage drop or bulky physical size associated with diode isolators!  Works great for alternators sensed at the alternator output (internal sense.) 

I had looked at that company.. it's not a diode based device, and it's not a solenoid either; I don't know what technology they're using.  I did read their technical data.. it looks like the device combines batteries when charging voltage hits 13.4v, and disconnects them at 13.2v

The voltage drop across the unit is extremely low.. I can't recall enough electronics theory offhand to remember if a power transistor has a voltage drop associated with it; if they weren't saying that there's not moving parts I'd say it's a relay inside. There are some current limitations on it.. the model you listed has a continuous limit of 50 or 75 amps I believe..

"Electrical loads on either battery will not draw from the other"..

If this device opens the circuit at 13.2v, of course they won't.. I mentioned that earlier. But they do mention that you can add a switch that combines all batteries for an added boost for charging.. which means the unit _does_ hook all the batteries in parallel when operating.

Did you see anything about batteries needing to be identical in age, CCA and type?

Jim

you wrote. " I had looked at that company.. it's not a diode based device, and it's not a solenoid either; I don't know what technology they're using." as far as i know what technology thay are use is as it has allways been with solidstate relays (solidstate = no moving parts), my boss said he used to ues them in the eary 90's in show and comp cars.

"Did you see anything about batteries needing to be identical in age, CCA and type?"

no i did not. from what i understand their product allows you to hook up odd battries.

correction. you said " But they do mention that you can add a switch that combines all batteries for an added boost for charging.. which means the unit _does_ hook all the batteries in parallel when operating. "

thay said  "If desired, you will have the ability to combine the batteries manually for a starting boost (the main battery must still supply substantial cranking current."

But they claim there's no voltage drop with their device.. research a solid state relay and see what kind of voltage drop you see with those. 

I did mean 'added boost for starting'.. sorry about that. If you can combine the batteries manually, it means that the device will allow backfeed from one battery to another. I suspect that this device also charges both batteries at the same time, ie: they are connected in parallel.

Personally, I have some doubts about the hellroaring stuff.. They never mention the technology they use, and the specs they provide don't seem right to me. They have heat sinks; evidently they are generating heat, which is power loss.. the one device dissipates 36 watts at 120 amps.. do some Ohm's Law (W=V*A) and think about it.

Hellroaring also sells solid state relays.. but they don't list a voltage drop spec.. everyone else does, but not Hellroaring

https://relays.tycoelectronics.com/datasheets/DS11-1006_ds_7-1773440-9.pdf 

But the main point of this discussion was hooking unlike batteries together, was it not? At this point, I haven't seen anything that warns against hooking different batteries together if you are using an isolator of some sort.

Jim