Need a new car battery

[kmckis1029]

perry you are a trip... always "correcting" stuff... if i was in the mood i would brain and fact joust with you over electrical stuff everytime... but im glad you add your point of view... keep threads interesting

[pfarmer]

Having a secondary battery can make things worse if not done properly.

The voltage regulator keeps an eye on the battery by turning current to the field (stator) terminal of the alternator on and off. By design it should not be a constant charge to the battery.

Simply adding a second battery can make things worse unless you use a "smart" configuration which will monitor the main battery charge before allowing the secondary battery to be charged while runing (different than using battery isolators). In general, adding a secondary battery is good for allowing the owner to listen to the stereo without the car running while ensuring the main battery is not drained. While driving, the proper solution is to use the properly sized alternator.

Keep in mind that my career was that of operation of electrical generation equipment up to and including 750 MWG hydrogen cooled generators, gas turbine driven generators, diesel, and hydro prime movers. and training others in their use.

The case here is the capacity of the alternator (110 amps) leaves it with about an excess of 70 amps over the fully loaded operation of the car which I measured at about 40 amps. The cable sizes in the Infiniti corresponds to these values which means you need to make some considerations if increasing the alternator capacity.

As far as how the charging system works on the Infiniti you may want to get back to me after reading the FSMs, this is not your father's Buick.

In the case of a charging systems 'float' this typically works by floating a charge to a battery at just above the system operating voltage compensating for the internal resistance of the battery bank. On an older car this would not be that important of a consideration but for newer vehicles which operate off of CPUs it becomes more critical especially when loads such as a/c, cooling fans, etc. cycle on and off. The loads on this type of system are usually directly connected to the battery bank unless the system has an ups where the ups powers the normal loads and the battery bank is charged to just above the bias of a blocking diode. Upon loss of the ups recifier the battery then is automatically connected into the circuit through the blocking diode provide a true uninteruptable backup.

Now while this may sound like something completely foreign to the Infiniti this is what I found when measuring current draws on the car. Basically right after starting the car the loads on both the negative and positive terminals were very close to the same. As the car ran the positive side stayed up with the negative side dropping towards a very minimal value to the point the clamp on meter no longer is accurate.

This brought me to look at the FSMs and further to understand what the alternator B,S,L,C, and E terminals really do. Two that are very telling here especially in regard to other posts on this forum are the C terminals connection to the IPDM and the E terminal connection to ground and how that corresponds to my observation above. We are looking at a simple UPS but for DC use.

As far as the second battery goes yes you want it to be 'smart' which is really not all that difficult to do depending on if you want to use it as a backup to the main system or a stand alone for the audio system only. Many of these are simple fairly low capacity batteries to full system capacity batteries for backup use. I typically listen for fairly short periods with the car off so I would go with a low capacity (hence small) battery in my trunk.

The trick with the Infiniti is that the main battery current draw (to ground) is what is used to determine its condition for the voltage variable control system for charging purposes which in its simplest form would not come into play for the second battery. However I think you could use the negative terminal current sensor for the secondary battery with a couple of simple modifications.

Of course you still do not want to outrun the 110 amp limit of the OEM alternator (actually appears to be a fat of 30% built in looking at the FSMs), but then I would think a 500 watt sound system would not be out of the picture (will have to see what the current draw would be).

Perry

[audtatious]

You are correct, I have not looked into the charging characteristics of the G itself, just relying on the years I've fought electrical limitations in cars due to sound systems and what I would call "best practice" guidelines. The general population, when selecting a battery, is usually of the "bigger is better" mentality and will replace a 500cc battery with a 800-1000cc battery. When talking about already strained electrical systems due to aftermarket audio equipment this is not a good thing as the long-term effects overshadow any placebo-imagined short term gains.

Now, going through the '08 coupe FSM I see what you mean. The battery current sensor monitors the battery ground cable and communicates the information to the ECM which determines if the battery needs charging and sends a calculated value to the IPDM E/R which then communicates to the regulator for the specific amount of power. It also looks like the system defines 12-13.6v as the default when alternator duty is 40% and will increase the voltage +.5v or more when the duty cycle hits 80% (settings viewed via Consult)......This is the normal operating flow and set variables for the system.

Now, in the case of my coupe, in which the alternator has a nominal rating of 12v and 150a, what happens when you are running the car with accessories/audio system on and you reach peak amps? Say you are running headlights, fog lights, A/C and you are in mixed-city driving, my assumption would be that you are OK as the alternator should easily be able to provide power to run all accessories in that situation (although I have not found anything showing what the maximum amperage is with all accessories running). Now, what if you added a high-end audio system on top of that which could pull 80-100a (Don't laugh, I've blown the 50a fuse numerous times with my PPI A600 "back in the day" and it was only 1 of 3 amps I had in the car)? My assumption would be, regardless of the electronics involved with the Infiniti charging system, that you would be in a scenario where you are pulling power from the battery which leads us right back to a battery drain issue. I didn't necessarily see anything within the charging system diagram which would limit such events from happening (which you also stated above).

[pfarmer]

Now, going through the '08 coupe FSM I see what you mean. The battery current sensor monitors the battery ground cable and communicates the information to the ECM which determines if the battery needs charging and sends a calculated value to the IPDM E/R which then communicates to the regulator for the specific amount of power. It also looks like the system defines 12-13.6v as the default when alternator duty is 40% and will increase the voltage +.5v or more when the duty cycle hits 80% (settings viewed via Consult)......This is the normal operating flow and set variables for the system.

Now, in the case of my coupe, in which the alternator has a nominal rating of 12v and 150a, what happens when you are running the car with accessories/audio system on and you reach peak amps? Say you are running headlights, fog lights, A/C and you are in mixed-city driving, my assumption would be that you are OK as the alternator should easily be able to provide power to run all accessories in that situation (although I have not found anything showing what the maximum amperage is with all accessories running). Now, what if you added a high-end audio system on top of that which could pull 80-100a (Don't laugh, I've blown the 50a fuse numerous times with my PPI A600 "back in the day" and it was only 1 of 3 amps I had in the car)? My assumption would be, regardless of the electronics involved with the Infiniti charging system, that you would be in a scenario where you are pulling power from the battery which leads us right back to a battery drain issue. I didn't necessarily see anything within the charging system diagram which would limit such events from happening (which you also stated above).

I run a similar scenario with my other car which has a 5 channel 100 watt rms per channel amp. It will drain the system down quickly with the car off. With the car running I never have an issue, but I do believe I am at or close to the limit. In the 'G' I would consider the second battery in the trunk with possible provisions to monitor it using the 'G' monitor system for charging purposes with the addition of a couple of components. From my observations I believe I would be ok, but again close to the limit of the rated power output of the alternator (although there may be a 30% fat). This assumes stock lighting, etc.

One thing to consider is that a larger battery should already have been charge since the car is running. If jump starting then there could be an issue if it is drained. I don't think it would be an issue then since it is monitored, its internal resistance would not in itself be that much of a factor and if concerned one could current limit it for charging purposes.

You are correct in that it will not fix an already taxed system unless the system could provide the average load based on short term cycles. You may have noticed now why I mention the interesting factor about the negative lead in regard to grounding cables and how this influences their design.

Perry

[audtatious]

While I have nothing against 5 channel 100w amps (I loved my a/d/s PH15), try a 400w amp running a 1ohm load and pushing 800w+ to go along with your 100w amp

Unless you are using the system for listening to music when the car is off then I would avoid a second battery altogether and look at ensuring you have a properly sized alternator. When driving around and jammin it would be eaten up relatively quickly and the alternator will still need to try and charge it which would strain the system and be annoying as hell when you can't properly hit those bass transients. The only positive is that with it properly isolated you would ensure the main battery itself is not drained.

[pfarmer]

While I have nothing against 5 channel 100w amps (I loved my a/d/s PH15), try a 400w amp running a 1ohm load and pushing 800w+ to go along with your 100w amp

Unless you are using the system for listening to music when the car is off then I would avoid a second battery altogether and look at ensuring you have a properly sized alternator. When driving around and jammin it would be eaten up relatively quickly and the alternator will still need to try and charge it which would strain the system and be annoying as hell when you can't properly hit those bass transients. The only positive is that with it properly isolated you would ensure the main battery itself is not drained.

I would agree if the battery was simply an addition to the main and not installed in a smart way as far as charging. And yes the alternator does have to be sized to match the load regardless of its presence. In the case of the second battery the idea is not to add its charging load in at the same time as the main although in reality it probably will not need to exceed about 10-15 amps if fully drained. While charging you could still use the audio system.

I listen to the system often with the car off. I haven't check the Infiniti yet but with the 300 m anything below the mid 11s means starting the car may not occur. I use the radar detector to observe it. I did watch my Infiniti today using OBD and it seems to stay at pretty close to about 13.05 volts (rounds up and down for extremely short periods of time) when running at full stock volume. Very well controlled and narrow bandwicth. Unfortunately the method doesn't allow observation with the car off. This does give some needed info when it comes to design of the smart system for the second battery.

Unlike how I have seen most connected I would only have the second battery come into play with the car off. Not needed with the car running and like you state the alternator needs to be sized to handle the system load anyway. This doesn't mean that if discharged you can't listen to the system off the main battery.

I would like to see what the actual capacity of the stock alternator is. It seems to be listed as 110 amps but there is some indication that it has enough fat to actually handle about a 500 watt (audio) amp with the second battery added in as well although probably best to simply keep it out until the main is fully charged..

Perry

[audtatious]

In your case a second battery would be fine as you are not really taxing the electrical system that much with your one amp while driving. The problem that some have is that they add multiple amps which have huge power consumption requirements that simply can't be sustained by the alternator. Adding a 2nd battery as a solution in that situation is not appropriate as they are simply adding another reservoir that the already over-burdened alternator has to charge. Even with adding an isolator and running the system off the second battery they only have so much storage in the second battery to utilize before it's drained and they are further limited by the isolator, thus the amps don't get the power they need, it sounds like crap and you can get clipping and such which can destroy the components.

Price also comes into the equation. Adding a good 2nd battery can cost $100 (or 200+ for an optima). 1ga power wire can run another 50-80 bucks for the good stuff. Aother 20-30 in terminals brings the basic cost to over $200 and that does not include the battery mounting kit nor the isolator, etc. The end result could be upwards of $300-400 to do it right which does not make sense when you can get a 190amp alternator for just over $300 (I saw $325 with exchange online)

[pfarmer]

In your case a second battery would be fine as you are not really taxing the electrical system that much with your one amp while driving. The problem that some have is that they add multiple amps which have huge power consumption requirements that simply can't be sustained by the alternator. Adding a 2nd battery as a solution in that situation is not appropriate as they are simply adding another reservoir that the already over-burdened alternator has to charge. Even with adding an isolator and running the system off the second battery they only have so much storage in the second battery to utilize before it's drained and they are further limited by the isolator, thus the amps don't get the power they need, it sounds like crap and you can get clipping and such which can destroy the components.

Price also comes into the equation. Adding a good 2nd battery can cost $100 (or 200+ for an optima). 1ga power wire can run another 50-80 bucks for the good stuff. Aother 20-30 in terminals brings the basic cost to over $200 and that does not include the battery mounting kit nor the isolator, etc. The end result could be upwards of $300-400 to do it right which does not make sense when you can get a 190amp alternator for just over $300 (I saw $325 with exchange online)

In the old days I did have something really unique and that was a battery I center tapped. The reason was that my car was a 6 volt positive ground and I wanted a then state of the art 12 volt transistor radio. The battery sat in the trunk for another reason and that was the 12 volt dynomotor for my a/c black lights. Starting the dynomotor was a trip. Basically turn all loads off and spin it up to speed, then reenable everything. A group of knife switches did the trick. My friend had one in his 12 volt Plymouth. He faired better but it was wise to turn off the headlights first. Great fun, no one else had anything like it and the dyno sounded like a small jet spooling up.

Perry

[pfarmer]

Price also comes into the equation. Adding a good 2nd battery can cost $100 (or 200+ for an optima). 1ga power wire can run another 50-80 bucks for the good stuff. Aother 20-30 in terminals brings the basic cost to over $200 and that does not include the battery mounting kit nor the isolator, etc. The end result could be upwards of $300-400 to do it right which does not make sense when you can get a 190amp alternator for just over $300 (I saw $325 with exchange online)

One issue with the 190 amp alternator is that there are some possible limitations due to the stock wire size. Replacement of the fusible link and possibly associated wiring also needs to be taken into consideration but that is a fairly easy task. The alternator needs to be done if the stock one is overloaded but the rest of the system may need a little refreshing as well so the cost could actually increase over the number stated.

Perry

[audtatious]

In the old days I did have something really unique and that was a battery I center tapped. The reason was that my car was a 6 volt positive ground and I wanted a then state of the art 12 volt transistor radio. The battery sat in the trunk for another reason and that was the 12 volt dynomotor for my a/c black lights. Starting the dynomotor was a trip. Basically turn all loads off and spin it up to speed, then reenable everything. A group of knife switches did the trick. My friend had one in his 12 volt Plymouth. He faired better but it was wise to turn off the headlights first. Great fun, no one else had anything like it and the dyno sounded like a small jet spooling up.

Perry

Sounds interesting for sure. I never had to deal with 6v systems

One issue with the 190 amp alternator is that there are some possible limitations due to the stock wire size. Replacement of the fusible link and possibly associated wiring also needs to be taken into consideration but that is a fairly easy task. The alternator needs to be done if the stock one is overloaded but the rest of the system may need a little refreshing as well so the cost could actually increase over the number stated.

Perry

For the newer G-style systems that might be a possibility ( ? ) and would need to be looked into to see if that would indeed be an issue or not. I'm sure if there was a limitation it would be the wire size between the alternator and the IPDM to battery and possibly ground which would need to be upgraded, assuming you are still trying to pull power from the factory wiring. Otherwize there won't be an issue from a voltage perspective as the HO alt is still staying within the 13-14.4v range. You can also upgrade to a dual output alternator (which most also include battery isolators) in which the audio system is connected directly to the alternator itself, with dedicated battery if necessary, and bypass the factory battery system charging lines.

If you spend a couple grand+ on upgrading car audio equipment it's a waste to not properly ensure the charging system can support it. The alternator is the heart and simply adding a bag to hold more blood does not increase the amount of blood from the pump to the extremities

[telcoman]

In the old days I did have something really unique and that was a battery I center tapped. The reason was that my car was a 6 volt positive ground and I wanted a then state of the art 12 volt transistor radio. The battery sat in the trunk for another reason and that was the 12 volt dynomotor for my a/c black lights. Starting the dynomotor was a trip. Basically turn all loads off and spin it up to speed, then reenable everything. A group of knife switches did the trick. My friend had one in his 12 volt Plymouth. He faired better but it was wise to turn off the headlights first. Great fun, no one else had anything like it and the dyno sounded like a small jet spooling up.

Perry

While still in HS prior to getting our drivers licenses I assisted a friend cram a 58 Pontiac engine (12v) into a 51 Ford (6v). Your bringing up knife switches brought back memories. We double dated and took turns in the back seat and......... Ahh the good ole days

[pfarmer]

While still in HS prior to getting our drivers licenses I assisted a friend cram a 58 Pontiac engine (12v) into a 51 Ford (6v). Your bringing up knife switches brought back memories. We double dated and took turns in the back seat and......... Ahh the good ole days

A lot of Pontiacs went into a lot of Plymouths as well. Not sure of the exact why since many others were stuffing Chryslers into GM and Ford products.

In any case for those that don't know what the dynomotor was. Basically you typically got these from Military surplus, ours were unique in that they were twelve volt which indicated to me a ground based application. Aircraft versions had various voltages such as 24 and 48 for their dc input. What you have here is a dc motor driving an ac generator. Sort of looked like two starting motors in size coupled in the middle.

When started the inrush and the following starting current were very high. Typically your headlights would dim way down if on and the car may actually stall out if idle is not kept high. Sort of sounded like you were spooling up a turbine. Once up to speed it had a certain whine to it, sounded a little bit like a Chrysler turbine car. Now you had a/c available for black lights, chandeliers, home based stereos, etc. Don't laugh we had a good selection of all of these in our cars.

It had a couple of features that most didn't realize. Basically it also acted like a condensing turbine/generator set does. That is if you had a sudden increase in electrical needs such as turning on your aircraft landing lights it acted like a shock absorber. For an interesting read on this concept consider that there is something similar sitting on the grid for the Florida Keys. In the case of hydro based systems this is a very common configuration. When a hydro is not generating it is often motoring with the runner out of the water by pressurizing a space under the turbine with air. A 60 mw turbine generator is now a 1 - 2 mw motor which makes a very good flywheel.

For sound systems does this sound familiar? Just a different method in a very different time.

Perry

[C-Kwik]

anything i should watch out for when buying?never bought a battery so i dont know what to look for.

While SF is usually colder than it is down here in socal, it still has fairly mild temperatures. I'd recommend a good deep cycle battery. While deep cycle batteries have slightly lower cold cranking amps relative to a typical starter battery of the same size, its likely going to be more than enough unless you see some seriously cold temperatures. The advantage is they don't go bad if you accidentally drain it. As they are designed for use in RV's and boats, they do not lose their reserve capacity each time it gets drained. I've never had to replace a deep cycle battery I bought so far. Though, in my case, every battery I've replaced was usually because of lost reserve capacity after several accidental discharges. May not be a big deal for many (perhaps especially with the G as my understanding is it can cut power to non-essential equipment when it detects the battery is running low), but personally, I'd rather be safe than sorry.