Size 34 Optima Battery w/positive ground

[Bob_Spidell]

Good day Olin, and all. Not to throw a wrench into things(sorry, no pun intended)but you have to be careful not to buy too large a battery. Unless you've changed out the generator to an alternator you may no longer have the capacity to keep the larger battery fully charged and it will eventually run down. Think of it as a water faucet filling a bucket vs filling a lake.

Sorry, but this makes no sense (I'm not an EE, but have some electrical knowledge). This statement seems to imply that car batteries--AGM or regular lead-acid--are in a perpetual state of discharge and that a higher-capacity battery will discharge more. This is not the case.

The demand on the battery--called the "load"--is the sum of all current draws. As long as the generator's capacity to supply current exceeds the load then the battery will be charging (the current needed to fire the plugs is minuscule; lights are a different story). The generator has to be able to maintain a little under 15V to overcome the internal resistance of the battery in order to charge the battery; if the load is such that the voltage drops much below that then the battery will not charge (lights will be dimmer and the red light on your tach may light up).

Further, the battery, any battery, will only supply the current required by the load. IOW, if the load is X amps, a smaller battery will supply X amps and a larger battery will supply X amps. The difference is that the larger (higher capacity) battery will supply X amps longer. If it takes, say, 500 amps to start your car--the initial current rush of a couple hundred amps lasts for only a brief time until the inductive impedance in the starter motor builds--and your generator supplies 20 amps it will take about 25 minutes to fully recharge the battery, regardless of its size or CCA rating.

Larger batteries will supply the load longer--this is called the "reserve"--than smaller batteries. An alternator will re-charge the battery faster than a generator, generally, but a generator will do the job eventually. The only penalty for having a "too large" battery is the extra weight and bulk you're hauling around.

 

[Robert560]

The biggest draw off the battery is the act of starting, not power consumption while driving. This can be exponentially higher than the 5 or 10 amps (or more) your car is using while running. If your alternator/generator cannot replenish the power lost during starting, you will be cycling the system below the full capacity threshold, which can result in a continuous (possibly very slow) decrease in battery charge. Also keep in mind that a starter really doesn't have a power draw "cap" on it... unlike a radio, for example, which uses a fixed current (not really fixed, but close enough, by comparison). A starter will consume more power if needed/available, which is why big motors take big batteries to crank in the first place... and also why it's so easy to kill a battery in old cars when you've got a "hot starter" problem.

Another factor is... yes, both a smaller and larger battery will supply the same X amps... the difference is that the higher the rating of a battery, the longer it takes to recharge (given the same recharge rate, and knowing that more power is drawn during the starting process). The attached photo/chart somewhat illustrates this. Granted, the chart shows time from full discharge, but the ratio remains proportionate, given all other factors equal.

Giving the above, it can be possible to create a battery problem by installing a huge battery in a car with a stock vintage charging system (not saying it will be a problem, just that it's possible). And if you've got a generator that can already allow for battery draining when you get stuck in traffic at idle speeds for too long... that means your battery is being consumed even more, requiring even longer charge time to get back to full.

To compound the problem... if you've added other electronic gizmos, or a high torque starter, or A/C, the problem gets even worse, since the battery is only charging off of what's not being consumed elsewhere. This can potentially mean a dead battery every few months (or quicker) and/or unless the battery is a true deep cycle, can lead to degradation of battery performance and longevity (batteries not continually existing at full charge can often start to degrade internally due to insufficient excitation).

Hope that makes sense. That's why I recommend getting a battery that's proportionate to your electrical system. I learned all this the hard way, many years ago, in an old musclecar that had this "ghost problem" of the battery dying every month and a half.

~Robert

 

[Bob_Spidell]

What the chart shows is that the greater the capacity of a battery the longer it will take to charge it from a fully discharged state--no surprise there. My point above is that the demand on a battery is determined by the load (E=IR), not the capacity of the battery, except for a split second when current is applied to the starter. In that split second, the starter motor is essentially a dead short, so the current draw is limited by the internal resistance of the battery, and a higher capacity battery will likely have less. After the motor has started to spin and the coils become saturated the inductive impedance in the coils are the limiting factor. So, yes, a higher capacity battery will discharge somewhat more current for a start than a lower capacity one--a lot more if you have to crank for a long time--and it will take longer to fully re-charge it, even with an alternator. If you start your car and don't drive it long enough to fully charge the battery it will eventually discharge and begin to sulfate, no matter what size it is (that's probably what happened to your muscle car, or you had a short somewhere).

The demand on a battery is determined by the load--except for briefly when starting--not the capacity of the battery. If you put a larger battery in your car and you're concerned it's not getting charged completely between starts put a float charger on it.

Here's a good site: https://www.batterystuff.com/tutorial_battery.html

From the site: "When buying a new battery I suggest you purchase a battery with the greatest reserve capacity or amp hour rating possible."

Then, drive your car long enough to charge the battery (or put a charger on it). Yes, an alternator with a smaller battery will charge quicker, but a generator with a larger battery will be fine if you put 20 miles on the highway after a start, or float charge it.

I've never heard the term "excitation" used WRT a battery, only WRT residual magnetism in generators. Batteries are a chemical reaction that takes place when the circuit is closed. It's affected greatly by temperature, that's why capacity is given as "Cold Cranking Amps"--the reaction doesn't work as well at colder temperatures. I guess you could say temperature "excites" the reaction, but unless you're at absolute zero there will be some chemical activity.

 

[Robert560]

So, yes, a higher capacity battery will discharge somewhat more current for a start than a lower capacity one--a lot more if you have to crank for a long time--and it will take longer to fully re-charge it, even with an alternator. If you start your car and don't drive it long enough to fully charge the battery it will eventually discharge and begin to sulfate, no matter what size it is (that's probably what happened to your muscle car, or you had a short somewhere).

This is essentially what I was saying. Thanks for clarifying... I just couldn't seem to get it out in a way that made sense.

Yes, an alternator with a smaller battery will charge quicker, but a generator with a larger battery will be fine if you put 20 miles on the highway after a start, or float charge it.

...or, you can just mate a big battery to a big alternator, and not have to worry about it

Maybe I'm just paranoid, but I really wanted a "set it and forget it" with the Healey. What you say above is basically what I had to do with that old musclecar I mentioned. It had a radical motor that required lots of power to crank, and idled low, which went below the generator's ability to supply at idle. Combined with lots of stop-and-go cruising, and I had an average load demand slightly greater than my average charge supply. What made the problem a real bear to solve was that before I put in the monster 1000 CCA battery, I had a smaller 420 CCA battery in it. The small one would have a heck of a time turning over that radical motor, couldn't do it at all when hot, but I never had any problems with it dying over time. So I put a new, bigger battery in, changed nothing else, and what the heck happened?!? It took me months to figure it out.

Turned out that the bigger battery was not only discharging more during starting, but also at idle, as it was keeping my headlights brighter at night during a long summer of stop-and-go cruising.

~Robert

 

[Bob_Spidell]

I think we're in agreement. There's nothing inherently wrong with a higher capacity battery in an older car, you just need to either drive it long enough to put a good charge on the battery or put a float charger on it.

On a side note, supposedly you can 'revive' a sulfated battery (I've never tried it):

https://www.ehow.com/how_6189994_recharge-old-dead-car-batteries.html

 

[Robert560]

Sulfation... right... I don't know where the heck I came up with "excitation". I think I was on a thought tangent of slow rotating alternators and field excitation, and managed to somehow merge that into battery charging. Sometimes I think I just outta just sit back, grab a beer, and slow my mind down a bit before I open my mouth.

At any rate... I can't imagine why anyone would ever want to do what they say in the ehow article. Especially if you had to drill holes in the battery to do it! That sounds a bit scary. When I first got my Healey, I found battery acid residue all over the trunk floor... I wonder if someone got carried away with their recharge attempt. I'll just stick to buying a new one

I guess maybe if you still had your original battery... or maybe a mint period-correct battery that just couldn't hold a charge anymore... then I guess it could be worth trying!

~Robert

 

[SideShifter Tri-Carb]

Well, since I still have the generator on my car, I am going to make sure I drive it for a long time after I crank it

While reading all of this, I got to thinking that the charging of a battery, regardless of system is regulated by a "voltage" regulator, not an amp regulator. So, to stir the pot up ever more slightly :crazy: , if the voltage setting by the regulator (say 13.5 v) is met, then there is no more flow of current to the battery. I wonder what voltage capacity a battery has. :confuse: Do the ACM batteries have a higher voltage threshold? Could it take more than 13.5 v to reach full capacity and amperage? If so, will the battery ever get recharged 100%.

I always heard that the battery function was to crank the car and the power of the car will run off the charging system with the battery being recharged in the process. This is true unless you add too many accessories, such as a fan, radio, defroster, electric windows, etc. The most power I could use is driving on a cold night in the rain on the highway. Coil, SU fuel pump, wipers, fan, OD, and lights. I think my generator can cover that.

Olin

 

[Bob_Spidell]

... if the voltage setting by the regulator (say 13.5 v) is met, then there is no more flow of current to the battery. I wonder what voltage capacity a battery has. Do the ACM batteries have a higher voltage threshold? Could it take more than 13.5 v to reach full capacity and amperage? If so, will the battery ever get recharged 100%. ...Olin

The battery will continue to absorb current at the charging voltage--13.5-14.4V, set by the regulator above minimum engine speed--until it is fully charged. The battery can be thought of, logically, as a capacitor: it will accept current until fully charged. The battery has no 'voltage capacity' per se, but above the higher charging voltage (14.4V or so) you will overcharge the battery and boil the electrolyte (sulfuric acid), possibly releasing hydrogen gas and potentially ruining your day. I ruined an otherwise good battery by charging it with a cheap, constant current charger--this type will continue to increase voltage to maintain a given output current--to the battery's demise.

The AGM batteries are still, essentially, lead acid batteries, so all the above applies.

I found a couple good sites for explanations:

https://www.bcae1.com/charging.htm

https://home.comcast.net/~rhodes/generator.html

 

[Ed_K]

Hi Olin,

If you have not bought your battery yet, I would suggest spending a little more and get the yellow top Optima instead of the red top. I found out the hard way that red top Optima batteries do not survive being completely discharged more that two times. I left some lights on for several days and then the battery could no longer be properly charged.
The yellow top Optima is designed to be completely discharged without any bad side effects. The Optima had a good warranty so I traded up to a yellow top with very little extra expense.


Ed

 

[Robert560]

Yellow top batteries are deep cycling, while the red top are just standard "starting" batteries. That's why the yellow will take far more draining abuse (and why they are more expensive).

I know a lot of people like Optima batteries, but I read a lot of negative reviews about consistency and reliability, which is why I opted for a different brand. Many people end up comparing Optima red top to other brands, but they don't realize they're comparing non-deep cycle to deep cycle, which makes the Optima red top appear to be a better deal... when in actuality it's the yellow top that should be compared against competitive deep cycle.

~Robert

 

[SideShifter Tri-Carb]

Hi Olin,

If you have not bought your battery yet, I would suggest spending a little more and get the yellow top Optima instead of the red top. I found out the hard way that red top Optima batteries do not survive being completely discharged more that two times. I left some lights on for several days and then the battery could no longer be properly charged.
The yellow top Optima is designed to be completely discharged without any bad side effects. The Optima had a good warranty so I traded up to a yellow top with very little extra expense.


Ed

Well, I already bought it, but I have not installed it yet. I have taken batteries back before unused. Are we all sure this is what I need? Is there any issue with buying a deep cycle battery that doesn't see much deep cycling?

Olin

 

[Keoke]

Well, I already bought it, but I have not installed it yet. I have taken batteries back before unused. Are we all sure this is what I need?

Well I do not know exactly what you bought.

However,consider the following: The red top Optima is specifically designed for systems that use an alternator.

Contrastingly. the Yellow top was created for cars using the generator.But a comparable "R" version of the red top is not available in the yellow top line except for a very light version of their battery that I would not recommend.

Consequently , I would upgrade to the yellow top # 34 Battery

Is there any issue with buying a deep cycle battery that doesn't see much deep cycling?

Yes I would give some consideration to circuit Malfunctions and human nature.---Keoke

 

[Robert560]

I think if you're buying a battery specifically designed to be a deep cycle battery used in automotive starting applications (Optima Yellow, Odyssey, others), then I don't think you can go wrong.

The only thing you have to be careful about is that, if you DO significantly drain the battery deep cycling, then you need to be careful how you charge it. Make sure you read the manual (I know... gasp!) that comes with the battery to insure you're charging it properly. This is only from a dead or near-dead state though. For normal use, nothing special needs to be done. I've had an Odyssey deep cycle battery in my Healey now for about 5 months now and it's been flawless.

One thing to keep in mind though, if you're on a budget... is that the vast majority of batteries in cars today are not deep cycle batteries... and they work just fine for many years of service. I got one because that's the battery I wanted, not because I thought deep cycling would serve me better in some way.

~Robert

 

[SideShifter Tri-Carb]

yes, I bought the red top 34R. I called avdvance and they said they would take it back, but that I had to wait till tomorrow for the D34 YT since it was not in stock. Remembering that they had a discount for online orders, I opted (no pun intended) to order it online and got 20% off. RT cost me $161 with just 15% off, and the YT cost $185 with 20% off plus I should receive a $50 coupon as well for the month of June for spending more than $100 online. That should cover the pain and suffering for not buying the right one n the first place. Thanks for all of your help. I will have to have the terminals facing the toward the fender, but I can live with that. Ed, I might need your hep putting it in

Along with what you guys said, to complete my decision process, I went to Optima's website and they stated the following in their FAQs

In any vehicle or equipment that will use the battery only for starting, lighting, and ignition (SLI) requirements and has a properly working alternator, the OPTIMA RedTop Starting Battery will perform extremely well, often providing up to two to three times longer life than conventional batteries. If the vehicle has few or no aftermarket accessories and uses a stock or upgraded alternator, the OPTIMA RedTop Starting Battery is the appropriate choice.

It is necessary to consider both the application and the charging system before considering which is the correct OPTIMA battery for you. For example, if you have a Ford Expedition with an aftermarket alarm system and you drive the car every day, the OPTIMA RedTop would be the correct choice since the amperage drain will be nominal and the battery would be recharged on a daily basis. However, if you store the vehicle for long periods of time with the alarm system engaged, you should use an OPTIMA YellowTop since the amperage drain over several weeks would damage a RedTop and reduce its life.