Topic: 67 Battery V. Alternator discussion

[Bossbill]

Someone PMed me about batteries vs alternators.

For now let's deal with the 289/289K engines.
The 67 standard battery is a group 22, with a 44 amp hour capacity.
 The HD battery is a group 24,  55 amp hour capacity and this is often conflated with the 55A alternator.

The Heavy Duty battery is a stand-alone option and I don't believe it has anything to do with the alternator. I don't think it means you get a 55A alternator!
From the wording on the option for this battery it does look like you can get a HD battery and still have the low end 38A alternator.

My particular car has the Heavy Duty battery option (Marti) and has other documentation that normal Mustangs don't have in the form of a Add/Delete sheet to deconstruct a Mustang and form the base for a Shelby.
This doc says delete 38A alternator and install a 42A alternator.
So I have a 55A battery but I have a 42A alternator.

[Bob Gaines]

Someone PMed me about batteries vs alternators.

For now let's deal with the 289/289K engines.
The 67 standard battery is a group 22, with a 44 amp hour capacity.
 The HD battery is a group 24,  55 amp hour capacity and this is often conflated with the 55A alternator.

The Heavy Duty battery is a stand-alone option and I don't believe it has anything to do with the alternator. I don't think it means you get a 55A alternator!
From the wording on the option for this battery it does look like you can get a HD battery and still have the low end 38A alternator.

My particular car has the Heavy Duty battery option (Marti) and has other documentation that normal Mustangs don't have in the form of a Add/Delete sheet to deconstruct a Mustang and form the base for a Shelby.
This doc says delete 38A alternator and install a 42A alternator.
So I have a 55A battery but I have a 42A alternator.

I believe that you will find that the base car with the 22 F battery also has the 42 amp alternator instead of the 38. I believe that wording is standard on the DSO sheet . I believe that the heavy duty battery option automatically triggers the additional higher output companion alternator and corresponding regulator . The 24 F red cap battery (heavy duty battery) is higher capacity and in most cases (not all) the higher capacity battery needs to be supported by a higher output alternator and companion regulator. Regardless of if there was a need car wise for the additional alternator output or not it was part of a package. A comparison example can be made to the 1969 drag pack option where for the small sum of just lower rear end gears alone a car automatically was upgraded to oil cooler ,lines ,adapter ,LeMans rods,balancer flywheel and crankshaft . The point is it not uncommon for one item to trigger other items to automatically be added.The higher output battery is typically paired to the higher output supporting components . In the world of the Ford replacement the components are typically of the higher output. The Ford service specifications guide for each different year 1965-1969 shows the higher output alternator with corresponding regulator. I am not a electrical engineer but it is reasonable to conclude that Ford did not make a conscious mistake in all of those years publications without correcting it if it needed to be. It appears it is a example of Fords way of doing things

[Bossbill]

I have no issue with you said. It makes sense.

But, specifically,  I don't think a 55 Amp hour battery requires a 55 Amp alternator.
I have heard statement to that effect (offline).

[Bob Gaines]

I have no issue with you said. It makes sense.

But, specifically,  I don't think a 55 Amp hour battery requires a 55 Amp alternator.
I have heard statement to that effect (offline).

I agree with that statement that the 55 amp hour heavy duty battery doesn't need a 55 amp battery to work. That is not the point of this discussion. Wether or not for what ever reason Ford automatically upgraded the charging system to  the 55 amp alternator to support the 55 amp battery is. For example if you bought a replacement at Ford what they typically sold you was the heavy duty 24 F battery battery regardless of your application!!  If it wouldn't work Ford would have done something different for replacements.  It is not that it wouldn't work but as I said in my last post it appears it is a example of Fords way of doing things.

[67gta289]

I have no issue with you said. It makes sense.

But, specifically,  I don't think a 55 Amp hour battery requires a 55 Amp alternator.
I have heard statement to that effect (offline).

It is true that one does not require another.  But as Bob stated, it could be that is how Ford decided to do things - it is certainly not wrong to match them up.

The 44 vs. 55 amp-hour value tells us only one aspect (albeit an important one) of the battery; how much it can put out.  What is missing is how long it can put out.

Think of differently sized batteries as different containers.  For discussion let's say that the group 22 is a 375 gallon drum with an outlet that can safely provide 44 gallons per hour flow.  The group 27 is a 500 gallon drum that can flow 55 gallons per hour.

The charging system (including the alternator) is the refilling device.  We have two options, 44 and 55 gallons per hour continuously.

If we are consuming over 44 continuously, but only have a refill capacity of 44, eventually we will run the container dry.  How fast depends on a few things the primary being the difference between input and output.  As we approach the end and the voltage drops, we get into calculus.  But no need to go there.

In reality, however, our cars use nowhere near 44 amps continuously.  Blower motor and AC compressor sure, but together those are maybe in the mid 20's.  Headlights can push that into the mid 30's.  But a cigarette lighter is short lived, as is the horn (unless in NYC at rush hour).  So in my opinion a 44 amp charging system should not be an issue, with one exception:

I did not talk yet about the #1 impact, namely the starter motor, particularly in a cold start situation.  This can drain a battery faster than anything, so if you have a hard to start big block in the winter and draw the battery down, it will want to gulp power to recover.  If at the same time you are tooting your own horn, or put the AC in defrost mode, it will take longer to normalize the battery.  Then if you stop at a movie, the car gets cold, and you have trouble turning it over, you could end up in a bad situation.

But if you drive long enough, if you are using less than 44 amps continuously, even the 55 amp-hour battery will be fully charged.

The most important thing to note is that by merely looking at the two numbers, and don't take time into account, you can miss the point.

But again, the easy answer is to match them up - there is less risk that way.

[J_Speegle]

Guess one step that might provide some insight would be to collect and post the alternator and battery codes from the build sheets (along with the car data) to see what it tells us. In that way we can side step what Ford wanted to do or put on paper with what they really did on real cars.  I'll look into that

[K-HESS]

OK for some input I have a build sheet for a 1967 Fastback 7T02K218xxx built on 3/21/67 with the alternator listed as 42 and the battery listed as 45. I also have a build sheet for a 1967 convertible 7T03A153xxx that was built on 12/06/66 with alternator 38 and battery 55. The Marti report also calls out "Heavy Duty Battery" as an option on the convertible. Both cars are 4 speeds with no A/C. The convertible also has manual top.