New alternator guidance

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JHZR2

JHZR2

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Hello,

Given the signs and discussion of my alternator and battery, I did a mini-test. I wanted to see how the alternator performed, so after charging the battery, I did a reasonable amount of driving today -probably 40 miles when all is said and done.

So, time for another request for guidance...

So I put the battery on charge for a long duration. I then got it up to >90% SOC, and went out for a long drive.

I put a cigarette lighter voltmeter on to see how things worked.

End of day, now, after doing three starts and shutoffs in the driveway, the battery is sitting at 12.72V, and after a few minor loads, sits at about 12.4-12.5, so it looks like the alternator CAN charge a battery, at least with some starting help.

Anyway, the alternator is a bosch rebuild. It has a 14V regulator. When driving today, cold start, I was getting about 13.6V. After a long steady highway drive, ambient temperatures between 73-77F, Im still only getting 13.6V from the alternator with just the engine on, and more or less from fast idle to 3000RPM.

The alternator will give 13.6V without anything but the engine on. Turn on the radio and AC/fan, and 13.35-13.4V is what it will put out.

Turn on the headlights, and we are at ~13V, with most everything but the defroster turned up.

I never drop below 13, but it is possible to drop below 13.2V pretty easily with a bunch of accessories on.

I commute about 9 miles each way, and most of the accessories (i.e. AC, fan, radio) are on all the time. Headlights will be on for the commute home as it gets dark earlier.

So, is my alternator too poor for the job? Is it in a situation where I should replace it? Should I just replace the regulator and brushes (they are external and I can do that relatively easy).

BTW, AC voltage running at idle is 0.3-0.4mV at the alternator, 0.1mW at the battery.

Your thoughts????

Thanks!
 
By the way the voltage regulator in my Mustang is set to 14.6V and I never have a problem starting it even after letting it sit for 2-3 weeks.
 
aha... nice.

I was looking at one made by hella, which was set at 14.1V as opposed to the bosch 14V.

I guess my question with all of this is, which is more important, voltage or current? Does wattage play in at all, i.e. if our parasitics total 100W, it doesnt matter really if it is fed 8.3A at 12V or 7.1A at 14V? So long as charging voltage is sufficient for the battery, if youre moving more or less amps is there a difference?

Id suspect that since an ampere is related to a mole of electrons, that it would be superior for a battery to be provided more amps, i.e. more moles of electrons at a lower voltage, so long as thermodynamics allows the recharge. Am I off?

In reality what is the benefit to being >14V if Im not using one of the "maintenance free", high Ca/Sb chemistries like in the Delco freedom batteries? Need I truly be worried about voltage or more about current?

Thanks
 
13.5 volts is a good float charge voltage for a battery. If your battery voltage measured at the lighter socket is dropping under load, maybe it's just a case of oxidized battery clamps or cable ends. A little corrosion works both ways. It can prevent the battery from charging fully, and it can limit available current draw. Make sure you have good connections on both the positive and negative battery cables.
 
Originally Posted By: JHZR2

I guess my question with all of this is, which is more important, voltage or current? Does wattage play in at all, i.e. if our parasitics total 100W, it doesnt matter really if it is fed 8.3A at 12V or 7.1A at 14V? So long as charging voltage is sufficient for the battery, if youre moving more or less amps is there a difference?


Voltage and current are both important. Increasing the voltage generally increases the current...which increases the wattage.

The only case where this isn't true is in the case of a switch-mode power supply like that used for computers. These power supplies are designed to consume as much power (wattage) as they need to supply the connected load. Increasing the voltage on these will decrease the current and vice-versa. But these are an unusual case.

For most loads, if you increase the voltage you will increase the current and therefore the total wattage consumed. Refer to ohm's law, which says that amps=volts/ohms. If we fed 14V into a 2 ohm load it would consume 7 amps. If we fed 13V into that same load it would consume 6.5 amps.


Quote:
Id suspect that since an ampere is related to a mole of electrons, that it would be superior for a battery to be provided more amps, i.e. more moles of electrons at a lower voltage, so long as thermodynamics allows the recharge. Am I off?


You are not off. To provide the battery more amps you must provide it more voltage.

Quote:
In reality what is the benefit to being >14V if Im not using one of the "maintenance free", high Ca/Sb chemistries like in the Delco freedom batteries? Need I truly be worried about voltage or more about current?


I suspect most car batteries available on the market now are "maintenance free" even if they have removeable vent caps. Johnson Controls confirmed for me that the Group 48 battery they make for Autozone is indeed a maintenance-free Ca/Sb formulation. I expect that this is true for their Group 49 battery as well and possibly all the car batteries they make.

Also if you are thinking about an AGM battery be aware that they require a higher charging voltage just like maintenance free batteries.
 
Quote:
It is my understanding that Johnson Controls makes
the Autozone Duralast car battery.
Is the group size 48 Duralast car battery a "low maintenance" battery (with
hybrid lead-antimony/calcium plates) or a "maintenance free" battery (with
lead/calcium plates)?


Quote:
Brian,

This is a maintenance free design, (Ca/CA).

Best Regards,
Jeff
Product Engineering
JCI_Power Solutions Group
 
13.5V at the battery is fine. When the alternators start to dump out, you'll see something like 9V.

No need for high output alternator unless you're running high wattage stereo, etc.
 
I have a cigarette lighter voltmeter and it's only about +-10% accurate, but useful to give a warning in case your alternator quits without lighting the car's warming light. Check with a real voltmeter.
 
Originally Posted By: AcuraTech
13.5V at the battery is fine.


That's not fine if the car has just been started and the alternator is still cold.

That is fine if the car has been driven all day and it's 95F out.

Quote:
No need for high output alternator unless you're running high wattage stereo, etc.


A high-output alternator is designed to produce more current. The current output of the alternator he has now should be sufficient, the problem is that the voltage regulator setting is not high enough to properly charge modern maintenance-free batteries.
 
Originally Posted By: oilyriser
I have a cigarette lighter voltmeter and it's only about +-10% accurate, but useful to give a warning in case your alternator quits without lighting the car's warming light. Check with a real voltmeter.


I back everything up with a fluke 179. Its close enough to be more than relevant. The alternator's voltage is just plain not high enough it seems...
 
That reminds me of something I was always curious about. Would it be beneficial to install a high output alternator on a car that doesn't really need that much current, but then increase the size of the pully? Wouldn't this have the effect of producing the required current, but with less parasitic load? All the parts in the alternator wouldn't be spinning as fast, while still delivering the needed current?

Or if you designed the system right, it could give better idle charging and voltage, and respond a little more linearly as engine speed increases?
 
I had a 130-amp rewound high-output alternator in my 1988 Mustang GT. The output at idle was not very good...under 13V sometimes.

I replaced it with a 130-amp alternator from a 1996 Taurus when the bearings started to make noise on the rewound alternator. The Taurus alternator has very good output at idle, never under 13.5V.

So a high-output alternator doesn't necessarily have good output at low speeds, especially if it's been rewound, as opposed to having been designed from the start for high output and good output at low speeds, like the Taurus alternator.
 
Well I put a new group 49 battery in, replacing the group 91 OEM battery that was in there. The OEM 91 battery I had in there was down at 12.4-12.5 when I put it onto my schumacher charger in the garage...

With the group 49 battery, I noticed that the alternator kept up a bit better - perhaps it was just my imagination though. With all the loads, it stayed a bit higher (ambient temp the same as last test), though when really hot after about 100 miles of driving, I did see that 13.2V is still possible.

All the same, the voltage on the group 49 battery never budged after the alternator fed it a bit... Being a new battery, and the old one potentially having a bad cell or two may be part of the reason.

Anyway, Im going to start by replacing the regulator with a $25 hella unit set at 14.1V as opposed to the original one, which is 14V, and was part of the rebuild - who knows if it was actually replaced with the "bosch premium" rebuild... Will give that a chance, then move onto the adjustable one if need be.

Im hoping that a slightly stronger output, a bit more care (i.e. battery charger on from time to time, at least as a trickle), and this group 49 battery (more capacity so my use doesnt draw it to bad territory too quick) will solve this issue for as long as I keep the car... which hopefully is a while, so long as rust doesnt get it...
 
most every MB uses a group 49. They are good batteries as they have a lot of capacity. Definitely heavy though...
 
test voltage at the alternator first! I've had new, clean cars with over 1V voltage loss under load from alternator frame to battery (-) post. Corrected with a 4-terminal homemade ground strap.

O(Alt)----O(intake)----O(body)----O(Batt -)

with an additional O(body)----O(ecu)

vehicle Voltage improved and the AT shifted much better afterwards.

The "intake" connection was made because:
1. the engine to alt ground was lossy, like .4 volt, and I wanted the injectors to be well-fed, and
2. wanted to minimize the "noise" seen by engine-connected sensors.

Best thing I ever did to that car (01 town & country)

M
 
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