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Will the factory alternator in my 993 charge my Optima RedTop battery or other brand AGM batteries as I drive?
My car spends most of its life in the garage with a CTek maintainer on between uses. But, if I take a road trip and am unable to use a maintainer for several nights, will the stock alternator "replenish" the battery charge while I am driving?
I'm on my second Optima 8025-160 which, after several years, is beginning to generate a little bit of white "powder" (maybe sulphate?) on the negative post, so I am looking to replace it.
Yes, your alternator will charge your battery just the same and doesn't distinguish battery type. My first Optima red top lasted 9yrs and I am on my second which is about 5yrs old. Only time I use a tender is the 3 mos during the winter when the car is. It used.
Hi Richard,
Sulfate on the battery posts does not indicate the need for replacement.
If you have any concerns have the battery tested.
My armchair test is that if the engine turns over easily you do not need to be concerned about the battery.
If it seems to be laboring a bit more to start than in the past I would clean the battery posts first and see if it resolves the issue over a short period.
Have a great Holliday,
Andy
35mA quiescent draw on a 70Ah battery is about 2 weeks so put it on the tender if it won’t get driven for a week or more.
if you’re driving daily, no problem. 993 electrics, like everything on the car, is well designed & manufactured.0
Richard - I have the same situation with my 993 - using AGM battery with CTEK maintainer. My understanding is that AGM batteries required a higher charge voltages than standard lead-acid (SLA). The CTEK outputs higher voltage for AGM (has a unique setting for AGM vs SLA), so you get a full charged battery. However the 993 alternator doesn't have the higher voltage required for AGM battery so can't full charge. I believe my 993 only outputs ~13.7V and an AGM battery would need higher. Voltage loss in the long cable to the battery from alternate doesn't help the situation.
My research is that
SLA - float charge is 13.4V and bulk charge is 14.2V
AGM - float charge is 13.8V and bulk charge is 14.7V
- however I find not the same voltages listed by every website, but in all cases the AGM voltages are higher than SLA
I believe you have to have the alternator voltage reach at least the float charge to reach 100% charge. If the 993 alternator voltage is below 13.8V than AGM battery won't be 100% charged, but still maybe 90% or so - likely enough for most road trips if the battery is overall in good condition. Once you get back home and use the CTEK will get the battery back to 100% charged. Bulk voltage is fast charging mode.
Others may have better info, just providing what I have heard / learned.
Will the factory alternator in my 993 charge my Optima RedTop battery or other brand AGM batteries as I drive?
Not fully.
I have a digital voltmeter in my 993 that is connected directly to the battery and while driving is sits between 14.0V and 14.2V. An AGM needs about 14.7V. I would know because my 991.1 that comes factory fitted with an AGM battery is at 14.6V to 15.0V (temperature dependent as it is on all FLA and VRLA batteries).
The Vset in our 993 regulators is 14.5V and by the time it gets to the battery out front, I sit at 14.1V plus/minus.
Hey Guys,
Thank you all for your responses. I've had my 993 for 25 years now and I'm on only the third battery - two RedTops after the original equipment battery. No starting problems (I hope I don't jinx myself!). The voltage readings are very good. The car cranks and fires up just like it always has. I upgraded my C-TEKs several years ago for my 993 and '81 SC, which has had an Interstate AGM in it for two years, so both have the unique AGM setting as mentioned by Bill 993. The question about whether our 993 o.e. alternator can fully charge an AGM is (out of curiosity) one that I have been meaning to ask for a while. Finding the sulphate on the negative post made me start thinking about whether it is time to replace the present battery - which is probably eight (8) years old. Andy, can the sulphate cause any damage to the surrounding area?
Thank you, again, to everyone and Happy (and safe) Holiday!
All the best,
Richard
AGM Charge & Float Voltages
Source: East Penn Technical Manual
Hi Alex,
On a newer car, the electronics are probably designed for these higher voltages. On a 993 or earlier car I would be concerned that the electronics would be damaged over time if the alternator was regularly pushing out voltage in the 14.5+ range.
Also, all one needs is enough starting capacity to turn over the engine at startup. Not sure if it matters that the battery is at 80% or 100% of its theoretical capacity. The manufacturer may have designed the excess capacity at higher charging voltages to make the battery that is compatible with both older cars with a 14.2V from the alternator to newer cars that may run a good bit higher. The excess capacity may also relate to having adequate cold weather capacity or extended service life.
Andy
Hi Alex,
On a newer car, the electronics are probably designed for these higher voltages. On a 993 or earlier car I would be concerned that the electronics would be damaged over time if the alternator was regularly pushing out voltage in the 14.5+ range.
On the newer cars such as my 2015 Porsche 991 or my Acura RDX, those batteries have a battery sensor on the negative battery post with a lead going back to I would assume the ECU to control charging. Honda started this back in the 90s to prevent unnecessary charging when it is not needed. I have a paper on this and it is also available on-line.
On the Porsche 991, you can see charge voltages changing on the MFD when in Normal, Sport or Sport Plus modes. Shortly after getting it, I was alarmed to see 14.8V and as high as 15.0V thinking something was wrong with the regulator. At the time I was unaware it came factory fitted with an AGM battery and those voltages are perfectly normal at 6 degrees C (see the AGM chart). That battery is 8.5+ years old now.
And 14.5V (not that you'll see it) in the 993 won't damage the electronics. Smart design will have over-voltage protection such as during boosting, etc.
On my Acura RDX, you can see a reduced charge voltage and then it swings up to 14.4V (conventional FLA battery)
Originally Posted by pp000830
Also, all one needs is enough starting capacity to turn over the engine at startup. Not sure if it matters that the battery is at 80% or 100% of its theoretical capacity. The manufacturer may have designed the excess capacity at higher charging voltages to make the battery that is compatible with both older cars with a 14.2V from the alternator to newer cars that may run a good bit higher. The excess capacity may also relate to having adequate cold weather capacity or extended service life.
Of course a battery at 80% will start the vehicle provided it has capacity and low internal R. The difference is a battery charged to a lower voltage is not a fully charged battery and that might cut its life expectancy. The battery in my old 1990 Toyota Tercel was at 14.4V or slightlly less due to higher temperatures all the time. It had the original factory fitted conventional FLA Panasonic battery in it and was 16 years old when we sold it.
But none of my vehicles with a standard voltage regulator has ever seen voltages in the mid 13s. Way too low.
12-24-2023, 03:14 PM
Battery Charging Question
