what voltage is your alternator giving you?

e9999

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So, I have in the past seen that the alternator ('03 OEM) on my earlier batteries was giving something like 14.4V right after startup, gradually going down to 13.9 V or so after a while of driving (with a dedicated voltmeter, not the dash one). This is just an impression from memory, not real tests. Those numbers seem fine, 14.4 is the standard bulk charging for FLA and it makes sense that it would go down when the battery is fully charged. OK.

However, after some possible electrical issues, I just replaced the battery with a new one which I assume to be in excellent condition and since paying attention to it, I saw that that the voltages seem noticeably lower. For instance, at idle in N without A/C (650-700 rpm) I get now about 13.6V, with A/C and fan on high it's more like 13.5V. When driving after a while, even at fairly high rpm for me (3K), it is around 13.7 , and I don't think it goes quite as high as 14.4V after startup now.
I'm happy to attribute that to the fact that the battery is new and really fully-charged, but I'm curious if there may be something else going on, so I gotta ask:

What voltages are you seeing at idle? Do you know what it is supposed to be per specs?
 

e9999

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that is a very big range. Any first hand observation?
 
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I am no expert but take great interest of charge from alternator and battery condition, otherwise it would be a mega pita the place I go.
'03 is fairly newish to me. Perhaps your brushes are worn depending on how many miles you have done. I have replaced brushes in a 1984 merc before which gave more volts, along with an internal clean up of any corrosion on wires.

But the voltage you are producing doesn't seem too bad to me, 13.6v is a typical float charge.

My 2h 80amp taiwanese bosch alternator is about 4-5 years old, been spinning around for about 80-100k. It would flood charge at start up at 14.1-14.2v at start up both starter and aux battery. But spare reg and brushes are not obtainable unfortunately for the bosch.

If I use fan, wipers and led headlights in a night storm it may go down to 13.6v or so. I am comfortable and happy with this.
As long as I see over 12.6-12.7v I know my batteries are not being drained and I know I can start in the morning. A happy battery in the morning without load is 12.8v but still ok at 12.6v to me.

When remote I use a small solar trickle charger and it may give up to 14.4v to 13.6v if sunny, but it is in a shady rain forest. so sometimes It doesn't go over 12.6v. Yellow Optima is way better than supercharge batteries but nearly twice the price, I have one of each at present.

My ctek smart charger on reconditioning cycle, when I have access to the grid, charge starts at 14.7v at flood charge then levels out, then raises back to 15.5v at the end, then a lower trickle 13.6v. This is good ,or the batteries cook if over charged at 16v, quickly shortening the life of the battery.

Grand scheme we want the battery to start the car for as many years as possible. It needs to hold a minimum of 12.6v. If it doesn't, it won't have a long life. This is a good way to test a cheap used battery at a pickapart. But a load tester is needed to see how many cold cranks it has if you really want to check the condition.

I have been getting about 5 years from the lower budget supercharge batteries in Oz, Century marine battery has lasted longer. Regular reconditioning on ctek.
I know my batteries are on the way out when the voltage drops lower and lower when I preheat glowplugs on my wilson switch. Especially winter season. The lowest has been 10.2v when glowing, it may go up again to10.4-6v but it does not crank the starter with much punch after glowing. Time to get a new battery.

On another note, one has to be wary of batteries on sale, they need to get rid of them or recondition themselves, cheaper to sell them quick. They rely that you shall have to do the foot work of going through the warranty paperwork. I got another supercharge on sale, it held 12.2v from the shop, the cold crank condition was ok on my tester. I reconditioned it myself with ctek, it glows and cranks but I know it shall probably not live long. It does hold 12.6v now after reconditioning.

Sorry for the long wind, I constantly monitor charge, v important. Over 16v bad, 13.6v good float, under 12.6v bad. Cold crank need a load tester or it takes a few cranks to start.

 

e9999

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thanks for the feedback. I went and picked the newest battery off the rack and checked the voltage. 12.7V in the store. At least that part seems OK.

I'm not worried about the 13.6V idle, to be clear, that seems OK, just curious about what the difference might be with what I had before, perhaps that was just a battery not charging fully very well back then, and the alternator picking up the slack.
 
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So, I have in the past seen that the alternator ('03 OEM) on my earlier batteries was giving something like 14.4V right after startup, gradually going down to 13.9 V or so after a while of driving (with a dedicated voltmeter, not the dash one). This is just an impression from memory, not real tests. Those numbers seem fine, 14.4 is the standard bulk charging for FLA and it makes sense that it would go down when the battery is fully charged. OK.

However, after some possible electrical issues, I just replaced the battery with a new one which I assume to be in excellent condition and since paying attention to it, I saw that that the voltages seem noticeably lower. For instance, at idle in N without A/C (650-700 rpm) I get now about 13.6V, with A/C and fan on high it's more like 13.5V. When driving after a while, even at fairly high rpm for me (3K), it is around 13.7 , and I don't think it goes quite as high as 14.4V after startup now.
I'm happy to attribute that to the fact that the battery is new and really fully-charged, but I'm curious if there may be something else going on, so I gotta ask:

What voltages are you seeing at idle? Do you know what it is supposed to be per specs?
I have similar experiences. I am also convinced the cruiser is smart enough to pump a little more voltage in when it's below freezing.

I had toyota replace my alternator along with some other bits a year back. The alternator they installed was defective and failed. The service guy said anything under 13.4V while running and they will warranty it.

Currently mine will do what you explained, start high at 14.4ish and then float around 13.5-13.9.
 

C6H12O6

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13-14V is a great range when you're running a lead acid battery. If you switch to AGM batteries (or LeFePO4?) they really want to see a higher charge rate. A bunch of us have swapped out the small 7.5A fuse in the engine bay fuse/breaker box and switch over to a diode that allows the alternator to charge a bit higher. I now routinely see 14.5-14.9V when running. Seems fine so far, and I haven't ready anybody else having issues, as long as you are running AGM batteries.
 

e9999

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wow, these things are really all over the place. did not expect that... but the battery is probably the main variable here, rather than the alternator.
 
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Is it possible it's just a smart alternator that drops voltage once the battery is charged?

Everyone here seems to have the same pattern of higher voltage right after starting, followed by dropping to low 13's.
 
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Don't forget to consider OAT in this. Heat decreases the conductivity, thus reducing the efficiency of the charging.
 
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geez really good input here! diode trick is a good tip, but commits to a certain battery.. I use my ctek when I get back to civilization regardless to try to maximize battery life.

The ctek manual explains the charge cycle and why.
 
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wow, these things are really all over the place. did not expect that... but the battery is probably the main variable here, rather than the alternator.
Aren't all of these apps/scanners were providing numbers from getting the voltage from the obd2 port . Might pay to take a few readings from the battery. I haven't done that in a while.
 
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Whilst we are here about charging batteries. I just got this a few months back $60aud on ebay, pretty good.
1660956670412.png
 
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13.3-14 normally. Heavy loads will take it down to 12.6 or so at a stop in drive. OEM alternator.
 

e9999

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^ mine never goes down to 12.6 even under heavy load. That seems low.
 
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Mine will go between 12.9 and 14.2 pending if just started and after running for a while and running different stuff. It used to worry me but it’s been this way for a year. Typically see 13.2-13.4 the most often after running a while.
 

suprarx7nut

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wow, these things are really all over the place. did not expect that... but the battery is probably the main variable here, rather than the alternator.
I think a part of that is that between model changes over the generation and LX/LC differences you have a real wide variety of possible loads at any given time on a random 100.

I was getting 12.4-12.7 when hot and idling with AC this summer. I had a weird no crank situation that had me questioning the alt health. I did the diode mod to the sensing line and now I get about 13.3 running at idle. 🤷
 
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I have a dual battery set up with a dual read out voltmeter in the cabin. I see a consistent 14.3 on my main and 14.2 on my house battery (both are AGM) in 99% of conditions. The difference between the two is probably due to the length of wiring and inline breaker. With the key on but engine off, I see 12.4 +/- 0.1 from my main and 12.7 from my house each morning. I’m currently running a 80 amp aftermarket alternator.
 

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