14V Charging: Why It Takes 3 Minutes?

Hi there.
Seat Terra, manufactured in 1992, a very old diesel vehicle with a simple design and no electronic components.
Maybe someone here has a tip for me.
After the engine starts, the alternator doesn't charge initially and takes approximately 3 minutes to reach 14 volts.
With a load connected, the voltage is approximately 13.8 volts; without a load, it's 14.02 volts, and at full speed, it's slightly lower.
Mass contacts are okay, the carbon brushes in the motor are new.
I'm not familiar with the effect that causes the Lima to take so long to reach its maximum charging voltage.
I'm going to replace the alternator later, and if that's the problem, I'd like to know what might have been broken on the old one.
Best regards, Frank.

Hi there,

Afterglow and high battery current draw after preheating and starting.
Since the bra probably isn't that big, it should fit fine.

Before you start tinkering around with it, clamp a current meter onto it and take some measurements.

Best regards, Michael.

Hi Mdonau.
Yesterday, I took everything apart, but unfortunately, the old alternator didn't fit properly mechanically.
The commutator looks very worn, almost completely damaged.
That's probably the reason, and the final result will likely only take a few more days.

Months ago, during the last measurement, she reached her usual 14 volts almost immediately.
Best regards, Frank.

Hi there!
I have some more numbers here.
The charging current of the old alternator reached a maximum of 3 amperes.

I've now installed a retreaded tire.
The charging current is now directly at 30 amps immediately after starting.
After a short period at 15 amps.
To my surprise, I noticed that immediately after starting the engine, there were only 12.5 volts at the battery (despite a charging current of 30 amps).
After about thirty seconds, the charging voltage suddenly jumps to 14.2 volts.
It does not automatically re-illuminate (measure), and there are no other consumers or electronics present.
Just out of curiosity:
What could cause this sudden increase in tension?
It doesn't really bother me, but I'm just curious about it.


Best regards, Frank.

F B wrote:

I was surprised to find that immediately after starting the engine, there were only 12.5 volts at the battery. (Despite a charging current of 30 amps). After half a minute, the charging voltage suddenly jumps to 14.2 volts.

Hi,

Did you measure the 30 amps at a point where it can only flow into the battery?
If so, the battery in the IMO likely has a defect.

Hi Ulf,
We measured it right next to the battery.
Of course, the battery might be faulty.
That cannot be ruled out.
'As a test, I can try installing a different new one.'
My friend still has one lying around.

The engine sounds slightly different when the charging voltage reaches 14 volts.
So, at that moment, the Lima needs to be working correctly.
That makes sense because the linear motor needs to be powered by force.
What I don't understand is that it charges at 30 amps with a voltage of 12.5 volts immediately after being turned on.
When the charging current reaches 14.2 volts, the sound of the motor changes.
Exactly the same effect was noticeable with my old Seat; after about 30 seconds, you could hear that the alternator was starting to work harder.
Unfortunately, I didn't measure that moment back then.
I suspect that this effect will still be noticeable even with a different new battery.
As I mentioned, there is no other electronic component besides the glow plug relay.
However, it does not have an afterglow function, and it only glows for as long as the indicator light is on.
As I said, I can live with it just fine, but I'm curious about how it happened.
Best regards, Frank.

F B wrote:

The engine sounds slightly different when the charging voltage reaches 14 volts. So, at that moment, the Lima needs to be working correctly. That makes sense because the linear motor needs to be powered by force. What I don't understand is that immediately after starting,

30 Amperes are being charged at 12.5 Volts.

Quote:

30 A x 12.5 V already equals 375 Watts. 30 amps x 14.2 volts = 426 watts.

When the charging current reaches 14.2 volts, the motor noise changes.
Exactly this effect was also noticeable with my old Seat; after about 30 seconds, you could hear that the alternator :roll:was having to work.} It somehow doesn't seem right that the engine noise should change noticeably due to "only" 11% more alternator output. . . }
Or what is the charging current when the voltage jumps to 14.2 volts?

Or how high does the charging current climb when it reaches 14.2 volts?

Hi Ulf,
It doesn't increase; instead, it decreases from 30 to 15 amps when the voltmeter reaches 14.2 volts.
I need to re-measure to see if the increase to 14.2 volts actually coincides with the reduction in charging current.
I don't have the equipment myself, so it will take some time before I can measure anything.

No, I don't understand it either.
Best regards, Frank.

F B wrote:

It doesn't increase; instead, it decreases from 30 to 15 amps when the voltmeter reaches 14.2 volts.

You probably have a significant resistance somewhere between the starter motor and the battery (which could be on the negative side).

However, I believe that even a battery that is still in relatively good condition should never exhibit a charging curve with such strange voltage and current fluctuations. If, for example, the afterglow effect ends (or another large power consumer is switched off) after 30 seconds, that could reasonably explain your measurements.

Hi Ulf,
All contacts have been disassembled, polished, and cleaned, etc.
Including both ground cables and all grounding points.
There is no significant voltage drop.
Neither the positive cable to the starter/alternator, nor the negative terminal or the car body.

We will double-check the measurements and possibly borrow a battery to test it out.
As I mentioned before, there is a preheating relay, but it doesn't stay on.
The measurements can be directly verified using measuring equipment connected to the glow plugs.
But I can only re-measure tomorrow/the day after tomorrow.
Best regards, Frank.

F B wrote:

There is no significant voltage drop. Neither the positive cable to the starter/alternator, nor the negative terminal or the car body. But I can only re-measure tomorrow/the day after tomorrow.

Okay... of course, the battery itself could also have an excessively high internal resistance.
During one of your next tests, try connecting the voltmeter directly to the alternator (at the charging terminal and the housing). If you observe the same voltage spike there, then the alternator or its regulator/brushes are likely faulty.

Short question about your measurements:

Do you measure it at idle speed or at a higher RPM?

Does your charging indicator light illuminate when the ignition is switched on and the engine is not running?

if so

Does your charging indicator light turn off after starting the engine without pressing the accelerator?


Furthermore, the tension between... is also interesting.

- Positive terminal and ground connection with ignition on and engine off.

- Measured at the battery with the ignition switched on and the engine idling.

- D+ and B+ measured directly at the LIMA.

Have you checked the current flow for both the 30A and 15A circuits? Is it always the same? (The ammeter doesn't even show a positive or negative reading.)

"Because if your battery is in good condition and fully charged, that would mean the alternator isn't charging, and you're seeing a battery voltage of 12.5V."

Hi Stefan,
Short question about your measurements:

Do you measure it at idle speed or at a higher RPM?

At idle speed, the voltage equals the battery voltage.
At 2000 RPM, the voltage increases to 13-13.5 volts.


Does your charging indicator light illuminate when the ignition is switched on and the engine is not running?

if so

Does your charging indicator light turn off after starting the engine without pressing the accelerator?

2 = yes
3 = yes.


Furthermore, the tension between... is also interesting.
- Positive terminal and ground connection with ignition on and engine off.

- Measured at the battery with the ignition switched on and the engine idling.

- D+ and B+ measured directly at the LIMA.


The days will be measured again.
Meanwhile, the battery has also been replaced with a new one, but the problem hasn't changed.
Before you ask:
Old alternator, old battery.
New lime, old battery.
New lime, new battery.
= no change to the principle that the battery only starts charging after a short period of time, as if it were initially switched off.

The excitation circuit will be re-measured again in the coming days.
Best regards, Frank.

Hi,

F B wrote:

The engine sounds slightly different when the charging voltage reaches 14 volts. So, at that moment, the LIMA needs to be working correctly. That makes sense because the linear motor needs to be powered by force. What I don't understand is that immediately after starting,

30 amps are being charged at 12.5 volts.

Quote:

Should we bet that the glow plugs will still be glowing? At least my '91 Golf2 and the '92 Passat have them as standard equipment, as does the beloved AAZ Toledo from '93. The rest is logical: the spark plugs draw current, the voltage drops, and the amperage is 30A (when cold, the spark plugs draw 4 x 15A, but after a few seconds, they regulate themselves down to half that amount).

When the charging current reaches 14.2 volts, the motor noise changes.

Quote:

It's normal for the motor to notice the 30A (400W electrically, which is roughly 1 horsepower mechanically) even when idling. In my Golf with a 90A alternator, I get 14V in that state, but as soon as the serpentine belt gets older, it starts squealing until the afterglow turns off.

The exact same effect was noticeable with my old Seat; after about 30 seconds, you could hear that the alternator was working hard.}

Conversely: the alternator has to work hard at the beginning, after the afterglow phase, the voltage increases because the alternator doesn't have to work as much, and the engine runs more easily.


Best regards, Uli.