2014 e350 4matic completely dead after replacing auxiliary battery
Out Of Control!!
Joined: Apr 2019
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From: Silicon Valley
W212 MY'14 M276-3.5NA @75kMi
voltage regulator
It can be difficult to understand if you don't know electricity, but I like to use the water analogy.
Voltage is like water pressure, current is water volume. So if you want to control the volume of water flow through something, like a hose, you do it by controlling the pressure.
Say you have piping system, like a sprinkler system. You have 10 sprinklers and they each flow 1gpm "if" the water pressure in the main pipe feeding them all is 50psi. Add one more sprinkler and what happens? If the source psi remains 50 then the pressure in the piping drops and now they all flow less than 1gpm. Raise the pressure to 55psi, for example, and they all flow 1gpm for a total of 11gpm. The point is you had to raise the pressure to get that extra flow. If you want more flow, raise the pressure. Less flow, lower pressure. So pressure controls flow just like voltage controls current. Hook up a 120V bulb to 240 and watch it flow a ton of current that it cannot flow at 120. Or a 3V flashlight bulb to 6V.
If you have a battery charger that has a switch for 2A or 10A, which is pretty common, that current is dictated by voltage. The 10A setting is higher voltage than the 2A setting. My favorite 10A charger, that some "borrowed", put out 20V to net 10A. A trickle charger of 1A would probably be somewhere around 14-15V? If you really want to read up on how it all works, read the book in the below link. It was my first elect book, when I was a kid, and I suggest to anyone who asks. Almost nobody reads it, but you're into all the car electronics so maybe? It's really well done, and not some boring school textbook. Quite the opposite. t least look at it:
https://n5dux.com/ham/files/pdf/Forr...lectronics.pdf
Same with the battery and alt. The alt needs to raise its voltage in order to supply more current or the whole system will suffer. Now each sprinkler, flowing at 1gpm, doesn't feel any different because it's pressure is exactly the same, which it has to be if it used 1gpm.
So headlights etc cause the alt to make more voltage to bring the current flow to normal.
The battery is like a big water storage tank for that sprinkler system. So instead of the city water feeding the sprinklers directly, it's feeding the tank, and the tank is tall enough to give 50psi. The city psi won't overfill the tank, it only fills it just enough. Like a battery charger, which it is.
You can say the battery feeds the car and the alt feeds the batt, which is more how I look at it. Or, like most people like to think; the alt feeds the car and only tops off the batt. The truth is both. The alt and batt are tied together so they both feed the car at all times. The battery has more current capacity and much quicker to respond, the alt has more voltage output and also feeds the batt. Which one powers what by what % will vary. Ultimately the alt powers it all, so I guess look at as how much takes a pit stop at the batt first?
I'm probably not doing a great job explaining, especially since there are other factors, but more less this is it.
Can the alt kill the batt? Sure, if it's regulator goes haywire and commands it to full output. It'll cook more than the battery too. Normally it won't allow more than ~14.8V and since voltage dictates current, it won't pump too much current into the batt. Assuming the batt is fine, not shorted or something. A shorted batt will trick the regulator into outputting too much.
juan: please don't. If you want to try and school me on electronics, at least read the book in the link first.
Your alt does >99.99% of a typical cars battery charging. It's what it does.
Voltage is like water pressure, current is water volume. So if you want to control the volume of water flow through something, like a hose, you do it by controlling the pressure.
Say you have piping system, like a sprinkler system. You have 10 sprinklers and they each flow 1gpm "if" the water pressure in the main pipe feeding them all is 50psi. Add one more sprinkler and what happens? If the source psi remains 50 then the pressure in the piping drops and now they all flow less than 1gpm. Raise the pressure to 55psi, for example, and they all flow 1gpm for a total of 11gpm. The point is you had to raise the pressure to get that extra flow. If you want more flow, raise the pressure. Less flow, lower pressure. So pressure controls flow just like voltage controls current. Hook up a 120V bulb to 240 and watch it flow a ton of current that it cannot flow at 120. Or a 3V flashlight bulb to 6V.
If you have a battery charger that has a switch for 2A or 10A, which is pretty common, that current is dictated by voltage. The 10A setting is higher voltage than the 2A setting. My favorite 10A charger, that some "borrowed", put out 20V to net 10A. A trickle charger of 1A would probably be somewhere around 14-15V? If you really want to read up on how it all works, read the book in the below link. It was my first elect book, when I was a kid, and I suggest to anyone who asks. Almost nobody reads it, but you're into all the car electronics so maybe? It's really well done, and not some boring school textbook. Quite the opposite. t least look at it:
https://n5dux.com/ham/files/pdf/Forr...lectronics.pdf
Same with the battery and alt. The alt needs to raise its voltage in order to supply more current or the whole system will suffer. Now each sprinkler, flowing at 1gpm, doesn't feel any different because it's pressure is exactly the same, which it has to be if it used 1gpm.
So headlights etc cause the alt to make more voltage to bring the current flow to normal.
The battery is like a big water storage tank for that sprinkler system. So instead of the city water feeding the sprinklers directly, it's feeding the tank, and the tank is tall enough to give 50psi. The city psi won't overfill the tank, it only fills it just enough. Like a battery charger, which it is.
You can say the battery feeds the car and the alt feeds the batt, which is more how I look at it. Or, like most people like to think; the alt feeds the car and only tops off the batt. The truth is both. The alt and batt are tied together so they both feed the car at all times. The battery has more current capacity and much quicker to respond, the alt has more voltage output and also feeds the batt. Which one powers what by what % will vary. Ultimately the alt powers it all, so I guess look at as how much takes a pit stop at the batt first?
I'm probably not doing a great job explaining, especially since there are other factors, but more less this is it.
Can the alt kill the batt? Sure, if it's regulator goes haywire and commands it to full output. It'll cook more than the battery too. Normally it won't allow more than ~14.8V and since voltage dictates current, it won't pump too much current into the batt. Assuming the batt is fine, not shorted or something. A shorted batt will trick the regulator into outputting too much.
juan: please don't. If you want to try and school me on electronics, at least read the book in the link first.
Your alt does >99.99% of a typical cars battery charging. It's what it does.
Let's just focus on battery charging only because this was our topic here.
The ALT regulates one voltage for the whole car regardless of what current goes where. The issue with having a flat Batt in this circuit is going to draw an extremely high current the ALT has no control over.
That uncontrolled "rate of charge" is destructive for both ALT and Batt. So I don't qualify that sort of abuse as "charging".
The only thing you can expect normally is to top off battery from 75% ir greater to 100%. This is still done without any current regulation.
The only reason it's acceptable is because the current remains small 25A for a short period. So internal heat is not extreme for too long. This is 250W, nothing to ignore!
Hands on instrumentation... let your battery get drained low then collect data with voltmeter, Amp-clamp and Hyundai LIN sensor.
You'll see what really gets regulated by Valeo ALT.
Last edited by CaliBenzDriver; Jan 10, 2024 at 03:29 AM.
Super Member
Joined: Aug 2004
Posts: 958
Likes: 248
E550 Coupe 2wd (2016)
I know it doesnt make sense, but if the batt is fine the charging is fine too, why is because of the voltage in the batt. Like the water, lets say you have a 14.8psi source filling a tank, but 14.8 is too much flow and it'll break something. If you have 12psi in the tank then you really only have 2.8psi to push the water, and that 2.8 is what dictates flow. 2.8v over wont over current the batt. You might say; but the batt is dead at 4v. Yes, but it will be 12 in a few seconds. So the battery itself is self regulating, to a degree, and the alt voltage is 100% set to work with a lead acid 6 cell batt, so its a perfect match. The entire electrical system in the car is also designed around that batt. If the standard batt was 8 cells, which would be better, then the alt and car would all be designed around that voltage.
You can see the batt self regulate on an old school charger that has no regulation, where it charges at high current for a bit, then current quickly drops as the batt voltage quickly climbs, then drops to nearly nothing as it climbs to >14.
So you'd need a short in the batt to reduce its voltage, then "too much" current can flow.
It's all rather simple, if you know electricity, and I believe that book is the best and easiest way to do that. It really is worth a read, imo.
I'm currently having a similar chat a work about thermocouples. How those work is shrouded in far more mystery, and I don't personally know anyone who knows how they work because what is taught, and found online is wrong. The guy I'm talking to has >35 years experience using them, but only knows what the internet says. Same story with batteries.
You can see the batt self regulate on an old school charger that has no regulation, where it charges at high current for a bit, then current quickly drops as the batt voltage quickly climbs, then drops to nearly nothing as it climbs to >14.
So you'd need a short in the batt to reduce its voltage, then "too much" current can flow.
It's all rather simple, if you know electricity, and I believe that book is the best and easiest way to do that. It really is worth a read, imo.
I'm currently having a similar chat a work about thermocouples. How those work is shrouded in far more mystery, and I don't personally know anyone who knows how they work because what is taught, and found online is wrong. The guy I'm talking to has >35 years experience using them, but only knows what the internet says. Same story with batteries.
