I assume that you mean some kind of voltage clamp such as a zener diode or a crowbar circuit. I have the electrical manuals for a 2000 Mitsubishi Diamonte and the 2010 Ford F-150 and some other cars and there are no clamps mentioned in any of them. If there are any clamps they're probably internal to the various modules in the vehicles but they give very little detail about the internals of those.
My understanding is that load dump clamping is handled by the alternator diodes having an intentionally low breakdown voltage of 60-100 V (the battery will normally clamp it to much less, maybe 16 V, but only if in good condition). I wasn't aware of any central load dump protection beyond that.
Common automotive standards specify a load dump spec as you describe, this is the waveform that remains after the other clamping in the system has taken effect.
Whether you need to worry about it depends on a) is it a product where you need to follow a particular standard? b) can you live with a small probability of it being damaged?
I have never seen (or at least recognized) such a device as a standalone unit. I don't think the standard load dump characteristics are as high as 100V, although I don't have any actual standards to read. And keep in mind that while very short duration pulses may not be absorbed by the battery due to inductance in the wiring harness, the many-millisecond sort of overvoltages simply cannot coexist with a functioning LA-battery in place. These sorts of things happen primarily if the battery fails open, is frozen or if there is a wiring problem. Otherwise, the LA-battery will absorb many thousands of amperes before it even allows the voltage to rise to double its nominal value.
I have never seen (or at least recognized) such a device as a standalone unit. I don't think the standard load dump characteristics are as high as 100V, although I don't have any actual standards to read. And keep in mind that while very short duration pulses may not be absorbed by the battery due to inductance in the wiring harness, the many-millisecond sort of overvoltages simply cannot coexist with a functioning LA-battery in place. These sorts of things happen primarily if the battery fails open, is frozen or if there is a wiring problem. Otherwise, the LA-battery will absorb many thousands of amperes before it even allows the voltage to rise to double its nominal value.
Good information. So the battery acts as an electro-chemical clamp of sorts? Trying to think back to electrochemistry in college to understand what happens in that moment, but I suppose the voltage source + series resistance model works okay too. As I read in some other threads, some people disagree with the philosophy behind load dump protection, implying that "you have other more serious problems to worry about" if you get a 200V load dump spike on the DC bus.
If its going to be anywhere it would be in the alternator. Its already got the high current connections, is the most likely source of a voltage surge, and doesn't require an extra module to be mounted and connected up, so maybe you should research OEM alternator specs?
Alternatively, is it profitable enough you can afford to eat the cost of replacing the small number that will blow due to a load dump?
Good information. So the battery acts as an electro-chemical clamp of sorts? Trying to think back to electrochemistry in college to understand what happens in that moment, but I suppose the voltage source + series resistance model works okay too. As I read in some other threads, some people disagree with the philosophy behind load dump protection, implying that "you have other more serious problems to worry about" if you get a 200V load dump spike on the DC bus.
I guess the same physics should apply, the regulator can only slew so fast regardless, it should experience a swell from any load-drop condition, switching lights, motors, etc. Though maybe none of those loads are strong enough to overpower the battery, in terms of height or duration of that swell (it might be shorter than the full load dump case, even if it's the same time constants in play, which might also not be the case).
As for the battery itself, it behaves pretty much symmetrically in charge or discharge, up to the point where charging is complete, and where other reactions take over -- primarily water electrolysis. Electrolysis is a runaway condition, where due to bubble formation, the electrolyte cross-section is reduced, greatly increasing resistance, allowing terminal voltage to rise further. I would guess a car battery can do a good 20, maybe even 40 or 50A for brief charging in a low-state-of-charge condition (terminal voltage < 14.4V), but won't sustain such high currents for long; and in particular, as cells begin to fully charge (and this happens inhomogeneously across the plates: the facing surface has a direct line of sight; the pores behind, not so much), gas formation takes over and internal resistance rises. I would guess the current drops to ~20A steady-ish-state for terminal voltages in the 16-18V range. So there's a bit of a negative resistance characteristic, over a fairly long time scale (seconds).
Alternator diodes fail occasionally and used to be replaceable, but their voltage rating varies wildly. Manufacturers are just cheap. Nobody is grading alternator diodes for controlled breakdown, although they might be avalanche rated for reliability.
Well, I've measured it...
Don't forget there's also gelled (sealed or vented) and AGM types out there. I don't remember which one I measured.
It's my understanding load dump doesn't really...happen? With a battery?
I guess the same physics should apply, the regulator can only slew so fast regardless, it should experience a swell from any load-drop condition, switching lights, motors, etc.
That's a good point...though hard to say without a ballpark probability of occurrence.
I suppose a general disclaimer can be made upfront that clearly outlines the DUT's tolerance to load dump. This puts more responsibility on the end-use installer to check with each vehicle. But, in the event that DUTs start failing, each will require some autopsy (which takes engineering time) and then follow-up negotiations (arguments?) with the customer regarding who's at fault. That's not great either.