Article on load dump - Page 1
Forum section: electronics / projects

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 24, 2024, 05:27:50 pm
content: For interest:https://www.seventransistorlabs.com/Articles/LoadDump.htmlQuestions, comments, discussion?Tim

author: fourtytwo42
author_rank: Super Contributor
timestamp: August 24, 2024, 05:57:18 pm
content: I can remember it being a scary thing in my youf!However modern semiconductors have largely put it to bed insofar as automotive electronics are concerned, you simply have to use the appropriate "load dump proof" regulator in front of your delicate micro or whatever.I wonder what happens with somewhat larger alternators/generators with a wound field, do they overvolt in the same way if the load is removed ?I guess there are not many we are all familiar with, I don't suppose a welder or arc lamp cares to much!But do the converter electronics in say a wind turbine have to be wary ?

author: ganfetsic
author_rank: Newbie
timestamp: August 24, 2024, 06:12:49 pm
content: Thanks.Load dump...when a customer brings it up, we always try and influence them to choose to simply switch out the high voltage whilst its high.Your regulator then gets a blip in its supply. but this may well not matter.Load dump is typically from poorly maintained autos.The most challenging load dump we had was a customer doing it for a tank , when the turret stopped rotating, the supply would shoot up to 200V (from 24V) for 2 seconds, and they wanted a converter up front to be able to buck that down to the normal input voltage so there was no break in the converter operation. (ride through load dump)

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 24, 2024, 07:30:48 pm
content: Quote from: fourtytwo42 on August 24, 2024, 05:57:18 pmKind of late to the party anyway, with EVs (hopefully..?) being the wave of the future. But in that case, the article still serves as a historical review or summary.And there'll still (always..?) be the rough, remote-environment, mining, military, etc. applications where engines and alternators get used.QuoteYeah, when you don't need much load current, just handle the voltage -- or drop it with a crude pre-reg, like a depletion MOS. Up to loads of a few watts, that's an easy way to get ride-through -- have done it *and tested* before.Gets harder when you need much more than that. Beefy dropper? Switch off the load (ridethru not required)? Wide range converter?QuoteIt may be more common than we like to think -- just this year I had happen, turns out it was the battery itself -- weak or broken internal connection. At first, I thought I had left my lights on while parked or something -- had ECU lights, but wouldn't start (solenoid chatter), managed to push-start it (manual transmission), but was really wonky, didn't seem to be taking a charge, would sometimes cut out completely? Particularly concerning / unexpected, the car also has electric power steering, not hydraulic, so when the bus tanked during a turn or maneuver.. gotta crank on that wheel all of a sudden!The real scary thing (with respect to the electronics) is how often it can happen: if the battery is just fuckin' toast like that, the nature of nonlinear loads on the bus (e.g. relays turning off when a sudden load e.g. headlights tanks the voltage) means that it very easily oscillates. The same effective inductance that causes the load dump at turn-off, causes a complementary voltage collapse at turn-on. Then relays cut out, loads turn off, process repeats at ~1Hz or a bit less. The poor electronics in that thing, that day!But with a battery, no one's the wiser. Basically a big enough bypass cap to deal with the inductance, and who cares. Momentary loads are sourced from the battery, and the alternator picks up the slack eventually.(Car wasn't "poorly maintained", well, maybe parts of it I won't argue about, but... the battery itself wasn't very old, under 5 years IIRC. Freak failure I would say.)QuoteDon't know offhand, would guess the electronics have enough capacitance to handle it (perhaps even supercaps, depending on how much and how long they can ride through for -- if a whole lot, potentially dealing with gusty conditions too). Depends on generator type of course, with that only applicable to wound-rotor types.The trick, or the annoying part really, about automotive alternators, is they're hella reactive. Large gap between rotor and stator, not particularly well optimized, relatively high frequency (100s Hz), piss efficiency (~50%?). If field current were constant and the output were low-leakage, the output EMF would be stiff -- a reasonable voltage source as you'd hope to see, and typical of most direct-grid alternators. Instead, with so much leakage between the rotor EMF and windings, it's got a high impedance or CC characteristic, hence the large OCV when step-loaded.AFAIK, the mechanism is only energy storage in the field winding, and the slew rate thereof; a sudden load tanks the voltage, field current is adjusted up (at maximum slew rate dI/dt = V/L) and it stabilizes, sudden unload peaks the voltage, field current is adjusted down (at some maximum slew rate) and it stabilizes. Probably the falling slew rate is given by a clamp diode and the field winding resistance; the regulator could potentially unload the field very quickly, say into a flyback clamp TVS, or at a symmetrical rate by H-bridge chopping the field winding (which returns excess energy to the bus, no TVS dissipation), but I suspect they just use the diode for simplicity, and live with the slow response.It's conceivable that a given application could control field current very quickly, greatly limiting such an excursion; given the standards, it seems automotive ones at least aren't doing this, but it's possible that industrial examples (besides having better magnetic design) do.Tim

author: gnif
author_rank: Unknown
timestamp: August 24, 2024, 10:04:24 pm
content: ganfetsic was banned, this is farringdon again

author: fourtytwo42
author_rank: Super Contributor
timestamp: August 25, 2024, 09:55:04 am
content: Quote from: T3sl4co1l on August 24, 2024, 05:27:50 pmI just thought of another load dump scenario, older diesel electric railway locomotives (those with generators vs alternators & DC traction motors) periodically fail with either traction motor or generator flashover, potentially load dump might be one of the mechanisms responsible.

author: fourtytwo42
author_rank: Super Contributor
timestamp: August 25, 2024, 10:07:28 am
content: Quote from: gnif on August 24, 2024, 10:04:24 pmHe's begging for money to set-up an ESC (drone motor driver) manufacturer on other sites likehttps://www.electro-tech-online.combut it looks like they removed the thread & possibly his membership after several days. He is still active onhttps://www.edaboard.com/threads/buck-inductor-land-pattern.412172/but maybe he keeps his nose clean there!Keep up the good work here please, it's been so nice not to have the power folder in particular polluted with his rubbish everyday

author: NiHaoMike
author_rank: Super Contributor
timestamp: August 25, 2024, 12:42:51 pm
content: Modern cars use switching power supplies, in which case it's a matter of designing it to have a good transient response like any other switching power supply. There would still be switching transients from wiring inductance but capacitance is quite effective at suppressing it.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 25, 2024, 12:59:11 pm
content: Kind of related, railway applications can involve wide voltage ranges too; if usually not much for transients. I wonder if they usually use alternators, or batteries and converters or what; but the standards I've seen don't usually have long transients like load dump. 8/20us surge, with a fairly high impedance (22Ω, or even more?) is usually about the worst, and that's easily handled with modest size TVS. Noise from overhead (catenary) arcing can be pretty nasty, but nowhere near the energy.Tim

author: jonpaul
author_rank: Super Contributor
timestamp: August 25, 2024, 01:06:45 pm
content: we used large area TAZ Motorola MR2525 and MR2535 on 12..28V Avionics bus in moving map indicatorModern equiv exist.Can clamp the alt load dump pulses.Jon

author: TimNJ
author_rank: Super Contributor
timestamp: August 25, 2024, 02:00:53 pm
content: Quote from: NiHaoMike on August 25, 2024, 12:42:51 pmI don’t know how much power modern car electronics actually consume. How much power for the ECU? 50W? 100W? Infotainment and anything with video processing I imagine must consume a reasonable amount of power.Anyway, for the various small modules scattered around the car, with small power requirements (let’s just say 5-10W), I imagine you can just slap a 100V Vin max. buck converter on it, and call it a day.But for the higher power modules, let’s say ~100W (if those exist), the efficiency tradeoff of wide input voltage range (far away from the nominal operating point) may not make sense. 100-150V MOSFETs that could be 40-60V, larger inductors, etc. Could end up with a large, inefficient converter, if you want to treat the load dump peak voltage as part of the normal operating range.I don’t know what is actually done in reality. Not in the automotive industry.I also had asked in another thread, a while ago, about the prevalence of vehicles with “centralized load dump suppression”, which appears to be a giant TVS across the alternator. I am still not sure about that.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 25, 2024, 03:03:14 pm
content: AFAIK, the alternator providing front-line protection is pretty pervasive these days. Avalanche rectifiers being the active part, why use plain rectifiers when you can clamp each winding at the source too? (Bonus, maybe the Vf is just slightly lower, but, again, with what overall efficiency the bastards have, and how much air they have to flow through them... also at the high operating temperature for that matter, I mean Vf will be a lot lower than in other applications so there's that too...) So, just press some relatively fat diodes into the metal housing, that need to be modestly beefy anyway for the current levels, and there you go.Loads have been generally increasing, AFAIK. Lots of little things to be sure, but big things like power steering, ABS, etc. too. Powered and particularly heated seats may be fairly big. And that's not even with the AC and cabin heat that EVs also need to provide (but those may be from dedicated converters, not the accessory circuit, I don't know). On the upside, LED headlights consume a lot less than incandescent, not that halogen were particularly poor themselves, but they were one of the bigger operating loads.Hmm, back-of-the-envelope feeling on power steering, probably isn't all that much? I mean I can crank the wheel cold if I need to, but it's not going to be fun; that can't be more than a hundred watts or so, though peaks could be a couple times higher. I guess it's funny even that it was hydraulic for so long (but, reliable at least?). ABS, I never actually looked into what they do, is it a hydraulic (and by extension, manifold/vacuum) assist process, and the electronics are just going to be solenoid (or maybe proportional) valves? Might not actually need to be much, 10s of W, albeit maybe with peaks to 100 if they're big, snappy valves or something, but nothing a capacitor can't deal with, or that a fuse would mind.Tim

author: SeanB
author_rank: Super Contributor
timestamp: August 26, 2024, 11:06:12 am
content: Many car manufacturers are moving to 42V for such power hungry systems, as the savings in wire thickness for the power feed is considerable, and the voltage is low enough to still be SELV, but still use most of the automotive rated fuse designs still. EPS can be peak currents of 100A, simply due to transients to start the motor fast, or stop it faster., and around 30A in operation, though normally lower. For a car that is well known to have the worst electrical system look for a early XJ Jaguar, one with the original generator and points, as that is horrid for noise on the battery voltage, no charge at idle, with ignition putting a 200V pulse on the battery every single time the points open, with even more hash as the regulator cuts in and out as RPM rises and the generator is switched in.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 13, 2024, 05:39:27 pm
content: Nicehttps://hackaday.com/2024/10/13/building-an-automotive-load-dump-tester/

author: Phil1977
author_rank: Frequent Contributor
timestamp: October 13, 2024, 05:55:28 pm
content: Quote from: T3sl4co1l on August 25, 2024, 03:03:14 pmThe electric power steering pumps can be quite strong: Typical passenger car pumps are AFAIK in the low kW-range, systems for trucks and buses go up to 28kW (!):https://www.moteg.de/en/products-and-solutions/power-steering-pump-eservo/But I suppose the controllers of these pumps prevent strong load gradients...PS: I only know about the full electrohydraulic power steerings that are completely electronically controlled and allow the board systems some kind of automatic steering like in the parking assistants. I don't know if there are weaker partially electronic systems for smaller cars.

author: johansen
author_rank: Super Contributor
timestamp: October 13, 2024, 09:49:26 pm
content: For what its worth...The energy stored in the inductance of the alternator windings is negligible compared to the time constant of the energy stored in the ROTOR which is what's energizing the stator coils.so you have a 200 amp load on the battery, and over 0.1 seconds the alternator ramps up to provide 200 amps of current. then the current stops, and for a brief moment the battery sinks 200 amps of current while the alternator shuts off.what's the impedance of a battery at 200 amps when fully charged? well turns out its probably a lot more than 1 volt per 100 amps.also if you all don't know this.. the cranking amp rating of a lead acid battery is the number of amps the battery can deliver while its terminal volts stay above 9v after 30 seconds. the Cold cranking amps are what it can deliver when its 0F and the volts stay above 6 IIRC.and in general, the short circuit current of a lead acid battery is equal to 30 to 40 times its amp hour rating. the CA is a fourth of that number.anyhow automobile electronics generally have to be designed to handle 80v surges for microseconds.. and lower voltage surges for a lot longer.when we all switch to lithium ion batteries which sometimes blow up, we won't have the sluggish alternator load dump problem because the battery impedance will be much lower..But God help you when you hook the jumper cables up backwards.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 13, 2024, 10:20:00 pm
content: Yep, the response is due to apparent/effective inductance, namely of the field winding (high inductance, modest supply voltage: only responds slowly), multiplied by mechanical effort of the alternator, hence the large time constant and high current capability when nothing actually stores anywhere near as much energy (a ~100s J inductor would be almost as big as the engine itself!).This and more details can be found in the articles.Tim

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 20, 2024, 08:37:54 pm
content: Some shots of undersized components:The flash on the last one was due to a blown transistor in the converter... whoops, the current sense circuitry doesn't work so well into a short-circuit load.Tim

author: MisterHeadache
author_rank: Regular Contributor
timestamp: October 21, 2024, 03:49:07 pm
content: FWIW, load dump testing is still very much a part of OEM automotive EMC qualification tests. Each OEM has slightly different specifications, but most refer to the ISO 16750-2 standard and sometimes to the ISO 7637-2 standard. Basically anything that touches raw battery voltage must pass load dump testing. Anytime I worked on a new product design that was being fed regulated 12V or 5V I was relieved that we were exempt from load dump.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 21, 2024, 05:03:40 pm
content: I suspect they're going to be less common going into the EV era, but as long as fueled equipment remains -- have worked with a client whose products are used in mining equipment, CAT is a major customer -- alternators will likely be a key part of their systems. Overvoltage and reverse tests may stick around; depends how accessible the LV bus is for purposes like jumpstarting.Last project we did, a little monitoring/junction box sort of module, think it was 6-40V nominal input, tested at 174V 2Ω load dump. I used a depletion MOS input circuit, so not only did it survive the 60V overvoltage condition, I had tested it at 80 or 100V continuously and it barely warmed up (sure is nice when you only need a couple 10 mA for the circuit within). Tolerating 200V momentarily was easy, and a MOV suffices for further transient protection, who even needs a TVS with this much dynamic range.Tim