What do these analog scope pictures say about alternator diodes - Page 1
Forum section: electronics / beginners

author: Dave3
author_rank: Regular Contributor
timestamp: September 02, 2022, 03:46:34 am
content: Do the analog scope photos below show excessive ripple from the alternators diodes? Scope settings (with 10:1 probes) seemed to provide the most "interesting" photos but maybe there are more appropriate settings? Thank you for looking!PROBLEM- Opel Astra H with mystery random parasitic drains for past few years.BACKGROUND- Car is driven just 1 or 2 times per week. Weekly, we use modern plug-in battery charger.- 1 year ago, replaced battery. Voltage drop tests identified dirty connections, cleaned lots of ground & power connections for much better results.- July, car sat for 2 weeks and battery went flat.- Last Wednesday, we did weekly battery charging. Saturday drove 2 hours on the highway. Monday battery read 11.6v. Charged battery again Monday night.TEST-Today, a parts store's electronic gizmo tested battery and alternator (including diodes) as good (with printout to prove it!).- With my DMM at the battery terminals, when car is off, battery shows 12.6v. When car is idling with no accessories, shows over 14v. When car is idling with accessories, shows over 14v.-Iwatsu analog scope-Iwatsu 10:1 probes-AC coupled-Connected probe to + and - battery terminals (via alligator clips)-For photos, car idling with no accessories (except daytime running lights)1886 - 10mV/div, 5ms1890 - 50mV/div, 5ms1897 - 20mV/div, 10ms1902 - 10mV/div, 10msVideo

author: amyk
author_rank: Super Contributor
timestamp: September 02, 2022, 04:11:55 am
content: Automotive voltages will be noisy in general largely due to the ignition system (I'm assuming this is not a diesel?)If you are trying to look for parasitic drain then I would recommend using an ammeter at the battery terminals while the engine is off. Pull the fuses for each circuit to identify what is taking the most.Note that lead-acid is very sensitive to being deeply discharged so sitting flat for any length of time may have severely degraded the capacity already.

author: Dave3
author_rank: Regular Contributor
timestamp: September 02, 2022, 04:34:28 am
content: Thanks @amyk. Gasoline engine.Last year, I thought we addressed all the voltage drop issues with terminal and wire cleaning.This summer, we found a big parasitic draw issue this spring by pulling fuses (OEM radio was cause and fix was removing it from car 24 hours and it reset). I'll still redo these tests again. . .

author: --Oz--
author_rank: Regular Contributor
timestamp: September 02, 2022, 05:31:10 am
content: I agree with amyk. alternators are noisy and the battery is the filter.Regarding battery drain which you already figured out. When I raced rc on-road electric cars starting in the early 80's, we made some hi-tech stuff for the day back then, but kept it for ourselves as long as we could for an advantage. Like battery IR meter, motor dyno, battery zapping (4000A pulse to weld the internal tabs for lower IR) to name a few. With the battery IR development, I noticed you can measure mV across good fuse and have an idea of the current draw, and later troubleshooting cars this really paid off, as you dont have to pull the fuses to check current draw, and as the cars got more computerized, pulling the wrong fuse first could trick you into thinking the issue was on that branch (but it shut down other stuff on another branch), but was not. Anyway, recently I came across this useful website that gives a good idea of the current going through a good fuse.https://www.techshopmag.com/tech-tip-volkswagen-diagnosis-for-excessive-static-current-draw/And a YT video on it.

author: Gyro
author_rank: Super Contributor
timestamp: September 02, 2022, 08:18:16 am
content: A possible, but rather more mundane, explanation for your random parasitic drain... The glove box lamp is fairly notorious on Astra H's. The clear plastic block holding the leaf switch and bulb contacts isn't up to the job and tends to soften, causing the lamp to come on intermittently when the glove box is closed. Over a few days of standing, this drain is more than capable of discharging the battery (go on, ask me how I know). Take the bulb out and your mysterious drain may well disapear. You may see signs of overheating too. The best remedy is to just leave it out.

author: Dave3
author_rank: Regular Contributor
timestamp: September 02, 2022, 02:35:49 pm
content: Thank you @--Oz--. In the past few years, we did those voltage drop tests a few times, which were quite useful. But we need to repeat, I suppose. The video and article that you posted are very clear.- Not all our fuses have probe terminals on top; we will buy a bunch from the local electronics store. Some of the square fuse types don't have probe terminals and I never saw replacements for them (see image below)- There is a fuse panel in the hatch that we never tested, so will have to check that.- We don't have an amp clamp referenced in the article (or ammeter) but at this point should get one.Thank you @Gyro. Years ago we removed the bulb from the glove compartment. The bulb-holder is poorly made. And the glove compartment latch is another weak point of the Astra.We really DO NOT want to change the alternator unless strictly necessary. Years ago we removed the 120A alternator; it was extremely difficult and time consuming. There just is no space. Incredibly difficult to reach/remove the wires. Then, removing the alternator, for which there is no clearance. Engine mount needs to be removed and engine moved to have a chance. This might be easier for different engine configurations, etc. Hence the scope images and video.http://astra-3.pl/tip-astra-h-fuses-relays-engine-bay

author: fordem
author_rank: Regular Contributor
timestamp: September 02, 2022, 03:26:12 pm
content: Quote from: Dave3 on September 02, 2022, 03:46:34 amIn my opinion,The image below is a "known good" waveform from the picoscope libraryhttps://www.picoauto.com/library/automotive-guided-tests/alternator-ac-ripple-diode-test/

author: --Oz--
author_rank: Regular Contributor
timestamp: September 03, 2022, 01:45:39 am
content: Quote from: fordem on September 02, 2022, 03:26:12 pmFrom a new car to a 40yo car, different makes/models, battery status, alternator condition, alternator load, engine rpm, where the scope probe is (and grounded) and scope scope settings will all effect what a alternator waveform looks like. Lots of variables.EDIT: I mentioned where the scope probe is connected, some of the old alternator regulators I have taken apart are not potted and can see the discrete components, and have access to the rectifying diodes, so if probed there, the signal is going to look alot different than at the output. Really old school regulators use relays (stoneage, some 70's and earlier), most use a linear and some use pwm style regulation. All off these add to the variables and different waveforms.

author: fordem
author_rank: Regular Contributor
timestamp: September 05, 2022, 01:51:36 pm
content: If you look closely you'll see the thread starter tells you where the scope was connected - and - if you look at the page the image I provided was taken from (and for which a link was posted), the instructions there will tell you where to connect the scope.The reason Pico Technology makes their reference waveform library accessible is so that users know what an "acceptable" waveform looks like - exactly what the thread starter was asking for help with.

author: Dave3
author_rank: Regular Contributor
timestamp: September 05, 2022, 04:09:09 pm
content: Thanks guys; all the comments have been helpful and educational.Unfortunately, the B+ terminal at the alternator is nearly impossible to reach (we upgraded the alternator pulley a few years so know!). Positive wire runs from the alternator, to the starter, to the battery...so I suppose scope readings could be more accurate at the alternator (rather than at the battery post).Anyways, we reran the scope at faster rates (down to 0.5ms and see basically the same images).More interestingly, we did a bunch of voltage drop tests from the negative battery terminal (to engine block, to alternator casing, to body) and are seeing some bad results (0.4v range). A few years ago we did similar voltage drop tests. so have "good" references. These were in the 0.2v range (and all 0.1v or less after cleaning terminals and connectors around the car).We are noodling on the DMM measurements from the battery positive to different ground points on the car (at idle, both with all accessories turned on & off). Some of these are as low as 12.8v.But maybe we just need to clean a bunch of grounds and connections around the battery. Also, the connections around the starter were never cleaned before as they are had to reach, so really need to crawl under the car and do this. Then redo voltage drop testing.Some Astra owners complain of the positive battery wire oxidizing at the battery clamp, so that might be a place to look if above cleaning does not help. There are some interesting debates on wires quality (aftermarket gauge & aluminum blends) plus how the wire should be attached to the terminal (e.g. soldiered, hydraulic clamped, etc.). Will cross that bridge if necessary.

author: Old Printer
author_rank: Frequent Contributor
timestamp: September 05, 2022, 05:51:50 pm
content: Quite possibly I am misinterpreting your troubleshooting work, but you seem focused on the charging system while saying the battery is draining while the car sits, even with supplemental trickle charging. With all of the electronic specs you are listing, most seem to be voltages where I would be looking for current loss (amps/drains). Clip-on clamp type ammeters are convenient, but are they sensitive enough to detect low level (mah) drains at 12 volts? Sorry if I have missed something, I not familiar with your previous work/posts.

author: MrAl
author_rank: Super Contributor
timestamp: September 05, 2022, 07:52:17 pm
content: Quote from: Dave3 on September 02, 2022, 03:46:34 amLooks like ripple with some slowly varying DC.Try turning on the heater and headlights see what changes.

author: --Oz--
author_rank: Regular Contributor
timestamp: September 06, 2022, 01:44:18 am
content: Quote from: Dave3 on September 02, 2022, 03:46:34 amCar electrical systems are noisy in general.You ask about the alternator diodes, yours are fine imo. You mentioned over 14V when the car is on, this is charging, so the alternator is fine.Now two questions:1. Is the battery still good? (holds a charge (AKA has capacity) and low IR to start the car)2. What is draining the battery while the car is off?There are many ways to test and answer these questions.A semi quick way to check for something draining the battery is look at the fuse voltage drops as I already posted, I been doing this method before the blade fuses were popular, works well.Quote from: fordem on September 05, 2022, 01:51:36 pmWell, thats what the OP subject title is, but seems mainly trying to find the reason for why is his battery draining. I know from scoping out many alternators, there is so many variables, one scope wave capture does not fit all cars.Looking at the picoscope scopes, looks purpose built which is good for that purpose, but seems pricey for the performance, that price you do get some good info (like waveforms to compare), but starting at $1600 for a 20MHz 4 channel scope is quite steep imo. Yes, I know, you are paying for the guides/etc. I would think the $60 usb Hantech would also work, but thats for another discussion. Edit: I found a review of the pico scope, pretty nice system, specially for ease of use.https://www.vehicleservicepros.com/service-repair/the-garage/tool-reviews/article/21258318/tool-review-pico-technology-picoscope-7

author: Circlotron
author_rank: Super Contributor
timestamp: September 06, 2022, 03:20:29 am
content: Quote from: Gyro on September 02, 2022, 08:18:16 amHave a look and see if the boot / trunk light isn't stuck on.

author: Jeff5
author_rank: Newbie
timestamp: September 07, 2022, 01:49:42 am
content: I haven't read the all the other comments so sorry in advance if I'm repeating. From the looks of the scope your not in a small enough time base to accurately view ripple. It appears that your scope is at 5ms per division, correct? Should be smaller time. The really quick ups and downs is your ripple. You want to make sure that you have all good looking patterns. Good looking pattern is nothing that stands out and looks different. Now as for any parasitic draws, the charging ability of the alternator does just charging or maintaining of the battery. If you have a dead battery and it needs to be jumped and as soon as the jump pack or cables are removed and the car stays running your alternator is fine. Now short trips are hard on batteries, they need to be replenished from the cranking they performed.Can you take a video of the scope while cranking and starting the car. 2 volts per division while keeping the trace up top. we are gonna try and get a look at the battery voltage during the starter surge current. battery will need to be charged for this test. If we can clearly see the voltage dip below 8.4 volts then the battery is no good.How many times has the battery died? Automotive batteries do not like being fully discharged. It will hurt the longevity just dyeing once. ( I have seen a battery get damaged by dyeing one time and I have seen them last a decent amount of time after dyeing several times, depends on what your battery wants to do).I assume that once its jumped it stays running and will restart the car repeatedly? Time is what causes it to die correct?

author: fordem
author_rank: Regular Contributor
timestamp: September 08, 2022, 02:13:45 pm
content: Quote from: Jeff5 on September 07, 2022, 01:49:42 amGenerally speaking, cranking discharge will be replenished within the first three to five minutes after the engine has been started - I'm one of the vehicle owners who adds accessory gauges to their vehicles - oil pressure gauges, ampere & volt meters, temperature gauges to vehicles that don't already have them - and I've watched that ampere meter, kick up to 30~40+ amperes on engine start, and by th etime I have the car out of the driveway and the gate closed, it's down under 5 amps.Now - I'm not operating in a cold climate, where I will frequently need to run heater, blower & lights on a short trip - that's what is going to prevent the battery from charging properly.

author: --Oz--
author_rank: Regular Contributor
timestamp: September 09, 2022, 01:52:15 am
content: Quote from: Jeff5 on September 07, 2022, 01:49:42 amThe scope/start test is a good battery IR test, but my little toyota truck and my 70 Camaro will show a lot different scope captures. A "bad" battery in the Camaro will run for another couple years in my little truck.If the IR is bad, he needs a battery. But he is having parasitic drain, first I would see exactly how much current its draining, knowing this and how long it takes to drain the battery will give an idea of the battery capacity (or reserve Ah (nothing to do with CCA or IR). This will also give an idea if a new battery is needed.OP: Do you know how much current its drawing and how long it takes to kill it?What your battery model number and how old is it.Have you tried the voltage drop test on the fuses, results?I get 7 years out of my batteries in my truck, I am on my 4th one and the truck is 28yo now with 320K miles on it. I do have a pretty nice 4ch 300Wrms amp for the stereo. About every 4 or 5 months, I stick a little 3A charger on overnight.

author: Dave3
author_rank: Regular Contributor
timestamp: September 17, 2022, 04:04:41 am
content: Thanking everyone for their helpful tips and comments. This was a roller coaster and which took a lot of research and work to sort through. But it was a fun project.1. Alternator diode testWe ran the scope at faster rates (see image below: 10mV/div, 1ms with 10:1 probes).--> There doesn't seem to be much AC ripple so guess that the alternator diodes are OK. Feel free to correct us here!2. Parasitic drain testWe locked the car (closing bonnet alarm sensor with a plastic clamp). Then connected DMM between the negative battery terminal and negative cable (without breaking the electrical connection).--> Parasitic drain around 20mA after about 30 seconds. We tried that test several times so assuming no abnormal parasitic drain3. Cleaned a lot of grounds and the contactsat the battery, alternator, and starter.Cleaning the grounds and contacts didn't really change voltage readings (we cleaned most of these terminals a few years ago).--> THE main ground wire was corroded at the starter side (underneath the car). Both the ring connector and copper wires were green. Really dfficult access so home-gamer probably could not cut off green wire and professionally recrimp a new connector (or try serious cleaning in-situ).--> Very low voltage readings from + battery terminal to BOTH chassis & negative - battery terminal.--> Both cables at battery (+ and - cables) still were hot to touch after running a lot of accessories for 10 minutes.--> Voltage drop testing from negative battery terminal - to chassis was NEAR ZERO. We were seeing above 0.5v at engine block, alternator body, etc. Engine idling with lots of accessories on. That was a good clue.4. Purchased additional ground cable& split corrigated plastic loom tubing for protection. We used some white string to map out a path and to estimate cable length. Basically followed main ground from starter to battery terminal, using zip ties. Took a long time as the ground was big and inflexible; plus had to avoid coolant lines, sharp edges, etc.Cable is copper, 1-AWG, 5-foot long, ring terminals from factory that we purchased from local wholesaler buddy; Standard Motor Products and he said cable was high-quality with good crimps. The car's factory ground was a bit thinner, so a thinner cable would have been sufficient and easier to work with.--> Voltage readings at chassis and - battery terminal fixed--> Battery cables no longer hot to touch5. VOLTAGE TESTING data(after cleaning terminals & after adding addtional ground, respectively). We didn't have an extra person to hold the accelerator pedal at high RPMs so only have data at idle.Car off12.7v, 12.8v battery terminal + to -Idling, no accessories14.2v, 13.9v battery terminal + to -Idling, lots of accessories (headlamps, radio, rear defroster, AC at high). Connected DMM to + battery terminal:*13.1v, 13.8v negative battery terminal -*13.0v, 13.8v chassis13.9v, 13.8v valve cover bolt13.8v, 13.8v engine block13.8v, 13.8v alternator body*68A ,81AAmp clamp at positive cable out of alternator (We didn't have the amp clamp before cleaning)CONCLUSION - We are guessing that corroded main ground wire prevented proper battery charging & caused hot battery cables. We still need to do some final work (e.g. voltage drop testing, put car on scope when starting to see lowest voltage, etc.) We will follow up with any additional findings.

author: Dave3
author_rank: Regular Contributor
timestamp: September 17, 2022, 04:44:45 am
content: Quote from: Jeff5 on September 07, 2022, 01:49:42 amThanks Jeff5 - here is a video with smaller time base; hopefully this is more useful.https://youtu.be/q-3w4qPUCJgQuote from: Jeff5 on September 07, 2022, 01:49:42 amI will try this weekend, thank you.Quote from: Jeff5 on September 07, 2022, 01:49:42 amI think the battery is 1 year old and died 2 times. We charged it immediately after dying.I thought time was killing the battery. Based on my last post, I think the issue was a corroded main ground (at the starter); so the alternator just wasn't charging the battery enough whilst we were driving (particularly at night with AC, lights and radio on). Will see in the coming weeks.

author: --Oz--
author_rank: Regular Contributor
timestamp: September 18, 2022, 05:05:53 pm
content: Quote from: Dave3 on September 17, 2022, 04:04:41 am"Hot cables",Exactly what cable and where?High resistance plus current = heat, this should semi pinpoint the cause.What can fool you is that copper conducts heat well, and a hot motor can heat the ground connection to the block, hot exhaust, etc.

author: Dave3
author_rank: Regular Contributor
timestamp: September 24, 2022, 05:34:54 pm
content: Quote from: --Oz-- on September 18, 2022, 05:05:53 pmDrove the car for an hour, partly highway.Both battery cables and both battery terminals were cold to the touchafterwards, so the additional ground wire solved that issue.Why did the positive battery cable ALSO cool down from replacing the ground?Alternator is charging battery well also.The battery was loosing about 0.3v overnight, so the parasitic drain issue continued (traced to OEM radio):- Running a multimeter in-line with the negative battery terminal was only showing ~20ma draw about 30 seconds after locking the car. The max/min multimeter has an irritating 15 minute auto-off function so we couldn't measure overnight. We tried to measure max/min about 30 minutes a few times with no results.- So we disconnected the OnStar-Display fuse overnight. No change.- We disconnected the radio fuse overnight. BINGO!Previously we had intermittent parasitic drain traced to the OnStar/Radio periodically calling; that was solved by unplugging and removing the radio from the car overnight. However, this summer, it seems GM pushed an on-line software patch to disable OnStar (as 3G service is being discontinued). We are guessing:- The factory radio glitched back to parasitic draw mode after some months- The OnStar 2022 patch glitched the radio, so the radio needs to be uninstalled overnight- The OnStar 2022 patch permanently glitched the radioShort Term Fix- disconnect radio fuseLong Term Fix Options- Disconnect radio and remove from car overnight [WE WILL TRY THIS ONE FIRST]- Consider some relay scheme using ignition switched 12v (radio has 12v constant and canbus line)- Upgrade radio with CDC40 Opera (requires matched screen or Tech2 programming from dealer). Some risk that this did/will not receive OnStar patch, so OnStar module would continue calling.- Aftermarket radio (that removes some functionality of radio (e.g. Voltage, Coolant temp, Ambient temp readings).