Coil-winding short circuit detection? HOWTO? - Page 1
Forum section: electronics / projects

author: aluck
author_rank: Regular Contributor
timestamp: December 15, 2012, 10:46:25 am
content: Is there any reliable way to detect coil-winding shorts in engine starter? Mine is drawing 140-240 Amps (as measured with a 400 Amp rated clamp meter) while cranking. It is 90 Amp rated, so 240 is too much on a high side. I think it's either shorted (not a complete short, but maybe slightly fried winding), or a damaged starter's bearing.A new starter costs about 800 USD, so I do not want to take chances.

author: nctnico
author_rank: Super Contributor
timestamp: December 15, 2012, 11:12:51 am
content: You can have it checked. That probably costs much less. Otherwise you can also try to buy one from Ebay. I don't know what kind of car you have but there are lots of car parts available on the German Ebay (ebay.de).

author: Skimask
author_rank: Super Contributor
timestamp: December 15, 2012, 11:23:24 am
content: An $800 starter? For what?Last time I saw a starter that expensive, it was on a jet engine, and it cost roughly $150K.If you had a short, it would take out more of the windings over time, and completely smoke the rest of it.My guess is that the starter is under too much load...like you say, bearings/bushing gone bad, misaligned on the flywheel, teeth are shot (bad engagement), and so on.

author: SeanB
author_rank: Super Contributor
timestamp: December 15, 2012, 11:41:58 am
content: Simple way to check is to remove it, then strip it apart ( 2 long bolts through the frame hold it together) and have a look. Most likely are worn brushes, worn bushes and dirt. The front pilot bush often wears a lot, as it is only a bronze unit and has a very high load on it. When stripped then cleaned you can replace the brushes if worn down ( you will need a 400W soldering gun or a gas powered soldering iron for this) and replace all the bushes. Lubricate the new ones after pressing them in to the housing with moly grease, and make sure the rear housing is half full of grease, while the front is just giver a thin coat inside before putting the shaft back. Pilot bush needs the cup filled with about 2 match heads of grease.To test the windings use a meter to check resistance from the commutator to the frame, should be open circuit or over 1M. To check the field coils do the same ( depending on make you might find one is connected to ground so remove this connection before test) and look for the same result. Shorted turns are not likely, unless there is physical damage to the coil, the wires used are very thick.Solenoid should be cleaned and the pivots lightly greased, no lube in the solenoid barrel. Check the bendix thread for no burrs, and allpy a thin grease coat to it's splines. Check the overrun clutch is able to turn relatively easy one way and not at all the other way, stiff in normal, loose and rattles is not, and needing brute force is also not good - turns without needing major effort is ok. Place a drop of oil on the seals there and let it penetrate inside, then wipe off the excess.Been a while since I overhauled a starter, must be 6 months ago............ My own, turned out to be poor contacts on the feed to the solenoid, so new spade connector and boot put on the lead.

author: amyk
author_rank: Super Contributor
timestamp: December 15, 2012, 01:55:02 pm
content: The 140-240A you get seems around right for an auto starter.90A might be the current when it's running unloaded.I've always wondered why BLDC motors haven't become common (if used at all) for engine starting; they can haveinsane power densities, and are much lighter and smaller than the traditional DC brushed motor.

author: NiHaoMike
author_rank: Super Contributor
timestamp: December 15, 2012, 02:05:12 pm
content: Quote from: amyk on December 15, 2012, 01:55:02 pmHybrids have been using them for over a decade, and the Chevrolet Malibu Eco is the first supposedly "non hybrid" to use one.We'll probably see that happening more when they start using synchronous rectified alternators for better fuel economy.

author: aluck
author_rank: Regular Contributor
timestamp: December 15, 2012, 02:49:25 pm
content: Quote from: amyk on December 15, 2012, 01:55:02 pmYes, it is rated for no load, but I still expect to get 180-190 Amps while cranking. Am I wrong?Actually, I think I should explain my line of resoning.The car is Subaru Forester 2.5XS (H4SO engine). Several years ago I installed a car alarm with a remote start function. It is a very convenient when you have -20C outside, like it is now. I just press the button on remote and the car is supposed to turn on the ignition and start the engine.Several days ago I tried to start the engine from remote. It didn't work. With engine turned off I have a nice 12.5V on battery terminals. While cranking voltage drops down to 10.3V, which causes car alarm to reboot (it is not supposed to work under 11V). The battery is almost new and fully charged. Obviously, it is not supposed to go that low. To check if it is a problem with my battery, I borrowed another battery (also fully charged) from my friend's car, and wired both batteries in parallel. Same thing, when I start the car - voltage drops, alarm reboots.When I start the car usual way, with ignition key, same thing happens - while cranking, the alarm reboots several times. But while the alarm is already disengaged, it is OK.I still think that it is a problem with starter. It's either shorts in windings or a bad bearing. If it were brushes, there wouldn't be a lot of current, and I wouldn't see a lot of voltage drop on battery.BTW, the battery is 140 Amps max, so 240 Amps are definitely out of question.Am I wrong? Any suggestions?..

author: nctnico
author_rank: Super Contributor
timestamp: December 15, 2012, 02:57:00 pm
content: Does the engine turn while starting? The problem is probably your car alarm. I've seen similar failures before. When its cold the oil in the engine is thick which makes it harder to turn and the battery is much weaker. Did your engine get an oil change lately? There is nothing wrong with your starter, its probably the crappy car alarm. You may solve the problem by connecting the car alarm to a secondary battery (for a motorcycle) which is connected to the main battery through (say) a 220 Ohm 10W resistor. The resistor prevents the secondary battery from helping the main battery for starting but is also allows the secondary battery to stay charged. A secondary battery does have its disadvantages like you need to disconnect both before working on the electrical parts of the car.

author: aluck
author_rank: Regular Contributor
timestamp: December 15, 2012, 03:02:58 pm
content: Quote from: nctnico on December 15, 2012, 02:57:00 pmWhen started by ignition key - yes, it does.I tried to start the engine and keep it running idle for a while, until coolant temp reaches about 60C. Then I turned it off and tried to start from remote again. Same thing - it starts cranking and immediately reboots.The alarm is not bad, and I've been using it for almost 5 years. No problems at all.I thought about putting a Schottky diode + electrolytic cap into alarm. It would prevent it from rebooting, but if the real problem is somewhere else, it still seems like a temporary solution. I don't think that the voltage is supposed to drop below 11V no matter what.Am I wrong?..

author: madires
author_rank: Super Contributor
timestamp: December 15, 2012, 03:11:35 pm
content: Quote from: nctnico on December 15, 2012, 02:57:00 pmActually he just needs to buffer the power supply for the alarm with a cap. A resistor for limiting current, a diode and a large cap are smaller, cheaper and more reliable than another battery.

author: SeanB
author_rank: Super Contributor
timestamp: December 15, 2012, 03:15:44 pm
content: Most likely worn bushes in the starter, most probably the one at the front of the shaft in the gearbox bell housing. You need to remove the starter and then drift it out then put in a new one. Most likely that will cure the problem, though check the flywheel teeth as well to see they have not been chewed up. Some wear is normal in the 4 spots the gear normally stops in. If the teeth on the starter are chewed up then you need a new bendix or a starter from a scrapyard.

author: nctnico
author_rank: Super Contributor
timestamp: December 15, 2012, 03:19:41 pm
content: In that case the battery will still be cold. Maybe you can park the car overnight in an underground parking lot which isn't so cold (above 0 C) and try again. Batteries really don't like the cold and the electrical parts on Japanese cars are usually rock solid. If you order a new starter it probably has to come from Japan! Ask about the delivery time of a new starter just for fun.

author: madires
author_rank: Super Contributor
timestamp: December 15, 2012, 03:24:08 pm
content: Quote from: aluck on December 15, 2012, 03:02:58 pmHow much Ah does your car battery got? 48Ah? Such a battery can't deliver 140-240A at 12.x V, especially if it's cold.

author: aluck
author_rank: Regular Contributor
timestamp: December 15, 2012, 03:33:15 pm
content: Quote from: nctnico on December 15, 2012, 03:19:41 pmIt's 21+ days. More likely it's going to be a month.And the cheapest one available to Russia is still 625 USD delivered.And - yes, if the engine is warm, and the battery is warm, I am quite sure it is going to start alright. But -20 C is quite a usual winter temperature here. And at least a week every winter we have -30..35 C.

author: aluck
author_rank: Regular Contributor
timestamp: December 15, 2012, 03:35:29 pm
content: Quote from: madires on December 15, 2012, 03:24:08 pmThe battery is 55 Ah.The question is: is that a normal current for winter start, or is it a faulty starter?..

author: G7PSK
author_rank: Super Contributor
timestamp: December 15, 2012, 06:51:48 pm
content: It used to be that anywhere between 200 and 400 amps were required to crank the engine from cold in winter, I would only be concerned if the starter was drawing that sort of current and not turning. Have you checked the battery terminals and coated them with Nocrode.

author: nctnico
author_rank: Super Contributor
timestamp: December 15, 2012, 10:13:52 pm
content: Quote from: aluck on December 15, 2012, 03:33:15 pmIn other words: it has to come from Japan and thus the starter in a Subaru never needs to be replaced otherwise they had it in stock.I like the hint about the battery terminals. Every problem I have experienced with cars not starting had to do with corroded or loose battery terminals.

author: TerraHertz
author_rank: Super Contributor
timestamp: December 15, 2012, 10:36:52 pm
content: Where are you measuring the system voltage during start? From the car wiring, or directly on the battery via probes jammed onto the top of the battery posts, not the cable clamps?If you are not measuring directly on the battery posts, I'd suggest taking the cable clamps off, cleaning the posts and inside the clamps with a wire brush till they are nice and shiny, greasing both with vaseline, then reassemble and clamp tightly. Also check the connection between the post clamps and the actual cables.A little bit of resistance at the battery connection makes for large voltage drops during starting.It's also conceivable that your near-new battery has developed a bad connection between cells. A garage can check this with a battery load tester.

author: aluck
author_rank: Regular Contributor
timestamp: December 16, 2012, 05:30:02 am
content: I know the problem with terminals, so I measured directly between battery's outputs. This way even a bended and broken ground wire or loose and corroded clamps wouldn't be able to interfere with my measurements.And I see that the voltage on outputs goes down to 10.3 V.P.S. Our dealers are not keen on keeping something "in stock", unless it is needed for newer vehicles covered by warranty. Otherwise they are not very interested in repair.

author: SeanB
author_rank: Super Contributor
timestamp: December 16, 2012, 05:43:24 am
content: I will still put money on the front bush, especially if the car is over 5 years old and the starter has never been taken out. Small 8mm bush that gets cooked and frozen alternately, along with having grinding paste blown into it from clutch wear. Hard to get out in most cars but so cheap to buy, you just need one the same ID, OD and length. Probably a standard DENSO part for most starters.

author: aluck
author_rank: Regular Contributor
timestamp: December 16, 2012, 08:13:19 am
content: SeanB, I am very sorry - did you mean brush?

author: SeanB
author_rank: Super Contributor
timestamp: December 16, 2012, 10:10:27 am
content: No, the small pilot bush that is in the bell housing, a common thing to wear and misalign the starter. Then it draws high current, and if left for long will destroy the ring gear on the flywheel. Flywheel is very expensive........Easy to check, pull starter out then look in hole to see the bush. If worn then change it ( easier said than done on some cars............. At least you do not have an Italian built car) and check again.

author: aluck
author_rank: Regular Contributor
timestamp: December 16, 2012, 12:30:59 pm
content: OK, will check that out.

author: aluck
author_rank: Regular Contributor
timestamp: December 24, 2012, 02:48:49 pm
content: The hardest part of the procedure was to unscrew starter's mount nut. It took me about 3 hour. Not convenient at all - had to lay down on engine, bend both arms, and twist my tongue in a very exact position.As you thought, it was a front bushing. Spindle had a huge 1 mm play. Replaced both bushings (made of bronze, very soft, so I just cut it with dremel). Starter draws about 170 Amps in peak, then drops to about 140 Amps.Thank you, guys!

author: SeanB
author_rank: Super Contributor
timestamp: December 24, 2012, 03:09:23 pm
content: They are not solid, but are made from powder pressed then sintered to hold them together as well as hold oil to lubricate. Hope you applied some CV joint grease when assembling them.

author: aluck
author_rank: Regular Contributor
timestamp: December 24, 2012, 03:47:20 pm
content: I asked guys who make a living on starter repair, and they recommended to use a mix of 50% 5w40 synthetic engine oil + 50% of lithium-based grease. They told me that it is better for low temps.

author: G7PSK
author_rank: Super Contributor
timestamp: December 24, 2012, 04:37:05 pm
content: Most bushes come ready lubricated if not it's best to heat the bush to about 100 deg C and then drop into oil as this will suck the oil into the bushing. The bushing material can be bought in meter lengths , many bearing suppliers will have such material in stock and cut to length as required.

author: KD0CAC John
author_rank: Frequent Contributor
timestamp: December 24, 2012, 05:09:13 pm
content: A lot of your number are wrong ,A fulling charged battery should be 12.75 volts .Without looking up the brand & model of your battery , and what the car requires , it should put out around 400 amps .There are 2 ratings for batteries , cranking amps - 32*F and cold cranking amps - 0*F , at 0*F most batteries have 80% less capacity .Again need to look up spec.s , the draw on the battery of 190 amps may be a little high but your volts [ 10.6 ] are low .Jump starting batteries , batteries are made up of cells , 12v - 6 cells , jumpstart is 12 cells , the battery - jumpstart is only as good as the worst cell in the string , so if you have 1 battery that is 10.6v with load , that is the problem = the battery .The easiest thing to do is remove the battery and bring inside and allow to warm up , room temp for lets say 6-8 hours , put on charger , with out knowing the state of charge or what size charger you have , it could take 6-8 hrs for a full charge .Now put the battery back in car and test amps & volts .What can happen is if there is a lot of attempts of turning over engine with all these issues , you can damage starter , as volts go down , amps go up , at least to a point .In cold climates , if the battery gets cold and the engine turns over slow , there is not enough current to drive starter & ignition system , so the plugs get fouled .The best thing to do is again bring battery in for a few hrs and warm up , if you did not draw the battery down too far , you do not even need to charge , just put back in .Then with modern electronic fuel injection , almost all computers is car with turn off the injectors if you put the pedel all the way to the floor , you need to do this to clear out the fouled plugs , then as after several revolutions of the engine , you should get a little bit of sputtering of ignition lighting off the remaining fuel , at this time let go of the throttle [ while still running the stater ] and now the engine should start .

author: aluck
author_rank: Regular Contributor
timestamp: December 24, 2012, 07:37:01 pm
content: Quote from: KD0CAC John on December 24, 2012, 05:09:13 pmI did not claim that mine battery was fully charged, nor discharged (i.e. below 12.4 V without a load).Also,Cold cranking amperes (CCA) is the amount of current a battery can provide at 0 °F (?18 °C). The rating is defined as the current a lead-acid battery at that temperature can deliver for 30 seconds and maintain at least 1.2 volts per cell (7.2 volts for a 12-volt battery). It is a more demanding test than those at higher temperatures. This is the most widely used cranking measurement for comparison purposes.http://en.wikipedia.org/wiki/Automotive_batteryMy battery DID provide 10.6 V, so it is up to spec. I know that this type of car (if not equipped with a car alarm) is capable of starting down to 9.8 V or thereabout. It is not good for car, but it is still possible.I do not see this as a problem with battery. It is still about -21C outside (-5.8F for all of my non-metric friends), and is going be this way for a couple of weeks more. I will let you know if bushing replacement had 100% solved this problem.