Pass Fail on starter motor test - Page 1
Forum section: electronics / beginners

author: tron9000
author_rank: Frequent Contributor
timestamp: September 01, 2015, 10:21:07 pm
content: I have a relative that works in a garage, she recently sent back a new starter motor that didn't work when fitted to a vehicle. Another motor was found and fitted and the car now starts.A test report on the duff motor was emailed and came back to her as working, all test criteria were within spec but all on the bottom limit. Especially the starter solenoid current: the reading was 31.8mA, but the fail limit was 31mA.The motor was tested by Bosch or a distributor under Bosch. I assume they have a full test lab and would definitely have some decent kit and some experienced and capable employees to boot.Out of interest, I asked if she could ask them what kit they are using to test the current with and how they are measuring the current (inline? clamp meter?) - I'm expecting a decent bench meter and inline.But 31.8mA out of a 31mA fail limit?...would anyone else want a second reading or opinion on that if it was you testing it?

author: flynwill
author_rank: Regular Contributor
timestamp: September 02, 2015, 03:54:31 am
content: What was the nature of the failure of the new starter? Did the solenoid fail to pull in? Hard to tell what went wrong, but solenoid current being close to the lower limit is a pretty unlikely candidate.

author: mikerj
author_rank: Super Contributor
timestamp: September 02, 2015, 02:44:35 pm
content: Quote from: tron9000 on September 01, 2015, 10:21:07 pmThat sounds at least two orders of magnitude too low for a starter solenoid. They typically take around 10 amps or so.

author: SeanB
author_rank: Super Contributor
timestamp: September 02, 2015, 06:34:21 pm
content: I would bet the starter sent back had been in storage for a while, and had built up a film on either the solenoid contacts or on the motor brushes, preventing current from flowing through the motor. The vibration from transport or the turning of the motor shaft would have likely removed the film and thus it passed, or the connector on the car side had corrosion, and the wiping of the contact on the removal and reinsertion cleaned it up enough to get it working again.If it is a VAG vehicle the ignition switch could also be faulty. There are a lot of recalls for those switches, I just had my one replaced ( as the steering column had to come out to get the clutch pedal assembly out so making it easy) and there have been a few batches with either poor starting issues or catching fire.

author: G7PSK
author_rank: Super Contributor
timestamp: September 03, 2015, 07:53:36 am
content: Testing of starter motors is usually done on a special test rig that puts a predetermined load on the starter motor, at least this is the case at all the places I have been to to either get a starter repaired, exchanged or a new one the same goes for alternators as well.

author: tron9000
author_rank: Frequent Contributor
timestamp: September 03, 2015, 09:46:48 am
content: Quote from: flynwill on September 02, 2015, 03:54:31 amWell its a garage with the simple work mantra of: its busted, replace it and move on! So there was likely no further diagnostic by the mechanic.Quote from: mikerj on September 02, 2015, 02:44:35 pmI'm pretty sure she said solenoid current. Will double check.Quote from: SeanB on September 02, 2015, 06:34:21 pmIt's a ford garage.- but thanks for the info, we have a VW Passat, so will keep an eye out for that one if it packs in (and hopefully doesn't catch fire!)That does sound like a likely and plausible cause though from a very typical situation.Quote from: G7PSK on September 03, 2015, 07:53:36 amOddly enough one of the tests that came back was "unloaded spindle speed" and "unloaded current".Cheers for the replys!