Off car alternator voltage regulator testing? - Page 1
Forum section: electronics / beginners

author: Chris Wilson
author_rank: Super Contributor
timestamp: July 19, 2014, 06:34:48 pm
content: Hopefully appropriately for an Australian forum, a country where they love the rotary engine, we have here a voltage regulator off a Mazda RX-7 FD model. I am familiar with off car testing Bosch regulators, but am a bit stuck with this one! I think Mitsubishi build the alternators and I attach a photo, hopefully below, cribbed from a well known auction site advert! I have a variable voltage, variable current bench supply and a 5W 12V bulb as a load. How do I feed the variable volts *IN* to the regulator to find its cut off voltage, assuming it's working? I suspect it is, the rectifier block is both physically and electrically faulty. But I want to check before buying a rectifier. Thanks.

author: Neverther
author_rank: Regular Contributor
timestamp: July 19, 2014, 07:33:40 pm
content: Lamp/resistor across the brushes (I'd say 1A max current for testing)Ground to ground and feed the variable voltage to the diode input (either the vreg has internal diode or uses diode on the bridge assembly). Connecting the same voltage directly to B+ shouldn't hurt, they are not the same voltage when running, but for testing its good enough.I assume L is lamp, you can either connect low wattage lamp to 12v and the other end to that connector, or just leave it. It should stay around same voltage that is fed to the diode input (current limited exciter for rotor before current is fed trough he diode input by alternator itself). Usually directly connected to one of the brushes.S, sense? No idea, havent had enounters with fancy alternator/car running detection systems.Just look voltage/current across brushes, its just simple voltage comparator.The cutoff is the voltage fed when the state across brushes changes (voltage on B+).

author: Chris Wilson
author_rank: Super Contributor
timestamp: July 19, 2014, 08:06:19 pm
content: Thanks, that worked fine, it seems to be working fine, although the cut off voltage is a tad high, maybe more load would alter things, I haven't tried that. But I believe it's fit for service, thank you very much!

author: Neverther
author_rank: Regular Contributor
timestamp: July 20, 2014, 06:44:44 am
content: What is the voltage?I'd rather have high around 14.7 than lower voltages. Higher charge voltage helps with the battery sulfation so it lasts a bit longer.

author: Chris Wilson
author_rank: Super Contributor
timestamp: July 20, 2014, 08:25:46 am
content: 14.9V was it's cut off.

author: mc
author_rank: Regular Contributor
timestamp: July 20, 2014, 10:30:53 am
content: 14.9 is probably a back-up voltage.The S terminal is a battery voltage sense connection, which you'll probably find will cause the regulator to switch at a lower voltage.With the lack of a voltage on the S terminal, the regulator is probably designed to default to a higher voltage on the mian B+ terminal.How regulators with remote sense act when the remote voltage isn't applied, can vary greatly. I've seen them not charge at all, charge at a higher voltage, or even jam at full output.

author: Chris Wilson
author_rank: Super Contributor
timestamp: July 20, 2014, 10:41:37 am
content: Quote from: mc on July 20, 2014, 10:30:53 amHmm, interesting, so if I also connect the "S" terminal to the positive input voltage it may cut off at a lower voltage? Safe to try? Whilst Bosch, or Bosch clone voltage regulators are cheap as chips here in the UK, these Mitsubishi alternator ones are very dear and hard to find. $300 US for a new one from Mazda!! Thanks!

author: Chris Wilson
author_rank: Super Contributor
timestamp: July 20, 2014, 12:34:11 pm
content: Quote from: Chris Wilson on July 20, 2014, 10:41:37 amBit the bullet, set a low peak current and linked the "S" terminal to the B+ and cut off is now a lower 14.4 V. So I am even more convinced this regulator is still fit for purpose and have learned a lot more as to how other makes function. Thanks again.