Voltage regulator duff - possibly alternator?

Bimble7116 · Post by **Bimble7116** » Sun Mar 24, 2019 9:57 pm

Guys,

Hoping for some learned intel on this battery charging snag on my 5th gen 2.0i Prelude. It’s very much like the problem Blockh3ad has reported, my battery is not being charged when the engine is running. The difference is - the ignition light does NOT illuminate - even though the voltmeter shows only 11.7 volts with the engine running.

I believe the car has a separate voltage regulator, but I’m not sure whether that’s right or not. If the voltage reg is separate from the alternator, can anyone please tell me where it’s located - and whether it could be the culprit in this case? Thank you

With best regards

Andy H

Scott560 · Post by **Scott560** » Mon Mar 25, 2019 8:25 am

the regulator , for the last couple of decades at least, has always been on the end of the alternator, where the multiplug and main 12v wire is attached.

for the hassle of removing the alternator to get to it (i assume), and the fact its probably harder to track down a regulator compared to an alternator, better off replacing the whole thing in my experience.

The battery light on the dash should come on before the engine is started - if it doesn't then worth investigating that first (bulb, associated wiring etc).

Bimble7116 · Post by **Bimble7116** » Mon Mar 25, 2019 10:06 am

Thanks for your reply Scott. I've been pricing up a new alternator this morning and ascertained that the voltage regulator is part of the alternator as you described.

The ignition/battery light works normally, in that it comes on with the ignition key and goes out when the engine starts - indicating all is well. It is not illuminating to indicate that voltage is down - putting a voltmeter on the battery with the engine running is showing 11.7 volts - surely that would be low enough for the light to come on...?

Scott560 · Post by **Scott560** » Mon Mar 25, 2019 11:45 am

the light is not a battery voltage low light, otherwise it wouldn't come on after you stop the engine (the battery voltage would still remain high for a little while).

The battery light (for older cars) is always a 'is their current going through the outer windings' light. Normally this will tell you if the alternator is dead, but you can end up with a half way house where your not getting the full voltage generator, but its doing something, so the light goes out. Bring back voltage dials i say...

Max · Post by **Max** » Mon Mar 25, 2019 1:33 pm

Ive done this on the type s, the regulator is in the alternator on mine, was a simple case of taking it off, split it open and take the regulator out, and test the regulator (as per workshop instructions) with a multimeter, i found it wasnt working as expected so bought one off ebay, installed it and put everything back together and now it works perfect. Total cost was £25.

Bimble7116 · Post by **Bimble7116** » Mon Mar 25, 2019 2:03 pm

Thanks fellas.

I've disturbed my alternator recently when changing the cam belt, so it'll be a good idea to check the wiring to ensure there's nothing amiss there, before lobbing out £130 for a new alternator. I note Max's successful experience changing the voltage reg on it's own - but if the wiring checks out, previous experience and a non start issue with this car, tells me to replace the alternator and have done with it.

Bimble7116 · Post by **Bimble7116** » Tue Mar 26, 2019 3:02 pm

Update

I put a voltmeter on the alternator main terminal with the engine running, it showed just over12 volts, the battery is showing just under 12 with the motor running. Satisfied the alternator has retired itself, I've ordered a new one.

This car has the most immaculate service history, so I know this is the alternator it left the factory with 20 years ago. Components lasting that long - means no reasons to chunter. The Prelude was due it's ticket tomorrow, now deferred to next week to give me time to fit the alternator and test the car accordingly.

Thanks again to all you fellas for your help. Much appreciated

With best regards

Andy H

89 UKDM BA4 4WS (resto job!) · Post by **wurlycorner** » Sat Apr 06, 2019 3:39 pm

Hang on...
The system is a little bit more complex than that on a prelude.
There is an ELD in the fuse box and some charging control by the ECM, it's not just down to the regulator in the alternator.
Also, if your battery light doesn't come on at all with the ignition on (engine not running) then that will also affect charge status.

The circuit diagram is page 4-23 of the manual and the fault flow chart is 4-24 to 4-26
The 5th gen manual doesn't include a description of how the system works at all (the 4th gen manual isn't much better, but there's a bit of an explanation on page 23-118 - it at least explains that there is much more at play than just the regulator).

Correct method to test the regulator if you get that far, is page 4-27 to 4-28 (although that description relies on a special tool to be able to test under load).