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View Full Version : Voltage regulator? RPM and cluster illumination



Galcobar
12-18-2012, 08:47 AM
Always had an issue where the headlights would dim slightly when I hit the brakes, but I noticed something a little different as the days have gotten darker (as in sunset at 4:30 p.m.).

All my interior lights -- instrument cluster, HVAC, window switch, even my aftermarket head unit -- react to both additional draws and to low engine speed.

Hitting the brakes, operating the window or even using the turn signal will cause the lights to dim, though the turn signal causes them to flicker in time with the signal.

I've also noticed in neutral that revving the engine will cause the interior lights to brighten.

Engine grounds have been refreshed with new wires and clean connections on the transmission and the alternator, while the ground connection of the battery has been cleaned.

The alternator was replaced about five years ago with a Toyota part. The car starts easily, but when starting cold started doesn't immediately come up to speed. The tach hovers for a couple moments below 1000 RPM, the oil and sometimes the brake warning lights illuminate, and the interior lights are dim. Then, without my input, the RPMs climb to the usual cold idle of 1800, the warning lights go out and the interior lights brighten.

I'd suspect connection issues, but this covers several different wire branches -- and my head unit has its own ground.

My initial thought is therefore the voltage regulator, but I thought I should solicit other input. And I can't figure out where to find terminal B on the alternator.

Unfortunately I lack a garage, heated or otherwise, to work in so between the temperatures and the near constant rain I'm trying to avoid a) being outside too long and b) manipulating half-frozen 23-year-old wire and plastic. So suggestions as to what I can test would be appreciated.

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TL;DR

Interior lights on different circuits all dim when RPMs are low or an additional load is placed on the system. Cold engine start begins with low RPMs, dim lights and illuminated warning lights momentarily before coming up to speed and proper brightness.

Too damned cold and wet to work outside for long, looking for ideas.

Suspect voltage regulator. Embarrassed to say I'm not sure where to find terminal B on the alternator to run the tests per the BGB.

rizin
12-18-2012, 11:09 AM
If you are looking to check voltage at the alternator positive to the post and negative to the case. When I haven't been drinking I might type more on this if no one has.

Galcobar
12-20-2012, 09:54 AM
So after figuring out which is terminal B (having never disconnected the alternator I didn't realize one was a post and one was a connector), tested for voltage at 1800 (cold) and 800 RPM (hot). At 1800 RPM and cold I was getting 14V, or just under. At 800 RPM and hot that dropped to between 14 and 13 volts. These readings held even with the blower on high and headlights on. It's barely above the minimum (13.9V cold, 13.5V hot) but still within specified parameters.

Unfortunately I don't have an ammeter to test power output. I might be able to borrow one later this week.

Shadowlife25
12-21-2012, 02:04 AM
Those signal readings are definitely in spec. Odd that you are still getting such dimming. How pronounced is it?
Also, are you sure that the lights coming on is not just the standard start up check?
(May sound silly to ask but every bit helps)

Galcobar
12-21-2012, 02:19 AM
The dimming from load is noticeable enough that I, um, noticed it. It's not an on/off difference, but pronounced enough that I can replicate it with a quarter-turn on my illumination rheostat.

I'm quite certain the oil and more recently the brake warning lights are not part of the standard start-up cycle, as prior to this pause in gaining RPM they did not illuminate. Moreover, they turn off at the exact moment the RPMs go up and the various lights reach full brightness.

acidice333
12-21-2012, 02:21 AM
Your diodes/rectify might be leaking/bad (AC ripple)

Set the DMM to AC, put the positive probe on the B+ and the negative on the battery.

It will read some but I dont remember how much is too much. If it leaks too much, it will wreck havoc.

Shadowlife25
12-21-2012, 02:24 AM
Your diodes/rectify might be leaking/bad (AC ripple)

Set the DMM to AC, put the positive probe on the B+ and the negative on the battery.

It will read some but I dont remember how much is too much.


Should be fine as long as he has it on the correct value fused output for less than (iirc) 10 seconds.
Plenty of time to get a reading.

Galcobar
12-22-2012, 12:36 AM
Your diodes/rectify might be leaking/bad (AC ripple)

Set the DMM to AC, put the positive probe on the B+ and the negative on the battery.

It will read some but I dont remember how much is too much. If it leaks too much, it will wreck havoc.

For clarification: B+ as in terminal B on alternator with the negative probe on the positive battery post, or do you mean to measure from the positive and negative posts on the battery?

Galcobar
12-23-2012, 09:18 AM
Ran the digital multimeter and got more definitive results. At temperature, with no load the alternator was producing 14.6V. With high beams, window defroster and full HVAC fan the voltage dropped to 13.3. I couldn't do any amperage tests because the meter's safe maximum is 10A -- the owner is an industrial electrician who deals in high voltage and low amps and I wasn't going to risk damaging his equipment.

Also confirmed the warning lights and low RPM start are not persistent. Letting the engine sit for about four hours after it got to operating temperature has the temperature gauge reading zero, though it climbs faster than after sitting overnight. However, the hesitation in getting up to fast idle (1800 RPM), the brake and oil warning, and the dim interior lights are not present when starting after a few hours.

Doowstados
12-25-2012, 05:24 AM
Your VR is definitely not the problem, though there is definitely cause for concern. The cold temperatures should provide you with a better than normal amount of resistance in those wires, so a decrease in brightness in the headlights and dash is odd.

I would recommend testing the battery on a bench while it is frozen. As cheaper batteries age they tend to become more sensitive to cold weather. It would become a major source of resistance and would explain why you didn't notice until now. Even if you have a new battery this is a good place to start, doesn't hurt to test.

Here's a decent article on how temperature affects batteries of all types:

http://batteryuniversity.com/learn/article/discharging_at_high_and_low_temperatures