rxspeed87

right now the voltage on my car reads between the 12 and 14 mark on my voltage meter inside the dash most the time but also sees dips below 12 volts at points when I hit the brakes or when I push in the clutch and the car goes back down to idle issues. the voltage gauge sometimes needs a flick to work to work as well. when I tap the brakes the lights dim for a second. then come back on
the alt is the silverrotor FD alt, and the battery is new batt (the old one was 11 years old)

but since I was having problems and the old battery was 11 years old I bought a new one
still having the same issue

when I had the guy at the autoparts store do a battery test with the battery out of the car and it tested fine, when he tested it in the car hooked up it came up with unstable voltage... I'm at a loss


when I put a volt meter up to batt it reads 12.5 or so with everything off and holds steady within .05-.1 volts at most but mostly just sits at 12.5


I'm at a loss guys any ideas

WAYNE88N/A

11 YEARS on a lead-acid battery? That's gotta be some kind of record, man, lol...

You don't have any of those funky add-on grounds, do you?

If not, check the mouting brackets & hardware for the alt- make sure all metal-to-metal contacts are clean & tight. You may also want to check your positive cable, make sure the terminal up top (I guess it's up top on those alts???) is tight, and the splice up the harness near the fuse box is in good shape.

You have the proper reference and field coil wiring at the back of the alt, right? Searching charging voltage could also be a regulator issue, and by logical extension the wiring going to the reg...

Another test to perform is to set your meter on its lowest voltage setting, and while running (the engine, not you), put one lead on the alt body, and the other down near the starter ground or rear housing/tranny area, as far as you can reach safely. If you get any voltage at all, say .1 to .3v, your housing-to-housing contact needs some work. This is easily fixed by bonding jumpers if needed...

Do you get "unstable" voltages just at idle, or at all engine speeds?

rxspeed87

when I did the battery test at the autostore it was with the car off.
never had a chance to do it with the car running yet

the funky grounds I have right now involve one extra ground wire going from the negative term to the primary coil pack mounting bolt... that is it. I did have a wire running straight off the alt to the pos cable at one point but that is gone.

the cable on the alt is nice and tight

but again this unstable battery voltage was when the car was sitting there not even turned on

and yeah something like that
think the batt came from 93 or so
it was the optima red top battery but I don't think it was a deep cycle design either...
still worked ok though you knew it was a little weak

WAYNE88N/A

The ground you installed at the coil pack shouldn't be hurting anything, basically it's acting as a bonding jumper, as long as the ground run from the batt neg to the chassis at the left strut tower is still intact (this is the same cable that runs to the starter area)

How does the meter perform on another DC power source (like a "D" battery or two)? It's not unheard of for a meter to flip out...

If the meter is known good, and she's not running, and the battery voltage is flipping out, I'd say a cell inside the battery is on it's way out. My guess for the day

FC884Life

Not to hijack this thread.. But is there any way to stop the headlights and panel lights from dimming when the brakes are applied?? My 88' GXL has been doing this ever since I got her.. Thanks for all the advice,

Jimmy

rxspeed87

wayne that is where things get weird though

when I first went in to buy the battery I put it in my car and had them test it
the tester unstable voltage

so we took that battery back grabbed another one of the shelf tested before putting it in the car and it came up good


put it in the car and tested again
the tester says unstable voltage

and I'm sure you know the meter types I refer to not just the standard DMM but whatever they use at the auto stores.
when hooked up to just a standard DVM though it seems to hold stable within .1 volts at most when just sitting there

where is this ground though going to the starter since I'm not sure where that is and I didn't see one on the left strut anywhere.

WAYNE88N/A

Man, you got something funky going on there...Pull all of the main fuses and the red positive cable from the alt and see if she still does it...Remember the main fuse is held in by bolts...Your negative batt cable runs to the starter area, some cars will have it terminated at the rear housing, at the front of the big starter bolt, and some will have it on the other side of the bolt, at the starter itself, under the nut...Your problem sounds more like a short in a capacitive circuit somewhere, but I can't think of where to look first for something like that. Have you tried removing that one ground you installed, just for troubleshooting?

FC88- sounds kinda like a charging problem, possibly the gang ground under the trailing coil pack needs a little cleaning...

rxspeed87

I haven't tried to remove the ground yet but will look at it. the one thing that sux is I can't see an issue just using my dmm very easily.

just out of curiosity what circuits get power with the key in the off possition?
if nothing else I will d/c things on at a time drive around see if I can find a difference and go from there or take it to the auto store and see it


how sensative are those testing things they use at the auto store or could it just be my dmm isn't quick enough to detect the change in current

WAYNE88N/A

Change in current??? I thought you said the car was "just sitting there" when you were performing the voltage readings. If the car was running, that's a whole other ballgame. Now you'll be looking at the alt/charging system instead of the battery, for instance...

I didn't say anything about removing a ground. Why do you want to remove the ground???

The top two rows of fuses in your cabin fuse box are all "hot" without the key on...Also all of the engine bay fuses are hot full time (some of their circuits are not energized, however, until the appropriate relays are actuated by the ignition switch)...

Parastie

By any chance did you get the alt tested?
Are you running an Efan?

rxspeed87

I've tested the alt before I put it in. the alt tested just fine about 2-3 months ago. I don't have an e-fan

wayne as far as removing the ground I was refering to the one you spoke about from the negative to the coil for trouble shooting reasons
when they guy was running the test for the battery the car was turned off, everything else was off but the reading he recieved back from the tester was "unstable voltage"

I'm at a loss here some other things I have noticed though I'm not sure if they are common or not

when reading the o2 during engine braking it reads -.1v but during normal operation it stays in the .3-.5 range

today when driving around it started at 14.2-14.6 during cruise but then after a while it ended up dropping to 13.5 range with a surge up to 14.0 every now and then all this lights on.

my voltage gauge doesn't always work but easy fix is to flick the front panel


though these are issues with the car driving.

the "unstable voltage" reading as quoted from the tester comes with the car turned off

WAYNE88N/A

Oh, THAT ground, yeah, forgot about that, lol. Yeah, remove it just for grins to see if anything changes. I wouldn't think so, but electricity is a funny thing...

Your O2 sensor reading is good. In fact, you've just verified that your TPS is adjusted fairly well, because the injectors are shutting off on throttle lift, and that's a good thing

If during electrical load application the voltage jumps around for a second, that's OK, that's just your voltage reg in the alt tweaking the field voltage to compensate for the extra loads. When she warms up, the alt voltage will tend to fall a bit, because the alt becomes more inefficient at producing power as it heats up. If you are seeing voltage surges during cruise driving, the alternator would be the first place to look...Was this new alt a rebuild?

I still have no idea why the batt voltage would be freaking out with the car off- it's one thing to have a steady amp draw with a short, but quite another to have the voltage actually surging up & down with no loads on the car. Weird

rxspeed87

the alt I am not sure what new or rebuilt. all I knw is it one of silverrotors deals

right now the tps is actually not hooked up being the green wire broke inside the wiring harness and I'm kinda afraid to touch it cause I don't want to start breaking more wires but when it was hooked up I had that reading

when reading the voltage on my DMM I can't find the voltage flickering by more then maybe .1v at most more often then not it changes only by .2-.5v but mostly steady
put a load on the car like turning on the lights or the defroster(man that is one hella load) and the voltage drops like it would with a short and again still fairly steady except for maybe .2-.5 flicker every now and dthen but mainly stable voltage

does yours flicker a little here and there when off (.2volts or so maybe)
if not I can go from there if yours does I'm stucking thinkging

WAYNE88N/A

I'm beginning to think you're chasing a ghost, lol...

With the car running, do the headlights (or any other lights) flicker? I'm not talking about dimming a bit with brake pedal application & such, I'm talking flickering while driving down the road...

Does the battery ever die due to not being charged properly after a drive?

Any other weird electrical problems, besides what you're perceiving to be a problem with the DMM? Besides what I've already read in your posts?

If you answered "no" to each of the above, you may not have a problem after all. Then again, you may have some funky off-the-wall little electrical (or alternator/wiring) problem. Either way, I'm out of ideas unless you provide some new enlightening insights.

rxspeed87

the lights do not flicker when driving around

I have had it happen a few times when driving down the road hit the brakes and the lights SHUT OFF and then come back on a second later

this last time around right before I Replaced my battery I started the car the clock was reset and the lights where doing that crappy not wanting to stay lit if the rpms got low or hitting the brakes they woudl flicker. startedjust fine just was having problems there
replaced the batter though and not a problem

WAYNE88N/A

OK, lights shutting OFF are not a good thing, lol...

That's a charging system problem, pure and simple...Did all of this start with the FD alt install? And again I ask, are the wires at the back of the alt in the right place? Because it sounds like you have no field control in your voltage reg.

Charging system, including wiring. Start there...

rxspeed87

here is something I wonder about though


the lights shouldn't shut off if the battery is good right even if the charging system is weak right?

but if the battery was weak wouldn't that stop the car from starting?

will check the wires at the back of the alt to see whats going on though and see if one came loose... which wouldn't shock me

WAYNE88N/A

Hmm, yeah, you got a point there. The headlights ground through a "gang" ground under the trailing coil pack (along with a bunch of other components), attached to the left strut tower, you can check that...

Sure it's not something simple like a loose battery terminal connection (or loose/corroded wiring inside the terminal)?

hugues

Has all this happened since the install of the FD alt ???

or you had the issue before ???

IF this happened after the FD alt install, I would strongly suggest you triple check the connections:

http://www.rx7.org/public/altxref.html

IF you had the issue before, then ask Wayne or Mark because there's nothing worse than electrical problems and those guys love them (I guess).

Hugues-

HAILERS

Correct me if I'm wrong, but the field is supplied by the diode trio in the alternator AFTER the alternator is up and running. AFTER the atlernator gets rotating and up and running, the field input from the wire at the back of the alternator does....squat. It's the 12v wire from the battery source to the regulator inside the alternator that controls/varies the field output (from the diode trio now) , once your up and running. Yeah, that's the way things work.

WAYNE88N/A

The diode bridges chop the AC waves down to DC, Hailers. Has nothing to do with the regulated output.Look at the schematic of the alt in the engine electrical section of the FSM (it's much better than the one in the wiring manual). See all of the little transistor doo-hickeys? Those are the guys that sense the ref voltage from the 12v input from the ignition, and they adjust the field excitation voltage (usually around 1/10th of the output required) to produce a nominal 14v charge under different loads.

Say the alt is spinning 2500 rpm steady, and due to the electrical loads on the car the alt is producing 30 amps (about 420 watts) of power, now turn the headlights on, and the voltage will fall, becuase the field strength was sufficient for 420W, not the 540 or so now incurred. Once the voltage drops, the regulator senses it, and increases the field voltage/current to produce a "stronger" output from the alt, to match the load. Don't have the schematics with me right now, so don't get into a "which wire does what" civil discussion. Just rehashing basic generator theory with you.

BTW- did you read my PM? I know you say you never read them, but mine will make your day. Or week, if you're that bored with life

WAYNE88N/A

Since I now have the FSM, I'm going to try to explain this to the best of my ability, but it's going to be tough without visual aids. I'm using for reference the schematic of the alt from page 5-6 of the "engine electrical" section...Generation theory was shoved into my head more than 20 years ago, and I've forgotten a lot (especially microcircuit and transistor theory) because I haven't used it in the "real world". Sound like a disclaimer to you?

First the stuff I know for sure: Look at the picture, the single coil below the 3-coil symbol is the field, or rotor coil. Sometimes these coils will be nothing more than permanent magnets (if the rpms are held constant, the output will always remain the same). In our alts' case, though, the current flowing through this coil must be monitored and adjusted to attain a desired output. A straight 12v source from the batt or ignition switch would therefore not serve this function- it would be acting as the permanent magnets mentioned above (and in most applications would result in about a 120 volt output).

Now look up a bit to the three-coil setup. These are the stators, they are the guys that generate electricity to charge our batts and run our cars. When the rotor rotates through the magnetic field of the stator, a voltage/current is produced in each coil. This voltage turns out to be a sine wave, or AC voltage- half of the wave is positive, the other half negative. There are three wave outputs produced per rotor revolution, 120 degrees peak-to-peak from each other. In fact, if it weren't for the diodes, we would all have a 3-phase AC generator on our cars. The diode bridges' job is to allow the positive portion of the wave to pass (in the top and right bridges in the pic) and block the neg portion of the wave. In the bottom bridge, the opposite happens- the negative portion is allowed to pass.

Now the thing that trips me out: on the right side bridge circuit, you'll notice that the output is electrically part of the field coil circuit. Why this is, it's beyond me, lol. Usually the field coil circuits are totally seperate from the stator circuits, IIRC. Only thing I can figure is that the 14.5v or so on that one side of the coil is dropped significantly by the power transistor circuit on the other side of the coil before the circuit is allowed to flow.

Terminal L of the alt is the lower, white/black wire on the S4 alts, and one of the checks the FSM has you perform is to check for 1-3v with key on. This sounds exactly what a field coil (or excitation) voltage should be, to get the juices flowing, so to speak, on startup. It must be the resistor inside the alt warning light relay (CPU) that's dropping the batt voltage to the 1-3v level. Once started, you will read the 14.5v or so at this terminal that the alt is producing, but this couldn't possibly be a field voltage now, as it would result in output voltages of around 140 volts. So, L is the field voltage when the alt is not running, but not when it is.

Terminal R, the black/white wire, acts as the field voltage reference when running, as far as I can tell. The amount of field excitation is totally dependent on what the two power transistors are doing.

Did I clear anything up, or make the whole subject fuzzier?

HAILERS

Well.......what I know about electricity is that if you flip the light switch one way the lights come on, and if you flip the sw the other way......they go off.

So I talked to me mum, and mum tells me that the diode trio, shown in RED in the jpg I attached, puts out the FIELD voltage once the alternator gets up and running. Me mum tells me that once the alternator is up and running, you could cut that white/black wire, and nothing adverse would happen, because the diode trio is supplying the voltage for the field and that voltage gets regulated by ...the regulator who gets a reference voltage from the battery (R).

She claims that the check relay pulls in if the alternator is not running and once that relay is pulled in the ALTERNATOR red light comes on, on the idiot light cluster. She says that once the alternator gets up and running, the voltage from the diode trio and the voltage from the check relay are the same and that makes the check relay drop out and the idiot light will drop out/go off.

Now, she says its up to someone else to explain how the regulator varies the current to the field. She had to go bake some biscuts and dig up some fishing worms and didn't have time to mess with this anymore.

JPG attached, I hope:

rxspeed87

just wanting to throw a few more questions in
if the car is off the voltage should stay rock solid right?
not eve a .1 voltage swing or anything?

if so what I plan on doing is removing fuses one by one out of the top row and see what happens.
but if I am not going to find anything out by it... well I donno


as far as the fd alt causing the problem I dont' know it seems to have happened since I put the fd alt on there but when I first put it on the car was running at the 14 volt line when the car was running
lights on
14v
fan on
14v
hit brakes
14v
defroster on
14v
and this was not try one then try another. it was try this one.... works ok keep this one going then and add another load


now it seems
car stays at 14v at first
drive 10-20 min
13.5v
turn lights on
13.5
hit brakes 12v
put car in revers 11v
turn defroster on 9v


sad thing is the car does worse with loads running then it does when with the car turned off
I can easily hit 9v (according the gauge no my dmm)
but car turned off but yet turn on all the same loads it might hit 11v or so



still though the alternator shouldn't affect "unstable battary voltage" when the car isn't even running right?

Adam

Um in not sure about the 9 volts...Mine never drops that low unless i have a dead battery...But i am having same issues..I have an 88 gxl, And its fine when i first start the car,But after it warms up the alt wont put any power out below 1k. I was sitting at the jack in the box waiting for my food In drive with the brakes on..Sitting at allmost 12 volts. like the car is OFF.I hit the gas put it in nutral its back up to 13 or 14 volts and stays there Unless the rpm drops...I dont get it..