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  #1  
Old May 14th, 2007, 01:16
DIGITRUCK DIGITRUCK is offline
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Question Where Should my Voltage Gauge Read After...

Hi,

'88 XJ Reman 4.0L and AW4 Tranny, A/C, Open Cooling System with CSF Rad, Tranny and Oil Coolers. Megawatt A/V/GPS/Computer/Lights/LEDs/etc. 170 Amp Aftermarket Alternator.

Ok, Just changed my Red Top with a Yellow Top Optima (damn, was $206.38 at Pep Boys). I turn on all electronics, everything's fine the Dashboard Voltage Meter at around the 11 O'Clock position (little before 14V).

BUT, as soon as I turn on the A/C the AUX FAN kicks in and the VOLTAGE GUAGE then drops to the FIRST line or notch. That FAN draws alot of current.
Plus, my LCD SCREEN nearly goes blank due to lack of current. It returns to normal soon as the A/C is switched off.

btw - I only have an oem 94 AUX ELECTRIC FAN now that's coupled with the oem CLUTCH FAN. I removed the second ELECTRIC FAN and put back the CLUTCH FAN.

Should the needle on the Gauge drop that low or is it normal? Where does your VOLTAGE GUAGE read after switching on the A/C? The above is when the engine is idling.

Thoughts, suggestions?

Thx.
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  #2  
Old May 14th, 2007, 08:22
Matthew Currie's Avatar
Matthew Currie Matthew Currie is offline
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Re: Where Should my Voltage Gauge Read After...

Simple answer: do not trust the voltmeter. Measure voltage at the battery. The voltmeter is notorious for dropping to a frightening level when you turn the fan on high. It's not actually drawing that much current, but it shares some circuitry with the meter.

An additional ground for the radio would probably be a good idea too. I seem to recall that my 87 put a lot of stuff through a common ground with the cigarette lighter, and strange things happened when that ground was inadequate.
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  #3  
Old May 14th, 2007, 09:13
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Blue XJ Blue XJ is offline
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Re: Where Should my Voltage Gauge Read After...

My factory volt gauge usually read about 11 when cold and 9 - 10 when the motor is hot. I installed an Autometer volt gauge, it never drops below 13 volts. I wouldn't trust the stock gauge
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  #4  
Old May 14th, 2007, 11:16
DIGITRUCK DIGITRUCK is offline
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Question Re: Where Should my Voltage Gauge Read After...

Quote:
Originally Posted by Matthew Currie
Simple answer: do not trust the voltmeter. Measure voltage at the battery. The voltmeter is notorious for dropping to a frightening level when you turn the fan on high. It's not actually drawing that much current, but it shares some circuitry with the meter.

An additional ground for the radio would probably be a good idea too. I seem to recall that my 87 put a lot of stuff through a common ground with the cigarette lighter, and strange things happened when that ground was inadequate.
I'm not sure how to measure voltage using a VOM. Do I just touch the probes to the battery terminals when the engine's idling and the a/c switched on?

Thx.
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  #5  
Old May 14th, 2007, 11:31
bfred bfred is offline
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Re: Where Should my Voltage Gauge Read After...

battery should read 12.5 volts w/engine off. While running,14.5 volts. If all the accesories your running are drawing more amps than your alternator can put out, your gonna have problems. Deep cycle batteries can store more power, but if your regularly drawing more currant than the alt. can produce, it is sure to drain it.
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  #6  
Old May 14th, 2007, 13:08
Pelican Pelican is offline
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Re: Where Should my Voltage Gauge Read After...

Yes -- touch the probes to battery terminals with engine off, engine idling with A/C off and engine idling with A/C on. If these are within spec, your LCD screen blanking may suggest a wiring problem.
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  #7  
Old May 15th, 2007, 00:45
DIGITRUCK DIGITRUCK is offline
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Question Re: Where Should my Voltage Gauge Read After...

Used the Voltmeter today and touched the probes to the battery terminals.

Does this look about right?

1. Engine OFF - 13.06 V (when engine cold it was 12.58 V)

2. Engine Idling - 14.20 V

3. Engine Idling

with A/C & AUX FAN ON - 13.30 V

with Computer/
Stereo ON - 14.30 V
3/4 Volume

BOTH ON
(A/C AUX FAN, STEREO) - 12.80 V


***When BOTH ON, is when the BATTERY VOLTAGE takes a hit! Should it drop that low and/or is it bad for my ALTERNATOR etc? OR, is it bad to run all my ELECTRONICS, LIGHTS and A/C simultaneously? Thx.
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  #8  
Old May 16th, 2007, 01:14
DIGITRUCK DIGITRUCK is offline
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Question Re: Where Should my Voltage Gauge Read After...

Quote:
Originally Posted by DIGITRUCK
Used the Voltmeter today and touched the probes to the battery terminals.

Does this look about right?

1. Engine OFF - 13.06 V (when engine cold it was 12.58 V)

2. Engine Idling - 14.20 V

3. Engine Idling

with A/C & AUX FAN ON - 13.30 V

with Computer/
Stereo ON - 14.30 V
3/4 Volume

BOTH ON
(A/C AUX FAN, STEREO) - 12.80 V


***When BOTH ON, is when the BATTERY VOLTAGE takes a hit! Should it drop that low and/or is it bad for my ALTERNATOR etc? OR, is it bad to run all my ELECTRONICS, LIGHTS and A/C simultaneously? Thx.
Hi, can someone please answer the question above and/or is this normal? Thx.
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  #9  
Old May 16th, 2007, 01:17
Rockslut Rockslut is offline
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Re: Where Should my Voltage Gauge Read After...

Seems like your alternator sucks
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  #10  
Old May 16th, 2007, 07:56
Matthew Currie's Avatar
Matthew Currie Matthew Currie is offline
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Re: Where Should my Voltage Gauge Read After...

Sounds as if your alternator is insufficient, but before getting too far into that, make sure that your belt isn't slipping when the AC comes on, and your wiring is adequate.

Battery voltage is good, and so is idle voltage when there's no big load. It seems to be dropping when the AC comes on. One test to see if you can isolate the problem might be to unplug the AC safety switch on the receiver dryer and run everything else, including high fan. If the voltage is measurably better with the AC clutch disengaged, I'd suspect the belt. Don't count on slippage here always causing squealing. Sometimes it doesn't.

You might benefit from having the alternator tested, and also might look into a clip-on ammeter, to see if you can determine just how much current all those accessories are pulling. I haven't looked into these gadgets recently. You used to be able to get a couple of different versions of ammeters that just slip over a cable. I have a basic one for starter draw (probably not sensitive enough for this job), but there should be another one with two slots, one for starter draw and one for lower ranges. Last I knew they weren't terribly expensive.

Remember that this serpentine belt must be very tight, and it helps to have a gauge (KRIKIT II, available at NAPA for 12 bucks or so - they will look at you as if you're from outer space when you ask, but they'll find it in the catalog). Without a gauge, the basic test is to twist the longest unsupported span. You should not be able to twist it more than 90 degrees.

If it isn't the belt, then you may just be pulling more current than your alternator can replace. It won't hurt the alternator, but obviously you'll need to do something if you want to run all that stuff at once.
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  #11  
Old May 16th, 2007, 08:07
Rick Anderson Rick Anderson is offline
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Re: Where Should my Voltage Gauge Read After...

Those voltages seem normal, except when you've got the both fan and stereo on, if it dropped to that with the headlights, I'd say its normal. How about with headlights on and at idle, that is the real test.

If the alternator has to make more voltage then the battery, to charge the battery, if the system voltage is less than the standing battery voltage (battery voltage with the motor off) then the battery will discharge at least to that voltage.

I.E. if you draw more current than the alternator supplies, the voltage drops, if it drops to the same as the battery voltage, charging stops, if it drops to less than the battery voltage, it starts to drain the battery. As the battery drains, its voltage will drop as well, and if you've been drawing off the battery the whole system voltage drops.

Don't forget, the alternator makes more power the faster it spins, its NOT unusual for voltage to drop a bit under a heavy load when the motor is at idle. The old, "dimming of the headlights a tiny bit at a stoplight is normal, if they dim a lot, then you have a problem."

Someone mentioned Deep Cycle Batteries, yes they are designed to drain completely dead, supplying a steady current during the whole discharge cycle. A car battery is designed to start a car, to give a big burst of current for a partial discharge and then recharge.

*A deep cycle battery may NOT supply enough of current burst to run the starter motor and start the motor.

*A Car Battery supplies that big burst, but it won't supply a steady current as long and it damages it to drain completely dead (i.e. shortens the life of the battery).

*They do sell some "Deep Cycle Car Batteries", that are a sort of a hybrid, that is kinda of half-way in between both types of batteries, giving better deep cycle performance than a regular car battery and better starting performance than a regular deep cycle battery. These are popular with car stereo buffs that have huge amps and subs that kill their regular car battery.
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  #12  
Old May 17th, 2007, 18:14
DIGITRUCK DIGITRUCK is offline
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Question Re: Where Should my Voltage Gauge Read After...

Quote:
Originally Posted by Matthew Currie
Battery voltage is good, and so is idle voltage when there's no big load. It seems to be dropping when the AC comes on. One test to see if you can isolate the problem might be to unplug the AC safety switch on the receiver dryer and run everything else, including high fan. If the voltage is measurably better with the AC clutch disengaged, I'd suspect the belt. Don't count on slippage here always causing squealing. Sometimes it doesn't.
Ok, I tested the Voltage again:

1. Engine Idling - 14.2 V

2. Engine Idling with A/C On - 13.3 V

3. Engine Idling with Stereo - 14.3 V

4. Both A/C and Stereo On - 12.8 V

***[Quote = Rick Anderson] Those voltages seem normal, except when you've got the both fan and stereo on, if it dropped to that with the headlights, I'd say its normal. How about with headlights on and at idle, that is the real test. [Quote]

What do you think? See below:

5. SAME AS #3 w/HEADLAMPS - 12.8 V

6. SAME AS #4 w/HEADLAMPS - 12.4 V

7. WITH A/C SAFETY SWITCH - 13.85 V
OFF (is it that plug on the glass window that bubbles with the A/C On?)

***I don't have a Tension Guage but was only able to twist the longest span on the belt 90 degrees. I'm trying to buy a Tension Guage and Induction Amp Meter. My local stores don't have a clue.
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  #13  
Old May 17th, 2007, 18:36
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5-90 5-90 is offline
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Re: Where Should my Voltage Gauge Read After...

Before you get too far into anything else - bear in mind that most alternators cannot generate full output at idle!

Repeat the last test (everything ON) with the engine idling, then open the throttle slightly to allow the engine to run 1200RPM or so. You should see the voltage pull back up to idling spec with things turned off.

It's possible to get an alternator that will come closer to full output at idle, but that's going to hurt - just to let you know. If you're cruising, you can have everything going - just bear in mind you're going to start using your battery when you've got to idle (that's what's happening - the reserve capacity in your battery starts getting drained when the alternator doesn't put out enough current to run everything.)

For the other issues - check with a NAPA or other small outfit - most of the guys "manning" the counter at the chains are not qualified to "man" a urinal properly. I know what you're talking about with an "induction ammeter" (I have one,) and I don't think Checker/Schuck/Kragens, AutoZone, or Advance have ever carried anything like that. I got my induction ammeter at a NAPA for a few bucks. The belt tension gage you're referring to is called a "Krikit," and is also available from NAPA for ~$15, as I recall. I need to get one myself.

There's a reason I say don't go to chains - most of the smaller guys have auto hobbyists behind the counter, who therefore have some semblance of an idea what they're doing. Honestly, I don't think most of the guys at the "chain" stores are qualified to give a urine sample, much less hand out the correct parts...

And yes, the voltmeter in the IP is a notorious liar - especially on RENIX (1990 and earlier.) I use mine more as "relative state of charge" indicators than anything else - I put a grease pencil mark on the face glass where I find the thing normally runs, and have a small sticker on a bottom corner telling me what that voltage is.
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  #14  
Old May 17th, 2007, 20:40
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Matthew Currie Matthew Currie is offline
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Re: Where Should my Voltage Gauge Read After...

[QUOTE=DIGITRUCK]Ok, I tested the Voltage again:

1. Engine Idling - 14.2 V

2. Engine Idling with A/C On - 13.3 V

3. Engine Idling with Stereo - 14.3 V

4. Both A/C and Stereo On - 12.8 V

***[Quote = Rick Anderson] Those voltages seem normal, except when you've got the both fan and stereo on, if it dropped to that with the headlights, I'd say its normal. How about with headlights on and at idle, that is the real test.
Quote:

What do you think? See below:

5. SAME AS #3 w/HEADLAMPS - 12.8 V

6. SAME AS #4 w/HEADLAMPS - 12.4 V

7. WITH A/C SAFETY SWITCH - 13.85 V
OFF (is it that plug on the glass window that bubbles with the A/C On?)

***I don't have a Tension Guage but was only able to twist the longest span on the belt 90 degrees. I'm trying to buy a Tension Guage and Induction Amp Meter. My local stores don't have a clue.
Yes, that's the AC safety switch I meant. I may be wrong, (oh, no, that can't be!) but from that set of figures I think you're getting slippage when the AC comes on, unless your AC clutch is fried and pulling too much current.
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  #15  
Old May 17th, 2007, 22:09
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AlabamaDan AlabamaDan is offline
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Re: Where Should my Voltage Gauge Read After...

When I'm not running the AC/Heater fan it's just below 14 amps according tothe stock gauge. When the fan is on it drops to about 12.5 amps. I just replaced the alt. The radio and headlights have little effect. It's just that fan!
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