That Wacky Previa and How it Needs Relays

[was.lost.but.now.found]

How much disagreement do you have between the SG and the DMM? Is it a constant? As in, it is off by say .05 V key off and .05 V engine idle? Or maybe .05 V key off and .15 V off during idle?

What I'm trying to get at is I interepreted your original post to imply that your voltage was too low for your headlights to function at the appropriate level. My response would be that even if the SGII is not reading the battery voltage with 100% accuracy, your voltage is still going to be higher with a load on the engine and alternator than that it would be at idle. Maybe I'm way off, but anyway it's an interesting discussion and cool comparisons you've made.

 

[Alaric Darconville]

How much disagreement do you have between the SG and the DMM? Is it a constant? As in, it is off by say .05 V key off and .05 V engine idle? Or maybe .05 V key off and .15 V off during idle?

I haven't measured with the multimeter at the alternator itself. I suppose I could move the SGII to where I can see it from the hood area and see what it says, or try to put the multimeter where I can see it. I think at idle the SGII also shows lower than 13V most of the time, anyway-- when I rev it up it'll go higher.

What I'm trying to get at is I interepreted your original post to imply that your voltage was too low for your headlights to function at the appropriate level. My response would be that even if the SGII is not reading the battery voltage with 100% accuracy, your voltage is still going to be higher with a load on the engine and alternator than that it would be at idle. Maybe I'm way off, but anyway it's an interesting discussion and cool comparisons you've made.

I guess I'm just seeing what the drop is-- I suppose at higher voltages there will be lower drops in the circuit simply because the bulb uses less current to get the same wattage, and therefore produces less resistance in the wire. Or something. (It's not like it's an electric motor, it's just a resistive load. My understanding of all that is still a bit limited). Regardless, there's a definite lessening of voltage drop when the engine is on (and the high beam shows a higher drop, since it's a higher wattage filament), as the spreadsheet bears out.

 

[was.lost.but.now.found]

Ok, after re-reading your first post about 5 times I think I finally get it. At first I just interpreted it as you were measuring the battery voltage but now I think I understand you are trying to measure the voltage after it leaves the bulb.

Why are you not using the battery ground to the bulb ground (hi/low specific) in each scenario? I'm not following why you are connecting the bulb ground to the battery positive. That sounds like it could have bad results. Maybe I still don't get, I don't claim to have a strong understanding if current and automotive wiring.

 

[Alaric Darconville]

HOW TO MEASURE YOUR VOLTAGE DROP

Connect the positive (red) test lead of a voltmeter to the car battery positive (+) terminal, and the negative (black) test lead to the + terminal of whichever headlamp filament (beam) you're testing -- use the bulb farthest away from the battery. Your voltmeter will give a direct reading of the voltage drop. Write it down.

Then, connect the positive (red) voltmeter lead to the ground terminal of the headlamp bulb, and the negative voltmeter lead to the negative (-) terminal of the battery. Your voltmeter will again give a direct reading of the voltage drop. Write it down. Add the two voltage drop figures obtained, and this is the total circuit voltage drop.

Just trying to follow this.

Going to redo it this evening if I can convince myself to deal with the heat and humidity, to be sure I'm hitting the right terminals.

 

[was.lost.but.now.found]

I have never done that before, and while the link you provided did not work for me I was able to see other similar instructions on the web. You seem to be following them to the letter, but something is not right because they are saying that the reading on your meter should be the amount of the voltage drop. That is, if the drop is 0.83 V like your chart indicates, then the meter would read 0.83 V, not 11.03 V like you got.

I wonder if the problem lies in trying to get a measurement from a twin type bulb that has both a high and low beam in one. There's got to be some kind of unique functionality with those that is messing with your tests.

 

[Alaric Darconville]

I have never done that before, and while the link you provided did not work for me I was able to see other similar instructions on the web. You seem to be following them to the letter, but something is not right because they are saying that the reading on your meter should be the amount of the voltage drop. That is, if the drop is 0.83 V like your chart indicates, then the meter would read 0.83 V, not 11.03 V like you got.

I wonder if the problem lies in trying to get a measurement from a twin type bulb that has both a high and low beam in one. There's got to be some kind of unique functionality with those that is messing with your tests.

Well, it's a ground-switched system, if that changes anything. There's a +12V feed to the bulb and then two ground legs (one for each of the two filaments) and so the ground is switched between the two legs, rather than having two +12V legs and a common ground. Or something.

It's something Toyota and a few others do, I guess.


But, yeah, I expected to read .83V (and there were instances that I did see something like that, but thought it was a red herring).

Alright, I'll redo the test tonight for sure (under the same condtions, and maybe another time with the engine at about 2000rpm (I'll move the SGII to where I can see it) and also documenting the SGII readings.

Also, I corrected the link in my above post. Here it is again: http://www.danielsternlighting.com/tech/relays/relays.html

 

[Kuryakin]

Stern's method is the right method. It measures the losses where it counts. Scan tools don't measure the voltage at the right places for this test.

HOW TO MEASURE YOUR VOLTAGE DROP

Just trying to follow this.

Going to redo it this evening if I can convince myself to deal with the heat and humidity, to be sure I'm hitting the right terminals.

 

[Alaric Darconville]

Alright, I'll redo the test tonight for sure (under the same condtions, and maybe another time with the engine at about 2000rpm (I'll move the SGII to where I can see it) and also documenting the SGII readings.

Stern's method is the right method. It measures the losses where it counts. Scan tools don't measure the voltage at the right places for this test.

I'm just *documenting* the SGII readings so that one can see how it varies from what is read at the battery itself. For entertainment purposes only.

Also, I know Stern's method is the right method. I never said anything that could be construed as to say it wasn't.

 

[Kuryakin]

I know YOU didn't construe it might not be the best way! And yeah, entertainment purposes only. I use my trusty Fluke 77 if I want a REAL voltage measurement!

I'm just *documenting* the SGII readings so that one can see how it varies from what is read at the battery itself. For entertainment purposes only.

Also, I know Stern's method is the right method. I never said anything that could be construed as to say it wasn't.

 

[was.lost.but.now.found]

I know YOU didn't construe it might not be the best way! And yeah, entertainment purposes only. I use my trusty Fluke 77 if I want a REAL voltage measurement!

Well I'm the only other one posting here, so can you please tell me where I said anything in this thread was the wrong way to do something?

But seriously, I've spent most of the thread educating myself on these techniques, I really honestly at no point tried to insinuate that anyone was doing anything wrong. If you follow all of my comments you'll see that early on I had a misunderstanding of what he was doing and what the goal was. Now I understand.

 

[Kuryakin]

Yeah, I suspect a lot of us could use a strong dose of humility..
:twothumbs

Well I'm the only other one posting here, so can you please tell me where I said anything in this thread was the wrong way to do something?

But seriously, I've spent most of the thread educating myself on these techniques, I really honestly at no point tried to insinuate that anyone was doing anything wrong. If you follow all of my comments you'll see that early on I had a misunderstanding of what he was doing and what the goal was. Now I understand.

 

[was.lost.but.now.found]

Yeah, I suspect a lot of us could use a strong dose of humility..
:twothumbs

Hah, I cracked myself up while writing that one, glad you took it in the goodhearted nature it was intended.

Now, on with the thread. I'm looking forward to Alaric's follow up with the new tests.

 

[fyrstormer]

I did measure voltage at the battery, both at idle and with the engine off, and in each case with the heater fan set to maximum, and with the lights on (of course).

Going down the road, the SGII reports upwards of about 14.2V (read from the computer, haven't had the VOM hooked up to the battery while on the road).

Your charging system should still read at least 13.5V when idling with all loads turned-on. If it doesn't, there's something wrong.

A lot of cars nowadays have grounding provisions not nearly good enough to provide adequate grounding when all loads are turned-on. A lot of car stereo enthusiasts add extra heavy-gauge grounding wires from the alternator to the battery, from the top of the engine to the battery (to improve spark throughput), from the headlights to the battery, from the stereo to the battery, and from the back of the car to the battery. (one might think a heavy steel frame would provide adequate grounding for the stuff at the back of the car, but strangely, it doesn't, especially if there's a stereo amp back there.) It's a bit of work to add all this, but it's a good idea nonetheless.

 

[Kuryakin]

For the purposes of this particular discussion, the issue is getting a reasonably accurate read on voltage drop, not necessarily system voltage, which is outside this particular discussion.

But you're right, few, if any, cars have decent headlight wiring. On all of my cars, I have a 6 gage wire going straight to the starter terminal or other convenient high current connection, I usually beef up the alternator to battery wire, and about half the time, as you mentioned, a decent ground, although I've had better luck than you. If there's a solid ground from the battery to the chassis, from the alternator to the chassis, I've usually been able to get less than 0.1 volts from the battery negative to the negative terminal at the bulb. In a few cases, I needed to run a ground back to the negative battery cable somewhere. Usually a lot of voltage drop on the ground side indicates a less than wonderful ground path otherwise. The steel chassis hasn't been where I've found the problem, it's poor bonding of everything that goes to it.

Your charging system should still read at least 13.5V when idling with all loads turned-on. If it doesn't, there's something wrong.

A lot of cars nowadays have grounding provisions not nearly good enough to provide adequate grounding when all loads are turned-on. A lot of car stereo enthusiasts add extra heavy-gauge grounding wires from the alternator to the battery, from the top of the engine to the battery (to improve spark throughput), from the headlights to the battery, from the stereo to the battery, and from the back of the car to the battery. (one might think a heavy steel frame would provide adequate grounding for the stuff at the back of the car, but strangely, it doesn't, especially if there's a stereo amp back there.) It's a bit of work to add all this, but it's a good idea nonetheless.

 

[fyrstormer]

On all of my cars, I have a 6 gage wire going straight to the starter terminal or other convenient high current connection, I usually beef up the alternator to battery wire, and about half the time, as you mentioned, a decent ground, although I've had better luck than you. If there's a solid ground from the battery to the chassis, from the alternator to the chassis, I've usually been able to get less than 0.1 volts from the battery negative to the negative terminal at the bulb. In a few cases, I needed to run a ground back to the negative battery cable somewhere. Usually a lot of voltage drop on the ground side indicates a less than wonderful ground path otherwise. The steel chassis hasn't been where I've found the problem, it's poor bonding of everything that goes to it.

I haven't had the "opportunity" to go fishing around in the electrical systems of very many cars personally, so some of my data points are second-hand; however, it's apparently pretty common to ground the alternator (and all the other on-engine electronics) to the engine block, then ground the engine block as a whole to the chassis. One car I saw actually had the engine-block grounding cable attached to the block using something resembling a snap-on connector, which naturally had gotten rather loose and rattly over the years. I've also personally seen grounding studs on the chassis that were painted and never stripped before the grounding cables were bolted-on. It's amazing not only how antiquated automotive electronics are nowadays, but also how many flat-out stupid mistakes the manufacturers make in order to save steps during assembly. These were not on discount-brand cars, either.

 

[Kuryakin]

Ayep. It's amazing what good bonding of the grounds can do to improve things. I've done all sorts of tricks, from spot welding studs to the unibody, brazing studs to the frame, etc. Unfortunately, bonding to steel in a manner where it won't rust is challenging, hence the alternates I've used. The only bolt on connection I've made work is slathered with Never Seez, serrated lock washers, and several coats of paint after assembly. Over the top? Possibly. But bad grounds are REALLY frustrating. I would use the term a*** retentive, but one of the monitors doesn't get the psychology reference, therefore, thinks it's rude! LOL

I haven't had the "opportunity" to go fishing around in the electrical systems of very many cars personally, so some of my data points are second-hand; however, it's apparently pretty common to ground the alternator (and all the other on-engine electronics) to the engine block, then ground the engine block as a whole to the chassis. One car I saw actually had the engine-block grounding cable attached to the block using something resembling a snap-on connector, which naturally had gotten rather loose and rattly over the years. I've also personally seen grounding studs on the chassis that were painted and never stripped before the grounding cables were bolted-on. It's amazing not only how antiquated automotive electronics are nowadays, but also how many flat-out stupid mistakes the manufacturers make in order to save steps during assembly. These were not on discount-brand cars, either.

 

[-Virgil-]

But you're right, few, if any, cars have decent headlight wiring.

Cars originally equipped with 6-volt electrical systems tend to have rather decent headlamp wiring once the electrical system's been converted to 12 volts! ;-)

I've also seen rather decent headlamp wiring on a fair number of mid-recent Hyundai products. I disassembled the headlamps from a 2003(?) Tiburon and was startled to find nice 14ga wire throughout.

 

[Kuryakin]

Ayep! Alas, most Hyundais are wrong wheel drive. The Genesis shows hope!

Cars originally equipped with 6-volt electrical systems tend to have rather decent headlamp wiring once the electrical system's been converted to 12 volts! ;-)

I've also seen rather decent headlamp wiring on a fair number of mid-recent Hyundai products. I disassembled the headlamps from a 2003(?) Tiburon and was startled to find nice 14ga wire throughout.

 

[-Virgil-]

Ayep! Alas, most Hyundais are wrong wheel drive.

Sounds like someone's never heard of Reverse gear!

 

[Alaric Darconville]

That's a common misconception. The headlights are actually designed for FFT, not RFD! (forward facing traffic/rearward facing driver).

(It seemed funnier a moment ago, but now it doesn't make as much sense... just a jab at the people who discuss LHD/RHD rather than RHT/LHT...)

Also: Still too hot out there for me to want to spend a few minutes doing the voltage tests again; maybe it'll cool off soon enough.