electrical system discussion.

[meerschm]

thought it might be useful and helpful to start a discussion on how electrical systems work.

point here is to further understanding and have a helpful discussion.


the generator includes an alternator, and internal regulator, which controls the field current in response to it's design and controls, to attain a specific voltage.

older model years have an internal temperature compensated regulator, which changes the voltage according to temperature. when it is wicked cold. (ten below for example) it operates as high as 15 volts.

in some of the newer years, GM added logic and elements to the internal regulator which lets the voltage be set according to a pulse width modulated signal.

it still is a voltage regulated generator. the regulator will increase the field current which makes a magnetic field that the pulley turns to generate the output current, rotating fields generate AC current, so the included diodes rectify to keep things flowing in one direction.

 

[BlazingTrails]

I will def get in on this when I have more time.

 

[meerschm]

sounds good, want to make sure we agree Ohm's Law has not been repealed.

 

[BlazingTrails]

Wow that really kinda sounds like you are calling me out? Are you going to educate me on ohms law? If you want to have a friendly conversation about this stuff I'm game. If you are of the impression that I need to be schooled, I have better things to do with my time. So which is it? Respectfully

 

[meerschm]

It caught my eye when you said that reducing voltage would increase current.

E=IR Volts=Amps times Ohms.

Voltage and current head in the same direction.

What did I miss? You can reply to my PM if you would rather.

Thanks

Mike

 

[BlazingTrails]

Your right, and that's ok I just want thinking about direct current. Which is shameful because I work with this stuff everyday. I have been tired lately what can I say [emoji21]

 

[Mooseman]

Are we talking specifically about our platform or electrical systems in general? If the former, one thing that ours do is that when it is cold (like below -10C), the alternator doesn't come on right away so as to not put a bunch of load on the cold belt. It will start charging about 5 seconds after starting the engine.

 

[meerschm]

I would not mind talking about both.

The generator in GMTs has an internal regulator. This internal regulator has two control interfaces with the rest of the electrical system.

One provides input, used to start operation. The system does wait a while at start up to let the engine get moving. (As it takes me a while to get moving in the morning) When it is wicked cold (ten or twenty below) you can really watch this happen.

The other regulator interface carries a pulse-width modulated signal that indicates how hard the generator is working. This signal is used internally by the regulator to provide energy to the rotating windings. The regulator generates a 400 Hz pulse wave, and the wider the pulses, the more energy is applied to the windings, rotating magnetic field is increased in strength, and more current is generated by the stationary windings to be rectified and output. The regulator changes this signal gradually, to avoid sudden load changes. Providing this signal to the computer gives the computer the ability to keep track of operation, and if needed, take action (like record codes and notify the driver)

In later years, the input signal to the generator internal regulator is more sophisticated, and uses a pulse width modulated signal from the computer to the regulator to set the desired operating voltage.

I like the description provided here:

http://www.motor.com/article.asp?article_ID=1606

 

[meerschm]

Your right, and that's ok I just want thinking about direct current. Which is shameful because I work with this stuff everyday. I have been tired lately what can I say [emoji21]

happens to the best of us. ( not that I am claiming that status)
What are friends for, except to keep us straight and correct our momentarily misinformed moments?

 

[The_Roadie]

Part of the issue comes from thinking too much about defined power circuits like motors under a constant horsepower (or kW) load. For those, reducing the voltage obtains an automatic increase in current because the load power needs to be satisfied by the product of V and A.

Resistive loads aren't constant power, and Ohms Law states the proportionality of V and A.

For homework, write an essay about Back EMF and how it relates to this situation:
http://en.wikipedia.org/wiki/Counter-electromotive_force

 

[meerschm]

Ok this is for Bill (and any interested bystanders)

The generator is different than an AC motor. Current in the rotor coil is controlled by the regulator, which is connected to the coil via brushes and slip rings. The rotor coil rotates (what else would it do?), making use of the energy provided by the pulley (from the belt, from the engine, ...from the fuel/air combustion), generates a rotating magnetic field which is tapped by the stationary coils to generate AC. The diodes are arranged to direct and combine currents from the multi-phase AC circuits so that the flow output is in one direction (also known as DC).

The AC motor does the opposite, generating the rotating field from current applied to the stationary coils, which is tapped by the rotor coil to generate motion. In most cases, the current in the rotor coil for a motor is not independently controlled, and does not exit the rotor assembly. there is no need for brushes or slip rings.

For the automotive generator, the interrelationships between the field excitation, rotating speed, rotational inertia of the rotor, changes in loads, engine speed, load to the engine, changing electrical loads must be accounted for by the designer.

Back emf is one way to look at some of the properties. it's impact has to be accounted for in the design of the regulator, and other components. (attempts to reduce the current in the rotor by the regulator will be met by the counter EMF from the coil, which has then to be properly handled, for example). When the rotational speed changes, say if you downshift or upshift, the dynamics of the rotating fields change. Since the voltage across a coil is a function of the derivitive (di/dt) of the current, you really need to use calculus to describe the relationships.

The way I think of it is, you used electromagnetics to turn electricity into motion. (or visa versa) it goes the other way too. Kind of like picking a fight with your wife. You just have to be careful and be prepared for the eventual response.

Hey, I am not shooting for more than a C plus here. I already graduated.

How did I do?

 

[The_Roadie]

My boss invented a Faraday flux sensor we're using to accurately measure di/dt risetimes in the 3-10 A/nS range. Competitive equipment is only working up to 0.6A/nS. Stray inductances in the picohenries are what we're working to reduce in the circuit now.

I like the way you think. And you're right, after you graduate it may take 40 years for you to need calculus again. Happened to me.

 

[coolasice]

damn all that electrical engineering stuff from college that I don't remember....

 

[The_Roadie]

What profession are you in that EE classes aren't relevant anymore?

 

[coolasice]

I went to college for Electrical Engineering Tech (2yr tech college, 2.5 yr University), and got my BS... searched for 2+ years for a career in my field to no avail.. (my fault is trying to stay within state close to family)... now been 10yrs out of college and never found a job locally in my field... so I now repair lottery terminals for the state (basically a computer.... nothing eet concerning about that). Most of the very technical stuff I don't remember as i never used it since, but basic things I remember.

couple years ago had a flood in the basement and lost all my engineering books/notes/design papers.

 

[meerschm]

I wanted to also talk about Battery voltage (and solicit any questions, or correction of anything somebody sees something that seems wrong)

The presence of a battery in the automotive system complicates and informs operation of the generator. The selection of a target voltage is focused on the needs and capabilities of the battery.

The car (or GMT in this case) will operate from just the battery, but not for too long. The generator design is focused on the need to recharge the battery (as well as operate vehicle). Batteries are wonderful things, they trade chemistry for electricity. Our nominal "12 volt" batteries will supply current and generate a voltage which depends on the load, temperature and state of charge (details of the chemical mix in the anode, cathode, and electrolyte). What makes them really great is that you can apply a voltage in excess of the open circuit voltage (voltage which can be measured with no load, or zero current drawn), cause current to flow into, instead of out of the battery, and the battery chemistry will reverse chemical reactions, increasing the 'charge' saved for future use. There is plenty of info relating open circuit voltage and charge, including here: http://autorepair.about.com/library/weekly/aa101604b.htm

The specific voltage selected for operation is not a simple thing. Too low, and not enough energy is stored. Too high, and you can alter the chemistry inside the battery, generate hydrogen gas, boil the electrolyte, kill the battery by sulfation, and all kinds of bad stuff.

I observed the voltage on my previous 03 Trailblazer using a ScangaugeII last winter. when it was ten below zero, the voltage was 15 volts. (vs more usual levels around 14 volts.) I looked into why this could have been the case, and learned a bit about the details.
The following discusses some of the temperature details in charging batteries:
http://www.tekrispower.com/pdfs/xantrex/Batteries%20-%20Temperature%20Compensated%20Charging.pdf

So it seems the internal regulator in the generator (for the early years at least) includes a temperature sensor which sets the target voltage depending on temperature. this lets the system actually charge the battery when it is very cold, and avoid boiling it to death when it is too warm.

The actual voltage selected by the engineering team is not, in my guess, driven by the desire to maximize battery state of charge.

 

[BlazingTrails]

I have noticed now thanks to the previous thread that my truck stays around 12.6 volts most of the time. Even if I put everything in the car on. The only time it is over 14 volts is the first 10-15 min it has been running from cold. Do you think that it would hurt the battery to manipulate this system to stay at 14.4 volts? I never really paid attention to it before, but it greatly affects the output of my stereo system. Annoying.....

 

[The_Roadie]

I have an intelligent battery charge/monitor systems in my trailer, and it never uses DC voltage that high except for the occasional burping impulse. Recommend getting a stereo with more headroom so you aren't always noticing clipping.

 

[meerschm]

Open Circuit Voltage Approximate State-of-Charge at 80°F (26.7°C)

12.65 100%
12.45 75%
12.24 50%
12.06 25%
11.89 or less DISCHARGED

This is from a chart in one of the above referenced links, 12.6 volts reflects the no-load reading for a fully charged battery (more or less, will change a bit with temperature)

if your truck is smart enough to stop charging the battery (which it can only do by manipulating the voltage target of the alternator), when it is fully charged, I would think twice before second guessing the engineers.

(the voltage which causes charging/overcharging is above the open circuit voltage, but operating in between can do nothing but warm up the battery and waste power.)

Picking a static (fixed) voltage level, there would be danger of over charging the battery when it is very warm, and not charging it at all when it is very cold.

If you go for a solution which can overcharge the battery, make real sure any battery installed in the passenger compartment is well-ventilated. (you always want to do this, but monkeying around with the operating voltage can make it worse). Also, be prepared for the electronics to complain too, if you do not provide for all the expected inputs/outputs, that act like the system expects.

 

[meerschm]

Which model year did GM move to the newer system with the battery control module that can set the voltage level of the regulator using the pulse width modulated signal?

 

[coolasice]

06 I believe uses the newer system with gbcm while 05 was just pcm controlled

 

[BlazingTrails]

This is the first vehicle I have ever had that wasn't sitting on 14.4 volts at all times when running. My stereo doesn't clip, just hits way harder when it is first started. Clipping haha. Funny guy [emoji34]

 

[The_Roadie]

Clipping haha. Funny guy [emoji34]

Not being a high power stereo guy, but working with 250KW pulse amplifiers, I was trying to understand how you could tell the system was running at low voltage. If it's not clipping, then I assumed wrong. Sorry. So there's nothing else left to suspect than slew rate limitation causing distortion in the waveform. For my 250KW pulse amplifier, we have four sets of capacitors at varying distance from the load. The closest are 5mm, then 20mm, then some more at 100mm which translates to 3-4 nS away, then the bulk of the energy storage is a foot away or 10 nS. Wonder if your issue is you need more capacitance closer to the amp.

 

[BlazingTrails]

It's not really a problem. I just really noticed it once someone brought it up in a thread. It sounds great either way, just simple ohms law here I believe. More voltage equals more output. I'm only running a 600 watt rms amplifier and 2 subs So I don't even have a capacitor. I will build a better system one day, it is kinda low on my priority list because I'm more off a performance guy. This was just some stuff I had laying around my garage. Btw, I'm a master electrician, and control specialist. I program ladder logic and work with timing on manufacturing machines. I'm Not an electrical engineer. Just for your general knowledge.

 

[Sparky]

Interesting, I'm pretty sure the only time my volt gauge is below the 14-ish range is when it is a cold start in the winter for that first 10-15 seconds. I think...

Ha, now I'm going to be watching that gauge a little more often to satisfy my curiosity!

 

[meerschm]

Does the dash volt gauge lie like the temp one does?


(er, I mean present a different answer than the OBD would report for the voltage)

 

[meerschm]

My boss invented a Faraday flux sensor we're using to accurately measure di/dt risetimes in the 3-10 A/nS range. Competitive equipment is only working up to 0.6A/nS. Stray inductances in the picohenries are what we're working to reduce in the circuit now.

I like the way you think. And you're right, after you graduate it may take 40 years for you to need calculus again. Happened to me.

http://www.ncbi.nlm.nih.gov/pubmed/21068992

went looking to verify your units (not that I doubt you, just like to follow up) I am guessing this guy is for medical imaging applications. lots of fun terminology. so your application is to use the flux sensor to measure current?

(and why do I feel like I should be looking for a Delorean someplace?)

 

[Mooseman]

Does the dash volt gauge lie like the temp one does?


(er, I mean present a different answer than the OBD would report for the voltage)

It's fairly accurate, fed by the PCM. Slow, but accurate. I checked it using my ELM327 and Torque.

 

[The_Roadie]

> I am guessing this guy is for medical imaging applications.

No. Everybody should know by now my entire career has been in semiconductor test systems. Started out 40 years ago testing diodes and transistors and SCRs. Very accurately and quickly. That's the challenge for production lines. Then ICs, and near the end of my career, back to power transistors, of all things.

So this is measuring the current through a device that's switching on or off in the presence of 600V and 500A, and taking 10-30 nS to do it. The product of the V and I during the transitions is the switching power loss, and devices are so good nowadays (low on-resistance) that the switching losses predominate, where it used to be the turned-on power dissipation.

 

[meerschm]

I meant the http://www.ncbi.nlm.nih.gov/pubmed/21068992%C2%A0

was focused on imaging sensors.

 

[Mounce]

Both of those links went to the website but said "the requested page does not exist"

 

[The_Roadie]

For me as well.

 

[meerschm]

Appl Opt. 1996 Jan 1;35(1):154-7. doi: 10.1364/AO.35.000154.
Fiber-optic Faraday-effect magnetic-field sensor based on flux concentrators.
Deeter MN.
Abstract

The principles and performance of a fiber-optic Faraday-effect magnetic-field sensor designed around an yttrium-iron-garnet (YIG) sensing element and two flux concentrators are described. The system design exploits the technique of polarization-rotated reflection in which a single polarization-maintaining optical fiber links the sensor head to the optical source and detection system. In the sensing head, ferrite flux concentrators are magnetically coupled to the YIG sensing element to achieve maximum sensitivity. The system exhibits a noise equivalent field of 6 pT/√Hz and a 3-dB bandwidth of~10 MHz.


From PubMed, which also leads me to think this is a medical sensing application, perhaps for an MRI sensor

(not that this has anything to do with a GMT electrical system.)

Sorry for the confusion.

 

[IllogicTC]

Just for fun.

W = A^2 * R = A * V
R = W / A^2 = V / A
A = sqrt(W / R) = V / R
V = W / A = A * R

Where W is watts, R is resistance, A is amps, and V is volts. Knowing two values will allow one to derive the other two values. This is yawner high school stuff (at least in MY high school we picked this up, during physics. We also all held hands and got zapped by a Leyden Jar) but to some it may be interesting.

 

[The_Roadie]

Ferrite flux concentrators *are* an enhancement I hadn't considered. Hmmmmm, that's gonna cost me some research time.

 

[meerschm]

Other electric thoughts. (not limited to GMT applications)

electric use in cars has been and will continue to increase.

electric power steering,

start/stop (where the engine stops at the light)

electric coolant pumps

electric coolant fans

electric adjusted shock absorbers

electric driven heat pump for HVAC



all this load leads to larger generator needs

which leads to clutch pulleys that allow engine to slow down while generator continues to freewheel. (saving belt stress)



and leads to operating batteries with lower charge level.

this lets the system turn up the voltage target while slowing down to capture some of the braking energy to use to start the car after you stop it at the light. (which also saves a tiny bit of the wear on brakes)


and this is without using electric for any of the propulsion as hybrids do.

 

[IllogicTC]

Other electric thoughts. (not limited to GMT applications)

electric use in cars has been and will continue to increase.

electric power steering,

start/stop (where the engine stops at the light)

electric coolant pumps

electric coolant fans

electric adjusted shock absorbers

electric driven heat pump for HVAC



all this load leads to larger generator needs

which leads to clutch pulleys that allow engine to slow down while generator continues to freewheel. (saving belt stress)



and leads to operating batteries with lower charge level.

this lets the system turn up the voltage target while slowing down to capture some of the braking energy to use to start the car after you stop it at the light. (which also saves a tiny bit of the wear on brakes)


and this is without using electric for any of the propulsion as hybrids do.

I've heard talk before of the future of electrical systems in cars being 24V. I don't see why it hasn't already come. I understand there's a "standard" of 12V, but 6V also used to be the standard and we haven't seen any cars on that in ages!

Thinking of electrical (or electronic) stuff, I saw a picture somewhere the other day bashing the big hard-on companies have for putting touch screens in cars. It said "The radio we wanted 10 years ago" and shows a touch screen. Then has "The radio we want now" and shows one with regular old buttons. I have to agree, touch screens are for the most part nothing more than an extremely-glorified button in the ways they're being used in cars. Some vehicles also have crappy UIs, or stupidly-slow lag between command and reaction time. And to top it off, of course you can't exactly use it very well without staring at the screen.

Some vehicles even integrate HVAC controls into the touch screen display. So now you have to stare at that while trying to fine-adjust too instead of just "feeling it out." Even a simple display which has a few buttons on the side with indicators displayed on-screen (a la ATMs for years and years) and a multi-function dial like BMW has would be perfect. Not all screen.

 

[meerschm]

quite a few large trucks use 24 volts.

there was a push for 42 volt systems, for cars, but not so much any more.

digital controls and better motors have reduced the push,

and all the electric car folks seem to each have their own standard in mind for propulsion voltage, and most use standard 12 v nominal for accessories.

 

[The_Roadie]

At one point 15-20 years ago, the concept was for one huge honkin' 12V feed wire going all around the vehicle, and every lamp, motor, actuator, coil, stepper, sensor, and control button would have its own address (like the "Internet of Things" concept will assign everything its own IP address), and just listen and talk on a common high speed data bus. The vehicles would need far fewer fuses and the weight of the wire would go way down.

And look that happened? We have a minimum of TWO fuse blocks nowadays, branch circuits have MORE fuses protecting individual functions, and the shared data bus is a HORROR to troubleshoot so they put in the two splice packs to break off individual modules from the bus.

 

[IllogicTC]

At one point 15-20 years ago, the concept was for one huge honkin' 12V feed wire going all around the vehicle, and every lamp, motor, actuator, coil, stepper, sensor, and control button would have its own address (like the "Internet of Things" concept will assign everything its own IP address), and just listen and talk on a common high speed data bus. The vehicles would need far fewer fuses and the weight of the wire would go way down.

And look that happened? We have a minimum of TWO fuse blocks nowadays, branch circuits have MORE fuses protecting individual functions, and the shared data bus is a HORROR to troubleshoot so they put in the two splice packs to break off individual modules from the bus.

And instead of a huge wire providing a sort of bus bar by going around the vehicle, there's how many lengths of wire in the average modern car?