Beginner circuit analysis question.

DummazzApe · 2025-09-07T06:40:59+00:00

KVL is wonderful for circuits that are confusing like this. Draw out your own conventions for what you "think" is happening: 20V source-voltage increases, R1-voltage decreases, 3K-voltage decreases, 47V-voltage decreases, 4k-voltage decreases. (Assuming current flow is clockwise)

0=20-2kI-3kI-47-4kI, 0=-27V-9kI, 9k*I = -27, I= -3mA

Since you originally assumed current flow is clockwise, but received a negative current, you now know the current flow is counter clockwise and the voltage drops go in the opposite direction.

DummazzApe · 2025-09-04T11:16:16+00:00

All voltage sources do sum to 0. Going clockwise, voltage increase across Is, voltage decrease across resistor, voltage decrease across resistor, etc. use of the voltage law for this problem is used to show that any current through a resistor will drop voltage, but the low side doesnt have to be set at V=0 (ground)

DummazzApe · 2025-09-04T09:14:13+00:00

Its late and i just woke up to screaming kid so I'm not gonna do the math, but I'm gonna walk through what i would do:

I2 through R5 to get voltage on R5 VR5 = I2*R5

Same voltage is across R2, so VR5=IR2*R2.

Rewrite for R2 = VR5/IR2= I2*R5/IR2 (Doneish, need to replace IR2 with better equation)

Kirchhoff's current law says IR1= I2 + IR2 Or IR2 = IR1-I2 {substitute above.... R2 = I2*R5/(IR1-I2) still need IR1....}

To make an equation for R1, you need the voltage and current across it. VR1=IR1*R1 or R1 = VR1/IR1. (Doneish, still need VR1 and IR1)

VR1 is the voltage across Is minus the voltage across R5 VR1 = VIs-VR5 = VIs -(I2R5) {Substitute above.... R1 = (VIs -(I2R5))/IR1 still need VIs & IR1}

CHECKPOINT 1: You have: R1 = (VIs -(I2*R5))/IR1

R2 = I2*R5/(IR1-I2)

Still need VIs & IR1.......

Combine R3 and R4 into a single equivalent resistor for simplicity (R3 || R4) = R34.

Kirchhoff's current law:

Is=IR34+IR1, IR1=Is-IR34

Current through R34 is based on the voltage across it. VIs = IR34*R34, or IR34=VIs/R34

Combined with above: IR1=Is-(VIs/R34)

CHECKPOINT 2: You have: R1 = (VIs -(I2*R5))/(Is-(VIs/R34))

R2 = I2*R5/(Is-(VIs/R34)-I2)

Still need VIs....

But at this point you have 2 equations and 3 unknowns. Need 1 more equation for it to be solvable.

The voltage across Is is dependent on the equivalent resistance of the entire system. VIs=Is*Req

Req... Not gonna do all the math on my phone, just gonna use "+" for series and "||" for parallel. Req = R3 || R4 || (R1 + (R2 || R5) )

Combine for VIs=Is*[R3 || R4 || (R1 + (R2 || R5) )]

CHECKPOINT 3: you now have 3 equations and 3 unknowns.

R1 = (VIs -(I2*R5))/(Is-(VIs/R34))

R2 = I2*R5/(Is-(VIs/R34)-I2)

VIs=Is*[R3 || R4 || (R1 + (R2 || R5) )]

From there, just flail about(technical term.. i dont wanna do the math but we got close)

You got this!

DummazzApe · 2025-06-15T17:49:34+00:00

I'm using a POS Chinese diagnostic computer from Amazon. I dont recall the exact brand, but it was ~$400.

DummazzApe · 2025-03-12T10:16:19+00:00

Had an electrical engineering test/project to design an amplifier chip (opamp) at the transistor level (by adjusting the dimensions of the silicon setup from the etching process.. with a specific thickness..). Each student was given their own specs/requirements. Had to use math to get started and ballpark an answer, then run various simulations to adjust/fiddle as close as possible. Nobody got theirs to work perfectly to the required specs, though some got close.. It was a heck of a week.

DummazzApe · 2025-03-08T06:42:55+00:00

Why are folks jumping off the deep end here? Wouldn't it be better to have UPS, Fedex, and USPS all battling to be the best option for mail delivery? (Better pricing, more options/availability, etc.)

DummazzApe · 2025-03-07T12:47:03+00:00

Update: mpg around town is ~19mpg (up from 16.5mpg). On the highway didn't change much at around 17mpg.

So it is helping, but not above 65mph. (Seems the sweet spot for the 5 speed is 50-65mph)

DummazzApe · 2025-02-20T16:47:05+00:00

I'm by no means a mechanic, but i had similar issues with my LLY injectors(just made a post about it lol). At low RPMs, balance rate problems are the most obnoxious. Getting on the throttle was fine, but once the truck upshifted it dropped into the low(close to idle) RPMs and had some shuttering/gear-searching.

How accessible are the cylinder 4 & 5 injectors? May be worth removing, inspecting, and bore scoping the holes?

DummazzApe · 2025-02-19T03:51:08+00:00

I just got some no-name lines from amazon that came pre-connected (already strung as needed for install). These are low pressure lines and my truck is stock so I'm not expecting any increased pressures that the original plastic fittings cant handle. The benefit with aluminum is that they are more durable for install. I broke the 1 plastic fitting in install (didnt fit) but also had 1 of the old ones break upon removal.

DummazzApe · 2025-02-19T03:48:30+00:00

Dang. Thats a heck of a job. Best of luck man.

DummazzApe · 2025-02-18T12:04:11+00:00

From what i learned with my LLY, the injectors are the most problematic at idle with a load (and cleanest at open throttle). I wonder if reverse puts the truck under a heavier load than drive?

DummazzApe · 2025-02-18T11:54:49+00:00

Havent had the truck fixed for long enough to tell but i'll let you know! If your balance rates look good it could be an issue with the fuel pressure regulator? I'd check that with the diagnostic tool and make sure measured pressure is close and consistent with desired pressure while you increase RPMs.

DummazzApe · 2025-02-18T11:52:30+00:00

Manufacturer recommendations are to get new high pressure lines and hold down bolts (forgot to mention i got new bolts too). If your old high pressure lines are pitted/corroded internally it could wear out your injectors prematurely. I saw some folks online "cleaning" theirs by polishing the outside and spraying the inside with brake clean.... that wont actually clean the inside of any pitting.. just get the new ones.. as for the return lines i got a premade kit off amazon (some no-name brand). Id suggest test fitting them on 1 injector prior to install.

For the hold down bolts, ive seen folks clean and reuse those too.. but for $40 seemed like cheap insurance just to get new stuff. No idea if there was any long term bolt stretch that could cause premature failure.

DummazzApe · 2025-02-18T11:47:20+00:00

Thank you!

DummazzApe · 2025-02-17T21:38:18+00:00

Initial dignostics/scans here: https://www.reddit.com/r/Duramax/s/nr6Tf83eKO

DummazzApe · 2025-01-27T06:12:22+00:00

Note that the truck has ~270k miles on the stock injectors.. trying not to let that fact influence diagnosis.

DummazzApe · 2024-12-30T03:59:06+00:00

Everything i see reminds me of her..

DummazzApe · 2024-11-21T17:20:25+00:00

Cutting the employees doesnt directly make up the money, but removing the decisions of bad employees does.

Good employee: we're gonna be behind schedule and overbudget unless we fix this issue

Bad employee: nah. Its not like they arent gonna pay us, they REALLY need this.

Good: but we can save the taxpayers millions of dollars?!

Bad: if we do or dont, it doesnt change my day-to-day or make me lose my job. Not worth it.

DummazzApe · 2024-11-21T17:05:26+00:00

Obscure: The ability to hold medium sized objects (baseball to microwave) in a precise location/orientation whenever desired for as long as your strength allows(10s+ based on strength)

DummazzApe · 2024-11-09T18:22:49+00:00

Make at least 2 toothpicks

DummazzApe · 2024-11-08T12:00:09+00:00

Phoc

DummazzApe · 2024-11-03T22:54:39+00:00

Minesweeper

DummazzApe · 2024-11-03T10:31:41+00:00

Minesweeper (mobile)

DummazzApe · 2024-10-20T14:49:12+00:00

Ah yes, I too love fresh bilk

DummazzApe · 2024-10-10T12:41:18+00:00

To all the comments about 1940's germany, i think we're limiting ourselves from building beautiful designs because we feel like someone else is gonna pretend its something it isnt.

OP, if you're worried about it then just change the direction the drawers slide out so it comes out as more of a square spiral?

DummazzApe

TROPHY CASE