Hello! Going through the flow chart of P0A94 / 555 for 2005 Prius. I'm confused when It comes to the formula on step 5 & 6, I don't get it. Temperature at the time of measurements was 17c. Hybrid Vehicle Motor resistance: U - V: 128.4 V - W: 128.2 W - U: 128.3 Hybrid Vehicle Generator resistance: U - V: 104.5 V - W: 104.1 W - U: 104.3 Everything checks out and is good for the insulation test and voltage test on the inverter stop test. So far, I'm going with the inverter being toast. .... Forum won't allow me to post the link to the Charm li diag for this.
Crazy how many people have seen this, yet don't want to help explain the math. I fixed the vehicle, I just want to know the how/why behind the math.
If the motor temperature is too high, the resistance varies considerably, which hinders determining malfunction. Therefore, measure the resistance at a minimum 8 hours after the vehicle has been stopped. Tester Connection Specified Condition* U (I14–1) – V (I14–2) Below 135 mΩ at 20C V (I14–2) – W (I14–3) Below 135 mΩ at 20C W (I14–3) – U (I14–1) Below 135 mΩ at 20C Apply the formula given below to correct the resistance. R20 = Rt / (1 + 0.00393 × (T – 20)) R20: Resistance converted to 20 C (mΩ) Rt: Resistance between measured lines (mΩ) T: Ambient air temperature during measurement (C) (f) Calculate the difference between the maximum and minimum resistance between terminals U – V, V – W, and W – U. Standard: Below 2 mΩ The temperature coefficient is used for calculation accuracy due to the fact that the measured resistance differs at different temperatures.
I have all that information, it's the formula that I don't understand. I wanted someone to maybe explain how to solve it, or point me in the direction of being able to learn this. Instead of just using chat gpt to solve it for me. I haven't solved a math equation like this in 20 years.
R20 = Rt / (1 + 0,00393 × (T – 20)) R20=128.4/(1+0,00393× (17-20))=128.4/(1+0,00393× (-3))=128.4/(1-0,01179)=129.93
Apparently, I'm missing something. This question seems short on information. Like the formula you're asking someone to explain? Or does everyone here have the flow chart of P0A94 / 555 for 2005 Prius sitting in front of them? Maybe I just don't understand the question..... Feels something like: There's a formula on page 92 of the 2005 edition of Encyclopedia Britanica. My result was 82.5 !! Can you explain the math behind it?
As Max demonstrated above, this isn't really calling on you to do much to 'solve' it. It is already arranged so that R20, the thing you don't know, is all by itself on the left of the = sign, so just take the Rt that you measured and the T at the time you measured it, plug those in where indicated on the right, do the arithmetic, and what you get is R20.
I was confused because of the crosshair symbol after the RT on the original formula. I've never seen that in school or anywhere else used in math. So I was like... the **** do I do with that. *edit.. for some reason this forum wont allow the crosshair symbol to be posted
Is that milli ohms? (m ohms) or Mega ohms(M ohms)? Uppercase or lower case M or m. Makes orders of magnitude difference in measurements. And where I come from, a completely different test instrument required for proper accurate measurements. I use a Fluke multimeter at home, but Megger megohm meters and milliohm meters in my job at a utility company
Yeah, nine of 'em. You need both specialized instruments for poking around the motor-generators. The megohmmeter to make sure the windings aren't conductive to other stuff they shouldn't be. And the millohmmeter to make sure they really do have the right (really low) resistance on the paths where they should conduct. The megger readings are more of a go/no-go proposition. Better be a lot of megohms or there's an insulation fault. Any time you see somebody bothering to take resistance readings and correct them for the difference between 20 ℃ and the actual temperature at the time of measurement, it's safe to bet that person is looking at the milliohm readings of the actual windings.
