Cottonwood
Roadster#433, Model S#S37
My P85D started production on 12/1, finished on 12/17, and was delivered on 12/23/14. Does that count as an early P85D?
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My P85D started production on 12/1, finished on 12/17, and was delivered on 12/23/14. Does that count as an early P85D?
Andyw2100
Well-Known Member
Well, I was going to say yes, because of when it started, relative to mine. But then I thought about it another two seconds, and realized that I'm pretty sure wk057, while having his car delivered at the same time my car was, also had his car started quite a bit earlier. (My car had a smooth ride through production and delivery.) So the timing of production start probably isn't a factor, or at least not as it applies to the three of us.
Cottonwood
Roadster#433, Model S#S37
BTW, I think that is great that you are pursuing this, but realize that 79A vs 80A has the same effect on charge rate as 237V vs 240V. It is of interest, but is only about a 1.25% difference in charge rate and charge time.
Andyw2100
Well-Known Member
I almost never charge at 80 amps anyway. I charge at 56 amps, because someone smart suggested that.
(It would just be nice to get to the bottom of what is going on. For all we know, this could be some hardware problem indicative of a bigger problem, or something that could eventually cause a bigger problem, so it's probably worth looking into.)
Cottonwood
Roadster#433, Model S#S37
I almost never charge at 80 amps anyway. I charge at 56 amps, because someone smart suggested that.
Touché
I agree completely.
Remember that the interface is an analog interface. The Charging Current offered is encoded as the width of the pulse (PWM Pulse Width Modulation). In the region of 80 Amps, each 4 µs of a 1,000 µs period is 1 Amp. That means an error in time measurement of 0.4% in the analog signal will cause this error. Of course, it's hard to buy an oscillator today with an error worse than a part in 10[SUP]-4[/SUP] or 0.01%. In the generation of the PWM waveform and it's measurement, it should be easy to get much better than 0.4% error, but as an old friend says, "There are only a few ways to do sometime correctly, but a nearly infinite number of ways to do it wrong."
That 1.25% extra time adds up!
Yes, I've seen 80/80, 79/80, 79/79 in order from least common to most common with only ~10% split between the first two. The P85 on the other hand is 80/80 nearly 100% of the time with flirting to 79/80 for a few moments rarely.
Yes, I've seen 80/80, 79/80, 79/79 in order from least common to most common with only ~10% split between the first two. The P85 on the other hand is 80/80 nearly 100% of the time with flirting to 79/80 for a few moments rarely.
billarnett
Member
I've only had my car a few days (VIN 69xxx, started production Feb 9) so I can't say what's typical but this afternoon I remembered this thread and tried 80A on my HPWC:
When I first started the charging cycle, it ramped up to 80/80 and then flickered back and forth between 79/80 and 80/80 for a few seconds before settling at 80/80. As you can see I'm fortunate to have a relatively high voltage. Do you suppose that matters wrt this bug?
I don't intend to use 80A regularly as my HPWC is connected to a 90A breaker (left over from my Roadster's HPC). I guess I could "legally" go as high as 72A but "someone" suggested 56A so maybe I'll use that most of the time. But why is 56A better than any other number between 40 and 72?
When I first started the charging cycle, it ramped up to 80/80 and then flickered back and forth between 79/80 and 80/80 for a few seconds before settling at 80/80. As you can see I'm fortunate to have a relatively high voltage. Do you suppose that matters wrt this bug?
I don't intend to use 80A regularly as my HPWC is connected to a 90A breaker (left over from my Roadster's HPC). I guess I could "legally" go as high as 72A but "someone" suggested 56A so maybe I'll use that most of the time. But why is 56A better than any other number between 40 and 72?
Cottonwood
Roadster#433, Model S#S37
Charging at 80 Amps with a 90 Amp breaker, besides not meeting code, puts you at serious risk of having the breaker trip. If you have #3 or larger copper wire, have your electrician see if the breaker can be upgraded with a 100 Amp breaker.
56 Amps is a simple math tradeoff. Because Ohmic losses and heat generated scale as current squared, charging at 56 Amps gives you a 70% charging rate, but cuts Ohmic heating to 49%, or about half of the full current heating.
That's interesting. Could we have an oscillator that is too sensitive to temperature? Is there a correlation based on geography?
billarnett
Member
I let it charge for about 20 minutes this evening at 80A. It never really settled down as I noted earlier, it kept jumping between 79/80 and 80/80. I also noticed similar behavior when I lowered the rate. And sometimes when I set the rate to N it settled down at N+1. This sure feels like some sort of a round-off error
I noticed after a few minutes that the cable from the HPWC to the car got a little warm. Not a lot, maybe a little less than the heated steering wheel. But certainly more than my Roadster's cable got at 72A. The HPWC itself was cold. The breaker itself was slightly warmer than the adjacent (idle) ones but cooler than the HPWC cable.
I have AWG 6 THWN-2 wire from the breaker to the HPWC but it's only about 12 inches long; my HPWC is mounted directly on the other side of the wall from the breaker panel. My reading of the ampacity charts says this wire is good for 75A. But I've set my car to 56A anyway. At that rate a full charge will take maybe about 8 hours. That's just fine for my needs. No sense in taking unnecessary risk, even a small one.
Andyw2100
Well-Known Member
Am I understanding correctly that your charging is going to be limited because a one foot piece of cable is too thin? If so, I've got to ask why didn't the electrician or whomever installed the HPWC use the correct cable, and/or why don't you have it changed now?
Yes I totally understand it's a small difference. I've pointed out as much earlier in the thread. For what it's worth the last two charges I've done I've gotten 80A and it hasn't reverted.
gg_got_a_tesla
Model S: VIN 65513, Model 3: VIN 1913
Fwiw, I've seen this fluctuation too at HPWCs at work that are capped at 64A. I've seen the draw stuck at 63A on a few occasions of late.
Andyw2100
Well-Known Member
Maybe it's just shy and doesn't want to go to service. Now if it would fix the clicking sound in the back seat when nobody is sitting there it could avoid service on Monday.
I let it charge for about 20 minutes this evening at 80A. It never really settled down as I noted earlier, it kept jumping between 79/80 and 80/80. I also noticed similar behavior when I lowered the rate. And sometimes when I set the rate to N it settled down at N+1. This sure feels like some sort of a round-off error
This is normal, according to Tesla - they leave some room for overhead to ensure the total draw won't exceed 80A. That, combined with rounding down, will make it show 79 occasionally on the left side of the "79/80" equation. I have a question into a couple of folks at Tesla about why it occasionally senses 79A as the pilot current value.
While the charts will show you that the wire is rated at 75 amps, the terminations are only rated at 75 deg C, which makes it only good for a 65 degree rating, which means 52A max charging current (continuous load rules).
Doesn't that mean that his Roadster HPC install on a 90A breaker was in violation of code?
The HPC was a 70A Clipper Creek device that could be configured for different currents. Assuming it was configured for the maximum, a 70A continuous load requires circuit conductor and breaker rating of 90A. Very few residential device terminations are rated for 90 degC, and most new are for 75 degC. As a result, #3 wire is required - while #4 is good to 95A from a conductor temperature, the termination temperature is also important. The 90A breaker on a 70A-configured HPC is not a violation. If wire smaller than #3 was used, then it was a violation.
An HPWC configured for an 80A continuous load requires circuit conductor and breaker rating of 100A. #3 is good for that. The 90A breaker is a violation.
Even if you set the car to charge at only 56A, if the HPWC is configured for an 80A pilot current, it's a violation.
You adjust accordingly if you configure the HPC/HPWC for a lesser charging current. The device is considered installer-configured, so you don't have to supply it for the possible maximum, only what's configured.
Yup. My impression was the HPC was installed with a 90A breaker and #6 wire. The mismatch of the wire and breaker was what drew my attention.
My P85 has always charged at 79/80 with an 80A pilot current (according to VisibleTesla). I've never once seen it go to 80/80. I asked service about this and they told me it's a rounding error and nothing to be concerned about. I haven't worried about it since. My voltage drops from 245v at 0A to about 237v at 79/80A.
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