Home Charge Rate Halved

[mikemillar]

My 2015 S85 has always charged on my 7kW home AC charger at 32amps/7kW. A few days ago I noticed a big reduction in datalogged nightime home load and found that the Model S was only charging at 16amps. Most days, at present due to
our current Covid-19 lockdown the car is not being and only charges about 3% to make up the vampire drain. Teslafi confirms this behaviour started on 21 March.

Yesterday, I had to make a short trip and last night at two O'clock I woke up, as one does at my age, I checked the App and sure enough it was charging at 16amps. I decided to investigate further and stumbled down to the garage. On the MCU screen, the charge rate was at 16amps and the + symbol was greyed out - it could not be increased further. When I reduced the charge rate, a noticed "Max rate 16amps" showed below the rate adjuster. I checked the cabling and there was no sign of overheating, everything was cool.

I tried stopping the charge and restarting - no change, it started again at 16amps, the maximum available. Then I stopped the charge, disconnected the cable and reconnected. This time, although it restarted at 16amps I was able to raise the charge rate to 32amps and it completed the charge at 32amps. After sleeping peacefully, thinking I'd fixed it, I woke up this morning and checked the App - charge completed. Teslafi showed 32amps for this latest charge. So I tried initiating another charge. Initially it indicated 32amps available but that reset to 16amps as the charge started winding up. What on the !*?* is going on? Another trip to my garage - 16amps max available again. Another unplug and restart - still only 16amps. So I tried a hard reboot.This now appears to have fixed the problem - I'll continue to monitor.

You would not notice this reduction if you night charge on the timer, unless you are a night owl, or datalog home consumption and/or use Teslafi. Then you need a big charge overnight and it's not completed in the morning. Has anyone else experienced this sort of behaviour?

 

[Electric700]

It could be that your power company is having some issues and there are voltage irregularities. Your car might be detecting this and reducing the current automatically as a result. To be sure, you could use the Tesla app and explain the issue. They can check your car's logs.

You can also try reducing the current slightly, to 25 A and see if that helps. Charges would take slightly longer but you might not even notice the difference, and less heat / stress on your electrical system would occur.

 

[jmaddr]

@Electric700 has a good idea...what is the voltage level when this happens? Too much sag and the car will lower the amperage.

 

[Rocky_H]

Huh. Now that one is odd. I thought I knew immediately what this was, because the 16A out of 32A seemed like the indicator of one of the modules in the internal charger failing. That's how the new Model 3s with the 32A onboard charger are built. It has two of those boards inside, so if one is going out, you will see only half the current. The 48A chargers have three of those. But then I noticed you said this is a 2015 Model S. It has the older chargers like mine that are 40A total and are not built with increments of 16A internal modules in them.

At first, I didn't think @Electric700 's idea was right about voltage fluctuations, because that will lower the current to 3/4 of your set point, so that should have been 24/32 amps, and that will allow you to turn it back up. But I did remember that it will try lowering to that 3/4 level and try again, but if it still sees a big voltage drop problem, then it will lower it way down and stay there, and I think that may be the 16A level. So that could be it.

 

[AmpedRealtor]

You may not plugging it in all the way. When the charger is not plugged in all the way, or there is not a good connection, it defaults to 16A. If the power is not good, the car will reduce amperage by 20% not by half.

 

[mikemillar]

Thanks for your various suggestions, Guys. At present, it's the first time I've noticed and looked into it, although it started happening 2 weeks ago and consistently remained at 16amps until I rebooted the MCU this morning. I'll see if it re-occurs. Regarding the voltage, interesting idea. I've just checked the Teslafi log, which does record average and max voltage, but it doesn't look like that's the problem. It's typically between 240-242 volts on the nights when it was charging at 16amps. The night before it started happening it charged at just under 32 amps with 234 volts average, so that doesn't seem to be the problem.

I initially assumed that, since it often throttles back the power towards the end of a charge anyway, the small 'vampire drain' recharge wasn't big enough to justify the full 32amps. However, the bigger charge last night refuted that idea. I've never had a problem with not plugging it in all the way either.

Maybe I've cured it now, could have resulted from a recent software update? But I thought it worth flagging up as something to watch out for. I'll report in a week, or earlier if it happens again.

 

[Rocky_H]

You may not plugging it in all the way. When the charger is not plugged in all the way, or there is not a good connection, it defaults to 16A.

Oh yeah, that's another good call out. I have seen that once or twice, but that is usually also indicated with an orange light on the charge port if it didn't go in all the way and couldn't latch. I would tend to think that one with someone very new to the car, though, who is pushing very lightly for fear of damaging something, rather than an older owner of a 2015.

If the power is not good, the car will reduce amperage by 20% not by half.

That is 25% off but yeah.

 

[mikemillar]

Charge rate was back to 32amps last night, so looks like the MCU reboot did it.

 

[Spacey73]

This has happened to me as well, always charged at 32amps but last couple of weeks it has been 16amps

Just updated software to latest last night to see of that makes a difference, also changed over from crappy Rolex dumb charger to smart Ohme charger.

It charges at 32 amps if I do it manually but on scheduled charge it only does 16 amps

 

[mikemillar]

Back to 16 amps for a 3% vampire topup again last night. This time a bit of fiddling with settings and reconnecting the power cable enabled 32amp charging. Certainly looks like a software glitch.

 

[mmccord]

Visually/physically check all your connections back to the main panel. You could have a loose or poor electrical connection. This could cause a fire, so it's pretty important to check it.

 

[mikemillar]

Visually/physically check all your connections back to the main panel. You could have a loose or poor electrical connection. This could cause a fire, so it's pretty important to check it.

Spot on, mmccord! - Problem Solved! Also, AmpedRealtor, your suggestion was partly right as well. The Type 2 connector was certainly properly plugged in OK, but I was getting multiple clunks and clicks from a contactor near the Model S charge port as it started trying to charge. I also got a message
“Charging cable may not be correctly plugged into vehicle” on the App.

I just checked all the terminals in the line from the distribution board and my Powerwall. Most were pretty tight, but one negative connector in a junction box took more than quarter of a turn. That seems to have fixed the problem - goes up to 32amps correctly now.

Slightly loose terminals can 'vibrate', loosen further and heat up, as I know, because the electrician who wired in the wall charger didn't fully tighten one and it got seriously scorched after a couple of months.

Thanks for all the advice and suggestions, guys.

 

[AmpedRealtor]

Visually/physically check all your connections back to the main panel. You could have a loose or poor electrical connection. This could cause a fire, so it's pretty important to check it.

^^ this

I had some weird charging issues at my last house for the last couple of years. It would go from 80A down to 60A. Other times the charge rate would halve to 40A. This happened after working without issue for 4 years. Tesla said the log showed incoming voltage spikes. Power company said it wasn't them. This back and forth continued until I moved to another house, requiring me to disassemble and relocate my wall charger. When I remove it from the wall, I was shocked to discover the entire jacket of one of the live 2 gauge wires had crumbled along its entire length, including the section inside the conduit. The copper had turned black with soot. And this was *after* I had an electrician check the connections!

Thank goodness I discovered the problem, it was a fire disaster waiting to happen! The vehicle behaved as designed and protected me from what would have probably been a disaster.

 

[mikemillar]

Wow! Just goes to show what can happen with high power cables if not properly connected! Glad I found my problems before something nasty happened. I guess you're talking 110 volt circuits with those currents? We're always on 240 volt in UK.

 

[mmccord]

2016-11-17 20.08.17

• mmccord
• Apr 13, 2020
• 1

This was my 14-50 outlet after about 18 months of operating without a problem, followed by a week or two of randomly dropping voltage. I replaced the wire & receptacle . Later I replaced the whole thing with a HPWC.

 

[Target]

EV charging is very much a pay me now, or pay me later situation. You can put in a nicely overbuilt system that won't give any issues, or you can go on the cheap and deal with issues down the road. The reality is that cheap almost always wins, and then we have challenges later.

I will agree that the modern Tesla gear and car software is quite good at sniffing out issues with service. To their testament, if you remember to the early days there used to be somewhat routine garage fires, they have dealt with that risk quite effectively.

 

[mikemillar]

That looks fried to a frazzle! Here's the charring on the blue negative wire to the RCBO in my Rolec charger. The screw was loose. Fortunately I found it before it got to the state of yours. I think the RCBO kept popping fortunately. The case had started to distort and melt.

 

[Electric700]

Wow, so you found and fixed the cause of your issue I hope?

 

[mikemillar]

Wow, so you found and fixed the cause of your issue I hope?

I hope so too! I tried a couple of short charges this afternoon, just to test it out. Tonight's charge should confirm that it's back to normal.

The problem wan't the one on my photo, that was found 4 years ago. But it was a similar issue at another connection.

 

[mikemillar]

Well, I'm baffled! Last night the timed charge was back at 16amps/4kW, admittedly for only 20 minutes/1%. This morning, we drove a 7 mile shopping round trip. Then plugged in and forced a charge - short hold at 16amps for 30 seconds then ramped up to 32amps! That seems to be the normal ramp up sequence. Stopped charge after a minute at 32amps, with the charge current selector showing 32amps. I also installed the latest update, nothing on that connected with charging though.


Then this afternoon I checked the charge current selector again - it's changed back to max 16amps! I’ve unplugged and re-plugged. Now 32amp charge showing. I've set a 10% charge for tonight. We'll see what happens. If it does it again I’ll ring Tesla and ask them to check the logs. I might just try my Tesla UMC charger on the 13amp supply and see what that does.