Periodic dips in charging speed at home, but not charging power

[beatle]

With the other threads related to slower charging at higher temps, I've been using ElectraFi to monitor my charges to see if it's affecting me as well. My charging power remains flat at 9.3kw (240v, 40A) but after a few hours of charging, I notice my charging "speed" in mph dips for about 10 minutes. It goes from 23 mph down to 16 mph. This recurs about once every hour until charging completes at 85%.

My only guess is that the battery is balancing itself and bleeding off excess capacity from higher cells after the pack reaches ~50% SoC. It seems a bit wasteful to balance at a low SoC to balance, but maybe they're just being super cautious? Or maybe it's not balancing at all? Since the charger power does not drop, I don't believe this is throttling due to a warm plug or other fault. The truck just decides to use its power for something else for 10 minutes and it doesn't go directly into the battery so the charging "speed" is temporarily reduced. I could probably observe a lower speed if I were to run the cabin AC or heat at the same time. Here are a couple screen shots:

When I charged last night from 62-85%, the dips appeared aft]er only an hour or so, perhaps because the truck was already above 50% (note the time scale is different here due to the shorter charge session):

I don't think anything is wrong, but it's interesting to see and I wonder what is actually happening.

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[Zoidz]

I don't use ElectraFi so I don't know anything about it. Taking only the graph into consideration, what is the Charger KW plot actually showing - actual dynamic charge current, or charge current setpoint?

 

[beatle]

I've used TeslaFi for years, but ElectraFi and the data gathered from Rivian is a little different. I believe Charger KW shows the amount of power being delivered or received by the onboard charger. Since I'm charging at 240v / 40A, that would actually be 9.6 or 9.7kw, so I'm guessing this is related to charging losses somewhere.

TeslaFi shows the actual voltage/amps of the session and I'm getting around 243-245v when I charge my Model S at 40A, so I don't think this is voltage droop.

 

[Zoidz]

I wonder if the AC is running to cool the battery? A plot of battery temperature would interesting to correlate, or not.

 

[beatle]

That's a good theory as well. I'm not sure of the power routing, but if the charger sees a solid 9.3kw, it sounds like electricity is coming into the charger and then going to a HVJB where some of it is distributed to the battery and some to the HVAC. The fact that the dip is a curve and not a sharp dropoff makes me think there may be something else though. I believe the compressor can ramp up, but that seems like a long time to do it, but I'm no HVAC expert. I guess I could try to time this to listen for the compressor to kick on and ramp up if I really wanted to know, though I typically charge overnight to avoid any potential heat issues.

 

[R1Thor]

I've commented on similar threads and people fought me on it because... ?

I had the same experience.
Which was *different* and concerning from the last year of my ownership, where even on the hottest days last summer, I'd not seen my L2 Charger dip in charge speed/power output.

After troubleshooting WITH RIVIAN, RIVIAN confirmed my wall charger was defective.

It's been replaced under warranty and I've not had my charge drop off since.

I'm not the first; others have experienced the same (I actually discovered this was abnormal within a discussion occurring on Discord with another dissatisfied Rivian L2 Charger user).

Everyone normalizing this as 'it's been hot,' there are probably a few instances where this is true.
However, it's not the 'norm.'

If we keep normalizing these expectations, people are going to start thinking everything is fine when it's not and otherwise missing out on having a defective piece of equipment replaced.

THAT SAID, Op didn't specify his charger, so I may be out on left field right now making that assumption. Maybe OPs charger or charge port, or battery is overheating. At which point, carry on (though I'd still try to find the root of that). The point of my post here is simply to say: if you think your charger is behaving abnormally, contact Rivian. Worst case, they confirm everything is behaving normally. Posting on the forums for people to opine about their expectations and experiences is not productive, in my opinion, especially when (threads like these) you're getting people giving incorrect information ('this is normal, don't worry about it')

 

[beatle]

I'm using a Tesla universal wall connector.

Thinking about the cooling aspect of the battery, charging at 9.3kw is really, really slow compared to DCFC, so perhaps the battery isn't being cooled. I'm not sure if coolant flows through the HVJB or onboard charger. Just running the coolant pump would not reflect this dramatic power consumption drop, and they probably want to keep running the coolant pump constantly during charging to help observe overall coolant temperature.

 

[SwampNut]

I've seen this in both the Tesla and Rivian. I pay no attention to it, so I'm not sure how much it happens on the Rivian. My whole-house energy monitor eventually identified part of the usage as cooling (it was able to ID Tesla cooling vs Tesla charging itself).

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