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Discussion Starter · #1 ·
Hi

It is well known that with DC charging, once a car hits 80%, the charge rate drops off quickly to protect the battery.

Is there a general rule with AC charging? Does the charge rate vary depending on the SoC?

Thanks.
 

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Renault Zoe 50
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Not really, no.

If you think about it even the slowest DC charge rate is near to what most cars charge at on AC.
 

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MG EZS 2020
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If you have a Zoe the rate will drop off a cliff at 99%, but this is because it's balancing the battery cells. Not due to any charging regime. Can take up to half an hour though. Best done on your overnight charge and does need to be done on a fairly regular basis.

I don't recommend you balance cells on a rapid though. You'll make no friends that way.
 

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Discussion Starter · #4 ·
Thanks both. I have a Mini Electric. Only had it 10 days, hardly had to charge it yet due to lockdown. I haven't had to rapid charge yet, will be using the car mostly for local trips so the Mini's limited range is fine for me. I have been reading up on the etiquette of charging on public/shared chargers, will be sure to stick to an 80% charge max on rapid to avoid making no friends :)
 

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Peugeot e-2008 AC charge rate drops at around 97% SoC to do the balance charge, I'd assume that all the other current PSA EVs do much the same. The rate drop is from around 32A to 8A maybe, and if you did try to charge above 97% on a rapid DC it will do much the same (I know because I tried it to find out whilst the Ionity chargers at Cobham were being run in. Done around midnight so as to only take up one of the 6 available chargers & no-one else turned up to charge anyway so no blocking. Ionity charger was showing at 3kW 97% to 100%).
 

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What point the rate on a Rapid starts dropping fast depends on the particular EV, it's not a hard-and-fast fixed thing. E.g Ioniq 38 kWh will drop noticeably once it gets to 50%! Yes the rate depends on SOC, batteries fill up slower as they get fuller. And the charge rate tapers down, so at 80% I'm down to maybe 14 kW max, but at around 90% maybe, I'll start to notice the tapering down even on a domestic EVSE as car will be dropping below 7 kW, think it ends up at about 1 or 2 kW by the time it's at 99-100% ! My last 80->100% takes about 100 minutes, even on a Rapid !!! Haven't timed it at home yet tho.
 

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Renault Zoe ZE50 R135 GT-Line with CCS in Aconite.
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If you have a Zoe the rate will drop off a cliff at 99%, but this is because it's balancing the battery cells. Not due to any charging regime. Can take up to half an hour though. Best done on your overnight charge and does need to be done on a fairly regular basis.

I don't recommend you balance cells on a rapid though. You'll make no friends that way.
I didn't think DC charging balanced the battery!
 

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Discussion Starter · #8 ·
The slowing of DC charge rates is quite well discussed, this is the graph for my Mini Electric (taken from ev-database.uk)

137532


I haven't seen any equivalent graphs for AC charging.
 

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Why wouldn't it? :)
I watched a Plugshare Television video by Dr. Euan McTurk ,who is far more knowledgeable than me on batteries , he said that you couldn't. I believed him, but I will do some research and report back.
7B1ADA39-5B2E-4190-9D8D-04A3BC3B6027.png
 
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Does the charge rate vary depending on the SoC?
In principle yes, the last (and first) part of the charge cycle of any lithium battery is always slow (watch your phone or laptop charge, they'll do the same). When this happens and whether you notice it or not depends on how they've designed the car. For example, my PHEV charges at 16A max from AC, but the last hour or so of the charge cycle is noticeably slower as it gets near the 100% reported SOC.

Lots of lithium battery chargers (generally, not specific to EVs) use CC-CV charging (or a posh variant of it), and generally speaking, the slow part starts when it switches between the CC and the CV modes. Worth looking up if you want a little background info on what's going on.
 
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