EVSE (Electric Vehicle Supply Equipment) for Home Use

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Master Geek

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#2961348 31-Aug-2022 03:09

JonoNZ:

What kind of charging performance do people typically see from their EVSE?

We have an ABB Terra Wallbox, 32A * 230V = 7.36kW theoretical max charging ability.

I see it draws about 30.6A typically, and voltage sometimes rises to 234V, so get 7.16kW charging, but also can see regular voltage drops to about 222V giving me 6.8kW.

Does EVSE equipment typically draw less than the max rated 32A, in our case around 30.6A? Is this some kind of safety margin built into the EVSE?

Is this normal?

Yes, it is normal for an EVSE to throttle its output amperage to somewhat less (an amp or two) than its setting. This is a safety margin... and your unit apparently has a margin of 1.6A/32A = 5%. As others have already pointed out, it'll be the supply voltage that'll affect the maximum kW that your EVSE will offer to your EV; and as your EV's battery nears its maximum charge level, its onboard EV charger will not draw all of the power that your EVSE is capable of supplying.

You had asked about "performance", well, there are *many* ways of measuring performance. If you're only interested in the speed of charging then it's indeed its really only its ouput kW that matters. However if you're also concerned about charging efficiency then you'll want to avoid using any EVSE that gets warm after a multi-hour charging session... because that'd be a signal of wasted heat... and you'll also want to avoid using extension cords on your "granny charger" (for safety as well as for efficiency)... and if you care about the load your charging session is placing on the grid then things get really complicated because it'll be your EV's onboard charger, and not your EVSE, that's likely to be the primary source of harmonic and superharmonic emissions (sometimes called "pollution") during your charging session, the primary reason for a power factor being less than the ideal 1.0, and resistive "overhead" (which I estimate as 300W for the onboard charger in my Nissan Leaf at any kW rate of charging). The meter at your home "should" (by law) be measuring kWh, but its measurement *might* be biased upward a non-unity power factor and/or by harmonic emissions (https://teslamotorsclub.com/tmc/threads/beware-smets2-meters.188061/page-2). It's the kVAr on your neighbourhood's local line and not its total kW that puts a thermal limit on the power that your lines company can deliver (through a stepdown transformer) to your neighbourhood. This is a bleeding-edge concern for some lines companies overseas (who are running near thermal limits for kVAr on some of the local lines), and also for regulators (in Germany and Canada who are now insisting that public EVSEs be accurately calibrated for kWh if they are selling electricity by the kWh)... but it'd be the rare EV owner in any country who is aware that their EV's onboard charger operates less efficiently at amperages below its maximum or that harmonic emissions of EV chargers are now a concern for some lines companies.

Some model of the Zoe Renault is, I believe, BEV-B in the diagram reproduced below from a (regrettably paywalled) article in the technical literature... and you'll need to know something about power engineering before you'd be able to interpret this diagram accurately. From https://ieeexplore.ieee.org/abstract/document/9203533/:

SaltyNZ

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2degrees

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#2961368 31-Aug-2022 08:18

JonoNZ:

Cool, thanks, do others experience similar performance with their EVSE or vehicle charging?

Although ours can do 32A I typically run it at between 14-20A because there are two feeds into the garage: there is a high-amperage feed (sufficient for the entire household draw) through a solar inverter, and a 25A feed which is the original feed from the house to the garage. This means that as long as the sun is shining I can draw 32A if I want, but at night I can only use 25A at most, and other stuff in the garage has to share that feed too (so if I want to use the dryer and charge the car, it's 14A, if there's nothing else happening, it's 20A).

Generally speaking, 14A+ is enough to give us at least 80% of a full charge overnight which is more than enough to be getting on with even if the car isn't 100% by the next morning.

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SomeoneSomewhere

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#2962173 1-Sep-2022 21:15

Displacement power factor only considers whether the power factor is leading/lagging, AKA capacitive or inductive. It ignores the effects of harmonics, and is sometimes referred to as 'cos theta' - the cosine of the phase angle.

Typically efficiency peaks somewhere around 50% load for most switchmode supplies, though I don't know whether onboard chargers comply with this trend. It's a tradeoff between constant standing losses (regardless of load), losses that are directly proportional to the output power, and losses that are proportional to the square of the output power (I^2 R, AKA copper losses).

cthombor

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#2962223 2-Sep-2022 02:56

SomeoneSomewhere:

Displacement power factor only considers whether the power factor is leading/lagging, AKA capacitive or inductive. It ignores the effects of harmonics, and is sometimes referred to as 'cos theta' - the cosine of the phase angle.

Typically efficiency peaks somewhere around 50% load for most switchmode supplies, though I don't know whether onboard chargers comply with this trend. It's a tradeoff between constant standing losses (regardless of load), losses that are directly proportional to the output power, and losses that are proportional to the square of the output power (I^2 R, AKA copper losses).

I'm pretty sure that most if not all onboard chargers on EVs are designed so that they operate very efficiently when run at 100% of their rated power. The highest-power onboard chargers *might* be designed to run a bit more efficiently at 50% of rated power... so that they aren't terribly inefficient at 25% of rated power (while not requiring the additional manufacturing expense of an adaptive power factor correction circuit).

My cheap-as-chips inline kill-o-watt power meter tells me that the 3kW onboard chargers on my 2013 Nissan Leaf and on my 2014 Nissan e-NV200 dissipate about 300W of the power I supply to them at all of the operating points I can easily access: 6A 230VAC, 8A 230VAC, 10A 230VAC; and at 6A 150VAC, 8A 150VAC, and 10A 150VAC (through a 3:2 autotransformer). This is consistent with the accurate measurements on the 6kW onboard charger for a 2015 Nissan Leaf published in https://avt.inl.gov/sites/default/files/pdf/fsev/SteadyStateLoadCharacterization2015Leaf.pdf, although I note that the inefficiency (when measured in Watts) has risen to about (9%)(6kW) = 540W at its 100% load point.

As many have noted, the onboard charger in the Renault Zoe has a very low power factor when charging at rates below 10A. One blogger has published measurements which (quite plausibly IMHO) indicate that the 21kW (!) onboard charger in (their model of) the Renault Zoe is reasonably efficient, even at 10A, if it is supplied with 3-phase power rather than single-phase power, but as with the 3kW and 6kW Nissan onboard chargers, the Renault Zoe's onboard charger is apparently designed to operate very efficiently at its highest rated power... but it is marginally more efficient at 50% power, and it becomes very inefficient when charging at 20% or less than its rated power. Here is single-phase efficiency data for the onboard charger in a Renault Zoe from https://canze.fisch.lu/charger-efficiency/:

Here is the 3-phase efficiency for this onboard charger, from https://canze.fisch.lu/charging-currents-three-phase/

Finally... I note that fast mode-4 fast-chargers "should" have highly adaptive power factor correction, if they are to operate efficiently when charging 24kWh batteries above 70% SOC (i.e. at 30kW or less, depending on the SOH of the battery, its battery chemistry, its temperature, and its charge-controller firmware), as well as when charging 80kWh batteries below 30% SOC (i.e. at rates up to 240kW for a battery whose chemistry, temperature, and charge-controller is allowing a 3C charging rate). That's a factor of ten in power... and using a non-adaptive power-factor correction circuit that is designed for 50% of rated load wouldn't be appropriate. Here are efficiency measurements for a 50kW fast-charger, from https://avt.inl.gov/sites/default/files/pdf/evse/ABBDCFCFactSheetJune2016.pdf:

jonathan18

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#2971983 23-Sep-2022 09:27

So my car has an LFP battery; while Tesla encourages charging to 100% at least one a week, I've read mixed messages about whether these batteries should be fully charged every night (ie, some claiming this will still result in faster battery degradation than if maintaining at a lower SOC).

My main question is: what would people recommend charging the battery to for the rest of the week? The current set-up (noting I'm using the standard three-pin charger so charging at c. 12km/hr) has the car charging to 100% on one night, then for the next four it drops to 85%; then 90% and 95% for the subsequent two nights.

Should I be sitting the rest of the week close to 80% and only charging back to 100% on one night? Or is it fine to maintain a regular charge closer to or at 100%

My second question relates to the battery calibration that happens when the battery is at 100%: based on the continued power usage, it appears to continue still be 'charging' even though at 100% - is it indeed the case that this process takes the same amount of power as charging, and how long needs to be allowed for it to occur? (I'm wanting to ensure it finishes within the off-peak time period, but also ideally make use of my free hour as much as possible.)

Thanks for any tips and advice.

[Note: I thought this was the most appropriate thread, but did consider either the M3, MY or general EV threads; happy for this to be moved if one of these is considered a better location.]

Dingbatt

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#2972018 23-Sep-2022 10:32

I am pretty much only charging my 3 (using the UMC) every 5 to 6 days. My usage pattern at the moment means it gets down to about 60-70% so I then charge it back up to 100%.

I don’t know if this is the ‘best’ way to do it but in my book it is minimising cycles. Trickle charging obviously matters less than fast charging but I’m trying to look after the battery as much as possible. I have only got below 50% on one trip in 6 months.

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jonathan18

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#2972025 23-Sep-2022 10:50

Yeah, the result of either a lack of hard evidence as to the 'best' charging techniques, or just contradictory information, it's difficult to know what the right thing to do is...

This is from Tesla's own site, but I'm not sure how to read that line 'keep your charge limit set to 100%': is that encouraging owners to charge every day (as it's not even clear that the encouragement to plug the car in when you are not using it is that it needs to be set to charge)?

Model 3 has one of the most sophisticated battery systems in the world. The most important way to preserve the high voltage Battery is to LEAVE YOUR VEHICLE PLUGGED IN when you are not using it. This is particularly important if you are not planning to drive Model 3 for several weeks.

There is no advantage to waiting until the Battery’s level is low before charging. In fact, the Battery performs best when charged regularly...

If your vehicle is equipped with an LFP Battery, Tesla recommends that you keep your charge limit set to 100%, even for daily use, and that you also fully charge to 100% at least once per week. If Model 3 has been parked for longer than a week, Tesla recommends driving as you normally would and charge to 100% at your earliest convenience.

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michaelmurfy

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#2972035 23-Sep-2022 11:01

The app now recommends you keep the charge limit at 100% too. This is to keep the cells at the same voltage.

I also recommend you getting a proper EVSE instead of charging from a 10a supply. Depending on your power plan you could actually save money with a 32a circuit (or even a 16a circuit).

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jonathan18

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#2972042 23-Sep-2022 11:17

michaelmurfy:

The app now recommends you keep the charge limit at 100% too. This is to keep the cells at the same voltage.

I also recommend you getting a proper EVSE instead of charging from a 10a supply. Depending on your power plan you could actually save money with a 32a circuit (or even a 16a circuit).

Yeah, it recommends leaving the charge limit to 100%, but that's not quite the same as saying as feel free to leave the car to charge to 100% every night. (I promise I'm not trying to be pedantic here; the imprecise wording Tesla uses totally leaves this open for interpretation.)

Our current charging methods are more than adequate for our purposes, and we'll never recoup the capital outlay of the purchase and install costs of a 'proper' EVSE.

We already have a 16A caravan socket where my wife's Leaf charges; if I need more than the 85sh km range I get from 8A charging during our off-peak hours I can use her socket for twice that range (I have the Tesla adapter and it works perfectly).

If I need more than 190sh in a single charge (and the only scenario I can see is having arrived back from a trip and leaving for another one the next day - which will be a very rare occurrence) I'm quite happy to pay to use a local DC charger.

I'll ask the question next time we have an electrician in as to whether it's feasible to upgrade our garage socket to 15A, but I imagine this will require at least re-wiring back to the switchboard (if even do-able), given the distance between the two.

Obraik

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#2972104 23-Sep-2022 11:55

The manual says to charge LFP cars to 100% daily, or once a week at a minimum. I'd recommend doing what the manual says. Remember you have an 8 year/160k km warranty on your battery - if the advice causes damage then Tesla is on the line to replace it at their cost.

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jonathan18

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#2972115 23-Sep-2022 12:28

Obraik:

The manual says to charge LFP cars to 100% daily, or once a week at a minimum. I'd recommend doing what the manual says. Remember you have an 8 year/160k km warranty on your battery - if the advice causes damage then Tesla is on the line to replace it at their cost.

As quoted earlier, it doesn't actually say that; rather it says: " If your vehicle is equipped with an LFP Battery, Tesla recommends that you keep your charge limit set to 100%, even for daily use, and that you also fully charge to 100% at least once per week."

That 'also' totally leaves space for it to be fairly interpreted that the other six days aren't necessarily a charge to 100%, that wiggle room could well be enough for them to argue they never advised daily 100% charging. If they'd really wanted to state that it should have been worded "If your vehicle is equipped with an LFP Battery, Tesla recommends that you charge your car to 100% each day, even for daily use; at a minimum, Tesla recommends you fully charge to 100% at least once per week."

All that said, it's certainly not like there's active advice from Tesla for owners of LFP-equipped cars to avoid regular charging and leaving the car at over 80%, unlike those with other battery chemistry; it's more that I had wanted some assurance that I wasn't risking increased battery degredation from keeping the battery over 80% much of the time as my daily mileage is pretty low (10-20km would be normal).

Obraik

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#2972134 23-Sep-2022 13:33

I think you're over analysing the wording lol. Keeping the daily charge limit to 100% means that the car will charge to 100% daily, given their advice elsewhere in the manual is to always keep the car plugged in. However, this is a discussion probably best moved to the Model Y/3 threads

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michaelmurfy

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#2974051 28-Sep-2022 11:10

Electric Kiwi now have an offer for EV owners: https://www.electrickiwi.co.nz/evnex/

We’re working with Evnex to give our customers a great deal on their charger, as well as the option of an interest-free payment plan so you can pay off the charger via your EK energy bills (subject to eligibility criteria). And as a MoveMaster customer, you already have the perfect power plan for recharging your EV with half price rates overnight (between 11pm and 7am).

If anyone does want to sign up to EK to take up this offer then feel free to use my referral: https://www.electrickiwi.co.nz/RAFeg5W29b - this isn't an advertisement for them but I know a few people who may be using "Granny Chargers" this may be good for. Evnex are a NZ company and make some pretty good charging equipment.

lchiu7

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#2975503 30-Sep-2022 14:53

I am new to the EV world having only just bought the Atto3 and charged it once at home using the supplied cable

From factory the Atto comes with a Type 2 10A charger that will charge at 8 amps

I also charged it once at a Chargenet station.

I was thinking of one of these for my garage

https://smartevchargers.co.nz/shop/wall-mount-ev-chargers/wall-mount-smart-ev-charger-32a/

Anybody have any experience of these?

JonoNZ

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#2975504 30-Sep-2022 14:57

No experience with that EVSE, but slightly alarming they mix up 7.6kW vs 7.4kW in the tech specs. 7.6kW is not something you see so let's just say it is max 7.4kW (230V * 32A = 7.36kW which is normal).

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