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Kia's specs say that the on-board charger of the US model of the 2022 Niro EV has a capacity of 7.2 kW. We use a Grizzl-e Smart EVSE set to 40 A, it's fed by a 50A circuit (which derates to 40A). At 240V, 40A means the EVSE is seeing 9.6 kW (or if the voltage sagged to 220V, 8.8 kW).

Right now the Niro shows the charge on traction battery as 60% and reports 6.0 kW (which I assume is the power being delivered by the on-board charger). That's quite a bit lower than I would expect from a charger that is rated at 7.2 kW and which seems to have an ample supply of energy available to it.

So, I have a few questions:

  • Is the rating of the charger the amount of energy delivered to the battery? Or, is it the amount drawn from the grid?
  • How large are the typical losses in an on-board charger?
  • How large are the typical losses in the EVSE?
  • Where does the rate typically peak as the traction battery is being charged?

To add to the puzzle, Kia lists the charge time for the Niro's 64 kW battery on a Level 2 charger as 9 hours 35 minutes, with a parenthetical 7.2 kW after the time -- they don't give a start or stop point, but that works out to 69 kW (if you don't account for the rate tapering off).

dlu
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1 Answers1

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Is the rating of the charger the amount of energy delivered to the battery? Or, is it the amount drawn from the grid?

Almost certainly power drawn from the grid.

Remember that chargers are sized based on fuse sizes. For example 230V, 16amp is usually said as 3.6 kW (although more accurately it's 3.68 kW). It's the current that matters, not voltage!

How large are the typical losses in an on-board charger?

The efficiency of power electronics that rectifies AC and converts it to different voltage DC is not 100%. More likely, it's 90%.

So a 7.2 kW charger, if it has low-resistance wiring, would deliver 6.5 kW to the battery. If you accept 10% voltage loss as well, it could even deliver as little as 5.9 kW to the battery.

How large are the typical losses in the EVSE?

Very close to zero. The supply equipment is not a charger, just a switch. It does communicate to the car how much the car can draw, though, on a pulse width modulated protocol. But the car has the actual charger, the EVSE has zero power electronics.

Where does the rate typically peak as the traction battery is being charged?

Using slow AC charging, you should be getting the indicated amount minus efficiency losses minus voltage losses. So 6 kW sounds a bit low but plausible if it has long wiring (and large voltage losses), and at the same time the efficiency of the on-board charger is 90% and it shows the power after losses, not before losses.

One aspect that can affect is that if it's cold, some of the energy can go to heating the battery. This should take only a while, once the battery is hot then the on-board charger should only charge the battery not heat anything.

Also, I have read that the built-in DC to 230V inverter of a Hyundai Ioniq 5 and Kia EV6 have huge 250W idle consumption. Apparently once you power on the inverter, you power on a lot of the electronics of the car that draw as much as 250W power. Sounds ridiculous, but apparently this is the case. If charging powers on those same electronics too, it's plausible that you need to subtract 250W from whatever you get after voltage and efficiency losses to get the actual amount going to the battery.

juhist
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