Verification of charging

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Mick787

Well-known member
Joined
Jul 11, 2018
Messages
56
Hi, this may sound a stupid question, but following the installation of a non tethered Rolec 7.2Kw 32A charging unit, is there a way to verify how quickly the car is actually charging?
We are using a BMW single phase cable. We know the car charge rate can be set to Low, Reduced or Max and with such a charger we should be setting it to Reduced or Max. What have other owners set their car charging rate to with such a charging unit and why? We have set ours to Reduced because we don't want to risk cooking the batteries.
We set the car's timer to deliver the charge during the cheap tariff time which is during the early hours of the morning.
 
Mick787 said:
Hi, this may sound a stupid question, but following the installation of a non tethered Rolec 7.2Kw 32A charging unit, is there a way to verify how quickly the car is actually charging?
Unfortunately, the i3 has no display that indicates any current charging information other than the estimated completion time. In general, the i3 doesn't display a lot of information in general that I would like to know about.

Mick787 said:
What have other owners set their car charging rate to with such a charging unit and why?
If your charging circuit has a 40 A or greater circuit breaker, there's no reason to set the charging rate to less than Max.

If your charging circuit's circuit breaker is less than 40 A, your Rolec should be configured to deliver a maximum current that won't trip your charging circuit's circuit breaker. If your Rolec cannot be configured to deliver less than its 32 A maximum current and your charging circuit's circuit breaker would trip at 32 A, you'd need to set your i3's charging power to Reduced.

Mick787 said:
We have set ours to Reduced because we don't want to risk cooking the batteries.
There's no risk of overheating your battery pack at 32 A because the battery pack's cooling system would prevent the pack from overheating. Your battery pack could be charged at 50 kW (400 V @ 125 A) without damage.

Charging at Reduced power would increase your electricity consumption (i.e., reduce charging efficiency) because of high voltage systems that consume power while charging. Charging at Reduced power increases charging time and thus the amount of energy consumed by the high voltage systems that consume power while charging.

Mick787 said:
We set the car's timer to deliver the charge during the cheap tariff time which is during the early hours of the morning.
I hope that this is working correctly for you. The i3's low-cost charging implementation has been very buggy and has not worked well in many system software versions.

Because this implementation prioritizes achieving a full charge above limiting the charging period to within the cheap tariff time period, many i3 drivers are surprised when charging starts before the cheap tariff time period begins. Charging at Reduced power could cause charging to start before the cheap tariff time period begins.
 
The i3's logic adjusts the charging rate based on several factors:
- the current battery SOC
- the temperature
- setting an internal timeframe or max rate
- the maximum output announced by the EVSE

FWIW, it does adjust the rate of charging on its own...the last 10% or so slows down considerably from the first unless the battery is very hot or cold, then, it will wait for the conditioning circuits to adjust their temperature to prevent degradation.

If your SOC is very low and it's cold out, the car will charge some immediately even if you have a low-cost tariff window set so the battery doesn't sit at that low temperature while nearly discharged to prevent damage. It usually then will stop and wait for your window.

While mostly used as a curiosity, if you're a little handy, you can add a voltage/power meter on the line feeding your EVSE. Mine's a hardwired version so it had an electrical box to make the connection. To make room for the meter, I added an extender to it then cut the proper sized hole for the snap-in meter to a cover to fit along with an inline fuse and an on/off switch, then wired in the meter I bought off of Amazon (less than $20). The one I have measures the line voltage, amperage, and calculates the wattage used (can be reset). FWIW, power=volts*amps. So, the higher your input voltage, the more watts you can push into the car. My 30A EVSE, with my voltage often closer to 250vac than 240 can max my i3 out. Most of the newer EVSEs tend to be 32A, but depending on your input voltage, may never use the full amperage because it maxes out the i3 with less. A larger one is useful if your input voltage regularly is lower, so you can still have a chance of maxing out the charging rate.
 
Thank you both for your answers, VERY informative. We will set the car to 'max'. It seems pointless to have it any other way!
 
Mick787 said:
Thank you both for your answers, VERY informative. We will set the car to 'max'. It seems pointless to have it any other way!
The reason they include limiting the maximum charging rate is if your EVSE might be on a shared circuit. Say you were using the included EVSE that comes with the car, plugged into your garage receptacle. But, that same circuit powers your garage door opener...things might work well until you open the door, and then you pop the breaker. By limiting the maximum load the car requests, you can coexist with that shared load. On a dedicated circuit (the best way to handle it), that should never be an issue.
 
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