EV Charging Efficiency Test - BYD Atto 3

EV Charging Efficiency using a BYD Atto 3

Comparing the charging efficiency of a portable 10A charger (Level-1 charger which comes with the BYD Atto 3) with a dedicated 32A Wallbox EV charger at different charge rates.

Here’s what I found:

  • 10A portable EV charger efficiency = 87%
  • Wallbox EV charger efficiency at 10A = 88%
  • Wallbox EV charger efficiency at 15A = 91%
  • Wallbox EV charger efficiency at 30A = 91%

For those not familiar with EV chargers, all portable plug-in chargers and home wallbox chargers are AC chargers. These use the standard Type 2 AC charge connector, unlike the fast or rapid DC chargers found at charging stations.

I used a single-phase 7kW ZJ-Beny EV charger, which can be adjusted anywhere between 4A and 32A, so I simply tested the charging rate at various levels and compared it to the actual charge rate measured in the vehicle. Like all EVs, the Atto 3 has an inbuilt charger that converts AC to DC when charging the large DC vehicle battery system. Not surprisingly, there are always some losses through the power conversion process. In this case, the vehicle’s inbuilt AC charger is where the losses occur; the actual EV chargers are not doing the power conversion process.

To measure the actual power and current draw from the portable 10A charger, I used a simple energy monitor and App. I used a Sungrow Hybrid Inverter with an energy meter (CT clamp) to accurately measure the power draw from the ZJ-Beny charger. Below is a graph of the results at various charge levels comparing the portable 10A granny charger to the Wall-mounted ZJ Beny EV Charger.

Results: The charging efficiency increases as the charge rate increases up to a certain point. Charging at 10A results in an efficiency of about 87%. There is very little difference between a 10A portable (Granny) charger and a dedicated EV charger set to 10A. Note: The extra 1% loss using the granny charger is most likely due to the cable losses through the 10m extension cord used.

The optimum charge rate of almost 92% appears to be around 15 or 16A, while with higher charge rates, the efficiency doesn’t change much right up to 30A. There is a 4% difference between 10A and 15A charging. See detailed information about charging losses
is this EV charging article.

Using Long Extension Leads

Here’s some more information regarding cable losses using long extension leads with a portable 10A charger. The longer leads (20m+) will decrease overall efficiency by another 4% or more, bringing the total efficiency down to around 83%. There’s more detailed information is this EV charging article.

It’s best to use the shortest extension lead possible when using a portable charger. Another option is to get a larger size extension cable. Most 10A leads use a small 1.0mm2 copper core wire, while 15A leads use a larger 1.5mm2 core (50% larger). It’s possible to purchase a 15A lead and replace the 15A plugs with a 10A plug, although, it would be better to install a 15A outlet also to enable you to use a more powerful 15A portable charger.

Thanks for this Jason. I had not considered the issue of efficiency reduction when using an extension lead.
Outlet i use when granny charging my EV is not close enough to the car for me to just use the granny lead so am forced to use an extension. Thinking that I will simply make one, minimum length, fat cable.
Good tip, much appreciated.
(Have been forced to utilize the granny charger of late while I wait for my zapped Victron Quattro to be replaced. (Lightning EMF damage, Victron say beyond economical repair)

I’ve also started testing out one of the cheaper 15A portable chargers, and so far, it has performed very well with no issues. It appears to be well-made and weather rated for outdoor use.

However, it’s rated at 15A but only draws 13A in the max setting. (other settings are 6A, 8A and 10A.)
This is still far higher than the 10A EV charger supplied with the Atto 3, which only draws 8A max.

Hi Jason
That is certainly an interesting product, something that has huge potential.
I limit my zappi’s output to 4kw so that I have sufficient remaining energy to carry all my other house loads. (My two arrays combined output is 7kw max).
A plug and play charging device that can deliver 3kw would work well for me and I should think, if properly marketed, could be the charger of choice for many people.