Just how lossy is regenerative breaking?

Attila's study tells the efficiency of regeneration braking is approx 50% on the Gen2.
The new 2004 Toyota Prius : EV efficiency measurements

Toyota's sales document says the battery power is 25kW on the Gen2 and 27Kw on the Gen3.

Ken@Japan

 

Well, I know from data collected that it's well capable of even more than 25kW peaks, (I've seen close to 30kW!) but the boost converter limits sustained power to not much over 20kW with the stock battery. If you have instrumentation, (and I know you do!) check it yourself!

If you have a non-stock battery system capable of sustaining a higher voltage, such as mine, then the power is indeed closer to 25kW. The stock battery ECU sets DCL (Dischage current limit) to typically 105A, and when under this kind of load, the stock battery voltage typically sags to around 200v. Even at max; 105A x 200v = 21kW, but in practice the HV ECU holds amperages to under 100A. Note that this is battery amps, so this doesn't mean you get that delivered to your MG's, as there is some loss in the boost converter. (not to mention the inverter!) 21kW at 95% efficiency is 19.95kW.

I've been datalogging for a long time, both before my PHEV conversion and after, which is how I know these facts.

 

His calculation is a little misleading because he did not taking account of the charging efficiency of the battery.

About 9791kVA go into the battery, if using 80% charging efficiency, it only
recovered 9791kVA x 0.8 = 7832kVA,
so the overall efficiency is 7832/18014 = 43%
This agrees what we have posted here before, ~ 40%.

 

BING BING BING, we have a winner!

But, REGENERATION is charging, so the REGENERATION EFFICIENCY is 80 % from Attila's results.

But, the EFFICIENCY OF REUSE is not, and in Attila's test it was 43 %. And this is what many non-engineers are asking when they ask about REGENERATION EFFICIENCY. ENERGY OF REUSE is the total efficiency of charging, and reaccellerating altogether.

These semantics is what confuses allot of people.

The Prius is not an electric car. So, its conductor and battery resistances cause extra losses at the level of acceleration Attila used. Besides rolling resistance losses. He did study what braking level made the most electricity, but not how to use that electricity.

The lesson from this is to avoid electric acceleration. Use the electric drive to maintain a speed, or at worse crest a hill rather than restart the engine.

In these usages, the current is low, and so are the losses due to the battery and conductor resistances.

I did the same calculation above from Attila's data several years ago. Its over on Prius Online: http://www.priusonline.com/viewtopic.php?t=8326&postdays=0&postorder=asc&start=0 .