wturber
1 MW
john61ct said:
Yes. It seems like a few of us wandered off in thought a bit. But a little off-track meandering isn't necessarily a bad thing.
As for the efficiency of the conversion, I understand that it would be wise to expect numbers in the 80-85% range. But I think this converter is more efficient than its mediocre pedigree would suggest. While I haven't done a good input/output measurement, my ride power consumption is right in line with what I see routinely being reported by folks not running a booster. Also, the booster never seems to get more than 5-10 degrees warmer than ambient - and that's even after climbing hills with the booster drawing 650 watts or more. At 90% efficiency, that thing should be pretty hot if it is actually shedding 60 watts of heat. I've wondered if its position on the seat tube is perhaps just a perfect place for good airflow. But that seems unlikely since I usually have a water bottle sitting in front of it on the downtube. Also, on 10-15 mph climbs, the airflow shouldn't be that good. My headlight that is drawing about 30 watts is mounted on the front of the bike with direct airflow and it is always much warmer. Almost as warm as the motor. So I gotta figure that the boost convert is shedding less than 30 watts of power which suggests a 95% or better efficiency. Of course, that is a boost from 36-42 volts to 54 volts. Boosting from 12v to 41v or 42v is conceivably a worse case. Some day I'm going to have to test this thing more carefully and objectively at different input voltages.
BTW, I am able to easily test the efficiency while charging of my Meanwell HLG 320H-42a "charger" using my Kill-A-Watt meter on the AC side and my battery's amp meter on the battery/charge side. After accounting for most of the parasitic draw from accessories on both sides, I end up with a 350 watt AC draw and 325.4 watts of supply on the DC side. That's a 93% efficiency and 25 watts of power being dissipated by the Meanwell "charger." And that Meanwell gets pretty warm after running for an hour or so - as you'd expect from 25 watts of continuous draw and no substantial airflow. With the lack of airflow, this is hardly apples to apples. But still, my boost converter never seems to even get noticeably warm.
Even at 80% (a likely worst case), the direct DC conversion makes the most sense because a dual conversion (12VDC to 120AC to 42VDC) is unlikely to do be any more efficient (90% x 90% = 81%) and the cost and complexity would be significantly greater.
