Have a 10s4p 37v6ah konion pack I'm testing stuff with before I build my DocBassJrâ„¢ 20s6p pack this winter. Thought I'd share my regen experiment from the other morning. Climbed my 1,600ft morning commute with the 3s2p Milwaukees as usual and brought the konion pack at 40.4v resting so not fully charged. On the ride down I hooked up the konions and set my descent speed to match 42.0ish volts on the CA, which was about 20mph and around 6-8 amps back into the motor. Did my best to maintain those settings all the way back down the 1,600ft and at the bottom the CA registered about .35ah of regen. For what it's worth.
Konion 37v 1,600ft Regen Experiment
- Thread starter pwbset
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How much did you use on the way up?
What is the length of the decent? If the grade is not steep, most of the energy from decending could go to fighting wind resistance.
What is the length of the decent? If the grade is not steep, most of the energy from decending could go to fighting wind resistance.
That morning (I believe it was Wed) I used 4.6ah going up, which shuts off my packs at LVC. That obviously varies depending on my pedaling mood. The descent is about 3.5 miles non-stop with grades between 8-11%. I was afraid to go faster than 20mph because the voltage reading on my CA would go rapidly upwards of 42v and don't want to hurt these batts too much or am I understanding that wrong. I assumed 4.2v is max for these konions. I wasn't worried about current because I think my 6ah pack would be able to charge at up to 18a no problem, but I don't recall seeing more than 8a on the CA going back into it.
mikereidis
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pwbset said:
Interesting. So you use 4.6ah uphill and get 0.35a downhill, for a input to output efficiency of 7.6%. If your motor, controller, battery etc. efficiency was 50%, that's a regen efficiency of about 15% ?
Yes, Lithium Manganese will do really badly if you charge them over 4.2v per cell. I have a number of such battery packs I've damaged by exceeding that. I will be using damaged batts for regen experiments, until I feel confident in my overcharge protection. IMO, you always need a big power wasting resistor when doing ebraking/regen, to dump the excess energy if and when your batts are fully charged. Probably more of a problem ebraking/regenning on a full charge; mostly if you have a hill to descend at full charge.
mikereidis
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pwbset said:
Tempted to say "Cool, I don't need a CA", but shouldn't the CA just calc 0.35/4.6 and get 7.6% ?
Or did you use about 2.3ah on the trip home and that was the denominator ?
pwbset said:
In my first post I stated that I switched packs for the decent down... so yeah, my bad... the 16% on the CA was all the regen into that konion pack because I "reset" the CA before the decent, but as you state I did spend a couple amphrs once I reached the bottom and had about 3mi more of relatively flat terrain.
Regen with the Crystalyte controller?
I am confused.
Why did you start your experiment at a status of more than 40V?
If you had 35V and keep your Regen current at around 6A you should never reach dangerous voltage levels.
I am using a Kelly controller (not yet utilising regen because of freewheel) but plan to installa second motor into frontwheel for breaking / regen.
It would be great if some of the experts here could open a thread explaining about the basic physics of regeneration / recuperation, about realistic efficiencies etc.
Example :
Going uphill at 250W (320W drawn from battery) approx 80% efficiency for 20 minutes consumes 107Wh
Going downhill at similar speed / current : what would be the amount of energy charged back into the battery / the resulting efficiency?
I am confused.
Why did you start your experiment at a status of more than 40V?
If you had 35V and keep your Regen current at around 6A you should never reach dangerous voltage levels.
I am using a Kelly controller (not yet utilising regen because of freewheel) but plan to installa second motor into frontwheel for breaking / regen.
It would be great if some of the experts here could open a thread explaining about the basic physics of regeneration / recuperation, about realistic efficiencies etc.
Example :
Going uphill at 250W (320W drawn from battery) approx 80% efficiency for 20 minutes consumes 107Wh
Going downhill at similar speed / current : what would be the amount of energy charged back into the battery / the resulting efficiency?
mikereidis
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hejo said:
Perhaps he was using another controller, or a regen add-on ?
I'm no expert on regen; "Real Experts" don't have time for these forums. But, I know electronics and the basic of newtonian physics.
There are IMO just too many variables to give a single figure or set of figures for regen efficiency. In the tests the OP did, the situation was virtually ideal, with a big hill down for much of the ride. I guess you could say that with nothing but a big hill down you get infinite efficiency: power out / power in = some number over 0.
I'd say the absolute maximum efficiency you could get on a trip ending at same elevation as it started is 49% if the motor runs at 70% efficiency for both uphill and downhill (0.7 x 0.7= 0.49).
This assumes absolutely no rolling resistance or wind resistance so is not achievable in real life.
I'd guess the absolute maximum added range (not efficiency) you could get overall would be 10%. Values of 1% to 5% would probably be more realistic under most conditions, considering the inefficiency of DC-DC coverters to up voltage for charging, charging losses etc.
My Prius is reputed to gain about 1 or 2% in mileage with regen, depending on many factors of course.
I'd say the biggest thing you could do to increase regen recapture on downhill is to keep your speed under aero thresholds of say 12-20 MPH. (With regen and not friction brakes of course.) Too much energy is lost to the wind otherwise.
In the end, I don't think regen is worth the trouble unless you have a lot of hills. Ebraking is IMO potentially wonderful though, and usually comes with regen.
hejo said:
I have a 4011 motor and pedal first 20a Clyte controller. The 4011 is really "slow", but as a side "benefit" at lower voltages is will cross no load speed and regen at a very low speed (like 12-13mph) hence my experiments. I only started at ~40v because that's where the pack happened to be. I will try it again next week with the pack voltage much lower as you say and see if I can crank more amps into it without over volting. Thanks for the tip!
Anyway... I'm only experimenting because, like Mike says, I have this perfect 3.5mi 1,600ft decent to play with each afternoon on the way home. Why I haven't built plug/resistor brake yet I don't know... that would save my poor brake pads so much stress!