More accurate Dyno Figures

After watching the video below I noticed the power and torque were much higher. This was before the tech changed some setting on the Dyno.

I extracted a plot from the shot of the TV screen and came up with the following.

We can see that the Road torque max is 5000N which equates to a shaft torque of 315 Nm.

I think the drive is cutting back torque after the peak at 20km/hr. The nominal peak at 28km/hr is a shaft torque of 283Nm.

As for RPM, The 28km/hr equates to 1178 RPM on the motor shaft.

The big dip is still evident, a little slower at about 52km/hr.

Scatter plot of RPM vs. Torque, Power

(Power is 10x.) The above data was captured from the Danfoss VFD.
This would indicate that the Dyno run yesterday did not reach peak power / torque.50km/hr = 2100 RPM. The motor torque from the dyno plot at 50km/hr would be 2100*.323/5.125=132Nm. This (very roughly) corresponds to the scatter plot at that RPM.
The dyno plot can be for all intents ignored unfortunately. I will go and see them and see if they can do plots at multiple single speeds.

Cyclic test result for 20Ah Greensavers

I have cycle tested the Greensavers and plotted the capacity. The results were disappointing HOWEVER please see the explanation from Greensaver. It seems I over discharged them. I probably incorrectly assumed the 100% discharge point was indicated by the "Discharge Characteristic Curve" in the data sheet. (see previous post for data sheet)

Director of R&D, Greensaver: "Two comments on the cycle life test result: (a) The cutoff voltage was too low. Overdischarge will cause low cycle life. It is suggested that the depth of discharge is limited to 80%, and the cutoff voltage is set at 11.4 ~ 11.5V.

(b) The average discharge currents were relatively high. In this case, the recharge current is suggested to choose the same rate of high current to improve the cycle life of batteries."

Point 2 would be difficult to implement due to the cost, size and primary current of chargers.


The capacity is normalised to 1Ah discharge as varying discharge currents were used. This eliminates the effect of the Peukert factor at different discharge rates. The 'waves' are caused by slightly different end point volatages at different currents.

Greensaver battery inter cell balance - After Discharge

To satisfy Tuarns (and my) curiosity, I discharged the battery to 11.5v at 20A, let the battery rest, then measured the individual cell voltages. Following are the results.

+
2.0919
2.0966
2.0994
2.0985
2.1004
2.0957
-

Average = 2.097083
Standard Deviation = 0.003079
Range is from 2.0919 to 2.1004 difference = .0085 volts (0.406%)

Again the battery seems to be well balanced.

Greensaver inter cell balance

Greensaver have been very helpful in providing technical details regarding their batteries.
They provided the following diagram of the top of the cell including the interconnecting links.



I drilled 5 holes in the top of the battery according to their diagram and measured the voltage of the 6 individual cells. The battery is measured at full charge. This battery has been (unfortunately) over discharged about 35 times and is only about 1/2 new capacity. A battery that has been cycled like this should exhibit significant imbalance between cells if the cells are not almost identical.



The results below are measured with a meter (not pictured) with 4 decimal places:

Cell : Voltage

+
1: 2.2402v
2: 2.2456v
3: 2.2452v
4: 2.2541v
5: 2.2490v
6: 2.2458v
-

Average cell voltage is 2.2466 volts. This is 100% charged including some surface change.

The standard deviation is .004616

The range is from 2.2402 to 2.2541. A difference of 0.0139v (13.9mv) or 0.6205%

I am not an expert in battery chemistry but this seems to be quite good.

Comments welcome.