Was brought up in a youtube post about considering the resistance of the leads themselves that could be added to the current sensing resistor.
I'm not going to consider anything that Cen Tech Harbor Freight meter says and will only rely on the Fluke's because of their quality.
So - the 123 Scopemeter showed me 0.65 ohms and the Fluke multimeter shows me 0.7. Averaging those shows me 0.675 ohms.
The leads of the Fluke multimeter have a resistance that bounces back and forth between 0.1 and 0.2 but hangs at 0.1 for about 75% but I'll just call it 0.15 ohms resistance to be conservative even though it is slightly less on average.
So if the direct current sensing resistor reading of that is 0.7 and we subtract lead resistance of 0.15 ohms that leaves 0.55 ohms as the actual reading of the current sensing resistor according to this meter.
The 123 Scope Meter accounting for using ground connected to the probe cable or the COM ground between both A & B ports, it comes out to be right at 0.5 ohms as the real reading and not 0.65 which doesn't account for lead resistance or other possible interferences.
So between both meters - lead resistance, etc... I'm going to pin the resistor at 0.55 + 0.5 / 2 = 0.525 ohms.
Using 0.525 ohms to calculate the input draw, here are the new numbers:
Time | Battery Volt | Resistor Volt | Resistor | Current Amps | Watts | Duty Cycle | Watt Sec/Sec | Watt Sec per Min | Running Time Min | Total Watt Sec |
8:42 | 18.83 | 0.0347 | 0.525 | 0.066095238 | 1.2445733 | 100.00% | 1.244573333 | 74.6744 | ||
8:50 | 18.62 | 0.0346 | 0.525 | 0.065904762 | 1.2271467 | 100.00% | 1.227146667 | 73.6288 | ||
9:00 | 18.53 | 0.0346 | 0.525 | 0.065904762 | 1.2212152 | 100.00% | 1.221215238 | 73.27291429 | ||
9:14 | 18.2 | 0.0344 | 0.525 | 0.06552381 | 1.1925333 | 100.00% | 1.192533333 | 71.552 | 32 | 2289.664 |
To be conservative, we will use the starting voltage and current to calculate draw so there will be a higher number to beat AND will use the higher duty cycle at the end! | ||||||||||
18.83 | 0.0347 | 0.525 | 0.066095238 | 1.2445733 | 100.00% | 1.244573333 | 74.6744 | 32 | 2389.5808 | |
Estimate of actual averages | ||||||||||
8:42~9:14 | 18.515 | 0.0346 | 0.525 | 0.065904762 | 1.2202267 | 100.00% | 1.220226667 | 73.2136 | 32 | 2342.84 |
The output still remains at 2883.96 joules - that is pretty dead on and won't change. I'm using the resistance of 3 X 100 ohm 10 watt power resistors and a current sensing resistor and I can tell you at that resistance at about 300 ohms plus or minus a couple ohms, that isn't going to change the reading at any significant level.
2883.96 / 2342.84 = COP 1.23
If estimating 25% in mechanical, then the estimated total COP is 1.54 but I'll leave it at 1.23 since I didn't measure the mechanical work of that wheel spinning at 4500 RPM.
So, forget what the resistor is rated at. Measure the resistance of your probes by making good contact with each other and keep them shorted. Whatever that is, subtract that from the reading you get when you measure the resistor because lead resistance will add to that resistor.
Keep in mind this is a one pass test and not multiple passes. I'll post something else later.
Any comments, questions or suggestions are welcome.
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