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How many amps?
Submitted by reikiman on Sun, 09/28/2008 - 13:34
The curiosity I've been having for awhile is what is the actual power use on my motorcycle. The curiosity is partly due to the range I've been getting (actually not getting) since in the past it had a hard time delivering more than 10 miles range whereas other e-motorcycles such as on the evalbum are supposedly delivering more like 20 miles range with an equal size pack to what's on the Lectra. However a couple weeks ago I fiddled with the rear end, put a little bit of slack into the chain, and the performance improved dramatically and it's now easy to get 10 miles range. Given that my commute is 10 miles I'm breathing a little bit easier.
The bike came with an analog amp & volt meter pair. I had them installed for awhile but I began to doubt the accuracy, plus I've got both paktrakr and cycleanalyst units and want to use them. The CycleAnalyst is the external shunt model, and the instructions for it say to verify with some other meter whether the CycleAnalyst is giving accurate readings. I don't at the moment have any other meter hooked up so it's a little hard to verify.
I bought the CycleAnalyst with a 500A shunt .. the way electricmotorsport's webstore is set up for the CycleAnalyst it seemed to me that a 100A shunt would give readings up to 100A and a 500A shunt would give readings up to 500A. With the analog meter it would give a 300A reading on takeoff and back down to ~ 100A for cruising. That led me to believe I'd need a 500A shunt and that's what I ordered. After installing it the A reading was nowhere near what the analog meter read. I finally talked with Todd about it and he straightened me out -- they normally use 100A shunts for all their vehicles because the 100A shunt will work with the CycleAnalyst to give measurements well above 100A. In the meantime there is a setting in the CycleAnalyst to adjust it for the shunt being used. It is the RShunt setting in the advanced section, however the CycleAnalyst instructions doesn't tell how to calculate what the correct RShunt setting is. Todd did a little calculations in his head and we put an RShunt value in, and while the numbers became a little more reasonable they were still a bit off.
The only way I have to verify the CycleAnalyst is the Kill-A-Watt power meter. I can plug the chargers into it and measure the KWH's used to recharge the pack after a ride. That'll give a ball park figure to the AH's used during the ride. And since the CycleAnalyst gives an AH reading it's possible to validate that the CA AH reading is near the Kill-A-Watt AH reading.
For example the CA, with the 500A shunt and after Todd's new value setting, it consistently claimed 13.5 AH for my commute. 13.5AH * 60v = .810 KWH ... however, the Kill-A-Watt consistently claimed 1.7 KWH to recharge the pack. To be sure the RShunt value Todd calculated was a guess and neither of us knew precisely what to program as the setting. Obviously the guess wasn't right because .81 KWH is nowhere near 1.7 KWH.
Todd just sent me a 100A shunt, I just installed it and went for a spin. The readings were more in line with the readings shown on the analog meter before. 300A for a full throttle takeoff, easy to get into the 150-200A range, and cruising in the 50-100A range. On the ride I just took the CA claims 21.4 AH used * 60v = 1.284 KWH ... it's on the charger now and I'll report later what the total was to recharge. In the meantime I think this is more in line with what the Kill-A-Watt is about to say.
I'm also planning to get the Amp measuring shunt for the PakTrakr. That'll also give its own validation.
That leaves a different question. Todd felt the A's used, if accurate, were quite a bit high. He felt that 20-50A would be more reasonable for cruising. Is the above out of line?