How many amps?

reikiman's picture

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?

before comments

Comments

Hi David,

what voltage are you running?
on my emax i need 40-50A at 57v to maintain 40mph.
if you are going faster, with much more acceleration with similar pack voltages, your readings look accurate.

i made a similar misake when ordering the shunt for my cycle-analyst. i have a 200A shunt, and the most i ever use is 70A. oops.

Matt

Daily Ride:
2007 Vectrix, modified with 42 x Thundersky 60Ah
Vectrix 60Ah Lithium Tyres Fuel Registration Insurance cycle analyst 2 x TC Charger & MC
conversion

reikiman's picture

It's 60v. The recharge this afternoon used 1.6 kwh which is pretty much in line with the 1.2 kwh claimed by the cycleanalyst.

Actually this afternoon I was being a little heavy on the throttle. For my commute I stay at 40 mph so I can make the full distance. In the past I had to stay at 40 and then cut over to a side road for the last half to let me stay at 30. On wednesday I'll be able to do the regular commute and see the amp rate when I have to hold speed to 40. ;-)

Mik's picture

Your Lectra seems to have about the same efficiency as the Vectux:

5kWh/ 1.6kWh = 3.125
-----
50km/ 16km = 3.125

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LinkOfHyrule's picture

Tip: If you know the resistance of a shunt, you can calculate the amperage flowing through by checking the voltage across it and applying Ohm's law. Same works if you know the amperage, but not the resistance.

And there's no problem with using a shunt that's oversized. The bigger shunts just have less resistance so they don't dissipate too much power/get too hot. As long as it's not so oversized that it doesn't produce enough voltage to get an accurate rating (e.g. a 1000A shunt on a 50A bike), you're fine. For an undersized shunt, as long as it doesn't get hot, then it's probably fine.

The author of this post isn't responsible for any injury, disability or dismemberment, death, financial loss, illness, addiction, hereditary disease, or any other undesirable consequence or general misfortune resulting from use of the "information" contai

actually with my oversized shunt im getting poor 0 point accuracy, due to thermo-electric effects, and the small voltages my cycle analyst is trying to measure on my oversized shunt.

not bad enough to warrant me going to the trouble to replace it, but annoying none-theless.

Matt

Daily Ride:
2007 Vectrix, modified with 42 x Thundersky 60Ah
Vectrix 60Ah Lithium Tyres Fuel Registration Insurance cycle analyst 2 x TC Charger & MC
conversion

LinkOfHyrule's picture

Weird. Shunts are specifically made out of material that doesn't change resistance with temperature much, unless you've got a small, unintended thermocouple in line somewhere?

The author of this post isn't responsible for any injury, disability or dismemberment, death, financial loss, illness, addiction, hereditary disease, or any other undesirable consequence or general misfortune resulting from use of the "information" contai

oh the resistance doesnt change, the unit value is correct.
its just the zero point value drifts with temperature, very much as you would expect from an un-intended thermocouple as you suggest.

the cycle analyst treats all readings <1A as zero.
my true 0 reading is roughly 1A on my cycleanalyst, so if i got the correct shunt the measured value will be less than one, and so the 0 point value would be accurate.

Matt

Daily Ride:
2007 Vectrix, modified with 42 x Thundersky 60Ah
Vectrix 60Ah Lithium Tyres Fuel Registration Insurance cycle analyst 2 x TC Charger & MC
conversion

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