# How many amps?

### Re: How many amps?

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 in July 2010. Done 194'000km

### Re: How many amps?

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. ;-)

### Re: How many amps?

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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There is always a way if there is no other way!

### Re: How many amps?

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

### Re: How many amps?

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 in July 2010. Done 194'000km

### Re: How many amps?

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

### Re: How many amps?

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 in July 2010. Done 194'000km

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