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How many amps is to much on a RS19


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With all the talk about BG wheel and fires in their 900 w pack's - due to "misuse" / excessive consumption compared to what they can deliver a question arises:  When is a consumption to large for these pack?    I have pulled 51 amps / 3970 watts going 55 - 60 kmph for ~10 minutes.  Is this "to much" ? 

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I can't tell you that for sure partly because the max current rating varies depending on cell temperature, but the M50T is often sold as a 10A cell. I think the RS is a 24s4p configuration, so per my understanding of how these things work 40A continuous from the pack would be the high end of its rating.

The way GW/BG reports 'current' adds some cloudiness but the common understanding is that they report phase current which is roughly 3x what's coming out of the pack. The 3x is an estimation, I haven't seen current probe measurements that show what the shape of the waveform is—if what's reported is an average current then 3x is reasonable BUT that means that peak currents are higher.

I'd guess a reported 51A is "a good deal of current draw", but I do not know if it's a problem in and of itself. It seems like 51/3 should be fine against a max of 40. What can be a problem is that during that 51A draw, there are small spikes well in excess of 51A as the wheel makes adjustments to bumps and rider input. It's these short term events that I think could be over stressing the cells little by little. I prefer a system that never allows more than 40A to be pulled from the pack, at any time. But like I said, I really don't know.

One thing that I don't see discussed very often is how these cells tolerate pulsed current draw, most of the data assumes a continuous load like a flashlight or vape mod. Our wheels draw current in pulses, smoothed by capacitors, but pulses none the less (the caps have to recharge between pulses). It's probably not terribly important, but it is a nuance that I think needs to be better understood.

Edited by Tawpie
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9 hours ago, Robse said:

With all the talk about BG wheel and fires in their 900 w pack's - due to "misuse" / excessive consumption compared to what they can deliver a question arises:  When is a consumption to large for these pack?    I have pulled 51 amps / 3970 watts going 55 - 60 kmph for ~10 minutes.  Is this "to much" ? 

As @Tawpiewrote the motor and battery current are two very distinct values - the relation is not intuitive.

It's

U battery * I battery = I Motor ² * R Coil + U Back EMF * I Motor

with

U Back EMF = kv * Speed.

If one assumes/guesses a R Coil of 0,3 Ohm, takes an Internal Resistance of the Batteries of 0,222 Ohm for the 24s4p config and a Battery Voltage of 90V one comes to roughly 44A battery current with your additional data (55km/h).

In this case the Power provided by the battery is ~3500 Watt, mechanical power output of the motor ~2700 W. Here the pwm duty cycle should be around ~87% and the begode power alarm should already have been active?

If one takes these data at 10 km/h the battery current would be just ~14A - 1250W taken from the battery and 504W mechanical output of the motor.

Anyhow, this roughly 44A, 11A per cell should be about within/at the border of the specification for cells. I'm not really sure which cell exactly is used?

Another question is if the used nickel strips can stand such 11A for longer times - like on sees in the tableiIVwEbKkmqV0Ktuob5q9CfwDfXIljTUCHtb1KXCP

of https://cellsaviors.com/blog/how-to-size-wire-fuses-and-nickel-strip-for-a-lithium-battery-pack (no idea about the seriousness of this page - but seem valid?) some 0.3 mm x 7 mm should be minimum nickel strip size. Especially these ~11A could be not peak current burden.

 

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