Range Anxiety: eBike "Battery Fuel Gauge" solutions

[Mike leroy]

Do you know of a battery with a "Battery Fuel Gauge" ? I like this list on Amazon. An industry standard. The Smart Battery Standard.

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A Battery Univ. article states:

"While the SoC information displayed on a battery or a display screen is helpful to the user, the readout does not guarantee the expected runtime. The fuel gauge resets to 100 percent on a full recharge regardless of how much capacity the battery can store. A serious miscount occurs if an aged battery shows 100 percent SoC while the battery’s ability to hold charge has dropped to 50 percent or less. We ask, “100 percent of what?” If, for example, 100 percent of a good battery results in a four-hour runtime, a battery holding half the capacity would run for only two hours. The user should know that the fuel gauge only shows SoC; capacity, the leading health indicator, remains unknown.

...

Device manufacturers are hesitant to install SoF into a consumer device that is readily accessible by the user. This is understandable because a battery ages, even during the warranty period, and the user would press for a new battery before the warranty expires. Device manufacturer are obliged to furnish a replacement battery if the capacity drops below 80 percent. Keeping this information hidden is seen as least disruptive. If made available, SoF would in most cases only be accessible by service personnel. "

 

[Mike leroy]

Found a homegrown solution on ES.

Key points:

• The controller already has a shunt for measuring current, which is easy to tap into, so this is what I used. The controller circuit is a tiny module about 1.5" x 1", covered in heatshrink, that just stuffs inside the controller case.
  
• The way it works is to store the state of charge of the battery (in amp seconds) in non-volatile memory (so it remembers it when the power is off) and just subtract the Ah used as you draw current from the battery, by measuring the voltage across the controller shunt. There's a reset button on the controller that if pushed at power on resets the gauge to 'full'. The actual capacity is programmed in the code - mine is set for 10Ah.
  
• It's not hard to build and the code can be programmed into the chip using free software and the same 5V serial interface used to talk to the XieChang controllers.
  
• The meter is a Lascar type EMA1710 and mounts with a single 5mm hole. It only has three wires, +5V, 0V and a 0 to 1V input. I fitted a couple of resistors to the back of it to step the voltage down from the crude PWM D/A output on the controller,
  

 

[Mike leroy]

A commercial fuel gauge

 

[Shea N Encinitas]

Lots of folks use the Cycle Analyst, not exactly a generic gauge, more of a controller and monitor. Some OEM uses include the Stealth Bomber, check em out if you have not already done so. -S

 

[Mike leroy]

Watts Up fuel gauge.

Lots of folks use the Cycle Analyst, not exactly a generic gauge, more of a controller and monitor. Some OEM uses include the Stealth Bomber, check em out if you have not already done so. -S

Shea,
Thank you. My understanding is that CA provides a wealth of info, but not exactly what I need.

I want to ride about 100mi per day in the Cascade mountains. I need an accurate device for battery's energy level to reduce range anxiety.

Accurately assessing the battery on the Mt. Shasta century course is a standard anyone can test against. I believe two batteries would suffice. I just need a device to process the battery status at any instant.

Mike

 

[Shea N Encinitas]

I've ridden with people that are running the CA, they basically watch the voltage and get a pretty accurate understanding of range, switching profiles as needed to limit consumption and extend range. Sounds like you are going to need about 40 or 50 amp hours, that's going to be a heavy load. -S

 

[Mike leroy]

I've ridden with people that are running the CA, they basically watch the voltage and get a pretty accurate understanding of range, switching profiles as needed to limit consumption and extend range. Sounds like you are going to need about 40 or 50 amp hours, that's going to be a heavy load. -S

Thank you. Does chemisty matter for 48V batteries? Would a Tesla NCA or BMW NMC chemistry make a significant difference over 100 miles? Assuming approximately 0.4Ah per mile, two 20Ah batteries makes a significant difference over bringing third battery.

 

[Shea N Encinitas]

I have no solid data on that. -S

 

[Mike leroy]

I've ridden with people that are running the CA, they basically watch the voltage and get a pretty accurate understanding of range, switching profiles as needed to limit consumption and extend range. Sounds like you are going to need about 40 or 50 amp hours, that's going to be a heavy load. -S

Shea,

I am starting to feel encouraged that I can cover the route with a single 20Ah battery. Perhaps, a 90 minute charge during lunch (69 mile mark) might be the most that is necessary to stretch a single battery?

Sounds like battery range can be extended with accurate tools and adaptive PAS profiles. Careful planning, rather than excessive $$$ or equipment, may be the most cost-effective solution.

Two or more SRAM XX1 chainrings may be necessary to adapt to different terrain. Assuming the gear ratios are totally dialed in, the key piece of hardware is a CA-compatible controller than permits flexible, user-configurable PAS settings, rather than hard-coded, factory preset PAS settings. I suppose the 750W, BBS02, 8Fun motor is the most common system for this purpose? At 48V, the BBS02 draws 15A.

I think the battery chemisty is the second most important decision. Need to investigate chemistry.

The Shasta Century ride is a good beginning model for the Cascade Mountains:

• For 47.3 miles of descent, with PAS off, would you lower the 40Ah estimate?
  • Or, did you already account for no power on descents?
• What categories of PAS profiles match the Shasta route?
  • How many Amp-hours per mile would you estimate for the 5 cases?
    
    • My guesstimates can be found at the bottom.
  • Would five, 20% increments be most effective? The PAS correspond to 1%, 2%, 3%, 4% and 6% grades.
  • Does PAS levels may make more sense when associated with gear ratios, rather than percent grades? Let's pick SRAM XX1, as an example.
    • six “X-SYNC” chainrings (28, 30, 32, 34, 36, 38-teeth)
      • Which chainring would you choose? Why?
    • 10×42 spread (10-12-14-16-18-21-24-28-32-36-42).
  • The max grade is 6% for 7.8 miles. Is max PAS of 100% adequate for 10mph at 60RPM?
  • The longest uphill is 15 miles at 1% grade.
  • Try to achieve 20mph on the 1-4% uphill grades.

Granted, the low PAS levels (100% max) would only double leg power at most. The obvious concern is avoiding the worst case, running out of electrical power.

I prefer going slower at under-powered consumption, rather than depleting the battery with over-powered PAS profiles.

(Link Removed - No Longer Exists)
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I created a Google Sheet with Amp-hour consumption cases for Shasta. I am only missing Amps to complete the calculations.

Mental first order approximation is 17Ah:

At 20mph, BBS02 draws ~2Amps on flat ground when pedaling at 100W and 100% PAS. 2A = 100W / 48V. Or, 0.1 Ah per mile.

Need to calc for 1% to 6% grade cases. Rough mental calc, every % grade multiplies force by that % * 100. In other words, 6% consumes six times the energy of flat land.

1% @ 12 mi ~ 2.4 Ah
2% @ 3.3 mi. ~ 0.9Ah
3% @ 13 mi ~ 4Ah
4% @ 11.5 mi ~ 4.5Ah
6% @ 8mi ~ 5Ah (? How many pedaling watts for 20mph )

~17Ah verify answer is correct. Calculated everything in my head. Note: if actually pedaling @ 200W, need to halve PAS levels .

In my case, 20mph, 185 pounds body weight, low PAS (30%), 60RPM, 400% gear-ratio, 29-inch wheels, 40 pound bike, 10 pounds battery, and high fitness level.

 

[Mike leroy]

I've ridden with people that are running the CA, they basically watch the voltage and get a pretty accurate understanding of range, switching profiles as needed to limit consumption and extend range. Sounds like you are going to need about 40 or 50 amp hours, that's going to be a heavy load. -S

The formal term is state-of-charge. The wiki page explains the strengths and weaknesses of different techniques .

I elaborate more on state-of-charge in this post about eBike battery chemistry and smart battery systems.