Watts = MPH eMotorcycle

General Discussion about large electric scooters and motorcycles and other things with no pedals.
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DrkAngel
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Watts = MPH eMotorcycle

Post by DrkAngel » Nov 25, 2011 12:55 am

I'm planning my eMotorcycle build.
One of the most important considerations is, "How much motor do I need?"!
After a lot of hunting I came across a nice graph, drawn from 2 aerodynamic eMotorcycle builds.
d-11-vs-125.jpg
d-11-vs-125.jpg (30.99 KiB) Viewed 7075 times
Speed to ............. watt usage ........Range w/8kWh battery
65mph requires nearly 6000watts - about 8HP ........ 87 miles
60MPH requires about 4750watts - about 6.25HP ... 101 miles
55MPH requires about 3750watts - about 5HP ....... 117 miles
50MPH requires about 3000watts - about 4HP ....... 133 miles
40MPH requires about 1750watts - about 2.35HP ... 182 miles
30MPH requires about 1000watts - about 1.35HP ... 240 miles
20MPH requires about 550watts - about .73HP ...... 290 miles

8HP to cruise at 65MPH!
10HP continuous, sounds about, proper minimum, need some extra for hills and headwinds!

1hour 20 minutes at 65MPH - Legal expressway speed
2 hours cruising at 55MPH - legal highway speed
8 hours cruising at 30MPH - stop & go would cut that, a fair bit.

Range at different speeds ... nice to know!
Last edited by DrkAngel on Nov 25, 2011 11:20 am, edited 5 times in total.
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Re: Watts = MPH eMotorcycle w/aero shroud

Post by jonescg » Nov 25, 2011 1:13 am

DrkAngel wrote:I'm planning my eMotorcycle build.
One of the most important considerations is, "How much motor do I need?"!...
There can only be one answer, and it's never enough :twisted:

I tend to go by seat-of-the-pants dyno.

If you want performance like a production 125, go for something with a continuous rating of 15 kW, peak of 25.
If you are after production 250 power, you will need at least 25 kW continuous.

If you want something that will round up 600s on a track day, you're going to need at least 75 kW continuous, with peaks of 125 kW.

The aeros on a bike are not great, and the best aerodynamic fairing makes them impractical. If you are commuting I'd try to avoid anything too complicated, but a smooth, pointy rear end and a good shield at the front has half the battle won.

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Re: Watts = MPH eMotorcycle w/aero shroud

Post by liveforphysics » Nov 25, 2011 3:45 am

jonescg wrote:
DrkAngel wrote:I'm planning my eMotorcycle build.
One of the most important considerations is, "How much motor do I need?"!...
There can only be one answer, and it's never enough :twisted:

I tend to go by seat-of-the-pants dyno.

If you want performance like a production 125, go for something with a continuous rating of 15 kW, peak of 25.
If you are after production 250 power, you will need at least 25 kW continuous.

If you want something that will round up 600s on a track day, you're going to need at least 75 kW continuous, with peaks of 125 kW.

The aeros on a bike are not great, and the best aerodynamic fairing makes them impractical. If you are commuting I'd try to avoid anything too complicated, but a smooth, pointy rear end and a good shield at the front has half the battle won.


This is all exactly my thoughts and experience as well.
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Re: Watts = MPH eMotorcycle

Post by DrkAngel » Nov 25, 2011 9:04 am

Looks like my "genuine" ETEK motor will fit my bill.
A discontinued, "landmark" motor.
Built by Briggs and Stratton, but often copied, and constantly referenced.
This is a permanent magnet motor, designed to be run continuously at 48V - 150amps.
48V x 150 amp = 7200watts x 84% efficiency = 6048 watts = 8HP+.
(88% peak efficiency)
But, motor is rated at 300amps, for up to 2 minutes, which means ~16HP available, from greenlight, for passing, or just, "getting up to speed".

Oh ... Motor only weighs 21lb!
Last edited by DrkAngel on Nov 26, 2011 8:16 am, edited 1 time in total.
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Re: Watts = MPH eMotorcycle

Post by DrkAngel » Nov 25, 2011 11:19 am

DrkAngel wrote:
Speed to ............. watt usage ........Range w/8kWh battery
65mph requires nearly 6000watts - about 8HP ........ 87 miles
60MPH requires about 4750watts - about 6.25HP ... 101 miles
55MPH requires about 3750watts - about 5HP ....... 117 miles
50MPH requires about 3000watts - about 4HP ....... 133 miles
40MPH requires about 1750watts - about 2.35HP ... 182 miles
30MPH requires about 1000watts - about 1.35HP ... 240 miles
20MPH requires about 550watts - about .73HP ...... 290 miles

8HP to cruise at 65MPH!
I believe that the "watts" were the watts input, not the watts output - HP.
So "HP" "required" might be 20-25% less, due to controller and motor % efficiency.
6+ HP might sustain 65MPH and 8HP should supply enough for modest hills & headwinds ... ? !!!
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Re: Watts = MPH eMotorcycle

Post by Doctorbass » Nov 25, 2011 11:24 am

I would sugegst to use the SWbluto simulator ( it work really well and is accurate when comparing real world data and simulated data)

On my Giant DH, to do 113kmh continuous ( 70MPH) i need 8-10kW input power ( on the calibrated C-A)

the swbluto simulator graph also have an option with power required at different speed on the X axis of the graph. you can put numbers like frontal area, temp, tire friction, etc..

At least it worked well for me 8)

BTW on your graph posted above, the slope is not realistic since usually, the slope of power vs speed will increase as you go faster. ( it's non linear and the slope increase )Doc
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Re: Watts = MPH eMotorcycle

Post by Kingfish » Nov 25, 2011 1:24 pm

DrkAngel wrote:Speed to ............. watt usage ........Range w/8kWh battery
65mph requires nearly 6000watts - about 8HP ........ 87 miles
60MPH requires about 4750watts - about 6.25HP ... 101 miles
55MPH requires about 3750watts - about 5HP ....... 117 miles
50MPH requires about 3000watts - about 4HP ....... 133 miles
40MPH requires about 1750watts - about 2.35HP ... 182 miles
30MPH requires about 1000watts - about 1.35HP ... 240 miles
20MPH requires about 550watts - about .73HP ...... 290 miles
IMO, these are overly optimistic numbers.

This last summer I ran 8kWh averaging between 23-29 mph and the best that I could do was ~165 miles on a single charge with pedal-assist. Granted, I had headwind, I had hills and fog and rain; never an opportunity to test the true distance on flat level ground. Hypothetically, I calculated that the pack range was 220-240 miles in perfect conditions.

To reach 65 mph, I presume it will take at least 3X capacity for the same distances. Wind and hills are the giant factors; they are always there to spoil a great pleasure ride.

Race Day is altogether different, and I trust the other gents for their word on that subject :wink:

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Re: Watts = MPH eMotorcycle

Post by DrkAngel » Nov 25, 2011 1:40 pm

Numbers are actual monitored "use" at level cruising.
eMotorcycles were a converted "crotch rocket" and a "shrouded" homebuilt.
Both designed specifically for good aerodynamics.
Wind resistance was probably less than that of a typical ebiker, pedaling?
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Re: Watts = MPH eMotorcycle

Post by noahpodolefsky » Nov 26, 2011 2:51 am

That graph is from the Schultz engineering bike with a dustbin fairing. It's real data, and it's correct (note that power is on the x-axis, speed on the y-axis...that's why the graph increases to the right instead of upward).

A regular bike without a fairing (or even a sportbike) will be somewhat less, probably by about 15-20%.

What jonescg said on power numbers is spot on, if you're comparing peak power. Just keep in mind that an ICE bike has a different power curve and a transmission...very different power delivery.

(and just to be picky, the Etek was made by Briggs & Stratton :) )
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Re: Watts = MPH eMotorcycle

Post by DrkAngel » Nov 26, 2011 8:13 am

My Bad ...
Still waiting on delivery of Etek ...
Been doing B&D power pack Nicd to Lithium upgrades all week ... sorry ...
Rechecked motor stats:
Efficiency upgraded from 84 to 88% (peak)
Weight lowered from 22 to 21lb.
B&S brand credited.

Etek Motor - by Briggs and Stratton

Image

Alternate description:

Etek Permanent Magnet "Pancake" Design , 20% lighter than standard series wound motors.

20 HP Peak, 8 HP continuous
Voltage........................50 VDC
Max Nonload Current.....6 AMP
Max Nonload Speed........3600 RPM
MIN Nonload Speed.........3300 RPM
Min Speed at 160 Lbln.....3200 RPM
Max Current at 160 Lbln...150 AMPS
Shaft Size .......................7/8" Dia. 2-1/4" long
Voltage Constant: 72 RPM per volt
Torque Constant: 1.14 in lbs/Amp
Continuous Current: 300 A 30 Sec.
Weight: 20.8 lbs
Motor Diameter: 7.91"
Motor Length: 5.64"
Shaft Keyway: 3/16" and runs the full length of the shaft
The Shaft has a threaded tap on the end.


FEATURES BENEFITS
50% smaller and 20% lighter (only 22.3 lbs.) than a competitive electric motor - high power to weight ratio.
Lightweight aluminum frame. Less turf compaction.
Provides DC (battery) electric power. Quiet, reliable power source.
Provides a maximum of 20 HP, 8 HP continuous.
“What makes the Etek motor technology unique is the use of copper bus bars rather than steel and copper wire as the basic building block of the armature. These copper bus bars are stamped, bent, coated and assembled into a thin rotary disk. End clips connect the tips of the bus bars to shorten the air gap between the magnets. Steel is inserted between the bus bars to shorten the air gap between the magnets. One of the most unique characteristics of the motor is that simply machining the edges of the copper bars produces the commutator. Since commutator is built in, there is no need for a separate assembly. The motor uses neodymium magnet technology.

The resulting motor construction is what conventional technologists would describe as a wave wound axial air gap brushed DC motor.Possibly one of the most significant performance features of the Etek motor is efficiency. While demonstrating high efficiencies under no or small loads, conventional DC motors experience a dramatic drop in efficiency (as low as 70 percent are not uncommon) as they are loaded down. This simply means that nearly a third of the valuable energy in the on-board batteries is going toward producing heat and other unwanted power rather than motion. The Etek motor technology does not use battery energy to produce its electric field in the stator. This is done by the neodymium permanent magnets. The use of copper bus bars gives the motor an extremely low internal resistance, which results in greatly reduced losses.”
Attachments
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Re: Watts = MPH eMotorcycle

Post by noahpodolefsky » Nov 26, 2011 3:23 pm

No worries. That little Etek is a great motor. [edit] Going 65 mph contiunous with that motor might be pushing it...maybe with a small and light bike (on flat ground and no wind). You'll probably need to gear it kinda high. If you have good airflow to keep it cool, might be OK.

Building an 8 kWh battery is a different story. That's a pretty big pack, probably over 200 lb of battery even in lithium. Might need to set your range expectations a bit lower.
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Re: Watts = MPH eMotorcycle

Post by Njay » Nov 26, 2011 4:12 pm

150A continuous is probably marketing BS, that motor should be more like 100-125A continuous. Unless you actively cool it very well, of course. Briggs licensed the technology from Cedric Lynch and manufactured it, so it's same base tech as LEMCOs and Agnis. I have one, it's waiting to convert an Aprilia RS 125. The motor has 1,11 lb.in/A torque (0,129 N.m/A). My gearing will be something around 1:3.91 (43 tooth behind, 11 at the motor) for ~58Mph (92Km/h) top speed.
I did some data collection on conversions using the same motor or very similar and arrived at the worst case consumption of 75Wh/Km, with minimum around 40Wh/Km.

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Re: Watts = MPH eMotorcycle

Post by DrkAngel » Nov 26, 2011 6:11 pm

noahpodolefsky wrote: Building an 8 kWh battery is a different story. That's a pretty big pack, probably over 200 lb of battery even in lithium. Might need to set your range expectations a bit lower.
My Lithium Ion Cobalt Polymer cells:
120 - 3.7V, 2160mAh LiPo cells
3.7 x 2.16 x 120 = 959.04
12s10p = 959.04Wh = .96kWh
Weight = 11lb 9oz, including tinned copper braid connecting all "posts"
x8 = 92lb 8oz + 5% for true 8kWh ~97lb

Other "builds" using these same cells Laptop-LiPo Recycled cells

Remember ... Lithium Cobalt cells have double the energy density - 1/2 the weight-size, of LiFePO4.
Last edited by DrkAngel on Nov 26, 2011 6:24 pm, edited 1 time in total.
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Re: Watts = MPH eMotorcycle

Post by noahpodolefsky » Nov 26, 2011 6:23 pm

I see - didn't realize you were using li-po. Are you sure recycled batteries have the true original capacity?

Either way, that's 960 cells to wire together and keep balanced. Have fun :)
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Re: Watts = MPH eMotorcycle

Post by DrkAngel » Nov 26, 2011 7:33 pm

noahpodolefsky wrote:I see - didn't realize you were using li-po. Are you sure recycled batteries have the true original capacity?

Either way, that's 960 cells to wire together and keep balanced. Have fun :)
I have the best 8kWh set aside. They come in handy 11.1V, 4.32Ah(paired) 6 packs.
Charged 5 months ago and they still show 4 of 5 power level leds. (a good sign)

Will build as:
2 Banks of 4 packs. 44.4V (49.2V - optimal charge of 4.1V)
Each pack 3s40p 11.1V 86.4Ah
4 rows of 20 tabs per pack (cells are paired) - just unroll the tinned copper braid and solder it down
Can always add 2 more packs for 55.5V - expressway speed

Balancing:
All 6packs will be freshly charged, then subjected to a measured-timed draw, final voltage should indicate, % of new, condition.
1 - best bank ... 1 - lesser bank.
After assembly I will fully balance 1 time, discharge to recommended depth, compare and note segments voltages, recharge, add cell-cells to any weak segment, discharge-repeat.
Until "perfected" pack will be inspected at ""full" and "empty".
I don't believe "Traditional" balancing to be necessary, tho I will monitor each cell-segment with an led volt meter low-voltage alarm.
If not abused, these type LiPo cells seem to gradually deteriorate at a steady, very predictable rate.
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Re: Watts = MPH eMotorcycle

Post by noahpodolefsky » Nov 26, 2011 8:38 pm

Sounds like a good plan.

You probably know voltage isn't a good indicator of SOC, you need to measure current and count Ah.

As far as balancing, I think you really need to keep an eye on them and balance every few cycles. Especially with a pack of severely unmatched cells. Up to you, of course.

I'll be interested how it turns out.
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Re: Watts = MPH eMotorcycle

Post by DrkAngel » Nov 26, 2011 11:24 pm

noahpodolefsky wrote:Sounds like a good plan.

You probably know voltage isn't a good indicator of SOC, you need to measure current and count Ah.

As far as balancing, I think you really need to keep an eye on them and balance every few cycles. Especially with a pack of severely unmatched cells. Up to you, of course.

I'll be interested how it turns out.
Beginning voltage - identical (I bulk balance, usually 12 - 6 packs)
Drain 1AH, or 2 - identical (4 iMax's with 1 Ah discharge, can even program discharge time 1hr, or 2 or ...)
Packs with same post-discharge voltages, should be nicely matched ...
160 - 6 packs /4 iMax = 40 hr of testing, swap packs and mark voltage every hour.
An easy week at my computer shop, on a side table, as I play solitaire ... waiting for virus scans to run.

These particular cells will be charged to a lowly 4.1V and discharged to a gentle 3.7V.
Determined as optimal by my mAh/100th V discharge testing.
Leaving massive safety margins, and extending life.
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Re: Watts = MPH eMotorcycle

Post by noahpodolefsky » Nov 27, 2011 12:13 am

Not trying to be argumentative, and maybe I'm missing something, but seems like you're still using voltage as an indicator. You need to match by internal resistance and capacity...a single voltage reading won't give you a good measure of either of those.

Voltage is pretty constant through discharge. So you can have two cells, drain 1 Ah, end up with one at 50% DOD, other at 80%. Both read, say, 3.8 V. Same voltage but not matched cells.

What happens then is as you pull more Ah, the weak cell goes off a cliff very quickly. Strong cells drive it do death. (And since these are lipo, possible fire)

Keeping it above 3.7 V / cell will help...but you don't know what each cell is doing if you only measure the pack. Also, if using conservative high and low voltage, you're not getting the full capacity.

Again, not trying to be negative, just explaining my thinking. Maybe you've got all this figured out
and I'm just not following.
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Re: Watts = MPH eMotorcycle

Post by DrkAngel » Nov 27, 2011 1:19 am

noahpodolefsky wrote:Not trying to be argumentative, and maybe I'm missing something, but seems like you're still using voltage as an indicator. You need to match by internal resistance and capacity...a single voltage reading won't give you a good measure of either of those.

Voltage is pretty constant through discharge. So you can have two cells, drain 1 Ah, end up with one at 50% DOD, other at 80%. Both read, say, 3.8 V. Same voltage but not matched cells.
"Voltage is pretty constant through discharge", you must be looking at those manufacturers discharge graphs.
Really, you should look at my discharge charts, a whole new world of information! Shocking is the difference in, at what voltage the most mAh is stored, between different brands..
Voltage seems to be a good indicator, especially if you measure in 100ths volt.
Lesser capacity cells, of same composition, lose mAh/100th V evenly (percentage wise), across the entire range of usable voltage, not all at the lower voltage. In fact, it seems that weaker cells lose a very noticeable amount, right at peak voltage. "Fade down" from full charge, is a great indicator of overall capacity.
noahpodolefsky wrote:What happens then is as you pull more Ah, the weak cell goes off a cliff very quickly. Strong cells drive it do death. (And since these are lipo, possible fire)
Each cell is pair bonded to 39 others. Total failure might reduce capacity by 2.5%. As noted earlier, all 3.7V banks of cells are, individually, voltage monitored, with additional, programmable, low voltage alarm, for each 3.7V bank.
4 modules, each monitoring 6s40p.
noahpodolefsky wrote:Keeping it above 3.7 V / cell will help...but you don't know what each cell is doing if you only measure the pack. Also, if using conservative high and low voltage, you're not getting the full capacity.
Recheck my mAh/100th V discharge testing. graph, I think you'll see that my "conservative high and low voltages" use nearly 90% of full capacity. Providing possibly, double the number of usable cycles ...
Last edited by DrkAngel on Nov 27, 2011 9:49 am, edited 1 time in total.
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Re: Watts = MPH eMotorcycle

Post by noahpodolefsky » Nov 27, 2011 2:38 am

The way you're taking data is interesting, but I think it's seriously misleading you. I'll just say it one more time, voltage is *not* a good indicator of capacity. mAh per 100th V also doesn't tell you much useful, because when you're actually operating a motor you're almost never right at that peak voltage. The voltage goes all over the place under different loads.

Anyway, you seem to have everything figured out. Just be safe.
-Noah

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Re: Watts = MPH eMotorcycle

Post by DrkAngel » Nov 27, 2011 3:32 am

noahpodolefsky wrote:The way you're taking data is interesting, but I think it's seriously misleading you. I'll just say it one more time, voltage is *not* a good indicator of capacity. mAh per 100th V also doesn't tell you much useful, because when you're actually operating a motor you're almost never right at that peak voltage. The voltage goes all over the place under different loads.

Anyway, you seem to have everything figured out. Just be safe.
Voltage is a great indicator ... at zero throttle.
All my graphs were made at minimal discharge rates (.2C), specifically, to minimize the distortion of "voltage sag".
Just have to coast for a couple seconds, to get good reading.

172.8Ah battery, even with motor at full continuous capacity, 150 amps, is drawing less than 1C, ... minimal voltage sag.
Less than .5C cruising at 55 MPH.
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noahpodolefsky
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Re: Watts = MPH eMotorcycle

Post by noahpodolefsky » Nov 27, 2011 12:38 pm

DrkAngel wrote: Voltage is a great indicator ... at zero throttle.
All my graphs were made at minimal discharge rates (.2C), specifically, to minimize the distortion of "voltage sag".
Just have to coast for a couple seconds, to get good reading.
Try this - take two equal cells both fully charged. Discharge one 500 mAh, the other 1000 mAh. Now let them rest for a minute or two, then measure the voltage.

Let me know what you get.
-Noah

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Re: Watts = MPH eMotorcycle

Post by TylerDurden » Nov 27, 2011 12:50 pm

DrkAngel wrote:Voltage is a great indicator ... at zero throttle.
Maybe with Pb.

Lithium variants have that wonderful flat discharge curve. The flatter the curve, the less useful voltage is as an indicator of remaining capacity.
Have a Nice Day,

TD

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Re: Watts = MPH eMotorcycle

Post by DrkAngel » Nov 27, 2011 1:41 pm

EZip with 25.9V LiPo 26Ah.
Volt meter, attached to my throttle "level" leds, works nicely.
Integrated with my mAh/100th V map, gives me a very accurate "fuel level" meter.
As referenced, with my trip odometer.

EZip 26Ah pack was built from the "defective - non-perfect" packs, the rejects.

Reject build:
Has non-balanced charged 50+ times and still maintained within 100th V equalized voltages.
Finally it developed 1 weak bank - tacking in 1 extra cell brought everything back, towards perfect.
After 40 mile leg of 100mile run, 26Ah rated, took 24Ah+, (iMax B8), to recharge, even though I used my "conservative high and low voltages".

Saved the best packs for my eMortorcycle and "44 Magnum" builds.
So ... yes, I am reasonably confident that my acquired LiPo cells are in good condition, near oem capacity.
A little learning is a dangerous thing;
Drink deep, or taste not the Pierian spring:
There, shallow draughts intoxicate the brain,
And drinking largely, sobers us again.

I enjoy enlightening ... and enlivening the spirit of the innovators.

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Re: Watts = MPH eMotorcycle

Post by DrkAngel » Nov 27, 2011 1:50 pm

TylerDurden wrote:
DrkAngel wrote:Voltage is a great indicator ... at zero throttle.
Maybe with Pb.

Lithium variants have that wonderful flat discharge curve. The flatter the curve, the less useful voltage is as an indicator of remaining capacity.
I prefer a more detailed representation, than a "flat curve"!
Map of the LiPo I am using:

Image

As should be obvious from the graph, voltage can, clearly, represent capacity!

I interpret this mapped cell as being usable from 4.1V to 3.7V, with, to 3.6V being an emergency, "limp home".

Judging, by area(=mAh) of, my rated, usable:
4.1V = 100%
3.98V = 75%
3.9V = 50%
3.83V = 25%
3.7V = Empty - with emergency reserve

Applicable only to these specific cells!
Different brands-formulations map with extreme variance.
WinForce 5700mAh RC LiPo looks wildly different.
A little learning is a dangerous thing;
Drink deep, or taste not the Pierian spring:
There, shallow draughts intoxicate the brain,
And drinking largely, sobers us again.

I enjoy enlightening ... and enlivening the spirit of the innovators.

New & Improved - Acronym Definitions

Index - Homemade Battery Packs - Updated - November 2015

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