Friday, June 8, 2018

Batteries [buy one or build one]


Without pedaling I use 47Wh/mile with about 400lbs total combined weight with my MtGoat Cycletruck [plan for 52Wh/Mile x 10m round trip = at least 500Wh per trip]. But if you can use your legs and keep it down to only 300lbs total combined weight 17 to 27Wh/mi is possible. But you should always plan for the worst conditions.

  • My motor will handle up through 72v nominal. [more voltage equals more Watt~hours! and More RPM per Ah~ But no increase in thrust]
  • And why not use a slightly higher capacity battery? Lower discharge rate? Steeper price-increase curve?
  • 14p x 2.9a= 40.6a [maximum output] output for each parallel pack
  •  at 60volts nominal = 224 cells = 2403.52Wh at 3.7volts each cell.
  • 16s x 14p x 10.73Wh per cell = 2403.52 Wh [at 3.7v]
  • Calculate “Ah” (amp-hours): Volts ÷ Watt-hours = Amp-hours [2403.52Wh {divide by} 60v = 40 Ah Amp-hour pack]
  • My battery compartment is a tight 11 inches wide by 7 inches by 10 inches tall = 224 cells. 231 cells would fit perfectly so I can use the 224cells, but I need to measure the holders. I think the holders are less than one square inch per cell. So there will be room to breathe. 
battery size for large cycle truck

                                    made by     EM3EV.COM

                          Battery life calculator

Calculate how many cells needed

voltage x amphours = available watt hours 
watt hours needed divided by available per cell Wh

Term Lexicon:
Wh = one watt for one hour
Ah = one amp for one hour
20:1 = twenty to one
Wh/mile = watt hours per mile
average over 4 miles on 
steep hills, fully loaded
This is the most watt-hours per mile I have used climbing a hill with cargo. I was hauling about 500lbs [total combined weight] returning home from the food bank in the rain. Driving up a long not very steep hill, a little over a mile 97.368Watt-hours; the total trip of 3.9 miles took 262.87Wh. Yet my controller never went over 40amps.

One day I was climbing a short hill with firewood in my trailer [two arm loads] and I forgot to shift down to my lowest gear of 20:1 from my high gear of 11:1; the high gear used about 1400w from the battery, and the low gear used only about 600w at the same speed. So I am thinking that a hub motor would use far more than 1400w. But I am not sure about that.

One trip to town, averaging 10mph in about a 13:1 gear ratio [I don't like to change the rear gears because the motor's pull jolts the freehub too much. I need to remember to shift gears by pedaling only]. My round trip was 8.32miles and used 6.434Ah [320.05Wh] with a maximum amp draw of 39.72 and averaged 38.46 Watt-hours per mile. In lower gear it would be closer to 50Wh per mile.

I never expected to get the amps up that high. But after all I am moving about 400lbs around our hilly streets. So now I can honestly tell people that they should buy at least a 20Ah battery pack for a cycle-truck. And a 36Ah pack would last much longer; if you can't use more than 50% with an 80% charge [shutting down at about 39volts] I have to charge to 90% to make a round trip because of the voltage drop when accellerating can be up around 5volts lower than the actual voltage left in the pack.

One day my pack's BMS shut down the power when I was climbing a short but steep hill in my lowest gear and trying to move too fast; drawing more power from the battery than was possible from the electrons left in it. When I “rebooted” by 'dis'- and 're'-conecting the pack, the voltage was still about 50v. I should have been watching the volt meter to keep it above the cut-off point.

To make a Lithium-ion battery pack last as long as it can, you really need to charge to only 80% because of the crystals that grow and short circuit the cells [see the video]. When you get home do not charge your batteries. Wait untill you are going to use it. I charge to 80% the night before, then up to 90% just before leaving on my trip to town. The last 10% takes so long to charge that it is not worth the damage. Lead acid batterys can be charged to “full” and kept there.

An over-sozed pack will last much longer that one just big enough to get you around because the pack has extra capacity to loose. A pack's total usable capcity will drop over a few years until you do not have enough capacity to power you full trip.

You can get much better mileage than I can if you use your legs. My knees are wiped out with arthris. 

[for MtGoat CycleTruckers with single gear systems]

With a higher voltage the RPM goes up at the same wattage you are using now. But what happens when trying to maintain the same slow speed? The good side effects are: less amps to climb the same hill in the same low gear, and less heat produced because the amps make friction heat in the wires.

A higher voltage is needed to compensate for a single low gear reduction needed to climb steep hills with heavy cargo. 72v is a much better voltage for hill climbing. And the battery can give more mileage at the usual cruising speeds, just because your vehicle will consume less amperage.

So make sure the controller can use a higher voltage. The large Cyclone motors can definitely do it. Then electronic controlling of the speed is needed to keep your ass out of trouble.

How to calculate "C" rates

The C rate is a nothing but gibberish. All you need to do is find out how much Amp-hours or Watt-hours are needed, then double or triple that for the actual size needed;
maximum Watt-hours for my 10mile round trip: 683.5 Wh [so I need at least twice this to keep from stressing]

operating current IB = C/ capacity/3 minutes = 25c? Sounds like gibberish to me.

Essential knowledge about lithium-ion batterys [click it]

The INR prefix is generally regarded as designating that a cell chemistry is “NCA” or Nickel Cobalt Aluminum. This is what Tesla uses (but…there are also several variations on the NCA recipe). The NCR prefix is the “NCM” chemistry, Nickel Cobalt Manganese. Listed below are the recently popular high-capacity cells on the market.
10A, 3.5-Ah, NCR18650GA Panasonic / Sanyo
10A, 3.5-Ah, INR1865035E Samsung

10A, 3.5-Ah, INR18650MJ1 LG

keep state of charge in a band
of around 20% to 80% whenever
possible for max cycle life.

Lithium-ion batteries do not like to be too full or too empty. So when calculating how many amp hours you need under stand that you need at least twice the total capacity of the pack. And due to the fact that these battery's capacity will go down over the life span, you should start with at least four times the amp hours that you need what you need.

You need a programmable 
controller to change the cut of voltage.
30% of 58.8v = 17.64v but
 my controller cuts off at about 39v which is 66.326% of 58.8v
yet 39v is 30.7% of 78.8v

The only way to compare two different voltages is to simulate them at the same wattage needed for the some job. Or simulate for the same grade etc. Then look at the amperage to see if the motor and batteries will stay cool enough.

You could play around with different amperage settings, but be sure to check the load line and the grade.

Yes the larger battery will run cooler as its 7P where the 15.5ah is 5p

How to balance all the cells in a pack?
To build a pack of 16s [in series] without the danger of over charging some of the cells; connect all the parallel cells together as one unit; then a BMS for 52v will have only 12 balancing wires plus the positive and negative ends [they count these as balance wires also, so there are 14 wires].

Charging at 5 amps is almost too fast for a 10 Amp-hour battery, but...not so fast for a 20 Amp-hour battery. When you charge your battery fast, all the time it will greatly reduce your batteries life expectancy. We recommend you stick to slow charging (4 hours or more) or go with a charger that can switch between fast and slow charges like the Luna Charger.

This is the best page to read about types of batteries: "Typesof Lithium-ion batteries

Charge and discharge rate: “Basicunderstanding of lithium based batteries”....if you are climbing a steep hill watch your amp meter. The controller will shut the power down, and you will need to reboot, by unplugging and reconnecting the battery. Knowing your pack's “C”rate [max amp discharge] can help you not over power your battery.

I think it would be best to just slow down when climbing in a lower gear. Then you could easily save your battery power. And using a higher over all voltage [like a 52v or 60v] can help keep the amps lower. And having a 32Amp-hour battery [or bigger] would help a lot; it takes a lot of power to climb steep hills with 450lbs [or more] total combined weight.

Acceleration and voltage 

If you don't want to spend a bunch of money on a CycleAnalyst or a cheaper meter for your e bike, just get an accelerator that has a voltmeter. Watching the voltage can tell you how much power you are using and how much you have left. And most importantly you want to keep the voltage above the cut-off point; it drops 5 or more volts when accelerating so a light touch can keep your vehicle from shutting down.

How to calculate cells needed for pack
LiFePo4 26650 cells (3300 mAh = 3.3Amp hours) x 3.2volts per cell = 10.56Ah [but the sellers say it's only good for 10Ah].... 2000 Watt hours ÷ 10Wh cells = 200 [12 p {in perallel} x 16s {in series} = 192 cells] x 6.75@ = $1296 [or 13p x 16cells = 208 cells x $6.75 = $1404]........ [16 in series = 51.2 volts nominal or 59.2v full]

These 26650 cells will need a much larger space, like a box that can fit under the rear rack or box. And they last only little bit longer than the Samsung 29E cells? At around 2000 cycles. But you don't need to fuse each cell. But there is avast difeance between cells, so ask at CandlePower forum.

The controller should turn the The 29E pack off at 3 volts per cell 14 x 3 = 42volts. [Or at 2.5v = 35v / and 14 cells x 4.1v {90%} = 57.4v or 14 x 4volts {80%?) = 56volts]

But the LiFePo4 pack should turn off at 2.5v per cell?? x 16 cells = 40 volts and I think that the only way to make them last longer is to charge to 80% or 90% only.

A high voltage with lower gears are the ideal configuration for a MtGoat Cycletruck. 72 volts will give you more speed [like up to 8 or 10mph] at the gear that drives at 5mph on my steepest hill with 52 volts. But if you use an even lower gear at 72volts you will have more hill climbing torque at that same 5mph; because of the increased amps. 

Calculating watt-hours and milage

The right way to build a battery?:

choosing a battery fuse wire size

Best way to solder?:

understanding batteries

"For a given torque and speed you'll need the same phase current through the motor regardless of whether or not you have a low voltage or a high voltage pack. The high voltage battery would have the potential to climb a hill at higher speeds if it is not phase current limited by the controller.

If you want to make a given Permanent Magnet motor [brushless] spin faster, you can either run it at a higher voltage, or keep the voltage the same and use a faster motor winding with fewer turns. The former approach will have your input electrical power at a higher voltage and lower current, while the latter would be at a lower voltage and higher current, but the total power (volts * amps) would be the same, as would the motor efficiency, heating, etc. However, the motor controller and external wiring can get hotter with the fast wind at lower voltage and higher current, unless you appropriately increase the wire gauge and mosfet resistance.

It takes power to climb hills, regardless of whether that is at a low voltage and high current or a high voltage and low current.

Battery amps has little to do with the amps actually flowing through a motor which is your phase current, and it's the phase amps responsible for controller heating and the motor heating. A lot of people fail to recognize this.

The motor controller is just a step down DC-DC converter, it can take a higher voltage battery and step that down to a lower voltage that is presented to the motor, and increase the current by the same proportion. So the controller can take 48V and 10A from your battery, and convert that into 24V at 20A flowing through the motor. That's exactly what a motor controller does, half throttle means that the motor is seeing only half the voltage of the battery, but in this state the amps flowing through the motor is double the current that you would see on the Cycle Analyst or other ammeter."

BMS / Battery

I've developed a super simple formula for finding a person's ideal battery size. It's hard to say how far a person will go per mile on each amp hour, how much pedaling they do, wind, rate of acceleration, bicycle, weight and so on, play a huge role in all of this. However, once you know your ideal battery size, multiply it by .43 and add that to the battery. So if 20ah is likely to get you to all the places you imagine going, multiply by .43 and add that number to the original number. So the math goes 20 times .43 is 8.6, 8.6 plus 20 is 28.6. Seeing as how there aren't too many 28.6 batteries, you'd round to 30ah. So you'd have a 30ah battery, this is part of the battery life extending magic occurs. I assume a tool like cycle-analyst would help with this, as I think it measures the consumed AH on the run. Multiply 30 by .7 and that will give you 70% of 30 or 21. Consume no more than 21ah and you'd be set, 21 would be your life extending level of discharge. You could go deeper, and slightly decrease the battery life if you really needed to and it wouldn't destroy the battery like discharging the battery to the dreaded 'lvc'. I think the reason for a123s greater lifespan (if that is true) is because if you abuse it, it'll survive, it won't get so hot when you discharge it so rapidly, and I think it might be able to handle deeper discharge better.”

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