Lead Acid vs Lithium Ion -- Is an AH an AH?

[pediman]

I want to run the Golden 750 Watt Front Hub on a pedicab. Trying to decide whether to power with three 12V, 32AH Lead Acid batteries or a single 36V, 16AH Lithium Ion battery.

The weight savings of the Lithium Ion is an advantage,  however carrying 2-3 passengers the total weight load would vary from around 650-800 pounds, so the weight saving is more marginal compared with a more conventional bicycle application.

My main concern is RANGE with the two setups. From talking to others, the three 32AH Lead Batteries will last around a day working the Pedicab. Have not found anyone running the same setup with Lithium Ion.

Dealer #1  told me that AH is AH whether it be a lead acid or Lithium Ion battery. Dealer #2  told me that the Lithium Ion battery was far more efficient and that I could expect to see close to an identical range between the 32AH Lead Acid battery and the 16AH Lithium Ion battery. I also saw some materials online that seemed to support Dealer #2 and explained it in terms of DOD (depth of discharge). The example used had the Lead battery only using 50% of its amp hours while the Lithium Ion battery used 80% which would then translate into a 20AH Lithium battery having the identical range to a 32AH Lead. 0bviously one of the dealers is wrong!

One solution I suppose is to carry and xtra 16AH Lithium Ion Battery and still save weight but first I'd like to know if that is really necessary. So is an AH an AH or are we comparing apples to oranges with these two types of battery technologies? Appreciate any help in this matter on which way to go.

Richard

[GM Canada]

just curious, what would three 32 ah SLA batteries weight? It's got to be up there! I don't know allot about battery technology, I'm surprized there is no one waying in on this topic. I know of at least a few here that have used both lithium and SLA.

My opinion is an AH is an AH. It is a tool of measurement so how can it vary? Thats like the old pound of feathers and a pound of gold. Which weights more?

Gary

[Leslie]

just curious, what would three 32 ah SLA batteries weight? It's got to be up there! I don't know allot about battery technology, I'm surprized there is no one waying in on this topic. I know of at least a few here that have used both lithium and SLA.

My opinion is an AH is an AH. It is a tool of measurement so how can it vary? Thats like the old pound of feathers and a pound of gold. Which weights more?

Gary

I had four 24ah batteries and they weight 6.8kg each  27.2kg total.  

32 ah pack Ball park figure of 9.06 KGs.  That = 27.2kg each.  If I can do it then anyone can.

That said.

A 32 amp SLA should be better than the 24ah if it is designed for heavy cycle use.  But SLA's really drop in voltage as they discharge and slump with a low impedance load.

If you get 1v dropo under a 30 amp load, the drop is a result of resistance so you can multiply 30 amps by one volt/SLA. So it adds up to 90 watts down all the drain.  If you get a drop of two volts (close to flat SLA) pack youre looking at (2*3)30amps = 180 watts down the drain.

So an SLA's ah is not an LI ah at higher c rates.

A whole Lithium pack would lucky to 1.5v under a 30 amp load, and 5 mins before they give up they still keep the rail voltage higher than SLA, an LI batt almost allows full volts till the end of it capacity..

So you would be lucky to lose 45 watts at a 30 amp load during your whole trip.  Massive difference.

If you were to dicharge an SLA at one amp, in this case an AH is an AH.  SLA's are Great for standby and for solar applications that do not require high discharge amps from the pack.  But for EV's and high demand apps, the SLA is great on the first leg of the run but the SLA internal resistance builds up over the discharge cycle and much power is wasted in the battery.

The 32 ah is an ok choice if it's plates are designed for cycle use.  Buyt like me you will have a time trying to strap them onto a frame.

I must say, I went through a lot of tires, spokes and stands, and all sorts of things that make SLA's a lot more expensive than just having to replace them every 6 to 8 mths.

My EV series 24ah SLA's @50% dod per cycle lasted between 6 to 8 mths.  

32 ah SLA at 50% dod may last you a year.

I assume 60kms range @ 100% dod, in the first 4 months then declines rapidly with regular use..

My 15 ah LI packs at 50% dod 2000 cycles, at this rate 5 years.. Approx 50kms max 100% dod range.

The Li packs have a cycle lif and shelf life.  There is still not much data on how long the LI packs will go for as the tech is not old enough yet.

It depends on hopw often you ride and how far you ride.  If you ride on week ends an SLA pack this size would be ok but heavy.


If you look at every sucessful combination of elements in the array of different chemisties you will see a patern of conductive and resistive elements with qualities that are used  to promote or impede the conductive behavior,  like the conductive calcium paste they use on lead acid plates or impedanced  coating Phosphorus in LiFePo.  Either to protect an element from electrolyte damage and or provide a conductive catalyst connection through a resistive medium or lower conductive metal.  


Without going into the atomic quantun mechanics and doing a 10 forum page PHD paper on elecrtochemistry I think you get my point


This is a list of the periodic table of elements listed in order of electrical conductivity.  Least conductiove to most conductive.

CM/1 ohm

106= 10⁶

5.0E-24 10⁶/cm ohm   Sulfur   S   16
1.0E-17 10⁶/cm ohm   Phosphorus   P   15
8.0E-16 10⁶/cm ohm   Iodine   I   53
1.0E-12 10⁶/cm ohm   Boron   B   5
1.0E-12 106/cm ohm   Selenium   Se   34
2.52E-12 106/cm ohm   Silicon   Si   14
1.45E-8 106/cm ohm   Germanium   Ge   32
2.0E-6 106/cm ohm   Tellurium   Te   52
0.00061 106/cm ohm   Carbon   C   6
0.00666 106/cm ohm   Plutonium   Pu   94
0.00695 106/cm ohm   Manganese   Mn   25
0.00736 106/cm ohm   Gadolinium   Gd   64
0.00822 106/cm ohm   Neptunium   Np   93
0.00867 106/cm ohm   Bismuth   Bi   83
0.00889 106/cm ohm   Terbium   Tb   65
0.00956 106/cm ohm   Samarium   Sm   62
0.0104 106/cm ohm   Mercury   Hg   80
0.0108 106/cm ohm   Dysprosium   Dy   66
0.0112 106/cm ohm   Europium   Eu   63
0.0115 106/cm ohm   Cerium   Ce   58
0.0117 106/cm ohm   Erbium   Er   68
0.0124 106/cm ohm   Holmium   Ho   67
0.0126 106/cm ohm   Lanthanum   La   57
0.0148 106/cm ohm   Praseodymium   Pr   59
0.015 106/cm ohm   Thulium   Tm   69
0.0157 106/cm ohm   Neodymium   Nd   60
0.0166 106/cm ohm   Yttrium   Y   39
0.0177 106/cm ohm   Scandium   Sc   21
0.0185 106/cm ohm   Lutetium   Lu   71
0.0219 106/cm ohm   Polonium   Po   84
0.022 106/cm ohm   Americium   Am   95
0.0234 106/cm ohm   Titanium   Ti   22
0.0236 106/cm ohm   Zirconium   Zr   40
0.0288 106/cm ohm   Antimony   Sb   51
0.03 106/cm ohm   Francium   Fr   87
0.03 106/cm ohm   Barium   Ba   56
0.0312 106/cm ohm   Hafnium   Hf   72
0.0345 106/cm ohm   Arsenic   As   33
0.0351 106/cm ohm   Ytterbium   Yb   70
0.038 106/cm ohm   Uranium   U   92
0.0481 106/cm ohm   Lead   Pb   82
0.0489 106/cm ohm   Cesium   Cs   55
0.0489 106/cm ohm   Vanadium   V   23
0.0529 106/cm ohm   Protactinium   Pa   91
0.0542 106/cm ohm   Rhenium   Re   75
0.0617 106/cm ohm   Thallium   Tl   81
0.0653 106/cm ohm   Thorium   Th   90
0.067 106/cm ohm   Technetium   Tc   43
0.0678 106/cm ohm   Gallium   Ga   31
0.0693 106/cm ohm   Niobium   Nb   41
0.0761 106/cm ohm   Tantalum   Ta   73
0.0762 106/cm ohm   Strontium   Sr   38
0.0774 106/cm ohm   Chromium   Cr   24
0.0779 106/cm ohm   Rubidium   Rb   37
0.0917 106/cm ohm   Tin   Sn   50
0.095 106/cm ohm   Palladium   Pd   46
0.0966 106/cm ohm   Platinum   Pt   78
0.0993 106/cm ohm   Iron   Fe   26
0.108 106/cm ohm   Lithium   Li   3
0.109 106/cm ohm   Osmium   Os   76
0.116 106/cm ohm   Indium   In   49
0.137 106/cm ohm   Ruthenium   Ru   44
0.138 106/cm ohm   Cadmium   Cd   48
0.139 106/cm ohm   Potassium   K   19
0.143 106/cm ohm   Nickel   Ni   28
0.166 106/cm ohm   Zinc   Zn   30
0.172 106/cm ohm   Cobalt   Co   27
0.187 106/cm ohm   Molybdenum   Mo   42
0.189 106/cm ohm   Tungsten   W   74
0.197 106/cm ohm   Iridium   Ir   77
0.21 106/cm ohm          Sodium   Na   11
0.211 106/cm ohm   Rhodium   Rh   45
0.226 106/cm ohm   Magnesium   Mg   12
0.298 106/cm ohm   Calcium   Ca   20
0.313 106/cm ohm   Beryllium   Be   4
0.377 106/cm ohm   Aluminum   Al   13
0.452 106/cm ohm   Gold   Au   79
0.596 106/cm ohm   Copper   Cu   29
0.63 106/cm ohm           Silver          Ag   47

As you can see that LI combinations have a lower resistnace than SLA.

Li is more than half the resistance of lead.  This doesnt make it twice as better.  You judge the losses over R from zero R and this makes the comparisons between SLA and LI a ratio set from 0 ohms and to the max resistance in ohms of the SLA. And SLA varies more as previosly mentioned.

[Bikemad]

My opinion is an AH is an AH. It is a tool of measurement so how can it vary?

Unfortunately things are not quite that simple in reality, because the actual capacity of a SLA battery will vary significantly according to the amount of current being drawn from the battery.
The typically quoted capacity for a SLA battery is based on a 20 hour discharge period:

20-Hour Capacity—This is a battery’s rated 20-hour discharge rate—its C/20 rate. Every battery is rated to deliver 100 percent of its rated capacity at the C/20 rate, if discharged in 20 hours or more. If a battery is discharged at a faster rate, it will have a lower ampere-hour capacity.

SLA batteries are very efficient at delivering low power (1/20C or less), but become far less efficient when the demand for power is increased or temperatures drop.
A fully charged 12Ah SLA battery at 25 degrees C in good condition should be able to deliver 0.60Amps (12A/20) for 20 hours continuous, but if the same battery is completely discharged in one hour it will only deliver a continuous current of 7.20Amps (7.2Ah capacity not 12Ah).
If it is discharged at 12 Amps (1C) it will only last for approximately 35 minutes before it would be completely discharged, not the 60 minutes that you might expect.

If a 12Ah SLA battery is discharged at 36 Amps (3C) it will only last for approximately 10 minutes, which is equivalent to 6Ah!

A 12Ah lithium battery with a 3C discharge capability should be able to deliver the same 36 Amps of current for almost 20 minutes, and will also maintain a higher voltage throughout while doing so.

I hope this helps.

Alan
 

[Leslie]

Yes Alan, its the internal resistance of the SLA that makes it lose energy under heavy loads.

Ohms law

I²R  That will do the trick.  Just square your amps and divide by the internal resistance of the battery and this = why SLA's don't do EV apps as good as LI.

The EV SLA when hot off the charged are fantasitic.  They have little voltage drop, but its not long till you will start seeing higher voltage drops further down the road.

The cycle type SLA @ 10% at 1c dod you need to look no further for a pack.  Especially if you only ride it once a blue moon.

Haaaa!  but when we buy an ebike some say "I will only ride it once a blue moon"  That changes once we do a few trips, and then we are saying "I love the bike I want more range or speed" I want Lithium.  I wouldnt not have guessed the advantages that LI have over lead until In tried both.

Lithium packs do own the SLA..  One thing but, on a fresh EV type SLA with no BMS you can go sick on the amps for a few months then its a big .

[DirtyGinge]

on that note, im seeing voltage drops from 54.6 to 46 within 5 minutes of my fresh li-ion GM battery at full throttle...is that normal, it does recover though, slowly....

still it is -5C in the uk at the moment ??

[Leslie]

No it isnt normal.  Not even close.

My pack goes from 52v to 49.5 for my whole trips..  Icve gone for two 20 kms rides with no charge in between and still see the same drops and it pops straight back to 52v as soon as I release the throttle.

If you have a bad cell this may happen or a  ground loop in the controller or motor wasting lots of power.  Water in the controller or plugs or motor maybe.

Check everything.

[Leslie]

Once you checked everything and sure its not excessive current use, try leaving you pack on the charger for three days.  Or better rig it up to a wall timer and have it switch the charger on and off every 30 minutes for 8 hours or so.

If you have a badly balanced battery using the wall timer allows the pack to charge and when the high cells reach max capacity the charger switches off but their maybe some lower cells in the bank.  When the wall timer switches off the charger, the BMS bleeds the high cells down to allow the bulk charge mode to kick in when the wall timer switches the charger back on.

On off on off.  Even take it for a 10 minute rides and hook it on the charger with wall timer,  Cycle any of the low cells up and allow the BMS time to bleed the high cells.

This may take days to get right in some cases. But if the cells are good it wont need to be done again.  An you will see the volts hold stronger.

[Leslie]

In my signature you see max amps and min volts.

I was drawing 52 amps and it read 49.7 then after riding it 20 kms or so that min volts went down a little bit at a time to 49.1.  Thats at 50 amps on a pack designed to do no more than 30 amps.


I also was going through a SSR relay and a 50 amps BMS shunt.  So you prolly get those volts min up a few points with out the SSR relay switch.

[Bikemad]

still it is -5C in the uk at the moment ??

Paul, -5°C should not be a problem for those batteries as it is still well within their recommended operating range:

Operating temperature
Charging 0 to 45°C
Discharging -20 to 60°C

Storage temperature
-20 to 60°C
Recommended temperature for long term storage is 23±2°C

Although they can safely be kept and used in temperatures as low as -20°C, they should be above 0°C while charging, so it would be advisable to bring them indoors, rather than charge them in an unheated shed or outbuilding when the temperature drops below freezing.

I only used my bike once in the bitter cold last week and the initial voltage of my LiPo pack was 29.29V which dropped to a minimum recorded voltage of 27.81V (less than 1.5V drop) under full load during the 40 minute ride, and quickly returned to 28.58V at the end of the ride.

Unfortunately my fingers took a lot longer to return to anywhere near their initial temperature.

I really don't like the cold!


Alan
 

[Leslie]

Yes but a lot of folk do report lack luster performance at low temperatures.

Cold temperatures will lower the discharge capacity of Lithium Ion laptop batteries (Co based), about 20% at -10C, when discharged at C/5 (i.e. normal) [1]. If the discharge rate is high (C vs C/5) then the low temperature capacity performance seriously collapses - by 50% and more - but only for the duration of the cold temperature operation. The reason for this is the temperature sensitivity of the electrolyte conductivity. Cold temperature discharge does not notably degrade the long term, cycle lifetime of the battery.

Hot discharge does degrade the cycle life. Repeated discharge at 45 deg C versus 20C lowers the cycle life by ~30-50%. [2] A major contributor to the loss of capacity life is electrode fatigue brought on by the expansion and contraction of the electrode lattice under charge and discharge; I suspect high temperature extremes accelerate this process.

[1]Vehicle batteries use a Fe based chemistry and nano structure which is more temperature stable than laptop chemistry, but still exhibits similar temperature behaviour.
[2]Linden, Battery Handbook