WHY “NOT” LEAD ACID
-Hope this Article help you out
Some people might still try to stick to the fact that Lead Acid is still the way to go. For them this article will be really useful. Checkout the graph below.
Wh/kg Gravimetric Energy Density-
Weight is the biggest killer for SLA chemistry. LiFePO4 being 3 times as lighter results in e times more energy density. Chemically, Li-Po is lighter than LiFe, but due to the smaller 5Ah size of Turnigy resulting in more unused mass (plastics, metal separator sheets, Lead Solder between terminals). Thus giving the larger a123 a upper hand
Wh/Liter Volumetric Energy Density –
SLA are generally occupy 3 times more volume than Lithium Iron Phosphates (A123), and whereas Polymers (LiPo, e.g. Turnigy) Occupy 10-15% lesser volume than Phosphate.
Volume: SLA>>> LiFe>LiPo
Coupled with lower discharge rates of SLA, the Lithium Chemistries win single handedly by a factor of 4.5.
$/Wh of energy –
Mathematically, SLA wins this department by a mile. Due to its lower upfront cost, many people are fooled into purchasing it, as LiPo being 4 times more expensive, and Li-Fe being 5 times more expensive.
But in real life, the cost of SLA is much higher compared to what energy output you get.
Peukert Effect is present in SLA batteries, which means more current you draw, the lower will be the final usable capacity. For example, SLA rated at 10Ah, if discharged at 2 Amps over 5 hours will give 10Ah, but if discharged at 10Amps over an hour, the result is 8.9Amps (11% Drop). 40Amps (4C) will result in as much as 20%. For a normal automotive scenario where 10C is normal, the capacity drops around 55-60% region.
If you multiply that factor with big voltage drop under load, the result is EVEN LOWER usable energy. Thus leading to Higher operational cost.
Relative Cost -
All three chemistries have certain cycle life until they lose 20% of original capacity. SLA has the lowest cycle life. So during its very short operational period (if everything goes well), the cost is still a lot.
Higher Cycle life of LiPo results in lower cost. Even higher cycle life of Li-Fe results in Even Lower cost.
SLA exhibits the poorest cycle life. Under normal conditions (low discharge rates of under 0.25C, and charge rates of 0.1C, 25’C ambient temperature) the life of SLA is around 150 cycles.
In real life, the cycle life is MUCH lower. We have heard cases of 80 cycles at best under EV conditions.
If you open up spec sheets of A123. At 10C discharge rates, it still manages close to 2000 cycles.
LiPolymers can maintain 80% capacity after 800 cycles.
W/kg & W/L, Gravimetric and Volumetric Power density-
Due to larger volume, more weight and lower discharge rate, SLA is put to utter shame as its competitors show performance of around 20x times.
FINAL Comparison – Relative Advantage
All the points were put to the relative scale and summed up. SLA being a lowest level was chosen as the yard-stick. The A123 is the best, but yet a close competitor to LiPo Chemistry.
SLA batteries can fume and catch fire.
A123 batteries were shot at with a gun, punctured with a nail-gun, cut chainsaw, vibrated at 150G and 500Hz. It passed with flying colors.
The only drawback with LiPo (Turnigy) is that it is slightly unsafe, but not by much. If punctured, it vents gases and heats a little bit. That’s about it.
REASONS BEHIND PURCHASING A123 NOW (within the next week).
This year (2010), A123 Systems signed an agreement with Shanghai Automotive Industry Corporation(SAIC) to share their Intellectual Property. Thus giving the rights to SAIC to produce A123 batteries under their permission. But SAIC are not allowed to cell the batteries to general public. The batteries that I am talking about are the second generation 15Ah and 20Ah prismatic cells.
But a person from SAIC are selling these batteries through the backdoor to EV enthusiasts at the cheapest possible price (for 20Ah cell $2.5/Ah, for 15Ah cell $2.36).
Compared to the next best & Cheapest Li-Phosphate battery are Headways. Li-Polymer are comparatively unsafe.
HEADWAY – 10Ah
|Voltage at max C||2.6||2.1|
It is clear that it is BEST to purchase the A123 Now.
Someone might argue about Thundersky batteries, as WHY DON’T wE PURCHASE those.
Thundersky cost $1.1/Ah but have a max of 3C discharge rate.
For running the motor we need 300Amps.
So either we can use a 100Ah Thundersky cell which costs $110
or We can use a 15Ah A123 Cell which costs $37.5.
Which is ONE-THIRD the COST…
Buying A123 is actually SAVING THE DEPARTMENT SOME MONEY.
Second reason, Thundersky and Headway are known to fail. But A123 are basically fault proof.