Lead acid vs lipo
A lipo pack of similar capacity a comparable discharge levels will have far less weight, significantly more voltage and capacity under load. It uses approx same volume but at high power delivers more run time and a more responsive motor. As a bonus they take less energy to recharge. A difference is lipo require different, new, care procedures which must be adhered to.
Weight and volume
Lipo has a far higher energy per kg which means it makes a much lighter power pack.
Comparing Panasonic's excellent LC-XC1238AP and the EST100 50 25
Panasonic LC = 16kg 12V*38Ah = 456Wh or 1kwh/32kg of mass using to
EST100 = 45kg 52V*100Ah = 4200Wh or 1kwh/11kg of mass
Packs of similar capacity and voltage weigh:
Panasonic 48V x 114Ah = 192kg
EPS100 50V x 100Ah = 45kg i.e. ¼ the mass
Each pack is similar in volume at 68.25 litres for the Panasonic and 65.5 litres for the EPS100.
Rated vs available power
Like all lead acids deep cycle run better when used to 50% discharge level. Lipo can run to 90% discharge at lower rates for virtually their entire service life.
The Panasonic pack is limited to a continuous discharge of about 1C or 5.5kw and peaks of about 14.5kw e.g. a starting peak of ICE .
The EST100 give the normal discharge rate as 1C/100amps/5.3Kw with peaks of 8C i.e. 800amps/33.6Kw i.e. 1 sec spikes.
The standard discharge rates / depth of discharge for a long lived lead acid (50%) and lipo (80-90%) give striking results also.
Panasonic discharging at 1C=114 amps is empty at 38.4v after 35 minutes. However, 50% discharge means a practical service life and at 114 amps gives 17 minutes run time. During discharge output start at 5500w and end at 4400w
Assuming the EST 100 can give only 80% of its rated capacity before cut off; at 114 amps the EST will be empty at 42v after approx 42 minutes. During discharge output start at 6300w and end at 4800w.
More practical still supposing a boat draws 500 watts.
At 50.4v/9.92 amps discharge the Panasonic has a capacity for 689 minutes and at half discharge 345 minutes or 5hr 44min;
At low power the EST100 voltage is up too and at 51.8v/9.65 amps it now has 90% of its rated capacity available, enough for 559 minutes or 9hr 20 minutes.
At high discharge rates the lipo runs up to 2.5 times longer at an average of 10% more power; at low power it runs up to 62% longer.
These figures suggest a lipo pack with 60% of the capacity of a lead acid pack could match its run time performance in all but long term high rate output; at 15% of the mass and .
Efficiency and Maintenance
Finally lead acid uses more energy to reach an equivalent charge. Pb uses about 25% more energy than rated capacity to charge. Lipos use a couple of percent more. So lead acid uses 23% more energy than the same capacity lipo. So the Pana pack takes 6840wh to charge and the ETS about 6100wh.
The above figures suggest for the same voltage a lipo pack 60% of the capacity of a lead acid, in this case 70Ah, would safety deliver the performance of a 114Ah lead acid at a mere 15% of the mass. 60% of the charge costs and 40% less space. Sounds better the smaller the boat.
Add to this the lipos mentioned come with a charging system which manages the cells full time so balance between cells does not become an issue and a warning system if it does. Lead acids do not have this safety / maintenance feature.
An then...lipos will not tolerate screw ups in charging. Go over 4.25v and the battery dies; discharge below 2.7v per cell and it dies; leave them fully charged for 3 months and they will suffer at least 10% permanent power and capacity loss; leave them in hot storage and they will age faster losing up to 10% capacity per year.
Or you can keep the cool and let the battery management do its job. Also charge to only 95% of capacity and you will markedly extend the life of the pack and avoid even the remotest over charging risks.
Andrew Gilchrist
fastelectrics.com
----- Original Message -----
From: Bill Heintz [mailto:bheintz@wans.net]
To: electricboats@yahoogroups.com
Sent: Sat, 28 Jan 2012 07:47:51 -0500
Subject: Re: [Electric Boats] Re: Marine Li-Po Batteries 51.8Vdc 100-200 Ah
On Jan 26, 2012, at 09:44, martin demers wrote:
> I would like to know what is the advantage with Li -po batteries in
> boats
A very good question Martin. [and I'm not sure I am qualified to
answer ;)]
I chose AGM (lead acid) batteries for my boat for pragmatic reasons:
I'm not a battery expert, and where I hope to travel, I don't suppose
I will find a whole lot. AGM's were a smaller initial investment, it
is easier to charge, and [I think] I understand the chemistry of it
enough to charge them properly and keep them sufficiently maintained.
If I travel and need a replacement, I can quickly get a replacement.
Until my wallet starts to get too heavy I will probably stick with
lead acid.
On oversimplified comparison . . .
Lead Acid: (includes flooded, SLA, VRLA, AGM, and GEL)
Advantages: cheaper, proven technology, easy to replace, chargers are
readily available, a large bank of batteries can be charged all in
series, no memory, high over-charge tolerance
Limitations: heavy (30-50 wh/kg), cannot be left in a low-discharged
condition, a deep cell battery has perhaps 300 cycles, high internal
resistance, takes a while to charge (8-16 hrs), contains Lead
Li-Polymer: (LiCoO2, LiMn2O4, LiFePO4, LiNiMnCoO2, LiNiCoAlO2, and
Li4Ti5O12 to name a few see Notes below)
Advantages: lighter (100-130 wh/kg), can be made environmentally
friendly (no Pb, Cd, or Hg), 1,000+ cycles, no memory, lowest internal
resistance of rechargeable batteries, faster charge (2-4 hrs)
Limitations: expensive, charging properly is critical, chargers are
expensive, (each cell needs to be monitored and charged individually
when charging), low over-charge tolerance, hard to find a dealer that
will sell you one suitable for a DIY-EV boat (24-48vdc boats are
either too big or too small)
In the Title Post, the battery chemistry refers to Lithium Nickel
Manganese Cobalt LiNiMnCoO2 (NMC)
Notes on Lithium Ion (Li-ion) and and Lithium Polymer (Li-po)?:
. Scientists and the media give Li-ion batteries unique names but
unless you are a scientist, this might cause confusion.
. The polymer hype of the early 2000s is still going strong, however
most users cannot distinguish between a regular Li-ion and one with
polymer architecture.
. All Li-ion polymer cells today incorporate a micro porous separator
with moisture. The correct term is "Lithium-ion Polymer" (Li-ion
polymer or Li-polymer for short.)
. Li-polymer can be build on many systems, such as Li-cobalt, NMC, Li-
phosphate and Li-manganese.
. As far the consumer is concerned, the lithium polymer is essentially
the sam as the lithium ion battery.
? - Batteries in a Portable World - Isidor Bunchmann - pp. 59-60.
See also "Battery Types" on www.BatteryUniversity.com, an up-to-date
reference for comparing different battery chemistries.
Types of Li-ion batteries: Table 2-10?
Chemical name
Material
Abbreviation
Short form
Notes
Lithium Cobalt Oxide1
Also Lithium Cobalate or lithium-ion-cobalt)
LiCoO2
(60% Co)
LCO
Li-cobalt
High capacity; for cell phone laptop, camera
Lithium
Manganese Oxide1
Also Lithium Manganate
or lithium-ion-manganese
LiMn2O4
LMO
Li-manganese, or spinel
Most safe; lower capacity than Li-cobalt but high specific power and
long life.
Power tools,
e-bikes, EV, medical, hobbyist.
Lithium
Iron Phosphate1
LiFePO4
LFP
Li-phosphate
Lithium Nickel Manganese Cobalt Oxide1,also lithium-manganese-cobalt-
oxide
LiNiMnCoO2
(10-20% Co)
NMC
NMC
Lithium Nickel Cobalt Aluminum Oxide1
LiNiCoAlO2
9% Co)
NCA
NCA
Gaining importance
in electric powertrain and grid storage
Lithium Titanate2
Li4Ti5O12
LTO
Li-titanate
Table 1: Reference names for Li-ion batteries. We will use the short
form when appropriate.
1 Cathode material 2 Anode material
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