View Single Post
Old 02-14-2012, 10:00 PM   #54
_cy_ OP
Beastly Adventurer
Joined: Sep 2011
Location: Tulsa, Oklahoma
Oddometer: 4,974
Originally Posted by 02TAC View Post
I actually decided to go with LiFe from experience with lithium batteries in my RC toys. Charger wise, as you can see in the previous photo, I use a quality balance charger that not only chargers the battery, but equalizes all the cells at the same time. I alos think Life and similar batteries are a good way to go with the weight savings and higher outputs. For most folks the cold weather issues won't be either as few of use ride when ti is really cold.

That said, my outdoor power equipment is staying lead/acid.
glazed eyeball alert....

soooo glad you weight in with your RC experience. a few post back I promised to cover differences between prismatic cells and cylindrical cells. each has it's advantages and drawbacks.

by the way if anyone finds anything that needs correction or clarification. please let me know. all this is from memory. which is far from infallible

no one runs li-ion packs harder than the RC crowd. that's where one finds bleeding edge technologies for chargers and li-ion packs.

RC folks were among the first to rip open Dewalt battery packs for their A123 26650 cylindrical batteries. technology advances/matures fastest for the most common cells. just as 18650 li-ion (lithium cobalt) had their time as the most advanced li-ion batteries available. until lithium cobalt batteries' more unstable characteristics caused way too many fires/explosions in consumer devices. prompting adoption of A123 or lithium iron phosphate chemistry. which along with lower energy density. also were much cheaper to manufacture. more importantly was very stable.

upon reaching full charge at 3.6v all of the lithium is transferred the anode. what this means is lithium iron phosphate batteries can still overheat, but will not go into thermal runaway and explode.

A123 cylindrical cells has the largest production numbers and contain most refinements of any battery of this type chemistry.

now let's switch gears to battery construction types. cylindrical cells are obviously round and metal clad. advantage is metal exterior protects internals for a very robust battery. very important for power tools. drawback is metal cladding and support structure could make up 50%+ total volume of cell. another very important factor is size of cells.

A123 26mm x 650mm or 26650 cells are the most common size. a D size li-ion cylindrical cell has been available for years but are less common. which leads to one of the most important factors when putting together higher amp hour batteries. cylindrical cells has to be wired in parallel to achieve high amp hour ratings. the more cells contained within a single battery, the more important balancing your cells become.

next up are prismatic cells ... which are commonly called li-po or lithium polymer packs. li-po packs can be made into virtually any shape. the most common shape is flat thin rectangular batteries. which are then stacked, making for a very space efficient package.

drawback is li-po packs have no external protection, so are quite fragile. a very real concern for li-po packs made from lithium cobalt chemistry. drive a nail through multiples packs... probably will get smoke, fire and an explosion.

fast forward a few years... now li-po are finally available in more stable lithium iron phosphate chemistry... think iphone 4 batteries and virtually all laptop mfg have switched to A123 chemistry cells.

note li-ion cobalt will be with us for many more years due to electronic devices with matching 3.7v requirements. greatest danger with lithium cobalt occurs during charging. battery packs from name brand electronics with lithium cobalt will usually contain protection circuitry.

due to higher energy densities and voltage requirements of existing gear. Lots of RC folks are still flying with lithium cobalt li-po packs. generally they are using sophisticated chargers with balancing circuits, charging at limits their li-po packs can withstand.

prismatic cells contain the same chemistry as cylindrical cells with one important different. Size... prismatic cells due to lack of external shell contain more chemistry within it's total bulk.

what this means is prismatic cells can be made with much higher amp hour ratings. some high as 100 amp hour per cell at 3.6v. one still needs 4x 3.6v prismatic cells to make a 12v battery. but a very high amp hour battery can be constructed with only 4 prismatic cells. less cells means it's easier to keep battery cells balanced. having balanced cells is no less important with a four cell pack, just easier to maintain balance with less cells.

here's a pic of A123 20amp hour prismatic cell. four of these would make a NICE motorcycle battery. main drawback would be costs...

_cy_ screwed with this post 02-16-2012 at 05:53 AM
_cy_ is offline   Reply With Quote