View Single Post
Old 01-23-2012, 04:34 PM   #21
_cy_ OP
Beastly Adventurer
Joined: Sep 2011
Location: Tulsa, Oklahoma
Oddometer: 5,939
Originally Posted by J117 View Post
The problem with amp hours though, continues. Some manufacturers of Lithium starting batteries, Shorai, Braile battery, and others, have chosen to differentiate between AH, and AH PBEQ. If Shorai or Braile ever makes a deep cycle application battery, then they will have to rate that battery in actual AH @ 20 Hr rate. Which, btw does not change for Lithium. There is no Peukert's law for lithium batteries. A lithium 100AH would discharge in 20 hrs at 5 amps, and 10 hours at 10 amps. But I digress. For starting motorcycles, Shorai and Braile know there are all of us persnickety BMW guys out here who want an 18 AH battery Darn it! So, they use AH PBEQ to compare their batteries to the Lead Acids we all have been using forever. The issue is that there are people who don't read the warnings, like (DONT USE ON ELECTRIC VEHICLES!!) because they figure that they have just figured out a way to power their electric tike off of a 2 pound battery. A Lithium battery that had an actual 18AH rating would weigh a lot more than 2 pounds. But, if you are just trying to start engines, and run lights while your bike is running and producing a charge, then you don't need a true 18AH. You need the equivalent to your old lead acid 18AH battery.

Moral of the story boys and girls is to use these batteries for what they were designed to do. (And when you disregard their purpose and try to run your laptop/coffeemaker/fridge/freight train off of them and it doesn't work , don't yell at their makers, go look in the mirror and have your anger management session.) A Shorai/Braile battery that is rated at 18AH PBEQ will only have an actual 6 AH inside of it in flat prismatic cells, not A123's, I have taken them apart. Granted, you can actually use 96% of that 6AH, but it will not run a 2 amp electric motor for 9 hours, it will run it for 3. And for the record, your BMW 18AH @ 10Hr rate starting battery will only run it for 3 hrs as well.
seems we have a real battery expert on board ... thanks for weighing in.

yes your comment about BMW folks wanting a real 18amp hour battery is dead on. thanks for verifying my comment about it's not possible for a real 18amp hour battery to weigh only 2lbs.

that's why a 20 amp hour lithium iron phosphate battery that weighs 6.5lbs is en-route. an external overcharge protection circuit will be used to prevent unlikely event of a battery fire. while lithium iron phosphate chemistry is extremely safe... there's several fires on record for the highly regarded and expensive A123 cells.

lithium iron phosphate batteries using prismatic cells are fairly new, so feedback is thin as yet. vs a long history of lithium polymer packs with the RC folks. NO one runs battery packs harder than the RC crowd. seems lithium poly packs are still chemistry of choice (for RC) due to higher energy density and just as important voltage compatibility with existing chargers/controllers.

which leads back to why IHMO li-ion batteries in motorcycles should have some type of protection circuit to prevent overcharge. over discharge will kill any battery... lead acid and li-ion included. just that li-ion operates on a narrow voltage range that may be different from your bike's charging system.

it's my intention to do high amp discharge tests at low temp with different chemistry. results of discharge tests with lithium iron phosphate will be especially relevant.

_cy_ screwed with this post 01-23-2012 at 05:01 PM
_cy_ is online now   Reply With Quote