Posted By East Broad Top on 05 Jan 2011 12:12 PM
.... Why does he have to bring the entire battery car in to be charged? If there's an "inherent flaw" in any of this, it's that it seems he doesn't have a "battery car" in the traditional sense of a car in which you can swap batteries in and out, but has a rolling battery pack that must be swapped out in its entirety for a new "rolling battery pack."
That's the problem I'd be looking to solve first. Choosing a particular battery chemistry would come second to that.
Later,
K
Well...see, that's another issue...where the battery is charged. One thing I think we've all learned is that it's not really safe to recharge a Li-ion battery INSIDE a car or engine. So, those choosing the Li-ion approach must remove the battery from the car/engine to charge it...preferably in an appropriate ceramic charging vessel (to contain any potential fire). Those ceraminc charging vessel's cost should be considered, like the charger cost, when considering Li-ions...or Li-Pos.
Second...charging times. Li-ions charge faster, so theoretically, you'd need fewer batteries to keep running continuously.
Third...size. Li-ions have about twice the charge density of NiMN/NiCads. Therefore, for a given weight or volume availability, you can get twice as much capacity on board...doubling run times/weight or volume.
Fourth...cost...and this is where the difference is. CR's 18v 2600 mah pack is $89. HF's equivalent capacity would be two1300 mah batteries...at $20 (they're on sale now for $9.99
http://www.harborfreight.com/18-vol...7029.html) .
Fifth...lifespan 1. We know that Li-ions have a 10x or better life span compared to NiCads when measured by number of recharges...assuming you recharge each type properly. If you use a crap charger (like that $5 one), the multiplier gets way larger. So, in the long look, even though Li-ions cost 4 times more, if you run a lot (and recharge a lot), then the Li-ion might be less expensive.
Sixth...readiness. One of the beauties of the Li-ion battery is that retain their charge after charging. NiMH/NiCads don't. So, if you have a recharged Li-ion battery that's been on the shelf for two months...it will probably power your engine just fine. That's not true for the NiMH/NiCads...after three months they're pretty dead...so they won't be "ready" for you when you want to operate.
Seventh...lifespan 2. We know that Li-ions lose about 20% of their capacity per year from internal chemistry changes. After 5 years they're dead if you store them fully charged. This is not true for NiMH/NiCad batteries. Properly charged, they last forever practically...but storing them fully charged means zip if you leave them on the shelf for months. But the devil in the details is "properly charged"...this requires a sophisticated charger...something way better than that $5 rig. I use a $100 Maha. There's some literature out there that says if you store Li-ion batteries at 80% charge, they last longer than 5 years. I just haven't found a charger that lets me automatically end charging at 80%.
In summary...if $6/ft track and $100 batteries are getting you down, those $10 batteries from HF sound like a good option to help with the finances...but I don't see em as a panacia.
