The Cub Report Version VIII-X-MMVIII
First off, I would like to personally congratulate all our French readers (as if.. LOL) on their country’s SILVER medal in the men’s 4×100 swimming relay.
Experts seem not to know why ratings are way up for this years summer Olympics. Of course, if you are actually watching them at home, you know the reason, HD baby! Finally, loads and loads of great looking HD programming.
Back to what we’re here for- rc news!
MaxAmps batteries is one of the true “sleepers” in our industry. Based out of the climatic Pacific Northwest, a virtual rc industrial dead zone, they’ve gone from a young man’s dream, to selling more lithium based packs than the nearly all the “big” names combined. And, most impressively, they’ve done it without selling their souls to GP and Horizon.
This week, MA made some big waves, and in more ways than one. The first being they finally got a ROAR approval on their lithium race pack. This was not easy for MA, or at least not as easy as it was for other more mainstream companies that were already in ROAR’s “good ole’ boys” network. Regardless of the political mess behind their approval, the new MA packs are gnarly, and are rated for 35C constant discharge.
MA also introduced their new “leaded” packs- Lithium based packs that come with lead weights under the battery pack. This is something no other company has done in the industry, and it’s a great idea for a couple reasons. Lead added to the packs not only help keep your chassis balanced, but also help meet the minimum weight requirements for sanctioned racing. Props to MA for coming up with something original that can actually come in handy at the track.
Seeing as how this is an Olympic week, I’m asking BigSquidRC readers to send in their votes to “America’s Dream Olympic RC Team”. If the summer Olympics actually held rc car racing as an event, what 3 American drivers would YOU like to see representing the red, white, and blue? Shoot your replies to firstname.lastname@example.org , and I’ll post your results in next weeks Cub Report.
Btw, last weeks report was probably the most positive and “nicest” report I’ve ever done, yet it yielded the most love/hate mail. Not sure what’s up with that, but keep the emails coming, it proves that at least someone reads this drivel.
On a slightly different note, this week, there has been a lot of talk about what constitutes “C” ratings on Li-po’s, and where capacity ratings come from.
Here’s the scoop for all you lowly rc industry insider wanna-be’s.
Capacity of a lithium based pack, is typically determined at the point of origin by design perimeters. Some underpaid, goofy toothed, marble mouthed engineer in China will sit there and calculate predicted capacity based upon how he has designed the cell. This is typically way off, as much as 20% from what I’ve seen first hand, in the actual end result.
And how is end result/real world capacity tested? By discharging a cell at a 1C rate. For instance, if you are testing a 1000 mah pack, you discharge it at a 1 amp rate, and if the pack meets specification, it will put out 1000 mah. This rarely happens, so it’s really up to the end seller (the reseller/rebranders putting their stickers on the cells) to test the cells they get in, and make sure “real” capacity is listed, regardless of what their manufacture in China says it should be. The better resellers do NOT list capacity as what the manufacture tell them it will be, they list it after their own testing at a 1C discharge.
Oh and, regardless if it’s a Lithium based back, a Ni-mh, or Ni-cad, the higher the discharge rate, the less mah the pack is going to put out. Like Duh. So if you think your Joe Blow’s Battery Shack 5000 mah pack (at 1C) should still put out 5000 mah under a 100 amp load (20C), you are living in a fantasy world- put down the crack pipe, and realize that you can not dodge the rules of physics.
Some consumers are wondering where those wonderful “20C Constant Discharge” ratings come from- just how is that determined? Once again, leave it to the Cub to educate the world. Here’s the scoop. It’s determined just like the capacity is for the vast majority of resellers! Some greasy, overworked, communist China-man mathematically predicts what the maximum constant discharge current should be based on cell design.
But here’s the kicker. This “rating” isn’t one where the cells will live very many cycles, this is just a prediction of what they can theorhetically survive one time. So, if your Joe Blow’s Battery Shack 1000 mah pack is rated at 20C, it will (maybe?) survive a 20 amp discharge. But, don’t expect it to survive a 20C charge very many times without a raging chemical fire developing.
From what I’ve seen first hand in the industry, you are lucky to get 5 to 10 discharges on most cells at it’s maximum constant discharge rate (based on the ratings the overseas manufactures state on their cells), with insane discharge temps and pee poor voltage. Now, that’s not to say that some American re-badgers don’t test their cells, and adjust their stated “max continuous C ratings” accordingly, as
that will vary with each company. But as far as what I’ve seen in the industry, those are far and few between. Most just print the rating that their manufacture gives them, and now you know where the manufacture “rating” comes from.
So, here is what I’ve proposed for a long time. A standardized “maximum continuous C” discharge rating SHOULD be determined this way.
1. No “horseshoe” in discharge curve at this rating (a horseshoe looking discharge curve indicates that a given cell can not handle the load applied until it warms up enough to do so)
2. Maximum temp of 140 F under given charge rate (temps above this start entering the danger area for most common chemistry/designed Li-po cells)
3. Must maintain at least 3.2 volts per cell under this load (anything below this also nears the a danger point for most common Li-po type cells)
4. Should be able to survive this rated discharge at least 10 times without thermal runaway or catastrophic cell damage (what’s the point if it can only do it once?)
So if you are in doubt of whether a certain Li-po pack can do 20C (or 30 or 35), what do you do? Only buy from reputable battery companies with awesome customer service. Great customer service is the single most important factor when buying Li-po packs (or nearly anything for that matter)! That way, if you do have a problem, or have a pack that will not meet your performance demands, they will take
care of you.
One last note on Lithium cells this week. Because of rule changes for 2009, full size Formula One racing will be forced to partially recover energy normally wasted during braking, and use it to help accelerate the car (KERS). So what the heck does that have to do with rc? Well, the Formula One teams spend BILLIONS each year on development, and now, part of that budget will be used on making sure their Lithium packs used for this regenerative braking are the best on the planet. If an rc company can get an inside scoop on the details on the cells they are using, they are sure to blow away anything commercially available right now. Of note, the Red Bull F1 team has already had to evacuate one of their buildings due to a Lithium battery fire. But, with the budgets the F1 teams have, they will solve the inherent dangers and performance downsides. F1 racing will get further with Lithium cell development in a few months than the rc world will in decades.
Hopefully that tech shows up in the rc world sooner rather than later.
That’s it for this week folks, be sure and get your daily dose of BigSquidRC.com , support your local LHS’s and tracks, and shoot us an email with the top 3 guys on your American “Olympic RC Dream Team”!