ASK Cubby, Version 04.07.2010- A Weekly Q & A Session
This week instead of posting questions that readers have submitted, I’ll be doing things a bit differently. The Big Squid RC Second Lipo Battery Shootout has been a ginormous hit, and with it’s success comes questions from those pesky message board pundits. So here’s some of the criticism off the message boards, and the reasons for why we conducted the shootout like we did.
“they (BigSquidRC) did not compare similar C rated packs”
The primary reason why we didn’t compare packs of the same “C” rating is because we tested what the companies sent us. When we approached all the battery companies we told them “look, here are our testing criteria, send us the battery that you think will do the best”. So while the C ratings of the packs are different between companies, it’s what they decided to send us (with 2 exceptions, more on that later). But to really boil it down, it doesn’t matter what the sticker on the outside of the packs says that its C rating is, as anyone can print “20C, 30C, or 80C” on their pack (and you’d be surprised how many battery sellers print whatever C rating they think will sell best on their packs, not what they were designed to do), what really matters is the end performance. It still amazes me how some consumers think the C rating printed on the outside of the pack is more important than the actual pack performance.
“we wanted to see higher discharge rates tested to see if the C ratings were true or not”
Anyone that wants to see a 30C labeled pack discharged at 30C has never done it before. LOL The reason why we didn’t do it is very self explanatory if you’ve ever done it. The packs in the shootout were mostly 2S 5000 mah packs, ranging from 20C to 40C. So lets say we wanted to do a 40C discharge, that’s a 200 amp continuous load. A 200 amp load isn’t hard to accomplish, anybody can go down to the local Pep Boys and buy a bunch of automotive headlights and 0 gauge wire. What inevitably happens is that you burn off a tab on the cell, lose connection, and party over. Packs that don’t burn off tabs skyrocket in temp and head straight for thermal runaway. For those that just “must” see what happens when you throw enormous C discharge rates on a battery pack, that will be an upcoming feature on BigSquid, but it’s really just a waste of a perfectly good battery pack. Look for the video and accompanying article in the next few weeks. 🙂
“the Zippy was actually the pack that won the price category because the Winforce pack you tested cost $50 not $7”
We get a lot of email here at BigSquid, and we got a LOT of email asking that Zippy be included in the next shootout. So we approached Zippy to send us a pack, but they did not. So we did what to magazines would be unthinkable, we bought the Zippy pack because we know how much our readers wanted to see it reviewed. After buying the Zippy, we had heard rumors of a pack that was better than Zippy but cost a third less. After a little research, we found the Winforce pack, which we also purchased because we just knew our readers wanted to see how a $7 pack would stack up. So if you think the Winforce pack really costs $50, you are looking at the wrong pack, because we’ve got the receipt for the Winforce to prove otherwise. Now we contemplated listing “in hand” prices instead of the “street” price, but that opens a huge new can of worms that include wildly varying shipping costs, taxes, and possible coupon use. In the end, it’s up to the consumer to get the best “in hand” price that they can.
“Three drivers is not enough to make an accurate driving test”
Ya know, we’d love to have had hundreds of test drivers evaluate the packs, as that would have provided more accurate results. But, let’s take into account time. Just how long would it take 3 test drivers to drive 8 packs? We had 8 ICE Chargers, so to fully charge all 8 packs only took 1 hour. So one hour charge time for 1 driver, 3 hours charge time for all 3 drivers. Now let’s say each driver drove each pack for only one full run. Let’s assume we got roughly 15 minutes of run time on each pack. For one driver that would be 2 hours of on track time, multiply that by 3 drivers, and that’s 6 hours continuous running on track. Let’s say you let the motor cool down to a standardized temp between each run (which we did, the motor started each run at 110 F), and let’s say the cool down period is only 10 minutes. For 3 drivers to run all 8 packs, that’s 24 total runs, 10 minutes between each run equals 240 minutes, right at 4 hours. At this point the test is sitting right at 13 hours, and that doesn’t include the occasional blown spur, busted shock cap, etc. So how long would it take if we’d have used 20 drivers, or 50 drivers? I don’t know, all I know is the entire battery shootout takes long enough the way it is. LOL
“driving the cars outdoors is not a good high speed test, as there are too many variables”
LOL If anyone would like to build BigSquidRC an immaculate 400 foot long indoor facility, please feel free. LOL But to be serious, the vast, Vast majority of people running high speed, or even just a basher blasting up and down the block, are doing it in worse conditions than we had during out shootout. We had a huge, pristine, freshly built, and not even open to the public highway to do our test on. We were very lucky to have such a great area to conduct our high speed runs on. We live in the real world, so we test in the real world just like an end consumer would.
“look at the voltage under load numbers compared to the top speed numbers, there should be a direct correlation there, if not then something is flawed. The voltage under load is the voltage put out when the car is running, which has a direct correlation to motor rpm and the overall vehicle speed.”
Eureka! That’s the real beauty of real world testing. The test bench says one thing, but can it really do it in the real world? Certainly the pack that got the highest top speed, the JGB pack, was putting out the highest voltage while under the load that was being supplied by the truck used in high speed testing. The JGB did not put out the highest voltage under a 30 amp continuous load on the Competition Electronics Turbo 35. We did not use an on board data recorder to find out exactly what load was being seen during the high speed tests, but whatever load it was, the JGB kicked a$$ on. If running up and down your street and kicking your neighbors butt is a priority, then the JGB should be at the top of your buying list. On the same order, the Hyperion did not win the voltage under load test, yet it handily won the on track driving test. On track driving really tests a packs ability to put out good voltage under a nearly infinite variance of loads, something that no discharge manufacture can come close to simulating at this time. Combine that with the human mind, the most powerful “computer/data recorder” known to exist in the universe, and you’ve got an ultimate test combo to simulate real world conditions, the only realm that the vast majority of buyers care about. The entire shootout is really geared towards the vast majority of users that don’t know what voltage under load even means, instead they just want to know what goes fast. There are plenty of hard core CBA heads out there, but this shootout wasn’t geared toward that minority.
“testing a 20c pack against 40c packs is like testing a 6 cylinder 2.0 litre engine against 6 cylinder 5 litre engines- pretty obvious which one is gonna develop more power”
I guess someone forgot to tell the Venom it was only a 20C pack then. Hah! But really, when you test a LOT of cells, you’ll find out that supplier A’s 20C’s might kick supplier B’s 50C packs a$$, and supplier D’s 30C packs are better than suppliers A’s 40C packs. That’s why the testing is a whole lot more important that the C rating on the side. Those that think that a 30C pack is always faster than a 20C pack haven’t tested very many battery packs.
“it didn’t sound like they had more than 10 cycles on each battery pack, would want to see how they preform after a summer of use not a few weeks of regulated testing”
I couldn’t agree more. Perhaps the most elite test of a Lipo battery is how it holds up 100 cycles down the road. But, once again, that darn time thing gets in our way. At a 1C charge rate, and 10C discharge rate, plus some cool down time between cycles, you’d be looking at 150 hours per pack for 100 cycles. We have 8 chargers, so we could do 100 cycles on all 8 in that 150 hours, but we simply don’t have that much time to sit around and monitor the packs. We are BigSquidRC, and we have a lot more testing than just batteries to do. The actual sellers of the packs should be the ones testing out to 100 cycles to ensure they are putting out reliable cells.
That’s it for this edition. Submit your questions and hate mail to cubby at BigSquidRC dot com! We do appreciate your questions, so send’em in!
YOUR Cub Reporter