Kokam 3200 SHD Lipo

[RC-Monster Mike]

Yes, Young, I have some heavy duty kimbroughs in stock. I can throw one in with your xl2400 if you want.

[lipomax]

Yeah, throw one in - send me the amount and I'll paypal that over to you asap!

[RC-Monster Mike]

You got it. :)

[Megazone23]

Is there a LiPo Primer out there for me to learn more about it or even batteries in general? I have no idea what you guys are talking about when you say stuff like "30C discharge" or "ordered 2s and 3s". If there were a dunce cap emote, I'd be using it right about now! lol

[RC-Monster Mike]

"2s" means two cells in series. "30c" discharge rate means 30 times the capacity of the cell (so a 3000 MAH/3AH pack that is capable of a 30c dicharge rate can safely discharge at 90 amps). "3p" means 3 cells in parallel. Now, throw away that dunce cap! :)

[lipomax]

I'll try to explain in more detail: The lithium packs that we use are called "Lithium Polymer" packs, but they're really "Lithium Ion Polymer".

Each cell is generally rectangular in shape and pretty flat. Also, each cell is 3.7 volts instead of 1.2 volts. Hence the voltages: 3.7, 7.4, 11.1, 14.8, 18.5, 22.2...

Lithium packs originally were not able to deliver the "punch" because of their high internal resistance and small sizes so in order to make a large pack, they would get several small packs and then hook them up in parallel. That's where the xSyP comes into play. The "x" is the number of cells in series (the overall voltage) and the "y" is the number of cells in parallel (to reduce internal resistance by just having a bunch of cells in parallel... also increases capacity). These days, with the larger cells in production, there really is no need to parallel cells anymore. I'm generally just running 3s, 4s, 6s, or 8s in my tc4 and emaxx. So for me, the number is simply the number of cells hooked up in series or "end to end". However, a 6 cell pack of Lithium cells is 22.2 volts vs. 7.2 volts for NiMH.

The "C" that you see all the time is the capacity. When something can be discharged at 10C continuously, that means that a pack can discharge at 10 x the overall capacity. So, a 3000 mah pack can discharge safely at 30,000 milliamps (or 30 amps) continously. You don't want to overdraw a lithium due to their explosive and somewhat fragile nature. These days, the newest generation is safely discharging at 20C rate (so a 3000 mah can discharge continuously at 60 amps). That's continuous - so an occasional peak at 100 amps for a split second shouldn't do too much to hurt it... we'll see about that soon.

The best feature of Lithium packs is their energy density. They are about 2x the energy density of NiMH so given the same weight of batteries, you'll run 2x longer. The newer generation of packs are also higher power density too now. A 20 ounce pack which is roughly equivalent to 10 sub C cells can deliver peaks of over 2000 watts!

I hope this helps. BTW, Mike, I've added just a little bit of slip to the stock slipper and got those cheapo plastic shafts... I'm gonna give it a go this afternoon.

10L, 6s, 18/66 gearing.

[RC-Monster Mike]

Thanks for the detailed explanation of Lipos, Young. And be careful with the stock slipper. Too loose and it will melt! Perhaps some rear cvds are in your future, and a better slipper! I am anxiously awaiting your test results!

[Megazone23]

Thanks for the detailed explanation -- I think I actually understand it all! :)

[lipomax]

I've done my first test run with the Kokam 3200 packs in my emaxx. Once again, 18/66 gearing, 6s and running in first gear, top speed is 35 mph (34.9 and 35.4 two ways). It gets to that speed in a HURRY too - you can't pull on the trigger - too much power. That's about right too - in theory, a 2450 rpm/volt and with 5.75 inch tires and 23.4 volts. will give that speed exactly. Voltage drop is only a couple of volts - approx 3 volts at 60 amp spikes. VERY low voltage drops!

Top speed was in excess of 50 mph, but couldn't get a good clean run. It's only 25 degrees and the tires and the suspension couldn't hook up with the ground.

After about 1000 mah, the motor was at 150 degrees, battereies at 65 degrees and the controller at 90 degrees. Keep in mind that it's 25 degrees outside so this motor is working too hard/and or not really that efficient. It used only 1000 mah after about 8 minutes of run. That should allow me to run about 20 minutes of good running in first gear. Peak amps in second gear was exceeding 100 amps while in first gear it was around 60 amps. Watts were around the 1500-1900 in second gear and 1000-1500 in first gear.


The Kokams at 6s would make an excellent battery setup for racing - however, I think a slower motor would be better and geared a bit taller. I had it going over 57000 rpm in first gear and that's just too fast. I think the 1600 KV motor would be a better racing motor for 6s. But you gotta gear it right - so instead of 18/66, I would need to gear it like 27/66 (if that's even possible) or go to a smaller pinion and lock it in second gear so top speed is around 35 mph. Should make the truck a little more controllable and everything will be a little more efficient and not as hot. Torque is really not an issue. Even geared for over 50 mph, the truck will flip backward instantly in second gear!

What graphs do you want to see? amps? watts? power?

[lipomax]

I'm coming to the conclusion that 8s is not necessary. Actually the Kokam 6s is giving out more power than the Polyquest 3100 mah 8s!!!

Then again, it's supposed to. But the polyquest has about 33% more energy density but less power density.

The polyquest 6s was noticeably less "kick", but still, WAY more than enough. 6s Kokam in second gear is not even controllable. I need to extend the chassis like 1 foot and get some super sticky tires etc.

[lipomax]

I think something's wrong with my BEC... this other servo has no power also... I think it might be the BEC - will test it soon.

[lipomax]

Well, here's am amp graph. It's in first and second gear.

[lipomax]

And here's the watts graph. BTW, this whole run was 950 mah. It's only running for about 7 minutes.

[lipomax]

That was too crowded so I went and tested again - this time only in first gear with one blip in second gear. This is for only 1 minute and used about 190 mah.

[lipomax]

150 mah per minute... based on that, I should get over 20 minutes of run. Here's the voltage graph - keep in mind this is in the middle third of the pack.