Pack recommendation for Revo

[BrianG]

My E-Revo weighs 8lbs without batteries and I want to keep the weight to a minimum, so I was looking at this pack (very last one on the page, which is sold out right now): 5s2p, 8Ah, 80A cont, 120A burst. The runtime should be quite long, but is this a good pack at only $165? I'm running a 10XL, Quark 125B, 16:1 total gearing, ~10 lbs with batts, standard maxx tires. Another plus is that it fits perfectly in the space I have.

[Serum]

Yeah, they seem to be okay. But what is their voltage like on 120A?

Considering you use a light truck, low kv motor and a decent gearing, it would be good to go with that 120A peak current and 80A continues.

With lipo used in RC, it's about the peak they can handle. My light weight maxx uses about 200-220 watts to stay at the 35 mph.

[BrianG]

I have no idea what the voltage is like under any load. The cells in that pack are only 10c cont/15c pulse. I was really questioning their quality since they are relaticely cheap. I've seen comparable packs go for much higher, although those other ones do not fit in the space I've allotted. I built a light truck specifically for racing so I want to keep the weight down as much as possible. The other alternatives I have either weigh too much, won't fit as nicely in the area I have, or don't have the runtime I'd like (5s2p Emoli, 16 NiMH, 5s Apogee LiMn). That 8Ah LiPo pack would be perfect if it was as good as it seems.

[Serum]

emoli's are heave, and so are the nimh's. The Limn cells seem to be good though.

Perhaps you can sent them an email and ask about these voltages.

I have got a better feeling with this company than with maxxamps, to tell you the truth..

[Batfish]

BrianG,
I don't know what your timeframe is, but I plan on getting two of the 4s1p 4000mah packs from TrueRC (when he has them in stock) and running them in parallel in my g-maxx. If you can wait a month, I can let you know how they perform in my vehicle.

My current packs (FMA/Kokam BalancePro 2s2p 6400mah) are incredible when it comes to handling my 8th scale buggy conversion. I ran it for about 25 minutes at the track last night and the packs never got over ambient temp of about 75F. Each of these packs cost me $200. The TrueRC packs together will be about $150 (including taps and connectors).

So I have high-quality packs to compare the TrueRC packs to.

[jhautz]

I use these cells from TrueRC, but in a 3s pack and 2s pack wired in series for 5s rather than one large 5s pack like you are considering. 2s pack sits on the motor side, 3s pack on opposite side for weight balance. My revo is a heavier truck than yours. 11 lbs loaded with batteries. 9XL and the Quark 125 as well. Mine runs great on them. Run time are ridicuously long. I have run bashing sesions for over 45min. Even pushing my truck really hard with WOT runns accross grass fields and such, the batteries never get hot. I overheat the esc before the batteries. When pushing my setup hard it peaks at 115A and I havent had any issues. I'm not a racer, so racing my put a little more stres on the batts than I do, but they never even get more than slightly warm, so there should be plenty of room to push if you want to. For the money, they are pretty decent.

Just my opinion.

[MetalMan]

YES.

You'll be perfectly fine with these batteries. I wouldn't be surprised at all if they only heat up 10 deg. F more than ambient.

Here's a graph:
http://www.rcgroups.com/forums/attac...hmentid=806053
As you can see the 10C falls short, but these are continuous discharges. Don't worry about the 6C (green) line, the guy's equipment just shut off. What's nice about these cells is that they hold a good 8C voltage, especially for the price. If you were to spend twice as much money, you might be able to get a pack with a lower capacity but 20C rate that can hold the same voltage at 15C, but that's twice the price!

As for quality, there shouldn't be anything to worry about there. This company is constantly looking for the cells with the highest value (performance/cost), and quite often I see graphs of cells that they are testing (to see if they meet the performance/cost that this company expects).

Soon True RC will also be coming out with some 3200mah cells that are 6mm x 45mm x 135mm, which will fit VERY nicely into 6cell NiMh battery compartments. By luck, I was talking with the owner of True RC, and he mentioned that he will need some RC car testers for these cells :). I got lucky.

[BrianG]

Batfish:
I don't really have a timeframe, but I do want to get this Revo done so I can practice racing because I simply suck as of right now. :) At $165, those batteries do seem ultra cheap compared to $300+. Some of that may be because they are only 10c batts. I'll see if I can wait, but you know how hard it is to do that sometimes. :) I still have my heavy bashing Revo to play around with, but from some informal "testing" in my basement using NiMH cells, the lightweight one handles very well and is so much quicker off the line. It's amazing what just a few pounds can do!

jhautz:
Yeah, I remember the thread where you said you were drawing 115A and the ESC was heating up a lot even though it is rated for more. I'm hoping that my lighter truck coupled with a higher turn motor will keep the current down somewhat. I may also pick up that Eagletree module I've seen talked about to make sure I don't overdo it on the batts. Despite assurances all around, I'm still a little hesitant about using Lipos in a MT, but the weight and power is really hard to pass up!

Again, it just seems those cells were unnaturally cheap for the capacity and was a little worried that it might be too good to be true - because you know what they say: if it sounds too good to be true, it probably is...

[MetalMan]

Did you see my post above? I think I may have answered a few of your questions/thoughts.

The Eagle Tree device is great. You can get it to record at up to 10 frames a second, with temperature, RPM, volts, amps, and watts. Mine has been working well so far :).

[jhautz]

Originally Posted by BrianG

Batfish:

Again, it just seems those cells were unnaturally cheap for the capacity and was a little worried that it might be too good to be true - because you know what they say: if it sounds too good to be true, it probably is...

I was worried about it also. Thats why I went with the 3s and 2s configuration rather than the single 5s pack. I figured if it didn't work out for the big truck I could still use them in the 1/10 staduim trucks. But Like I said. So far all good. I have maybe only 10 runs on them so far, but no issues to speak of. I actually am planning on getting a second set. I talked to Dan at TrueRC just a couple days ago and he is expecting more cells in proabably next week sometime.

[jhautz]

I was looking at the eagletree as well, but I havent exactly figured out what all I need. It lloks like ther is a base module and then all kinds of additional sensors that need to be purchased. If the base is $150 and the other modukes you need are anywhere for $40 to $150 additional each, thats just getting to expensive.

What measurements is the base $150 module able to take, without any additional sensors?

[MetalMan]

I'm talking about the Micropower, $70 and then like $5 for RPM and $5 for temp. sensing.

[jhautz]

Nice. I never got past the front page where it shows the $150 unit. That Micro one would be a worthy investment. I'm gonna have to think about that.

[BrianG]

Originally Posted by MetalMan

Did you see my post above? I think I may have answered a few of your questions/thoughts.

The Eagle Tree device is great. You can get it to record at up to 10 frames a second, with temperature, RPM, volts, amps, and watts. Mine has been working well so far :).

I saw your post, but I must have been typing mine while you posted.

I've read good things about that Eagletree device. It's all but impossible to get any kind of accurate measurements otherwise. Although, I would probably pick a faster sampling rate since some current pulses may be too short to grab at 100ms, or it might grab a sample at the midpoint of a pulse and not the peak which is what you want to see. Of course, this reduces the time you can record, but for initial current measurements, this will be fine.

An rpm sensor would be nice for getting a true measurement of speed and true kv ratings of a motor. Most people seem to be going faster than a calculation using the published kv rating would account for, so these motors' kv ratings must be underrated somewhat. I plan on adding a supplemental heatsink ("model 31" from this page) to my 125B and the 10XL has a RCM heatsink so temps aren't really a problem.

As I said a different thread, my battery has to fit in a 147mm x 50mm x ~60mm area. That 8Ah pack will be really nice. And since others have tried it, I feel more comfortable about it now. Now to wait for them to come in!

[squirrel]

would it be feasable to run 2 of the True RC packs together on a truck?

how would i go about wiring this?