RCM Lipo impressions
 

I picked up a couple of Mike's new lipos (5s2p 5Ah 25c) and ran them around a little. I don't have an eagletree and the outside temps are a bit nippy, but they ran great!

After having problems with my GTP and MBX5/CORR conversion (blew ESCs), I decided to discharge the lipos for storage along with my 4s2p 5Ah Maxamps pack. But I figured I would do a little testing at the same time so I charged everything up fresh.

I use a custom CC discharge circuit (darlington transistors and power resistor setup) that will draw 10A from batteries ~10v up around 5s (the transistor and resistor setup gets quite hot even with a fan at 5s - but that's 185w too). I hook up a balancer and use a voltmeter to monitor cell voltage to get to my desired 3.5v/cell storage level.

With the MA 4s 5Ah pack hooked up, that 10A load dropped the voltage by 0.48v. When it hit my 3.5v/cell threshold, it had taken out about 2300mAh. Various cell LEDS on the balancer (LBA10) would flicker on and off during this time. Removing the load brought the no load voltage up to 3.73v/cell.

With Mike's 5s 5Ah packs hooked up, the same 10A load dropped the voltage by around 0.08v (fluctuated between 0.07 and 0.08v). When my 3.5v/cell threshold was reached, it had taken 4.36Ah out of the cell. Cell 3 on the same balancer flickered for about 30 seconds once. Removing the load brought the no-load voltage up to 3.67v.

Cell resistance is not linear so you can't really say how much voltage will drop at the rated C value simply by using the 10A load and voltage drop figures. Yeah, it's not the best test, but it certainly hints at a lot as far as performance goes.

Dang if that isn't a huge difference in drop! Only at 10a too!

Yeah, the drop is quite a bit different, but also the amount of mAh taken out of equal capacity packs @ 3.5v/cell is huge too. Tells me the discharge curve is far flatter for more of the charge.

Eventually, I'd like to build a 100A+ constant current device to test the higher currents, but dang, the transistors and power resistor setup is kinda big. 10A takes two 2N3055 transistors, with an NPN darlington transistor driving both bases to keep the current gain high (prevents loading, and resulting v drop, of the regulator that drives everything). 100A would take 20 of those transistors, not to mention the fans and heatsink! 100A @ 18.5v is 1850w... that's a LOT of heat!

I'd like to use FETs, but not sure how to drive them in linear mode as well. They would definitely be much easier to parallel (no current-hogging due to negative temp coefficient) than transistors...

yea mikes new lipos are BADASS! they run stone cold and have unreal punch we are running it with 1515 2.5 in a st-rr and its an awesome, i have the same setup coming for my truggy this week. plus since they are shorter than the enerland cells it leaves more room on the chassis

I was looking at these for my matrix, seem like they are worth it :) Mike better stock up for xmas

Couple things before I comment on your test:
1) BrianG actually blew ESCs? It's about time!
2) Most manufacturers state a storage voltage of about 3.8v/cell for the newer generation cells (older cells used 3.70-3.75v).

Now, your results from that test indicate excellent results. I just can't get over the fact that you used a fan... At least you had an obvious reason for doing so.

my sentiments exactly:lol:

I recently received one of Mikes new packs and they are indeed great!

lol, the MMM V1 flamed to a crisp. The odd thing about that is it was running great with super temps of ~110*F (I checked periodically). I stopped for 10 seconds while talking with glassdoctor then it just started smoking and then flamed. The ESC is completely destroyed. It desoldered the power wires and crisped the BEC wire. The BEC still works fine once I replaced the wire. I sent that ESC in for a V3 replacement (but I did say I would take several bad V1's instead - but marked to void future warranty claims. They said they will send a V3. I tried. :smile:).

The HV110 popped a capacitor spewing cap guts onto my GTP windshield. Must have been a weak one because the other 5 look perfect (no puffing). Sent that in too.

This sucks though because until now, I've never blown an ESC. I'm getting a Quark 125B to replace the HV and will run it on 5s. The V3 will go back into the MBX5/Corr, but I still think the Quarks are smoother. If I could get another Quark 125B instead of a MMM, I would in a heartbeat.

And yeah, I don't mind using fans, where they make sense to do so. Dissipating 185w in a stationary setup requires a fan ... or an EXTREMELY large heatsink ... and I would like to have some work space on my 8' X 3' workbench. :smile:

I set a 3.5v/cell termination simply because of the 10A load. I anticipated more voltage "rebound" once the relatively high load was removed. I should use 3.6v/cell when doing this to Mike's new cells since they drop quite a bit less, but anything from 3.6v/cell to 3.8v/cell should be just fine.

I just received my packs (2 2s 5200mah hard case). from Mike all the cells are 3.85v reading in the balancer. its take about 40min to fully charge for each pack at 2.5amp
now all the 4 cell reading 4.20 on the charger.

Do I have worry about my new MMM (just got it from tower last week so I think its v3) or its ok with Mike lipos?

my setup e-maxx + 4.5 hv motor + 2x2s 5200mah hardcase + MMM + 12/72 gearing

but mike lipo's looks great and nice built all the cells are equal. its seems they balanced very well.

The batteries won't be the weak link. If the controller is a V3, it should say V3 on the bottom of the box/package it came in (at least my V3s do). :)

Yep, all v3 controllers have a big fatty v3 sticker on the bottom.

Thanks. yes there are v3 sticker on the bottom

Couldnt you get an old audio amplifier and make something from that? I just threw one away that had been in my garage for some time. Wouldv'e paid that forward to ya.

I must have missed your response JT. Yeah, a car amp heatsink would work, but still not nearly big enough for 1850w. Even a large 1000w rms car amp only has to dissipate ~600w (class AB amps are around 60% efficient), which is one third the power that I would need to. And amps don't run at their max power constantly, unless you like listening to sine waves, so actually it is dissipating probably around 200-300w. So, I would definitely need a really big sink AND fan setup for this!

Anyway, I played around with Mike's new lipos today. I ran down a pack to LVC. Let me tell you, they dump quick! One second you have full power, the next you're done. Usually, if you let the pack sit for about 10 seconds and try to move again, it will have enough oomph to get the vehicle back to you. Not these. When they're done, they're done. Period.

I put the pack on the charger and it was right at 15.1v still after about 5 minutes. Not much rebound (good!). As soon as I started the charge, the voltage increases quickly. I only put about 400mAh before the pack was at 18.5v. The voltage increases slowly from there to CC/CV. So, the discharge/charge curve for these cells are really flat! And the cells stay within ~.08v of each other at any time so far. So, as you can see, I have nothing but praise for these so far.

And I missread yours! I didnt see the 1850W....I had actually been referring to home audio, but even those wont achieve 1850W....well, anything that I'd throw away wouldnt achieve that.

Hi Brian,

If you're looking for a large controllable load to discharge with, I have a few ideas.

How about taking a Monster Mamba, put it in brushed mode. Very Controllable with a servo tester.

Then for a load, how about a regular space heater? Inductive coils that get glowing red hot, but are "cooled" by the fan which circulates the heat.

Just hook your monitoring equipment up between the ESC and the Batteries being tested.

This should be good for 100 amps + like you're looking for.

If you desire 200 amps+, I'm sure there is a way to parrallel a couple of "brushed" mode ESC's since this type of operation doesn't require any type of EMF for timing or switching.

On the load, to raise it's Wattage output capability, I would think increasing airflow should raise the limitation before the coils melt down.

Just a few thoughts. :yes:

do we know who makes these packs? or what other companies sell relabeled ones? just trying to see if I can find other reviews for the same pack.

@sikes: Hmm, I guess I missed your post. Using a high current ESC to provide some adjustability sounds like a great idea. As for the heating coil idea; I dunno. Ideally, this system should be usable to test 2s packs up to 5s packs (maybe even 6s), but the resistance needed to generate enough current at 2s is quite low and not sure if a heating coil is made for such low voltage. I'll have to dig around. I guess light bulbs would work too, but then up against the wide voltage range issue again.

@gixxer: I've heard speculation that they were "chargery" cells, but when I look at their site, I don't see any 25C 2.5Ah cells (only 20C), which is the packs I have are made from. I think only Mike knows...

Has anyone ran the 5200mah 2s packs yet?

i think its time mike should put out some erevo lipo combos, when he gets his next shipment in... i know that his 3s2p 5000s fit and also the 2s3p 7500 version (there are 6 total cells in each pack x2 for either a 6s 5000 or a 4s 7500 setup) i think theyll sell good especially with the 2s3p 7500s to use with the new brushless edition revo to be out mid january (same time mike will have more lipos in)

If he did the 7500 2s, i'd be looking hard at them for replacement of my 8000 maxamps for my T4, I plan to run Pro truck in RC pro this year

If I could get a 25c 2s 7500 that would fit in my e-revo, I would get at least 4 of them. Sounds like mike has found a great battery for us! BrianG, thanks for the review

I picked up some chargery lipos. They are different from Mikes. also, mike confirmed that he is not using chargery lipos.

I ran them 9 minutes then my shocktower broke. Next day go bashing again and run them about 11 minutes and this time my rear shocks head come out. all that only one charge. Now my charger read my lipo voltage 3.72v. So I think will give you about 25-30 minutes

I can told you they run cool and hold the voltage.

what type of balancer connector does it use?

The ones I have use Thunderpower balance plugs.

I have run about 7 or 8 cycles through my packs, they are rediculously powerful compared to zippies... 2 of them paired with the MMM combo is pure win... full review will come later on...

Oh Man, I'd definitely suck up some 7500 2S packs for sure.....


Sssshhh, it's ridiculous, unless Websters have sunk to a[nother] new low :wink: :rofl:

has anyone tried the 6s 2500's? i think they would work great in my rc8, but would the "c" rating be enough on 6s? runnin a 1512 3d @15/46 and am looking to upgrade from my MA 4000 pack i run right now. i know the recomended min. is 75A for the mmm but these packs are looking better each time i drool over them. any thoughts? runtime is not really an issue on the track 10-15 mins would be plenty.

They can handle that setup. I tested the cells on 5s in a truggy with a 1515/1y geared for 50+mph. They held better voltage under the same amp draw as my MA 5000mah pack, so if you are using a MA 4000mah pack, these will have a bit more snap.

You ran a 2500mah lipo on a setup that draws ~100a? Dang, you must have some good lipos. :lol:

It saw peak amp spikes of around 170 or so amps - the packs held over 3 volts per cell all the way to 160+ amp spikes - this was during the testing phase before I offeed the packs here. Yes, they are good cells. :)

Any update on when they're going to be available again?

X2....I'm looking to buy some 3S packs today or tomorrow....!!!

I have a 4500mah 5s pack from Mike. I only have a few cycles on it but it is proving to be a good buy, I actually ordered another one. My setup is a RC-Monster converted RC8T, MMM esc, 36-70-1600 Medua/1515 2.5D, 54/17-19 gearing(17 w/1515, 19 w Medusa). I'm getting a solid 10 minutes hard bashing in thick grass and the Lipo is getting to about 106*, motor at 140*( Medusa was slightly hotter ~155*), esc~90*. Although the ambient temp was only about 50* I still don't think that those temps are horrible for running in grass. I wanted to thoroughly test my setup before my first race! I think if I can do 10-12 minutes hard bashing in grass then 10 minutes on a track shouldn't be to bad.

I would think you'd get more than 10 minutes - or am I missing something? I get 20-25 or so running my Flux on 6S Zippy 4200's, and 20 minutes in my Revo (MMM/1515 2.5D) on Nue 5S 4900's. I realize the Revo is quite a bit lighter than your 8 - but I'd still think you'd be in the same ballpark.

Must be tall grass.....!:lol:

I think run time is very subjective. Most of us might be suprised if we actually put a stop watch on our run times (which I have never done) - and driving styles, etc prolly contribute significantly.

Actually the RC8T is prolly about 2-3lbs lighter than the REVO!!! Driving style has a lot to do with runtime and temps as does the terrain. Grass is one of the harshest terrains to run an RC on, it put way more load on everything than you could imagine. Gearing is also a big factor. Just cause you think your RC is fast doesn't mean it's going 40MPH ( not pointing my finger at you or anyone) but Brian's calc is the greatest tool! I was geared for 40MPH, running in grass, non-stop with lots of speed runs followed by lots of start stop. As I said, I'm basically doing some shakedown runs before I get to the track. Realisticlly 15 minutes shouldn't be hard on a track. Also my run is timed, I have a timer on my radio and I use it to figure run time

i get 18-20min on my zippy-h's and flightmax's.... 4s 5000mah each... both in my sc8 and rc8t geared for 39 and 42 respectively....on pretty big tracks...

I only get 23 mins out of a 4s 8k mah in my e-revo with 38mph gearing. Its all about how you run

25c 2600mah 18volt
 

Will these packs hold up to 2200 mmm combo in a erevo geared 18/54 and will they fit. The way i understand it is if hooked up in para all numbers double up right i/e 2600 go's to 5200 67.5 go's to 150 amps and so on right or wrong.