brushless and A123 questions
 

Hey all,
I tried out my E-maxx today with new Batteries, I was really hoping for a big boost from my previous packs. (6c 3300's) for 14.4 Volts

I was disappointed in the performance gain. Seemed kinda minimal improvement. My setup is as follows

wanderer 9XL
BK 12020 controller
Big Joe Tires
Forget the exact tooth on the pinion, I think it is 15.
A123 6s1p. (20 Volts)
Everything else is stock.


Now for the questions.
1) Do I need to go to a 6s2p pack??
2) What chassis would fit these packs and work good for bashing? (Packs are 3s side by side. I put one pack on each side of the stock chassis even though it did not fit...... (Had to rig it temporarly to test)
3) I am thinking about smaller tires.. Maybe the proline mulchers 40 series and some of the axial bead less rims. Would tha be a good set up?
4) What else is really needed for Bashing... Steering upgrade?

Highflier

You really do need to go to a 2P configuration with the A123 cells. In 1P configuration, they drop a lot of voltage under load and then can't deliver the current. In 2P configuration, you'll see a bigger difference.

As for bullet proofing the E-Maxx, it's gonna take a lot of upgrading. I won't say that the E-Maxx is a "weak" truck, but I will say that it has troubles withstanding the rigors of a brushless system, especially if you run that 9XL on 6S A123.

The Axial bead lock rims look nice, but they didn't hold up very long for us. The tires kept popping out.

Heres my suggestions:

FLM chassis
Proline or UE servo saver
Proline Crime Fighter MT tires
Proline standard dish rims. (I would go with 23mm)

6s2p seems like alot of weight. what would give me better accelearation.
6s1p
or
5s2p

Oh and how well can you fit 4 3s packs into the FLM extendedd chassis? I have 3s packs since that is what I use in RC combat airplanes. Which by the way is a blast.

Off to go check out prices on the Chassis and servo saver...

Thanks for the advice!
Highflier

Well I just scored another 10 cells of A123, So now I have to figure out how to configure them.

Still need answer on if I should go for 5s2p on this drive train

9xl wanderer
BK warrior 12020 controller

Highflier

5S2P will give you more punch, but it's kind of an unfair comparison.

In any case, if 10 cells is your limit, then 5S2P is the way to go. If you are considering going with the A123 cells, you really need to decide if they are indeed what you need, or whether they will acutally give you any benefit.

As you noted, they are very heavy. A 5S 5Ah lipo pack will cost you about the same as a 5S2P 4.6Ah A123 pack, but the lipo pack will give you better runtime and a higher voltage.

The lipo pack also weighs juat a bit over a pound and the 5S2P A123 pack will weigh closer to two pounds.

The A123s offer a quicker charge time, but only if you have a charger capable of allowing you to avail yourself of that benefit. I run mostly 5S2P 8Ah packs and get around 45 minutes of runtime with those and they charge in an hour. With the A123 pack, I'd get around 25 minutes, but they charge in around half an hour. Until I can get a charger that can charge at a 20A rate, I'm going to stick to lipo.

i just noticed last night looking at my flm ext. chassis, there is alot of room behind the trans with the stock speed controller gone.

My charger can charge A123 at 8 Amps, Also you can create a Charger that will charge them in under 10 minutes for very cheap... There is a thread about it on Ezone. It's not much more then 18 feet of wire connected to a 12 volt car battery.

However charge time is not my biggest concern. I would go Lipo but it's the cost. a 4s 5Ah pack is ~$200.00, and a 5s is $250.00 I was able to snag 10 cells of A123 for just under $100.00

I'll give 5s2p a try and see if I am happy with Power. I would like to have enough so that if I punch the throttle while I am already going 10mph that there is enough to spin the wheels.

Since I am just bashing it I don't think weight will be a huge issue. After all 10 A123 cells probably are not much different then the stock NMHI packs


Thanks for the info.


Highflier
PS. I will be happy if I get 20-30 minutes of bashing time per pack. I'll have enough cells if I do this right to have
4 3s airplane packs
or
2 5s2p E-maxx packs

you'll be happy with 5s a123 packs...and like you said, you can share the packs with your plane. another note about them is that they have a charge life of over 1,000 cycles - lipo is only a bit over 200. that was the selling point for me - plus they're stupid safe (which i need). you can abuse these cells all you like (within reason) and they hold the same voltage and runtime.

Like Clod pointed out, the adv of the A123s cells are safety, durability, lifespan and cost. I run A123s, but I may get 1 ltwht lipo pack for racing. Also note, that the A123s do not lose performance over theirlife span, only capacity. The IR actually goes down w/ age, so they get better, but lose capacity only. NIMH IR goes up ovr the life, so they lose power and cap. In short A123s are heavy but badass cells.


FWIW tho, they are limited to 70A discharge (30C) before they drop alot of voltage. You are prolly pulling 100A+. You need 2P.

5S2P is nearly equiv to a good 4S lipo pack. Mine weighs 780g. My TrueRC 4S 8K pack weighs ~700g, so... Runtimes were 25min vs 1hr bashing around.

you lose a bit of top spd w/ 5s over the 6S, but much better runtime and not abusing the cells. For a basher the weight is not that big of deal, and still weighs less than a 12cell NIMH pack.

OTOH, you could just run upto 8s A123 on the BK. You could do that, get a cooler motor, like a 11XL or so, adn end up in a better place.

The motor would be more eff, so more power to the ground and less heat, amp draw would be OK for a 1P config, so you could lose some weight over a 10cell pack. A 8S1P pack should weigh less than 650g. I'm now running a 10S A123 pack w/ a 1100 kv motor and everything runs dead stone cold. :) Once you go HV you don't go back.

thanks for all the help so far
 

I don't think so the BK controller is rated to 20NMHI cells right? I thought 6s A123 cells would be the limit
I have thought about 4s2p and getting a 7xl or 8xl motor instead of the 9xl

Eventually I may get another power train and give this one to my wife. Strange as it sounds we go for walks in the park 1-2 miles and bash out E-maxxes on the way. We just carry a spare pack and turn around before the first pack is dead. Funny thing is she has a 100% stock maxx and mine is stock except the motor/controller. I have been running 14.4 volts on the system till now. My system still has more power and the run time is at least 25% longer :)

The 5s2p may be perfect for me, since run time is more importent then top end... However punch is so much fun :diablo:

Highflier

PS. I am down to 2 different chassis.
FLM ext or a super sized one from RC-Cellar that is extended by 5". Anybody try that one out for bashing.. As a basher which would be more fun..

That's if you are figuring the voltage limit @ 1.2V/cell, but NIMH charge to ~1.45V/cell off the charger, which would be ~29V for 20cells. 8S A123 would charge to ~29V. BK is a little dumb tho, that's why few use their controllers anymore, so you'd have to confirm everything. I know for a fact 6S lipo was common on the controllers, tho not sure if anyone ever ran 7S (maybe due the the odd # of cells tho.)

Anyway, running higher V does not mean more top end if you match it to the proper motor w/ lower turns. You are just making power w/ V instead of so many Amps. The end result is less wasted power and less heat. A 8s1p setup would run cooler and longer than a 4s2p setup with a similarly matched motor. You don't need to experiment if you don't want to, just letting you know the option is there.

6s is the limit I would go.. simple because I know a guy who tried 6s lipo and had 2 controllers fail. First then the replacment. He was told that he had overvolts and that they would not support him anymore. 6S A123 is obviously below the spec and closer to 5s lipos.

I went with the 9xl so that I could run higher voltage. 5s or 6s seems to make sense to me right now. It has to run cooler then a 7xl at the lower voltage.
I am thinking that the 5s2p maybe the sweet spot for me. I just need to find a way to test it without having a big hassle with Batteries.

For charging I plan on using zip chargers (8-10 min for a 3s pack. I'll run 2 at the same time and then I will take the 2s packs and put them in series and charge as a sinlge 4s pack at 8 amps on my hyperion charger.

So If I get 2 complete setups I can charge one while I run the other. The charge should take about 15-20 min. I most likely will only have battery swap as my down time :)

All this for a fair cost
$200 for dewalt cells (20 cells)
$200 for hypersion charger/balancer
$20.00 for 2 zip chargers

so for a total of $420.00 I can run 1 E-maxx nonstop for 1000 plus runs.

As a added benifit when I fly my combat planes I will have 4 3s packs and will be able to fly non stop also :) here is a funny one for you. The combat planes are cheaper then the trucks:yes: They break far less I can crash them in midair or into the ground and most of the time the repairs if any are below 5.00. The cost of the planes is cheaper also. If there is anybody in the philly area that wants to check them out let me know, I could use a local truck guy to help me along on the E-maxx.

Highflier

hooooo boy, good thing i don't live closer - combat planes would be fun... i'd be too tempted to get my own. or a jet. always thought jets were cool too, but mucho more expensive.

yea jets are expensive. It is a blast to watch 2 planes flying 40-50MPH collide head on. it makes a nice popping noise then you hear both pilots go full throttle and try to get up some airspeed before they hit the ground. You score 1 point if you hit a plane and he crashes into the earth while you manage to fly away.

The most commonly broken items are control rods (6 for $2.00 and 5 minutes of labor) and Props. 2.50 a peice and 3 minutes of labor. I would guess that I crash about 10 times typically before I need a repair. I even have a guest plane ijn case a freind visits :)


highflier

NP on the cells. MGMs rate their controllers based on the highest charge voltage, tho BK is so screwy I don't know if I'd push it either.

Anyway, I ran 5S2P w/ my 8xl/mm combo and it was great. The 9Xl should be too.

Where in philly are you? Do you ever race the truck? Where do you fly the planes?

>I'm now running a 10S A123 pack w/ a 1100 kv motor and everything runs dead stone cold. :) Once you go HV you don't go back

@Finnster
Great to hear that your plan worked out. I really would be interested to see a new thread of your setup (with pics). btw welcome to to the 10s efficiency club:lol:

Truck is to stock to race right now. IMHO it is barely bashable. However I hope to be bashable plus a little once I get the Chassis, UE steering, 5s2p pack, new tires and rims. I am planing on proline mulchers 40 series unless sombody talks me out of it. I want some sort of beadless rims.. Advice???

I fly the planes at local schools, I am actually north of Philly by 20 miles. But I did not expect anybody to know where Holland PA, was.

I'll be getting most of the stuff ordered in the next 2 days. I can not make up my mind on the chassis... that is my biggest issue right now :(

I'll post a link soon that showes a little e-combat.

highflier

Yes, I agree, 5s2p would be the indeal way to go with A123 batts. A 6s1p will only get you 1080 watts roughly, you need more than that to give you the 'brushless grin'. :diablo:

I run a 1512/3D on 7s1p A123 pack and I get up to 1500 watts from it, I get roughly 15 mins runtime, and I can charge it back up again in 25 mins. It's great. I also have a 7s2p pack I use mostly though. I am thinking about trying out some FlightPower 6s packs sometime.

Just for reference, each M1 cell can deliver a 'solid' 180 watts. When I say 'solid', I mean 'useful' power that can be drawn by an R/C power system.

Hey, you are just ~5mi from me. I'm just S of Doylestown. I know Doylestown has a big RC airfield @ Turk park, but anywhere would do.

IDK about chassis, left the maxx along time ago. My fav tires are mashers for a good go-everywhere tire, but I hear badlands are also good for that. Mulchers are great for very loose dirt, but too hard of a surface and they will wear quickly.

@ Otello:
So far I am loving it, but amp draw is quite a bit less than I expected, I've only been able to pull 45A out of it. It does ~40mph w/ really strong TQ. The ET data shows quite a bit less power than the 8XL combo (upto 120A), but you don't see it. I chalk that up to the good motor and eff. If anything I cert could have gone with the 1515/3D (1360 kv,) altho the power is great and I can add some cells if I want to go nuts. I'm planning a post when I get everything sorted out.

@Finnster
When first using a 1100kv (Fun 600/11) motor with 10s A123 i also didn't see spikes above 40-45A. With HV and the right motor the power is lesser wasted in heat. I also saw 100-200 Watt less on my eagletree with the same feeled amount of power in comparision to my 4s setup. At 1200-1400 Watt with 4s you will need 80-100A. At those Amp levels motor efficiency might be at 80% (at most with a Feigao). This translastes to 240-380watt in wasted heat and 960-1120Watt of usefull power. To reach 960-1120 Watt with 10s A123 you would only need 1050-1250 Watt because your motor still is in the 90% efficiency range (35-45A). So get yourself used that you will see lesser Amp and Watt spikes with the same feeled amount of power than your LV system due to higher overall efficiency ... which also translates to a slightly longer runtime.

Looking forward to your thread.

Sorry for offtopic (thread highjacking).

Well I am starting to lean back to 6s2p for my setup. I just made a charger that will charge a 3s pack in 10-12 min. The charger cost me less then $10.00 and worked like a charm. Put 2300 MAH in the pack in no time at all. For bashing do you think the extra weight will really mater?

Highflier

What kind of charger did you make? A simple CC charge with a cutoff?

I can not take credit for the idea. It is being called a zip charger.

I used 20' of 18 guage speaker wire. Put a deans on one side and alligator clips on the other side. plug the battery in and connect the alligator clips to a deep cycle battery. You just watch the voltage (I used watt meter) until it hits about 11.5 volts and your done. This setup gave me a 6 amp charge rate. I think I will cut about 5' of the wire off so that I can get closer to 8 amp charge.

Just a warning wire length and guage are critical to the charge rate. Don't mess with it unless you have knowledge or comments from others. Oh this will only work with 3s packs. But that is fine for me.

Do you think 12 of these cells in the e-maxx will be to heavy?

Highflier

12 M1 cells is about the same weight as 14 NiMH cells, but has 36% more energy under it's belt, and much higher discharge capability. It would have about 2200 watts of usable power, but, you would never use that much in an R/C, even a MT.

I like to use my 7s pack for times when I want the Revo to have great agility, and it performs at roughly 5s lipo equivalent. I also have a 7s2p pack, and I get a pretty decent boost in punch, and it has marathon runtime it seems with the 1512 motor. The 7s2p pack doesn't feel that heavy, believe me.

A 6s2p pack should be perfectly fine, if you are not a 'every last ounce' racer.

I think that is the route that I will go then 6s2p. At least until I decide to get a new ESC that could handle higher voltage.

I tried my Zip line charger last night.
I discharged 2000MAH from a 3s pack
Then put it on the charger. 15 min later it was fully charged and had taken 2300 MAH. I am going to make another one of these chargers so that I can charge packs as fast as the e-maxx will use them :)

Highflier

Oh, so it sounds like this zip charger is relying on the resistance from a long and smaller gauge wire to limit the current.

A better way would be to build a simple constant-current source using a high current transistor like a 2N3055 or similar. You'd still have to monitor the voltage (or add other circuits to do the cutoff), but this setup can be made to have an adjustable and constant current.

You could also use a regular NiMH charger since those are CC chargers. Still have to monitor the voltage.

When charging A123's, does the voltage dip at all at the end of the charge? If so, you could set the delta peak value of a NiMH charger to a really small value...

Highflier, that really does make me nervous when I hear you using the 12v battery 'mod' as a charger, I have seen it be done, but I prefer some decent electronics.

Brian, the A123's don't dip at all, but instead anything over 3.8v/cell, the voltage takes off like a sky rocket. At that point will most likely be very damaged if allowed to go over 4.0v/cell. But I hear 4.0v/cell is actually doable with these things.

If you want to use JUST CC, then you could use 3.8v/cell and use roughly 10 amps or more per 1p configuration, and then terminate charge once voltage is reached... I believe this will get you 96% SOC.

That method is called the "nuclear charge" as I've seen it. Yeah, basically the wire is to provide some small amt of resistance so its not quite a dead short. Like a CV charge w/ barely limited current. I saw a wattmeter graph of it, and some of the initial charging was like 40-50A+ :eyes: but obviously tapered off towards completetion. The idea is you try to match the # of cells to the lead batt, ie for 10S you would hook up to a 3S lead batt, then cutoff before it overvolts. Some people were charging M1s in like 5min depending on current limiting.

Sounds too risky to me. I think I'll stick to a more controlled CC/CV charge...

Yeah, I'm sure they will survive it, but your cycle life would be way down to about that of lipo's, but that's just a guess... maybe it doesn't even effect it? After all, A123 HAS demonstrated a 5 min charge, although they used a pulse type charge, to get more mah into the cell.

All,
With the proper length of wire the charge rates are oK. Mine started at about 8 AMPs. There is a on going thred over at RCgroups about this. The tester is up over 100 charges and is yet to see any change in cell performance.

The Problem with using my NMHI charger is that they will never see the end of charge. thus if you do not watch closely the voltage will continue to climb way above 12 volts until the cell pops. Then it is toast. The benifit with the Zip charger is that no mater how long you leave it connected it will never climb above the votage of the deep cycle battery (13 volts or so), Also as it appoaches full charge the rate of charge slows down Mucho. Thus as long as you don't fall asleep it is unlikely that the voltage will get much above spec, and even if it does, it will only be slightly above spec and all reports I have read so far state, no damage done. Most say it would be bad to leave it for extended time but I have not read about any tests of that. keep in mind that the charge rate was down to 3 amps by the time the cell what 95% charged. It probably would have been below 2 before the cells were getting to 4 volts per.

All that said, Yes there is room for improvement. The charger works great, I would only ask for one thing. When the charge voltage reaches 11.5 volts to have it auto terminate.

Highflier

Well, a simple high-current voltage regulator with a series resistor to limit the current would work too. As the battery reaches the voltage or the regulator, the current will drop accordingly. Or, a voltage regulator with a current regulator in series with the output. Set the V reg to the terminating battery voltate + the C reg drop-out voltage.

Yes CC CV charger would be the ideal solution. But this took minutes to create and cost next to nothing. Oh and it is so easy to make if you know how to use a wrie cutter and a soildering iron you can make it :)

I figured out my wire lengths.
I settled on 15' of 18 guage wire. A dead pack started at a charge of 12 amps but quickly droped to 8 amps and hovered theere for 15 min or so. at that time the voltage was 11.5 and I called it charged. Thus I can charge packs in 15 min. That is faster then the brushless E-maxx will discharge them. I am happy!!! Now I am looking forward to a new stadium brushless conversion.. It will use just a single 3s pack I Figure I will get about 10-15 of good run time per pack. I will be able to use 1 pack for 1/10 scale and 2 or 4 packs for the 1/8 monster truck.

Highflier

Yes, but you also would want a decent charger to keep the lead acid batt topped up. As well, you would need a 12v battery in the first place, if not, you are paying at least $100 for a good deep cycle lead acid, at least I would want a deep cycle batt for that.

It's a fast way to charge at the very least though, and I don't know of a programmable power supply that can deliver 20 amps and charge 3s for under $200.

Ah, maybe I did not make myself clear. I use it with a deep cycle battery at a field. There is no electricity at the field.

My deep cycle came from Walmart. I think it was $80.00 But I use it as a source for my Lipo chargers also.

At home I use a PC converted P/S to powr my A123 compatible charger. It does not matter there if it takes a few hours to get all my cells charged up. When I use that I charge at 5 amps. Even though charger will handle up to 8.

I use a battery tender for the Deep cycle. I just connect it and forget it as it enters a maintaince mode once the deep cycle is fully charged. My deep cycle is going on 3 years now and it is not leting me down.

Highflier