Because I'll probably eventually go brushless, I'm going to start with LiPo batteries right off the bat so I won't have "useless" NiMH packs sitting around post-conversion. As top speeds aren't too important to me I'll settle on a pair of decent 2S packs to wire in series. The goals are:
Little wasted expenditure after brushless conversion
Easy conversion to and from brushless motor/ESC
I think I'll need to buy:
2x 2S LiPo packs (to be determined)
1x 4S Low Voltage Cutoff
Extra connectors/wiring to make a Y harness, and to add the LVC
I think the wiring should go something like this:
The pair of batteries will attach to the rightmost pair of black/red ESC inputs, and the leftmost pair, which apparently just short inside the ESC to connect the batteries in series, will be left untapped.
Does this setup let the ESC's BEC do its job?
If not, can I wire each battery directly to the ESC as with NiMHs, and connect the 4S LVC to the "most negative" and "most positive" battery inputs? The goal is to run without a separate BEC.
I read that LiPo batteries cannot get wet. Is this true? Would minor dampness from running around in snow or even the occasional splash though a small puddle be ok? I don't plan on using the Revo as a submarine, but doing some winter wonderland bashing would be fun. Alternately, would using A123 cells make the packs more water resistant?
(Images stolen from http://scriptasylum.com/rc_speed/_wiring.html and tweaked)
Last edited by kirbysdl; 06-25-2008 at 04:50 AM.
I would run each lipo to each connector on the ESC. I don't know how the BEC in the Traxxas EVX works, but IMO it is meant for the voltage of one battery, and 2 would blow it out (again, I have no idea what I'm talking about, just speculating ). IMO it's best to leave out the series adapter and use both ESC connectors.
For balancing, I'd do what you are doing and wire up 1 harness to balance both batteries at a time and use an Astro flight "Blinky" Balancer. It's a very cheap balancer that works well and is very light--ideal for your application.
Lipos getting wet: Last winter I ran my electric Rustler through all kinds of snow and got my Maxamps 2s2p lipo soaked several times and it never had a problem, so I'd have to say they're OK getting wet (I've also gotten my MA 3s 6k lipo wet, and my new 2s 8k lipos wet).
Which lipo: After the testimonies from people that own them, I went for the Maxamps 2s2p 8000 mAH lipos for my E-Revo. They give awesome run times (not sure how long, I always break something or something malfunctions before I can empty them ) and great power when combined with my Neu 1515 1.5D. You'll want to check the size of them (Maxamps has sizing info on their site) but I'm fairly sure they will fit. I haven't run them long enough to say what they're like in the long run, but after owning other Maxamps batteries I'm sure I won't be disappointed (and I got the 3 yr/300 cycle warranty on each of them, so IF something goes wrong they'll fix them for me ).
Do you have a link to the lvc you are going to use? I ordered everything else but forgot the LVC.
Thanks for the diagram.
Dunno if posting links to stores is allowed, but search the web for "Novak Smart Stop 4-Cell LiPo Cut-Off Module"Originally Posted by e-mikey
Last edited by kirbysdl; 06-25-2008 at 07:45 AM.
That's probably best to make sure the BEC works, but I don't know if the LVC will work correctly if wired according to the second diagram.Originally Posted by Unsullied_Spy
Thanks. I figured I'd do something like this for charging and balancing, but my main concern right now is how to deal with the LVC. Any other ideas?Originally Posted by Unsullied_Spy
Thanks, that's helpful. I forgot where I read that LiPos can't get wet, but it's a bit scary.Originally Posted by Unsullied_Spy
I'm sure they're decent, but people have said that their prices are mostly for handholding (pre-soldered connectors and model-specific battery matching, for example) and that you can get similar performance for better prices elsewhere. What I end up buying is dependent mostly on how lazy I am. =)Originally Posted by Unsullied_Spy
That's true, I paid over $160 for mine even after my discount and you can get a TrueRC, for example, 8k 15C pack for MUCH less than that (don't remember exactly how much though). I just went with them because I know Maxamps, primarily the Hyperion balance taps which are a MUST for me because that's all I have.Originally Posted by kirbysdl
I just set my new E-Revo up with a Novak 4 cell smart stop - and it's wired like the 'alternate wiring' image you have there. I pushed the tabs out of the evx2 connectors with a pliers (gently) and soldered on to the evx2 connections, then snapped the tabs back in. Red (positive lead) from the smart stop goes to the red on the left battery connector (looking from the front of the car) the black (negative lead) goes to the black connector on the right.Originally Posted by kirbysdl
I could post some pictures if you'd like.
liposhield cell pro is a good lvc. you can wire the EVX-2 to have the batts go to one connector. ie you terminate the other connector.
I think the whole LVC thing is a bit overblown. Heres why. it will be obvious when the model starts slowing down. If you disconnect the batts at that point your lipos will be fine. you need to disconnect them anyway after a run because if you store them connected they will run down and ruin them LVC or not.
I run lipos on my emaxx.im running 7 cell MA 4700's right now on the new e-revo as i cant get my hands on another MMM and i dont want to fry the cheapo titans in one weekend. when i had the EVX-2 and the titans on the emaxx with the lipos things get very hot as the lipos produce much more current than the Ni-mh's.
just make sure you have your MMM and Neu or Kershaws on order as the titans wont last.
On the subject of waterproof i dont have issues with the maxamps. i get the hard case baked in you cant get that with the TrueRC batts. check where the wires come out of the pack- that's the only place water can get in.for insurance you could put a dab of silicone.
I wouldnt submerge them but my boys run through puddles and mud all day long and batts arent an issue -actually the lipos seem better sealed than the nimh stick packs.
Wellington, Florida RC Racer
Please do post pictures because the way I read your post, is not the way the 2nd diagram is drawn. Is your LVC wired to the red on one battery lead coming from the ESC and to the black on the OTHER battery lead coming from the ESC?Originally Posted by epthegeek
Yes, and that's what the diagram shows - if you follow all the crisscrossing. The red thin line from the LVC touches a red lead from the EVX that goes to the 'top' connector, and the black line that goes to the 'bottom' connector. They cross over, which is exactly what they do on the real evx2.Originally Posted by Sneaky Pete
I'll take pictures after work today for clarification.
Oh! I see it now...the battery leads cross! Thanks!Originally Posted by epthegeek
I've never run an EVX2 (brushed=eww ). When you bridge the inner set of power wires and just hook your packs to the outer set (feeding the full 14.4v), how does the ESC BEC work? Normally, the BEC is powered via half the full battery voltage. Bridging the battery before the ESC leaves the BEC input floating.
Also, does the BEC power the internal low-power ESC circuits (mainly the brains)? Or is it there just to power servos?
Can you connect the novak 4s lipo smart stop lvc like this? (instead of a seires y-harness for battery why not a y harness for lvc?)
Last edited by MambaRustler; 06-25-2008 at 05:13 PM.
Slash 4X4 PE:MM/Medusa 3300KV
Because it's not necessary. You don't have to Y-Harness anything. The alternate wiring diagram from the first post works fine.Originally Posted by MambaRustler
can you put the pictures up
As soon as I get home from work I'll snap some and put them up. Just over an hour or so.Originally Posted by saydee1800
Originally Posted by epthegeek
please post the picks
so do I have to cut the wires on my evx-2?
Ok, so here are pictures of my install.
First off, I used a pair of pliers to gently press out the contacts from the male connectors on the EVX2 so that I could solder the wires to them directly. Once that's done, you can snap them back in -- or if you're paranoid, replace them with fresh new plastic housings for male plugs so they snap nice and hard.
The red lead from the novak goes to the red wire on the left plug, and the black lead from the novak goes to the black wire on the right plug. This is exactly the setup in the "alternate wiring" diagram at the first post of this thread. You can clearly see that the red wires for the traxxas connectors cross over. The red lead in the left plug is actually from the right side.
And for completeness sake a picture of the location of the novak installed, I used the double sided tape the novak came with to stick it flat down in front of the EVX2 since there was room.
I hope that helps.
I have a real noobie question, What's all this accomplish? Is this what I need to do to run lipos stock and not burn out my titans?
I plan on eventually going brushless, but not untill I figure out how to drive.
I ordered 2 - TrueRC 6400mAh 7.4V 2S2P pack 15C Continuous
2 - 7.4V, 8000mAh, 2S2P, 10C
Does all this apply to me if I want to use them in my revo?
Thanks for the answers.
Originally Posted by e-mikey
This adds an LVC or "Low Voltage Cutoff" to the system. Its not for the motors, its actually to protect your batteries. Lipo batteries, like the ones you just bought, should not be discharged below 3 volts per cell. Doing so will shorten their life, and perhaps destroy them. The LVC stops the ESC from discharging the batteries past this point, thus protecting them from an overdischarge.
In short, yes, this applies to you
Thanks, it's being ordered now.
Just hook a 2s lvc to the battery input that supplies the BEC. That pack always runs down first.
If you use a 4s lvc for both packs, the pack that feeds the BEC could drop below 6v before the lvc trips.
Rustler with Stampede Body Mounts, Masher 2000's, Futaba 3PDF Radio, Tekin Rebel ESC, Magnetic Mayhem 23/87, SG2 Amber 14/87, misc 8-cell packs, RPM all around, Lunsford Turnbuckles.
When my EVX2 was still in my E-maxx, I just used a CCBEC and bypassed the internal BEC altogether.
This allowed me to use a single Li-Saver LVC because both packs in series were being drawn from identically. It also facilitated the use of my Eagle Tree to see the voltage from both packs at the same time and helped keep the temps down on the EVX2.
Save 10% of the money you make..... you'll never regret it.
Thanks for the pics! I'm glad my second hunch was right. =)Originally Posted by epthegeek
While that makes sense, investing $25 to ensure the safety of some $200 batteries is pretty cheap insurance.Originally Posted by alangsam
I figure i'll be in training mode (50% throttle) to begin with anyway. Should that help the heat?Originally Posted by alangsam
Thanks for the report!Originally Posted by alangsam
epthegeek said it's not necessary, which is true. However, your diagram is in fact wired incorrectly. You're effectively giving the LVC battery leads a parallel view of your batteries (2S voltage), meaning the LVC would shut off immediately.Originally Posted by MambaRustler
Any other opinions about this technique? Which pack is the one that powers the BEC? What impact does the BEC make on the relative draw on the two packs? Thanks for all the help!Originally Posted by kschauwe
So you Know I called Novak Last night and this is how they said to do it. Thanks for your pictures they are very helpful. I didn't know I could get those wire out of the plugs and reuse them
Whatever you do, do NOT wire it like this! Wiring the batteries in series, but hooking the LVC up to both 2s packs in parallel will short out a pack via the LVC leads! Don't forget, when two packs are in series, one of the red leads is at half total pack voltage. So, you are shorting out the most positive pack. Since the LVC leads are so small (gauge-wise), you'll burn those up way before you can harm the battery, but still not good and there's a very good chance you can start a fire.Originally Posted by MambaRustler
This is the correct approach to keep it simple iMO... the only other way to do it properly would be actually putting cutoffs on each side. As kschauwe stated the side w/ the BEC will always drain faster and there is a real possibility that you could drain that side too low and ruin the battery. On high end ESC's you don't have the internal BEC setup like the evx-2 is, this is a cheap way to save money, but it also makes it so you can't get away with just one cutoff for the entire voltage (ex MMM on 2x 2s2p running 4s). The other fix would be snag a external BEC run both batteries in series into one side of the evx-2 and just close the circuit on the other battery input. This would allow for a proper 4s lvc.Originally Posted by kschauwe
Last edited by stumblin; 06-26-2008 at 10:33 AM.
eRevo Neu 1515 1.5d MMM Maxamps 4-2s2p8k 2-3s2p8k
That's the way I did it, and it worked like a charm.Originally Posted by stumblin
Thanks for the help, I was going to connect it like that when i got myOriginally Posted by BrianG
Slash 4X4 PE:MM/Medusa 3300KV
So which side is the one with the bec? a picture of an evx2 mounted on e-revo showing the bec side would be great.Originally Posted by stumblin
Thanks for the help without you guys i would have killed something
Slash 4X4 PE:MM/Medusa 3300KV
FWIW, I just ran my lipos all the way down to the smart stop cutoff for the first time last night. When I slapped them on the hyperion, the low one was reading 6.0 and the other was just above, like 6.3 -- so the BEC side didn't go lower than 3. Without any extra BEC, without any serial adapters. Just wired as shown in my snaps above.
ok well now am confused what should i do go with the alternate wiring for a 4s novak lvc?? or 2s novak lvc on the bec side?? I cant decide help me out
Slash 4X4 PE:MM/Medusa 3300KV
Which ever you prefer, all the info you need is right here in this thread.
READ THE FAQ!
So which side has the BEC circuit? The argument against measuring both packs when one pack is more heavily drained makes sense, but where would you connect the 2S LVC? In the pics in the original post, would it be the top or bottom pair of wires? Thanks!Originally Posted by epthegeek
Easy way to tell/find out: Just connect a single pack to both set of power leads in turn; the side that turns the esc on, but wont run the motors is the BEC side- wire the 2s LVC to that set of leads.
READ THE FAQ!
Err, just so I'm clear here (I'll be wiring this tonight, I hope)...
I have 2 2cell lipo's coming. I need to wire it like in the second diagram (like the photos above show), Correct? So the positive lead from one battery, and the negative lead from the other?
And I do this with a 2 cell smart stop? Or would that be with a 4 cell smart stop, and for a 2 cell smart stop I just wire it to both leads on a single battery?
(I have a 2 cell LVC coming in)
If you are using a 2 cell LVC then you want to hook it up to both wires of one battery lead. If you used one on each lead, you would be looking at the total voltage which would never get down to the 6v, if it did you have problems. You need to find out which side has the BEC which is told how to do above, but I will repeat. Plug in one battery and see if the esc will turn on, if it won't switch sides and see if it will turn on. You won't have any power just a light on the esc and power to the servos. Whichever side allows the esc to turn on needs the 2 cell LVC. I don't know for sure, but the evx-2 may be weird about powering on with 1 battery. If the way I mentioned doesn't work, try and power it up with both batteries and then unplug one side. If it makes the esc light go out right away, you have unplugged the BEC side. If it stays on, the BEC side is still plugged in. Try this with both sides to make sure you have found the correct side. Once you have found the correct side, you can pull the wires out of the black connector and solder directly to them and put them back in like shown in the picture (the picture does one on each plug, but you will do both on the same plug).Originally Posted by kraegar
Edit: Just another idea to throw into the original post. The 4 cell cutoff uses 12.5 volts for cutoff, so if you aren't running fans or anything off of the BEC besides the servo it will probably work fine. As long as your batteries aren't farther apart than .5 volts you will be fine. If your lowest one is at 6 and the highest is at 6.5 the LVC will kick in and you'll be fine. A lot of people don't recommend going all the way down to 3 volts/cell anyway, so I would still recommend the 2 cell because it will give more consistent/safer results.
Last edited by trx33; 07-02-2008 at 09:48 AM.
Ok, glad I asked. Neil had explained this to me also, but I got caught up in the pictures and nearly missed that. lol.Originally Posted by trx33
Instead of messing with the connectors directly on my EVX2 I plan to make a short patch cable and wire the lvc in there, so that if I ever want to return it to stock or whatever, it's undamaged in any way.
Thanks for the re-clarification TRX33! I am going to be doing this within the next couple of weeks, and for some reason this is what I am dreading the most. I would hate to ruin any electronics. The jumper idea isn't bad either. So would you just put a TRX connector on both ends; one to plug the battery into, and one to plug into the EVX2, and on the one that plugs into the battery (BEC side) you would have the 2s Smart Stop on it. Sound correct?
This is all why I was considering the Cell Pro version that you didn't have to do any soldering on, but then I read it sucks. Oh well, solder away!
Eat my road grit, liver lips! -Clark W. Griswold