Anyone frying Nimh packs with stock 3905 E maxx?
 

I've been trying to help a friend of mine with his stock E maxx.

The truck is brand new and completely stock.

So far, it has totally destroyed 2 sets of 7 cell Nimh packs. The first set was a pair of Electrify Great Planes 3000mah packs. They were brand new but turned into sizzling bacon during the first run. After about 10 minutes, the shrink was melting off, they were blazing hot and several cells were leaking.

The second pair was a set of 3800mah packs rated at a 38 amp discharge rate. Again, they go so hot, the shrink is melting off. It appears to me that 3 cells in one pack were about to burst. No leaking this time, but they're shot.

His motors are fine. Drivetrain is fine, no binding or anything. The ESC runs somewhat hotter than I think it should.

Just wondering if anyone else out there is running into this?

Any thoughts?

I'm running 4500Mah 6 cell packs from all-battery.com with no problems at all. Packs get warm but nothing crazy. But I did just fry 2 7cell venom packs in my BL revo and those packs cost twice as much as the all-battery ones and had half the performance. I guess this isn't to much help but if you wanna spend another $60+S&H and try some from all-battery I'm a firm believer of their packs!

Well, the best thing with nimh cells is to not buy them, and go directly to lipo. See how he just wasted the cost of a decent used lipo charger, and will most likely buy more nimhs, at least worth the price of a pair of decent lipos.

Now it is best to build your own packs, from good quality loose cells. Good quality loose cells cost as much as decent lipos (protech?), require assembly, and will benifit from a high quality charger that most likely has lipo capability.

The best cheap cells I found were the 3500 tenergy cells, all other cells from tenergy were not good. All venom lipos and most other premade packs are cardboard cells, that have maybe a .0003c rating, or worse. The duratrax large capacity premade side x side packs look nice, but are close to the price of cheaper lipos.

Nimhs are just too expensive. My lhs sells venom 4200 6cell stick packs for 55 bucks, and I tested a pair in a blackjack brushless boat. Stock boat, that recommends a pair of 4200 packs for power. 16.5v at rest, 10.8 under load before the esc would hit some sort of lvc. That equated to half throttle runs, and about 3 secs of acceleration under full throttle.

Like I said .0003c rating!

Lincpimp, where are you finding decent Lipos priced about the same as NiMh packs? Also though the E-maxx isn't setup to run LiPo, no lvc. I've debated the Lipo change and can't justify the cost for what I need. I would need a minimum of (2) 2s packs and a charger, looking in the $300 range. I have 2 chargers and 2 NiMh packs that cost me a total of $130 and I can charge both packs at once! But if u can enlighten me as to where I can get Lipos and a charger for that I'd love to switch!

Well, I seem to be able to find hyperion 5i chargers used for about 30-50 bucks. A balancer such as the equinox would be around 20 bucks. Figure about 10 bucks for tap adapters.

For lipos, try this out: proteck 4000 20c 2s lipo

So, I figure a pair of those lipos, charger and balancer can be done for under 200. Plus you can wire the packs in series during charging, so both can be charged at the same time. Not bad, IMO, and should be able to outdo any nimh, 20c = 80amps, even if they are 15c lipos that is still almost twice what a great nimh can output.

Thanks, guess I better start saving!

A friend of mine started running his new emaxx with 14 cells East Power 4200 (medium price range). They only lasted a few runs with his stock setup. While running he heard 2 plops. 2 cells were venting.

BTW: He now runs 6s2p A123 with a Neu 1515/1y (MGM 16018). But shifted these components back again to his Mugen Mbx5t since it handles a lot better (no wonder here). But for bad weather runs, the new emaxx is his first choice.

Most nimh cells above 4000mah are way to sensitive when it comes to handling. IB4200 were banned in fall 2007 from racing in norway and sweden due to a few incidents where they "exploded" during charging. My last Nimhs i used were GP3700, which never reached above 3300mAh and dropped quickly in capacity. My first A123 pack still takes more then 2200mAh after almost 100 cycles. Nimhs only deliver good performance when they come hot from the charger. But if you charge them too hot they quickly loose capacity. So: If you want performance you will quickly loose capacity. A vicious circle of death.

Well My friend called Traxxas. It seems they want the motors AND the ESC returned to them. They suspect a problem.

It makes me feel good to see they are willing to stand behind their products.

Way to go Traxxas! :yipi:

Everyone that I have personally known that has run 7's in their Emaxx has ended up having problems in one way or another. Granted, most of these were in the old style emaxx. I traced my issues back to the plugs, but others have had problems other than plugs similar to those you described.

BTW, I shopped for a long time for a used Hyperion, and I NEVER saw one for less than 75.

I might howver, try some of those ProTek batteries....but I'm a little leary of the low price......

I'll bet that the power leads going into the ESC are being shorted internally. The ESC would get warmer than usual, though not on the FETs. The motor would operate normally. But the batteries would see constant high current draw and so would become very hot. Did you notice any melted plastic on the bottom of the ESC?

Some people are running the protek lipos with success, but i do not know how much they really know.

I have not paid more than 60 bucks for my hyperion chargers (I have 3) and 2 of them came with balancers, an lba6 and a v-power. Guess I can scare up some good deals, huh?

Any suggestions on how to safely run lipos in a stock e-maxx? There is no lvc and no tabs to solder anything to.

You can solder to the traxxas connector, or buy a li-saver and make a y harness for it with traxxas plugs.

Sounds like you are using poor quality nimh packs.

I would disassmble the Nimh packs are resolder them side-by-side with good quality battery bars. You'll want to get some shoo-goo in-between the cells to strengthen them up for the bumps and jumps. Also if they are bare cells you'll want to get some individual cell shrink wrap before assembling so no shorts are caused.(the venom cells are all bare cells which come in those crappy carboard tubes)

I picked up the venom 5000Mah packs for my stock 3905, ripped them apart and reassembled them side-by-side with orion platinum battery bars and some deans 12g wire with the new traxxas connectors hangin' on the end. These batteries are running awesome for me about 20 min run times with good power.

The problem with pre-assmbled Nimh packs is that they use cheap thin batttery connectors that create alot of resistance and if you pump too much through them they fry up.

A little bit of time and effort makes even cheapy Nimh packs into something a bit better.

That's just my chime in tho.. :whistle: