2 NiMh in series

I posted this in another part of the forum but figured that this forum was more appropriate and hopefully I will get some more help.

I have an E-Revo, Feigao 8XL, MM ESC, Medusa BEC, standard gearing. Initially, I ran two (brand new) Venom 6cell 4600 packs in series. I was able to experience the power of 14.8V, but it only lasted for 2 minutes - that is no exaggeration!

Attached are the photo's of my setup (series harness). Please help as I'm sure I should get more than two minutes of runtime.

Thanks.

Additionally, I just got a Flightpower 4s 5350 and got ~10 minutes of runtime. This also seems a bit short, but I unhooked the battery from the charger after 65 minutes and I figure it wasn't done charging - am I right?

[BrianG]

First of all, there are no pics attached.

Second, runtime will depend a lot on gearing. If geared for high speeds, more power will be pulled from the cells. Also, check your drivetrain for binding or undue resistance. I get over 13 minutes on 14 GP3300 cells on a 9XL...

If you charge a 5350 mAh pack at 1C (5.4A), it will take a little over an hour. The cycle starts with a constant current phase until the pack reaches 4.2v/cell. Then it switches over to constant voltage and the current slowly dwindles to usually ~1/10 of your charge current (540mA in your case). A proper Li charger will stop when it is finished. Removing it beforehand just means you won't get the full charge.

Thanks Brian.

I have standard gearing, with the FOC. I can't image there being any resistance as I've looked it over like 10 times.

I'm running the MM ESC and have fussed with the settings a bit. I ended up on the "autolipo" voltage cutoff setting because it let me run the battery down and still let me maintain control of the steering. When I had it on the "No voltage Cutoff" or the "5V cutoff setting, it just did the funky chicken dance - leaving with no control.

Thanks again.

[BrianG]

Don't know what's causing the "funly chicken dance", but you don't want any kind of lipo setting when running NiMHs. So, when running NiMHs, shut it off. When running lipos, set it to the correct value (can set the voltage you want via the Castle Link). To eliminate ESC setup issues, set ALL the Castle Link settings to default values and start over. Still don't know how you can have such bad runtimes even with improper settings.

Are you shifting into secong gear ever (assuming you are still using the two-speed setup)? What pinion/spur are you using? Are you using a center diff?

It's not shifting into second. Now that you mention it, she also fails to shift into second when I use the 4s Lipo pack. This is extremely weird since it runs fast as crap with the 4S, but I never heard her shift into second.

I'm using the standard pinion spur gear with standard clutch bell (38 / 15)

I'm not using the center diff, but using the electri-clutch that came in the Teckno conversion kit.

On an unrelated note, your BL 8eight is beyond sweet. That is going to be my next car, but the wife said I have to wait until I get back from Iraq.

Back to the subject: thank you for your time and effort in helping me figure out my problem.

[BrianG]

You may need to lower the shift point. Or maybe it is already locked in second somehow?? Hard to say since I can't see it in person. 8XL on 38/15 should be fine, especially since you have the two speed intact.

I don't have an 8ight, maybe the Hyper 8 is what you're thinking?

No problem! That's what we're here for....

Sorry, I was mistaken - it was the Hyper 8, but it too is totally sweet. Let me look at it being stuck into second gear.

Played around with the shift point and the adjustment screw was pretty much tightened clockwise. I adjusted the shift adjustment screw and the times for the 2 NiMh's in series was the same (3 minutes of peak running - however, 30 seconds of that was me having to run and flip the truck back over).

I also have a 2s Maxamps 6000 and it ran for 17 minutes.

Oops, sounds like the 4S is done charging, let me go test the new shift point.

More frustration -

Just ran the 4s and it was hella fast - for less than a minute. When I had it on the charger (Hyperion 0606i) it only charged for ~40 minutes. It's a 4s/5350. I set the charger to 5350 maH and it doesn't even come close to this charging rate (I read the lengthy post on this issue). I didn't have it hooked up the the balancer because it naturally has a different plug than what's on the included hyperion balancer tray.

Now, to summarize. My two 7.2 NiMh's in series only runs for ~2 minutes and now my 4S only runs for ~1 minute. When I'm running the NiMh's, I have the MM set on "No Limit" and when running the 4S, I have the cutoff set on "12V". I've calibrated the MM, but no dice.

Surprising, my 2s is the ONLY battery that runs for >15 minutes.

Oh, I took new pics of my "series" plug for the NiMh's.

[BrianG]

Your Y adaptor looks OK, so no problems there.

Assuming a totally depleted 5350mAh pack, charging for 40 minutes means it only put about 3500mAh back in. If this is true, and your runtime is only 1 minute, that means you are pulling 210A average!!!! If that was happening, you'd have some serious heat issues. 4s @ 210A is over 3000w.

Also, because you are able to put only 3500mAh back into the pack, this tells me that maybe the LVC in the MM is cutting out too early. Since your setting is 3v/cell, that usually means that the ESC is pulling very heavy current causing the battery voltage to dip.

So, your runtime, charge time, and LVC cutoff activity seem to agree with the theory that something is causing very high currents to flow.

If you do in fact have an 8XL, that makes no sense at all. Your symptoms describe what I would expect to see in a very high kv motor. You say your truck goes "hella fast" (SouthPark fan I assume?). Do you mean the top speed is very fast, or the acceleration? If the top speed is beyond expectations, I wonder if you have a misbadged motor??

Curious: How are the temps on the battery, ESC, and motor after your 1-2 minute run?

I have not taken temps because it is ~0-10 degrees outside with the windchill. The action of me touching the motor/esc actually adds heat.

I have an 8XL. Very high current flows? Hmm, I have Dean's plugs and my BEC is a Medusa 3.5 Amp (5/6V). There is no binding or catch points in the transmission/drivetrain area/CB - spur gear area. Additionally, I checked the spur gear and it's adjusted correctly.

This sucks, hella much (I've lived in California for a longtime, but I do like SouthPark).

I think I figured out the problem. After consulting with the LHS "expert", he checked the resistance on my series connector - it was good (<0.002 ohms), he recommended cycle charging the battery. I put it through a complete Discharge/Charge cycle (both NiMh batteries) and ran it today for ~11 minutes. That's 5 times more run time than before.

I never really noticed how many amps were going into the packs before, but I figure it could not have been near capacity. I'll cycle the batteries one more time in hopes of improving runtime.

As for the Flightpower 4s. I finally got a hold of the correct balance connector for my charger and when I hooked everything up, commenced the charge, nothing happened. It said that the charge was complete. I noticed that the pack had become puffy on both sides and decided to call Flightpower. They told me to destroy the battery (bucket of water and 1 cup salt) and that a new one was in the mail - great customer service.

[crazyjr]

I'm sure you already know this, but use a bulb discharger to make sure the battery is at zero. the light show would be impressive but dangerous