Battery Questions

[giftacrylic]

I have an E-Maxx w/ a 8XL and 9920 geared 22/66. Runs great on 16 cells without getting hot (Throttle EPA set at 80-85%). The problem is my runtime. My GP 3700's loose considerable power after 7-8 mins at the track and I need a 10 min run for the A-Main race. The batts are 9 months old and were run and cycled regularly. Could my batts have bad or gone flat?

[neweuser]

No, the runtime is about normal. You can increase your runtimes with lipo, or change your gearing a tad. Changing your gearing won't do as much though. you could also increase your mah

[BrianG]

What Neweuser said, and maybe going to a 9XL, or even a 10XL, or a more efficient motor altogether (LMT/Neu). The higher turns count will pull less current and increase runtime. I run 14 x GP3300 unmatched cells and 10XL on a Revo (9.75lbs loaded, total gear ratio ~16:1) and I get about 15 minutes. I'm not running quite as hard as a good driver in a real race would, but pretty close.

16 cells on an 8XL is a little on the higher side of 40k rpm, which is where efficiency starts to fall.

[giftacrylic]

Actually, I am turning 36K rpms at the loaded value. How would the MaxAmps 5s2p 3000mah(2s2p and 3s2p) work with my 9920/8xl setup? Would the motor draw too many amps for the controller?

[squeeforever]

You need more like a 4 or 6000mah setup.

[go4gold]

Try 20/66 gearing. That should help with the run time and still have good speed and a ton of torque.

[giftacrylic]

At 20/66 my motor runs hot. Squee, I meant 6000 mah. Would the 6000 mah MaxAmps lipos be OK on my 9920/ 8xl setup? Not in the mood to buy another controller as I am also running a brushless CRT and brushless Hyper 7.

[squeeforever]

Yea, those should be ok. I see what you meant, now. 2S2P made of 3000 mah cells.

[go4gold]

Originally Posted by giftacrylic

At 20/66 my motor runs hot. Squee, I meant 6000 mah. Would the 6000 mah MaxAmps lipos be OK on my 9920/ 8xl setup? Not in the mood to buy another controller as I am also running a brushless CRT and brushless Hyper 7.

I run a feigao 8xl 9920 ubec 20/66 on 14 cells with no heat issues.Runs pretty descent on 12 cells too

[Serum]

I would use a 4S2P 4000 setup of maxamps. The runtime will be great, with a very nice punch. You only need a LVC (low voltage cutoff) the nicest one i could find, for a cool price, is the liposhield from dimensionengineering.

http://www.dimensionengineering.com/LipoShield.htm

[giftacrylic]

Serum, thanks for the lead on the LVC. Now for chargers. I have a SuperBrain 977 that will charge up to a 3s lipo so I need a cell balancer. Or would I be better off purchasing a new charger? I would like to be able to charge at least 2 packs at a time.

[Serum]

If you want to charge all the cells at once, you are better off buying a new charger i think? (depending on your personal state of mind in terms of patience)

[giftacrylic]

I did not mention that my 977 can charge 2 batts a 5 amps each. Which chargers and balancers work well on lipos?

[squeeforever]

I would recommend one of the E-Stations chargers with a E-Station PB6 balancer.

[giftacrylic]

Has anyone tried the "e-Station BC-5 Balancing Nicad/NIMH, Lipoly Charger"? It has a balancer built in and monitors the cells individually.