Battery problem

[rcyeddo]

Hey I bought a new 8.4 for my rc10 b4 and it runs slower than my 7.2 battery. I tried the battery on other cars and it works fine. Can anybody help me with what's going on?

[Sixtysixdeuce]

Most likely has a lower discharge rating. Think of it like water; voltage is pressure, amps is volume. Watts are total power, a product of volts*amps, just as total volume of a liquid would be the product of pressure*volume.

Your battery is both the reservoir and pump, the ESC is essentially a valve. Increasing pressure by going to a higher voltage battery means nothing if the volume isn't there. Basically be the equivalent of switching from a garden hose to a homeowner grade power washer and trying to fill the same bucket; the latter generates a lot more pressure, but it cannot deliver the volume.

The power potential of an electric motor means nothing if the power supply cannot deliver. Battery power or discharge insufficient, ESC not capable of transmitting enough power or wires too small, the motor will not realize it's potential.

You don't say what power system you're running, but you need to be aware that, while far more efficient, brushless systems have a much higher power demand under heavy throttle than brushed systems. That's why the lithium-polymer (LiPo) batteries have such high discharge ratings (C rating). The C rating is the multiplying factor of the battery's total capacity: a 5,000 mAh pack with a 50C discharge rating can deliver a maximum of 50*5,000 milliamps - 250 amps - instantaneously. The same 5,000 mAh pack with only a 20C rating peaks out at 100 amps.

[stulec52]

Most likely has a lower discharge rating. Think of it like water; voltage is pressure, amps is volume. Watts are total power, a product of volts*amps, just as total volume of a liquid would be the product of pressure*volume.

Your battery is both the reservoir and pump, the ESC is essentially a valve. Increasing pressure by going to a higher voltage battery means nothing if the volume isn't there. Basically be the equivalent of switching from a garden hose to a homeowner grade power washer and trying to fill the same bucket; the latter generates a lot more pressure, but it cannot deliver the volume.

The power potential of an electric motor means nothing if the power supply cannot deliver. Battery power or discharge insufficient, ESC not capable of transmitting enough power or wires too small, the motor will not realize it's potential.

You don't say what power system you're running, but you need to be aware that, while far more efficient, brushless systems have a much higher power demand under heavy throttle than brushed systems. That's why the lithium-polymer (LiPo) batteries have such high discharge ratings (C rating). The C rating is the multiplying factor of the battery's total capacity: a 5,000 mAh pack with a 50C discharge rating can deliver a maximum of 50*5,000 milliamps - 250 amps - instantaneously. The same 5,000 mAh pack with only a 20C rating peaks out at 100 amps.

that's a great explanation !!

just one thing, I read that the 8.4 pack actually performs the way it was expected on another car.
So, perhaps on the RC-10 there is something else going on ?
maybe try the RC-10 again with the 7.2
then double check your speedo settings
then also check you are charging the 8.4 correctly.

[rcyeddo]

The speed control I'm running is an xp sc450- brushless esc with a reedy 540r 3300 kv motor,the battery runs with as much power as my other 8.4 batteries on my traxxas slash,just bought the rc 10 2 weeks ago it is a rc10b4.1,the spec on esc says it can run2-3 lipo,6-8 nimh. It does perfectly fine with 7.2,thanx for help!!


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[rcyeddo]

Yes what sixtysixdeuce makes a lot of since, so sounds like May need new esc?


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[Sixtysixdeuce]

Yes what sixtysixdeuce makes a lot of since, so sounds like May need new esc?

No, not if it's fine with a 6 cell NiMH. What make & model is the 7 cell pack you bought? Not that an upgrade would be a bad thing; I'm no fan of the stock AE ESCs. Take a look at Hobbywing stuff, such as the Xerun 90 amp (about $70). Far better performance and tunability than the AE unit.

Is the Slash a brushed model? That may explain why it performs OK in the TRX but not the brushless AE.

Having said that, your ESC has LiPo cut-off, and 2 cell LiPo packs can be had for $30 or less on eBay. I'd say just grab a couple of these and be done with it:

http://www.ebay.com/itm/350823207794?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

Soft packs, but good batteries, very high discharge (50C cont., 100C burst). Personally, I prefer soft pack batteries. I'm running several of these in some pretty hungry vehicles (4 pole motors, both 540 & 550 size, as opposed to your Reedy 2 pole 540 can), and they perform well.

[rcyeddo]

The battery pack that I bought is a venom 5000 mah 8.4,the slash I have is also brushless,and I also have a phoenix xt brushless that the battery pack seems to run fine in.


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[rcyeddo]

O and just wanted to add that the 7.2 that I'm running is also a venom 5000 mah


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[rcyeddo]

I'm not sure what the speedo settings are that stulec52 mentioned?


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[rcyeddo]

I'm thinking the battery might have to much power for the gear box may have something slipping in their


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[Sixtysixdeuce]

I'm thinking the battery might have to much power for the gear box may have something slipping in their

Certainly a possibility. Check the slipper clutch and diff. Either one being too loose will be a problem getting power to the ground.

[rcyeddo]

Well wasn't the slipping ,definitely a power loss when I go to that 8.4 battery,I'm lost


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[Coelacanth]

Could be overlooking the obvious; the battery could be defective. Can you bring it with your car back to the store and have them try another battery with the same approximate rating? Or, did you test the questionable battery in another car?

EDIT: Nevermind the last part, I see you've tried the battery in a different car and it seemed to run fine...but that doesn't rule out the battery being defective, just yet.

One thing I've learned working in computers for nearly 2 decades, is never assume any brand-new electronic component works perfectly. The failure rate of even brand new electronics is actually a lot higher than people might expect.

[rcyeddo]

I just noticed something else,when I have the 7.2 on the car it seems like It have a lot more power going forward then in reverse,when I have the 8.4 on the car it seems like there is more power in reverse then in forward.,still at a loss


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[rcyeddo]

Still no luck with power loss,I also have a new traxxas slash brushless, a thunder tiger phoenix,a redcat caldera and a traxxas rustler brushed,any suggestions on taking any parts off of any of these to hop up the rc 10?


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