FUBAR VXL

Guys,

Im running my Slash 4x4 VXL and as you know it comes with a 8.4V 3000mAh Nimh.

I was REALLY impressed with the battery - good power, good speed, just not the best length of a run time.

So, Ithen tried my son's 7.4V4000mAh LIPO - thihking that it would be an improvement - yet it was not.

Im assuming, since my Slash is a 4x4 that it really needs the higer volts (8.4) vs the lower voltage (7.4) - so to really run the Slash with solid power and speed - should Iinvest in an 11.1V LIPO? If so, what mAh do you suggest? A 5000 is around $80. An 8000 is alot more...

Im just stuck between the higher voltage Nimh vs. a lower voltage LIPO - so Iguess the only solution is an even higher voltage LIPO...

Thoughts?

FUBARVXL
Rustler VXL
Slash 4x4 VXL

nitrosportsandrunner

what is the "C" rating of your 2s lipo. It should have the same (if not slightly more) punch than the 7cell nimh.

But if the "C" rating was low then it wouldnt put out enough amps (punch)

Also, the "C" and mah work together.

I use 2s 30c 5000mah lipo packs.

But to answer you last question, a 3s lipo is a HUGE difference over the stock 7cell.

Go buy a 3s 30c 5000mah sky lipo pack off hobbypartz.com.

FUBAR VXL

All the high mAh LIPO's (that are in stock everywhere) are the 25C.

Is 25Cenough to run the Slash 4x4 with good power and speed?

Im looking at the DuraTrax 7.4V 8000 mAh 2S 25C LIPO - its $73 at Tower Hobbies.

Im just afraid the 11.1V batteries may be too much for me - Im a beginner and "speed" is not a priority to me - but maintaining 4x4 power is very important - as is a good run time.

Thanks,

FUBAR VXL
Rustler VXL
Slash 4x4 VXL

ThunderbirdJunkie

My Feedback: (3)

What was the C rating on the 4000mah battery?

In anything brushless, a 2S LiPo should walk all over any 7 cell NiMh all day, every day.

cummins driver

My Feedback: (31)

What you are worried about here is amperage.

The way it is calculated is to turn the MAH into a decimal and then multiply it by the C rating.

So lets demonstrate:

Say we have a 4000mah 25c lipo

4.0 x 25 = 100amps

Now lets say its an 8000mah 25c lipo

8.0 x 25 = 200amps

And lets look at a 5200mah 30c lipo

5.2 x 30 = 156 amps

So you can see the mah and C rating BOTH are just as important. A very high C rated low mah battery still wont have good amperage. And vice versa. Voltage also has no effect on figuring the amperage the battery can provide.

Id reccomend 120amps or better for a slash 4x4, although id say a 100amp battery would be ok. The higher the voltage, the less amperage that is needed as well because it is more efficient.

Hope that all makes some sense and helps with your decision.

Foxy

Surprised nobody mentioned this yet...A fully charged 2s lipo is 8.4v. No comparison, the lipo will be better in every conceivable way.

kistner

My Feedback: (10)

The 7 cell nimh would charge higher than 8.4 as well, not that I disagree with the lipo being better. The nimh would be considerably heavier.

SyCo_VeNoM

also the NiMh's voltage would be at 8.4volts very quickly (like 1-2 mins tops) where the lipo will still be up around there so being over the lipo temporarily isn't a huge issue IMO

phmaximus

Yes i was confuse bu the OP's first post, I disagree 100% with all my tests even with a brushes slash 2wd The lipo was heaps better with torque & speed....

All i can say there must of been something going on with the lipo he tested...

nitrosportsandrunner

You can buy a pair of 2s 30c 5000mah packs off hobbypartz.com for $54 shipped. Thats a better deal than a single 8000mah $73 pack IMO.

The slash 4x4 on 3s is alot. truck can wheely if it gets traction...or just wheely at speed from the body and chassis catching the air.

If you wanna race the 4x4, drive on a track...then stick with 2s.
if you wanna bash hard or do speed runs on the street, 3s.
Note that a 3s is much more likely to cause stripped spur gears and snapped driveshafts.

FahrtAutoRC

I was going to mention this but only now stumbled across this thread. The LiPo will be lighter, hold its peak better, so on and so on. One thing I would NOT recommend is going 3s. The VXL systems are notoriously weak-hearted and prone to failure, I'd buy one cheap Turnigy LiPo and then save my funds for a better ESC, IMHO

FUBAR VXL

Thanks guys for all your replies.

Based on everyone's responses, I have determined that the best of both worlds would be a 7.4V 5000 to 8000 LIPO for my Slash 4x4. Im definately not going with an 11.1 - not worth frying my gears over it.

Im leaning towards the 7.4 8000 for the longer run times...

I would definately look at one of the mentioned 5000 mAh batteries - but they always seem to be Out Of Stock, no matter what website I check.

Ill let everyone know what I end up getting and the overall results once I get a few runs in with it.

FahrtAutoRC

Finally someone realizes that mAh=run time, NOT power. Go with the highest C rating you can in your price range, check out the Turnigy NanoTech LiPos

kistner

My Feedback: (10)

power = volts X amps

you cant take amps out of the power equation, bigger MAH can mean more power

phmaximus

Bigger mah rated batteries wont loos as much volts under load compared to a lower mah rated battery...

For top end speed voltage drop is important to know

SmOkEeJay

SPC makes a very good battery. I run a 2s 5000mah 25c in my Rustler and it does very well. I have a 8.5t 4000kv motor.

LaTuFu

My Feedback: (1)

I run the SPC Racing 8200 mAh 25c 2s batteries in my Revo and Summit.  One of them would be great for long run times in your Slash, assuming it will fit in the battery tray.

Foxy

mAh has nothing to do with power, it's a unit of capacity. C is the load rating unit for batteries and directly correlates to power (Watts). Look at it this way; an 8000mAh battery can be 25C (capable of delivery 25*8 amps at 7.4v = 1480Watts) or it could be 1C, only capable of delivering 8A = 59.2Watts).

kistner

My Feedback: (10)

And yet you used the capacity in your calculations both times. I did not say higher capacity always means more power, but it is a factor of it.

Foxy

But it's not a factor of power. It's just a figure used as part of the calculation due to the way the unit C was designed. The fact that batteries of the same mAh can have different power delivery characteristics is all someone needs to know to understand that mAh (capacity) is not in any way related to power (Watts). The power could still be calculated without knowing the mAh. You could say the power delivery unit was 5 elephants, then nobody would know that it was relative to the mAh. The fact that it is relevant to mAh is simply due to the convenience for discerning any number of additional calculations. Think of it this way...a car with smaller diameter wheels accelerates faster for the same power and weight than a car with larger wheels, does the wheel size have anything to do with power? The rollout length is absolutely critical in determining wheel horsepower, but in no way relates to the power of the engine, it's just a number used in the calculation.

Anyway, just clarifying so noobies aren't confused thinking that when they pick up an 8000mAh battery its more powerful than a 4000mAh pack (for example), the way your post was phrased could indicate that. I think my clarificatoin was an important one, I'm not trying to call you out, I know you know what you are talking about dude

phmaximus

Hows I got my GT Power Watt meter today...


Should be able to prove wrong some miths about the amount some setups current draw... and how the votlage drops.
Once i get a few RPM sensors for my cars I can go into more detail with the relation ship in speed.

Over the next few months I will be testing 3 touring cars(4x4, FF & drift) truggy, Slash 2wd and a crawler on a 2s lipo & some on 3s....

Was at the track last week and a guy had a 150a hobbywing ESC in a 1/10 truggy.... just wish i had my 35a truggy to show him i was getting the same preformance at a fraction of the cost. and there was no way with his gearing it was using anything neer 1000a on take off

More brain food
Power = voltage x current
Power = force x velocity
Power = rpm x torque

kistner

My Feedback: (10)

Maybe I am missing something. if you have a 4000mah battery at 25c and a 8000mah at 25c wouldn't the larger battery have more amps available? The only calculation I've seen used is mah times c rating gives amps.

Foxy

You're not missing anything, that would be true of batteries with the same C rating. Which is exactly my point, it's the C rating that matters, not the mAh. To use your own example... A 4000mAh battery of 40c, an 8000mAh battery of 15c. Which can deliver more power? See what I mean?

phmaximus

Yes that's correct. But that doesn't mean higher mah batteries have a higher amp rating. It's all about mah and there c rating together.
For example u can get a venom 2s 2400mah reciver battery but it's only rated at 0.5c that's only 1.2 amps max
Where u can get a zippy 2s 350mha micro sct battery thats rated at 20c that's 7amps
So rember mah ratings mean nothing all by them self. And neither does the c rating. It's all about there amp rating, witch is mah devided by 1000, times the c rating

phmaximus

How's just playing with the watt meter inside.... On a slash 2wd just running under 3 meters at full throttle, not much room inside.
It's pulling 57.35amps and peak watts 395.3... Might play around more in the morning, it's 21:30 here