Savage Conversion

Wow you were very helpful suicide, answered all of my questions!!

A lipo would be nice but as you said - on an offroad truck having to be mounted on the side isn't the greatest idea..

I do have a charger that can charge 3 cell lipos, so that would be ok but then i would need a balancer and the discharge protection (does that run on the truck??) which is even more money so I'd probably just go with 2 7 cell 4000 mah packs run in series.

Approx how much run time would that give me on a 9xl do ya think?

[suicideneil]

Yeah, the LVC device is run on the truck, connected between the batteries & rx- when the voltage drops below a certain level, it triggers an alarm or kills the power so you cant over discharge the batts by accident, or something like that. As for run time with Nimh, provided you get good cells then I would have thought 10-15 minutes would be about average for general bashing- maybe slightly shorter if you do some high speed runs, but in that region anyway. I get about 10-15 minutes using cheapo 4300mah packs with my Hv6.5, so with the much more powerful XL motor run time should be similar using good batteries.

Damn so how are these people getting 40+ mins of runtime out of their batteries? Using really expensive lipos?

[BrianG]

For a given amount of mechanical output power, there are only a few ways to increase runtime:
- Use larger capacity batteries
- Use higher voltage on a higher resistance motor (reduces current)
- Use a more efficient motor (higher % of power gets to the ground rather than wasted as heat)

Originally Posted by FLMSavage

Damn so how are these people getting 40+ mins of runtime out of their batteries? Using really expensive lipos?

I get around an hour runtime on a single pack in my revo, my setup is: TrueRc 8Ah lipo with Neu 1515 1y motor and quark 125 esc. I have an average amp draw of 10.16 amps; it is probably lower though because this was taken from an eagletree graph where I tried to get the highest amp draw possible to really see what kind of numbers my lipos put out... BTW BrianG, what was the math again to see how much runtime you would get?(ex: 8Ah lipo, you draw 10amps average, you get X runtime)??????

Bye

[BrianG]

Originally Posted by cemetery gates

BTW BrianG, what was the math again to see how much runtime you would get?(ex: 8Ah lipo, you draw 10amps average, you get X runtime)??????

- Since we measure runtime in minutes, multiply your Ah rating by 60 to get Amp-minutes.
- Then divide by the runtime you get (in minutes) to get average amp draw.
- Or, divide the amp-minutes by a known average amp draw to get runtime in minutes.

You can use this information to figure out how much extra runtime if you get a higher capacity pack. Example: Let's say you get 10 minutes on 3.3Ah cells. That is 19.8A average. If you upgraded to 8Ah cells, you'd get 24 minutes of runtime. Really, you could just divide 8Ah/3.3Ah to get a capacity ratio, and multiply that by the present runtime to get the same answer, but the other way seems to make more sense to people for some reason...

If you know you get X minutes on a given pack, you calculate the average amp draw. Then, a general rough rule of thumb says that your peak current draw will be about 6x your average draw. So, if you are drawing 15A average, your peak will be around 90A.

For a 8Ah pack drawing 10A, runtime will be around 48 minutes (8Ah X 60 minutes. 480 Amp-minutes / 10A is 48 minutes). Of course, since batteries hardly ever reach their rated capacity when drawn heavily, you can shave a few minutes off that.

[suicideneil]

Im gonna have to start writing these things down.