17.5 tips and speed secrets
#241
Joined: Mar 2009
Posts: 2,944
From: Santa Clarita, CA
#242
the whole LiHV thing is a non-issue. if you run at a track where everyone else is doing it and the racers have basically decided it's ok, then what's the harm? of course you can't do it at a big race. sure it's against ROAR rules, but so is charging over 1C and having a battery hotter than 5 degrees above ambient and just about everyone does that.
occasionally i'll walk around the pits and peep people's chargers to see what they're charging to. i've seen one guy charging to 4.35v but he's in the intermediate class so i don't care about him. i've never caught an expert guy charging over 4.22v (which is what i do as well. when pulled off the charger, the pack is 8.39-8.40v. confirmed this at a "big" race where they tech'd batteries).
occasionally i'll walk around the pits and peep people's chargers to see what they're charging to. i've seen one guy charging to 4.35v but he's in the intermediate class so i don't care about him. i've never caught an expert guy charging over 4.22v (which is what i do as well. when pulled off the charger, the pack is 8.39-8.40v. confirmed this at a "big" race where they tech'd batteries).
#243
I recently picked up a brand new Orion 3200 and the IR numbers are so high I'm not sure I will use it at all. They are typically around 4.0mOhms. As socket said I don't usually use batteries once they get this high let alone run new packs with this high of IR. It's a bit frustration since they advertise low IR....nothing you can do I guess.
Socket can you comment on super shorty packs? I had bad luck with the 2800 but would like to have a pack that is around 150grams or a little lighter would be ok. This way I can fit it under my rear waterfall farther than a full size and also use an under battery weight for super low cg. Thanks!
Socket can you comment on super shorty packs? I had bad luck with the 2800 but would like to have a pack that is around 150grams or a little lighter would be ok. This way I can fit it under my rear waterfall farther than a full size and also use an under battery weight for super low cg. Thanks!
#244
I recently picked up a brand new Orion 3200 and the IR numbers are so high I'm not sure I will use it at all. They are typically around 4.0mOhms. As socket said I don't usually use batteries once they get this high let alone run new packs with this high of IR. It's a bit frustration since they advertise low IR....nothing you can do I guess.
Socket can you comment on super shorty packs? I had bad luck with the 2800 but would like to have a pack that is around 150grams or a little lighter would be ok. This way I can fit it under my rear waterfall farther than a full size and also use an under battery weight for super low cg. Thanks!
Socket can you comment on super shorty packs? I had bad luck with the 2800 but would like to have a pack that is around 150grams or a little lighter would be ok. This way I can fit it under my rear waterfall farther than a full size and also use an under battery weight for super low cg. Thanks!
#245
Joined: Mar 2008
Posts: 5,717
From: At dirt tracks in Michigan!
This is how the internals of a Lithium Polymer battery looks

With that being said, the battery manufacturer determines the tolerances. The plates and how they transfer the power through the tabs is all part of this process. So how they manufacture the batteries determines the internal (inside the battery) resistance. Now the mah or milliamp hour of the battery is determined through the size of those plates. So an 8000mah battery can have the same internal resistance of a 200mah battery and vice versa. The size of that plate creating the larger milliamp hour does not increase voltage. They merely act as a larger fuel tank in the simplistic nature. Danny of SMC discusses this a lot on his facebook. He honestly is one of the most beneficial people to the industry. For stock a lower resistance pack will allow for more power to be transferred into the esc to be converted to the power needed for the motor.
Higher resistance = smoother (makes electronics work harder)
Lower resistance = punchier (makes electronics work easier, creating more power)
Higher mah = more run time
lower mah = less run time but possibly lighter (LRP sells these as lcg packs)
What I run in my cars:
Stock buggy 4250
Stock stadium truck 5400
Stock SCT 5400
I have ran the 4250 in all my vehicles until the 5400 have come out. I can make run time with the 4250 in stock sct (probably the most load pulling class raced at big races) but I can feel the discharge curve hitting its limit at eight minutes after two minutes of warm-up laps.

With that being said, the battery manufacturer determines the tolerances. The plates and how they transfer the power through the tabs is all part of this process. So how they manufacture the batteries determines the internal (inside the battery) resistance. Now the mah or milliamp hour of the battery is determined through the size of those plates. So an 8000mah battery can have the same internal resistance of a 200mah battery and vice versa. The size of that plate creating the larger milliamp hour does not increase voltage. They merely act as a larger fuel tank in the simplistic nature. Danny of SMC discusses this a lot on his facebook. He honestly is one of the most beneficial people to the industry. For stock a lower resistance pack will allow for more power to be transferred into the esc to be converted to the power needed for the motor.
Higher resistance = smoother (makes electronics work harder)
Lower resistance = punchier (makes electronics work easier, creating more power)
Higher mah = more run time
lower mah = less run time but possibly lighter (LRP sells these as lcg packs)
What I run in my cars:
Stock buggy 4250
Stock stadium truck 5400
Stock SCT 5400
I have ran the 4250 in all my vehicles until the 5400 have come out. I can make run time with the 4250 in stock sct (probably the most load pulling class raced at big races) but I can feel the discharge curve hitting its limit at eight minutes after two minutes of warm-up laps.
Let me know if this helps:
What if we compare them to plain resistors. Let us take two resistors that have the exact same resistance. If you put them in series, the overall resistance doubles. If you put them in parallel, the overall resistance is cut in half. If you pass a current through the set in parallel you will have a lower voltage drop.
Now, instead of resistors you have lipo cells (3.7 volt nominal) rated at 2000 mah, with an IR of 4 milliohms. Take those two cells and put them in series. You'll have a 7.4 volt pack with 2000 mah and 8 milli-ohms of resistance. Now put two of these cells in parallel. You will have a 3.7 volt pack with 4000 mah and 2 milliohms of resistance. Just like the resistance of resistors is cut in half if you put two identical ones in parallel, the same holds true for battery packs. If you add another "1s pack" to it in series, you will end up with a 2s pack with 4000 mah and an internal resistance of 4 milliohms.
Going a step further, instead of having two identical cells and putting them in parallel you simply make a cell that is twice as large. Assuming the tabs and other wiring isn't an issue, the internal resistance of that larger cell is smaller than that of a smaller capacity cell of the exact same chemistry and quality (or roughly the same as two cells half its capacity in parallel).
Comparing it to your fuel tank analogy, you need to add an additional fuel pump to make the comparison roughly similar. We can equate the surface area inside the cell to the fuel pump in a gas tank, so if you add another gas tank and fuel pump to your truck, that is more similar to adding an additional cell in parallel than just adding a larger fuel tank. Now that you have an additional fuel pump, you can draw more fuel without starving the engine. Same holds true for cells in parallel or simply larger cells.
Sorry if I rambled.
Last edited by Krio; 08-22-2016 at 12:11 PM.
#247
Joined: Oct 2004
Posts: 3,360
From: Michigan
#248
Joined: Mar 2009
Posts: 2,944
From: Santa Clarita, CA
#250
Tech Rookie
Joined: Jan 2008
Posts: 13
From: Buford, GA
Just coming back to R/C after 25 years off. Ive read this thread from page 1 and there is a lot of good info. Thank you all for sharing.
I want to run 17.5 in b6d. Its a smallish local course track, clay med to high traction. Im thinking SMC shorty battery, with fantom 17.5.
What about an ESC recommendation please? Earlier in the thread there as talk that certain ESC could not be as good as "the fast guys".
I want to run 17.5 in b6d. Its a smallish local course track, clay med to high traction. Im thinking SMC shorty battery, with fantom 17.5.
What about an ESC recommendation please? Earlier in the thread there as talk that certain ESC could not be as good as "the fast guys".
#251
That's what motor and battery I have, but haven't ran the car yet so I can't give you any feedback on how it performs. Seems like for stock racing something like the Hobbywing Justock would be a good fit, or if you want to spend a little more, the Reedy 800z is a popular choice.
#253
Just coming back to R/C after 25 years off. Ive read this thread from page 1 and there is a lot of good info. Thank you all for sharing.
I want to run 17.5 in b6d. Its a smallish local course track, clay med to high traction. Im thinking SMC shorty battery, with fantom 17.5.
What about an ESC recommendation please? Earlier in the thread there as talk that certain ESC could not be as good as "the fast guys".
I want to run 17.5 in b6d. Its a smallish local course track, clay med to high traction. Im thinking SMC shorty battery, with fantom 17.5.
What about an ESC recommendation please? Earlier in the thread there as talk that certain ESC could not be as good as "the fast guys".
#254
#255
Just coming back to R/C after 25 years off. Ive read this thread from page 1 and there is a lot of good info. Thank you all for sharing.
I want to run 17.5 in b6d. Its a smallish local course track, clay med to high traction. Im thinking SMC shorty battery, with fantom 17.5.
What about an ESC recommendation please? Earlier in the thread there as talk that certain ESC could not be as good as "the fast guys".
I want to run 17.5 in b6d. Its a smallish local course track, clay med to high traction. Im thinking SMC shorty battery, with fantom 17.5.
What about an ESC recommendation please? Earlier in the thread there as talk that certain ESC could not be as good as "the fast guys".



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