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Old 05-04-2008, 09:51 PM   #1
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Default LiPo and NiMH equivalents--- Formula?

Is there an equation out there that helps to determine similar LiPO and NiMH packs? For example, I'd like to set up a class that would use 3200mah 7.4v LiPO. Is it safe to assume that the NiMH battery that would complement this would be a 3200mah 7.4v?
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Old 05-05-2008, 07:58 AM   #2
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Is there an equation out there that helps to determine similar LiPO and NiMH packs? For example, I'd like to set up a class that would use 3200mah 7.4v LiPO. Is it safe to assume that the NiMH battery that would complement this would be a 3200mah 7.4v?
if you work out a ni-mh battery to have 70-75% charge/discharge efficiency at 30 amps, as they do get awful warm. (lipo is near enough 100. about 98 to be exact.) you can work it out from that. a 3300 lipo is about the same as a 4200 ni-mh. but there is no exact way to do it, as they both work differently.
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Old 05-05-2008, 05:37 PM   #3
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wouldn't buy anything that small. if i can buy something and charge it up half the time of a nimh battery, while getting double the use out of it.. why would i not take advantage of it as a consumer?
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Old 05-05-2008, 05:55 PM   #4
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wouldn't buy anything that small. if i can buy something and charge it up half the time of a nimh battery, while getting double the use out of it.. why would i not take advantage of it as a consumer?
I can buy a 350 chevy V-8, but I am not allowed to run it in my MINI STOCK 4 banger car...

I can buy a 22 gallon fuel cell, but we're only allowed to run 8 gal. fuel cells.

Just because you CAN buy something doesn't mean that is what needs to be allowed to run. (You can get NiMh batteries larger than SUB "C" too)

back to the question, they are not really comparable for many reasons...one of which is WEIGHT and Discharge curve. That doesn't mean that for local 'FUN' racing they can't be mixed. (The quality of the driver...is probably going to be more important)
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Old 05-05-2008, 08:35 PM   #5
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hi,

from a recent race, i think a 3200 lipo is much more powerful than a 3700NiMH. also lipo allows better weight distribution for a better handling car.

but for fun yeah mix em all

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Old 05-06-2008, 09:13 AM   #6
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I ran my EP4200s and my SMC4000 lipo back to back in my Losi JRXS-R this past weekend. I have weighted the Lipo pack to equal a NiMH and the only difference I could imagine there was would be that the weight on the lipo is a little higher than on the NiMH thus possibly raising the center of gravity a bit on the Lipo. Otherwise everything was exactly the same including Track temp, tires, 17.5 brushless, etc.

My lap times with the NiMH were 2 tenths faster on average than the Lipo. hot Lap with the NiMH was late in the run and 3 tenths faster than the hotlap with Lipo.

I still love my SMC Lipo though.
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Old 05-06-2008, 03:17 PM   #7
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what about runtime? surely the lipo will run for a lot longer?
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Old 05-06-2008, 05:11 PM   #8
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MAH is Millie Amp Hour. Same number same number of amps discharged over same amout of time. Gas tank the same size. Higher MAH Nimmhs tend to have higher Voltage. Lipos tend to be consistent in the voltage. Voltage drop offs, and loss from IR will change performance. runtime should be very similar.
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Old 05-07-2008, 03:03 AM   #9
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MAH is Millie Amp Hour. Same number same number of amps discharged over same amout of time. Gas tank the same size. Higher MAH Nimmhs tend to have higher Voltage. Lipos tend to be consistent in the voltage. Voltage drop offs, and loss from IR will change performance. runtime should be very similar.
it all depends on how they measure it though. a li-po will deliver most of the rated power due to the low internal resistance. a 4200 ni-mh measured at 300mah discharge will only deliver 70% of that at 30 amps, due to the resistance. thats where the heat comes from.
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