Li-Po or NiMH? I'm confused.

[RC-Monster Mike]

I created an excel file that calculates the info. I enter tire size and motor/voltage info and it gives me speed in each gear. I have all the calculations from the tranny reduction to the diff reduction entered into the formula. I also have allotments for 1/8 diffs, center diffs, etc. in the spreadsheet, so I can pretty accurately figure out almost any combination for the e-maxx. The formula doesn't take into account wind resistance or voltage drop or tire ballooning, but with some thought when entering in the voltage (based on experience), it is very accurate. I also can adjust tire size for big foes, 1/8 buggy tires, etc..

[lipomax]

Hey, before you give up on Lipos: First of all, I *DON'T* know for sure if it was the lipos! I was charging my 12 cell emaxx pack too at the same time and my Triton charger had on occasion, never "peaked" and would charge till the GP3300's melted the solder joints and came apart. Melting solder joints meant that the batteries got OVER 400 degrees F. Last time I checked, paper has a flashpoint in the 400 degree mark too. Those batteries were simply sitting on top of a cheap plastic table! Talk about smart huh? Especially since just a month or two prior, they blew up in my garage. At the same time, a AA charger was on... and so was the Astro 109 charger with TP 1900 11.1 volt pack. I SUSPECT it might be the 3s 1900 mah TP pack because the pack that I charged PRIOR to that the day before was a 2s4p TP8000 mah pack... I still wonder if the charge setting was at 8.0 amps for a 1900 mah pack! I might actually purposefully charge my 2000 mah packs at 8 amps just to see what happens. If nothing happens, it could've been the NiMH!!!!!!!

SO, whatever happened, I can't blame one battery over another. I've had NiCads BLOW up when I charged them with my homemade 5 minute charger (I charged them at 20 amps!!!!)

SO, all batteries ARE DANGEROUS. All batteries should be charged with caution and with supervision and if not, charged in a container where they could blow up and not harm anybody. So, Liborland, I don't think you should quit lipos so early.

My 2cents worth.

[lipomax]

BTW, Mike, I have an excel file that has different vehicles, different KV motors, battery voltage, RPM, tire diameter, pinion, spur blah blah blah just like you! Hahaha That's pretty interesting. I started doing it back when I was 14 or so years of age on Appleworks spreadsheet. Back then, it was done so I could measure speed, motor RPM, tire RPM, and stuff based on a speed trap and I had different ratios etc. I used it and came to the realization that sometimes a super large pinion will actually be slower than optimal gearing. After a couple hundred entries, the old Apple IIe would take a good 3-4 minutes just to recalculate and that's how I got an IBM AT. Fast forward like 17 years... and now we have Excel worksheets. LOL

I've found voltage drop pretty minimal actually in speed runs. Most of the voltage drop occurs during hard acceleration, but as it nears top speed, voltage drop is usually within 10% of "voltage". Have you noticed that too?

[liborlad]

Guys, are these spreadsheets confidential, or are you prepared to send one over for me to play around with, it would come in handy for sure.

I hear what you are saying Lipomax about all batteries being dangerous. In normal circumstances though it seems pretty clear that LiPo's are far higher up the "death & mayhem" scale than NiMH.

I think I'll stick with regular batts for the time being and look into LiPo's further down the line when I have more experience. Thanks for all your input.

[HotnCold]

And Mike also has it on his palm computer so he can check and change combinations at the track. Its really pretty cool... But that eagletree - Now thats the sheezy.........

[RC-Monster Mike]

Lipo- Yes, I have found the spreadsheet to be very accurate for calculating top speed. I usually use 1.1 volts or 1.05 volts per cell and can get the speed within a mph or so of real life. I guess great minds think alike ;)

Liborlad - In my opinion, the LiPos are only more dangerous than the Nicad and nimh because they have more energy. The same precautions must be taken with either battery. I have seen plenty of nimh and nicad batteries blow up at the track over the years. I LiPo will just have more energy per pack, so is that much more dangerous. With respect and diligence, the packs will be very reliable and safe. The batteries won't spontaneously combust, as some posts suggest. If misused, they may be dangerous, just like all batteries.

[lipomax]

Okay, try going here for a copy of a simplified version of my excel worksheet.

http://home.comcast.net/~youngsongdmd/rc.xls

[rcjmaxx]

I have a lipo setup I'd like to get your opinions on.I have an Emaxx with the 9L/9918 combo,with 14 3300 cells installed,a steel rolecage and stock tires the truck weighs 10 lbs 2 ounces.As a basher I run 15/65 gears,for top speed I run 18/65.I love the performance I get with this setup but want more runtime.I'm looking to go with 2 PolyQuest 4400 3s lipo packs in parallel,what can I expect in runtime and performance?Would 3500 4s be a better way to go?My charger can charge up to 3 lipo cells.I run 40 mph with no problem,will I be able to exceed this by much? Thanks

[RC-Monster Mike]

The 3s Lipos will reduce your top end quite a bit compared to the 14 cells you are using now. Your punch will probably be pretty close, depending on the cells you use. I would pick up a couple 3s packs and a couple 2s packs and run them in pairs (a 3s and a 2s in series to give you 5s). This would be like a little over 15 cells worth of voltage (nicad/nimh), so you could drop a tooth or so and retain your speed, but pick up some runtime from the lower weight and increased capacity.

[lipomax]

Mike mirrored my thought here. I'd agree with Mike here. Going 5s 4400 mah lipos will give you approximately 40% more run time geared for the same speeds. With the higher voltage, you would have to drop a pinion gear or so. That would reduce amperage. In addition, the MUCH lower weight will also reduce amperage some more.