krone6

Hey all. Decided to join an r/c forum finally and found this is an active one. Did a little searching but didin't find any section on batteries and decided to post this. My question is lipos are fast and good, but what makes them fast and good?Sure they don't get a memory and are light weight, but beisdes wouldn't they still be similar to nimh?Let's take 2s and3s lipos only in this example. A 2slipo is still 7.2-7.4 volts just like a 6 cell nimh.

My other question is if a lipo doesn't get a memory, why bother discharging ever?Why not just keep on recharging over and over?

Thank you on any help.

Shabbernigdo

liops have higher indivigual cell voltages and higher discharge rates.

Jeremy Z

They have higher power density for their weight. A LiPo has about double the capacity for its weight when compared to an equivalent NiMH pack.

They also act as a stiffer current source, so when you hammer the throttle, it just goes faster instead of pulling the pack voltage down under load.

They also have a great shelf life. No need to keep topping them off all the time.

krone6

Thanks, and what about the discharging part?They don't get memory and can last up to a year w/o being recharged again. So why discharge at all?

Oh, and i can't wait to try out my lipo, had it since saturday but my charger won't be here till this wensday. Ehh, no racing for me today.

redfisher1974

You dont have to discharge them.

nitrosportsandrunner

there is volts, and then there is amps. lipos put out more amps(in general) compared to a nimh pack of the same voltage. doing so while being lighter!

krone6

Thanks. Answered two of the questions i couldn't find on google.

Pinolelst

If you don't intend on using them for awhile (a couple weeks ) you should discharge them down (or charge them up ) to a storage voltage = to about 1/2 charge.I use ~ 3.8 v per cell as a benchmark.Otherwise they may degrade if left fully charged for long periods

hope this illuminates
Steve

dockman2

The reason lipo's put out more power is that they have much lower internal resistance compared to nimh/nicad cells. That not only allows you to draw more power from them but it gives you more usable power as opposed to it being wasted as heat. Thats why you will get longer run time from a Lipo of the same Mah as a nimh even though your faster as well.

Access

LiPos store best at 40-60% discharged, or roughly half charged (open circuit ~3.7V). This minimizes the degradation over time which is one of the basic downsides of the chemistry. As time passes, even if the battery is simply sitting on the shelf, it degrades.

"My question is lipos are fast and good, but what makes them fast and good?"
Elemental chemistry?
They're just much more developed. Lithium ions have a very high difference in electrochemical potential, and both the ions themselves, as well as the polymers used to contain those ions are lightweight and space-efficient. Lithium cells do have to be manufactured in a more controlled environment, so they were expensive at first. But now volume manufacturing and cutting out the middleman has in some cases made Lithium ion batteries cheaper than the Nickel-metal hydride ones.

They're not at all similar to NIMH, the only real similarity is that they are both batteries. LiPo and brushless motors together are what was required to get electric RC trucks similar or exceeding performance to nitros and other fuel-powered RC trucks, so naturally some of the sanctioning bodies like ROAR tried to make that technology illegal so that it did not pose a threat to nitro. All they did was manage to hold back the revolution by a few years. Today 1/8th scale electrics aren't uncommon and in the coming few years, we'll see consumer systems marketed toward 1/5th scale and up.

BTW when people talk about things like 'internal resistance', 'voltage', and 'current carrying / load' this is a statistic or measurement of performance. Those things aren't "what makes it better", they are simply measurements that show they are better. What makes it better again is the design, the chemistry, etc.

mrbonez

Access that reply should be a sticky now i finally get it

krone6

Didin't think anyone would post after the questions were answered but all the better. Access's and dock's posts really became clear on why lipos are so much better.