LIPO
 

Anybody got a good lipo diagram/manual type thing I could look at? I don't really understand all the 20C, 3s, 1P stuff....
Thanks!

RE: LIPO
 

Here's a good start? http://www.scriptasylum.com/rc_speed/_lipo.html

RE: LIPO
 

Let me break it down for you:

C = battery capacity. So when they say "20C" it means the maximum discharge rate is 20 x the capacity of the pack. So on a 5000 mAh pack, you could discharge it at 100 A. (20 x 5 A or 5000 mA)

P = # of parallel cells. Paralleling cells doubles capacity but the voltage remains the same. So if you have a 2P pack, it means there are two sets of cells in parallel.

S = # of series cells. This is how you think of Ni chemistry packs. In Nickel packs, all the cells are in series and the voltage is additive. Capacity is determined solely by the capacity of each cell. Once in a while, someone will parallel nickel cells, but not often.

So, for example, if someone wrote 4S2P 20C 5000 mAh:

It means 4 series sets of 2 parallel cells. Each LiPo cell is 3.7 V nominal, so the voltage will be 14.8 V. Each cell has a capacity of 2500 mAh, so paralleling them yields the 5000 mAh.

More important is the capacity, 5000 mAh. Nothing complicated here, and the discharge rate. Don't use it in a set-up that will draw more than 100 A, or your puff it and ruin it.

You'll need to get a balance charger to keep the cells in balance, so they charge evenly and don't puff or burst into flames.

I came from planes, where LiPo is the norm. There are penalties in price & safety for LiPo great weight & size advantage that is offered.

IMO, you're better off with nickel battery packs and brushless motor/controller for now.

RE: LIPO
 

sweet. thanks a lot guys.
would this set-up work?
http://www.hobbycity.com/hobbycity/s...idProduct=7468
http://www.hobbycity.com/hobbycity/s...idProduct=8247

RE: LIPO
 

In a particular vehicle it would work fine as long as the charger wouldn't time out. I can't tell if there's a safety max timer or not. Possibly a lok at the manual and the vehicle that you had in mind would help to be more specific.

RE: LIPO
 

I got a rusty! An old one with an almost new mamba max set up. (5700kv) I don't really care about the run time. (10 to 15 minutes is fine for me, therefore the 2350mah pack will be just right.) All I want is power and speed and this looks like the cheapest way to go!

RE: LIPO
 

I think that is about only half enough battery for a fast rusty. I'd recommend getting at least a 4000 or whatever will fit in the battery box (4000-5000 mah)

RE: LIPO
 

the battery looks good but Im not so sure about the charger..try to get a turnigy accuel 6

RE: LIPO
 

so you are saying that a higher mah= faster speeds? How is this true?

RE: LIPO
 

And if I did get the charger above, could I just plug it in through the balance socket and it will charge and balance at the same time?

RE: LIPO
 

higher mah = longer runtimes, higher voltage, or the higher the number before he S, the faster you will go. 2S is 7.4 volts, which is a little more than a 6-cell nimh or nicd, 3s is 11.1 volts 4s is 14.8 and so on, increasing by 3.7 volts each time. One thing I would suggest it get a hardcase lipo. Is basically like the lipo in the link, but it has a hard protective plastic casing over it. Lipos are pretty soft and can be damaged fairly easily if they get hit hard on you chassis, or by rocks...but a hardcase lipo would be a little bigger and a little more expensive.

RE: LIPO
 

I didn't say that , but it is true to a point. Given two batteries that are from the same manufacturer or family the higher capacity battery will hold voltage better while under a load close to it's max. That voltage will make the vehicle faster. If neither battery were being operated close to their max currents (like in a regular xl-5 rustler) then there may not be a noticeable difference in speeds.

The reason I recommended twice as much battery was for it's ability to deliver twice the current in your vxl. The biggest difference in both cases is going to be runtime (directly related to capacity mah)

RE: LIPO
 

A couple things:

- That battery is a 2350 mAh and rated 25C continuous. Therefore, you'd better know that your motor setup is not going to draw more than 59 A. Do you know what your input current is with a 3S LiPo? If not, ask around.

- That is not a hard case LiPo. If you crash and smoosh one of the cells, you could have world-class fire on your hands. They smoosh easily. The scary thing is that you don't always know it until later. Everything seems fine, you pack it up in your car, head home, and all of a suddenly your car is on fire. Consider a 4000-5000 mAh pack with a hard shell.

- If it has enough ampacity, it would be fast, on account of being so light.

- Maybe I just didn't see it, but you have to know that the balance tap on the pack matches with the jack on the charger. Did it say somewhere that it does? There are lots of different plugs, so you either have to match them, or be willing to buy the right tap and solder it on. (make sure you know what you're doing, or you'll short it out, and you guessed it, fire again)

Lithium fires are no joke either. My dad had a pack go up. The pack had been crashed and dented. We didn't see the damage. he put it to charge, in a glass baking dish on his bench. When he was sanding the leading edge of a wing, it lit off. He said it was a bright green flame about 2 ft. long, and he was damn glad there was nothing in its path. His bench was a hollow core door, so it is good that he had it in the glass dish.

RE: LIPO
 

That is the best explanation of a lipo that I have come accross so far. Good job Jeremy and thanks. It has helped me too. I have been researching this **** to death!

RE: LIPO
 

Hey, no problem chummer.

Maybe this will help even more.

Attached is a quick & dirty Paint image of a 3S2P LiPo. You can see the three sets of 2P configuration. + to + and - to -. These are the black connections.

Then, each parallel set is put in series: + to - and - to +. These are the red connections.

Sounds like it would short, but it won't unless you also connect the outside two. (blue)

Blue is where the output of the pack is. The connections points are the little black dots.

The balance taps would come out from each red connection, and the balancer would just compare the voltage of each set of parallel cells. If they are not even, the balancer will discharge the high one a bit at a time, continuously, until they're even.

NiCd and NiMH cells kind of self balance as they charge, just by being connected together in series. For some reason, lithium doesn't do this.