Lipo advantages?
 

I'm considering jumping to lipo's but first I would like to know what's the real advantage of lipo's. Is it just the weight savings? And while we're on the subject what lipo's or how many lipo's would I be able or should I run with an 8XL/9920 combo in a 12lb supermaxx. I'm not the sharpest tack when it comes to understanding all this electrical stuff :P: but if you talk real slow it might sink in. :) Thanks and I hope santa was good to everyone.

Lipo holds the voltage more under load than nimhs. You can run 5s or 6s lipo on the 8xl.

Constant output of power! if you run nimh, the speed and performance will slowly decrease over time, but with lipos, the speed/pefroamce is the same in 15 minuties and 1 minute during the runs. Also, lipos got MUCH HIGHER mah! longer run times! :) Also, its coudl be used as an effective terrorist devices!<---That part has been very useful to me lol j/p!

Just for a comparison what would a 5s or 6s be equal to in nimh cells? and would the run times be almost twice as long using the same gearing?

Hey nbcaz be careful about the "T" word...... I heard that GEE-DUB-U :devil and the boyz are watching.:eek: It's sad that even crossed my mind but I guess what they say is true about history repeating itself.:W:

5s Lipo would perform like 16 cells. 6s Lipo would be like 19 cells. Runtime depends on actual capacity, but for the weight of Lipo, you can easily get twice the capacity over NiMh and still have a lower weight.

Thanks metalman. I know this is going to be like asking the Chevy vs. Ford question but what are some of the prefered sources for lipos and a good lipo charger that I won't need to take night classes to understand:P: Thanks

http://www.maxamps.com has good deals on Lipos. What you get really depends on how much you are willing to spend. A cheap 5s Lipo charger:
http://www.rc-monster.com/proddetail...charger&cat=19
For anything above 5s Lipo, you would either have to go with the Astroflight 109 (which isn't CC/CV), or spend $100 more.

When you change to lipo's do you still use dual packs or is it just a single pack. I want to know for future configuration of my maxx, I'm try to decide where to mount the esc, ubec and if I only will be straping on one battery pack instead of two that changes the game a bit. It sure would free up space on the chassis. Thanks.

You can charge dual packs together, and always treat them as one pack. This would complicate balancing, unless you got 2 separate balancers (if you were to use them). Or, you could always have 2 packs and charge them separately.

That brings up a quick question: How are parallel cells, like in 4s2p packs, charged without this same concern? The wires between each cell must be hooked to each parallel set right?

So the prefered method is a single 5s or 6s pack, right? It seems that would be simpler. What are the dimentions of a pack that size?

That depends upon construction of the pack. If a pack is built into 4 groups (or blocks) of 2 cells in parallel, then all 4 groups are put into series, then there should not be any concern about charging. Basically, the 2 cells in parallel act as one (1) cell, and always maintain the same voltage between the 2. For this setup, only one balancer would be needed.

Taking 2 series packs and putting them in parallel requires more attention. The cells in one pack cannot balance themselves out with the cells of the other pack. The 2 packs together will maintain the same voltage, but that is different. For 2 packs to be put in parallel during charging, 2 balancers would be needed.

It is always best to get 2 2s2p packs and hook them in series than it is to buy 2 4s1p packs and hook them in parallel. It is much better to charge 2 packs in series than to charge 2 packs in parallel.

The way you have a pack set up depends on the capacity of the cells. If you want 4000mah, and can only use 2000mah cells, then the ideal configuration would be to have a parallel and series pack, as described above.
The dimensions of a pack depend upon the brand and the capacity.

I'll be using 9920/8XL combo on my supermaxx. Ideally I would like to use just one pack. I'm sure there are many packs to look at but I'm looking at the one below. It may be a little much for the 9920. Does the 99 amp rating on the esc refer to a cotinuous draw or a peak that it can sustain? Sorry to be so thick headed on this stuff but I'm still going through the learning curve on this lipo stuff. Thanks.

http://www.flightpower.co.uk/proddet...p?prod=4200022

That pack should work just fine. The 9920 is more than capable of handling that setup. It is rated to handle 99amps continuous.

Thanks, I think it's starting to sink in. Not sure I fully understand the parallel or series thing yet but I'll keep reading the threads and what ever else I can get my hands on.

If you have any specific questions on series/parallel, just ask. I can draw up a diagram for you, as that would be the easiest way to learn.

I'm still a little confused (what else is new).
So when you go LiPo, can you replace the dual NIMH packs with one single LiPo? Or do you still have to have 2 LiPo's on each side just like the stock setup?
Thanks.

Either way. If you want to keep a Lipo on both sides (and put them in series like NiMh), then get 2 packs. If you want to run 4s Lipo, then get 2 2s packs. For 5s Lipo, get a 2s and a 3s pack. For 6s, get 2 3s packs.

Would it be okay to stack two 3s packs on top of each other, provided I could securly mount them?

Yes, you could, but some double-sided tape between the two would help.

Yeah, I was thinking that or velcro.

Now that I've got a pretty good understanding of lipos, I have a couple of questions about chargers and power supplies.

1. I will be using high mHa lipos (3700+). What features should I look for to properly charge my batts? Do I need a charger that can charge more than 5 amps? Recomendations?

2. I would like to have a power supply that I could run two charges at the same time from or would it be better to have two power supplies, one for each charger. Recomendations

3. How long does it take to charge lipos?

1. You can use any charger that can charge at 3.7amps or less. Lipos (unless otherwise stated) should not be charged higher than 1C, where "C" equals the capacity in amp-hours.

2. You could use a single or dual chargers. If it were me choosing, I would pick whichever setup that would be cheapest.

3. 90% charge in 1 hour (at 1C charge rate), and 1 1/4 - 1 1/2 hours for full charge (at 1C charge rate).

Thanks again MM. Is it possible to run two chargers at the same time off one power supply?

You can if the power supply can put out enough.

ie...10 amps output to use two chargers charging at 5 amps each. I guess you would also need enough output terminals also. right???

yes. i would get the one metalman uses. he can tell you which one to get. i have a n-power and like it but it can only put out 10 amps.

The link to the power supply I use isn't working right now. It is rated at either 10.5 or 12.5 amps (can't remember). It would be able to handle 2 chargers charging up to 3.7amps and for up to 4s Lipo on each.

EDIT:
Now that the link is working,:
http://www.emtel.com/search/product_...t_id=EMV15012V
It is rated at 12.5amps.