What batteries to buy and why?

I liked the flight powers too. After comparing the available packs, I found that the 5000 packs are likely too long for a buggy application. They are too long for me anyway. The 4900s look like the way to go for buggies, although they are still a bit too long for my battery tray.

I think I'm going to try the Kokams. Whether they are better compared to the flightpowers is debateable, but at this point it won't kill me to have second best. I just want something better than what I've been running.

Besides, from what I've read, the Kokams take a bit more rough handling than other lipo cells do. I hope that they are the ticket.

[glassdoctor]

I bet you have some Kokams by next week :)

Oh, I hope so too. I'm down to a single polyquest 4400mAh pack. I don't think it has quite the umph that I want, but it's a nice pack none the less. It never balances for more than a few seconds. My maxamps packs sometimes need to be left on the balancer after charging has completed.

I'm just trying to sort out the balancing taps issue. It's not going to be a big deal. I just don't have any TP pack side taps handy. I'll order some.

[BrianG]

As far as taps go, you can just get some short adaptor cables, or make them yourself. I wouldn't worry too much about that...

[glassdoctor]

I think this is what you want right... 6 pin TP taps?

Tanicpacks.com seems to have them for $1.50 ea or in bulk :)
http://www.tanicpacks.com/catalog/pr...roducts_id=695

And shipping is $1.00 for orders under $30

They also have some velcro straps for $1.99

I just ordered a pair of velcro straps and several servo plug extensions for wiring fans, becs, etc... and a rx pack for hte nitro... :036: :005:

Maybe ThunderPower Extremes?

Or heck, A123s if you can take the weight...

I'm going to go with the Kokams for sure. They may be second in line in terms of performance, but I think they'll be more tolerant of the harsh conditions to which it appears that I subject my equipment. I tend to charge my batteries and then run them until the lvc kicks in. I do 90% of my running on a track, so it's constant on/off on the throttle and I need heavy duty batteries.

Although there seems to be a flightpower craze here, there seems to be quite a following for the Kokams on other sites. I'm going to give them a try. They can't possibly be worse than what I had before.

[Dafni]

Heavy duty batteries? Go for Gold!!


Just my 2 cents. Nothing against the Kokams, I never had some.

[skellyo]

Daf, those sure are pretty batts...glad I've got myself some of them. 3 sitting on the shelf and 1 more on the way. :D

[gixxer]

http://forums.radiocontrolzone.com/s...d.php?t=235232 these new kokam packs look like they should be good too.

[skellyo]

It's a shame that Kokam only has a small cluttered graph for the 4000mAh cell.

However, from what I see of the 2400mAh cell discharge graph, it's not anything special. For example, here's a comparable capacity flightpower 2500mAh cell graph:

http://www.flightpower.co.uk/core/da...0curve_600.jpg

Notice that it remains above 3.4V until about 80% of pack capacity (2000mAh) versus the Kokam pack only staying above 3.4V for just over 50% of pack capacity (~1200mAh).

[glassdoctor]

The 4000 cell graphs look a lot like the Flightpower 4900s from what I recall, although the edge may still go to the 4900s. But they are in the same league as the 4900s at least. So there is promise in the new 30c line of kokams. I'm told there should be a couple new sizes every month or so unti the whole line is 30c.

The last two lines are 40c and 45c.... voltage is sagging but that is huge amps.... 160 and 180 amps.

The 20-30c lines are very good... in the 3.3-3.5v range for most of the capacity. I would like to see the capacity hold up a little more... oh well.

[skellyo]

Originally Posted by glassdoctor

The 4000 cell graphs look a lot like the Flightpower 4900s from what I recall, although the edge may still go to the 4900s. But they are in the same league as the 4900s at least. So there is promise in the new 30c line of kokams. I'm told there should be a couple new sizes every month or so unti the whole line is 30c.

The last two lines are 40c and 45c.... voltage is sagging but that is huge amps.... 160 and 180 amps.

The 20-30c lines are very good... in the 3.3-3.5v range for most of the capacity. I would like to see the capacity hold up a little more... oh well.

I'd just like to see a graph that's large enough to read. They may match up well with the Flightpower 4900's, but why the heck they decided to plot 5C increments all the way to 45C on one graph is beyond me. If you have a link to a larger graph, please post it...I'd really like to see it. The engineer in me just loves colorful plots. :027:

[BrianG]

People seem to obsessed with how much the voltage drops under load. While perfectly valid for high current draw systems, it may not be as important for lighter systems where current is not so extreme (and therefore neither is voltage drop) and the user simply wants runtime. Sure, the less the votlage drops under load is closest to an electrically ideal cell, you're gonna pay for it. A racer who is concerned about having as much voltage with as little weight as possible is not the same person who wants max runtime for a pack that will simply fit into the location they have. The racer is gonna want just enough runtime to finish the race while being light weight. That will require a high C cell to supply the needed current for the relatively low-Ah pack. The other person will use a larger, heavier pack with greater Ah. But since the Ah is so high, the C rating can be lower to get high currents.

So, I think there ought to be a special graph plotting capacity vs. voltage drop under load vs price, etc for each category of cells. Something that would instantly show the relative value (or "bang for the buck") of each battery type - kinda like the scatter-type plots I've seen done for computer systems. One pack may not be the best performer as far as v_drop goes, but if the price and capacity are ok, it might be worth it to the individual.

Let's face it, there are a lot of newbs just getting into lipos and all these numbers can get confusing. After reading this thread, they may think they now "need" Flightpowers or whatever and that may not be necessarily true depending on the application.

[glassdoctor]

Yes... but this is the best way to compare batteries. We don't use batteries like is done on these discharge tests, but it does allow us to compare how two batteries perform under the same conditions.

Exactly how that translates to real-world performance may be debatable, but it's better than being blind and in the dark when it comes to choosing batteries.

It's like a motor dyno... we don't use motors that way but it gives "stats" so as to compare. You can say your car dynoed 700rwhp instead of saying it's so fast it can't hook up without slicks....

I know the #'s can get "blah blah blah".... :) but.... what are we to do? :D

If it were not for these graphs from mfg and customers... we would be at the mercy of the sellers which would NOT BE GOOD!! ;)

bang-for-your-buck value is a whole other deal.... but again it requries looking at the same type of data, plus a $$ curve as you said....