Batteries, Balancers, and Chargers... oh my!

[Mallanaga]

i searched... there were a couple threads, but nothing substantial... and they were old. let's do this right. with this thread title, any search will pull this up. OK, let's get started. i'm taking the electric jump... and i'm craving info. i have posts all over this forum, and i am getting a slew of great info. now let's get the batteries out of the way... i am sold on LiPo / Li-Ion. so... let's start there.

CHARGERS
after doing a little digging, i think i want this:

• Charges NIMH, NICD, and Lipoly
• This is our best all around AC/DC charger
• 1-14 NIMH-NICD and 1-5 Lipoly Cells
• Up to 5 amp charge rate
• Comes with data port

Of course, the AC/DC part means that you can charge directly from an AC wall supply while at home or from a 12V DC battery/power supply.

price ~ $120

i will soon be owning a mini-T, which i will be taking brushless (2s, 1000-2000 mah), and eventually, i will have my E-Revo (4s, 6000-8000 mah), so that charger can handle both.

good buy? good all around charger?

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BALANCERS
now... what exactly is a balancer for? are they necessary? if and when i need one, i would be going with:

• 2-6 cell smart balancer
• Network 2 units together for 2-12 cell balancing
• Comes with 2S & 3S Adapters. Others available seperately.

price ~ $50

good buy? good all around balancer?

Balancing, and more specifically the NEED to balance is a hotly contested subject right now. In my experience and opinion, if a pack (especially just a 2 or 3 cell car pack) actually requires balancing during any time during it's lifespan, you'd do well to look into another brand. That's a harsh viewpoint, and may not be shared by many openly, but it's my honest opinion from working with many many brands for many many years.

Basically, you can view balancing a lipo pack like a continuing process of matching NiMH cells. NiMH cells are manufactured by the billions and due to this large scale of production economy, each and every one is slightly different. Just about everyone is familiar with the process of starting with a large sample group of NiMH cells and matching their internal resistance (voltage under load) and runtime. There are very few factories producing just a few brands of these cells, so the same process needs to be used for all of them. Lipos are a little different. There are dozens of factories producing hundreds of brand names of lipo cells, and they vary radically in both performance and safety. The same brand name may even source cells from several different factories! Making sure the pack containing multiple cells will perform consistently with the cells inside "in balance" ovedr time is an issue that is totally dependent on the individual pack. As stated above - some you’ll never have to worry about, some you’ll NEED to worry about from day one.

Since we’re naming names here, I’ll lay it all right out on the table. Kokam America uses a patented construction process and an almost entirely automated manufacturing line. They are also the only lipo brand I’m aware of that actually owns it’s own factories, so the brand and the factory are actually one in the same. Due to these unique features, each and every cell off the line actually IS the same as all the rest. Kokam’s main business is supplying the aerospace industry (both private and government projects) and remains the only "hobby active" lipo factory I'm aware of that can make that claim. In my own experience, Kokam packs will provide a full cycle life without becoming imbalanced as long as they are not abused. Combined with their non-flame chemistry and excellent output performance, it’s easy to see why Kokam is the brand of choice for my own personal vehicles. The only downside to the Kokam line of packs is their price compared to other brands (and in this case - you really DO get what you pay for), and the lack of a pack that fits the 18T and similar vehicles.

A close second are the Apogee Magnum packs. Apogee is the only brand I’m aware of that truly factory matches the cells within each of its packs. The manufacturing process may not be quite as consistent as Kokam, but it’s made up for by an extra step before pack assembly. Apogee Magnum packs will also provide a full cycle life without worry of balancing as long as they are not abused. I’ve used and recommended Apogee brand packs for both surface and aircraft since the inception of the company, and continue to do so to this day. Apogee was the first to provide a non-flame chemistry pack specifically for the car market (the Magnum 3800mah) and now offers a great Magnum RC18T/B pack.

Tanic packs have recently introduced an excellent and elegant solution for the car market. Tanic has provided some of the highest performance lipos to the market for many years now. They have recently become compatible with the CellPro automatic balancing charger for a true and easy "Plug and Play" solution and thus have become an excellent entry point for thousands of racers to safely experience all the benefits of lipo power. Balancing is performed each and every time the pack is charged (via the CellPro charger) which virtually guarantees the pack will deliver a full and balanced cycle life to the user. Along with an ESC or external device to provide a proper cutoff voltage, there is almost no chance of damaging the packs. It’s no wonder these packs and charging systems are so popular in the newly emerging lipo racing market right now.

As far as charging through the balancing connector - if you do, there are caveats. First - only charge at an extremely low charge rate - say no more than 0.5A regardless of the capacity of the pack. Second - use of the balancing connector requires a matching connector to plug into an external balancing device (Kokam Lipolizer, AstroFlight blinky). CONSULT THE PACK MANUFACTURER/DEALER for advice as to what balancer device to use, and when/how to use it for your brand of pack.

As a general rule, ALWAYS charge and discharge through the main (heavy guage pos and neg) battery leads just like you would for a NiCad/NiMH pack. Balancers all work in different ways, and some you can charge with, and some you cannot. I'd recommend using packs from the list above, and then not worrying about having to balance them at all.

One of the main Lipo brand folks and I discussed the balancing ports on their packs a while back, and he dubbed them the "PPP" ports. "PPP" standing for Paranoid Placation Ports. In other words - they are only there to satisfy the few overly concerned folks, and largely go not only unused, but aren't even recommended to be used from the factory brand itself.

So basically - with good packs in the first place, don't worry about it.

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as for BATTERIES...

Lipo pack companies have much more competition now than they did a year or two ago. Just a sample of companies that have good packs are Maxamps, Apogee, Flightpower, Kokam, Orion, and Thunder Power. I'm sure there are other good brands. Least expensive are maxamps, the most expensive are Flightpower. [...] Like anything you get what you pay for, if you can afford to buy well now, it will be money well spent. I'd stay away from no name ebay packs, their C rates often do not live up to
what is printed on the label.

and...

Low Kv rated motor systems that use high cell counts are more desirable than high Kv/low cell counts for a few reasons. The higher voltage system will run cooler and more efficiently than a lower Kv system. There is also more starting torque with a low Kv motor. The drawback is that running a higher cell count means more weight from the batteries. It's also more expensive because high cell count batteries cost more money. Trying to find a happy medium between cell count, weight and efficiency is key to a good system.

Voltage
The # of cells in the pack determines voltage. Each cell is 4.2v fully charged. Most folks are comfortable with the fact that each cell in a NiMH/NiCad pack is around 1.5v fully charged, and the same principles apply to lipos.

6 NiXX cells = around 9.0v fully peaked, and pack rated as 7.2v (1.2v/cell) as its "nominal" voltage. 2 lipo cells = 8.4v fully charged, and pack rated as 7.4v (3.7v/cell) as its "nominal" voltage. 3 lipo cells = 12.6v fully charged, and pack rated as 11.1v (3.7v/cell) as its "nominal" voltage.

As you can see, "nominal" voltage is fairly arbitrary in both cases, as it's neither the fully charged voltage, nor the fully discharged voltage, but somewhere in the middle.

Current output capability
Lipos are commonly rated as "10C" or "15C" or "20C". The "C" stands for the capacity of the pack in Mah (milliamp hours). The "10, 15, and 20" stand for how many times of the capacity the pack can deliver continuously in amps.

So a 3800mah pack rated at 10C can deliver 38A continuously. A 3800mah pack rated at 20C can deliver 76A continuously.

"Ratings" can be misleading however. Apogee, Kokam, Orion, Peak and Tanic all have an impeccable record of their products standing up to what they SAY they will deliver.

So what does this have to do with anything? Well, lipos are subject to the same rules of performance as any other battery. They are still an electron storage device - just in a different package and configuration than you're used to seeing. The main parameter controlling a battery's performance is internal resistance. The lower the internal resistance, the more amps (speed/punch) it can deliver, the higher the voltage (speed/punch) it will maintain during that delivery and the cooler it will be at the end of the delivery.

So the above "10C" 3800mah pack would give lower top speed, less punch, and be hotter at the end of a run than the "20C" 3800mah pack. The exact same run will also use more mah from the 10C pack than it would from the 20C pack.

So the (actual) "C" rating of a battery is important to know, but what else affects performance?

Mah Capacity
One of the most interesting things about lipos is that as the Mah of the pack goes up - so does the output performance. As above - a 10C 3800mah pack can do 38A. If we parallel two of those packs together to make one 7600mah pack, we can then get 76A from it. From the above, we know that the more amps the pack is capable of, the more speed and punch are available, and at a lower pack temperature. So ideally, we'd want to run the most mah that can fit in the car, and have that pack be "rated" for the highest reliable "C" rating we can find. This maximizes speed and punch, and minimizes heat within the pack.

Just like you wouldn't want to run the GP1100 pack from your 18th scale car in your 10th scale car, you wouldn't want to run too small of a lipo for the performance that you want.

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:whack: if there's any info people could give here, that'd be great. i'll update the original post as needed to keep it pertinent, relevant, and current!

 

[sweetdiesel]

Great all around charger and balancer. If you run packs that are less than 5000mah rated capacity, you'll be fine with the 5 amps that the EOS5i puts out. Most lipo packs are rated to be charged at 1C max, with the exception of Kokam and Apogee packs which can be charged at 2C.

Lithium cells will charge up to 4.2 volts, and drop to 3.7 volts under load. The "S" designation for lipo packs lets you know how many cells are wired in serial. The "P" designation tells many units are wired in parallel.

Example 1. A 4S 4000mah pack is made of 4-4000mah cells wired in serial, serial wiring adds the voltages of each cell, so 4 x 3.7 volts per cell = 14.8 volts total pack voltage

Example 2. A 4S2P 8000mah pack is made of 8- 4000mah cells, 2 banks of 4-4000mah cells wired in series, and each bank of cells wired in parallel. Parallel wiring does not increase the voltage of the cells, but increases the pack capacity (mah). The pack is still 14.8 volts, but the capacity is doubled.

Lithium packs are rated for voltage (by cell count and how they are wired), capacity (in mah-miliamp hours), and C rating.

Horsepower can be measured in watts. Watts = volts x amps. To increase power you can either increase the volts, or increase the amps. Volts and amps are limited to what your motor and ESC can handle. Once current draw is a constant, increasing the amps (battery capacity) will increase your runtime. Many folks also experience that a higher capacity pack also feels "punchier", mainly because the initial acceleration of a motor draws the most current.

The C rating tells you a few things. It tells you how much current the pack can discharge in amps continuously, and there is also a burst rating, which tells you how many amps the pack can discharge for a second or two. Packs that have higher C ratings are more favorable than lower C ratings, obviously because they can output a greater amount of energy with the least amount of weight. So to figure out how many amps a battery can output, take the C rating and multiply it by the Ah rating of the pack.

Example a 20C cont. rated pack that has a capacity of 6000mah can output 120 amps continuously

20 x 6 amps (1000 miliamp hour = 1 amp hour) = 120

A balancer is required for lithium cells because of the way they are wired. During the discharge cycle there is potential for a cell or cells within the pack to output more current than the rest of the cells in the pack. When this happens, the pack becomes "unbalanced". Subsequently, when the pack is re-charged the cells with lower voltage will continue to stay at a lower voltage, while the other cells will be overcharged, since a lipo charger will charge a pack up to it's given rated voltage. Since lithium cells are to be used within a specific voltage range, you can see where an unbalanced pack will eventually become damaged due to under/overcharging. The balancer's job is to bleed the excess voltage from the cells within a pack until they are all nearly the same voltage. In general, the cells within a pack should never be more than .05 volts of each other. A volt meter can be used to measure individual cell voltage at the pack's balancing tap, which is where you connect the balancer to. When combined with the LBA10 balancer and a data port cable, the Hyperion EOS5i dp will tell you individual cell voltages of the pack. 2S packs will require less frequent balancing than higher cell counts. Very high quality 2S packs will rarely require balancing because their cells are closely matched. In general high quality packs will require less frequent balancing.

 

[FastEddy]

The Lipo-suction King has spoken.

 

[Mallanaga]

SD... do you seriously pull this poop out of your head? you are good... real good.

i definitely can appreciate electric R/C way more than nitro, due to my background in physics. being an engineer, it all makes sense. i'm no physicist, but PHY108 was a pretty great class.

i think once i actually have some of these components in my hands, the learning curve will slowly melt away. i just like to know as much about something as i can before i go jumping into the ice water.

in the mean time, thank you again, SD. anyone else who wants to chime in... don't be scared! this is Oz, after all

 

[Mallanaga]

updated...

 

[sweetdiesel]

Now that you have decided on 4S 6-8000 mah packs for your E-revo project, the first charger will still get the job done. But, if you want to minimize your time charging packs, go with a charger than can output at least 8 amps and 135 watts such as these below.

http://www.b-p-p.com/proddetail.php?prod=e_EOS_1210i

http://www.bantam301.20m.com/902.htm

So basically - with good packs in the first place, don't worry about it.

Shawn said that they would not need balancing as long as they are not abused. Electronics can fail, LVCs can hiccup, all without any fault of the user. Balancers are cheap insurance. It's up to you to decide whether or not to use one. I suggest you re-read your updated post carefully, evaluate the packs that you plan on running... and choose wisely.

Also the LBA10 when used in balance mode while charging, does not charge through the balancing taps. It charges through the main power leads of the pack, and simultaneously bleeds excess voltage through the taps.