[liftbag]

Vado leggermente OT per ricollegarmi ad un argomento saltuariamente trattato anche in questo topic.
Io concordo in pieno con tutto quanto esposto da gregor su helifreak.
Per chi legge in inglese è piuttosto interessante e completo con dati che mi mancavano.

Originalmente inviato da gregor

I have 3 different chargers I'm using and have a variety of both serial and parallel adapters for the mCPX cells. First, I'll tell you once you start flying a decent cell, you may never touch the eFlight cells again. I gave all of mine to a friend when I switched over to the Hyperion 240s. Here are some comments from my experience charging both serially and in parallel.



Serial Charging

• Every cell individually monitored by the charger. A single cell failure could be detected by the charger and the charge cycle terminated.
• Not good for cells of different sizes. As the cells fill the smaller cells will fill faster than the larger cells. To continue charging the larger cells, the charger will have to bypass the charge current on the smaller cells. Depending on the charger the bypass current can be as low as 250ma, or as high as 1 amp. The charger may have to reduce the over all charge current of the balance bypass current required exceeds the balance bypass currently the charger is capable of. This could extend the charge time.
• Not good for cells of different states of charge. The charger will attempt balance all the cells and may need to reduce the over all charge current if the balance current capabilities cannot keep up. This coujld extend the charge time.
• May be able to charge the cells at higher rates. On my FMA Cellpro 4s, the charge rate is 4 amps for 2s through 4s. But for 1s the charger is limited to 3 amps. Charging 6 cells a time in parallel would result in only 500ma to each cell, or less than 2c charge. Charging in series I would be able to easily reach the 5c rating for the Hyperions.
• FMA chargers have a unique wiring scheme. When charging in serial you must have a cell connected to each of the battery connectors on your adapter. That means if you have an adapter that chargers 6 cells, you cannot charge a single cell. You must charge at least 6 cells at a time. iChargers wiring scheme lets you add in as many cell or as few cells you need. The FMA PL8 has an option to support this mode.

Parallel Charging

• Handles different cell sizes transparently from the charger. When charging packs of different sizes, the current is divided between cells, with more current automatically going to a larger cell. When charging at the maximum charge rate of the cells, this means that the larger cells may recieve a higher than desirable charge rate. However, because the charger may not need to reduce the overall charge current, the charge may complete faster.
• Handles different charge state transparently from the charger. When connected in parallel, before the charge starts, the higher cells will equalize with the lower cells by delivering current to the cells in the lower state of charge. The bulk of this happens fairly quickly and if the cells are in drastically different states, can result in charge rates exceeding the cells max charge rate for a few seconds or less. A difference of 0.2v between cells does not produce notable current from the high to the low cell. Though there is often grave concern from the user community regarding this issue, tests have shown that due the very flat voltage discharge of lipos the delta between a high and low pack does not produce harmful rates and duration of currents. In short "Myth busted".
• Can be faster than serial because all of the balancing happens directly between the cells. The charger will never detect an imbalance and will never reduce the charge rate.
• Cells are not individually monitored by the charger. Any issues with the a single cell may not be detected by the charger or operator. The operator must take more responsibility to know the state of health of each cell. Because each cell is discharged individually in the model, it can become quite obvious when one cell has degraded. For multi-cell packs used in larger helicopters, use of cell voltage checker before and after the charge is a good practice.

My general rules of thumb

• Parallel charging is generally easier, faster and simpler.
• Be aware of the health each cell. Discontinue use and dispose of any questionable or aged cells. (regardless of how the cells are charged).
• Use serial charging when there is a wattage or current advantage (as in my Cellpro 4s example)
• Regardless of serial or parallel charging, charge only cells of similar size, age and state of charge together. Not a technical requirement in all cases, just my own best practice.
• Be organized about keeping the charged and discharged cells seperate. I have old servo box that I put a partition in. Charged cells go on the left and discharged cells go on the right. When in doubt check the voltage of the cell before connecting to the charger or putting it in the model.
• Only use a quality charger from a reputable brand. Low quality chargers (I would put the elfight charger in this group) are notorious for over charging or under charging cells. In some cases contributing to premature cell degradation or cell ignition.

Fonte: HeliFreak - View Single Post - Turnigy Nanotech for mCP-X available now.....