WannaFly_06

hey guys, I setup my Pirahna charger as follows for a 7 cell 8.4 volt 2/3A 1100 mAh NiMh battery and it completed charge in 32 minutes:

NiMH battery type
1100 mah capacity
1.2 A (amp current rate)
8mV/C (Sensitivity level) (per Towerhobbies tech dept)
0ma (trick rate)

The Electrifly batteries I have, state "Charge at 125mA for 10-12 hours, Trick charge @ 35ma"... however, my trickle charge settings are only 100mah and 200mah increments, nothing lower then that..

Just curious if I did something wrong or if this is how these batteries charge


I'd appreciate any advice you can give on this.. also, do these batteries usually come charged already?

guver

My Feedback: (325)

It delivered around 587 mah and is possible the battery was partial charged or it was new and not fully formed. If you use it and watche the second cycle it may come right up to over 1000 mah when chargeing. Your settings lok good and if the batt is dead should take an hour to charge. The mv usually is 3-5 for the nimh 2/3 A cells , but I have also had to double this setting on the digital piranha.

critterhunter

The Pirahna Digital Peak Charger (or similar models) are great chargers, offering features found on chargers costing twice as much. However, the instructions are not very good and are even incorrect in certain portions. I'd go to the E-Flite Power Sources forum and search for a thread on this. We went through all the setup options for various batteries with it. In short, if charging a nimh pack I normaly set the m/v threshold at 5 or 6. Increase it more if the pack seems to false terminate but be careful. Too high a m/v setting and the pack won't indicate to the charger that it is done. The m/v setting determines how many volts the pack must drop when it peaks (the voltage on a peaked pack will start to fall instead of rising). Nimhs don't drop as much in voltage as nicads when peaked. Nicads might use somewhere in the 7 to 12 m/v range or higher. The m/v is per cell. The charger will automaticly take your setting and times it by the number of cells in the pack for the proper voltage number for the pack to drop. An easy way to tell if you have too low a m/v setting is to throw the pack back on the charger instantly after it's peaked. If the pack takes more than 50ma of capacity then your m/v setting is too low and the pack is false peaking (A pack voltage generaly climbs while charging but may fall a little here and there as the process of charging goes on). When the pack is really peaked it's voltage drop will be more than these false drops that may false terminate the charge. Nimhs should NOT be trickle charged. Turn it OFF on the charger. Only Nicads should be trickle charged and you have to be very careful as to just how much trickle is too much. When I say trickle I mean the tiny trickle charge mode the charger will go into after the normal charge is done, not a slow regular charge (well below 1C) that some people call a trickle charge. A slow charge can be healthy to a pack every ten or twenty cycles or more. For instance, 1100ma 7 cell nimh packs....I normaly charge those at .9 to 1 amps for a "normal" charge with a m/v setting of 5 or 6. If I want to give it a slow charge I'll charge it at .2 or so amps. Keep in mind too that the m/v setting may change if you charge at a really slow or high rate. Say you had an 1100ma nimh pack that is said to be able to handle 2C charge rates (2.2 amps). You might want to bump the m/v setting higher, in the 6 to 9 m/v range or so. Or, if you are charging really slow (.2 amps or so) you might want to lower it to 2 to 4 m/v. That's because at a high charge rate the voltage flucuation may be more wild while the pack is in the process of charging, while at a slow rate it may be more stable. Just remember to stay around the pack to keep an eye on it when experimenting. Too high a m/v setting and the pack might not terminate and you've got a fire hazard on your hands. You should also set the capacity higher than the pack is raited for. For instance, if the pack is 1100ma try setting it at 1500 or 1600. That's because the pack may be better than it's capacity raiting and be able to take more. If you have the capacity setting at 1100ma I think the charger will stop once it reaches that number even if the pack hasn't indicated to the charger via the m/v level that it's done charging. However, once again keep an eye on the pack because you are eliminating a safety feature. Feel the pack as it chargers. If it is getting hot (warm is OK) then something is wrong. You are either charging at too high an amp rate or the pack is over charged and the charger hasn't been able to tell it's peaked (the m/v setting is too high). Remember as well that when charging something like AA Energizer 2500ma nimhs (many of us use them in our TX) that they prefer a slower charge rate than the normal 1C that most plane packs charge at. I baby mine at around .3 to .5 amps, but may go higher if I'm in a hurry. At the lowest charge rate they take a good ten to fourteen hours to charge. I set the m/v setting at around 5 or 6 and then check on the pack within a few hours. If it has stopped charging and I knew the batteries were near dead I know it has false terminated and set it at 7 or so and restart. Power surges in the house (such as a washer coming on) can also lower or raise the charger's voltage and falsely trigger the m/v.

WannaFly_06

thanks for the help on this.. i've gotten all 3 batteries charged, but haven't gotten the plane fully assembled yet.. It's about 40% there, tomorrow I plan to work on it and get it almost complete.. Come Monday, I'll have my servos to put in it and i'll be ready to go