cheapskate.brok

iTrader: (10)

Yup. It also depends on your charger, as most standard issue digital chargers are rated at 50W, so breaking it down will mean;

P=IV
50=(4)V
12.5=V

So yeah, you can charge your 7.4V (2S) 4Ah at 4A.

MTX3-B

iTrader: (5)

Care to elaborate on the equation? Sorry i have zero knowledge.

Assuming a similar charger but with higher watts say at 100W, does 1C charge yield any performance advantage in the output (with the same capacity of the battery)?

Thanks.

jarrydtan

iTrader: (1)

Do correct me if i'm wrong.

Power/P (in Watts/W) = Current/C (I) x Voltage/V (V)

I think there's a minor error in brok's explanation, where:

We first assume the power output of the charger is 50W
Voltage is set as a constant, which would be the batteries voltage = 7.4V. Assuming the battery is 4000mAh and you are charging at 1C, the current output from the charger into the battery is 4A. Following the equation:
P = I x V
P = 4 x 7.4
= 29.6W
The power is the consumption of the process to charge the battery. Since the consumption is smaller than the overall power output of the charger (29.6 < 50), such charging process is possible.

There's no difference if the charger's power output is higher. Only when its lower then there is a problem. You wouldn't be able to charge at 4A if the charger power output is lower than 29.6W.

Simply put, think that the power is the amount of energy in your body. For instance, if you have 100% energy, you can climb stairs which will take 15% energy. But you wouldn't be able to weight-lift if it takes 150% energy, right?

mikecan8

iTrader: (2)

Dear all,

I believe this thread is to discuss why is Lipos dangerous. To me, its the best thing that has happened to RC. Anything in RC is dangerous, look at the motors, the ESCs, all the products are dangerous, but as long as you understand it and know how to use it, its as safe as anything.

I do not believe any charger out in the market are any different in terms of chargin, they all work on the algorithm of the software to charge the batteries. I believe the software is very closely related to each other.

As for the power or watt of the charger, its got nothing to do with the ultimate power of the battery that it charges, but the greater charger power means more cells it can charge. Just look at the amperage that the charger can charge at and you can then be sure that the charger can charge the battery of upto how many mah. 5A max charging current on charger = can charge battery of up to 5000mah.

As for storage, do not store your lipo at full charge (8.4V) or at min charge(6.4V) as it will cause the battery to be expanded. It will be alright to store the lipo at about 60% charge, i.e. if you have a 4000 mah batt, you can store the batt at about 2400mah capacity or 5000mah can be stored at 3000mah capacity.

So just know your stuff and you would be alright. Stay safe.

MTX3-B

iTrader: (5)

Nicely said Mike! Very informative.

At least newcomers (and old timers as well) would really understand what they are getting into. Perhaps the differences among the chargers are so minute. The high end chargers (expensive ones) would probably have better quality of its materials and a host of other features which we may not need. The basic ones would do the job nicely. I find that storage mode in most of the chargers available in the market today is really a nifty feature.

But this is only the beginning.... at a more advanced level (not really recommended for casual bashers and budget minded racers alike) we see racers discharge (at high amp) their LiPo batts and charge them on a warmer tray. Not to mention charging the LiPo higher than recommended C rating (2C and above). For my application, it could not feel any difference save for it cuts down my charging time (to fit the racing schedule).

I also believe there are differences among various LiPo batteries (with the same capacity and discharge rating) in terms of its lifespan -given the same usage and the normal treatment of the batteries. I could not really tell using new Brand A or Brand B batts. Perhaps the actual power consumption (real output) of the batts was never materialised given the fact that i m only running on M-Chassis 2WD. Perhaps all that buzz of 20C, 25C, 30C doesnt really apply.

But one thing worth noting is that a higher capacity LiPo will outshine a lower capacity batt. 3200 vs. 4000. U could really tell the difference.

Oh well...enough for the ramblings....

Enjoy the world of LiPo.

devious17

iTrader: (1)

You may relate the discharge rate denoted by the 'C' as the diameter of a water faucet. The bigger the 'C' the larger the diameter of the faucet (assuming the diamater of the pipe before the faucet has the same measurement) in allowing higher water capacity flow at any given duration. The *Mah would be the 'water tank' connected to the pipe and faucet.

To maximise the benefit of a high 'C' output the 'funnel' should be capable of receiving the 'C' to ensure 100% power transfer through put.

However, the 'C' rating is not an industry standard. Brand A 25C may not be the same as Brand B's 25C. Average li-po cycle from reputable brand is observed to be around 40 to 50 cycles only from experience.

I always store my li-po's at 3.8V per cell as a rule of thumb. Charging should not be over 4.201V per cell which is in the safe zone for li-po. A voltage of 4.220V per cell is hovering around the edge of over charging.

Toh WL

iTrader: (6)

Lipo batteries are dangerous if abused & operated by novice. If all of the precaution are taken.

The last thing we need to look is the charger. I did read b4 some LIPO charger will not provide accuracy reading, volt & current control. Hence most of the unforsee events came from there.

The only way perhaps, those who are in using LIPO for years. To give a recommended charger. So newcomers will not waste money on batteries & chargers.

xxafiquexx

iTrader: (3)

haha.. cerita saja power..

Toh WL

iTrader: (6)

No la bro, just give suggestion that can help others. That is surely good enough. Unless if you have your own experiences. Feel free to share and contribute.

MTX3-B

iTrader: (5)

My first LiPo charger is Team Orion Avionics, a reliable charger, the voltage output seldom goes beyond 8.40V, max 5.0A, No built-in balancer (am using TrakPower balancer). Very light and compact design. I like the feel and the look of the charger, build quality is good. It is ORION...

Second charger is Hyperion - max 6.0A, discharge 1.0A. So far so good. No complaints. It has the storage mode. U need to purchase an external port as the existing balancer port is catered solely for Hyperion LiPos. I bought it based on recommendation from friends and based on positive reviews of users.

I have also used GT Power V5...didnt quite like it...it has the tendency to overcharge and the charger is very hot.

to cool down the charger, get a fan.

hope that helps.

devious17

iTrader: (1)

If you have a charger that requires an outboard balancer try not to charge the lipo through the balancer instead charge the li-po via the dean plug (or whatever plug you have installed) and balance the li-po using the balancer independently.

If your charger has the graphical view (i.e - Tahmazo T30+ ) you would notice that by charging through the balancer the graph wont be as stable as compared to independent charging of the battery and balancing it.

Lithium Polymer

iTrader: (4)

Cells sold today as polymer batteries have a different design from the older lithium-ion cells. Unlike lithium-ion cylindrical, or prismatic cells, which have a rigid metal case, polymer cells have a flexible, foil-type (polymer laminate) case, but they still contain organic solvent. The main difference between commercial polymer and lithium-ion cells is that in the latter the rigid case presses the electrodes and the separator onto each other, whereas in polymer cells this external pressure is not required because the electrode sheets and the separator sheets are laminated onto each other.

Since no metal battery cell casing is needed, the battery can be lighter and it can be specifically shaped to fit the device it will power. Because of the denser packaging without intercell spacing between cylindrical cells and the lack of metal casing, the energy density of Li-poly batteries is over 20% higher than that of a classic Li-ion battery.

The voltage of a Li-poly cell varies from about 2.7 V (discharged) to about 4.23 V (fully charged), and Li-poly cells have to be protected from overcharge by limiting the applied voltage to no more than 4.235 V per cell used in a series combination. Overcharging a Li-poly battery will likely result in explosion and/or fire. During discharge on load, the load has to be removed as soon as the voltage drops below approximately 3.0 V per cell (used in a series combination), or else the battery will subsequently no longer accept a full charge and may experience problems holding voltage under load.

Early in its development, lithium polymer technology had problems with internal resistance. Other challenges include longer charge times and slower maximum discharge rates compared to more mature technologies. Li-poly batteries typically require more than an hour for a full charge. Recent design improvements have increased maximum discharge currents from two times to 15 or even 30 times the cell capacity (discharge rate in amps, cell capacity in amp-hours). In December 2007 Toshiba announced a new design offering a much faster rate of charge (about 5 minutes to reach 90%). These cells were released onto the market in March 2008 and are expected to have a dramatic effect on the power tool and electric vehicle industries, and a major effect on consumer electronics.[citation needed]

When compared to the lithium-ion battery, Li-poly has a greater life cycle degradation rate. However, in recent years, manufacturers have been declaring upwards of 500 charge-discharge cycles before the capacity drops to 80% (see Sanyo). Another variant of Li-poly cells, the "thin film rechargeable lithium battery", has been shown to provide more than 10,000 cycles.[citation needed]