Figuring amps and voltage in to watts

[FE_Chris]

Well, after being out of RC for a couple/few years the wife gave me the go ahead to spend some money. I purchased several things including a Protek 610 DUO charger w/ a 25 amp 350w PSU.

http://www.amainhobbies.com/product_info.php/cPath/1574_116/products_id/187710/n/ProTek-R-C-Prodigy-610-DUO-LiPo-LiFe-NiMH-DC-Battery-Charger-6S-10A-200W-x-2

http://www.hobbyking.com/hobbyking/s...dProduct=17423

Not much info on the charger out on the net, but Protek has a pretty good rep I think, so I figured what the heck. The PSU should work OK. As long as it can hold it's voltage under load. The last hobbyking PSU I got worked well so I thought I would try another.

Anyway, I just wanted to know what the formula's were to figure charge rates. Like for instance, if I would like to charge my Zippy 5000Mah 2s lipos @ 10amps, how many watts will I be drawing from the PSU? Just looking for a little info. As of now, I am only going to be using 2s packs. But in the future I might get some larger ones and it's been so long I can't remember the math to figure wattage out.

Thanks.

[Boaterguy]

Amps*volts = watts. 7.4*10= the watts you are drawing, too lazy for math right now

[FE_Chris]

Thanks. So 74 watts charging a 2s @ 10 amps. Is there any room for error in this? Meaning, say I had a 75w PSU. Would that actually cover it?

Another thing. Looks like all the new Lipos are coming with 2c and 3c charge rates. The ones I ordered say you can charge at 3c. A few years ago some had concerns with the longevity of the batteries being affected by such a high charge rate. How does this stand with today's lipos?

[Boaterguy]

if you have proper cooling yes, you can use 74 watts.
I have never charged more than 1C, all I have owned is an accucel 6 and an onyx 230, 1C charge set rate.
I don't know if charging 5000mAh at 10A is the best idea. it is possible, and I know lots of people do it, but I almost always charge at the cap rating, so 5A for 5000mah, sure it takes about an hour, but lipo's are very sensitive. slow charge at 1/10 so .5A, if you wanted to do that, nobody slow charges much anymore.

[sailr]

I charge all of my hyperions at 2C. My packs are all 5000mah. No problems.

[Boaterguy]

I don't understand what charging at 1C vs 2C means, if you are charging at a certain amperage rate, does that not determine the C rating?

[sailr]

If the pack is 5000mAh (5 amps), then 1C is 5 amp charge rate, 2C is 10 amp, 3C is 15 amp, etc.

[Boaterguy]

oh, so you don't change the C rate of the charge, you just doubl the charge rate, that makes sense. thanks.

[Chilli]

If your charging a 5000 mAh pack at 5 amps, you are charging it at 1C and it will take roughly an hour to charge a totally discharged pack.

If you're charging the same pack at 10 amps then your charging rate is 2C and the packs will take half the time to charge.

No benefit to charging at a higher rate other than having your packs charge quicker if you're short on time. You charger will be working harder and hotter with the increased charge rate.

1C has always been fine for me.

[Boaterguy]

I read an article somewhere that charging at lower rates (0.1C) was bad for lipos, but other places it is good, it was a while ago some i'm wondering if it has changed?

[JIM MARCUM]

To find either watts (P), amps (I), or volts (E) the standard is the "PIE" formula. It's a fraction with P (watts) over I (amps) times E (volts). To find any of the three just put your finger over the number in the fraction you don't know & do the math. IE: How many amps (I) will you draw when I=300 watts & E=44.4 volts? Answer: divide 300 watts (P) by 44.4 volts (E) = 6.8 amps (I). It's really not as hard as it sounds.
JIM

[FE_Chris]

Thanks for the replies guys. I have another question that is off subject and I guess I should have asked before I purchased the charger, but here goes. From the pics it looks like this charger comes with the JST-XH balance adapters. Could someone verify this for me? Maybe no one knows but thought I would ask....

http://www.amainhobbies.com/product_info.php/cPath/1574_116/products_id/187710/n/ProTek-R-C-Prodigy-610-DUO-LiPo-LiFe-NiMH-DC-Battery-Charger-6S-10A-200W-x-2

Scroll to the bottom. looks like JST-XH to me!!! I sure hope so.... lol. Thanks.

[kookie_guy]

7.4*10= the watts you are drawing, too lazy for math right now

LOL! Really, 7.4*10 and you are too lazy for math? You are multiplying by 10, just move the decimal to the right. lol

[Boaterguy]

In grade 9, school ended, let the brain atrophying begin

[ryan_t888]

Hello Chris

The actual true wattage during charge will vary depending on where you are during the cycle. You can start a flat LiPo around 7.2v charge at lets say 10A.20 Minutes later it may be 8.0v at 10A. This will yield a greater wattage.

Near the end of the charge you will reach peak voltage of 8.4v at the 10A.

7.2v @ 10A = 72w
8.0v @ 10A = 80w
8.4v @ 10A = 84w

The 84 watt value will be the peak amount sent to the battery at that charge rate. Once it hits this peak, the wattage will fall back down to 0.

Factor in the power consumed by the charger and you will get the total wattage for the charge that will be drawn from the power supply.

Ryan