yetti831

Hi,

I received a cheap lipo charger when I bought an RTF EDF. One light was is to go on when the power source is plugged in, and another light is to go on when the battery is plugged in. When the battery is charged, the one light goes off. However, when I plug in my power source, both lights go on and never go out. Well, I'm having another charger sent to me, but in the mean time I was timing my charges (dumb, I know.) I wanted to know if I was getting a full charge or not, so I went out and bought a digital multimeter. I'm using two 11.1v 1300mah packs. I put the multimeter to the 20V setting. My first battery was reading at 11.68v, and the second at 11.58v. Am I doing this correctly? I know that each charged cell should be around 4.2v, so the pack should read 12.6v when fully charged. Is this correct? Am I using the correct setting? Thank you for your time.

Attached is a scan of my charger. Thank you again.

opjose

Nope not right at all.

Why not keep this all together with your original thread?

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You need to measure the battery under load.

LiPo's start out with a higher voltage that drops under load not just it's voltage.

If you apply a constant realistic load, you can measure the amount of time before the battery hits a lower voltage limit.

This helps you determine the capacity of the battery.

Since a LiPo can have a bad cell, you could have a decent voltage reading, even when under some load...

But stick that battery back into a plane and you'll see that something is amiss.

That is one reason I suggested you may want to invest in a good computer controlled charger.

The CC charger lets you check the condition of the cells, the battery capacity, run times, etc.... all info that is helpful for you to know.

LiPos have relatively fixed lifetimes or cycle times. As you charge/discharge them their capacity diminishes... another reason to invest in the CC as this helps you to determine when your battery may no longer be safe to use.

You'll next wonder what "load"?

Well your best bet is to put the battery on your plane and measure the draw and run time... ideally with a watt meter connected between the battery and the ESC.

A static resistor load gives you unrealistic results, whereas a watt meter and the actual plane, gives you real world measurements.

BTW: On your F-35 the draw is QUITE high for the battery provided, so you need to avoid full throttle and keep the throttle in the mid range.

yetti831

In other words, my multimeter is worthless? Thanks for your time.

ChuckW

Yes you are checking the static or open circuit voltage properly but like opjose mentioned, that only tells you so much. I've seen batteries with great static voltage that fall on their face when loaded.

opjose

Worthless?

No...

Only for this purpose is it of little value...

It serves many others however and should be part of your RC "tool pack".

It does not need to go to the field with you, but you'll want to hang on to it as you work with RC electronics and planes.

yetti831

Yeah, mine seem to be doing very poorly when loaded. I can at least tell when my pack is fully charged, right? I'm ordering a good CC, but I won't have it for a few days.


P.S. I want to take a gamble with these mystery packs. Is it a gamble, or is it just stupidity?

[link=http://cgi.ebay.com/2x-25c-1500mAh-11-1v-11-1-LiPo-RC-AKKU-Battery-2Pcs_W0QQitemZ150315705605QQihZ005QQcategoryZ34056 QQtcZphotoQQcmdZViewItemQQ_trksidZp1742.m153.l1262]Mystery Packs[/link]

jetmech05

Your meter looks like a knock off of a Fluke meter...Most meters of this kind do not but a load on the system being tested...so all you're reading is voltage without any load applied....once a load is applied voltage can drop off to unsafe levels.....
I remember reading a magazine story a few years back where a group of folks were involved in a big scale event..it's like day 3 or so and they have a good chance of winning...I can't remember the details.. they checked the batteries with a fluke meter, had good voltage...the aircraft crashed on final....after the crash they checked the battery voltage under load and lo and behold...unsafe

yetti831

Okay, thanks guys. One thing I noticed is that one of my packs, when it's finished, does not get warm. The second pack, however, gets warm. What does this mean?



Are these good for the F-35?


[link=http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=7344&Product_Name=Rhino_1750mAh_3S1P_20C_Lipoly_Pack]Rhino's[/link]

ChuckW

I bought a couple of these last year. They worked fin except that they were not the stated mAh capacity. Probably just a labeling issue. Can't comment on the Rhinos although I've thought about getting a couple to try.

opjose

Given the actual draw of that EDF, the packs tend to get HOT, not just warm.

I'll bet that the one that stays cool is the same one you complained about not getting adecuate power from... correct?

The Rhino packs are a good value.

yetti831

Yes, but they are both pretty terrible. I might be getting 3 mins of fairly moderate flight. So, what's the problem? Bad cells? Unbalanced? Plain fried? I'm pretty sure I didn't overcharge them. I always am right by them, and they never get hot. Man, I can't wait for my CC.

opjose

It sounds like you are not getting a full charge into the batteries.

A full charge should give you about 2 minutes of FULL THROTTLE flying or about 5 minutes at 60% throttle.

That's right! You don't get very much!

A fully charged pack should show a bit higher voltage than what you are reporting...

When you get your CC charger, cycle the batteries once, then charge them up and do a capacity check.

You should be able to draw about 1100mA out of the packs during a discharge cycle.

At 20C you may be able to pull about 22-24A out of the packs AT MOST, but here is the thing, that EDF will pull 32A-34A!!! More than the batteries can put out!

This will cause them to get warm quickly at low throttle or HOT at high throttle.

That is why I've mentioned that a 20C 1800mAh battery is better suited to your plane, than the 1300's that are included.

yetti831

Interesting, thanks!

The replacement pack that I got is 18c. This is the one that gets hot. Is the stock battery 20C?


I charged them both to around 12.58, so that seems full.


Thanks a lot.