battery charging problems and questions

[mjmccarron]

stay-fun,
Thank you for your work on this. Very interesting and it proves what I have been able to pick up on the subject. I still plan to conduct a similar experiment but I'm still buried in work from my real job. Here's a link to some more information. It may be more rudimentary than what you need but you can never learn too much. IMHO

http://batteryuniversity.com

We tend to use LiPo's in a less than ideal way and charge them with than controlled conditions (potentially). With a little knowledge we can improve their service life and avoid accidents.
Mike

 

[JohnC]

Here is my question:

I have a DX7s Transmitter with a 2000mHA 4.8V NiMH pack. The manual says that it will reach full charge when plugged into the wall wart that comes with it. It also recommends not charging it longer than 12 hours.

No matter how much I charge it, the battery icon indicator never goes above 90%, and the voltage indicator goes up to around 5.4 volts.

Why is this? Is it typical of Spektrum DX Transmitters?

 

[Viktor2415]

Lipo battery charger

Hi Flite Test, I'm new to lipo batteries and have a quadcopter that came with a 3.7 V 500 mAh lipo battery and its proper wall charger. However, I can't fly it longer than 6-7 min with that battery, so I purchased a bit bigger 3.7 V 2000 mAh lipo battery and tried charging it with the same charger. On the bottom of the charger it says the output is DC 4.3 V @ 800 mA. Is this current okay for charging a 2000 mAh battery or should it be exactly 2 A? Thanks!

 

[pressalltheknobs]

Hi Flite Test, I'm new to lipo batteries and have a quadcopter that came with a 3.7 V 500 mAh lipo battery and its proper wall charger. However, I can't fly it longer than 6-7 min with that battery, so I purchased a bit bigger 3.7 V 2000 mAh lipo battery and tried charging it with the same charger. On the bottom of the charger it says the output is DC 4.3 V @ 800 mA. Is this current okay for charging a 2000 mAh battery or should it be exactly 2 A? Thanks!

2000 mAh does not mean the battery needs 2A to charge. It gives a guide as to the max charging current you can use. Unless otherwise specified most lipos can be charged a 1C * the capacity so you may be able to charge the 2000 mAh battery with as much as that much current but you can charge it with less.

Whether your wall wart will work property with the 2000 mAh I cannot say. In theory it should work but it will take a long time vs the 500mAH. It is possible given it's not smart that the it is not set up to work properly with a 2000mAH battery.

You can try it in a safe location and see if the charger or the battery get very hot and switch it off if it started getting too hot to touch. A safe location would be away from anything that can catch fire easily preferable outside on concrete. If you have to it inside select the location carefully.

 

[Viktor2415]

2000 mAh does not mean the battery needs 2A to charge. It gives a guide as to the max charging current you can use. Unless otherwise specified most lipos can be charged a 1C * the capacity so you may be able to charge the 2000 mAh battery with as much as that much current but you can charge it with less.

Whether your wall wart will work property with the 2000 mAh I cannot say. In theory it should work but it will take a long time vs the 500mAH. It is possible given it's not smart that the it is not set up to work properly with a 2000mAH battery.

You can try it in a safe location and see if the charger or the battery get very hot and switch it off if it started getting too hot to touch. A safe location would be away from anything that can catch fire easily preferable outside on concrete. If you have to it inside select the location carefully.

Thanks on suggestion, yes the wall wart turned pretty hot to touch after some time even though the green LED lit on to indicate it charged. However, I'm not an expert to lipo batteries, but read some articles about the proper charging. It said that max. output voltage should not exceed 4.2V, when I plugged it in my quadcopter after adding it throttle to lift it off the ground it didn't managed and turned itself off automatically, because when I later checked the output voltage of the lipo with a multimeter it showed 4.25V which is far too much. Do you maybe know is there any cheap way for me instead of buying another charger to make some sort of voltage reg. circuit to regulate the charger's output from 4.3 to 4.2V, because I can't get it cheap in my country. Any suggestions??

 

[Viktor2415]

Could you please let me know could I make a voltage regulating circuit using lm317 voltage regulator with a standard wall adapter and then when the output voltage is regulated to exactly 4.2V from one of the dialed higher voltages connect it dirrectly to the 2000 mAh lipo battery? My standard wall adapter specs are: 3, 4.5, 5, 6, 7.5, 9 and 12V @ 1A. And ofcourse to know if it's charging properly connect the leads of the lipo in paralel with the multimeter to monitor the output voltage? I'm asking this because I feel not to start making something wrong. PLEASE?

 

[mjmccarron]

The LiPo charge algorithm is far more complicated than for Nicad or NmHi. It's not as simple as constant current or constant voltage. It's actually a combination. LiPo''s charge constant current up to a set voltage at which time the charger goes into a very tightly regulated constant voltage mode. This mode is tightly regulated as LiPo's can be seriously damaged by going over voltage. The CV mode lasts until the charge current falls below a set threshold for a set period of time then the charger shuts off completely and has NO trickle charger phase. A simple voltage regulator such as a LM317 is only a small piece of the necessary circuit to properly charge Lipo's. It can be done but would require a very good understanding of how LiPo's charge and very close monitoring. There are quite a few inexpensive LiPo chargers available for less than $30. IMHO that would be money well spent. If you are into electronics and want to design your own, I would recommend learning as much as you can about LiPo's and going from there. I have actually designed several LiPo chargers using a micro controller to monitor and control the output but the cost of building one vs buying one is huge. In any event, please be very careful how you charge LiPo's and remember, after heat comes fire. I value my hobby room well above the cost of a charger.

Mike

 

[Viktor2415]

Thank you very much for info, I really didn't know charging this batteries can be that complicated However one more thing, I also read about the safety LiPo bags that should be used for keeping this batteries while charging. Is this really necessary if I'm using a dedicated LiPo charger? I wonder why aren't they included with tablet or cell phone batteries in case of overcharging?

 

[mjmccarron]

The safety bag is a good idea because of the abuse or batteries are subjected to. For the most part, they are not necessary. In the case of a cell phone or laptop computer, the batteries are never subjected to high levels of vibration, impact or severe over discharge. They are generally safer to begin with. Lipo's used in model planes and multi's get banged around, over discharged etc. Over time these minor abuses can cause something to go wrong inside the battery during the stress of charging. It's rare but possible. Also, due to the variety of batteries one might have, it's possible to not set the charger properly and cause a problem although most chargers won't let you make huge mistakes. It isn't a must to use a lipo bag but taking some precautions against fire spreading in the unlikely event of a problem is just a good idea. I use a metal ammo can. It's kind of like why the seat cushions in an airplane can be used as a floatation devise. You hope to never need it but it's nice to know it's there just in case.

Mike

 

[pressalltheknobs]

Thank you very much for info, I really didn't know charging this batteries can be that complicated However one more thing, I also read about the safety LiPo bags that should be used for keeping this batteries while charging. Is this really necessary if I'm using a dedicated LiPo charger? I wonder why aren't they included with tablet or cell phone batteries in case of overcharging?

The simple answer is yes it is. When you charge an RC Lipo battery there is a small risk it will catch fire. Lipo fires are explosive and self sustaining. They cannont be put out only contained. You should always charge RC LIPO batteries in some kind of fire retardant container and never charge them unattended and you should pay attention to how well they are balanced. Also you should always store RC LIPO batteries is a fire retardant container since occasionally one will spontaneously catch fire. Generally this is due to damage and/or being unbalanced but it is not provable those are the only reasons.

Do you have to do this?... well no one is going to make you. If you want to risk burning your house down feel free to not follow the advice.

A lipo charging bag is reasonably cheap and effective way of containing the fire so you can deal with it and will keep the heat and flames away from the flammable material that you should not have been charging near but of course were. You can use some other fire proof container or charge them outside on a concrete floor as an alternative

Compared to cell phone lithium batteries, RC Lipos are generally much bigger, are contained in a thin plastic membrane rather than hard shells, are more prone to damage in use and and you are responsible for how they get charged rather than some clever circuit. Most lipo fires happen due to charging errors. Also most cell phone batteries are 1S which since a single cell can't get out of balance with itself are much less prone to charging problems.

You are required to carry any spare lithium batteries including cell phone and computer batteries as carry-on on airlines so it not like there is no recommended precaution for these. It just that the risks are considered lower due to the way they are packaged and used.

 

[stay-fun]

Hey, this topic is alive!

OMG Viktor, you are asking for YOUR HOME ON FIRE! USE A DEDICATED LIPO CHARGER. (yes, that's all caps for a reason, I very rarely ever use all caps)

So here's the explanation. LiPo batteries have sensitive chemistry when it comes to the voltage. Fully charged, a LiPo battery has a voltage of 4.2V. If you go to 4.1V, you have 10% less energy in your battery. Go to 4.3V and your house is on fire. That's how sensitive this is, and why you need a dedicated charger.

About phones: phones have this charging circuit built-in, and are therefore "safe". Phones that have a removable battery also have a hard battery case, but phones that come with a non-removable battery usually haven't (ask me how I know ). RC batteries don't have any circuitry built in, so the safety circuit needs to be built into your charger.

But what about over-discharging? Well the model usually has a low-voltage cutoff, but this still doesn't make it "safe" when a battery has multiple cells. One cell can still get too low. Fortunately, your model will likely fall out of the sky before the battery catches fire due to low power, and also charging is more risky than discharging. So yeah.

Honestly, 6-7 minutes of flying on your model is really good. Using a battery with 4x the capacity will make it a lot heavier, hard to fly and your flight time doesn't increase 4x because it has to work harder to keep all that stuff in the air. Just go with multiple 500 mAh batteries.

 

[Viktor2415]

Okay I will keep that in mind, but what do you mean by using multiple batteries? Could I connect say two 500mAh batteries in parallel to give me 1000mAh without shorting them bouth out?

 

[Viktor2415]

One more thing, can someone please help regarding the type of lipo battery for UDI U818a quad, because when I connect this 2000mAh battery I bought from http://www.ebay.co.uk/itm/111247469588 to my my quadcopter it spinns propellers only to about 50% of given throttle and then turns itself off automatically. When I connect its stock battery it works fine spinning the propellers at full throttle. Not sure is this because this battery is designed only for use with ipods, GPS, PSP and tablets and not with rc models??

 

[pressalltheknobs]

One more thing, can someone please help regarding the type of lipo battery for UDI U818a quad, because when I connect this 2000mAh battery I bought from http://www.ebay.co.uk/itm/111247469588 to my my quadcopter it spinns propellers only to about 50% of given throttle and then turns itself off automatically. When I connect its stock battery it works fine spinning the propellers at full throttle. Not sure is this because this battery is designed only for use with ipods, GPS, PSP and tablets and not with rc models??

Most likely because it has a protective circuit
"Built-in protection circuit PCM for prevent over charging or over discharging"
that limits current draw.

 

[stay-fun]

Okay I will keep that in mind, but what do you mean by using multiple batteries? Could I connect say two 500mAh batteries in parallel to give me 1000mAh without shorting them bouth out?

What i mean is to fly one battery, and when it's drained, you land and replace the battery.