Multiple Battery Charging Confirmation

[Hawke]

Hi, I've just got my mCPX and I'm loving leaning to fly it. I'm eager to get more flying time so I have ordered four more Turnigy nano-tech 300mah 1S 35c Lipo batteries and a 2 Pin JST to 6 x E-Flight Ultra Micro plug Charging Harness.

I have done a lot of reading on the batteries and want to check I have things right before I start charging so I don't burn my house down! As far as I understand it, even though the instructions for the mCPX say you should charge the stock batteries at 0.7 amps the batteries will last longer if they are charged at 0.2 amps (but will take longer to charge). Does this mean I can use the stock charger to charge two stock 200mah batteries with the above charging harness if I set the charger to 0.4 amps and leave the other plugs on the harness empty? Or 3 stock 200mah at 0.6 amps Or two nano-tech 300mah at 0.6 amps? Also, would I be able to charge all 6 batteries (2 stock 200mah and 4 nano-tech 300mah) and 0.7 amps and just have it take longer to charge?

I do understand that with the cable I'm using I'll have to have all batteries at a similar state of discharge before linking them together for a charge and I'm obviously going to have to get a better charger if I want to charge all 6 in a decent time frame but will this work for me in the mean time?

I would be very grateful if someone could confirm my understanding of this.

Thanks.

[berley114]

Hi Hawke,
when using your charging harness... do NOT mix the 200mah with 300mah lipo's.
I am not sure of the stock charger's capability but ...... with something like an imax B6 lipo charger ....
You can just charge 2x 200mah stock lipo's at 0.4A and leave the other connectors empty.
You can just charge 4x 300mah nano-tech lipo's at 1.0A and leave the other connectors empty.
When using a parallel charging harness, ideally the Mah of each lipo should be the same.
when you fly it is a good idea to time your flights, i think for the stock Mcpx probably about 4 minutes of flight for each 200mah lipo? perhaps 5 or 6 mins for each of the 300mah?
You can check your lipo's with a simple digital checker such as.... http://www.brchobbies.co.uk/?page=sh...ditem&item=183
i am sure you will get more info with further replies soon. hope this helps....

[UKHelibob]

Hi, I've just got my mCPX and I'm loving leaning to fly it. I'm eager to get more flying time so I have ordered four more Turnigy nano-tech 300mah 1S 35c Lipo batteries and a 2 Pin JST to 6 x E-Flight Ultra Micro plug Charging Harness.

I have done a lot of reading on the batteries and want to check I have things right before I start charging so I don't burn my house down! As far as I understand it, even though the instructions for the mCPX say you should charge the stock batteries at 0.7 amps the batteries will last longer if they are charged at 0.2 amps (but will take longer to charge). Does this mean I can use the stock charger to charge two stock 200mah batteries with the above charging harness if I set the charger to 0.4 amps and leave the other plugs on the harness empty? Or 3 stock 200mah at 0.6 amps Or two nano-tech 300mah at 0.6 amps? Also, would I be able to charge all 6 batteries (2 stock 200mah and 4 nano-tech 300mah) and 0.7 amps and just have it take longer to charge?

I do understand that with the cable I'm using I'll have to have all batteries at a similar state of discharge before linking them together for a charge and I'm obviously going to have to get a better charger if I want to charge all 6 in a decent time frame but will this work for me in the mean time?

I would be very grateful if someone could confirm my understanding of this.

Thanks.

Your understanding is correct. The main limitation on multiple battery parallel charging with the stock charger is the current that it is able to supply. Any of the common '4 button' chargers will provide enough current to charge many batteries in parallel in a reasonable time but depending on which one you buy you will probably need to buy a separate power supply as many such chargers are not mains powered. You can use an old (but working) PC power supply to provide the necessary 12 volts if you have one available.

There is no problem in mixing the capacity of batteries being charged in parallel as long as their voltage is roughly the same. I do this all the time and set the charge current to that which I would use if all the batteries had the same capacity based on the lowest one being charged. So, charging 2 200mA, 2 250mA and 2 300 mA batteries I set the charge current to 6 times 200mA (1.2A). In practice I have charged up to 12 at a time.

There is an effect (look up Thevenin's Theorem) that apparently will cause more current to be supplied to the higher capacity batteries, but when this was suggested to me I could not make head nor tail of it so have stuck to using a charge current based on the lowest capacity battery for the most part. The charge time may be extended but is safe and kind to the batteries.

[Hawke]

Thanks for the replies berley114 and UKHelibob.

when using your charging harness... do NOT mix the 200mah with 300mah lipo's.

When using a parallel charging harness, ideally the Mah of each lipo should be the same.

There is no problem in mixing the capacity of batteries being charged in parallel as long as their voltage is roughly the same. I do this all the time and set the charge current to that which I would use if all the batteries had the same capacity based on the lowest one being charged. So, charging 2 200mA, 2 250mA and 2 300 mA batteries I set the charge current to 6 times 200mA (1.2A).

There seemed to be a lot of confusion about mixing capacities when I was reading up on it. I was under the impression that you could mix capacities when charging in parallel but not when charging in series, is this correct? Also, when you say that their voltage should be roughly the same do you mean how much they have been discharged (I assume the voltage drops as the battery is discharged)? When I time the 200mah batteries and stop after four minutes flight I know they have all been discharged by approximately the same amount, is there any way to work out how long I would have to run the 300mah batteries for so they have discharged to the same voltage level as the 200mah batteries?

when you fly it is a good idea to time your flights, i think for the stock Mcpx probably about 4 minutes of flight for each 200mah lipo? perhaps 5 or 6 mins for each of the 300mah?

I started timing my flights after I noticed a drop in flight time, I got five or six minutes out of the stock batteries for a few flights but this soon dropped and it was forcing me to land after four minutes. Since I've been timing my flights and stopping at four minutes I've noticed the batteries will easily run to four minutes again. I'll defiantly go easier on my 300mah batteries when they are delivered.

Also, I just wanted to double check that, when I charge in parallel, the charge current doesn't have to be a specific multiple of the batteries capacity, as long as it isn't greater than what the batteries can handle?

Thanks again for your replies, I'm loving learning to fly on this little beast and your help is invaluable.

[UKHelibob]

There is no problem in mixing capacities when charging in series or parallel. In series the same current flows through all of the cells whilst in parallel it is shared between them.

Rather than rely on a battery being at a specific voltage after a flight of a particular duration it is better to measure the voltage. I use one of these, or at least it looks similar 2in1 Lipo Battery Low Voltage Tester 1S-8S Buzzer Alarm | eBay You can plug the mCPX batteries straight onto the first 2 pins.

Charge current, either series or parallel, can be set to suit yourself and how kindly you want to treat the batteries.

[Hawke]

Thanks for the confirmation.

[SmileyMan]

Save discharge voltage ( like within 0.1v) and number of cells for parallel. (i.e. You can not mix 2S and 3S batteries).

Same capacity and cell voltage for serial (cells have to be the same capacity in each battery for the balance). You can mix cell numbers in batteries.

Serial charging far more tricky to setup.

Examples.

Parallel
2x3S 2000mah with 4x3S 1000mah
Charger sees 1 3S 8000mah battery

Serial
1x3S 1500mah with 2x2S 1500mah
Charger sees 1x7S 1500mah battery

Steve.

[Hawke]

Cheers for the reply Steve. Great examples. I think that clears it up. There seems to be many conflicting opinions on this, I'm surprised there isn't a simple guide/sticky about this. So, to re-iterate for my understanding and maybe anyone else who reads this:

Parallel Charge: Discharge Voltage and Number of Cells have to be the same. Capacity and Cell Voltage can be different. Charging cable can have some connectors empty.
Series Charge: Capacity and Cell Voltage have to be the same. Discharge Voltage and Number of Cells can be different. Charging cable cannot have any connectors empty.

Charge current for both a parallel and series charge should be set based on how the charger sees the battery, as per SmileyMan's example:

Parallel
2x3S 2000mah with 4x3S 1000mah
Charger sees 1 3S 8000mah battery

Serial
1x3S 1500mah with 2x2S 1500mah
Charger sees 1x7S 1500mah battery

If you want to slow how fast the batteries degrade with use, when charging set the charge current to match the total capacity (mah) that the charger sees. If you want the batteries to charge faster, set the charge current higher but don't exceed the maximum the batteries can handle.

So, I think I've got that correct but I do have a couple more questions:
1) Does anybody know the maximum charge current for the stock 200mah 1S 3.7V 30C and the Turnigy nano-tech 300mah 1S 35C batteries?
2) To parallel charge 6 mCPX batteries, at the total capacity the charger sees or greater, I'll need to upgrade from the stock charger (700mah/0.7amps max output) to one which can provide a higher charge current to match the rate I want to charge at. To series charge the same batteries I'll have to upgrade to a charger that can handle multiple cells. Is this right? Which I the best route to take?

Thanks in advance.

[Hawke]

You can check your lipo's with a simple digital checker such as.... http://www.brchobbies.co.uk/?page=sh...ditem&item=183

Rather than rely on a battery being at a specific voltage after a flight of a particular duration it is better to measure the voltage. I use one of these, or at least it looks similar 2in1 Lipo Battery Low Voltage Tester 1S-8S Buzzer Alarm | eBay You can plug the mCPX batteries straight onto the first 2 pins.

I'm looking at upgrading my stock charger to one that can charge 6 batteries at once and was wondering if there is one available that includes a voltage tester such as the ones above or will I have to/is it better to buy this separately? Can anybody suggest a good charger for my purpose that I can get for a good price in the UK?

Thanks in advance.

[whirlygig]

The Accucel-6 is a very good charger at a reasonable price,and the one that I use, the C6 X-charger is also very good and the Imax B6 is good if you get the genuine one,not the copy.

These are all pretty good for up to 6-cell charging.

I use a multi-meter to check my cell voltage,I've never had one of those small voltage checkers that was any where near accurate.

A good way of remembering charging at 1C is as follows :-

For example, say you had 3 x 1s, 3.7v, 300mah lipo's :-


Parallel- Add capacity together, keep voltage the same. i.e 3 x 300mah = capacity 0.9, voltage 3.7v

Serial- Add voltage together,keep capacity the same. i.e 3 x 3.7v = 11.1v, capacity 0.3

Apparently some charge lipo's with varying capacities,but personally,I stick with the same capacity when I charge mine.

[UKHelibob]

Using a multi-meter may give more accurate results but it is not as convenient as using the simple device. There is no need for adaptor leads, which bring with them the possibility of shorting the battery because of the exposed connections. Just push the battery on the first 2 pins and read the value.

Accuracy of the device does not matter, just that it is consistent, so that batteries are of similar voltage when connected together. It is also very handy to have with you when flying if there is any confusion as to which batteries have been used and which have not.

Any of the '4 button' chargers available will do the job of charging mCPX batteries. Most appear to use the same firmware to control the charging but be aware that the majority require an external power supply. I use an old PC power supply. There is plenty of information available about converting them for this use.

[Gecko501]

Hi hawke. I was in your exact position not so long ago and this is the thread I started

http://www.rcheliaddict.co.uk/showthread.php?t=74912

Also I drew these pics to help my understanding on the difference between series and parallel

Parallel



Series


Charging at 1C is best practice and as mcpx batteries are single cells I find it easiest to charge in parallel. I got the IMAX B6 from hobby king, leave the charger at 3.7V and just sum the mah of each cell I am charging to determine what A I need to charge at.

If you want to charge at 2C then multiply the A value by 2 and for 3C multiply by 3.

There are a few links in my original thread that are very helpful and I have read them a dozen times.

Best of luck

[whirlygig]

Using a multi-meter may give more accurate results but it is not as convenient as using the simple device. There is no need for adaptor leads, which bring with them the possibility of shorting the battery because of the exposed connections. Just push the battery on the first 2 pins and read the value.

Accuracy of the device does not matter, just that it is consistent, so that batteries are of similar voltage when connected together. It is also very handy to have with you when flying if there is any confusion as to which batteries have been used and which have not.

I've yet to find one that is consistent.

That's why I use a multi-meter.

For the extra money I can check all my 1s and 3s batteries, confident that I'm getting a reading that is pretty accurate.

[cjcj1949]

It is a good idea to keep a check on each battery when you parallel charge. Lipos do die eventually and often die short circuit. When this happens with one battery being charged there is no problem as the charger will detect it and stop. With other good batteries in parallel this could be a problem as the good batteries will discharge through the faulty battery. Parallel charging is not a proper solution but something that works most of the time. It assumes all the batteries are equal and that current is therefore divided equally. It is not a good idea to mix different capacity batteries as this multiplies the current going into the lowest battery. A small difference is ok. Fuses and ampmeters in each lead are a good idea as otherwise you are relying on connectors always making a good contact and that is not always the case. Lipos are not predictable unfortunately and do cause fires.