Parallel charge question (for MCPX batteries)

[mixfisto]

Hey all, I just bought a new Bantam Charger (BC6DX-II) and before I do anything stupid, I wanted some help

I have spent a lot of time reading up on parallel charging, etc, but as I was about to start my first charge, I realized I don't quite "get it" just yet.

What I want to do is:
- parallel charge 5 300mah Nano-techs at the same time (for my stock MCPX) and
- parallel charge 6 550mah Hyperions at the same time (for my BL MCPX)

Could anyone give me some settings or advice? I'd like to charge these as fast as it safely doable!

I would highly appreciate it

[Cheetah62]

When parallel charging you add the individual capacities together, as though one pack, to calculate the charge current. Apply the C-rated charging limit for the packs if you want to go higher.
For example: 5 x 300mAh cells = 1500mAh total capacity. 1C charge rate would be 1.5A. 2C would be 3.0A. Etc.

Excellent article here:
http://sites.google.com/site/tjinguy...allel-charging

[mixfisto]

Thanks Cheetah... that makes sense... the thing I was mostly concerned with was the C rating. So I guess you basically multiply that as well (1 battery at 1C = 6 batteries at 6C)?

[Cheetah62]

NO!
You check the batteries to see what their charge rating is. It should be printed on the label somewhere. If not, do not assume anything. Use 1C unless listed otherwise.
You can use that to raise your charge rate, as I showed above.
If the charge rate limit on a particular pack is 3C for example, then you take the parallel current value and multiply it by three. Use the C-rating of the lowest-rated pack in the parallel set.
You don't multiply the C-rating by the number of packs.

[mixfisto]

AHH... OK got it...thanks!

[chuteopn]

Cheeta,
on the same question, i have a Thunder ac680, I am able to change the max capacity
on the charger for the particular battery i,m charging. i.e. 200, 300 maH. Lets say i,m charging 4, 200mah batteries in parallel. 4 x 200 = 800. at 1c i charge at .8 amp, but do i need to bump the max capacity up to 800 maH, or do i just leave it set at the 200 maH. What the battery is rated at.
Thanks for the help.
Chute

[2001rotax800]

Not to step on Cheetah62's toes, but yes you up the capacityto 800, that way the charger does not shutoff when it reaches 400mA's. The batteries need to have 800 total(400 each).

[Cheetah62]

Yes.
When parallel charging the packs are treated electrically as one large pack with a capacity equal to the sum of the individual packs. The charger does not know how many packs are connected, so you have to tell it what charge rate to use based on this calculation.

[Cheetah62]

Originally Posted by chuteopn

Lets say i,m charging 4, 200mah batteries in parallel. 4 x 200 = 800. at 1c i charge at .8 amp, but do i need to bump the max capacity up to 800 maH, or do i just leave it set at the 200 maH....

I'm not familiar with that charger, but your charge current calculation is correct.
1C charge rate would be 0.8A.
Normally you would not tell the charger what the pack capacity is, as this isn't really relevant. Just like knowing the size of your gas tank doesn't really matter at the gas pump, your charger doesn't know or care how large your packs are. You just pump until it's full. How much you put in depends on how much you used since the last fill up.
You program the charger with the initial charge current, based on the calculation above. It will start the cycle at the programmed current, and then adjust the charge rate by measuring the cell voltages. When the cell voltages reach a predetermined value, somewhere around 4.2 V, the charger thinks the pack (cells) are "full" and ends the process.

Here is a good read:
http://sites.google.com/site/tjinguy...-chargers-work

[chuteopn]

Thanks Cheeta and Rotax,
Still trying to figure out this charging thing. A Newb, can ya tell!
HAHAHHA
Here was my thinking, if i had 4 200maH batteries run down to 80%, which is about 3.5 minutes on my mCPx. I've used up 160 maH roughly in each battery. the default setting for a 3.7v battery in the charger is 500maH. 4 in parallel at 160 = 640.
Maybe im thinking way to much into this, but wouldn't that leave it short of a total of 800?
i didn't want to overload the cells by max at 800, or will it shut down after batteries have reached their max? but didnt want to leave them short at 500 either.
Your time and help is greatly appreciated.
Finally got this thing to stay inside a 6' x 6' box hovering !
thanks again!

[Yamahajrp]

The way a charger sees the state of the batteries is full charge of a 3.7v battery is 4.2v it doesn't put a set amount of milliamps into the battery, when it gets close to 4.2v the charger reduces the charge rate so it doesn't over charge, my charger drops it 1/10 of the set charge rate to finish the charge 1/5 of the set charge rate if doing a fast charge. If you are charging 3 batteries in parallel I believe that it will balance the batteries, like if one is at 4.18v during the charging cycle and the other is at 4.20v it will actually drain a bit from the higher into the smaller, someone more knowledgeable will correct me if I am wrong on the balancing part.


E-Razor450, mcpx v2(144mm tail, cnc alumni sash), DX6i

[desertstalker]

Originally Posted by Yamahajrp

If you are charging 3 batteries in parallel I believe that it will balance the batteries, like if one is at 4.18v during the charging cycle and the other is at 4.20v it will actually drain a bit from the higher into the smaller, someone more knowledgeable will correct me if I am wrong on the balancing part.

It is not possible for anything connected in parallel to have different voltages, so at no time will any of the cells be at a different voltage. If you connect them that way then yes, the higher one will discharge into the lower ones to balance them out.

[Gregor99]

Originally Posted by desertstalker

It is not possible for anything connected in parallel to have different voltages, so at no time will any of the cells be at a different voltage.

While that is true, the only time cell voltage equals "state of charge" is when nothing is connected to it. Put a load on a cell and the voltage drops. Remove the load and the voltage will bounce back after a short rest. Not back to where it started but higher than the loaded voltage. Same thing for applying current to a cell. Its voltage increases. Remove the current and the cell voltage will sag back to reflect the real state of charge. This is why chargers have a constant voltage stage.

This is what happens when you connect two cells in parallel that have different states of charge. While the voltage on each cell is the same, the state of charge is not. Since they are connected, the higher cell will charge the lower. But once they get close, the current between cells becomes very low. A difference of 0.05v may take up to 20 minutes to equalize between two cells in parallel. The only way to really know the state of charge is to disconnect the pack from the parallel charging cable, let it rest and then take a voltage reading.