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Help! Parallel Charging Different C ratings

#1
Can I parallel charge batteries if everything except their C rating is different? For example, if I have some CNHL 4s 1300mAh 70C batteries, can I parallel charge them with the 100C versions, assuming they're also 4s 1300mAh?
 

d8veh

Well-known member
#3
Parallel charging can be tricky. It works OK if the batteries are run in parallel, which keeps them at the same voltage as each other, but if you use 4 different batteries for 4 different flights, they'll all be at different voltages. If you connect batteries, which are at different voltages to a parallel board, something's going to smoke. Be careful, it's not funny when a lipo catches fire!.
 

Bricks

Well-known member
#4
Parallel charging can be tricky. It works OK if the batteries are run in parallel, which keeps them at the same voltage as each other, but if you use 4 different batteries for 4 different flights, they'll all be at different voltages. If you connect batteries, which are at different voltages to a parallel board, something's going to smoke. Be careful, it's not funny when a lipo catches fire!.
Not as critical as most seem to think when hooking batteries to a parallel charging board hook the main connectors first ) not the balance leads ) the batteries will equalize after about 5-10 minutes it does not happen instantly it actually takes some time.

Say I am done flying for the day and have 4 batteries 2 I have flown and 2 I have not I will hook the 2 I have flown first to the charging board let hem equalize. Then add 1 of the fully charged batteries let them equalize then add the 4th by that time I find my batteries may already be at storage level. I will hook up my balance leads then turn on the charger and let them balance many times the charger is on for only a couple of minutes.

I have done this many times using a voltage checker and have had no issues.
 
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Merv

Well-known member
#5
I've had trouble parallel charging. I've had one cell on one battery not make contact & not be balanced. No way to see this until you charge and use a cell checker to see if all your cells are balanced.
 

sprzout

Knower of useless information
Mentor
#6
Only batteries I parallel charge are my 1C batteries for my TinyWhoops and UMX planes...no stress on whether the cells balance or not. :)

Plus, less of a fire hazard should one go south. Don't get me wrong, it's possible for it to get bad, but not as horrible as say, a 4s pack touching off outside of a BatBox or Lipo sack (which you should be charging your batteries in, regardless!). I know several guys in my club who have gone off from their battery packs while charging at home, and their den, garage, or living room ended up going up in flames. I know, I'm probably preaching to to the choir about this, but be safe when you charge - I don't want ANYONE losing their home because a battery puffed and exploded.
 

Merv

Well-known member
#7
Anybody tried series changing? Take two 3S packs and charge them is series as a single 6S pack. That way you know all of the cells are making contact.
 

d8veh

Well-known member
#8
Anybody tried series changing? Take two 3S packs and charge them is series as a single 6S pack. That way you know all of the cells are making contact.
That would work with a charger that charges through the balance leads, like a BC168 charger, but a normal iMax type is going to struggle with the balancing, so will probably take a lot longer to charge the lower voltage pack.
 

Merv

Well-known member
#9
That would work with a charger that charges through the balance leads, like a BC168 charger, but a normal iMax type is going to struggle with the balancing, so will probably take a lot longer to charge the lower voltage pack.
I agree that it would take longer than a single pack. I would think it would be quicker than charging two packs, one at a time. Even if it does take longer than two packs, I don't have to be there to put the 2nd pack on.
 

Bricks

Well-known member
#10
When it comes to charging Lipos your best friend is your hand. Once the charger is hooked up and running give it a few minutes and feel your battery packs if ANY of them feel warm stop. More then likely if one battery is warm it is going to have a bad cell in it or if it takes way to long to charge. Every battery I had go bad it started to feel warm while charging.
 

Hai-Lee

Old and Bold RC PILOT
#11
The best and SAFEST way to charge 2 batteries at the same time is to use 2 separate chargers.

The batteries are at less risk of damage through massive inrush currents due to battery pack terminal voltage differences and inadvertent incorrect connections. Chargers are almost as cheap as a decent battery pack and a second charger will give longer battery pack life than a dodgy 2 battery pack charging method.

Serial charging is easily possible if the packs involved are identical but in parallel there is a real possibility of battery damage or worse.

Just an educated opinion!

Have fun!
 

d8veh

Well-known member
#12
I agree that it would take longer than a single pack. I would think it would be quicker than charging two packs, one at a time. Even if it does take longer than two packs, I don't have to be there to put the 2nd pack on.
I doubt it, but it depends on the difference in voltage between the two packs. If they're nearly equal, two 3S packs will charge in the same time as one, but if they're a few volts different, it'll take forever. The charger will switch to balancing mode as soon as a cell from the higher pack reaches 4.2v. Balancing current is minimal and it goes through an iterative process of charging and discharging. The balancing system is only meant to deal with very small voltage differences between the cells.
 
#13
There's a lot of misconceptions about parallel charging. Joshua Bardwell is a very respected person in the RC community and well known to Flitetest/Rotor Roit crew, and has some good videos on parallel charging.