Choosing the right charge rate for lipos?
I recently got a 3 cell 11.1V 20C zippy lipo from hobbyking. I was trying to find the right charge rate to use, but I couldn't find anything on hobbyking that said what rate to use. Do you guys have any recommendations?
Replies to This Discussion
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Permalink Reply by Daniel Gru on -
Always 1C!
Keeps batts going long and fresh ;-)
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Permalink Reply by Tom Hastie on -
Charge rate depends on the mAh capacity of the pack. Drop the "h" and you have the save charge current.
So:
2200mAh - charge at 2.2A.
1350mAh - charge at 1.3A.
etc.
It should take roughly an hour to charge a fully depleted back.
These days alot of people charge at higher currents assuming that you have a balancing charger capable of it. Twice or triple the 1 hour charge rate are sometimes advertised. I would only suggest doing that if you know what you're doing though. Charging an unbalanced lipo at excessively high rates can result in a fire.
Tom
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Permalink Reply by Morli on -
Irrespective of what higher charge rate you choose ,if the LiPo is unbalanced( usually after using it couple of time ) the smart charger with built in balancer drops charge rates to 0.3 A ( mine does) if the difference between the cells are more than specific limits. I choose 0.5 A charge rate always for any thing less than 2200mAh. Higher capacity gets 1A dose max in my case. I am in no rush usually. I normally don't deplete the Lipo more than 50-60% capacity. When I deplete them more( 2 cases) , I lost the LiPos where I could recover one one of them :(.
except for few EP planes, I use LiPo + Ubec only to power Rx and servos powered by nitro/gas engine models. this also goes to Trex600N too. So charge rate is 10-25% of the total capacity and not 1C for me.
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Permalink Reply by Grant Parker on
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Thanks! That clears things up a lot. Now my question is: do most modern charger/balancers know when a battery is completely charged and stop charging when that point is reached?
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Permalink Reply by Nathaniel Caner on -
Grant,
There are as many chargers as there are batteries to chose from. The important look for are that the charger is specifically designed to charge Lipo batteries, and that it is capable of "balancing" your pack.
Here is why you want to use a balance charger:
Your battery is made up of (3) 3.7 volt cells of a given capacity, unless all cells are in balance with each other of the cells will end up with a lower voltage than the others. With a non balancing charger your charger will only see the TOTAL voltage of the pack. This will cause the non balancing charger to over charge the (2) higher voltage cells. This is a very dangerous condition. Over charged cells can swell to the point of bursting and a runaway reaction can occur resulting in a VIOLENT fire.
Here's an example:
Total pack voltage= 10.0 volts
cell 1 3.5 volts
cell 2 3.0 volts
cell 3 3.5 volts
Maximum pack voltage= 12.6 volts=4.2 volts per cell
Your charger uses a constant current/constant voltage charging method as follows:
Initially it will apply a constant current bringing the capacity up quickly, then as the pack voltage increases it will reduce the current to keep the pack voltage a constant 12.6 volts.
In the above scenario the problem with a non balancing charger is that the pack will overcharge the (2) higher voltage cells because the TOTAL pack voltage is below the 12.6 max voltage even though the (2) cells would be over the max of 4.2 volts per cell
12.6 volts
cell 1 4.366 volts
cell 2 3.866 volts
cell 3 4.366 volts
Even a single charge cycle like this can damage the pack. Repeated charging like this will certainly destroy the pack. Not to mention be very dangerous.
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Permalink Reply by Grant Parker on
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Ok, I have this charger/balancer. I couldn't tell from reading the description if it had a feature to stop charging when done. I have heard about the exploding issue, which is why I wanted to know if it had a feature to stop charging when done.
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Permalink Reply by Martin Seven on -
That's one of the popular workhorse chargers. It's reliable and yes, it does sense when the battery is fully charged (i.e. each cell is at 4.2 V).
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Permalink Reply by Grant Parker on
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Ok, that's good to know. Do you know of a manual to it anywhere on the Internet? I've been looking, but I can't seem to find one.
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Permalink Reply by Nathaniel Caner on
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Grant,
As far as I can tell this charger is designed for LiPo, that's the good news, however I don't see any reference to balancing circuitry. When you plug the battery in to charge, do you connect one cord to the output of the battery and one to the balancing tap? If so it's a balancing charger, if not it's not. If it doesn't have a balancing circuit you run the risk of eventually either over charging the battery or not fully charging one cell and eventually running the pack with that one cell below 3 volts and killing the pack. In the end your charger is one area where it's best to go with a really good unit. You invest a lot of money in your batteries, and have a lot riding on them.
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Permalink Reply by Grant Parker on
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Yeah, I have one cord on the main charger and one on the balancing. Do I need to plug in the balancing cord all the time, or should I only do it some of the time?
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