It’s a bit of a funny story…I lost my cell phone charger, so I thought I’d use my LN-5014 to recharge it, I mean I can set it for low-power LiPo batteries too, right? So I did and was able to charge up my phone. However, in the process I went over the charger instructions and noted I can charge up to 18V LiPo (5 cells in series) packs at 5A.
So… I was wondering if I had a pack I’d run in parallel at 7.4V 10000 mAh, could I put it in serial to 14.8V and charge it at 5A? Since I want to get around 10-12 Ah worth of battery for my computer controlled bot (probably some kind of Mega scale Scout), and I’d prefer not to have to buy another charger. So I was wondering if this was a bright idea, or incredibly stupid?
It’s not a good idea to charge lithiums in series, unless there is circuitry to monitor the voltage between the cells. Despite what your charger claims to be able to do, I think charging five LiPo cells in series is a Really Bad Idea. You could easily destroy some of the cells due to overvoltage.
I assume that what you have is two “7.4V 5000 mAh” packs, that you plan to run in parallel. Those packs are already 2 cells in series, so you shouldn’t put anything else in series with them when you want to charge them.
Also, 5A is a really high charge rate (too high). You shouldn’t try to charge them at more than a couple of amps.
In any case, follow the charging specs given by the battery maker.
If you intend to charge Li-Po’s in series make sure that the pack has a cell balancer wire harness installed and use a HECELL cell balancer You can get them on ebay. I’ve been doing this for about 1.5 years now in all my robots with no troubles. As for charge rates just dont exceed the mah rating of the battery individual cells. i.e if you have two 7.4v 2000mah packs in parallel for 7.4v 4000mah do not exceed 2000mah or 2 amp charge rate.
If the pack is 5000 mAh charging at 5 Amps is fine. That’s only 1 C.
And charging cells in series is fine. An 11.1 Volt pack is just 3 cells in series. And everyone charges those.
Charging multiple packs in series is fine so long as all the packs are identical, meaning all new, never used and same brand, capacity, C rating, and age.
I f you plan to charge a pack that contains more than 6 cells, it’s a good idea to use a lipo balancer. The more cells, the better chance that over time, one cell will fall out of balance.
The thing that you should be worried about is charging your 2 packs in a series setup then using them in a parallel setup. Bad idea. The cells are being exposed to 2 different balancing states. While charging, they are in series and the cells are trying to naturally balance their voltage/capacity in series. In parallel, they are trying to balance themselves as 2 packs. You will cause alot of problems. If it was two 2 cell 7.4 Volt packs, probably ok. But with a high cell count in 2 large packs, you have to either keep them in series or in parallel for both charging and discharging.
You can use your 2 X 5000mAh packs in parallel for 10,000 mAh. When you have to charge them, separate them and charge each pack as a 7.4V 5000 mAh pack, one at a time on your charger. Then reconnect them in parallel to use them. If you are doing this, I’d strongly suggest investing in a lipo balancer for charging. And Astro Blinky balancer can be had for under $25. I recommend the Hyperion EOS ($30) or the Apache 505 balancer ($20).
If they are still hooking up in parallel to total 4000mAh, they can be charged as a 4000 mAh pack. Which at 1 C is 4 Amps. If you had a 4000mAh single pack, you wouldn’t charge it as a 2000mAh. You’d charge it at 1C or 4 Amps. 2 identical packs in parallel are exactly the same as one larger pack, so long as they are treated the same kept in parallel.
I charge my 30C lipo packs at 2C and have never had a problem. Lipo fires from charging are from overcharging, usually, or charging at the wrong voltage. Almost any lipo can take a 2C charge in reality. But 1C is the norm and should be stuck with.
Yea, I always assumed to be using some kind of balancer. Its really silly to not spend the extra ($20-30) for a balancer when shelling out over $300 for your packs.
Unfortunately its looking like I should just suck it up and buy a 10-15A capacity charger. Anybody have a model they can recommend? I’d prefer something under $300
Since I don’t really like the idea of either having to buy another LN-5014 knowing I still have to work around 5A limitations, or charge each piece of my total pack and having things take twice as long.
Oh well, worth asking.
One final thing, I was under the impression LiPos could only be charged at 1C or higher. Could I just charge my 10Ah pack at 0.5C? I know it would take longer, but at least it would lower the bar to me actually getting a pack.
Actually, most maufacturers and hobbiests alike recommend charging lipos at 1C OR under. It’s not recommended to charge lipos at over 1C.
Charging your packs at 500mAh is fine. You can charge them at 100mAh if you like. The important thing is tha tyou use a quality charger that can properly calculate the packs remaining capacity to keep from overcharging it. And that you charge at the proper voltage.
AND they need to be at about the same state of charge. If one is at a lower charge, you will over-volt the one with the higher charge. [You can reduce the risk by charging at a much lower rate.]
All this talk of series/parallel connections and high charge rates makes me nervous. I think the “R/C crowd” is bending the rules for proper handling of lithium batteries…
If you want to see a “benchmark” for how to properly handle multi-cell lithium packs, look at the laptop PC industry.
Perhaps you should not over generalize quite so much on this point.
I would put that certain individuals seem to have a more cavalier attitude about what constitutes safe and proper handling of Li-ion cells than several of the professional individuals have expressed as being appropriate. They also seem more than willing to share their own fortunate experiences as some sort of fact. We can only hope they don’t manage to get someone else hurt or cause them significant loss due to fire before their own luck runs out.
Thanks Eddie, those are fair statements - I concur.
I can’t help but have an excessively ‘conservative’ attitude, since I’m involved in the design of a LiIon battery assembly. Our design has at least 4 types of protection in the HW (overvolt, undervolt, overcurrent, over/under temperature), and at least 3 types in the software (which I implemented - overvolt, overtime, overdischarge). Since the pack includes 3 sets of cells, my code also manages how/when to connect the cells in parallel during a discharge.
I absolutely agree that the proper precautions need to be taken when dealing with lipos and I in no way condone going against manufacturers recommended practices. 1 C charging is well within safety ranges. And running separate packs in parallel or series always has it’s risks and one MUST be aware of the precautions before doing so. If identical packs are used and one pack is never used outside of the parallel or series arrangement, and balancers are used on large cell count packs, they are just as safe to charge and use as NiMh. It is when people use one pack for a plane and then hook it back up in series and end up puffing a cell in the dead pack, that gives lipos a bad name.
I hope that no one ever has to experience a lipo fire. They are nasty. And people have almost lost their house from an unattended lipo. But there are alot more people that have got battery acid all over from shorting out NiCd and NiMh packs. And there are actually very few people that have experienced lipo fires. A lipo cell igniting is just so much more extravagant and destructive than a Nicd seeping acid, that just one story can spread fast and seem like it’s happening to everyone.
I know a few young and old R/C plane guys I wouldn’t encourage to fool with mating lipo packs. But with the proper precautions and respect, a competent person can safely use lipos in series or parallel. I assumed that Tillin and the others here are more than competent enough to exercise common sense.
By far the best way to get more capacity or more voltage, is to just build a bigger pack out of many cells that are all brand new, identical and unused. That way there is no chance of using a group of cells outside the arrangement. Or buy a premade larger pack that all ready has many cells wired in parallel and series inside. And use a balancer.
I am quite aware of the potential issues with using LiPos. This is why before I even buy a pack, I’m asking lots of questions. The only LiPo I’ve ever attempted to recharge on my own (as opposed to using the charger with whatever device they came with) was my 1000 mAh 3.7V cell phone battery. I’m the first to admit I’m really stupid when it comes to this, and won’t be experimenting with anything until I think I know enough to keep safe. I mean I didn’t know I could charge them at less than 1C.
Safety aside, charging two separate packs together is not a very good idea. This is because of balance and unless the cells are balanced their life span will be severely shortened. I’m assuming these packs have been cycled several time since they were and probably not broken in. In which case they are probably already unbalanced enough and by charging 2 packs in series your just making it worse. However, if they are cheap batts and you dont want to shell out the dough for a balancer then I guess it doesnt really matter.
See my second post in the thread. I always had planned on a balancer. Also, remember, this whole thread is hypothetical. I don’t actually have any LiPo packs yet. (Not counting the little pack in my cell phone that started this thought experiment when I reread the charger’s instructions.)
The main reason for trying to charge in series was I honestly didn’t know I could charge LiPos at less than 1C. Even on this forum while never stated directly, many things implied that LiPos had to be charged at 1C. Browsing online on RC forums showed people charging at 1C, 2C, 3C, 5C (yes, I did see this), etc. but never under. As stated by many people here, RC people a. Generally have newer LiPos that can safely handle charging at a few times capacity and b. Sometimes tend to bend the rules a little bit.
Now that I know that I can charge at less than 1C just fine, I can keep my LN-5014 and charge at whatever fraction of the capacity 5A turns out to be. Since the pack I’m planning on is in the 10-15Ah range, this will be 0.5-0.3\C respectively.
Seriously, lots of people won’t.