I want to build me an electric longboard, and I was planning to run it off of 4 or 5 11.1 volt laptop batteries... I want to wire them in parallel (The sets of 11.1 volt), and charge it as one big battery with only 2 wires... (If it's possible.) I have a TRITON Electrifly computerized charger/discharger wit one three pinned thermal probe, for Li-Ion, Lead Acid, NiCad, And NiMH batteries. I need to know how to wire the batteries (If it isn't just straight forward + to + and - to -) and what my settings should be on my charger. If there is any information that you need, just ask, and I'll try my best to get it to you. Thanks!
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5\$\begingroup\$ Laptop batteries tend to have their own management systems and may not even charge without the laptop; you might be better off building a pack from scratch from 18650 cells. Getting it wrong is the cause of all those 'hoverboard' fires .. \$\endgroup\$– pjc50Commented Sep 23, 2016 at 20:28
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3\$\begingroup\$ Another cause of fires is also users like OP that have no clue how to treat LiIon batteries and are unwilling to learn how to treat them properly. Also laptop batteries are not suited for high power applications not even when you place them in parallel. I advise you not to go ahead with this project for your own safety. If your cells start to burn and your board does not work, don't say I did not tell you so. \$\endgroup\$– BimpelrekkieCommented Sep 23, 2016 at 20:41
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3\$\begingroup\$ Battery cells have max current discharge rates based on type of annode and maybe other details of construction. Premium laptop batteries will have high capacity for the size, allowing longer run times with the same size pack. Power tool and skateboard batteries should be selected primarily for their ability to tolerate very fast discharge. As FakeMustache says, it is most unwise to use laptop batteries for a high drain application such as a skateboard. Also, it is foolish to use scavenged batteries in a high-drain application. Fire is a real possibility. \$\endgroup\$– user57037Commented Sep 24, 2016 at 3:41
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3\$\begingroup\$ Ultimately, series parallel it doesn't matter. If you make a battery pack that can be drained in 20 minutes or less, you need high drain cells. If you make a giant battery pack that can run your longboard for an hour or more, then you can use laptop cells. But that will be a physically very large battery. \$\endgroup\$– user57037Commented Sep 24, 2016 at 3:44
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3\$\begingroup\$ if I harvested all of the 18650 batteries from the laptop battery packs Think about that for a monent: why are these battery packs discarded and cheap to buy ? Are they still any good ? Nope, the batteries have worn out. Yet you want to use them in an application that they cannot even handle when they were factory new. \$\endgroup\$– BimpelrekkieCommented Sep 24, 2016 at 12:32
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2 Answers
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You may not be able to charge multiple cells at once with this charger, unless it features a balancer (or even multiple channels with separate control). If charging multiple cells is supported (which is not uncommon for RC model chargers), then read and follow the manufacturers instructions.
The reason for this is, that the charger needs to know the current in each cell. This is not possible, if you simply put them in parallel.
For laptop batteries, you will likely not be able to charge them at all, unless you rip off the casing and connect to the raw cell.
CAUTION: Lithium cells may self-ignite or even explode if mechanically damaged or overheated or shortcut. They may do so after a while even if they look OK initially. Several Samsung S7 have melted, just because the battery compartment is a fraction of millimeters to small.
When working with lithium battery cells (charging or pulling current from them), keep in mind that you are dealing with a little device with enormous energy density. This is a property that modern batteries have in common with old style explosives. Its not quite as dangerous a nitroglycerine, but certainly more dangerous than Plasticine.
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1\$\begingroup\$ Vibration is also a huge problem in something like a skateboard. If the vinyl wrapper on the 18650 cell wears through, or if it erodes due to use of incompatible glue, then when the two cells touch, it can be a dead short of one of the cells. Because the metal can of the cell is actually connected to the anode. \$\endgroup\$ Commented Sep 24, 2016 at 3:51
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If you can match the cell voltage, Ah capacity then they will share the current.
Initial difference 10mV/10mΩ is a 1A drain until equal so match as well as possible
The strongest battery i.e. the one with the lowest ESR and highest cell voltage supplies the most current.
In case of fault, there should be a Polyfuse added to each bank for safety such that a short cct prevents fire but handles a few second surge. ( Measure your motor DCR and battery V to determine peak current V/DCR
They can be charged in parallel but weakest series cells will fail first. But weak parallel cells means the strongest battery may be charged with more than it's share of current, so don't charge too fast.
Thermal sensing is wise.
Stalling motors or starting uphill inclines demands 8~10 x its rated current. So be careful about heat.
