Newbie battery question
- Thread starter georget
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Without knowing more about your cells (chemistry, brand, protection) and what you're trying to accomplish (what are you trying to power), it might be hard to answer your question.
I was planning use them to jump start my car which will require at least 10amps. The batteries are Li-Ion that says samsung 18650-26c (not sure if that is the c rating). i got these batteries from an old laptop, several of these. not sure how to wire them buti was thinking of 6s2p. I am guessing that would be 24v 16amps, right ? not sure how the calculation is done here. i wired them so with balance ports and checked the voltage and it read 24v but how do i measure the amps with the Voltmeter. The voltmeter is only rated for 10A. So i tried hooking this battery to the car and turned the key, i hear clicking noise. Normally thats when the battery does not have enough amps to power the starter.
So i am little confused about the wiring or i could be wrong about the 16amps and the 6s2p setup. As far wiring goes, i've wired the 6 batteries in series and another 6 in parallel to each battery. like in the link here. Where am i going wrong ?
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Are you sure your car has a 24 volt electrical system? You normally see those only on heavy trucks and equipment.
Its actually 12. I am planning to use it for a truck too. Hence 24. As for now we'll just stick to 12. I know to get a 12v off the batteries and connecting 6 in parallel will increase amps. So i wired them 3s6p and that would output 12v @16amp. All charged and tried starting an my suv did. It was clicking.
So i wasn't sure if those were actially able to deliver that 16amp. How can i confirm this. I could start with lipo 12v 8600mAh.
I know, I will be using a bms once i figure this out.
"So i plan to use these to jump start my car. That will require 24v @ 10amps"
Not sure where you are getting your current figures. A typical car engine will take much, much, more than 10 or 16 amps to crank. More in the neighborhood of several hundred amps on a warm day and 500 or so amps on a cold day. 10 amps is barely enough to make the starter solenoid click. Now if you push 10 amps or so, in to a low car battery for an hour or so, you might get it to crank enough to start.
Not sure where you are getting your current figures. A typical car engine will take much, much, more than 10 or 16 amps to crank. More in the neighborhood of several hundred amps on a warm day and 500 or so amps on a cold day. 10 amps is barely enough to make the starter solenoid click. Now if you push 10 amps or so, in to a low car battery for an hour or so, you might get it to crank enough to start.
A car can start with a lipo 12v 8amp. It just needs it for a few seconds. So i was just trying to do that with Li-ion.
http://youtu.be/UBp8YGY5ouk
http://youtu.be/UBp8YGY5ouk
They are using an RC LiPo pack, not 18650 cells from a laptop battery. The former are designed to handle large currents, the latter are not. Indeed, most laptop 18650s have protection devices (CID/PTC) that will prevent you from drawing the large currents necessary to jump start an automobile.
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HorizontalHunter
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I originally typed the answer here but I deleted it. I would feel terrible if you injured yourself, or worse, injured someone else.
Please don't persue this espicially with recovered batteries from a laptop battery. It is extremely dangerous and the fumes from a battery failure can be deadly as can the shrapnel. Do some reading in the dangerous side of batteries.
Bob
Jump-starting a car requires a huge current for a very short time, so what you want to look at is the pulse-current rating (vs. sustained current). Unfortunately, there is no industry standard for specifying pulse-current ratings, and they are often quoted so imprecisely as to be useless (not to mention exaggerated ratings).
Well i guess those batteries are not meant for the job. i was thinking of using as a phone charger or maybe a laptop secondary source of power both with a BMS installed. how do i know the amp rating i've got them wire 3S6P as per this link. Am not sure of the amp rating to charge them at. i am guess its 2.7 x 6 = 16.2mAh. So should i charge them 16200mAh ?
Any advise on this would help.
Any advise on this would help.
You can find jump starter packs on eBay for $40 (or less if you are patient with auctions). It will be difficult to beat that price much with a DIY project unless you already have some of the components available for free.
One cannot stress enough that such a DIY project can be extremely dangerous if not implemented correctly, so I would not recommend embarking on such unless you have extensive knowledge of Li-ion battery safety issues and also the requisite electronics knowledge. Is it worth risking serious injury to save $20?
One cannot stress enough that such a DIY project can be extremely dangerous if not implemented correctly, so I would not recommend embarking on such unless you have extensive knowledge of Li-ion battery safety issues and also the requisite electronics knowledge. Is it worth risking serious injury to save $20?
A 6P pack has 6 cells in parallel so you multiply the current ratings by 6. You also need to consider the ratings of the BMS.
Don't overlook the problem of the car's generator charging the pack after it starts (some cables use Schottky diode arrays to prevent that)
Don't overlook the problem of the car's generator charging the pack after it starts (some cables use Schottky diode arrays to prevent that)
You won't be able to jump start cars with such low current limits. Before you even think about the BMS limits you need to consider the limits of the cells, which will be limited by the internal PTC (unless they are cells rated for very high current). Beware that cell current ratings are sometimes grossly exaggerated by rewrappers, esp. Efest.
