I am fairly new around lights and batteries……so…I saw the terms ‘High Draw’ and ‘High Discharge Rate’ referring in this case to 18650 batteries. I thought they were basically the same terms,so can someone explain the difference? Thanks,HB
pretty much the same
high draw could be interpreted as a light that demands high draw, high discharge, a lot of current… etc (all the same)
high discharge rate refers to batteries that can give a lot of juice! (amps, or current)
here are some 18650 batteries that give the most draw
sony v4tc - most
samsung 20r
panasonic pf or pd
No difference.
Except perhaps that you might often measure the draw in Amps and the rate in C. C is also Amps, but in relation to the total capacity. So a discharge rate of 1C for a 2000mAh battery is 2A, but for 4000mAh battery 1C is 4A. You may talk of different battery chemistries and compare their discharge rates. Or preferred charging rates, also typically measured as C.
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So using the Sony VTC4 specs here:•Dimensions: 65.0mm (L) x 18.2mm (D)
•Weight: 45g
•Typical Capacity: 2100mAh
•Min Capacity: 2000mAh
•Max Continuous Discharging Current: 30A
•Discharge cut-off voltage: 2.5V
•Voltage: 3.8V
•Full Charge Voltage: 4.2V
This has a 15C discharge rate?.
I also notice that the High Draw 18650 batteries are lower in capacity(2000 mAh),plus they are ‘not protected’ compared to the higher mAh (3400mAh),which are mostly or all are ‘protected’….why is that?Thanks,HB
The protection circuits protect, among other things, against too high discharge. And batteries are typically made with a compromise between discharge rate and capacity. So high capacity batteries often have a lower intended discharge rate, While batteries that are intended for a high discharge rate often have a lower capacity. It may be different chemistries or different manufacturing.
This is also true for any given battery. If you discharge a battery at a very high rate, you get a low total usable capacity. And if you discharge at a low rate you are likely to get a much higher usable capacity. This also means that a flashlight that can be extended to use two batteries instead of one typically will last significantly longer than double the time on two batteries than one. For really “good” batteries the difference in capacity between high and low discharge rate may be smaller than for cheaper batteries. Things like internal resistance and wear over time and cycles also influence this.
It is difficult to make a protection circuit for a battery that is intended for a high discharge rate. It has to be able to handle a high current, and not see that as a short or too high discharge. Much easier to have protection circuits on batteries that are intended for lower discharge rates.
Some batteries with protection circuits can not be used in some high draw flashlights. The protection circuit would break the current.
So would unprotected high discharge batteries in torches with built in protection circuits trip those circuits, or are the permanent in torch circuits better at dealing with amps due to less size restrictions? Assuming high quality. Obviously there are varying circuit qualities.
Thanks,everyone!
One reason for using batteries with protection circuits is that the likelihood of catastrophic failure is significantly reduced. The both the battery and the charger must be faulty at the same time for your house to burn down. Or both the battery and the flashlight has to be faulty at the same time.
Drivers will only protect from over-discharge, not over-current, so there's no circuit to trip like what a protected cell does.
Thankyou. So the torch will trip at a low V (3, 2.9v or thereabouts), but does not see amps. The battery circuits might see both?
Yes, the circuit on a protected cell will disconnect the cell if the voltage is too high, too low, or if the current exceeds the set limit.
Different drivers handle it in many different ways. Some keep stepping down until it's at the lowest level and then turn off. some step down but don't turn completely off, some don't give any warning/step down at all they just shut off and leave you in the dark, and many more.
Ahh, so many roads to take and one basic direction.
Draw is, by definition, intended to apply to the device that needs the electricity. The beefed up driver has a higher draw than the stock one. Literally drawing or taking current from the source.
Discharge rate, again by it’s very application, is intended to apply to the source itself as an indication of being capable of supply large amounts of power at a time.
It all gets misleading, because we tend to think of needing light as a prolonged thing. Darkness is not fleeting. I’ve often wondered why a cell with only 2000mAh capacity would need the ability to discharge in a matter of minutes. The reason being that it’s not intended for flashlight use. The intended “vehicle” these cells are designed for have the ability to supply a charge virtually all the time, or is backed by sheer numbers, making the individual cell much more lightly used. The cell (or “battery” as it’s a set of cells used together) is used hard in bursts then only used lightly…allowing it to recharge and recover until the burst is needed again. So using these high discharge rate cells in a constant drain device is not in keeping with it’s intended design. Oh, they work for our needs, but not for very long at all and not as well in the long run as others.
The Sony USVTC4 might have higher numbers, but does it actually supply more power to a flashlight? My MT-G2 bearing M8 doesn’t think so. For me that’s another puzzling area. If a single cell is rated for 22A delivery, or 30A delivery, why then do we not see that? Why do we see 6A? The MT-G2 is rated as having a maximum 3A draw, targeting that level as a safe number that is more likely to make the output and longevity it’s maker desires. We here know that this emitter can be pushed well beyond that 3A, in fact it performs up to a ceiling of 16A! So, given a cell that is 22A capable, and using 2 of those, why is direct drive only making 12A? Wouldn’t it be reasonable to assume that with 2 cells in series a much higher amperage would be seen? But it just isn’t so, neither in Samsung nor Sony trim. The 10A rated PF fares no better, although it performs longer due to it’s considerably higher 2900mAh capacity.
Suffice it to say though, when using this kind of cell it is prudent to believe it is fully 10, 22 or 30A capable in a direct short circuit scenario! It WILL cause major issues if abused! There is enough potential there to weld parts together instantly, then building heat in such a short time as to make it nearly impossible to break the short circuit. Be aware of this when building a light using these very potent cells!
Typically, the standard Li-ion chemistry is so potentially dangerous to abuse that the protection circuitry is a good stop-gap measure for those unwilling to go the extra mile in maintaining them. The high discharge chemistry cells are inherently safer and much more tolerant of abuse, so not as likely to need that circuitry and much less likely to fit within the limitations of same. These chemistry’s were designed to take the abuse, as they were designed for pack use in very high draw vehicles, be it very strong power tools or electric automobiles.
I am no expert in the field (whatever defines that as none of THEM seem to agree on anything) so the above is my reflections on what I’ve seen while in this hobby of ours. In other words, my opinion. As with all such opinions, take mine with a measure of salt and draw your own conclusions.
Enjoy!
Well that answers another question.
Because of this:
If the cell can't keep the voltage up to the level required to hit a certain current, it won't. Those "30A discharge" claims may look nice, only problem is they don't bother to tell you what the cell voltage will be when discharging at 30A. Measure the input voltage on a few lights while they're running, see if the volts/amps you measure line up with the Vf graphs.
With plenty of overhead room why do 2 cells fare no better?
And why are the companies allowed to rate a 3.7V cell as 30A if it can’t supply 30A at 3.7V?
Because a MTG2 with two cells is not much different from two XML2s in series powered by two cells in series. You hit the same Vf-vs.-Vin wall.
For each ~3.3 volts of LED you have, you need that many cells + 1, and a buck driver, to get higher current than is possible with 1 cell/1 XML or 2 cells/1 MTG2.
Perhaps one technology is outpacing the other
http://www.mtnelectronics.com/opencart/index.php?route=product/product&path=59_88&product_id=50
This battery gives a good balance of reliability, output and protection. Japanese panasonic NCR18650PF cell inside. 2900mah capacity. 10a discharge, better than the avg battery. Seiko protection circuit. Be careful with some of the cheap 18650 batteries that claim to have a protection circuit. Sometimes they have what appears to be a circuit but it won’t trip or protect.
A High Draw device, in this case a flashlight, draws or”consumes” higher amperages ( like those modified by Vinh and others).
A High Discharge Rate refers to the cell that can drain or Discharge at a higher rate thereby giving that device its required amperage without sagging (as compared to more ‘normal’ cells.)