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Mar 09, 2014, 02:39 PM
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Question

How do you know how many amps an 18650 LiPo can safely discharge?


I am curious, if I want to build a battery pack with 18650 LiPo batteries, how do I know how many amps I can safely draw from the battery pack?

If you need an example for a battery to answer the question, you can use this random battery: UltraFire BRC 18650 3.7V 4000mAh Protected Rechargeable Li-ion (http://www.miniinthebox.com/ultrafir...k_p308292.html)

I would be wiring these in series to create a 14.8v, or maybe an 18.5v battery. I am using a CC BEC PRO switching regulator with a 50.4v max input and I have adjusted to output 12.5 volts. I'm now sure if that information matter, but I wanted to make sure I gave you as much info as I could

This is being used for a portable stereo, not an R/C device. I want to listen to some music while playing around with my toys So I have this all hooked up to a 100 watt amp and a couple of speakers. What I am trying to do is make sure that there isn't any issues with a lack of current needed to power the amp by using these 18650 batteries. And since I am using a higher voltage battery than I am sending to the amp, hopefully that means I will have extra run time from the battery too.

Thought? Input? Thanks a ton guys!
--Zach
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Mar 09, 2014, 03:59 PM
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18650s are not lipos they are cylindrical li-ion. And unfortunately it's very difficult to get the information you need. Most specifications simply don't tell you. But typically 18650s can handle no more than about 1.5-2C. Even the really good ones like Panasonics rarely get past about 3C e.g. 10A or so.

Steve
Mar 09, 2014, 05:06 PM
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flypaper 2's Avatar
As Slipstick says, most are low powered batts, but they do make some high powered ones for power tools. I made up a pack from the low amp ones and the plane wouldn't get off the ground. I bought some made for the power tools and they work fine. In fact I have an electric chainsaw that I made power packs for, from the Molicel high amp batts and they work fine. The 18650 is the size of the batt. 1.8 mm dia. and 650 mm long. They do make bigger ones in the C cell size. I charge them on the lipo setting on the charger with no problems.
Hope this helps. Google Molicel and you will get a lot more details.

Gord.
Mar 09, 2014, 06:43 PM
BVH
BVH
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Just to point out that any of the trustfire capacity ratings that indicate much more than 2500 mAh are mis-truths. No one makes an 18650 that has a capacity of more than 3600 mAh and those are just starting to trickle out - by Panasonic. Panasonic 3400's are fairly easy to get now. If you want the best 18650's stick with Pannys.
Mar 09, 2014, 06:59 PM
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I HAVE that Ultra(crap)fire. It's ACTUAL capacity is @ 1000mA. Pretty much anything ***fire is junk.
Here's a link to extensive reviews.
Some of them have a decent discharge rating but these are lower capacity and a different chemistry. The A123 (LiFe) are quite good but only 1100mA. The 'usual' 18650 are LiCo02 and have a higher capacity. Panasonic is one of the best for output, capacity, and reliability.
The IMR (manganese) type tend to have lower capacity but higher output....in general. Like any of these batteries, believe nothing until tested and PROVEN. If it's really cheap, it's probably junk.

A LOT of them are "protected" cells. Pay attention. There's a big difference in handling protected vs. unprotected cells.

DO NOT, ABSOLUTELY DO NOT CHARGE THESE IN SERIES UNLESS YOU PUT A BALANCE PLUG PROPERLY IN PLACE OR WIRE UP A CIRCUIT TO BALANCE THEM LIKE A LAPTOP WOULD HAVE.
Mar 09, 2014, 07:30 PM
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Thread OP
WOW! You guys are absolutely amazing Thank you soooo much for the information. Sorry, I did mean Lithium Ion... not LiPo. Thank you for noticing slipstick

When I make a battery pack, I'm guessing I need to be able to provide at least 5 amps. It is difficult to measure what the max amps being used is by the amplifier, but the fuse on the amplifier is a 5 amp fuse so clearly it doesn't exceed that.

Maybe someone can tell me this. If a battery is a 1500mAh rating, is it safe to assume that most standard batteries can discharge their full capacity within one hour or anything? So for example, a 1500mAh battery would be dependable for 1.5 amps for 1 hour without overworking the battery? And do I understand the C ratings correctly? Like a 2C 1500mAh battery would be able to discharge twice its capacity in one hour which would make it dependable for 3 amps for 30 minutes?

And my last question is, if you are connecting in series, do you add the amps from each battery?

EXAMPLE: So if there is 2 standard 3.7 v 1500mAh batteries connected in series, does that mean I would have 7.4v 1500mAh battery that can provide 3 amps for one hour (theoretically)?


Thanks again everyone... SOOO helpful! Hopefully I didn't ask too many questions. I'll do better next time
Mar 09, 2014, 07:38 PM
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Thread OP
Oh yeah, and thank you for the link to that page, flydiver. VERY helpful
Mar 09, 2014, 07:55 PM
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flydiver's Avatar
You need to spend some time looking at that link and discharge curves for batteries of interest.
Here's one for Ultrafire 3000.
The trouble is there IS NO Ultrafire. ALL their batteries are some (junk) they found and shrink wrapped it. You can get 2 different batteries from the same batch. There is absolutely no telling what you will get.

You might want to spend a bunch of time in candlepower forum or budgetlight forum. What you are after is only sorta related to RC. There are a bunch of sticking points.

By the time you figure out how to do this safely, and get the proper equipment and batteries, it may end up exceeding the budget you were thinking based on cheap Ultrafire cells. Guys in the know recommend discharging them and tossing from the start to save yourself the grief.
Mar 09, 2014, 10:36 PM
BVH
BVH
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No battery is going to give current in Amps, equal to its' Amp hour capacity for one hour. Look up "Peukerts Factor" and it will explain why. Battery capacity ratings are derived from .1C current draw tests. In-theory, a battery will give its' full rated capacity when the current draw is one-tenth its' capacity rating - in Amps.

You're sort of half-right on a battery being able to give 2 or 3 or 5 or whatever times its capacity in Amps - but not for one hour. It just means that "in-theory" it can provide X x's "C"apacity in Amps for a period of time until it is depleted. The higher C rate you draw power, the less capacity you will get - Peukerts Factor again.
Last edited by BVH; Mar 09, 2014 at 10:42 PM.
Mar 10, 2014, 04:08 AM
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Quote:
Originally Posted by zach26276
Maybe someone can tell me this. If a battery is a 1500mAh rating, is it safe to assume that most standard batteries can discharge their full capacity within one hour or anything? So for example, a 1500mAh battery would be dependable for 1.5 amps for 1 hour without overworking the battery? And do I understand the C ratings correctly? Like a 2C 1500mAh battery would be able to discharge twice its capacity in one hour which would make it dependable for 3 amps for 30 minutes?

And my last question is, if you are connecting in series, do you add the amps from each battery?
1C discharge means the current(amps) that would theoretically use the full capacity in one hour. 2C means twice that current for half hour etc. So you have understood that.

But when you connect in series you add the voltages only NOT the current. So any number of 1500mAh batteries in series are still 1500mAh and are still subject to the rule 1C = 1.5A, 2C = 3A etc.

Steve
Mar 10, 2014, 06:33 AM
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everydayflyer's Avatar
Why not just purchase a 7- 12 Ah 12V sealed (AGM) Pb battery and use it. These run from around $15-$20 for the 7 to 8 Ah ones and and perhaps $35 to $40 for a 12-18Ah one.
Mar 10, 2014, 11:15 AM
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Thread OP
I was originally going to do this with a 12v 9Ah battery, but I noticed the volume from the speakers was quickly dropping as the battery was used for a short time because the voltage was dropping. Plus, it would be nice to have a bit less weight in the case

This is why I originally installed a voltage regulator. I was planning to install higher voltage battery and then when it got down to 12v I was going to replace the battery. I wish I could use the SLA battery though since they are cheap and reliable... unfortunately the voltage just drops too quickly and I only get to use about 20% of the capacity before the voltage is too low
Mar 10, 2014, 11:28 AM
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Thread OP
Quote:
Originally Posted by slipstick
1C discharge means the current(amps) that would theoretically use the full capacity in one hour. 2C means twice that current for half hour etc. So you have understood that.

But when you connect in series you add the voltages only NOT the current. So any number of 1500mAh batteries in series are still 1500mAh and are still subject to the rule 1C = 1.5A, 2C = 3A etc.

Steve
This was extremely helpful. Thank you for clearing that up. I wish all batteries would have a C rating on them, just like they do the capacity.


Quote:
Originally Posted by flydiver
You need to spend some time looking at that link and discharge curves for batteries of interest.
Here's one for Ultrafire 3000.
The trouble is there IS NO Ultrafire. ALL their batteries are some (junk) they found and shrink wrapped it. You can get 2 different batteries from the same batch. There is absolutely no telling what you will get.

You might want to spend a bunch of time in candlepower forum or budgetlight forum. What you are after is only sorta related to RC. There are a bunch of sticking points.

By the time you figure out how to do this safely, and get the proper equipment and batteries, it may end up exceeding the budget you were thinking based on cheap Ultrafire cells. Guys in the know recommend discharging them and tossing from the start to save yourself the grief.
THANK YOU! I will definitely check out that other forum too and continue to review those battery profiles. I think I should have used a different example though for the battery... I wasn't really considering an Ultrafire. I'm glad I did use that example though so I know they are junk now

Thanks again everyone! If I have any other specific questions I'll post another thread. For now I think I have plenty of information to review. Thank you for pointing me in the right direction
Nov 17, 2015, 09:52 AM
Registered User
Quote:
Originally Posted by flydiver
I HAVE that Ultra(crap)fire. It's ACTUAL capacity is @ 1000mA. Pretty much anything ***fire is junk.
Here's a link to extensive reviews.
Some of them have a decent discharge rating but these are lower capacity and a different chemistry. The A123 (LiFe) are quite good but only 1100mA. The 'usual' 18650 are LiCo02 and have a higher capacity. Panasonic is one of the best for output, capacity, and reliability.
The IMR (manganese) type tend to have lower capacity but higher output....in general. Like any of these batteries, believe nothing until tested and PROVEN. If it's really cheap, it's probably junk.

A LOT of them are "protected" cells. Pay attention. There's a big difference in handling protected vs. unprotected cells.

DO NOT, ABSOLUTELY DO NOT CHARGE THESE IN SERIES UNLESS YOU PUT A BALANCE PLUG PROPERLY IN PLACE OR WIRE UP A CIRCUIT TO BALANCE THEM LIKE A LAPTOP WOULD HAVE.
Correct me if I'm wrong and I have absolutely zero vested interest in this company , But I've been told by many suppliers that the
Ultra-Fire batteries are the most copied battery out there.
That said , yes most of the copies are total junk. I even saw where
one manufacturer put a much smaller cell inside a 18650 size
cylinder.
I have a pair of these garbage cells and they voltage dive under
just a 5 amp load. And thats the pair wired in parallel.
Nov 17, 2015, 11:04 AM
Registered User
flydiver's Avatar
Quote:
Originally Posted by C George
Correct me if I'm wrong and I have absolutely zero vested interest in this company , But I've been told by many suppliers that the
Ultra-Fire batteries are the most copied battery out there.
Near as I can tell, and I've been a regular participant in BudgetLightForums and CandlePower for years, there IS NO ULTRAFIRE, unless you call an assortment of companies that shrinkwrap outer skins on whatever crap they get their hands on a company. They do not make batteries.
You can get OK Ultrafires....IF (big IF) they happen to put a decent cell in it. You absolutely cannot depend on it.
You can reliably get crap. The higher the milliamp described, the more likely it's garbage since there simply are NO Li-on 18650 batteries over 3500mA. You easily can find ones that say they have 4000, 5000, and I've even seen 8000mA advertised.

There ARE some Trustfire batteries that are OK, especially the 26650 since they are less common and less likely to be fake. Trouble with Trustfire is they are copied a lot also so getting real ones is problematic. Panasonic are some of the best and even they are now getting copied. Apparently it's not too hard to make a pretty good looking shrink cover.

If you don't have the knowledge and the tools to diagnose the quality of the battery do not buy from anyone but a reputable source that has vetted the cells for you.


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