Lithium-Polymer (LiPo) Battery Primer

[Vercingetorix]

Got my elite lipo and charger, etc. yesterday.... They (both of them) are awesome... But my roiginal idea didn't work.... The lipo didn't fit in the mag shell, so I pretty much sliced the mag shell in half, got out some bubble wrap, made a little sack out of the bubble wrap, perfect size for the lipo, and taped the bag in... Now it still looks like a convincingly real mag, but I can fit the lipo.....Perfect (although I went through like 4 dremel ez-lock cutting wheels in the process )... But I have one question, what rate should I charge the 3300mah 3s lipo at? 3.3a/h? or something else? Is more charge rate acceptable? For reference, I am balance charging it, so that is ok... The charger is great, small, and perfect... The only bad thing about it is the adaptor that came with mine for using the supplied attachments didn't work, but I just made one with babana plugs and deans/tamiyas, and it works fine... This part was a freebie anyways, so I don't care....

[infected]

Got my elite lipo and charger, etc. yesterday.... They (both of them) are awesome... But my roiginal idea didn't work.... The lipo didn't fit in the mag shell, so I pretty much sliced the mag shell in half, got out some bubble wrap, made a little sack out of the bubble wrap, perfect size for the lipo, and taped the bag in... Now it still looks like a convincingly real mag, but I can fit the lipo.....Perfect (although I went through like 4 dremel ez-lock cutting wheels in the process )... But I have one question, what rate should I charge the 3300mah 3s lipo at? 3.3a/h? or something else? Is more charge rate acceptable? For reference, I am balance charging it, so that is ok... The charger is great, small, and perfect... The only bad thing about it is the adaptor that came with mine for using the supplied attachments didn't work, but I just made one with babana plugs and deans/tamiyas, and it works fine... This part was a freebie anyways, so I don't care....

 

Your charger should have come with instructions on how to set the charge rate. My charger figures it out on the fly, and I've not used any other charger with a lipo so I can't tell you for sure. I thought the rule was to never exceed 1C. so if you have a 3300mAh battery, then you should charge it at a rate no higher than 3.3A.

[Vercingetorix]

Your charger should have come with instructions on how to set the charge rate. My charger figures it out on the fly, and I've not used any other charger with a lipo so I can't tell you for sure. I thought the rule was to never exceed 1C. so if you have a 3300mAh battery, then you should charge it at a rate no higher than 3.3A.

Yeah, I figured it out earlier today... Its very easy to set charging rate.... I will be charging my battery soon..... I have got the lipo sack now, turns out it was drop shipped, hence why it came later.... Still waiting for BHI to get their *albartroth* in line and ship me my damned stock magazine pouch Then I can feild it with a lipo... Oh, and the lipo checker is pure awesome, but tis to fragile (imo) to leave in my vest.... It'll have to stay back at the staging area.....

[infected]

Oh, and the lipo checker is pure awesome, but tis to fragile (imo) to leave in my vest.... It'll have to stay back at the staging area.....

 

I must agree.

[AustrianGuy]

got my lipo today and resoldered it already, now i've got 11.1v and 2200mah in a XM177 Handguard. i love technique....

 

[infected]

Awesome.

[greg]

That's just great.

 

Now get some deans on it, will ya!

 

 

Greg.

[AustrianGuy]

already tamyas on it, sorry. initially i wanted to solder on deans but i only had some tamyas left at home. i need to order some deans next time, i just forgot to

[tangman]

Great thread , has really helped me in my semi transition into Lipo's. I have been after a buffer tube Lipo for a while now as

 

1. I have all my AEG's rear wired for easy maintenance (all M4 series so just pop out the front pin and slide the upper off)

 

2. The particular stock I wanted to use doesnt have a battery storage capability, having thought of other avenue's (redi mag battery, battery bag, battery sling etc) I figured that Lipo would suit my needs the best.

 

So I bought a few Flight Power Evolite 7.4 800mAh Lipo's as recommended by Justin Kovacs in the buffer tube Lipo thread a few pages back.

 

Had these rewired today, charged them up and they are superb. The rate of fire is definitely on par with my Vapex 9.6 2200mAh NiMH.

 

Just got a few question's as I'm still a bit cautious about the whole deal.

 

Lipo Alarm's. Basically I'm after the most simplest, neanderthal, no brain option here

 

I had thought about getting this one

 

http://www.rcscale.co.uk/eshop/proddetail....rod=LIPOALARM-A

 

and was wondering if anyone had any experience's with it or anything similar? If I'm not mistaken there are 2 set's of 3 LED's. 3 LED's for the 3 Cell's of a 11.1?

 

I'm using 7.4's so only 2 of those LED's should light up? I'll assume green means okay and red means the voltage is running low, but I assume the buzzer will let me know anyway , speaking of which, would these be loud enough to hear during a game?

 

I have no idea on the size of a 5 cent coin, would this fit in an M4 buffer tube as well as the battery? Doesnt have to be flush, just as long as it fits in the tube or small enough so that the stock could fit over it.

 

I would rather have it in the AEG and stop mid game to go change the battery rather than checking in between games as the possibility of the Lipo dropping below 3volt's would drive me nuts.

 

The charger I have now is a basic Duremax one which charges the Lipo via the balancer plug, does the job but its a bit poo!

 

The socket for the balancer plug was REALLY tight, or the balancer plug on my Lipo's are too big which I doubt is the case as I have 4 of them and all were damn tight, on charging my 2nd battery I managed to push the socket out of place due to the amount of force I had to use to get the plug in. So now I've removed the top half of the plastic casing and charge it like that (kept the bottom half of the chassis on so none of the circuits would short etc).

 

So a new charge is inevitable, after having a look around I though the IMAX B5 would suit my needs best. I would prefer to have an all in one charger that I can use for my Lipo's and my NiMH's.

 

Has anyone got one? If possible would you be able to give a quick review/comments on it?

 

http://www.rcgroups.com/forums/showthread.php?t=724255

 

I read the review here and it looks pretty positive, the one thing which has me slightly worried is that you (the user) decide the charge rate.

 

The chap in the review (and I quote) says "I did lower the charge from 2A to 1A for my smaller 1250mah packs.", as I am using 800mAh pack's, would 1A be too powerful for it and damage the cells?

 

Lastly (thanks for reading ), sometimes when I plug my Lipo in, tuck the wires into the stock tube etc etc and slide the stock over the stock tube it doesnt work, it's as if there isnt a battery plugged in. Everytime this happened all I needed to do was unplug the battery and plug it in again, each time I did it though the way the wires were routed in were slightly different.

 

Just wondering if anyone would know why this happens? The wires are a complete cluster*fruitcage* once they are inside the stock tube, balancer plug and the power connect wires all squashed together but I assumed that wasnt the case as I'm pretty sure my Crane stock batteries do the same as well?

 

I had Dean's connectors soldered on and they were done very well so I don't think it's a connection problem there :S

 

Thank's for reading and any help!

[ChaosNZ]

I'm pretty sure you need to get an Alarm for a 2 cell and the 3 cell one won't work with a 2 cell, just remember any kind of alarm or read out device you plug into a lipo will also draw a small amount of current, i wouldn't recommend leaving them plugged in for any length of time.

[tangman]

Cheers dude, I just ordered some of the Lipo alarms from Ebay which claim to be fine for 2 or 3 cell batteries. They were cheap so if it doesnt work I won't be that bothered .

 

Thats a very good point about the alarm drawing some of the current, hadn't thought of that at all so I guess I'll have to do the checking in between games

[infected]

Cheers dude, I just ordered some of the Lipo alarms from Ebay which claim to be fine for 2 or 3 cell batteries. They were cheap so if it doesnt work I won't be that bothered .

 

Thats a very good point about the alarm drawing some of the current, hadn't thought of that at all so I guess I'll have to do the checking in between games

 

FYI, I don't use a lipo alarm. My near 500 fps M14 has run 4 games on an 11.1v 2200 Mah lipo, and only used about .7V of it's usable charge. It's semi only, but a current hog with it's high torque motor, and high fps spring. I just use a checker the day before the game, and charge it if it is close to the 3v per cell lower limit. Then I check it one more time before the game starts.

[Vercingetorix]

My lipo came charged with like 11.5 volts of charge when I got it.... I have maybe shot 1000 rounds with it already, and its still at like 11.4v of charge....

 

How much is the lowest you should carefully go (not the maximum lowest, just a point where you should stop using it and charge it) per cell? 3v? 3.2v? Mine are all at like 3.6-8v per cell atm, so when should I charge it?

 

Thanks!

[infected]

My lipo came charged with like 11.5 volts of charge when I got it.... I have maybe shot 1000 rounds with it already, and its still at like 11.4v of charge....

 

How much is the lowest you should carefully go (not the maximum lowest, just a point where you should stop using it and charge it) per cell? 3v? 3.2v? Mine are all at like 3.6-8v per cell atm, so when should I charge it?

 

Thanks!

 

When it gets down to 3.1v per cell you should charge it. If any one of your cells gets to 3.1v charge it, just to be safe. Don't wait till all of them are @ 3.1 though, do it as soon as one of them hits it. Greg and others might disagree, but that's the rule I'm following right now.

[tangman]

FYI, I don't use a lipo alarm. My near 500 fps M14 has run 4 games on an 11.1v 2200 Mah lipo, and only used about .7V of it's usable charge. It's semi only, but a current hog with it's high torque motor, and high fps spring. I just use a checker the day before the game, and charge it if it is close to the 3v per cell lower limit. Then I check it one more time before the game starts.

 

Thanks for the input mate, I ended up buying the Maxpro LCD-6 Battery Detector.

 

There's a PDF instruction manual online and after reading it I'm a bit puzzled...the part I'm confused by (and I quote from the manual)

 

"Instructions

 

1. Input unit voltage should be 3.00V-4.99V. If the unit voltage is less than 3.00V, there will be no display on the LCD screen. If the unit voltage is above 4.99V it will hurt the LCD-6""

 

What is confusing me is the part where it mentions 4.99V. I thought each cell in a lipo pack (regardless of overall voltage e.g 7.4v 11.1 v) was a 3.7V cell?

 

So therefore, why would the cell read above that? I know I'm definitely missing something here as the pictures I have seen of the LCD-6 in use show voltages higher than 3.7.

 

 

Or am I totally of the mark here?

 

I'm concerned that as soon as I plug in my Lipo to check the voltage that it will be over 4.99V and therefore damaging the LCD-6.

 

I read through Infected's articles a few times and tried to look up measuring Lipo voltage's but I couldnt find a definitive answer.

 

In a lot of the RC forums I came across the general consensus was that a fully charged single lipo cell should be around 4.2V, again I'm confused as I thought each lipo cell was 3.7V?

 

Thanks again for any help and input!

[infected]

3.7v is the NOMINAL charge level. In all actuality, you're battery will charge higher than that. Take a NiMH 8.4v cell. At a full charge and rested, it'll sit near 9v, but it's an 8.4v battery. So you're nominal 3.7v lipo cell will actually charge to about 4.2v per cell at full charge.

[tangman]

AHA!

 

Now I get it , I'd never previously measure the voltage on my NiMH's so I didn't know that they would be at a higher voltage once charged.

 

Thanks again

[greg]

When it gets down to 3.1v per cell you should charge it. If any one of your cells gets to 3.1v charge it, just to be safe. Don't wait till all of them are @ 3.1 though, do it as soon as one of them hits it. Greg and others might disagree, but that's the rule I'm following right now.

 

No disagreement here:

 

All the literature I have, states not going under 3, or over 4.2v per cell.

 

So having a 3.1v basement, seems like a good idea.

 

 

Greg.

 

 

 

[tangman]

Back onto the topic of charging Lipo's, would someone be able to post the formula of how to work out the recommended charge current for "x" battery pack?

 

I read the following article but I'm not sure if I understand it currectly

 

http://www.bmfa.org/resources/lipobatteries.html

 

"The maximum charge rate should be 1C, eg. 0.7A for a 700 mAh cell. For best charging, low charge rates should be used where possible. "

 

By cell do they mean the individual cell? Or do they mean the whole pack?

 

I have a Flight Power Evolite 7.4 2S 800mAh 20C, so should I charge that at 0.8A or 0.4A (assuming the cell's are both 3.7V + 400mAH each).

 

I have just ordered the IMAX B5 Charge, which as far as I know requires you the user to choose the charging current which ranges from 0.1-5.0A so I'd like to make sure I understand all of this before I use it!

 

Thanks all

[infected]

Correct. If you have a 800mah battery PACK, you'd charge at a maximum of .8A. Now if you're charger is a good quality one (I don't know much of anything about the Imax B5), and has an auto setting, you could try that. Remember, the cooler the charge, the better.

[tangman]

Fantastic! This thread and your articles have answered pretty much everything I wanted to know about Lipo's

 

Thanks again!

[greg]

I have a Flight Power Evolite 7.4 2S 800mAh 20C, so should I charge that at 0.8A or 0.4A (assuming the cell's are both 3.7V + 400mAH each).

 

It's .8A or, more appropraitely 800mah.

 

I have the same bat & charge at 800mah. No probs.

 

 

Greg.

[cleanshot]

Just ran across this and I love it. Finally someone that agrees with me that Li-pos are the way to go. I ahve been using 11.1v 2400 mAh batteries in my M14 since I bought it and upgraded it and I can usually get around 8,000 rounds from a single charge before it gets into the danger zone.

[HiOctane]

This may have been said a lot of times I didn't read the thread but I did read the article on LiPo's and it strikes me that being a design engineer I know a little about electronics and the point at which it says that the motor will only draw what it needs is wrong... A motor doesn't DRAW power, it has to be fed it. And the more power you put in the faster it will go. Even if this speed it more than the motor was designed to handle...

[infected]

This may have been said a lot of times I didn't read the thread but I did read the article on LiPo's and it strikes me that being a design engineer I know a little about electronics and the point at which it says that the motor will only draw what it needs is wrong... A motor doesn't DRAW power, it has to be fed it. And the more power you put in the faster it will go. Even if this speed it more than the motor was designed to handle...

 

Regarding current, the motor will demand what it needs, and no more. You can't force current into the motor, it requires a certain amount to operate at 100%. This is why discharge rate is important. You need to be able to support the current draw of the motor. This is why if you try to use an 8.4v mini battery on a motor and drivetrain setup that needs 22A to operate, it heats up as the motor trieds to draw more current than the battery can provide. Use a 7.4v 2200mah lipo that can provide 66A, and the motor will only demand 22A as that's what the drive train needs to operate.

 

Now Power is different. The drivetrain will need a minimum of a certain amount of power to drive it, but given more power (wattage), it will increase the RPM of the motor. You do this by increasing the voltage.

 

To this effect, you must choose your li-poly based on current discharge capabilities first, and then voltage to set your ROF.

 

And a motor DOES DRAW POWER. I was an Electrical Engineering student in college, and worked in the automotive electronics industry for several years before going into IT. You can have a 6v 50,000mAh battery and drive a motor to 100% of it's operational specs as long as your discharge rate is high enough. The problem that most people encounter is that thier NiMH batteries can't bring a motor up to the 100% operational specs (rpm's), off current discharge alone. To increase the ROF (or rpm of the motor), the voltage must then be increased. See, if you have 2 batteries, both able to produce a constant current discharge of 15A (one a 8.4v the other a 9.6v), but your drive train needs 22A to run at 100%, neither can provide the necessary current needed for the motor and drivetrain. What you will see however, is that the 9.6v version is able to supply more voltage, thus increasing the Power (Wattage). Battery number 1 126 watts, battery 2 144 watts. Since Wattage is a measure of work done, you'll find that there is more work done with a higher voltage battery, and therefore more rpm's.

 

The idea with the li-poly is to achieve the same amount of work with less voltage, and less space. A 7.4v 2200mah battery will take up about the same amount of space as the battery number 1 in the above example. But, it'll produce 488.4 watts of energy. Will the motor use all of this? No, because the battery can discharge 66A, but the drivetrain needs only 22A. So in essence, it'll only use 22A*7.4v=162.8W. Note that is not the total Power that this battery can provide, but it is capable of doing more work than either battery in the above example, but the motor is still only using 22A. Unfortunately manufacturers do not tell you what the max continuous power rating for these motors are. So is this over driving the motor? Well, no real way to know that I can tell. Once you meet the current requirements for the motor, you can adjust the Power to achieve different RPM's.

 

I think you might have thought (and maybe I have a typo somewhere), I was talking about the amount of power a motor DRAWS, when I was talking about the amount of CURRENT a motor DRAWS.