Understanding LiPO terminology????

[Slats]

Just trying to get my head around some of the jargon used for LIPOS

Can anyone tell me for example what this means?
LIP0 3S 2200 25C
I figure the 2200 in mA and its a Lipo - BUT what does the 3S mean?
and what doe the 25C mean?

Moereover, what the heck is balancer?

Thanks
John

[KevinMc]

Just trying to get my head around some of the jargon used for LIPOS

Can anyone tell me for example what this means?
LIP0 3S 2200 25C
I figure the 2200 in mA and its a Lipo - BUT what does the 3S mean?
and what doe the 25C mean?

Moereover, what the heck is balancer?

Thanks
John

Hi John,

The 3S refers to the configuration of the pack, in this case indicating that the pack is built up from 3 series wired cells. Each LiPo cell nominally measures around 4V*, so what you're looking at is a ~12V pack*. Similarly 2S means you're dealing with a (nominal) ~8V pack*.

As compared to NiCd's and NiMh's, LiPos are (were) much more limited in how fast you can safely dischage them. Failure to understand this leads to them puffing up like a marshmallow in a microwave. The 25C refers to the fact that this pack can safely be discharged at 25 times it's capacity. Since you're dealing with a 2.2Ah pack, you can safely pull (2.2 x 25) 55A. Although not a problem for submarines, airplane and heli-folk need to pay careful attention to this figure. If their discharge rates can exceed this value, changes need to be made. This can either be by using a larger capacity pack, by paralleling up packs, or by using a pack that's got internally paralleled cells. (Sometimes you'll see packs advertised as 3S2P, which indicated that each of the three series elements is built from two cells in parallel.:eek:)

As for a balancer, when you discharge packs at high rates the cells can get out of balance. This means that within the pack the "charge level" of each cell is nolonger the same. This is becomes a problem when charging since LiPos are very unforgiving of being overcharged. A balancer looks at the voltage across each cell of the pack and "harmonizes" them to the same level.

*Note that the voltage used for a LiPo cell varies between 4.2V at full charge and 3.0V empty. You'll see pack voltages specified by anything between these two numbers.

[Albion]

excellent info

[Slats]

Thanks - appreciate it
J

[Outrider]

Kevin's post is a great sensible explanation of LiPos. There are a few more things you might want him to comment on. Among these are balancing chargers and the preventative under voltage cut-off.

Basically balance chargers take advantage of electrical connections made to each cell for the purpose of monitoring and controlling each cell's voltage during charging. The concept being to match each cell's voltage as closely as possible to the others. That's why you need the balance wires to each individual cell--to allow comparison and as a means of balancing the charge. Unfortunately, there's no real standardization of balance connectors, as each manufacturer seems to like their own, especially if it gets you to buy their balance charger. Fortunately, there seem to be plenty of adapters available.

More things to think about chargers are:

DC only or AC/DC? Most are DC only. I find that limiting.

Does it have a balancing unit included? Many don't.

Will the charger handle different chemistry batteries? Call me cheap or demanding, but I want to use the same charger on anything from Lead Acid to a LiPo--some will do this.

Preventative under-voltage cut off for LiPos. Simply put, if you let a LiPo get to an excessively low voltage, they tend to become unusable. You need to make sure your voltage never drops below the acceptable limit. (I think it's like 90% of rated.)

Jim

[KevinMc]

Hi Jim,

Good point on the low voltage cut-off. I've generally seen low-voltage cut-off expressed as a voltage (instead of % capacity) but the exact voltage also varies from manufacturer to manufacturer. The figure I've seen most frequently is 3V/cell.

[roedj]

Kevin, anyone?,

I've been told by some very experienced Li-Po users that I should never deplete a Li-Po battery below 80% of its capacity. I have found this same guideline elsewhere on the I-net. For example, the 1300mAh battery sold by Caswell should never be depleted below 1040mAh ( 0.8 X 1300). I'm told that you may get away with discharging it below that level a few times but in the end the battery simply will not give its expected number of charging cycles. Now, to be fair, these Li-Po users are fixed wing and Heli fliers who regularly use discharge rates of 10C to 20C where the scale ship types may be hard pressed to go beyond 2C. Maybe that makes a difference in the 80% guideline, I don't know.

I have a charger that tells me how much I put back in when I charge it. If I end up putting more than 1040mAh back in, I overused the battery. Unfortunately, the 1040mAh is reached way before the individual cell voltage comes even close to 3.0V. My typical data seem to say that the 1040mAh point is reached when the voltage is still around 7.2V having started out at around 8.4V for the Caswell 2s Li-Po battery. I just keep track of the time I use it and establish a chart for myself of when it's time to come in and switch out batteries.

I am using your LiPo Guard in a surface ship I have but it's used as my absolute last line of defense and not as a guide as to when to recharge.

Looking forward to your future products,

Dan

[KevinMc]

Hi Dan,

From all the researching I've done I've found repeatedly that 3V/cell is a safe threshold for cutting off LiPo cells. But understand there's a difference between "safe" and "healthy". The LiPo Guard's "emergency blow" feature is designed to provide a warning before damage is done, but that's not the same as ensuring a long life. I read a very good analogy once for charging/discharging LiPo cells, likening it to a rubber band. If you stretch it (discharge it) right to it's limits every time you use it you can be sure it's gonna wear out faster. Like you I treat my LiPos with care with the intention of extending their useful life as much as possible. Consequently when I fly my electric aircraft I don't start a flight if I'm significantly down on power, and I don't deliberatly fly right 'till the low voltage cut on the throttle kicks in - I apply the same logic to my subs. If the LiPo Guard is only giving me one LED for its charge state sure I could eek out a little more run time but it's certainly better for my batteries to stop there and move to the next one or call it a day.

Your attitude for use of the LiPo Guard is a wise one - Treat your batteries with respect and use common sense. Monitor the charge state on your cells using the LEDs of the LiPo Guard (or volt meter) and only count on the "emergency blow" feature for a last line of defense. I'm sure your LiPos will reward you with a longer life for it!

[roedj]

Kevin,

Thanks for your reply. When I attach your Li-Po Guard to a fully charged, around 8.4V, Caswell 2s Li-Po I see all three LED's light up. Maybe the Li-Po "thinks" it's attached to a 3s battery, I'm not sure. Can you tell us what voltages you have set the LED's to go on/off at? For example, I find that I've reached my 1040mAh discharge somewhere around the 2nd LED going off leaving only one green LED still lit. I, too, start to think it's time to switch out batteries when I see only one green LED still on.

Thanks again for your wonderful products.

Pssst, Kevin, how about a depth regulator?:)

Dan

[He Who Shall Not Be Named]

That's great dope, Kevin.

I've chopped off the balance leads on my LiPo's. I figured that since my typical submarine loads are bellow the 3C rate that I'm not shocking the cells too much; that cell balance will not get so far out of tilt that a normal 'all cell' charge is good enough to get the pack back up to full charge.

Did I screw up here or did I once again demonstrate my briliance, charm and good looks?

I've got you LiPo Guard in four of my boats so far and it's a God-send!

David,

[Outrider]

Some of the small RTF (Ready to Fly) helis come with LiPos that don't use balance charging. The ones I've seen are generally 2 cell small capacity (e.g. 7.2V, 850 mAH). My sense is that these packs can be operated with little risk. I haven't seen bigger batteries (higher capacity, more cells in series) regularly operated without balance charging. That said, my experience is with RC Helis which, as you note, have a much different, and much higher, electrical current demand. Maybe this is one of those "your mileage may vary" situations.

One thing you lose by not using the balance charger leads is battery health monitoring. The balance chargers I have monitor and alert for charging faults. Given the LiPo's potential for incendiary mischief, and the high value of subdrivers, I'll keep my balance charge leads intact and in use. My risk tolerance profile is different than yours, though, since I have to buy toys you can just make! It's good to be the king...

Jim

[He Who Shall Not Be Named]

Some of the small RTF (Ready to Fly) helis come with LiPos that don't use balance charging. The ones I've seen are generally 2 cell small capacity (e.g. 7.2V, 850 mAH). My sense is that these packs can be operated with little risk. I haven't seen bigger batteries (higher capacity, more cells in series) regularly operated without balance charging. That said, my experience is with RC Helis which, as you note, have a much different, and much higher, electrical current demand. Maybe this is one of those "your mileage may vary" situations.

One thing you lose by not using the balance charger leads is battery health monitoring. The balance chargers I have monitor and alert for charging faults. Given the LiPo's potential for incendiary mischief, and the high value of subdrivers, I'll keep my balance charge leads intact and in use. My risk tolerance profile is different than yours, though, since I have to buy toys you can just make! It's good to be the king...

Jim

LOL.

Indeed.

David,

[KevinMc]

Hi Dan,

When I attach your Li-Po Guard to a fully charged, around 8.4V, Caswell 2s Li-Po I see all three LED's light up. Maybe the Li-Po "thinks" it's attached to a 3s battery, I'm not sure.

Let's be sure about what we're talking about - When you *first* connect the LiPo Guard it does a "cell count test" and sequentially turns on a green LED (from left to right) for every cell it sees. (For your pack it should only count to two.) But when it's done counting all the green LEDs with then be briefly extinguished and the "cell charge state" will be indicated using all four LEDs for both 2S and 3S pack types. So after the first 5 seconds or so a fully charged 2S LiPo should show all four LEDs on.

Can you tell us what voltages you have set the LED's to go on/off at?

That's dependant on the results of the cell count test - For 2S it's 0.6V/LED above 6V, so when you see one green (and the red) LED on you're measuring something above 6.6V (but less than 7.2V). For 3S LiPo the LEDs work according to 0.9V/LED above 9V.

Pssst, Kevin, how about a depth regulator?:)

While I can neither confirm nor deny that any such project may or may not be in the works, one might speculate that it's a natural follow-on project... ;)

Given the LiPo's potential for incendiary mischief, and the high value of subdrivers, I'll keep my balance charge leads intact and in use.

Jim,

That's very well put - I've followed the same approach to leaving balancing leads in place on my LiPos. That said I also have a couple of packs that didn't come with balance leads, so far I've not gone to the trouble of tearing those packs down to install them just for sub use. (I believe there to be a greater risk to catastrophically losing a pack during charge than during discharge anyways. YMMV.)

[roedj]

Kevin,

In re - depth regulator
Kevin wrote: While I can neither confirm nor deny that any such project may or may not be in the works, one might speculate that it's a natural follow-on project...

Dan responds: While I can neither confirm nor deny that any such purchase would be in the works, one may speculate from the original question that it's a natural follow-on purchase ...;)

Good knowledge about the voltage trip points/cut-offs on the LED's. I'll try and correlate that data with my "time at sea" logs.

Thanks again,

Dan

[Outrider]

Relative Risks Between Charge & Discharge

(I believe there to be a greater risk to catastrophically losing a pack during charge than during discharge anyways. YMMV.)

I share your opinion that charging is the most dangerous phase of operations. For discharge, I'm more worried about running past low voltage cut off than about the possibility of explosions. I don't want to ruin a pack, nor do I want to have loss of power from overusing a pack.

My background is in helicopters. Lose power at the wrong part of the fight envelope and your heli is toast. R/C subs have it much better, since the fail-safes really work and because gravity and speed are less of a threat to a sub than to a heli.

This has turned into a very useful thread. LiPos are very different from other chemistry batteries. They're not AAs--there's a lot to learn to ensure you can get the best use from them. Anybody want to talk about LiPo "puffing", expected service life, and, not to be too green here, disposal? I don't know all the answers, but each of these is important, too.