Very interesting lipo charging warning! - RC Groups
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Mar 10, 2018, 11:55 AM
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Hugo Flynow's Avatar

Very interesting lipo charging warning!

I just got some 4s 3600 and 4000 Admirals.

I was reading the care and feeding sheet and it states that NOT to charge the lipo if it is below 3.7v per cell! It states that the lipo is unfit for charging if below 3.7v/cell.

I never run my planes below 3.8 but .....I've never seen that conservative of a charge warning before.

Just thought it an interesting thing to mention....
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Mar 10, 2018, 12:56 PM
It's A Great Time To Be Flying
MrEFlyer's Avatar
It's good advice to not run the batteries down too far but "NOT to charge" seems a little extreme. It must be they want you to throw the battery away and buy more from them.
Mar 10, 2018, 01:07 PM
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You can try to charge overdischarged lipos but you have to be careful. I think they are being way conservative at 3.7V per cell. The minimum is more like 3.3V per cell.
Mar 10, 2018, 02:11 PM
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Hugo Flynow's Avatar
I am surprised...and think it is an overly conservative warning, and one I never saw at this voltage.

I just found it interesting enough to post here....for reasons I'm not sure.

Yes 3.3 is rock bottom for a cell. I've had lipos puff from running to 3.65 back (EDF) when I was less knowledgable....

I mean they are quality Admirals rated at 40C...I almost wonder if it's a typo.
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Mar 10, 2018, 05:35 PM
Space Coast USA
hoppy's Avatar
3.7V is about 80% discharged. That requirement doesn't make sense.

Can you show the paragraph(s) that reference that?
Mar 10, 2018, 05:43 PM
Frankenstein recycled packs
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Mar 10, 2018, 06:58 PM
pull up -- PULL UP!!!
There's so much information and mis-information on lipos out there. Who knows what to believe? I think everybody just quotes something from someone else, but changes it a little bit just for grins.
Mar 10, 2018, 08:49 PM
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Hugo Flynow's Avatar
One pic is the full sheet.

Other shows just the paragraph I'm talking about.

Also it does not read as "Chinglish" at all. Very concise.

Again...I find it as odd as you all do.....but interesting enough to mention as food for thought as to what one manufacturer considers voltage too low.
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Mar 11, 2018, 03:00 AM
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The bit about not charging any battery that has unbalanced (> 0.1v) cells seems odd too. Okay, imbalance can indicate cells going bad, but the whole idea of balance charging is to bring them back to a balanced state, isn't it?
Mar 11, 2018, 07:54 AM
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Hugo Flynow's Avatar
Originally Posted by abenn
The bit about not charging any battery that has unbalanced (> 0.1v) cells seems odd too. Okay, imbalance can indicate cells going bad, but the whole idea of balance charging is to bring them back to a balanced state, isn't it?

Yes that is odd as well....but you see, these lipos were replacements sent to me from MRC to replace a bad batch with bad cells.

I also thought I could balance charge to compensate, but while my charger struggled with the bad cell, it overcharged the other cells to 4.24.

Is uneven cells the same as bad cells??? Maybe yes maybe

I compared these instructions with my other brands of lipos, and these are very odd, and extremely conservative.

My Roaring Tops say to be careful when they hit 3.3. Which is more the norm....
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Mar 11, 2018, 08:11 AM
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hoppy's Avatar
I asked Tom to join the discussion. Maybe he can clarify the directions.

By the way, any of you who want to get rid of any packs with cells under 3.7V can send them to me.
Mar 11, 2018, 08:21 AM
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Hugo Flynow's Avatar
Fair enough.

I am a fan of Admirals and a big fan of MRC....

I just never saw 3.7v/cell as unfit for re-charging before.
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Mar 11, 2018, 10:12 AM
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What if the BATTERY is NOT at fault ??

Then it will recharge normally. Like 1 motor lead circuit has a higher or lower resistance than the others. Happens. That lead / cell would always be different fro the other 2 cells before charging.
Mar 11, 2018, 01:09 PM
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Hi guys, I've not read trough this entire thread so if I've missed a question, please feel free to ask. First, I'd like to mention the instructions are conservative. We'd prefer to error on the side of caution.

Next, let me address the imbalance in cells. Balance charging is NOT to bring an unbalanced battery back into balance. Balance charging is to keep a battery pack in balance. The reality is no battery pack ever has 100% perfectly matched cells. As much as manufacturers like to say they match cells, they can never be perfectly matched. This means the cells can charge at slightly different rates in a good pack. Hence the need for balance charging. We test every Admiral battery before we ship it. If a pack is .05 or more out of balance, we discharge it and destroy it. We've found we can balance those packs but they will go back out of balance within 1-5 uses and the weak cell will go bad after 10-15 uses. A pack which is 0.1V out of balance is bad. DO NOT attempt to charge. For example, if most cells are at at 3.71V and one cell is at 3.61V, you have one cell which is weaker when compared to the other cells. When you attempt to charge a battery pack this far out of balance, many charger brands on the market will overcharge the good cells in an effort to bring the bad cells into balance with the good cells in the pack. This faulty charger logic can result in a fire. I've heard about too many fire stories and it is almost always this exact situation. If you do manage to get a pack back into balance, the overwhelming majority of the time it will go back out of balance within 1-3 uses. The fact is, there is a bad cell or weak cell and charging it is dangerous. The pack will not perform properly in flight. If you charge a good pack and it takes 15 min to charge and you follow it up with an out of balance pack and it takes 30 minutes to charge and balance, this is a good indication a cell is too weak as compared to the other cells in the pack. Why is the cell bad or weak? It can be from running the battery down too far, improper storage, C rating too low for the application, IR too high, cells no longer matched, etc.

Lastly, I'll address the 3.7V recommendation. The 3.7V mentioned in the instructions is measured at rest at room temperature, 5 - 10 minutes after flight. When you discharge your pack below 3.7V, you are going beyond the voltage where the cells like to "rest". Call it an equilibrium. I'm not saying hitting this level or below during flight is bad. Clearly, you will hit way below 3.7V per cell many times during the flight. Any of you who have data logged or used telemetry see the cell voltage sag and rebound depending on how much throttle you are using. This is why I mentioned the 3.7V is at rest, at room temperature, 5-10 min after flight. When measured within these parameters and you go below 3.7V per cell , make no mistake, you are harming the battery. Going below 3.7V (when measured after a flight) causes the IR to go up and life span to go down. Every time you do this, you are weakening the pack, lowering the C rating, and shortening the life span. If you measure IR, you will see this. BTW, when you measure IR, make sure you always do it at the same voltage and same room temperature. You must keep all parameters the same in order for your IR measurements to be most accurate and meaningful. This is a great way to see the health of a pack. BTW, IR varies based on the size of the battery. i.e. a 5000mAh cell will have lower IR than a 500mAh cell. Also, I've tested many chargers which measure IR and they all vary. We took 5 different charger brands and measured IR of the same pack and the results were vastly different. I've even seen different results when measured on different chargers of the same charger brand/model. Your IR results are relative to you and only you. Measure a new pack and write down the IR, voltage, and temp. I always log this for my packs. It is a good way to see the health of the packs. Anyway, back to the 3.7V per cell recommendation. I mentioned IR because you are hurting the cells every time you run down past 3.7V (again, measured at rest at room temp). Personally, I aim for my packs to be at 3.8V per cell measured after I land. If I go a little past to 3.75V per cell no big deal. If you regularly go past 3.7V per cell, you are hurting you packs. You are effectively lowering the C rating.
Last edited by Tom.MotionRC; Mar 11, 2018 at 01:22 PM.
Mar 11, 2018, 02:20 PM
Space Coast USA
hoppy's Avatar
Tom, thanks for joining in.
I think the concern is over the "Never charge a battery pack which is below 3.7V/cell"

I can understand that point if it read "Never discharge a pack below 3.7V/cell (resting). But the way it reads now (to me), is that if I happen to run a little too long and the pack ends up at 3.65V/cell it should be what, discharged and tossed?
I don't think that's what you meant, is it?

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