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Checking Single Cell Battery Voltage

Old 04-01-2018, 03:20 PM
  #1  
birdDog
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Default Checking Single Cell Battery Voltage

Anyone who monitors their 1s batteries might be familiar with how difficult it is hold them little buggers down and get a reading with a meter.

Simple solution. Make your own leads. A few inches of wire. In most cases a couple bullet connectors and the mating connector. For me, it was easier to just buy a $3 charger with 5 charging leads and just snip them off. One for my meter and the others for various small aircraft builds.

Certainly makes battery maintenance easier.
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Old 04-01-2018, 04:09 PM
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dereckbc
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If you have a DMM it is real easy to do if you roll your own cable. You get yourself Breakaway Header Pins with the correct pitch, a short length of red/black zip cord, a short piece of heat shrink, and two banana plugs to fit your DMM.

Just break off a pair of header pins, solder the zip cord to the short pins to the header and banana plug, and then apply some heat shrink to the header to cover the solder joints.

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Old 04-01-2018, 05:24 PM
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Wildflyer
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I have done this a few times when I could not find a matching connector.

1 Find a piece of wire, resistor lead. brass rod or something that fits. I'll call them pins.
2 cover the end of the connector with wax paper
3 poke the pins through the wax paper, --Don't rip it!
4 apply epoxy around base of pins
5 when cured solder wires to the top of pins for leads.
6 cover the connections with epoxy.
7 file to shape.

I'm not sure JB Weld conducts electricity so I wouldn't recommend it.

I had to make a new charge connector for my dads ProLine Tx many years ago, this way. Then I housed it inside a .45 Colt ACP cartridge, drilled out the primer and let the wires come out there through a piece of fuel tube.
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Old 04-02-2018, 04:36 PM
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Kosh
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I use this and it works for all kinds.


https://www.banggood.com/AOKoda-AOK-...r_warehouse=CN
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Old 04-02-2018, 05:45 PM
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Citabria32Yankee
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Originally Posted by Kosh View Post
I use this and it works for all kinds.


https://www.banggood.com/AOKoda-AOK-...r_warehouse=CN
Got mine @Amazon.com Donít know how I lived without it!!!
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Old 04-02-2018, 07:40 PM
  #6  
solentlife
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My chargers have adaptor leads to show state of these ... but of course I need charger powered up.

Nigel
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Old 04-02-2018, 08:21 PM
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Citabria32Yankee
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Originally Posted by solentlife View Post
My chargers have adaptor leads to show state of these ... but of course I need charger powered up.

Nigel
I got that HiTec X4 micro Charger last week, and itís better tha I expected.
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Old 04-02-2018, 08:26 PM
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dereckbc
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Originally Posted by solentlife View Post
My chargers have adaptor leads to show state of these ... but of course I need charger powered up.

Nigel
Kind of took the words right out of my mouth. I have two Chargers an iCharger and PL-8. Both can read each cell voltage at any time. Any charger worth having should charge all cells the same value like 4.2 volts. If it does not you have a POS charger.

However Top Balance does not tell you squat about a Lithium Pack. All it tells you is that each cell is at 100% SOC, it does not tell you the capacity or health of the pack, So checking fully charged cells does not tell you anything other than your charger is doing what it is suppose to do.

So hopefully by now you should be asking what good is knowing the voltage of the cell if it does not tell you anything? It means nothing at the Top, but tells you a lot at the Middle and Bottom.

After a flight is a great time to check cell voltages, because that is when they will NOT be equal. Why? Because cell capacities are not equal. A Top Balanced lithium pack voltage is only equal at the TOP and telling you the cell is fully charged. But after discharged is where you can tell if you have a good battery or not.

Example say you have a 3S pack and two cells measure 3.6 volts and one is down to say 3.1 volts, that pack is ready to be shot with a 22 cal riffle and soaked in a bucket of salt water over night before disposing.

I have another expensive hobby, racing golf carts and DIY EV conversions. Even belong to a local club. We learned a long time ago that Top Balance and Balance Boards are the number killer of Lithium batteries. We figured out a way to prevent destroying our lithium batteries. We Bottom Balance the cells and only charge the weakest cell to roughly 90%. When you Bottom Balance you know two things:

1. 2.5 volts per cell = 0% SOC
2. 2.5 volts per cell = 0 AH capacity.

The killer of any lithium battery is over discharge. The weakest cell in a pack is what gets killed by all the other adjacent cells. The weakest of lowest capacity cell reaches 0% long before the adjacent cells reach 0% SOC. In an EV we run 35S to 100S so a dead cell does not show itself in total pack voltage. So when the weak cell reaches 0%, the adjacent cells drive the polarity negative and destroys the discharged cell. If you are lucky no fire.

Bottom Balance eliminates that problem. All cells arrive at 0% SOC at the same time because that is the balance point. So the voltage is only equal at the bottom, not the Top. The other benefit is all cells have the exact same capacity at any point. All the cells maybe rated say 100 AH, problem is Chi-Com POS LFP cells ratings are +/- 10% so in a 35S pack the weakest cell maybe 90 AH and the strongest is 110 AH. Bottom Balance, and when you charge all cell capacities are equal. You only charge until the weak cell reaches full charge. We usually only take it to 90% to double cycle life.

Take away here is NOT to Bottom Balance because it is not possible with a LiPo pack dues to the integrated design. You cannot put all the cells in parallel. The point is check the cell voltages when the pack has been discharged. Ideally they should be equal, but they will not be equal. As cell ages, their capacity deteriorates at different rates and wil show themselves when discharged. My magic number for retirement is a spread of .1 volts at the bottom. So if fully discharge no cell below 3.0 volts and no cell higher than 3.1 volts.

Fully charged should always be equal. If not get a new charger.
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Old 04-03-2018, 12:19 AM
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Fascinating. Single cell batteries. That little single cell checker looks handy. It annoys me that they are labeled 1S.
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Old 04-03-2018, 12:23 AM
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Citabria32Yankee
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Originally Posted by birdDog View Post
Fascinating. Single cell batteries. That little single cell checker looks handy. It annoys me that they are labeled 1S.
Ditto!!!!
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Old 04-03-2018, 08:15 AM
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solentlife
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Bit confused "derekbc" ...... thread is about reading single cell batterys not multi cell.

I can understand OP as I also have various single cell LiPo's for indoor MR's and Heli's ... as well as my Car Race Lap-timer .... the plugs are awkward to use a DVM on.

One question : Do you not think it a bit dangerous to advise 2.5V for discharge of a LiPo cell - when its generally recognised to try not go below 3.0v ... some advise 3.3V ? New comers to the hobby may read 2.5V and think it fine to bang away at their LiPo's till that extreme low figure ? Not trying to start an argument ... just asking.

Nigel
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Old 04-03-2018, 02:40 PM
  #12  
dereckbc
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Originally Posted by solentlife View Post
Bit confused "derekbc" ...... thread is about reading single cell batterys not multi cell.
Not at all, I was responding to your reply.

Originally Posted by solentlife View Post
One question : Do you not think it a bit dangerous to advise 2.5V for discharge of a LiPo cell
Nope not at all. I was referring to LFP cells used in EV's. LFP = LiFePO4.

LFP = LiFeP04. Should have made that clear, and assumed folks would know no other industry would dare to use LiPo's for liability issues. LiPo's are just too dangerous.
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Old 04-03-2018, 04:08 PM
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solentlife
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Hi Derekbc ... my chargers comment was based on voltage checking single cell batterys such as LiPo's .... I have the leads to do that. As regards multi cell LiPo / LiFe etc. of course we resort to the old balance lead !

Sorry - never seen LFP as abbreviation for LiFePo ... so missed that. I see LiFe ... LiFePo ... but not LFP.
I know its presumptious - but I assumed and I think most others did - that OP was talking about single cell LiPo as found with many indoor / small stuff ... with the small connectors difficult to hold steady for the DVM.

Nigel
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Old 04-03-2018, 06:11 PM
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Citabria32Yankee
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Originally Posted by Kosh View Post
I use this and it works for all kinds.


https://www.banggood.com/AOKoda-AOK-...r_warehouse=CN
Don’t know how I lived w/o this. AOKoda AOK-041
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Old 04-03-2018, 09:20 PM
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dereckbc
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Originally Posted by solentlife View Post

Sorry - never seen LFP as abbreviation for LiFePo ... so missed that. I see LiFe ... LiFePo ... but not LFP.
LFP = LiFePO4 Lithium Iron Phosphate
LMO = LiMn2O4 Lithium Manganese Oxide
NMC = LiNiMnCoO2 Lithium Nickel Manganese Oxide
NCA = LiNiCoALO2 Lithium Nickel Cobalt Aluminum Oxide
LTO = Lithium Titinate Oxide
LCO = LiCoO2 Lithium Cobalt Oxide

It is the short form for the alphabet soup. Ironically LiPo has no meaning because a true LiPo Lithium Polymer is not what we call a LiPo. A true LiPo is a plastic substrate with very high internal resistance that never found a market and no one makes them because there is no application for them.

What we call a LiPo is a variant of LCO aka a hybrid. LCO has excellent energy density which is required but high internal resistance. LCO are the bad boys of Lithium batteries that make the news FIRE. So get the resistance down, a liquid electrolyte is added making them even more dangerous. FWIW Tesla Motors is the only EV manufacture that uses NCO cells. No one else would use them because of the risk involved. Example the Leaf uses NMC.

Anyway I digress.
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Old 04-04-2018, 07:05 AM
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I always just used the ballance plug readers. They plugged right into the jst plug I used on mine.
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