Batteries ESR meter

[xokia]

Received my ESR meter today and just grabbed my turnigy 65-130c 6S 5000mAh to try out here is what I got.

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Here are a few others
Nano-Tech 1300mAh 3S 45-90C 32-36m ohm 6 batteries
Eflite 1350mAh 3S 30C 50-62m ohm 2 batteries
Nano-Tech 2200mAh 3S 45-90C 20.7-25m ohm 6 batteries

Nano-Tech 5000mAh 3S 65-130C 10.5m ohm 2 batteries

 

[Tony]

ÂÂI think it would be pretty cool to know what the mΩ of a pack is and know what one is your best pack. Nice purchase.

 

[xokia]

ÂÂI think it would be pretty cool to know what the mΩ of a pack is and know what one is your best pack. Nice purchase.

For me I care that I can actually tell if a battery is actually better and not depend on the C rating of the battery.

This ESR meter can read the ESR of each individual cell in a pack. And that's actually the real useful information.

What I have found so far is the turningy 65-130c cells roughly come out 2m ohm per cell across 4 different batteries. 18 different cells

The turningy 45-90c I get between 5m-10m ohms per cell across 12 different batteries. 36 different cells

For the elite I get about 20m ohms per cell. Across 2 different batteries. 6 different cells

I also measured my 130x 65-130c 2S batteries they came in at 30m ohms per cell. Based on this info I think they are full of poop. I measured a Hyperion 35c 2S and got 30m ohms per cell. So that tells my hobby king is over stating their 130x batteries by 2x

With these numbers you can begin to see the difference. The individual cell resistance reveals more information because you can compare against any cell instead of just like S rated batteries.

All these measurements were taken at storage level charges and at 72 degrees.

 

[Slobberdog]

me is dumb so can you explain the relationships with the info above

ie m ohm to "C" rating

 

[BOKI]

Xokia; Looks like a really nice meter !

 

[xokia]

me is dumb so can you explain the relationships with the info above

ie m ohm to "C" rating

That would be hard to do since I don't know where this C rating stuff came from to begin with. It tries to be a number representing the current capabilities of the battery. But how much should the voltage sag with that rating? That isn't represented in the C rating. C rating is hocus pocus that I think they came up with to sell more batteries and try and make it less confusing for the consumer. But the number is easily fudged as you can see with my 130x batteries. The manufacturers won't publish ESR which sucks!

The ESR does a better job of telling you the capabilities of the battery.

Let for instance compare two batteries that are the same
Nano-tech 1300mAh 3S 36m ohm
Eflite. 1350mAh 3S 62m ohm

Now say we have an average load of 32 amps which is typical for these batteries in my 300x

The voltage drop out of the battery would be
32*.036-12.6=11.448v
32*.062-12.6=10.616

We all know the voltage effects the speed at which the motor spins. Battery 1 has more voltage available to give to the motor resulting in more power. We can also calculate how much power is wasted inside the battery as a result of the ESR.

For battery 1 we have a 12.6-11.448=1.152v drop
For battery 2 we have a 12.6-10.616=1.984v drop

So 32*1.152=36.8 watts wasted in battery 1 as heat
32*1.984=63.5 watts wasted in battery 2 as heat

63.5-36.8=26.7w additional watts that battery 1 will supply to the motor that battery 2 just wastes as heat.

Obviously battery 2 is going to come down significantly hotter then battery 1. Heat also effect the battery life so battery 2 likely wont last as long as battery 1.

I typed this out quickly before work hope that helped and hopefully I didn't make to many mistakes If something is confusing just ask.
I am a geek that likes numbers and data to make decisions on. This allows me to do that. Unfortunately I don't have to many other brands of batteries to compare against yet. But now I can buy batteries and know if its a better battery or if it's is just fancy advertising.

And if you've been paying attention to my comments about stiffening caps you can begin to see why having capacitors with a really low ESR is important. For that situation you have right around 1-2v drop that you are trying to improve. If the caps own ESR drops 1-2v that cap pack just becomes a heater and does nothing to improve ripple voltage. It would be nice if they published the ESR of those cap packs so that you can actually make an informed decision. I haven't looked into them much myself so I can't make any further comments about them.

 

[xokia]

So I got to measure a set of pulse 65C 6S 5000mAh batteries yesterday and those measured about 1.44 mOhms. So they are better than the turnigy's but signifacantly more expensive.

 

[coolgabsi]

Those can save lives... My charger has this built in.

Good packs will have anywhere from 2-4mOhm per cell

Bad pack of it goes 15 or more

 

[Tony]

Just measured one of my small packs. It's showing 45mOhm lmao. I think it's bad.

 

[xokia]

Those can save lives... My charger has this built in.

Good packs will have anywhere from 2-4mOhm per cell

Bad pack of it goes 15 or more

So the thing I don't like with the ESR meters built into the chargers is that temperature effects the ESR reading significantly which is inversely proportional to the temperature. What you will usually see is that the ESR goes down as you charge. Which isn't actually what happens. The real ESR is pretty stable and doesn't really change over different charge levels. I try to measure ESR at 71 degrees F so that my readings can be compared with one another. When you charge a battery you are also heating the battery up so ESR is less accurate.

ESR will appear to go down as the battery gets hotter and go up when the better is cooler.

 

[coolgabsi]

Right... I measure right before charging when neither my batteries not charger are hot

That works perfectly fine