Giant Shark Closed for New Business

Chris001 wrote: Hi Mike,

Could you do a quick test for me, check the voltages of the cellmeter against your iCharger and the same again for the internal resistance, just curious how closely they agree with each other.

The answer is...they don't

iCharger Cellmeter iCharger Cellmeter
4.18 4.182 5 6
4.17 4.161 2 2
4.16 4.156 7 2
4.15 4.184 5 2
4.15 4.146 6 2
4.15 4.188 4 5

3 hundredths of a volt worst difference - that cannot be significant. Also what unit of internal resistance are we looking at?
If under load conditions those voltage values are consistent then surely we have to take into consideration the microscopic quality of the welds or the thickness of the connecting tabs or the cleanliness of the connector pins on the balance plugs?
Surely only a full load test will show the real internal resistance of the cells and those appear to be open circuit voltages?

I notice that the Cellmeter spec says it can measure the capacity of LiFe batteries. I thought the discharge curve for LiFe made this impractical. Is this a genuine feature or just marketing hype?

Resistance is measured in mOhm
Voltage is with no load.
From memory, internal resistance does not change under load.

To be honest, the absolute value is of no real importance. Knowing the numbers is, however, a good sign that something is going wrong. If you record the iR and monitor it over time you will know that your battery (or cells within the battery) are getting close to needing a replacement.

The reason why I said they don't is that, for example, cell 4 has equal lowest voltage on the iCharger but 2nd highest voltage on the cellmeter. Also, cell 3 is highest iR on the iCharger but equal lowest on the cellmeter. IOW, treat the readings with a pinch of salt.

Thanks Mike,

To be fair it's not a fluke meter so it comes down to whether the accuracy is acceptable to the user. I noticed mine, the hobby king version, occasionally significantly misread one cell voltage by enough to make the whole pack look further depleted than it was. My iCharger showed it was actually okay. But for on the field as a quick reference to which is the full pack or did I over stress the pack on the last flight it's going to be handy.

AlanF wrote: I notice that the Cellmeter spec says it can measure the capacity of LiFe batteries. I thought the discharge curve for LiFe made this impractical. Is this a genuine feature or just marketing hype?

I certainly would not trust it. Do a google search for "life discharge curve" and you will see why a voltage reading of life will tell you nothing other than it has "between 70% and 20% remaining"