ProgressiveRC ESR - Manual

ESR Meter For 2
– 6 Cell Lipo Packs
OVERVIEW
A Lipo pack can be considered as a perfect stable voltage source in series with a small series resistance: its
ESR, or Equivalent Series Resistance. Also known as IR or Internal Resistance.
This resistance or ESR, is made up of the total resistances of each cell plus the resistance of the
interconnections, the power leads and the contacts of the power connector. Once we have chosen a pack, the
only one we have any control over is the connector which represents only a small percentage of the total.
It is the ESR which dictates how the pack is likely to perform, both in the short term; ie holding its output
voltage and delivering more power, and in the longer term, its probable life in number of cycles.
Measuring ESR requires special equipment as a typical value is a tiny fraction of an ohm, and also because
ESR is measured across a live power source, ie a cell or battery.
ESR
– The effects
What does ESR do? In a nutshell, it drops volts, wastes power and heats up and damages the battery. Thus
we are looking for the Lipo with the lowest ESR.
If we take a good 3S 2250mAh pack as an example with a pack ESR of, say 15 milliohms, then if the motor is
taking 40A, the voltage delivered to the motor is 0.6V higher than a poorer pack with an ESR of 30milliohms.
An extra volt drop of 0.6V doesn‟t sound much but it is about 5.5 – 6% of the motor volts and will result in 10 –
12% less power at the prop. which is significant and noticeable. The other effect is that the better pack has an
internal power dissipation of 24Watts heating it whilst the poorer pack has 48W so it gets a lot hotter and as a
result is likely to have a shorter life.
The equation is complicated by the fact that the ESR has a negative temperature coefficient (heat reduces the
ESR), but in essence the above holds true
Operation
The unit is self powered by the pack under test, the only controls are a mode switch and an operate button.
ESR is measured at high current to simulate real operating levels.
Wh
en connected to the pack, the display will read the voltage of the pack if switched to „Pack‟. If the meter is
switched to „Cell‟ and the search connector plugged into two adjacent pin positions on the balance connector,
the meter will read the voltage of the cell corresponding to those two positions. Moving the search connector
allows measurement of any cell in the pack.
To take an ESR reading it is only necessary to press the operating button and the unit will display ESR for
about 3 seconds and then r
evert to reading voltage. In „Pack‟ mode it will read the ESR of the whole pack plus
the connector and leads. This is a practical measurement as it is measuring the total resistance in the circuit
that the ESC will see in practice.
In „Cell‟ mode it will read the ESR of just the individual cell that the search wire is connected to via the
balance connector, excluding all other leads and connectors. In the „Cell‟ mode the instrument is using a true
4 wire Kelvin connection enabling the user to very accurately compare the ESRs of each individual cell in the
pack.
SPECIFICATION
Mode Measurement Range
ESR Resolution Accuracy Voltage Res. Voltage Acc.
Pack 0 – 250 Milliohms 0.3 Milliohms <3% 40mV <0.5%
Cell 0 – 30 Milliohms 0.04 Milliohms <2% 10mV <0.3%
Measurement current: 16A.
Maximum Pack Voltage: 30V.
Protection: Unit is protected against reverse polarity on both main power and search wire inputs.
Range: The unit can measure any Lipo pack of 2
– 6 cells in the range of 500mAh – 6000mAh.
Size: 45 mm x 100mm x 130mm (1.8” x 4” x 5”)
Weight: 200g (7 oz)
Standard Connector: T-Plug