For versions with Normal and Low Range PLV, initially set the PLV range to Normal (factory default).
Servos typically draw fairly high current when reversed quickly, but on the ground, this current doesn't last long. Because VoltMagic is a high speed monitor, you can test on the ground and get similar results to hard flying.
On the bench, stir the sticks for a few seconds with the battery at ~50% charge. Check the PLV (LEDs 5-8 blinking). If none, you're done.
If your VoltMagic has two PLV ranges (2008 and later) you can select Low Range PLV if LED's 5-8 are blinking in Normal Range. Re-test by stirring the sticks. (See Table 2 for the trigger points for peak low voltage.)
Although "Normal Range PLV" is desirable because it means there is less voltage drop in the system, "Low range PLV" is often necessary with high powered servos. Feel free to try and improve the PLV, but it's OK to simply select "Low Range PLV".
Troubleshooting PLV that's too low (red or yellow blinking)
For non-regulator setups, bypass the switch harness by plugging the battery into the receiver. If you have a non-R/C type connector on the battery, make an adapter. Stir the sticks again and note the PLV. Whatever the increase in PLV, the switch harness is responsible for that much voltage drop. If greater then 0.1 to 0.2 volts, see items 2 through 4 below.
The remaining PLV (voltage drop) with the switch harness removed is from the battery pack itself, see item 1 below.
For regulator and non-regulator setups, you can reduce load by disconnecting servos. Repeat the stick stir test and note the improvement in PLV. This can help evaluate the demand versus supply of the electrical system and give you an idea of the magnitude of the issue.
1a) Batteries with high internal resistance. These cells usually have a large mAH rating relative to their size. Cold temperatures will make the PLV lower. Also, batteries that have failing cells. As batteries age, their internal resistance (impedance) goes up, and their voltage goes down. This may happen well before their maH capacity decreases significantly.
Many batteries experience too much voltage drop with the peak current of 4 or more digital servos. Old batteries can also develop excessive voltage drop.
Packs with low
internal impedance that are designed for fast discharge are
necessary for digital servos. The Sanyo 1950FAUP is a
good fast-discharge example NiMh battery (see before
& after example below). Most un-regulated LiPo and
LiFe RX packs will work fine. However, many Li batteries
have excess voltage drop with high current just like NiCd or NiMh
The lower the impedance rating, the better. Hangtimes
has a good selection of low impedance, fast discharge
batteries. The common NiCd or NiMh meant to work with $20
servos in a trainer isn't want you want for digital servos.
If the regulator works, but has very low PLV during peak current transients, you probably should use
components with more ampacity. Note that the higher ampacity
don't use a single R/C connector to feed all of the load.
Many switch harness assemblies have greater then 0.5 volts loss
at peak amps. As mentioned earlier, just eliminate the
switch to see how much PLV improvement happens -- Whatever the PLV
improvement is exactly how much voltage the switch is dropping. The higher the amps the more the voltage loss.
We strongly suggest trying the Futaba HD
switch, just sand off the tabs
if necessary. Use it as a baseline to compare with other switches.
The typical R/C connector drops at
least 0.1 to
0.2 volts at five amps IF the connector is in good
condition. R/C connectors
were designed long before high current digital servos
existed. Replacing the battery connector alone can raise PLV 0.2 volts (or more). We suggest using a
Deans or PowerPole. Regulator setups often have this same issue.
The best battery and regulator setups don't
have all the servo current feeding thought a single R/C connecter.
For single battery setups, the Futaba HD switch harness can be modified
to feed the receiver with twin leads. Dual battery setups should use dual switches.
Regulators that output through a single R/C connector often have
Although there are many power solutions available, budget, weight, and space may dictate a simpler approach. Reduce the peak current by using lower power servos where possible. An engine throttle is one place to look at. Most digital servos draw high amps just trying to move as fast as possible, even with no load. Consider an analog or "sport" digital servo for some functions.
Note: Low PLV is a sign that the servo amperage exceeds the capacity of one or more components of the electrical system. Trying to solve a low PLV problem by replacing a switch, battery, or regulator using the same exact component probably isn't going to improve PLV unless there is a malfunction.
BEFORE and AFTER EXAMPLE
Four Futaba 9252 servos plus one 9251 connected to a Futaba 601 gyro in a helicopter. With a generic 4-cell 2700 battery and a generic "heavy duty" switch, the PLV was less then 3.4 volts.
Substituting a battery pack with Sanyo 1950 FAUP cells, a Futaba HD switch modified to feed the RX with twin leads and a Power Pole (or Deans) connecter on the battery; the PLV was 4.6 volts.
Both tests were after a full charge followed by a 1200 mah discharge. 1200 mah isn't quite half discharged on the 2700 mah battery, so this is not the worst case scenario for it. Both batteries were cycled and tested for proper mah capacity. Results with different components will vary, but the difference in this comparison is dramatic.
Regulators are not immune to these problems either. Different regulator / battery setups can also show a wide variation of capability. The average voltage output of a regulator shouldn’t change as the battery discharges. However, the voltage at the receiver will still change with load, especially sudden changes. Note that OV (over voltage) is always caused by the regulator itself and is usually a sign of immanent failure.
If you have a voltmeter and want to verify accuracy, here's a quick test that most users can do themselves:
Discharge a 4 cell battery (assuming a 4 cell pack) down to 3.8 volts at 0.2 amps. The voltage will go up after the discharge is complete. Connect the battery to a "Y" harness, connect a voltmeter to the "Y" and then plug voltmagic into the "Y". Don't connect any servos; just let the milliamps that voltmagic draws slowly pull the battery voltage down as you read the voltmeter. The LEDs will blink as the voltage decreases below the trigger points for peak low voltage listed in table 2 in the appropriate instructions.
VoltMagic - Don't take off without it!