Herb-RCU

I was considering buying a VoltWatch meter for my planes, but I didn't feel like spending $10 when I already had a voltmeter. I have a battery lead that I can plug into the battery and then I can hook up the bare wires to the voltmeter.

At what point should I stop flying the plane for a 4.8V battery? The VoltWatch only has "low safe max" lights but no voltages.

Herb

Phil Cole

You should load the battery while measuring the voltage.
A 27 Ohm 1 Watt resistor connected across the voltmeter input
would do the job.

4.8 V is a safe minimum voltage to start a flight, assuming you'll
only be up there for ten or fifteen minutes.

A fully charge pack will be between 5.4 V and 5.7 V
A fully discharged pack will be at 4.4 V.

These voltages are all with the 27 Ohm test load applied.

DGrant

My Feedback: (4)

My voltwatch seems fairly accurate to my ESV, meaning when VW says "low", meter agrees just at the red-zone. Try it, it's not a bad way to go. I bought one to fill in a dash on a few planes, and it looks cool in there.

Herb-RCU

What is an "ESV"? My other question is how do I get a 27 ohm 1 watt resistor? I went to Radio Shack and while I can get resistors that add up to 27 ohms, the power doesn't work out. Maybe I'm forgetting something, but does power add in series as well? This seems to make sense, but I can't be sure.

Thanks.

ftomteen4cat

ESV - expanded scale voltmeter. Refers to analog meters, instead of reading from 0-15 volts, they may only read from 10-14.
This makes the value somewhat easier to read, improves interpolation, reduces the effect of parallax error, and improves overall accuracy. Analog meter tolerances are given in % of full scale, vs % of indicated value. Parallax error is a result of looking at the needle off-axis. Some meters will have mirrored strips on their faces to reduce parallax error. Interpolation is approximating an indicated value when the needle lies between markers.

You could put two 56 ohm 1/2W resistors in parallel. This would give you 1W, 28 ohms.. better than 4% accuracy to 27 ohms.


-edit - corrected 'interpolation'

Jackjet

My Feedback: (1)

Herb,
go to the nearest Radio Shack and buy yourself a digital voltmeter-it does NOT have to be the expensive one either-then get yourself a 12volt car dome light to connect across your test leads-now you can see just how much your voltage really is.The light blub I use draws 700milliamps-thats a good load to test with.This is what I use to test my jet with-and this plane is 16years old.


Jackjet

Herb-RCU

Thanks for the help. I will try one of the options that was described here.

Herb

Bigkid

The #44 light bulb from Radio Shack works for me. Its a 4.8 V-250ma, which is very close to what most receivers will draw.

Rodney

Just get a 22 ohm, 5 watt unit at Radio Shack. It is close enough to the recommended 27 ohm. I use a 10 ohm 10 watt on mine as that gives a better indication of what happens under load. Note that these resistors will get quite warm if you leave them connected very long; if you use too low a wattage rating, they will burn in two. Rod