Voltage question.

[Dave Neptune]

I just finished doing a bit of a rewire on the ole' girl. Now I am doing more checking of voltages and they are a bit "higher" than they were, shorter runs and new wire and connections. I now see almost a full volt higher when charging which leads to my QUESTION. I have 3 digital volt meters and they all read differant. I have a volt meter demand display on my VHF, another on my GPS/Plotter (Garmin) and my hand held DVM. They all read higher as I expected but not so high when running.
I pulled out 4 ~ 17' runs of #4, and now my longest run is 3 feet to the starter. When Ericson wired her in 70' copper must of been much cheaper.

Guestion~~~Is there a good thing to check the DC voltage of for a good base line to sort of check the DC voltage calibration on a GVM?

Dave Neptune

[ndutton]

Dave,
If it's calibration you're after I'd suggest a way that has a side benefit. If it were me I'd remove my alternator and take it to Lewco Electric. Ask them to dyno test it (they have an amazing dyno for just that purpose) and report back the voltage output at various RPM's from 500 - 2000 (should be constant). Reinstall it and compare your handheld DVM to the report measured at the alternator output. You may have a calibration screw on the DVM to adjust. If not you'll at least have a known % deviation to apply. This way you'll always have a base voltage on board to test your DVM in the future.

Not related to calibration but Lewco will also be able to measure the maximum amperage you can expect at 2000 RPM or whatever your typical cruising RPM might be. In my case I learned my 100 amp alternator maxxes out at 50 amps @ cruising RPM.

Other thoughts:

• What is the voltage range between different meters you're reading?
• The VHF and GPS are reading voltages at different points on the electrical system so some variance is expected due to wire resistance and resultant voltage drops. The newly calibrated DVM can be used to measure voltages at the VHF and GPS connection points to compare.
• With your new and improved voltages (nice, by the way) you may want to revisit the coil resistance exercise as it applies to electronic ignition system amperage. Shawn's experience was he had no problems until he cleaned up his electrical. Afterwards it was coil carnage.

[JOHN COOKSON]

Calibrate the hand held to a fresh 9 volt battery or some other source of known voltage.
Then, if possible, read the voltage at the terminals of the other two devices. That way you will know if it is the meter on the devices is reading incorrectly or if is the true voltage at the device.
How much difference is there? You may need a correction factor. Or maybe something like "if the meter (on the device) reads between X and Y the battery is fully charged and the device is getting full voltage."

TRUE GRIT

Edit: Neil was a little ahead of me!

[ndutton]

Edit: Neil was a little ahead of me!

Maybe so but we are in complete agreement. I'm liking that!

[Dave Neptune]

So far

The one on the VHF seems constant. I had it hooked to the new panel in the nav-station and used a set of jumpers that fit the VHF and wired straight to the "house batteries"~~no change in reading. The GPS is hooked to the same panel and the voltage reading on it varies as to the brightness setting on the back lite. It, the GPS, did the same before as far as varying as to brightness setting. The old wiring saw a hi of 13.8 when fully charged and now with the new I'm showing 14.7.
I did wire the engine in an unorthodox manner. I am taking my power from a panel (#6 wire) that leads to the cockpit and stock main power panel. I checked the voltage to the coil where the alt wire hooks up and the voltage through the key switch is good, maybe a .2v drop when on between the battery voltage and the voltage at the coil (longest run). I did not check while running yet but do not suspect a weak connection to the alt input.
I am thinking of having the alt checked as I had it off and on many times during the rewire work. Don't think I dropped it or banged it either. I does hang at around +5~7 amps (luv the new gage 280 degree sweep) charge when I think the batteries are full. It drops to zero and back once in a while so I do suspect the regulator possibly.

Like the fresh 9v idea John.
Neil, not sure of the output vs rpm senario unless the pulleys are tha same diameter. I have a shop around the corner that has the test equipment and they know me. I may drop it off for a rebuild too, it's been almost 4 years now.
I'm going to get anothe DVM today and do a comparison that way too. The one in my tool box at home shot craps and it only fell about 8 feet.

Thanx, Dvae Neptune

[edwardc]

Most battery chemistrys have a voltage that varies with both their state of charge and their condition.

Ni-Cads are an exception. A Ni-Cad will maintain a fixed 1.25 volts per cell throughout most of it's discharge curve, falling abruptly at the end of its capacity. This makes them useful as a low-precision calibration source (on the order of +/- 50 mV, or 0.05 V).

[Al Schober]

A good DC voltage reference is a zener diode. Radio Shack 276-563 is a 12V 1W zener - $1.99/2. Use with a dropping resistor to limit current to 80ma or you'll smoke it (perhaps why they sell them in pairs??). A 40-50 ohm resistor should be good for a 15V supply (battery charger or alternator).

[romantic comedy]

I just measured a new 9 volt, with my Fluke multi meter ( FMM)

The FMM, says that the NV of a 9V, is higher then 9.

fwiw, ymmv

[sastanley]

Rc is right...

A 1.5 volt alkaline cell new is about 1.63-1.65v.

A 9 volt alkaline cell in my experience is also more than 9v when new.

A rested 12v boat battery, should show 12.6 volts when fully charged, at rest in my experience, for several days or even a few weeks. Both of my Gr29 Wal-mart Everstart deep cycle's were at 12.7 30 days after I brought them home from the boat when I checked them in my 50° garage over the winter..I think I even successfully proved the cold cement theory/hoax by not having them on a block of wood and they were still at 12.7 volts after 60 days. I hooked up a charger to both of them in January and it ran for 3 minutes and said it was charged up at 13.1v. The summary is that they sat for 90 days and read at least 12.6v.

A 2 volt cell = 2.1 volts...that is a slight disparity.

Unfortunately, a 9v battery at 9 volts is not fully charged Neither is a 1.5 volt cell...1.63 to 1.65 seems to be charged to me.

[ndutton]

Neil, not sure of the output vs rpm scenario unless the pulleys are the same diameter.

They're close enough for gubmint work.

[romantic comedy]

The pulley ratio to RPM, is pretty simple to figure.

Just divide the pulley diameters to get a ratio. Then multiply the RPM by it.

But it is not all that important, as Neil says. You are just looking to see if the output is steady.

FWIW, my 100 amp Balmar alternator will put out 80 amps, according to my ammeter. That is what I have seen so far.

[Administrator]

They're close enough for gubmint work.

With this gubmint.....

Think twice before coming to Maryland, where even the rain is taxed....

Bill

[joe_db]

I have a 15 volt zener across my alternator. They can save you from switch malfunctions, but may melt while doing so.

A good DC voltage reference is a zener diode. Radio Shack 276-563 is a 12V 1W zener - $1.99/2. Use with a dropping resistor to limit current to 80ma or you'll smoke it (perhaps why they sell them in pairs??). A 40-50 ohm resistor should be good for a 15V supply (battery charger or alternator).