Voltage drop(s)

[pcmpete]

I just replaced my two alternators trying to resolve a low voltage issue.
My setup is as follows:
2 Mercruiser 377’s with 70amp alternators
2 starting batteries
1 house battery
1 generator starting battery.

When I measure the voltage at idle rpm I get the following results:
At alternator - 14.3volts
At battery terminals - 13.4volts
My Vessel View displays 12.9volts

Why the voltage drops?

Thanks

 

[sam am I]

Ohms law....V = I*R

Voltage (drop) = Resistance( wire gauge/connections) * Current (though said wires/connections)

a) The higher the resistance/s at some current flow, the higher the voltage drop across the/those resistance/s.

b) The higher the current flow through the/those resistance/s, the higher the voltage drop during that current flow.

The fix?

You can't do much to reduce current unless you have some problematic loads that are lower then they should be (not your issue)............Soooooo, one option left?

Decrease resistance where you can...........

1) Check for crappy connections (grounds and positive feeds), fix as needed
2) Increase wire gauge to reduce resistance/s where needed (see "a" above)

 

[pcmpete]

Ohms law....V = I*R

Voltage (drop) = Resistance( wire gauge/connections) * Current (though said wires/connections)

a) The higher the resistance/s at some current flow, the higher the voltage drop across the/those resistance/s.

b) The higher the current flow through the/those resistance/s, the higher the voltage drop during that current flow.

The fix?

You can't do much to reduce current unless you have some problematic loads that are lower then they should be (not your issue)............Soooooo, one option left?

Decrease resistance where you can...........

1) Check for crappy connections (grounds and positive feeds), fix as needed
2) Increase wire gauge to reduce resistance/s where needed (see "a" above)

I do have the Mercruiser DTS with Axius system, I don’t know how much load this puts on the system. I have only owned the boat for 4 months and still learning its setup and functions. Thanks

 

[dingbat]

It would be interesting to see voltages with the batteries at “rest”.

A lot of battery to be charged with 70A charging system

if the DTS is drawing down your voltage, you have battery issues

 

[Alumarine]

I haven't checked Vessel View but I know other devices such as GPS/Fishfinders as well as ECU's on cars the voltage shown is often .5 volts lower than my multimeter'.

 

[dingbat]

I haven't checked Vessel View but I know other devices such as GPS/Fishfinders as well as ECU's on cars the voltage shown is often .5 volts lower than my multimeter'.

Can’t speak for ECU but GPS/fish finders use internal power supplies to regulate and step down (+5v) the incoming current for use by the electronics.

I asked tech support the same question a few years back. Asked them if the display voltage was raw or regulated.

They didn’t know the answer. Would have to test and call me back, which they did by the way.
Confirmed for myself that the unit is displaying “regulated” voltage.

Your results may vary......lol

 

[sam am I]

Confirmed for myself that the unit is displaying “regulated” voltage.

@dingbat

This is odd...So the displayed voltage you see only really then indicates the health/status of your(a) GPS/FF internal regulator's output voltage? And is derived from a 5V regulator?

My Garmin (and other past manu's) are definitely monitoring the units "raw" 12V inputted supply voltage............Engine running, it says 14.3V, engine stopped, it say 12.4V.

If monitoring/displaying a regulated output, how would it's output voltage change (go up or down) and reflect any sensible representation of it's inputted "raw" voltage unless the regulator simply failed as a short? (or the reg's overhead became too small, < 1 or 2V typically).

Wouldn't a properly functioning regulated output just be more of less the same always? e.g., 14V in = 5V out, 12V in = 5V out?

In fact, if the reg (linear or switching) is doing it's job and it's of today'ish technology of a LDO type, 6-30V in = 5V out +/- 0.1%........Weird design!! Thinking someone is not quite on the right page........

 

[dingbat]

@dingbat

This is odd...So the displayed voltage you see only indicates the health/status of your GPS/FF internal regulator's output voltage? And is derived from a 5V regulator?

My Garmin is definitely monitoring the units "raw" 12V inputted supply voltage............Engine running, it says 14.3V, engine stopped, it say 12.4V.

If monitoring/displaying a regulated output, how would it's output voltage change (go up or down) and reflect any sensible representation of it's inputted "raw" voltage unless the regulator simply failed? (or the reg's overhead became too small). Wouldn't the regualated output just be the same alway? 14V in, 5V out, 12V in 5V out? In fact, 6-30V In = 5V out........Weird design!!

Troubleshooting a boot problem with the unit. It would start boot process then stop. Pretty obvious the boot sequence is waiting for something......times out then freezes.

Display read 12V, gauge, battery, and connector at back of unit all at 12.7

Didn’t make sense unless the display was behind a PS or regulator of some sort. Called Garmin tech support who confirmed the display was regulated voltage.

Makes perfect since from an electronics standpoint.....but most users assume the display reads raw voltage.

This is a on GPSMAP Multi-function display. Full featured. Supports live video feeds, etc. Pretty sure my EchoMap Sounder does the same. Don’t know for sure. I would have to check since the volt meter/gauge at the helm is my primary means of monitoring on-board voltages

 

[sam am I]

Display read 12V, gauge, battery, and connector at back of unit all at 12.7

Mine was doing that exact same thing few yrs back, called Garmin, took him with me on the boat give him measurements, he said "FW notes didn't say this issue was an included fix, but try anyway. My display voltage was almost 2V off from back connector voltage read right on the pins, the FW update fixed it! It is spot on now with my Fluke.