Alternator voltages - should they be fluctuating much?

[George_SD]

Got some partial results:

First of all, it does seem that voltage drop is causing me to worry, even though there may not be as big of an issue as it appears on the surface.

I've got three different voltage measurements
12.64v at the engine battery via multimeter (house bank was showing a very similar charge)
12.5v shown by the basic voltage monitor wired to the MFD breaker at the panel
12.1v shown by the MFD ?!

This last one really tripped me up, as at that point I would have assumed that the battery has no charge and is deeply discharged. It appears that the there is a hole 0.5v drop in a 14awg or 12awg cable. It is a bit long since it runs from midship at the panel all the way along the starboard side, then to middle of stern, turns back and up into the binnacle or about 20ft in total.

So i guess i can't trust MFD for the voltage reading and need to keep in mind that it is off by at least 0.5v. Ideally, I should add a battery monitor (like the Victron) with a shunt. Just need to find some $ for it.....

I didn't get to test alternator output unfortunately.


On the plus side, i think I've fixed a well known Yanmar start button issue that many suffer from (voltage drop as well essentially). I've removed all butt connectors in the chain from the button to the starter solenoid and crimped new terminals to freshly cut ends of the existing cable and the engine started right away on two tries.

[Sailmonkey]

Well, an mfd isn’t touted as an accurate voltmeter

[hlev00]

The MFD might have some corrosion on the connectors.
Harry

[Compass790]

AFAIK, (I'm no electrical expert) your hitachi should be a 13.8v setpoint VR.
Voltage sounds too low to me. Coming off a shore power charger your battery should be up to VR control voltage very fast assuming your engine starts within a few seconds.
I wouldnt have thought the thermal cutout on the alternator should come into play with the drain from your display & autopilot being so little your alternator would hardly be very warm. We have a Bosch 55 amp alternator that i can adjust its amperage output & when its putting out say 12 amps it is only a bit warm but at 35 amps its hot like 80oC.
Yes I'd guess the MFD voltage to be incorrect, we have the same issue on our Hummingbird fishfinder/plotter voltage readout.
I would guess your battery would suffer from undercharging if you were away from shore power for any length of time if voltage at battery is only 13.2 when engine is running.
The minimum float voltage after 2 hrs motoring should be 13.5v. Most have over 14v
Ignore the MFD & measure your voltage under power with DMM at battery.


Agree with previous posters you need to check alternator output in amps with a clampmeter if DMM voltage check at battery shows its less than 13.5v whilst engine is running.

[George_SD]

Originally Posted by hlev00

The MFD might have some corrosion on the connectors.
Harry

Brand new MFD installed a month ago. Checked the wire from breaker in panel to a freshly crimped connector on the MFD. I can cut off and replace the crimp connector on the breaker just to be sure, but everything looked very good.

[Wotname]

Originally Posted by Compass790

AFAIK, (I'm no electrical expert) your hitachi should be a 13.8v setpoint VR...............

Hmm... maybe on some older Hitachi IR alternators but all the new ones I have seen in past 2 decades vary from 14.2 to 14.6 V.

YMMV

[Compass790]

Originally Posted by Wotname

Hmm... maybe on some older Hitachi IR alternators but all the new ones I have seen in past 2 decades vary from 14.2 to 14.6 V.

YMMV

Quite right too cobber.
Glad you chimed in, it was a memory lapse. Our ysm8 35 amp one is 14.2 volt VR setpoint. I thought a 2GM20 would have the same alternator.

Makes it almost certain he has an issue.
Shuda checked before posting.
I did say I'm no electrical expert. lol