Mastervolt Mass Combi question

[Yellowjacket]

Older Mastervolt Mass Combi (2500?) on sailboat.

When charging the house bank, with charging "on" on the Mastervolt (Mvolt), the voltage consistently reads about 1.3V higher than it does on meters attached directly to my house bank.

When I turn charging "off", the reading on Mvolt for Battery Voltage drops to match what the meters attached directly to battery read. This at least establishes the the Mvolt voltage sensor is not hooked to the start battery.

My worry is that as I try to set charge voltages, the Mvolt is reading about 1.3 volts high. Therefore, rather than charging at 14.40 volts for absorption, I am actually charging at about 13.1 volts, at the battery. On the other hand, if I'm not understanding this, it might be a mistake to change the setting to charge at 15.7 volts. For six hours.

This also explains other anomalies: SOC is different (higher) when charged off main engine (Balmar regulator) and genset (Balmar regulator) or solar (Victron MPPT controller).

Does anyone have some insight for me?

[CatNewBee]

Check all cabling, connections, fuses for corrosion, clean them up and fasten them.

You should not have a voltage drop of 1.3V between the Mastervolt charger and the battery. You can also use a voltmeter along the line to search for the voltage drop while charging current is flowing to identify the cause.

There are many videos on YouTube showing how to use a voltmeter properly and how to search for a bad connection under load.

Like this:

https://www.youtube.com/watch?v=9aioZN33xsA

[Yellowjacket]

So the Mastervolt is not measuring voltage at the bus or battery, but reporting its own output at source? My newbie mistake. My solar controllers and other voltage gauges measure at battery bank. I've calibrated my voltage meters, analog and digital, and will go hunting for the loss/drop. Thank you.

[john61ct]

No charge device without a dedicated voltage sense wire is able to measure voltage at the bank.

How could it?

[CatNewBee]

Originally Posted by john61ct

No charge device without a dedicated voltage sense wire is able to measure voltage at the bank.

How could it?

... by pulsing the current.

interrupt charging current output for a short time, measure the voltage without load - no voltage drop - than turn on the current again and continue charging.

But it can still be incorect, especially if there are loads turned on, that share part of the cabling from the charger to the battery poles (power distribution rails, fuses etc).

Another way is just variating the current a little and measuring the voltage variation.

delta V / delta I = R

So you can calculate the resistance of the connection wiring and estimate the voltage drop - and dynamically compensate the output voltage in relation to the flowing current to maximize charge efficiency on the battery terminals.

[stgermain45]

Sound advice to grab a voltmeter and sleuth it out.



A related note about the Mass Combi -

Make sure your dip settings are correct if you have AGM batteries. An installer got ours wrong on both our Mastervolt Chargemaster charger and our Mass Combi charger/inverter as the manuals are pretty misleading. There is an "AGM" dip setting BUT (per Mastervolt Tech Support) for 12V this setting just adds .55V in float. Since float voltage is already programmed at a set value (13.3V in our case +/- with temp compensation), the dip switch setting adds and overcharges batteries during float.


Doesn't sound like your issue but a tidbit that might be helpful to someone...

[john61ct]

Do these allow for user customized profile settings beyond the set of canned ones?

[Garrettw]

Barring internal charger malfunction, sure sounds like a high impedance connection somewhere. Because this is a Mass Combi, I assume the wire gauge is more than enough for the charger output current? What's the voltage drop at the MasterVolt DC terminals when it is in inverter mode and is outputting high kW?

[Yellowjacket]

Originally Posted by john61ct

No charge device without a dedicated voltage sense wire is able to measure voltage at the bank.

How could it?

Yes, I realize that. Older boat, at least 7 (+) sense wires attached at four different points on the system, coming from unmarked cable runs buried in unaccessible locations.

[Yellowjacket]

Originally Posted by Garrettw

Barring internal charger malfunction, sure sounds like a high impedance connection somewhere. Because this is a Mass Combi, I assume the wire gauge is more than enough for the charger output current? What's the voltage drop at the MasterVolt DC terminals when it is in inverter mode and is outputting high kW?

I'd assumed everything would not seem as normal as it does when operating if there was an internal malfunction, but do not know these chargers at all – obviously, since I did not know there was not an external sense wire.

Yes, the wire gauge should be sufficient. It is the same gauge as all of the other high amperage leads (windlass, 300 amp genset shaft drive alternator, etc.) #4? About the size of a man's index finger.

I've been a little reluctant to poke around the MassCombi with a volt meter when hooked to shore power since (1) I'm learning on the fly and (2) I'm by myself. Unfortunately, some of the original labeling has been removed / come off at the bus bar in the engine room. I have, however, sanded all the ground wire connections at this bus bar and am capable of finding which of the bus bar leads are from the MassCombi.

Still working on it …