Mastervolt CombiMaster 12V/3000W-160A charger cutting out

[NewOrca]

Looking for some help with a baffling charging problem:

In bulk phase into 1200AH house bank (starting at about 80% SOC), charger current ramps up to about 130A (over ~60 seconds), then drops to zero, CombiMaster switches to "Inverting" for about 5 seconds, then briefly to "Off", then back to "Bulk" to repeat the cycle. Very inefficient charging! This continues until battery voltage reaches about 14.3-14.4V, when charging current finally settles to 110-126A with no further "sawtooth cycling". Once Absorption phase is reached the charging current ceases to cut out, and slowly declines as normal.

The above occurs when the charging source is a 5.5KW Onan generator, whose monitored output ramps from 0W up to about 2600W before dropping back to zero as above. Monitored output voltage does not drop, staying approximately constant at 119-120VAC.

HOWEVER, when the charging source is shore power the above cycling does not happen! Bulk charging current ramps up as above from zero to about 160A, power from shore ramps up to about 2800W at 109VAC. Although charging current never cuts out, it does cycle back and forth between about 135A to 154A.

[smac999]

Check the gen freq. it might be going out of range causing it to switch to inverter. My first guess would have been voltage going out of range while loaded. But you say it’s good. I would make sure.

Basicly once loaded it does not like the input and switches to inverter. It’s acting as a ups. Once off and the load is gone. It accepts the now correct ac input and turns back on.
Loads up gen. Something changes (voltage, freq etc). And off again.


Once the load gets smaller the ac power becomes more stable and the charger stays on.

[NewOrca]

Thanks smac999 for the ideas. I agree it is probably something out of bounds from the generator, but I'm not able to see it by watching its output monitor. It could be something so transient that I can't catch it, but the Mastervolt is very fast to switch into Inverter mode. The generator frequency is quite stable at 59.8-60.0 Hz, mostly 59.9. The charger always trips when the generator is outputting about 2600 W; I couldn't find anything else that correlated with tripping. One difference between the generator and shore power is the voltage: the generator is around 120 VAC while our shore power is down around 109 or even 108 VAC under load. I may need an oscilloscope to catch what's causing this, unless by chance someone else has dealt with this before.

[DFletcher2]

Yes, I have the exact same Combimaster 12/3000/160 and it has the exact same problem with only my Westerbeke 10.0 BTDA. So your problem is not just with your Onan. No problem for mine with shore power. Responses on this forum included installing a Mastervolt USB Interface P/N 77030100 to monitor and adjust. I am trying that. Mastervolt is making life difficult for us sailors with marine generators.

[samwhit]

Have either of you found any solutions to this? I am experiencing the same thing with a both my 6kw Northern Lights generator AND while connected to shore power. It's driving me absolutely crazy while trying to charge the batteries out here. Thank you!

[NewOrca]

Hi Samwhit,
I got ahold of Mastervolt at tsusa@mastervolt.com and worked with David Freeman (800.307.6702 direct). It turns out that this was a known problem with a particular lot of Combimasters. My unit was still under warrantee and MV agreed to replace it.