I have a Multiplus 2 charging a 1000Ah LiFePO4 battery bank.
The Multiplus changes at 120A continuously no problems when on shore power.
However if I try and do the same with my 4KW MDKBH Onan generator it struggles the charger runs, and then it trips and goes onto the inverter. After a short period of time it starts charging again and then the cycle starts again, cuts off, drops back onto the inverter, and then starts charging again.
I can cheat it slightly by dropping the charge rate to say 50A and it will charge continuously, I can then creep the current up slowly 5/10A at a time and it will eventually get up to 120A after a while, but it’s a pain that it doesn’t work from the initial startup, it seems that it needs to warm up, but a 4KW generator should be run a 3KW load without too much of an issue.
I have changed the input from shore power to generator.
Is there another setting that I need to change on either the Multiplus or the Cerbo, am I missing something???
When running the generator, have you changed the ac input current limit setting? I wouldn’t go over about 27 amp max. It’s not recommended to run any generator at 100% of rated capacity, and there will also be a derate based on ambient temperature and elevation.
I am running on 240V and the only load on the generator is the Multiplus-charging(about 12A), I will check the loadings but I would envisage it to be in 3kw mark which is about 3/4’s of the generator rating so I don’t see why this should be an issue.
Unless there is an issue with the voltage regulator not making the voltage stable enough or the throttle/governor is working properly to keep the frequency stable enough for the Multiplus 2.
I am trying to establish what is causing the issue here, if it’s the generator or a setting in the Multiplus, the fuel system on the generator has recently been overhauled, checked and re-calibrated.
Some clarification is in order. The spec I found for your generator says 115/230 single phase @50 hz. You mentioned 240v which would imply a North American 2x120 multiplus @60hz. Can you post what voltage/hz is your generator configured for, and the exact model of inverter?
If you have a 60hz inverter the lowest frequency accepted under wide input is going to be 45hz. If the generator is 50hz you may be dropping enough under sudden load to cause the disconnect. These smaller generators can have a hard time maintaining proper frequency under medium to heavy load.
Sorry for the late reply, I have been very busy over the last couple of weeks….
We are based in the UK so are set and running at 50hz not 60Hz
Yes my generator is 115/230v I am running wired up in the 230v configuration, originally it was running at 230v however I have recently increased it to 240v to try and eliminate the possibility of a voltage drop, I will return it to 230v as this is what our shore supply is.
The voltage is only set on the regulator.
Part of the Onan/Cummings sales pitch was that it was very voltage stable so I don’t think this is the issue unless I have a failing component.
My inverter is a 50hz one and is what the shore supply is.
Something is causing the Victron Multiplus 2 to cut out during charging and it will do it if I start charging at around 50/60A (50% of the charger capacity) and slowly increasing the current 10A at a time… I will eventually get to the full capacity of the charger but it may take anywhere between 30mins/1hour to allow me to increase it.
Hi all, I am still having this issue (hardly surprising as I have done nothing about it).
Another post came up on another forum, and it was talking about non-linear loads and harmonics……
Basically that a Northern Lights generator(and I suspect this is for all generators), you shouldn’t load the generator more than 20% if it’s capacity with non-linear loads, otherwise the harmonics will cause issues. I think this seems to be the issue I am seeing.
I would like to load the generator more than this and try and eliminate the cutting out.
When googling this it comes up with an isolation transformer between the generator and the load.
Has anyone seen this, resolved this, or think it will work??
Any help would be appreciated.
In my experience, Onan generators can’t handle their rated load AND put out a clean waveform. As their load increases, so does the variability in frequency and voltage. I have a few recommendations you try in this order, unless you already have:
Set your A/C input current limit to 75%-80% of the continuous output rating (not the advertised rating)
Enable dynamic current limiter and if you are using the generator start/stop function on a Cerbo, then enable a 30s or 60s warm-up interval.
If it’s still wonky then disable UPS mode
If it’s still wonky then enable Weak AC
If after all that it’s still wonky, then get the thing serviced by a Cummins dealer.
Check the Onan voltage regulator (AVR) for “Droop” setting. This should be set to 0% (zero)
You can have a look at the VRM - advanced - generator measurements graphs to see what is odd at the moment the problem arises.
Post pics in this topic so we can have a view and maybe advise you on this.
Is it in a Delta-Y connection (2 phase 110V coils) ?
Is it rated 4 kiloWatt or 4 kiloVoltAmpere?
Is it rated 100% service factor or 80%
What temperature Class generator F or H ?
Lots of numbers but very important
It looks like a winding temperature safety problem
tHd-A Harmonics current (3rd/9th/12th can f#ck up the generator coils and AVR sensing) can be measured with a DC clamp Ampmeter, but still says nothing about the voltage sinus disfom percentage. tHd-V sensed in the AVR will imbalance the AVR controller output, it should be visible in the VRM generator voltage graph as fluctuations.
The harmonics is what I am thinking the issue is, will an isolation transformer isolate the harmonics from the Multiplus affecting the generator??? If not what are my options???
An isolation transformer of that size is very expensive.
An option is to fit an AVR with harmonics filter, you probably have the most inexpensive AVR original in your generator.
Request your generator supplier for a quote to fit a new AVR capable of “tellecom” or tHd filtering.
If this is 4 kVA generator, a 3,2 kW load is maximum applied at PF0.80i (inductive load) 16.6A x 240V x PF0.80i = 3187Watt
The PF (power factor) load of an inverter is likely PF1.0 and therefor only to be loaded at 3200W / 240Vac = 13.33Amp
Thanks phaseshifter, and yes the generator details are totally correct, the Multiplus charger is 12OA at 14V, but with the losses say 2kw would be some where in the range of where we would be, well below the 3.6Kw you are saying. I am lucky to get 1/2 (60A) of this before it all becomes unstable.
Yes the isolation transformer is expensive, but so is a blown up generator…. Also we are a steel hulled boat so possibly we should also have an isolation transformer to eliminate any stray currents risk??? However it’s not been an issue so far.
If a isolation transformer will eliminate the harmonics and it would stop any stray current risk it would be the way forward, but as I think the harmonics is the issue I would like to know if the isolation transformer would resolve this???
Hi Michael,
It is important to review graphs from VRM monitoring when the generator is supplying power to the MultiPlus.
can you post pic’s from the graphs for generator Vac/Aac and Hz and for the Batteries the Vdc/Adc and BMS cell Volt difference?
Your generator is a 1 phase 2-coiled stator with an imbedded digital AVR in the generator control unit (according to Cummins data) so probably well filtered
for harmonics.
so manny things to investigate first, for instance;
1-How far is the generator from the Multiplus? what cable size and how long is this cable? Are there loose connections inside the generator connection board or in a control cabinet/ fuse holder?
2-Harmonics tends to worsen the effect with high cable resistance (in fact an isolation transformer has low impedance (inductive resistance for higher frequencies like harmonics)
3-There is also a possibility that the generator rotor rectifier bridge has a leaky or faulty diode or varistor, both can make output voltage unstable.
Thanks again phaseshifter, there is lots to consider, I am away on the boat for the next two weeks on next Friday, so hopefully I can try and get some details back to you:+1:
I will be intouch:+1:
to see what is odd at the moment the problem arises.