Victron System - Generator Suggestions

Hi there,

I’m in the process of having my Victron system upgraded and i am looking for a generator to compensate for those rainy summer days.

The system will be completely off grid.

Any suggestions on generators that the installer can use?

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Welcome here.

What size system will you be installing, do you know yet?
Victron recommend you use a generator the same size if not bigger than your inverter/s, since it must ideally be able to handle the entire load.

There are some technicalities with generator earthing and Victron inverters, @plonkster will be able to advise best, all I know is the typical small Chinese generators from Builders etc. does not work well, if at all, it was discussed here somewhere in the past.

I would not necessarily say I am the best generator expert. In this case it might not matter too much though. A lot of the issues people have with generators are in hybrid systems that also operate as ESS systems when the grid is on. The inverter then has a grid code selected for the AC input, which sometimes makes it a bit picky about what it will accept.

For an off grid system, this is much less of an issue. I would suggest a Diesel generator, running at 1500rpm, ideally the same size or slightly larger than the inverter. I don’t have much experience with petrol generators, and those small ones that stutters every 6.7 seconds because someone sneezed near the air intake will probably cause you only heartache.

@plonkster Is this where you’ve been hiding out all these years. You helped me with my initial victron install 6 years ago. Your other friend is going to do the upgrade for me now :slight_smile:

We are installing 3 Multiplus II 5000’s

The purpose of the genie is not to run the load, its to slowly charge the batteries.

Would you by any chance have a link or two for these type of genies you are referring to?

I was contemplating this generator. Its only on special for 4 more days.

But not sure if it will work nicely with the GX device to switch on if batteries are below a certain level.

However, i have the feeling you are referring to these generators or possibly this one

This generator seems to good to be true … (3000rpm though)

The problem is, you won’t be able to configure things for the generator to only charge the batteries, it will firstly take over any loads and only then use the surplus capacity to charge the batteries, hence Victron’s recommendation that it should be a similar size to your inverter.

I guess you can come up with some clever automations to turn off all heavy loads as the battery SOC drops under a certain threshold, just before the generator starts up, then only turn on those heavy loads again after the battery has been charged back up to a certain SOC and the generator switches off. This however might not be too practical, especially in a off-grid system.

Something else you have to consider is the size of your batteries and how long it will take a generator to charge it back up. The smaller the generator, the longer you’ll have to listen to it while charging up your batteries. There’s nothing worst than having to listen to a generator all through the night, petrol or diesel, silent canopy or not.
Choose a bigger generator and you might only have to run it for a hour, rather than 4.

Indeed, those smaller Diesels is what I would prefer for myself, but of course, they are double to three times the cost of the cheapie petrol. That 5.5kVA is probably going to be fine, I just cannot guarantee anything.

Re. Victron and generators, they have put in a lot of effort to monitor/stop/start generators that can link to a Venus/Cerbo.

I would start there.

One document of the possibilities:

The links in the attached doc is very valuable, thanks.

Thx, i read in one of Victrons tests the following:

For a 50Hz output, the engine of a direct drive genset with a 2 pole alternator must run at
3000rpm. With a 4 pole alternator, rotation speed is reduced to 1500rpm. More poles, and
lower rpm, are not practical.
Gensets can therefore be split into two broad categories: those running at 3000rpm and those
running at 1500rpm.

Like plonkster mentioned (I never doubted) 1500rpm according to their tests in this doc is also easier on services as well as more silent and uses less fuel.

I for the life of me just can’t seem to find any reasonably priced 1500rpm generators. The “reasonably priced” ones are all 3000rpm.

It also appears as though going using the “Generator Start/Stop” on the GX is more feature rich than ESS when connecting via the relays on the inverters itself.

But i am not too bothered with the connection details though, i have 100% faith in Jaco to connect this the best he sees fit.

It’s just the purchasing of the generator that is a bit scary for me. I want to make sure i get the right first time.

Apologies … never responded.

Yeah, let me not create another thread for cheap generators.

Instead I’ll be heeding the advice of the experts here and look at 1500/3000rpm diesel genies.

What size system will you be installing, do you know yet?

Just doubling my system. Going from around 5kw panels 10kw, upping my batteries from around 15kw to roughly 30kw and inverters from 3x3000’s to 3x5000s

Biggest thing is getting it done right. I initially did a self install, so you will prolly see a name and shame with pictures of “how not to install solar” :slight_smile:

4 pole 1500 rpm or 2 pole 3000 rpm is not an electrical difference, It is a mechanical difference to bearings and such.
A 600rpm Lister on a DC generator through an MPPT direct on the batteries would probably outlast you and me both.


Not too long ago I missed out on a 15 kVA Lister by 30 minutes or so, a old lady on a farm sold it for R4k. I’m still kicking myself.

Exactly, but it is usually easier to find out the RPMs of the engine than the configuration of the alternator.

A Diesel is happiest around 1500rpm. Most tractors and many lorries have their red line at 2500rpm and you almost never go above 2000rpm anyway. When you’re running a plow or some other implement, you typically select a gear that allows running at 1500rpm all day long.

While you can increase the RPMs (and in passenger vehicles they do that, up to around 4500rpm), it involves shortening the stroke and lightening the pistons, playing with injection timing, and so forth, all things that make it less efficient.

You can also run the engine at 1500rpm, but use belts and a 2:1 pulley ratio with a 2-pole alternator. My father’s workshop setup was like that (before they got Nampower).

Some time ago I bought a Kubota RK60 (6HP single cylinder 2400rpm diesel). Since it is water-cooled, my plan is to run it as a combined heat and power plant, giving about 2kW battery-charging @1500rpm with 2kW heat to the geyser (and 2kW lost and not recovered). The cooled exhaust will need to run into a rock bed to kill some noise and catch the dust produced under load.


So… while I was on holiday I heard that apparently, some people are selling Diesel generators with a center-tapped alternator. What in the world of unholy contraptions are these things? A generator cannot be connected to a house in South Africa unless it can be TN bonded (center-tapped cannot), and I would think anyone spending more than the average amount of money on a generator is very likely to want to install that as house backup…

Anyway, just wanted to add that: Apparently being expensive isn’t a guarantee that the thing will be fit for purpose.

that would surely suck.

What symptoms would it give if it was a “center–tapped” alternator?

First, you will get a voltage measurement between earth and neutral of about 115V. This either indicates that it is center-tapped or unbonded.

(Due to capacitive coupling through the air and other insulators, an unbonded alternator will tend to show roughly half the voltage from live and neutral to earth anyway, when measured with a high impedance meter, such as a DMM, so this test may not be conclusive).

To find out which one it is, sometimes a visual inspection will tell you. Opening the junction box on the alternator will reveal three connections with the middle one physically earthed. Although there are other ways to work this out.

The easiest way is to put a load of around 50W to 100W (such as an incandescent lamp) between neutral and earth, while also measuring the voltage. If it is center-tapped, the lamp will dimly illuminate and the voltage will remain around 115V. If it is unbonded, the lamp will remain off and your neutral/earth voltage will drop to close to zero. In this case, you can simply bond neutral to earth yourself (and must, to comply with SA regulations).

I think most small generators are centre-tapped for safety reasons.
(There may even be regulations mandating it, but I don’t know for sure).
I know there are SA regs that state under no circumstances are these mobile jobs to be connected to a house.

You can modify some by moving a wire, but I think you can’t get to it on the Honda range.

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Yup. For mobile use, the idea is that the maximum voltage in the system, relative to ground, is 115V. Not safe-safe, but a lot less dangerous than 230V.

Ironically the same reason holds for the American split-phase setup. Technically they have a 240V single-phase supply like most of us, but by adding the center tap and making two “legs”, it is made safer.