Genny - diesel or petrol?

[Willie Trombone]

I like the look of this one...
http://www.bundupower.co.za/bp5s.php

Anyone know them?

What about lpg?
http://www.bundupower.co.za/bp8s-g.php

 

[$m@Rt@$$]

General rule of thumb - diesel has less running costs than petrol but is more expensive to service.

 

[ambo]

Another issue worth considering is that you are not legally allowed to store more than 40 litres of petrol on your property whereas you can store 210 litres of diesel. This is according to Jhb by-laws but I think the other metros will be similar.

 

[Willie Trombone]

Another issue worth considering is that you are not legally allowed to store more than 40 litres of petrol on your property whereas you can store 210 litres of diesel. This is according to Jhb by-laws but I think the other metros will be similar.

Good point!

 

[ChocolateBadger]

Wouldn't petrol be quieter?

 

[Beachless]

Wouldn't petrol be quieter?

Nope petrol is typically higher reving so the diesel gennies are quieter.

 

[savage]

Nope petrol is typically higher reving so the diesel gennies are quieter.

Diesel runs at much lower RPMs yes... Diesel gensets are typically at 1500 or 3000rpm only. Diesel engines are typically also much stronger than petrol, and therefore have bigger alternators. You won't easily see a Petrol genset over the 12kVA mark.

Gas gensets are (relatively) new in SA. Whilst I have heard good things about them overseas (where LPG is supplied by council in pips, similar to your water, and thus readily available), in SA i have never seen them used before, and also have no idea in terms of LPG usage, or how much LPG is required. You may have a problem here obtaining LPG at 2AM in the morning when you're running out, whilst it's easy to drive down to your local petrol station at 2AM in the morning to get Petrol/Diesel....

 

[reactor_sa]

Another issue worth considering is that you are not legally allowed to store more than 40 litres of petrol on your property whereas you can store 210 litres of diesel. This is according to Jhb by-laws but I think the other metros will be similar.

In that case most of us break the law everytime we go home and park a car in the garage.

 

[savage]

In that case most of us break the law everytime we go home and park a car in the garage.

Keyword that you're missing is STORAGE. Fuel inside a properly designated fuel tank (i.e. be it a 65L petrol tank in your car, or a 200L tank in your generator), is different to a 250L drum standing in the corner of your garage, filled with Petrol...

 

[Willie Trombone]

In that case most of us break the law everytime we go home and park a car in the garage.

 

[Paul_S]

Nope petrol is typically higher reving so the diesel gennies are quieter.

Most diesel generators in the 1-10kVA range run at the same speed (3000RPM) as small petrol generators.
This is because they use a two pole instead of four pole alternators.
The larger units (typically 10kVA+ and diesel) which have four pole alternators can run at 1500 RPM.

1500RPM = four pole alternator generating 50Hz
1800RPM = four pole alternator generating 60Hz (USA)
3000RPM = two pole alternator generating 50Hz
3600RPM = two pole alternator generating 60Hz (USA)

Inverter generators are different though. Because they decouple the alternator from the output load and use an inverter to drive the output load, they are able to run at much slower speeds under light load conditions. This makes them a lot quieter than the standard petrol/diesel AVR type systems which have to run at a fixed speed to maintain 50Hz or 60Hz (USA) frequency.

BEWARE
A diesel engine is not suited for constant light loads because it will glaze the cylinder heads.

Read more about generators and that issue here: http://www.turnermorris.co.za/category-pages/generator-basics

Don’t supply a diesel generator when the unit will not use at least 75% of its potential load. The unit will only last for a day or two. Diesel engines don’t like to run without any load. They will glaze, and a major engine repair will be due within the warranty period. Your customer will expect a warranty and we will refuse. Avoid this unpleasant situation at cost.

Plenty of info on Google ...

 

[Willie Trombone]

Most diesel generators in the 1-10kVA range run at the same speed (3000RPM) as small petrol generators.
This is because they use a two pole instead of four pole alternators.
The larger units (typically 10kVA+ and diesel) which have four pole alternators can run at 1500 RPM.

1500RPM = four pole alternator generating 50Hz
1800RPM = four pole alternator generating 60Hz (USA)
3000RPM = two pole alternator generating 50Hz
3600RPM = two pole alternator generating 60Hz (USA)

Inverter generators are different though. Because they decouple the alternator from the output load and use an inverter to drive the output load, they are able to run at much slower speeds under light load conditions. This makes them a lot quieter than the standard petrol/diesel AVR type systems which have to run at a fixed speed to maintain 50Hz or 60Hz (USA) frequency.

BEWARE
A diesel engine is not suited for constant light loads because it will glaze the cylinder heads.

Read more about generators and that issue here: http://www.turnermorris.co.za/category-pages/generator-basics

Plenty of info on Google ...

That's quite an issue there. A couple of days? Eish...

 

[savage]

Most diesel generators in the 1-10kVA range run at the same speed (3000RPM) as small petrol generators.
This is because they use a two pole instead of four pole alternators.
The larger units (typically 10kVA+ and diesel) which have four pole alternators can run at 1500 RPM.

1500RPM = four pole alternator generating 50Hz
1800RPM = four pole alternator generating 60Hz (USA)
3000RPM = two pole alternator generating 50Hz
3600RPM = two pole alternator generating 60Hz (USA)

Inverter generators are different though. Because they decouple the alternator from the output load and use an inverter to drive the output load, they are able to run at much slower speeds under light load conditions. This makes them a lot quieter than the standard petrol/diesel AVR type systems which have to run at a fixed speed to maintain 50Hz or 60Hz (USA) frequency.

BEWARE
A diesel engine is not suited for constant light loads because it will glaze the cylinder heads.

Read more about generators and that issue here: http://www.turnermorris.co.za/category-pages/generator-basics

Plenty of info on Google ...

That is news to me... It's strange that *no* vendor makes mention of this at all for any of their generators purchased...

Seeing that the engine runs at a constant RPM (1500RPM or 3000RPM), the engine rotates at a constant speed, and as does the alternator. With the engine at a constant speed, I can't quite understand how less load will harm the CYLINDERS for the *engine*

Overloading a generator can harm the ALTERNATOR yes, but I fail to see any mechanical or electrical reason why UNDER loading will harm the *engine* of the generator. The electrical load may have an impact on the alternator, but I highly doubt (even more so in the case of under loading) that a load can harm the engine itself.

Almost all big generators have overload protection and massively complex control panels. All the control panels (that's worth something) monitors the alternators for OVERLOADS (and shuts down), but I have not yet seen one single unit that monitors UNDER loads...

Also brings up an interesting point of topic as a lot of vendors recommends you to regularly run and test your generator... Most would do that without transferring load to the generator as transferring load may be disruptive.

 

[savage]

Well - there I've learned something new today.

 

[Paul_S]

That is news to me... It's strange that *no* vendor makes mention of this at all for any of their generators purchased...

Seeing that the engine runs at a constant RPM (1500RPM or 3000RPM), the engine rotates at a constant speed, and as does the alternator. With the engine at a constant speed, I can't quite understand how less load will harm the CYLINDERS for the *engine*

It was news to me too but there seems to be enough info out there to back it up.
Even Wikipedia mentions it.

Diesel engines can suffer damage as a result of misapplication or misuse - namely internal glazing (occasionally referred to as bore glazing or piling) and carbon build-up. Ideally, diesel engines should be run at least 60% to 75% of their maximum rated load. Short periods of low load running are permissible providing the set is brought up to full load, or close to full load on a regular basis.

Internal glazing and carbon build-up is due to prolonged periods of running at low speeds or low loads. Such conditions may occur when an engine is left idling as a 'standby' generating unit, ready to run up when needed, (misuse); if the engine powering the set is over-powered (misapplication) for the load applied to it, causing the diesel unit to be under-loaded, or as is very often the case, when sets are started and run off load as a test (misuse).

Running an engine under low loads causes low cylinder pressures and consequent poor piston ring sealing since this relies on the gas pressure to force them against the oil film on the bores to form the seal. Low cylinder pressures causes poor combustion and resultant low combustion pressures and temperatures.

This poor combustion leads to soot formation and unburnt fuel residues which clogs and gums piston rings, causing a further drop in sealing efficiency and exacerbates the initial low pressure. Glazing occurs when hot combustion gases blow past the now poorly-sealing piston rings, causing the lubricating oil on the cylinder walls to 'flash burn', creating an enamel-like glaze which smooths the bore and removes the effect of the intricate pattern of honing marks machined into the bore surface which are there to hold oil and return it to the crankcase via the scraper ring.

Hard carbon also forms from poor combustion and this is highly abrasive and scrapes the honing marks on the bores leading to bore polishing, which then leads to increased oil consumption (blue smoking) and yet further loss of pressure, since the oil film trapped in the honing marks is intended to maintain the piston seal and pressures.

Unburnt fuel then leaks past the piston rings and contaminates the lubricating oil. Poor combustion causes the injectors to become clogged with soot, causing further deterioration in combustion and black smoking.

The problem is increased further with the formation of acids in the engine oil caused by condensed water and combustion by-products which would normally boil off at higher temperatures. This acidic build-up in the lubricating oil causes slow but ultimately damaging wear to bearing surfaces.

This cycle of degradation means that the engine soon becomes irreversibly damaged and may not start at all and will no longer be able to reach full power when required.

http://en.wikipedia.org/wiki/Diesel_generator

 

[savage]

Well - from what I'm seeing, it only happens when the generator is idle and do not have any load at all. A load even as low as 30% is sufficient and it is also generally tied to cold ambient temperatures which reduces the temps around the cylinders.

Most generators won't idle for very long and will be shut down automatically when power is restored, so not a big issue. It most certainly also does not happen "in a couple of days."

When wet stacking occurs, it is also fairly easy to get rid of it, if it is caught in time, simply by putting more load on the generator for a few hours. It's as simple as a few 1000W lights for 3 or 4 hours

I don't think I am personally going to break my head about this one, just yet. I have a buddy that is a commercial diesel mechanic (working mainly on big trucks / tractors). I'll be sure to pick his brain on this as well when I see him again

I still don't get exactly how a engine running at a constant RPM, can be hotter or colder though. The only thing that I can think of, is that maximum RPMs are either 1500 or 3000, and the generator actually turns much lower at less loads.

 

[Paul_S]

I still don't get exactly how a engine running at a constant RPM, can be hotter or colder though.

Easy. Cylinder temperatures have nothing to do with RPM.
The lighter the load the less fuel needs to be burnt the less energy (heat) is generated.

 

[savage]

Easy. Cylinder temperatures have nothing to do with RPM.
The lighter the load the less fuel needs to be burnt the less energy (heat) is generated.

The lighter the load thing got me. But it was explained to me nicely now by my father in law (master electrician - industrial). I never knew this, but the more the load on the alternator (i.e. load), the less the alternator would want to turn. Because the alternator would naturally want to turn less, the engine would work harder to turn it at a constant RPM. Thus yes, a low load on the alternator would mean less load on the engine. Definitely learned something here today

It's easy to sort this out though (still), by just putting some more load on the generator. Couple of hair dryers, strong lights, stove, etc.

PS: The same happens to petrol engines (and even (old) cars). And in a car the resolution to fix the issue is the same... Open the throttle and take the car for a long, fast drive to properly work the engine.

 

[pulling wire]

Its always a good idea to purchase a generator that's going to run at 1500 RPM as opposed to 3000 RPM, the engine will last longer.
I know with 3 phase power its important to balance the load on each of the phases, and sometimes (as last resort) the electricians need to install a load bank in order to achieve the balance.
Very important to correctly spec the generator required, as with most motors your start up load is usually double the watts/amps requirement once running. you need to consider that you only want to run your generator at 70% capacity and you need to take into consideration the effect altitude has on the engine/alternator its 1% per 100m above sea level.
Its also not a good idea to run the Generator under too little load as that would mean the glazing of the cylinders.
There is much to consider when purchasing a generator above 10kva.

 

[lawrence@netcomp.co.za]

Ollie

I have a Generac 13Kva running off LPG Gas bottles. Being in the IT industry, I have supplied many different sizes of Gennies to my clients.
When it came to my own decision, I wanted something that looked less industrial and also not as noisy as my portable 6Kva Ellies Gennie. once I heard about the Generac, I went to see it and was immediately impressed with it's build quality and design.
I had it installed about a year ago and have not had any issues. It seems to have a 1000cc Honda or similar twin engine in it. It stands right outside my home office and I must say, it is a hell of a lot quieter than a diesel or petrol. You have to install it with the ATS to make it a totally seamless integration. The gas installation must be done by a licensed installer and has to comply with normal gas installation rules. I have it running off 2 x banks of 9KG gas cylinders (one being a standby set) The law states that you are not allowed to have more than 100Kg gas on the property, so it is within the law to do this type of installation. I believe it is quite economical and have recommended this Gennie to many of my clients. I have also been impressed, over all, with my dealings with Carly at Bundu Power and can recommend this type of solution to everyone. The unit also runs off Piped Gas. It has a maintenance cycle that runs the unit for about 5 minutes, once a week, if no power outages were experienced. Remember, that most Diesel gennies don't have weatherproof cowls and this must still be included, as well as exhaust extensions, etc.