Generator 2pole (3000rpm) vs 4pole (1500rpm) power/size Q

[vas]

good afternoon all,

having finally fixed my yanmar (various air in fuel issues) I did some calcs and realised that other than creating lots of noise, having a 3000rpm 8KVA generator is pointless for me.
So, was thinking if I should get a smaller 1500rpm generator and be done with!
I've already paid more than 400euro for good quality sound insulation and probably need another 400 to finish off with debatable results... If I can get a s/h genetor for around that much, I may go ahead.

Facts:
yanmar 2GMF 11hp @3000rpm MECC ALTE MR2-160/2 8KVA
now keeping the yanmar and considering that it's doubtful this small 2cyl diesel it will be making more than 5hp @1500rpm (checked some graphs seems to be around that)
WHAT should I be mating it with? 4, 5, 6 kVA?
my needs (watermaker, rarely aircon, or battery charger) don't need more than 12-14A < 4kVA
finally for what it's worth, my generator has a MD35 mounting.

any ideas welcomed!

V.

 

[vas]

replying to myself...

since the generator is an old school thing with two hefty capacitors-no AVR or whatnot- do I have a chance of running it at 1500rpm and convert the hopefully 110V it will produce to 230V through a 4-5KW step up transformer like this :
VT-4000 Step Up/Down Voltage Transformer, 4000 Watts – Voltage Converter Transformers

My only concern is that maybe the generator wont produce anything at less than 2000+rpm so no 110V to start with, easy enough to test tomorrow.
Just wondering for any flaw in the logic!

Anthony?

cheers

V.

 

[rafiki_]

Vas, I have a 6KVA on my Azi. No air on though. It is a Koehler, 3 cyl and very quiet. You really need to be in the cockpit to hear it. However I don’t think it would power your a/c

 

[vas]

P, should be OK, mine is a 28kbtu unit (iirc) doesn't even use 15A when running!
yours is v.quiet because it's 1500rpm, mine's screaming it's balls off at 3k rpm (redlines at 3600 or something...

V.

 

[ARE]

5hp is 3.75kW, so with losses don’t expect anymore than 3.4kW max.

Motor starting loads may also be an issue at 1500rpm with such a small engine.

 

[vas]

5hp is 3.75kW, so with losses don’t expect anymore than 3.4kW max.

Motor starting loads may also be an issue at 1500rpm with such a small engine.

watermaker and stabs STAR pump are on inverters so soft starting, no issues there.
OK, checked, aircon run in cool mode is 7A, heat a bit more, startup current though is 36A .
BTW, there's also a 3KVA Victron Multiplus now onboard and that could "top up" the needs of any starting engine, so should be ok.

A, is my idea of temporarily playing with a tranformer running the engine at lower rpm, viable or plain silly?

V.

 

[Portofino]

Have you ran it 1500 rpm ?
If so sufficiently quieter ?

 

[ARE]

watermaker and stabs STAR pump are on inverters so soft starting, no issues there. TBH, haven't checked aircon start current...
BTW, there's also a 3KVA Victron Multiplus now onboard and that could "top up" the needs of any starting engine, so should be ok.

A, is my idea of temporarily playing with a tranformer running the engine at lower rpm, viable or plain silly?

V.

Lower rpm will be lower frequency. You can’t do that.

that’s why the number of poles denotes the engine speed, 2pole = 3000rpm 4pole = 1500rpm 8pole = 750rpm.
The only way to slow the engine is to belt drive the generator speed back up to 3000rpm.

 

[vas]

Have you ran it 1500 rpm ?
If so sufficiently quieter ?

hell yes! the difference is really amazing. Haven't actually checked if this old generator will be producing anything at 1500rpm (talking about the step up transformer hack)

V.

 

[vas]

Lower rpm will be lower frequency. You can’t do that.

that’s why the number of poles denotes the engine speed, 2pole = 3000rpm 4pole = 1500rpm 8pole = 750rpm.

oops. forgot about that you are right A!
Hz was the way I was initially measuring the rpm of the engine on my arduinos (no alternator on and no crank sensor either)

So only option is to replace the generator bit with a 3.5kW 4pole job, correct?
wonder if I can get any s/h at decent price!

cheers

V.

 

[Portofino]

Something like this maybe ? Belt + suitable pulleys 2 to 1 so the 1500 rpm engine can spin it at 3000 rpm
Clarke 6kVA, 3000rpm Alternator (1 phase)

Or google “Power take off generators “ .

 

[bristoljim]

Something like this maybe ? Belt + suitable pulleys 2 to 1 so the 1500 rpm engine can spin it at 3000 rpm
Clarke 6kVA, 3000rpm Alternator (1 phase)

Or google “Power take off generators “ .

Once you go to belt drive you can easily choose engine revs up or down to match a generator,the GM engines arnt too bad for noise @ 2000 rpm
Jim

 

[vas]

PF,

juggling in a particular frame and space, a 30-50kg generator alternator with pulleys et al in reference to a 50kg 2cyl diesel yanmar is not easy nor cheap...
If I go ahead with this project, it will be a (hopefully) 400-500euro 4-5kW 4pole generator that will mate perfectly and securely to the engine preferably using this BD35 frame.
and tbh, I doubt I'll go ahead in this as it seems to be a bit too much hassle for what it's worth unless of course I do come across a cheap s/h one!
Realistically, with my summer vacation pattern, I'll probably use the generator for 6-7h this summer (assuming we do get to use the boat for July and August!) for the watermaker.
The rest will be via inverter while motoring with the IVECO alternator + solar returning most of the amps lost to the Trojans.
Same with hot water tank heating - not convenient (I think!) to connect to an engine.

Jim, you are right at 1500-2000rpm the 2GM sounds sweet (and fairly quiet)
Don't want to even think how many belts /pulleys I'd need to pass 5+hp from the flywheel to the generator though...
Not really feasibly imho and I've done my fair share of improbable things with the boat, but I'd draw the line there!

cheers

V.

 

[ARE]

PF,

juggling in a particular frame and space, a 30-50kg generator alternator with pulleys et al in reference to a 50kg 2cyl diesel yanmar is not easy nor cheap...
If I go ahead with this project, it will be a (hopefully) 400-500euro 4-5kW 4pole generator that will mate perfectly and securely to the engine preferably using this BD35 frame.
and tbh, I doubt I'll go ahead in this as it seems to be a bit too much hassle for what it's worth unless of course I do come across a cheap s/h one!
Realistically, with my summer vacation pattern, I'll probably use the generator for 6-7h this summer (assuming we do get to use the boat for July and August!) for the watermaker.
The rest will be via inverter while motoring with the IVECO alternator + solar returning most of the amps lost to the Trojans.
Same with hot water tank heating - not convenient (I think!) to connect to an engine.

Jim, you are right at 1500-2000rpm the 2GM sounds sweet (and fairly quiet)
Don't want to even think how many belts /pulleys I'd need to pass 5+hp from the flywheel to the generator though...
Not really feasibly imho and I've done my fair share of improbable things with the boat, but I'd draw the line there!

cheers

V.

Onan use a belt drive on their 4kW and 6kW units, the engine runs at 2400rpm and the belt drive (6 rib poly v belt) runs the generator at 3000rpm. It works perfectly. Ideally the engine and alternator need to sit next to each other.

 

[vas]

Onan use a belt drive on their 4kW and 6kW units, the engine runs at 2400rpm and the belt drive (6 rib poly v belt) runs the generator at 3000rpm. It works perfectly. Ideally the engine and alternator need to sit next to each other.

interesting didn't know that! Is it a "sealed" enclosure where this takes place, or open like the waterpump/alternator pulley setup?

I can see the point, 2cyl kybota 480cc running at 2400rpm for 4kW
compared to my yanmar 2cyl 590cc 13hp@ 3400rpm, tbh not much in it.
I guess that's why these seem more square than typical generators.
Are there any pics of this 4/5KW ONAN with the lid off by any chance A? Interesting to see how many belts/pulleys they employ! Doh, missed the bracket in your post, so just a 6rib poly v belt for 4-5hp, not bad!
TBH, will be a fair amount of work and if I only get down to 2.4k rpm I'm not gaining much, will have to see the power curves of my 2GMF and see what I can get at around 2k rpm when it's nice and quiet.


V.

 

[ARE]

interesting didn't know that! Is it a "sealed" enclosure where this takes place, or open like the waterpump/alternator pulley setup?

I can see the point, 2cyl kybota 480cc running at 2400rpm for 4kW
compared to my yanmar 2cyl 590cc 13hp@ 3400rpm, tbh not much in it.
I guess that's why these seem more square than typical generators.
Are there any pics of this 4/5KW ONAN with the lid off by any chance A? Interesting to see how many belts/pulleys they employ! Doh, missed the bracket in your post, so just a 6rib poly v belt for 4-5hp, not bad!
TBH, will be a fair amount of work and if I only get down to 2.4k rpm I'm not gaining much, will have to see the power curves of my 2GMF and see what I can get at around 2k rpm when it's nice and quiet.


V.

I will send you some pictures tomorrow, I have one here in bits at the moment.

 

[Assassin]

Not sure of your set up or layout, so here goes.

You can dampen or suppress noise in various ways, can you replace your silencer or fit an aftermarket item which better dampens the most offensive frequencies? this is something we do on industrial engines and the latest silencing technologies using squish type methodologies better silence without affecting the flow, some actually improve it.

Can you fit additional silencing, cars and lorries have soundproofing and while tins comes ready moulded you can get various types of soundproofing in lengths or even rolls, while most vehicles use various forms of popper clips to hold them in position, there is the option of using glue to attach it and the favoured types are epoxies or rubber based glues.

 

[vas]

thanks,

you are of course absolutely right in your suggestions, just to give some extra info, my layout is as follows:
e/r insulated (not perfectly) with 40mm special v.bloody expensive sound thing with a rubber barrier in the middle and an aluminium foil outside. Glued and bolted on the bulkhead and salon floor (well e/r ceiling really)
Have a few spots I need to do and the cable ducts to salon and lower helm to insulate as well.
Exhaust has both a vetus silencer and a duck thing before it, so it's OK. Further it goes to the stbrd underwater exhaust, so really no noise from the exhaust.
Main issue is that the GRP "box" of the generator, a five piece internally insulated assembly was in such a sorry state and soaked with oil that I removed it and scrapped half of it during the rebuilt.
Further I'm reluctant to building/fitting a new one as I really like to have a decent visual contact with all my engines and that's not going to happen if I enclose it. Had a few horror stories with friends boats and enclosed old generators, don't want to have the same! And even like now, noticed a small weep from the seawater pump of the yanmar that was rebuilt 30h ago (more or less) so need to remove it next week and get it redone again - probably just the seal this time.

So, going 1500rpm seems an easy way to lower noise, together with the fact that I don't really have a need for the full 8kVA output of mine.
It's really a balance between cost of insulating vs cost of replacing the generator with a 4KVA 1500rpm one.
I'm finalising the rewiring of the lot due to the installation of the Victron Multiplus 3000, meaning I'll route all gen output through the Victron so starting current for the aircon (the only big starting load as the other two have soft-starting inverters installed) will be catered for by the Multiplus no matter I have a 3, 4 or 8kW generator.

My initial search for smaller brand new 4pole generators gives me 600euro for a 3.5KVA one. Cannot seem to find a cheaper one, if anyone can, please let me know!
Then it's the issue of mounting it to the yanmar, my MECC ALTE has a MD35 flange fitted and bolts straight on. Generator has only got a bearing at the far end, and floating mating to the engine side, doesn't seem that easy to find a small new generator with this mount... It's easy if I go 8-10KVA+ but I need to go small not large!
FWIW, the 2GMF produces 13hp (9.7KW) at 3400rpm (DIN6270A), ~11.7hp (~8.7KW) at 3000rpm and only ~5hp (~3.7kW) at 1500rpm. As ARE says that's only good for a ~3.5KVA generator
if I go the pulley route (and without knowing the cost of pulleys which I'm afraid could be significant) I can get a 3000rpm (2-pole) 4KVA one for 200euro. What if pulleys/belts/brackets/messing about are another 300euro?
So doesn't seem to be viable solution. Waiting to see ARE's pics of the small ONANs that employ this, pretty sure they will have a custom cast item mating them and will decide...
Maybe I should first try to improve insulation only my back is not at it's best to twist and bend to reach all these cavities and fill them up atm...

cheers

V.

 

[Portofino]

We have a small 3.5 so average is really 3 to play with MASE that is powered by a 400 cc single cylinder Yanmar .
Its air cooled the engine so has a finned cylinder head like a motor bike .I think it’s spins a bit lower than 3000 , more like 2800 or something? It’s all we need and it’s light less than 100 kg and consumes 1/3 rd L / hr .It powers our 62 k Btu Aircon with room to spare .A finned engine does not have the luxury of a water jacket for noise suppression btw .
So my start position is worse than yours ?
Its got an insulated box that consisted of 4 covers which easily remove for access .
Initially it was noisy .

So I researched the issue carefully .Even viewed new 1500 at boat shows as well .

Exhaust is out the stern .About 10 Cm above the WL and I like to hear the trickle tell tale of the water pump .
Water pump is for the charge air cooler to cool the air in the box .No water touches the engine or the gen windings .So it’s basically never gonna die ...rot out .
The box obviously needs an air in and out so it’s cant be totally enclosed .
Existing box does not cover the base as that’s the air supply route in / out .A fan draws air in one end cools it ( via the seawater charge air cooler ) before blowing it over the fins .This is hot ER air btw .

Anyhow apparently it’s the shape + material of the Immediate surrounds that are as important as the sound proofing its self.
No no s are plywood that super resonates , flat surfaces worse with plywood .
Sure the density of the surround material , the box and thickness helps .
Mine is in the centre over the V .So sound coming out from under is deflected at an angle not bounced straight back .
Its between too 800 L fuel tanks .They have to drop to 2/300 L for the adjacent sides to become hollow so to speak.
The flat BH behind it I fitted that soft knobbly foam sound proofing to break up the flatness

So having analysed / surveyed it I made sure the existing panels fitted tight , a few had warped = gaps .New rubber straps to keep it tight .
Bought some after market sound proofing to glue inside the existing.These were lead lined on the outside and like a sticky 5 mm adhesive tar on the inside ,Again nice gap free fit ,Primarily used for car bulkhead insulation. Quite heavy btw ....a good feature .
This made a huge reduction there and then .

Then re did the ER ceiling in some after market sound insulation.It had some I just added another layer on top ....some Al honeycomb stuff bolted / screw attached .

In the end as well as hushing the main engines the geny significantly hushed up . It just a faint hum now .

So it might be worth re adjustment of the surrounding surfaces ..change the texture + materials + checking the existing box fits .
Basic stuff like that perhaps remount it so it’s not sat on the flat surface .....then complete the ER sound proofing properly.

 

[vas]

PF, I agree, but easier said than done...
Started today though by the basics, bolting down the 20mm ply plate that the gen sits on and securing with M10 bolts and nuts the steel frame to this ply. ATM all was wobbling about as I'd not bothered fixing them since the gen rebuilt and all the messing about.
Definitely more secure, minor noise reduction. Went about with my mobile with a dB soundmeter app and measured the following:
aft deck 49dB
salon 48dB
lower helm 47dB
corridor at the cabin level 44-45dB
bow cabin door closed 39dB
salon with gen off 25dB

got a few more pressing issues to solve (install a TECMA and sort out some issues with venting hot air from the fridges) once I get through them I'll look at it.

V.