240v alternator

[robertevans]

Hi I am refiting my boat, I am thinking of fitting a generator and a 240v alternator to engine as a backup.
most folks have a honda backup but these are costly.
my problem is this i want to use the 12v engine alternator just to charge engine battery and use the 5kw 240v alternator to charge house batterys and apliances washer dishwasher ect
1. will the 240v alternator only put engine under load to the amount of load its put under ie if no load is put on it no hp of engine will be lost.
2. this 240v alternator makes 240v at 3000 revs this is not a problem set engine at 1500 and have alternator pulley half diam of crankshaft pulley, this is fine if i am just using engine to make 240v, but while on the move under engine if i need more speed the alternator will make more volts what can i fitt to stop this.
thanks in advance robert

 

[BobOwen]

What you're speculating about sounds like a good idea but in practice is difficult to achieve on a boat engine.

Electrical generators run at a fixed rpm. With no electrical load they use low fuel levels. As the electrical load increase, the engine is supplied with more fuel, but rpm are maintained at a fixed speed.
You would need some automatic device to operate the fuel rack to achieve this on a standard engine with mains alternator.
Your boat engine, set for say 1500 rpm and no electrical load will drop in rpm as the electrical load is applied. The throttle would need to be opened up to maintain 1500 rpm and closed again as the electrical load decrease. In other words, constantly varied to maintain 1500rpm on the alternator.


Which also leads to the second question too. Generators run at fixed speed because any variation in rpm from the alternator design speed, will give you a different frequency output - which will upset / destroy many electrical items.


It would be much easier to have a good 12V alternator (2 if you need it) with a decent regulator (Sterling etc) setup for all batteries and use your generator as a stand alone for those mains powered devices.

Though its difficult to imagine a general purpose engine regulator being available for a multitude of engines and installations, there may be some device available I'm unaware of, so other forumites may be able to help there.

 

[robind]

How did landrover deal with their set up I remember being operational and receiveing 240 volts from a running landrover engine?????? was there a hand throttle or some voltage regulator?

 

[Salty John]

I agree.
In fact there is a device called a Sea Power generator in the USA that electronically compensates for the varying speed of the engine to maintain ac current at a constant frequency. I've just deep-sixed the one that came with my boat because it was unreliable, and the original manufacturer has gone out of business. A separate generator set is a much better idea, if your ac requirements can't be met by inverter or shore power.

 

[BobOwen]

I couldn't find anything in a quick search on the web about a 220 alternator for LR. Perhaps it was from an inverter with 12V in - 220 ac out?

LR also do welding alternators to allow mobile welding too - but only when stopped! Throttle control is much easier here - theres either load on or not so you'd only need two throttle settings. Tickover and on load.

Many cars have some device fitted that maintain rpm when under heavy load. This is used at tick over and the A/Con compressor comes on for example. You can see the rpm dip, then recover.

I think its little more than a nudge to the throttle though I seem to recall the last Jap car I had, used something a little more sophisticated. Can't remember quite what it was though. Maybe some vacuum operated solenoid that pulled on the throttle with load?

 

[vyv_cox]

Suggest you talk to Beta Marine. I have an advertisement of theirs in a magazine that seems to offer exactly what you want. However their website doesn't seem to mention it. Could be worth a phone call though. http://www.betamarinenc.com/betauk.htm

 

[Ships_Cat]

With a marine diesel (assuming your boat's engine is diesel) you will find that it is speed governed so that when the alternator (or any other load) comes onto it, it will maintain its speed unless it is poorly governed or the increase in load is so large that the engine bogs down.

But that does not solve the problems of managing the alternator excitation and frequency with ordinary changes in engine speed, etc.

I have not followed up the reference that Vyv_Cox has given but another (or perhaps it is the same?) avenue that may be worth exploring is the electronic control systems used on variable speed generators (as you are probably aware generators are normally governed at a set speed in order to manage frequency).

They manage the situation by converting the output from the alternator to high voltage DC then converting that back to AC using inverter technology - which for your case really could lead you to just simply getting around the whole problem by using an ordinary regulated DC output alternator into an inverter.

Personally, I would not go down the 230 volt alternator path you are travelling except if driven by curiosity rather than practicality.

John

 

[robind]

How about an extra pulley on the crank and a large car alternator from a breakers (Bosch from an Audi) along with a couple of batteries and a cheap invertor, max cost a couple of hundred quid! Oh and a switch and a light to excite the coil!

 

[nimbusgb]

The most elegant way I can think of to solve this problem is a hydraulic pump attached to the engine with an hydraulic drive to the 240v alternator. The alternator speed could be throttled sperately to the main engine. As long as the 5kW was available you would have a stable systems.

It would however be a custom system and as mentioned before, using a large alternator and installing an inverter is a much simpler, cheaper and more reliable solution

 

[vyv_cox]

I always assumed that wind turbines (the big ones) needed to get up to synchronisation speed before they could generate to the grid. When I visited one I was told that this is not the case. They generate almost as soon as they are turning and the electronics sort out the synchronisation. The one I visited was a 5 MW unit but in the light wind of the day it was producing a couple of kilowatts! So there are evidently ways of sorting this out but as a pretty much non-electrical person I leave the explanation to others.

Vyv

 

[Ships_Cat]

I have only worked in hydro so not that familiar with wind, but I think the older wind generators worked as you assumed with them being cut in at some speed below synchronisation, around 85%, and the grid would pull them up and help keep them synchronised (I assume because the generators are so small the influence of one out of sync on the grid is negligible - but see comment below). The modern ones are variable speed and electronically controlled so cut into the grid at some early stage of rotation, but I don't know the electronic details.

My understanding is that there have been a few issues with frequency stability on grids that have a considerable part of their generation capacity from wind so the synchronisation must be weak. I don't know, but suspect that each turbine is so small that the grid plays a part pulling them into synchronisation (so operates a little like a fan) so if they all start wandering then the grid becomes unstable if there are not big synchronised machines (hydro/thermal/nuke) on it as well to keep the grid solid.

John

 

[trouville]

If you really have to have a 240v generator(i used mine less than once a year!)Then just buy a cheep 2 stroke 650w or 1800w or even 2200w (the last two being the noisy ones) Throw the engin overboard and run it from a double pully drive from your diesel.
An old lawnmower manual or car electrmagnetic cluch added to disengage.The generators hear at a jumbo cost from £60 to just over £100,Chucking the 2 stroke engine over the side might invalidate the two year garentee!!!

 

[TrueBlue]

Beta know a lot about generators and gen sets. i have a SeaPower originally supplied by them and it's still going strong.....

They now supply a unit made by Electrolux, but it's not cheap,round about £2.5k and they probably will only fit it as part of a new engine.

Your best bet - especially if you don't want to spend loads of cash is to get either a 3kW generator - lots off eBay. I just bought a new one for £165..

Better still a Diesel set for some 300 squid. Safer. Jolly heavy at 90 Kilos.

 

[JVL]

Machine mart sell 220v alternators

 

[roly_voya]

Re: 240v alternator Beta generator

I got all the specs for this but it is really designed for canal boats - they do an exallent fully encapsulated setup to drop in to a canal boat. Problem is you need a canal boat sized engine room to fit it! A far better option for any sea boat seemed to be a seperate desel genset in soundproof enclosure. although it is more expensive the noise from funning the main engine just for power is a problem apart from the risks from underloading the engine. If you dont have roomefor the desel set (which I didn't) then as others say go for a little portable 1Kw will run a 50ah charger. I would say though that if you want to use it regularly it is worth looking at the low noise 4st. as they both much quieter, use half as much fuel and hapily run at light loads which cloggs 2st and gumms up the rings on diesels. My solution was to fit an inverter capable of running the kettle then use a small gebset to charge the battery, that way you can have a 1Kw genset suppling appliences up to 3kw which is much more eccanomical