Putting the kettle on

[onionbargee]

[Tesla]

The engine is rated at 42HP at full speed, at tickover it may not have any power to give, just push the throttle a bit if it bothers you.

 

I don't think I phrased my question very well, what I was wondering is how people determine what revs best match the alternator?

 

Cheers,

 

Bernie

[nicknorman]

The engine should be capable of driving the alternator at max load it can produce at any rpm. Depending on the engine size and alternator size, it could as has has been suggested, be geared up too much, but then it would also be an issue after starting in the morning with low batteries. Probably either live with it, try to increase the revs a touch before putting on the kettle. A 42hp engine shuld be able to run a 110A alternator at idle, though it might struggle a bit so probably better for the engine, and for the alternator cooling, to run the engine slightly faster, say 1000rpm, when the kettle is on. Ultimately the engine installation will have been designed to tolerate the alternator on max load at idle, though not necessarily to tolerate it gracefully.

 

As to those who say using an electric kettle is "massively inefficient" etc, I would disagree if the engine is already running because you are cruising. With the engine running already, much of the inefficiency is present already, and adding some extra load to the alternator increases the fuel burn by a reasonably efficient amount (frictional losses etc not really increasing). Diesel is cheaper than small calor gas cylinders in terms of energy per buck, and I would doubt that, even allowing for the inefficiency of burning diesel to generate electricity, vs burning gas too heat the kettle, that an electric kettle would cost more to run. And even if it did, it would be pennies and inconsequential compared to the cost of running a boat.

 

I say stick with the electric kettle - less water vapour (steamy windows) and it has auto-switch off. Just try to have the revs slightly above idle when it's on.

[Guest]

But please, only if you keep it in the gas locker and only use it outside the boat.

 

 

To the OP - I sometimes run a small lawnmower or vacuum cleaner off my inverter. I find everything is happier all round if I lift the revs from tickover to about 1500rpm, which is where the alternator reaches its peak output.

Same observation here on similar engine.

[Keeping Up]

Lifting the engine revs is a good (and simple) solution.

 

If as in this case the alternator is geared so as to give a very high output at low revs - which is normally a very good thing - then simply raising the revs a little above tickover cures the problem.

 

On the other hand our alternator doesn't reach anywhere near its maximum output until the engine is doing at least 1250 rpm. If I am going to be using a heavy electrical load I always raise the speed to this level to allow the alternator to have a better chance of keeping up with the demand.

 

SO if the alternator gearing is either too low or too high, it is a good idea to increase the revs. And as it is difficult to find a gearing which is neither too low nor too high for all possible circumstances, just increase the throttle when needed (or increase your tickover speed if the bnat will still then travel slowly enough.

 

Incidentally with a name like Tesla you should surely know all about electrics?

[nb Innisfree]

I would advise OP to set his tickover higher, with our 24v 100A alternator the load at tickover is about the same as the prop according to the ammeter, alt is almost at full output so as a rough estimate the engine is under a 8-10 BHP load when maneouvring slowly, Tickover is set fast at 1100 RPM as it would struggle at its correct 1000 RPM, engine is LPWS4.

[ditchcrawler]

Well my engine doesn't like the kettle on at 400 rpm, I wouldnt expect it to.. It may if I changed the pulley ratio but that would only be because the alternator wasn't doing anything . I get full charge rate at just over 600 rpm with a happy engine and that suits me. Lots of engines in boats are set to tick over at their absolute minimum speed and as Aurther said there is no power left for anything else.

To all you that say the engine should be able to handle full load a tick over. Next tine you run the engine at Rickover when you are away from your shore supply, just look to see how many amps your 100 amp alternators are actually delivering.

Just speed the engine up a bit.

[sueb]

First I need to get gas, then a gas cooker

Definately the best option.

[Tesla]

Incidentally with a name like Tesla you should surely know all about electrics?

 

Indeed however I have only owned Tesla for 5 weeks of the 1040 or so weeks since it was built so I have to claim newbie status...and the right to ask stupid questions....on that note more tomorrow, regarding battery charging....(I can almost hear the groans). I do promise not to ask questions about toilets though if that is any consolation?

 

Thanks for all the advice.

 

Bernie

[Wild Is The Wind]

We are using an electric hob to boil our kettle but will use gas when our cooker/gas is installed.

 

But to avoid putting it on too often, we have a large flask which we fill each time. Lasts for ages and piping hot.

[DHutch]

Wouldn't a plain stove top kettle, on an electric hob, use less power than an electric kettle?

Cant see it would, just more opertunity for losses, in addition to those with a kettle.

 

That said, i would be fairly surprised if you had an alternator big enough to drag down your engine, even at tickover, although I would more than expect it to notice the increased load. However with a large domestic alternator and the right (wrong?) pulleys it could be possible. At which point, i would simply suggest increasing the revs a little before adding the load.

 

 

Daniel

[nicknorman]

To all you that say the engine should be able to handle full load a tick over. Next tine you run the engine at Rickover when you are away from your shore supply, just look to see how many amps your 100 amp alternators are actually delivering.

Beta 43 with 175A alternator, standard idle of 850rpm, alternator puts out about 150A at 850rpm, however the belt does complain a bit, engine hunts a bit, and everything is happier at about 1000rpm

[RLWP]

Beta 43 with 175A alternator, standard idle of 850rpm, alternator puts out about 150A at 850rpm

 

<snip>

 

That's pretty impressive, I'm surprised an alternator will deliver that much at so low a speed

 

Richard

[nb Innisfree]

That's pretty impressive, I'm surprised an alternator will deliver that much at so low a speed

 

Richard

 

Ours is larger at 100A@24v, it has twin 13mm belts with 2:1 step up and when we first start up and excite it the alt churns out 100+ amps at an engine speed of 1200 RPM, though when it's hot it needs more revs.

[nicknorman]

That's pretty impressive, I'm surprised an alternator will deliver that much at so low a speed

 

Richard

All down to the pulley ratios of course!

[RLWP]

All down to the pulley ratios of course!

 

Ahhh, 850RPM engine speed

 

That makes much more sense

 

Mind you, I was looking at an alternator today on a 2 cylinder Lister with about a 1.3:1 ratio. I'm amazed it generated anything at all

 

Richard