What size inverter?

[tomandsophie]

Hi,

I'm new to this forum - just found it via Jim Shead's website. Looks like a great place to get some questions answered. My wife and I have just submitted our order for our new boat (57ft widebeam) which should be ready for us to move in at the end of next summer. Very very exciting, can't sleep at night for thinking about it!

Anyway, I was hoping somebody out there might be able to help with finding out what size inverter I need to buy. Basically, the only things we need mains power for are charging up the laptop, running a mini-system stereo, and occassionally watching a video on a small 14in TV/video combo. We might get a DVD player too. I know we need to get a pure sinewave inverter (as I will be running the laptop off it) and I think 350w looks like the right kind of size. What do you think?

Cheers, Tom.

 

We will be buying a washing machine in the future, but we intend to run that directly off a generator seeing as a 3000w inverter costs thousands!

[nbtafelberg]

I have 1 kw inverter, but we are on a shore line normally, one solution is to have a big generator and use the Jenny when the invertor is not big enough.

 

My DVD player EATS batteries.... I managed to see the first 10 minutes of the Passion of the Christ, Jesus didn't get anywhere NEAR the cross before my batteries died.

 

If you have a shore line life gets a lot easier except when you are travelling, but, as time goes on you learn how to manage your batteries and power effectively.

[Gary Peacock]

We fit a 2kw inverter and a 3.5kw AC generator to all our boats the generator priority is set up to power the washing machine.

 

But always remember it's not the size of the inverter that is of primary importence but the size of the battery bank needed to power it.

 

I have an Excel spread sheet that you enter the equipment and run times of electrical items on your boat into, it will then suggests inverter/generator sizes.

If you have Excel on your PC and any body would like a copy drop me a mail.

 

 

Gary

[Alastair]

You don't need pure sinewave for your laptop, as it has a transformer to change the ac to dc. I'd suggest a small inverter to start with - Maplin sell stirling 350W for about £50. Nothing you've listed uses much power.

[tomandsophie]

So it sounds like we ought to get a 350w inverter for general use - tv, dvd, laptop, etc. and get a genny for the washing maching. Will the dvd and tv run ok off a modified sine wave? I have heard stories of flickering screens etc.

Does anybody know if a normal £100 washing machine will work off an 1800w inverter? Some people have told me that I will need more like 4kw or 5kw to power one - what do you think?

Thanks for all the advice...

[Richard Bustens]

Hi Tom

Try this web site there is loads of usfull info on hear

http://www.sterling-power.com

[wynd lass(nb.Black Pearl)]

We had a maplins inverter(600w) and it fizzled(literally) after a few hours, so we bit the bullet and bought a stirling inverter.....

 

Stirling is highly recommended, if it goes wrong its put right-no questions asked!(as we found out, you gets what you pays 4)

Edited November 1, 2004 by wynd lass(nb.Black Pearl)

[rog guiver]

Use the washing machine while cruising when the water (engine heated) is hot and the alternator can supplement the batteries. This will allow you to disconnect the heater in the washing machine (and remove/ safely stow the cables) which is the BIG load.

 

The motor only uses loads of amps on starting then reduces to acceptable levels.

 

We had a 1500 heart inverter on the last boat and the washing machine setup as above worked well.

[tomandsophie]

Use the washing machine while cruising when the water (engine heated) is hot and the alternator can supplement the batteries. This will allow you to disconnect the heater in the washing machine (and remove/ safely stow the cables) which is the BIG load.

 

The motor only uses loads of amps on starting then reduces to acceptable levels.

 

We had a 1500 heart inverter on the last boat and the washing machine setup as above worked well.

<{POST_SNAPBACK}>

 

Sounds like an excellent idea, thanks. How about whether to get a modified or pure sine wave inverter? Will everything run ok off a modified sine wave, as the difference in price is HUGE!?

[sjcollins]

Use the washing machine while cruising when the water (engine heated) is hot and the alternator can supplement the batteries. This will allow you to disconnect the heater in the washing machine (and remove/ safely stow the cables) which is the BIG load.

 

The motor only uses loads of amps on starting then reduces to acceptable levels.

 

We had a 1500 heart inverter on the last boat and the washing machine setup as above worked well.

<{POST_SNAPBACK}>

 

Rog

 

Stupid question - presumably the thermostat is linked to the heater or else the machine would just stop?

 

Steve

[tomandsophie]

Use the washing machine while cruising when the water (engine heated) is hot and the alternator can supplement the batteries. This will allow you to disconnect the heater in the washing machine (and remove/ safely stow the cables) which is the BIG load.

 

The motor only uses loads of amps on starting then reduces to acceptable levels.

 

We had a 1500 heart inverter on the last boat and the washing machine setup as above worked well.

<{POST_SNAPBACK}>

 

Did you have a modified/quasi sine wave inverter or pure sine wave?

[Martin]

We have a top of the range Bosch washing machine of standard household type.

We bought it for the 1600rpm spin speed which aids drying.#

It is full of fancy electronics such as load balance sensors and froth sensors and these keep water and electricity usage to a minimum giving it its A+ rating.

It is run from an 1800W Continuous (2400W Peak) Sterling Quasi-sinewave (modified sinewave) inverter with no problems.

The engine is run while washing so that power drawn through the inverter is replaced by the alternator as it is used.

We didn't bother disconnecting the heater as we wash at 15 degrees perfectly happily anyway.

 

I did suffer a broken alternator drivebelt one day and ran a full wash cycle without the alternator for support without noticing.

Everything survived I am surprised to report!

 

In my experience, you can suggest you will only run a TV or small stereo from your inverter, but it won't be long before you wish you'd got a bigger one when you find your drill or sander won't work!

 

Again, don't worry about Pure Sine Wave for the laptop - it doesn't need it.

You can probably buy a 12v adapter for it too.

Mine is charged from the fag lighter in the car and will run for the evening without plugging it into the boat at all.

[tomandsophie]

Thank you very much - excellent advice there (just what I wanted to hear!).

So it looks like we'll get ourselves an 1800w Sterling quasi-sinewave inverter and a washing machine!

By the way, have you tried running a hotter wash? Just wondering if it would work for washing whites?

[Webchem]

What you mean it doesn't all go in together on 40 degrees!

 

Teehee

[John Orentas]

Tomandsophie.

 

The general rule should be to get a inverter double the size of your maximum load, efficiency drops off rapidly at the top end of their spec. As has been previously stated lap-tops and other devices will not need a pure sine-wave unit, some of the most unlikely equipment will give problems, equipment with electronic timers, variable speed motors and cheap battery chargers. But there are no set rules, you must try them out. If there is a 12 volt option always go for that.

 

With the washing machine question. Some have speed conrollers, others have multi-wound motors, the latter is the better bet, but it is hard to find out which is which. Try to avoid fancy electronics, but most important get one with a reasonably low power consumption. People will tell you it works for them, and I am sure that is true, but in my view it is madness to heat water from your electrical system, disconnect the heater internally and you may need to doctor the thermostat too.

 

Again some people will say that it is the size of the battery bank that is crucial, that is not really stricly correct. Every bit of energy that is used must ultimately come from your alternator no matter what add on charging aids you may have.

 

John Squeers

[rog guiver]

With regard to disconnecting the heater the way our machine worked was, if the fill had not reached the required temperature (source water temp too low) then the heater would click in. Once the temperature was reached it would click on to the next part of the cycle.

 

Hence with the heater disconnected it was the case of waiting for the engine to have heated the calorifier to an acceptable temperature.

 

The Heart inverter output a modified/quasi sine wave.

[John Orentas]

Rog.

 

Thats why you have also got to de-activate the thermostat.

 

John Squeers

[Alastair]

I have to add to John's comments about charging. Do remember, no matter how big a battery bank etc, you have to put back in the power someday, somehow.

[claymore]

Ah ha, this was something I was kind of thinking-ish of myself over the weekend and I was going to post a question but maybe somebody could answer it here? I've got a laptop I want to run - dvd player, digital tv tuner thingy, etc - and was wondering what inverter to get..... but, the laptop runs (so it says on the transfomer) on 19vDC, so I plug it into mains 240vAC which is then converted to 19v dc, so it seems a long way around things to go from 12vDC to inverter 240vAC back to 19vDC? So anyone know or recommend where I can get a 12vDC adapter for the laptop, last time I looked there wasn't one available for mine from the manufacturer, and what's miliamps(mA) - spelling? - how does this affect things? Noticed that the transformer for my laptop says something like: Input 110-240vAC1400mA Output 19vDC3950mA? is this the same as 1.4 amps and 3.9 amps, if so will I need a 12v adapter rated at 4 amps?

got a headache now thinking about all these numbers!

Thanks?

[rustyduck]

Another point about inverters - the sizing will also depend on whether the load is inductive or resistive.

 

Think of an inverter size that's rated around double the normal load if you've got resistive loads (kettles, lights etc).

 

For an inductive load (motors - fridges, drills, Hoovers etc) treble the load size.

 

The only problem going for a really big inverter (apart from the price), is that they may take more power when not actually powering anything.

[John Orentas]

With laptops and other hi-tech tackle, I would advise that you stay with the supplied or recommended power supplies and other accessories, you may lay yourself open to problems with warranties.

 

It is a round the houses approach, but if there is not a 12 volt supply unit available, run it through your inverter, it sounds like a simple matter but d/c to d/c converters are technically quite difficult things to produce.

 

The 4 amps @ 19 volts you can take to be a 'maximum load' the laptop will probably not use anything like that much power. Your interpretation 1.5 A input and 4 A output is correct, and yes if you find a suitable low voltage supply unit it would need to be.

 

Input - 12 volts d/c.

Output - 19 volts d/c 4 amps.

 

If you havn't yet got your inverter buy one with a rating approx. double the maximum you require, a modified sine wave type I am sure will be ok

 

John Squeers

Edited November 2, 2004 by John Orentas

[tomandsophie]

Wow, this really is the place to get all the answers! Thanks everybody. I think I'll opt for getting a modified sine wave 1800w Sterling inverter. It sounds like that should supply our power needs for the washing machine and it only costs £350 from moore power. Pretty good. I just wish I could try it out first to be sure.

Thanks again everybody

[Martin]

So many people think there are problems with quasi-sine inverters and certain devices that contain electronics, speed controllers, digital timers and so on.

It would be useful to know how much of their advice comes from experience and how much is just the passing on of information that may or may not have been true some years ago.

 

I use only a Sterling quasi-sine inverter for power on the boat - I have no land line or generator.

I run the following - all on 240v from the inverter:

High-end stereo including CD and minidisc recorder, cheap Panasonic stereo in the bedroom, Sony TV, Panasonic VCR, Dell laptop and computer with LCD monitors, MIDI keyboards, Roland digital sound module, vacuum cleaner, iron (lowish wattage of course), washing machine (with digital controls, fuzzy logic and all manner of froth sensors and balance sensors), variable speed orbital sander, variable speed drill, variable speed jigsaw, variable speed router, variable speed Kenwood Chef, variable speed Braun hand blender, drill charger, three phone chargers, camera battery charger, camcorder battery charger, NiMH battery charger, two variable speed mini-drill thingies, Clarke air compressor (for the airhorns and airbrush), sump pump, headlamp and other odds and sods.

The only thing we have ever had fail on this power supply was the microwave/grill that we brought with us from the house - and this wouldn't work because it was rated from 1500W but took much more to actually get going.

 

Everything I buy, I check the wattage of - but apart from that, I plug it in and away it goes!

 

Can anyone give me any actual examples of appliances which won't run on a Sterling inverter?

I don't know what all the fuss is about and would hate for someone to spend thousands of pounds on sophisticated kit on the basis of anecdotal evidence or what someone once heard on the towpath.

I have heard of someone whose TV would not work on a Heart inverter, but mine is the same model and I have no difficulty.

 

Don't get me wrong folks - I'm not suggesting I know better than you, it's just that I have consistently ignored the warnings and gone ahead and bought stuff anyway - and it has worked!

So much so that I consider the warnings to be hype.

[Richard Bustens]

Fair point

it would be good if I dont have to buy a pure sine wave inverter, was only thinking yesterdat that i would buy a quasi and one of the small specials for the tv, but then i wondered if the washing machine would work with it .

The fridge freezes should be ok as with the rest of the bits i want to runas they are eyther heaters kettle or motor driven things, and i dont want a micro-wave as i as yet have not found a usfull purpus for one, except to dry wet wood as ime turning it.

Dawn was quite ok about me taking it into my workshop from the kitchen as she only ever used it as a bread bin anyway.

[rustyduck]

Good grief Martin,

 

Is there any space to move on board with that lot

 

Apart from that though, I think there is much sense in what you say, dear fellow.

Edited November 3, 2004 by rustyduck