Power Conversions 12v to 240v

[Bob Blues]

Thank you to all the people who responded about my plan to put a Recording studio on my boat following on from that. I have a question about power conversions and batteries life.

 

For example

 

One piece of equipment runs at 400W at 240 v which equates to 1.66A

Using the same formula A=W/V this would give me 33.33 A

 

Is there any loss when you step up voltages through a inverter?

 

Using the example in the last posts 550Ah running to 1/2 would give me 225Ah at 12V and at 33.3 A this would equate to 6.7 hrs. of life

 

Am I on the right track or have I missed something?

 

Regards

 

Bob B

[Keeping Up]

You should reckon on an inverter being only about 90% efficient, ie about 10% loss.

 

Also you've missed out the effect which I mentioned - Peukert - which dictates that you get less power from a battery if you take high currents. EDited to add: this makes your battery treat the 33.33 amps as if it was actually 40 amps; but since one half of 550 is actually 275 and not 225, you can expect 6.8 hours.

 

This of course assumes brand new batteries (which they won't be for long) and also assumes you have charged them to 100% to start with (which is unlikely).

Edited January 21, 2011 by Keeping Up

[Naughty Cal]

Also you will have other items on the boat running, such as batter chargers, fridge and freezer, lighting etc. all of which are using power also.

[alan_fincher]

The other thing you need to consider is that the inverter is maybe 90% (ish) efficient when you are using it.

 

If it remains turned on when you are not using it, then it will draw current, but do nothing useful.

 

So depending on how you use it, the answer may be worse than "only" 90% overall.

[Chalky]

There's also the base load of the inverter as well. As well as the conversion loss the inverter will use some power to run its internal circuitry - about 400ma / 0.4A for the one I've got. May not sound like a lot, but all these little bits soon add up.

Have a look at the smartgauge website for an explaination of Pukerts. http://www.smartgauge.co.uk/technical1.html

[deletedaccount]

Don;t forget you'll only be able to stick 50-100 amps back into your batteries an hour running the engine. Altenators are never as good as the number would lead you to believe. If you're on shore power I'd be surprised if you've got a charger bigger than 50amps and it might only be 20amps.

[Pretty Funked Up]

Thank you to all the people who responded about my plan to put a Recording studio on my boat following on from that. I have a question about power conversions and batteries life.

 

For example

 

One piece of equipment runs at 400W at 240 v which equates to 1.66A

Using the same formula A=W/V this would give me 33.33 A

 

Is there any loss when you step up voltages through a inverter?

Bob B

 

There are loses. Easy way to cover it all is to divide by 10

eg: 400w will draw 40A @12v

[Bob Blues]

Thank you I will take this into account. The Honda gen will give me about 900W when out moored the cut. I have taken on board the comments about noise so I can only work during the day which isn't too bad.

 

So divide by 10 works for me for thanks

 

Bob B

[Bobbybass]

Actually..In my mind there is a bigger problem than power.

I make sure noone outside knows I have a good TV..musical instrument..laptop etc..

 

I think...only think..that if (Some..) passers by know you have musical instruments...they will hear them after all....recording gear..hi-spec generators...that you should make darn sure you never leave the boat alone... you may need that shotgun as word gets around !!!

 

But only..my opinion..

 

Bob

Edited January 22, 2011 by Bobbybass