Power Inverter: How many watts?

[ingalp01]

Hey guys and gals... I'm wanting to put a power inverter on my Cabin Cruiser. I figure I can hard wire it into the exsisting 120 v wiring that feeds the 3 outlets on the boat.

My question is how many watts should I need to power up a couple of 9 inch diameter fans? And maybe a coffee pot for sporadic use. Beyond that, all the lights in the cabin run off of 12 v.

I think I already know how to do all of the install, seperate the battery banks and such, but just don't know how big of an inverter I should get.

Thanks...

 

[Robbabob]

Re: Power Inverter: How many watts?

I will assume you need more amp load than your existing 120V circuit can provide. Regardless, you need to wire the new inverter into the 12V circuit, not the existing 120V.

Just a little information.. others will have far more....

Happy boating!

 

[H20Rat]

Re: Power Inverter: How many watts?

just look at the labels... Coffee pots can take a fair amount, you will need at least 1000 watts to be safe. Inductive loads (electric motors) take a HUGE amount of current to start, even little electric fans. Take the current draw on the fan label and triple it to be safe. (again, 1000 watts would probably be more than sufficient for a small fan)

Personally, I've never heard a person complain they bought too big of an inverter. And once you have it on board, its going to be used for all kinds of things you didn't expect. I'd go with at least 2000 watts if not 3000.



(Robbabob, i'm guessing he doesn't have ANY existing inverter, the wiring is just for shore power only. He wants to connect into the outlets for power delivery.)

 

[themaniam1]

Re: Power Inverter: How many watts?

I have a 1000w inverter. I almost never use it except for when using the blender or something like that for short times. Your batteries will never hold up to running something like a microwave so getting a bigger inverter will be a waste of money. Oh, 120v fans will drain the system a lot faster then 12v. We use a couple of 12v and have a few battery operated fans. We switched out all our lighting (nav, cockpit and interior) to LED and now we never have a battery issues and can run our 12v fans all we want.

 

[joed]

Re: Power Inverter: How many watts?

You need at 20% more than the rating of the coffee pot.

 

[rwidman]

Re: Power Inverter: How many watts?

Hey guys and gals... I'm wanting to put a power inverter on my Cabin Cruiser. I figure I can hard wire it into the exsisting 120 v wiring that feeds the 3 outlets on the boat.

My question is how many watts should I need to power up a couple of 9 inch diameter fans? And maybe a coffee pot for sporadic use. Beyond that, all the lights in the cabin run off of 12 v.

I think I already know how to do all of the install, seperate the battery banks and such, but just don't know how big of an inverter I should get.

Thanks...

You CAN NOT hardwire the output of the inverter into the existing shore power wiring. Well, you can, but it would be a stupid and dangerous thing to do.

If you were to hardwire the output of the inverter into your existing shorepower wiring, the prongs on the shore power inlet would become "hot" and be an electrocution hazzard when the inverter is powered. That is a safety issue.

Aside from the danger of doing this, when you connect your boat to 120 volt shore power, it will "backfeed" the inverter and ruin it At least, that solves the safety issue.

One choice is to install a transfer switch that lets you select shorepower or inverter power for your boat's wiring. Marine stores sell these.

Another chouce is to purchase anadapter for your shore power cord so you can plug it into the outlet on the inverter.

For your situation, I would recommend buying 12 volt DC fans and plugging the coffee pot directly into the outlet on the inverter and leaving the boat wiring alone.

120 volt AC on a boat can be vary dangerous if not done correctly. If you decide to actually connect the inverter to the boat wiring (other than with the shorepower cord as above), I strongly suggest that you have a qualified pro do it.

 

[ingalp01]

Re: Power Inverter: How many watts?

Thanks for all the help.

I know that you wire the inverter from the 12v system. But I already have 120v outlets on the boat that can be powered up by the shore power system. The outbound end of the inverter can be hard wired into that exsisting wiring system and would therefore power up my exsisting 120v outlets when I wasn't on shore power.

I have two batts that manage my house side electronics at 12v, ie. lights, stereo, water pump, refrigerator, etc. I just plan to use the inverter for the two small fans and occassionally a coffee pot, so I think I should be good.

Additionally, I could put a small solar panel on the boat to assist with keeping these "house side batts charged, although they do charge when the engine is running as well.

Thanks again.

 

[ingalp01]

Re: Power Inverter: How many watts?

I had fully intended on installing a transfer switch, or at least an in line off switch to prevent the power from backfeeding to the shorepower outlet.

Basically a three way switch would allow me to choose "Shore Power" or "Inverter Power" Or isolate the 120v installed outlets alltogether.

I'm not an idiot, and although not a certified electrician, I am more than capable of doing a safe and intelligent installation on my boat. I understand electricity and all the implications of choosing the inverter.

Basically after reviewing most of the input, I think 12v fans, and a 12v coffee pot may be the way to go, and then I can use more advanced electronics on shore power only, if I so desire in the future.

 

[rwidman]

Re: Power Inverter: How many watts?

Let's clear up some missinformation here:

12 volt DC coffee pots may take a half hour or more to brew a couple cups of coffee. There are better solutions.

Inverters are typically about 90% efficient. 1000 watts input for 900 watts output.

A microwave oven can be powered by an inverter. You just need a big enough inverter and enough battery power. The "watt" rating of a microwave oven is the "cooking power", not the power consumption (the power needed from the electric line or inverter). This power requirement will be listed on a label on the back or in the owners manual. A 700 watt microwave will draw about 1100 watts from the line or inverter.

I run my inverter and coffee pot (not at the same time) from a 2000 watt inverter and a bank of four 100 AH batteries.

The safe and efficient installation of an inverter is far more difficult and costly that it would seem to someone who has never acually done it. The inverter cannot be mounted in the engine compartment, yet the DC cables must be very short and very heavy gauge. Proper circuit protection myst be provided. The inverter hets hot in use and must be ventillated. All 120 volt wiring must be installed safely and according to code.

BTW: The inverter draws a standby current even if no appliances are being used so you need a way to turn it off or disconnect it when it;s not in use or it will be a constant drain on your batteries.

 

[mike343]

Re: Power Inverter: How many watts?

A one KW inverter will draw about 100 amps dc to power a coffee pot or microwave. Most battery ratings are given for a 20 or 25 amp current. So for each KW you need about four batteries. Inverters work but take lots of batteries and big wires. I can't imagine a 3KW inverter (at full load) on a small boat.

 

[Jeepster04]

Re: Power Inverter: How many watts?

You would not need over a 2,000 watt inverter for a coffee pot. At most 1,500 watts would do fine.

We run a full size fridge, large LCD tv, some select lights, and a coffee pot off of our 2,000 watt inverter. Given we usually do not run them all at the same time, we've never had an issue with the batteries going dead over 7-8 hours if we use the appliances wisely. We do have 6-6volt golf cart batteries though.

 

[Lyle29464]

Re: Power Inverter: How many watts?

A good marine inverter can be hardwired to you shore power. When the shore power is unplugged the inverter by-passes it and uses your on board battries as a source. It is all automatic. Only problem is if you leave 110 volt things on and the shore power is unplugged you will run the battries dead.

 

[Jeepster04]

Re: Power Inverter: How many watts?

A good marine inverter can be hardwired to you shore power. When the shore power is unplugged the inverter by-passes it and uses your on board battries as a source. It is all automatic. Only problem is if you leave 110 volt things on and the shore power is unplugged you will run the battries dead.

Exactly. Some inverters switch so seamlessly that electronics never go off. Ours is kinda old so it will turn the TV off when we go off shore power or the genset. Would love to upgrade as it takes some stuff a while to reboot(IE satellite)

 

[rwidman]

Re: Power Inverter: How many watts?

A good marine inverter can be hardwired to you shore power. When the shore power is unplugged the inverter by-passes it and uses your on board battries as a source. It is all automatic. Only problem is if you leave 110 volt things on and the shore power is unplugged you will run the battries dead.

OK, you geniuses go ahead and try it and let me know how it works out.

You cannot feed a single AC circuit from two sources at the same time. You must have a way of disconnecting one or the other. The cheap way to do this is to unplug the shore power cord and plug it into the inverter (same for a genset). The better way is with a transfer switch that switches all three conductors to either source. This can be an automatic switch or a manual switch. A very few inverters are available with a built in automatic transfer switch. Mine has one. Most do not. It does not matter if it's a "marine" inverter or not.

 

[alilley]

Re: Power Inverter: How many watts?

let me start off by saying that i am in a truck 6 out of 7 day a week and we do not have shore power. if we want out house hold appliances to work we need to run inverters. i have run one for years. i personally like the 1500 wat ones they are just a good size and will do many things for you. i e i descideed to "push mine to limits" one day and ran my microwave, tv, dvd, 2.1 surround sound, laptop, 9 inch fan, electric buffer (i was making it work hard by pusing into my fuel tank and loading it down) all at the same time. i was watching the guage on it and it only cam up to about 75% of the load it could handle. now this was a cobra brand inverter running 4 guage wire direct off the battery and truck running. that piticular inverter willl run you about 180.00 at a truck stop. power drive does have one of same size on sale for 120.00 you can find that one at pilot or a loves truck stop.

now with that being said as said before you would be suprised as to what kind of 12v appliance you can find at a truck stop heck they have 8 in fans ovens coffe pots you name it they just about have it.

me personally what i would do is go to walmart and look in auto section and see if they still have the 8 in fans on 12v. mine was only 11$ then you could just plug in your currrent coffe pot into one of your current 110v plug ins and save a lot of money

if you are dead set on putting in an inverter what i would do on a boat situation is as follows......get a seperat battery all together. mount it. a battery isolator (it will charge 2 differant batterys but they will not drain each other) and hoook up as directed that way you have no worries about draining your main engine battery wile out in the water.

my self i would run a cobra 1500 watt. get the remote poweer switch which will add for a lot cleaner install. and if you need to run extention cords and power bars then you would have more then enough power to do what ever you want

 

[Silvertip]

Re: Power Inverter: How many watts?

And you can also forget the "small" solar panel to help with battery charging. You would need a panel about the size of your boat to even begin charging the four batteries (or even two of them). Look at the output rating for those smaller panels. Look for WATTS. A 9 x 12 inch panel puts out just enough power to keep my garden tractor battery topped off during winter storage. That should give you an idea how big a panel you need to "charge" four batteries. This entire scheme is simply dangerous and a waste of batteries, battery power and money.

 

[Lyle29464]

Re: Power Inverter: How many watts?

OK, you geniuses go ahead and try it and let me know how it works out.

You cannot feed a single AC circuit from two sources at the same time. You must have a way of disconnecting one or the other. The cheap way to do this is to unplug the shore power cord and plug it into the inverter (same for a genset). The better way is with a transfer switch that switches all three conductors to either source. This can be an automatic switch or a manual switch. A very few inverters are available with a built in automatic transfer switch. Mine has one. Most do not. It does not matter if it's a "marine" inverter or not.

Mine has been that way for 23 years. The inverter does the switching. I am not much for talk Bring money you can lose on a bet and I will teach you something new. well not so new. When I plug in the shore power the converter clicks and switches over from the battery. I can do it any time and going from shore to batterys and back again. biggest problem is the window A/C it groans a bit before starting up on the invertor.
It would suck the battery down in an hour.

Just noticed you are about a 30 minute drive from me. Great chance to make $1000 bucks in 30 minutes.

 

[rwidman]

Re: Power Inverter: How many watts?

Mine has been that way for 23 years. The inverter does the switching. I am not much for talk Bring money you can lose on a bet and I will teach you something new. well not so new. When I plug in the shore power the converter clicks and switches over from the battery. I can do it any time and going from shore to batterys and back again. biggest problem is the window A/C it groans a bit before starting up on the invertor.
It would suck the battery down in an hour.

Just noticed you are about a 30 minute drive from me. Great chance to make $1000 bucks in 30 minutes.

What you're not understanding is that your inverter apparently has an automatic, built in transfer switch that automatically switches the boat's wiring from shore power to inverter power. Most inverters do not have a built in automatic transfer switch.

I discussed this in a previous post. It wouldn't be fair to take your money.

 

[Lyle29464]

Re: Power Inverter: How many watts?

What you're not understanding is that your inverter apparently has an automatic, built in transfer switch that automatically switches the boat's wiring from shore power to inverter power. Most inverters do not have a built in automatic transfer switch.

I discussed this in a previous post. It wouldn't be fair to take your money.

Nice side move. It's a rare person that would turn down the grand. I have always know that my inverter switches to 12 volts if it does not have the shore power or Generator. I was telling the OP that he needs one that does this when you started the name calling. Anyway I still believe he will be better off with the fully automatic switching because it rules out a major screwup.

 

[Jeepster04]

Re: Power Inverter: How many watts?

What you're not understanding is that your inverter apparently has an automatic, built in transfer switch that automatically switches the boat's wiring from shore power to inverter power. Most inverters do not have a built in automatic transfer switch.

I discussed this in a previous post. It wouldn't be fair to take your money.

Most marine inverters do indeed have an automatic switch built in. Not sure what type of inverters youve been looking at. Our inverter is around 10 years old and it has an automatic switch built in, its nothing new.

An example:

http://www.westmarine.com/webapp/wc...toreNum=10109&subdeptNum=10544&classNum=11281