inverter for space heater! what models are working well........

tbone999

Seaman
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Jun 8, 2010
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hey i have a n older bayliner liberty 20ft cuddy, i have been on a mission to have it wired up for shore power so that when we head on our weekend trips its just a easy plug in. 99% of the reason for this is for a heater,only other things id most likely be run would be a batt charger and charging a cell phone now and again. I have made some headway on ebay getting a inlet, and batt switch as it only currently has a single batt, but now im looking at inverters. I understand most heaters use 1500w or so and i have read about 1500w inverters not putting out 1500w and 2000w only running at around 1200w of power, so my question is what are the good 1500 to 3000w inverters??? at a decent price point?? please feel free to let me know if im wrong about any of the above........

cheers
 

NYBo

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Oct 23, 2008
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Impractical, even without factoring in the loss efficiency from the inverter. You would drain down a single battery to half charge in less than half an hour. You would be better off with a small, quality (quiet) generator on the swim deck.
 

Teamster

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If the shore power is 110 couldn't you run the heater off that??
 

erie_guy

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Jan 16, 2007
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I'm afraid that you need a huge bank of batteries to feed your inverter - if you want to run a 1500 watt heater. You might consider using the engine's hot water and an automobile heater/fan assembly to heat the cabin. . . . Or perhaps a small propane "vent-free" heater could be found that you could run on a 20# portable propane tank - stored on the swim platform. Keep in mind that propane is heavier than air and leaks will migrate into the bilge resulting in a very big hazard (boom)- if any spark is made.

erie_guy
Port Clinton, OH
 

bobdec

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Aug 12, 2010
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Rule of thumb (using 20% inverter loss worst case) multiply the device amperage requirements by 12 to find the 12 volt input load to the inverter.. A 1500 w heater / 120 volts draws 12.5 amps from the inverter. Multiply the 12.5 amps by the 12 factor (12.5 X 12) = 150 battery amps to supply the inverter. A setup to supply 150 continuous amps on a 20 ft cutty is an impractical solution. Also I think 1500 W is to much for a 20 ft cutty cabin size, but even a little 500 Watt heater would need 500/12X12.5= 50 amps from the battery. Your looking at requirements for heavy gauge wiring directly to the 12V system with appropriate fusing to feed the inverter. And 50 amps will probably deplete a battery in less than an hour unless the engine is left running when the heater is in use. That's assuming your alternator will put out 50 amps at idle..
 

thumpar

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Jun 21, 2007
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If the heater is only needing to run when away from the dock under power you could just tap into the engine cooling water supply like a car or truck does. It is not uncommon to use the engine heat to heat the cabin. You could then use a 120v heater when at the dock on shore power.
 

tbone999

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Jun 8, 2010
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...... i was hoping to only use the inverter set up at dock(shore power) and well under away only. On shore power i want to be able to use a hot plate, make coffee etc... well im running all i want the inverter for is to run one 1500w heater. I understand it will kill a single batt set up, thats why i am adding the switch and a second deep cycle. With the engine running (3.0 merc) and two large deep cycles this inveter idea of mine wont work??
 

smokeonthewater

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Dec 3, 2009
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If by shore power you mean a normal 30 amp service then it will run all that and a heater just fine

if all you will have is one or two 15 amp outlets then you will need to unplug the heater while using the hot plate

no even with dual batts or your engine running you don't have the power to run it... now if you installer 20 batts then sure you could run it a few hours

for heat while the engine is running you need to install an automotive style heater as mentioned above... uses hot water from the engine and a 12 volt fan
 
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thumpar

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Jun 21, 2007
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...... i was hoping to only use the inverter set up at dock(shore power) and well under away only. On shore power i want to be able to use a hot plate, make coffee etc... well im running all i want the inverter for is to run one 1500w heater. I understand it will kill a single batt set up, thats why i am adding the switch and a second deep cycle. With the engine running (3.0 merc) and two large deep cycles this inveter idea of mine wont work??
Just use the shore power to run the heater and the engine heat when under way. No need for an inverter.
 

H20Rat

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I understand it will kill a single batt set up, thats why i am adding the switch and a second deep cycle. With the engine running (3.0 merc) and two large deep cycles this inveter idea of mine wont work??

Even with dual batts and the engine running, you will drain BOTH batteries fairly quickly. You probably have a 60-75 amp alternator. With the other electronics running (fuel pump, ignition, etc..) you probably are taking 15-25 amps off the top. So that leaves around 40 amps free. But the catch is that is at a fairly decent RPM. At idle you are going to be barely breaking even the way it is, ie, the alternator is putting out the 15-25 amps that the boat requires just to run.

It comes down to the fact that making heat with electricity requires A LOT of power. Talk to a electric or hybrid car owner... They own heavy winter coats! Running the heater in an electric car destroys your mpg's.
 

thumpar

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Not only what smokercrater stated but with an inverter you also loose efficiency though that. To get 1500 watts off 12 volts you are looking at 125 amps. When you add the loss through an inverter you are around 150 amps. The heat off the engine is free.
 

tbone999

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ok you guys have sold me that an inverter isn't the way to go, ill still install the shore power as i have already bought the inlet. what's the best way to get heat from my engine?????? and if im not running an inverter for my shore power im guessing ill need some sort of breaker????? or should i have say a 3000w inverter that is only powered by shore power?????

thanks for all the help
 

KD4UPL

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Feb 13, 2010
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I'm starting to get the feeling you don't know what an inverter does. If you're plugged into shore power you have absolutely no use for an inverter. An inverter supplies 120v AC from a 12v battery. When plugged into shore power you just have 120v AC directly from shore.
If your shore power inlet is 30 amps you will need a breaker panel to distribute it as 15 amp or 20 amp circuits. If your shore power inlet is only 15 amps anyway then you can just hook up the outlets and no breaker is necessary but I would still include one.
It should be fairly easy to find an engine heater kit to install on your boat. It would include hoses, a heat coil, and a fan and some ducts.
 

Ned L

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Sep 17, 2008
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Thank you kd4upl, exactly what I was going to say.

Think of the 120volt electrical system that is in your house, now put that wiring in your boat. The shore power cord is just like the service entrance that comes from the pole to the meter on your house.
With "shore power" your boat is wired for 120 volts with lights and receptacles just like your house.
This is completely different than the completely separate 12 volt system that is already on your boat.
Think of an inverter like an 'adapter' that lets you run SMALL household items usually temporarily off a battery,
 

thumpar

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Jun 21, 2007
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To add to KD4UPL's post the factory manual has instructions on where to tap in to the cooling system to hook up the heater. I thought about doing it to my 2.5l (almost the same motor as yours) but got a different boat first.
 

tbone999

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Jun 8, 2010
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Thanks guys I clearly know less then I need to know, I bought a 30amp self grounding (hubbell) inlet. I'll need to do a lot more digging! What thumpar what was this heater kit called???
 

JoLin

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Aug 18, 2007
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ok you guys have sold me that an inverter isn't the way to go, ill still install the shore power as i have already bought the inlet. what's the best way to get heat from my engine?????? and if im not running an inverter for my shore power im guessing ill need some sort of breaker????? or should i have say a 3000w inverter that is only powered by shore power?????

thanks for all the help

There's a good write-up of a shore power installation here...

http://www.boat-project.com/index.html

If you take the time to read through it (you should), you'll see that it's fairly complicated, and quite a bit more expensive than just buying a shore power inlet and some wire. An incorrect installation poses the risk of electrocution, fire and potentially 'leaking' current into the water, which in turn creates a risk of electrocution and electrolysis for you and your dock neighbors.

A certified marine electrician should either do your install, or inspect everything before you apply any power to it.

My .02
 
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