Inverter Question... - SailNet Community

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Go Back   SailNet Community > On Board > Gear & Maintenance > Electrical Systems
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  #1  
Old 07-20-2009
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Inverter Question...

I want to install a 2500 Watt inverter on my boat with a single 110V outlet in the Galley.
a)My battery bank is only Two 100 amp hours deep cycle batteries.
b)My intention is to use the outlet (inverter) while the engine is running to run either the microwave(1000W) or fancy coffee pot(1500W).
c)Not sure the exact output of my alternator on my engine, but i'd guess it's something like 30 amps.
My question is: For short uses of under 5 minutes, would my battery bank & alternator together do the job???

I also assume that while plugged in (110V)at the dock, the inverter could be used without worry full time, as my battery bank is being charged? (again, not sure the specs of my battery charger, oops).

Are my "close enough for government work" assumption going to work in these senarios???? thanks gang!
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The short answer is no. If you are on dockside 120VAC, then skip the inverter, just plug directly into the shore power.

The current draw from the inverter will overwhelm your system. You will have to size conductors for the maximum current, (2500 w @ 12.5 VDC) which is enormous at 200 Amps. Engineering factor and voltage drop will push that value to nearer 250 Amps.

That current will melt your batteries, and they will run down into your bilge, where you will have to clean them out with a shovel. Obviously your engine alternator is hopelessly under sized - so no help there.

(Although your batteries are 100 ah, they will not put out 100 Amps for an hour. Nowhere near. So the "just for a minute" scenario won't fly, either.)

Either stay with shore power, or buy a genset that can deliver that kind of power. Sorry.

Best Regards,


e
.::.
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Old 07-20-2009
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You would be surprised on how many amps a coffee pot pulls. I have a Grind & Brew, and the pull on it is almost 100 amps to heat the water. Running the engine helps, but not if you don't have the housebank sized to meet the needs of the job.
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Old 07-20-2009
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Lets do the math. A 1500 W coffee pot will draw 125 amps at 12Volts continuosly from your battery. For 5 minutes or 1/12 of an hour this would be roughly 14 amp hours which is no big deal. Of course there are coversion losses and you cannot rely on the 20amphour rating of the batteries at such a high draw level... But even at twice the draw level you are still ok regardless of your alternator size. A 30 amp alternator would take an hour of run time to recharge your bank.
I'd feel more comfortable if you had a bit larger bank but I am thinking you are OK with this approach as long as you are careful in your use
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Old 07-20-2009
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thank you all for your thoughts!
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Old 07-20-2009
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Quote:
Originally Posted by eolon View Post
The current draw from the inverter will overwhelm your system. You will have to size conductors for the maximum current, (2500 w @ 12.5 VDC) which is enormous at 200 Amps. Engineering factor and voltage drop will push that value to nearer 250 Amps.

(Although your batteries are 100 ah, they will not put out 100 Amps for an hour. Nowhere near. So the "just for a minute" scenario won't fly, either.)
Well I had a 2500Watt Inverter and everything was sized correctly and we could run even greater than 1500W (125amps/12V) loads. The big difference in my set up was battery bank size but there is no reason you can't draw 125 amps of current for 5 minutes.
It is correct that you will get far less than the rated 200 amphours (1.5 hours to flat...or .75 hours to 50%) which is calculated on a 10 amp draw.
Wet cell batteries prefer to be discharged at not more than 20% of rated amphours or they heat up and can self-destruct. Thus a 600amp hour bank would be preferrable....but for 5 minutes, I don't think any harm will ensue.
If that is a concern...asailor could switch to AGM's or Odysseys for significanlty lower internal resistance and no worries.
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Cam, the issue I saw was that even running the engine, the draw on the housebank is large. The output from the alternator won't keep up and with only 100 amps in reserve, there will be a large voltage drop as well. Plus, a ten-cup coffeemaker runs about 10 to 15 minutes. Makes it a tough setup for coffee as that is around the outer edge of the opperation curve.
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Oh...I agree...a 10-15 minute run would be too much. I was relying on the OP's 5 minute time. Even at 5 minutes...that extra battery would be advisable.
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The real question would be, why? Why do you need to run a microwave and coffee maker away from the dock? Of course there is the theoretical question of whether it can be done. The practical answer is yes, but it will probably fry your batteries and be a PITA to recharge and eventually replace them. And asailor thinks he needs to run an inverter while on shore power. Maybe he should figure out how to run the microwave and coffee maker at the dock, before he tries at anchor.

But of course, I like instant coffee and warm beer. So who am I to give advice?

Scott
Gemini Catamaran Split Decision
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Scott, you are talking to a guy who's first purchase for the new boat was a Cuisanart Grind & Brew. I have to have my good cup of coffee (more like a pot of coffee to be honest) in the morning, and it tastes even better when on the boat! It's why I learned about inverters and how to make sure I was always able to grind and brew that great cup of coffee.
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