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Go Back   SailNet Community > On Board > Gear & Maintenance > Electrical Systems
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  #1  
Old 12-05-2011
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Xantrex Inverter or 12 VDC Appliances?

I am in the middle of a winter project of installing a Xantrex 3000 Watt inverter in my 28ft sailboat and I am beginning to have second thoughts on why I am doing this.

First off, I only have 2 Grp 27 Deep cycle batteries onboard switched through a Perko 1\2\all switch to the main DC switch panel and I donít think these are the types of batteries that are best for the hi-demands of an inverter. I was going to change one of these batteries to a cranking battery and wire it directly, (via a fuse and normally open relay) to the inverter feed. Second, I was in a big truck stop the other day and I was very surprised to find a whole aisle of 12 volt coffee makers, toaster ovens and mini crock pots, mini-ovens etc.

So I am standing there with my coffee thinking why am I installing this oversize inverter, xantrex 120vac transfer switch, xantrex remote on/off switch etc ( got em all for real cheap) when I could use some of the appliances I saw at this truck stop?

Do these 12 volt appliances work good?
All I guess I really wanted to use was my 950 micrwave to heat food and drinks up.

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Jeff
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Old 12-05-2011
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Your group 27 batteries are not able to power the inverter at any kind of load for more than a few minutes. A 3000 watt inverter will have a full output draw of nearly 250 amps. Also, even run with low output it will use a higher amperage than a smaller inverter running in a more efficient range.

At a minimum I would power the inverter with 4 golf cart batteries in series/parallel, giving a bank of 425 to 450 AH depending on brand. 6 golf cart batteries would be better for use of more than a few minutes.

What are the items you want to run with the inverter and can these jobs (making coffee etc) be done using the stove you have instead?
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Old 12-05-2011
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Yes, I agree. But unfortunately my boat does not have the space for all the additional house batteries.

The interior galley area cabinetry has been redone and the stove/oven has been permanently removed.

Any experience with the DC appliances?






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Old 12-05-2011
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Jeff, ac or dc, 12 volts or 120 volts, really isn't significant here. Yes, there are some differences. An inverter may waste 10% power as it operates. And 220vac appliances may be more efficient than 110vac. And DC systems need charging, which always requires more power than it stores. There are pros and cons to all of them but I suggest the only thing that matters in your situation is WATTS.

You want to run a 950 watt microwave, which probably consumes about 1200 watts on the innput side to have that much output. Watts will be watts (not really, but close enough) regardless of AC or DC.

1200 watts from a 12 volt source will pull 100 amps, maybe for two minutes warming your coffee. Twenty minutes cooking dinner. That's something like 200 amp-minutes for the coffee, 2000 amp-minutes for dinner. Except we talk in amp-hours, so we divide by sixty, the coffee needs about 3AH to get heated, dinner needs about 33AH.

Your two group27 deep cycle batteries (and you want deep cycle, not SLI) might be rated 100AH each, although 80 is probably more realistic. You don't want to cycle them below 30-50%, so using the two combined, you can draw about 80AH before it is time to recharge. Or 40AH is you don't combine them and alternate them.

Nuke two dinners, and you have to recharge. Or...just run the engine and alternator to power the microwave. There are just limits to what you can do with a small powerplant (engine, battery, quantum reactor, whatever) and ac or dc won't make much difference in that.

Yes, DC appliances work. Take a second look in the truckstop, see how many of those brands are featured on the PBS cooking shows. They may not rival the quality and features of 110 appliances, but you don't see many skinny truckers out there, they must be cooking on something, huh? :-)

Either way, you'll still need to make and follow an energy budget. Reheating coffee is best [not] done in a good Thermos. And those $20 single-burner butane stoves you can buy in any dollar stove, are quietly being used in an awful lot of boats.
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Old 12-05-2011
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Old 12-05-2011
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I agree, get a counter top stove of some kind. It is the least expensive solution.

And your batteries which are probably 80 AH each are measures at the 20 hour rate - in other words 4 amps for 20 hours. At the larger draw of an inverter I doubt they would give you 40 AH each before the inverter shut down.
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Old 12-05-2011
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Quote:
Originally Posted by jefndeb View Post
Yes, I agree. But unfortunately my boat does not have the space for all the additional house batteries.

The interior galley area cabinetry has been redone and the stove/oven has been permanently removed.

Any experience with the DC appliances?







One cable clamped, wing nuts, no positive terminal protection and no vertical restraints. Time for battery installation 101
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Old 12-05-2011
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Agreed,

I guess I was thinking that if with my 40 amp alternator (beta Marine Beta 20 engine) and the engine running I could heat up a quick dinner or tea for the wife and then let it run a while for a recharge.
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Old 12-05-2011
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I doubt your 40 amp alt will put out a continuous 40 amps, less even as it heats up. If you are using an inverter with its massive draw the alt will heat up quickly.

If the inverter is installed you need a much larger battery bank, and I agree with boatpoker, there are battery issues in any case.

I would install a small counter top stove like an Origo.
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Old 12-05-2011
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Jef :

The inverter really is too large for the battery bank.

The amperage needed will shorten the battery life, even for quite mild AC loads.

Your 950 Watt microwave will be pulling something of the order of 60 A.

That really is into starter motor territory.

Your battery voltage will drop, and your alternator (and belt) will be groaning under the load.

There are high-capacity alternators available out there, like the Ample Power system. I have one, rated to 100 A continuous with the cooling air at 91 C. I have had that one for 19 years and it works fine, though almost never used above about 50 A.

I have no latent interest in Ample Power, apart from it being a good unit.

What is the smallest draw microwave available out there?
.

Last edited by Rockter; 12-05-2011 at 05:48 PM.
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