Power Inverter Question

[Rick2413]

I presently have a xantrex 1750 watt inverter(1500 watt continuous) on my boat. It has two outlets. The electrician wired a standard house plug(which plugs into one outlet of the inverter) and wired the other end into the power panel for use when switched from Shore Power to Inverter Power. I have three 850(if memory serves) Deep Cycle batteries. When using the 750 Watt microwave, the microwave makes a real labouring sound like its struggling and most times does put the inverter into alarm.
There are two reset breakers on the inverter. My question is, within the inverter circuit, are there two separate 750 watt outputs or a 1500 watt output shared by the two plugs? I'm trying to figure out why a 1500 watt inverter won't run a 750 watt microwave. If two separate circuits, is there a way to wire the two 750 outputs to provide the panel with the full 1500 watts?

 

[Don S/V ILLusion]

I have the same inverter Rick and it runs our 900w microwave with no problem. This makes be think you have one of two issues:
1. battery capacity insufficient to run the inverter to full output. Don't know what "850" batteries are but my 440 amp bank may be of higher capacity. I am assuming your batteries are at or close to full charge as that could also trip the inverter, and
2. Bad connections and loss of current feeding the inverter from the batteries. Analogous to this possibility is insufficiently sized battery cables for the run to the inverter.
This inverter can produce 1500w total (from either plug or 750 from each)
It should work regardless of the fact the microwave isn't a pure resistive load.

 

[sailingdog]

Rick—

Inverters, like generators, are generally rated for a resistive load. You could probably plug 15 100-watt light bulbs into the sucker and kill your batteries fairly quickly, or your wife's 1500 watt blow-dryer.... and it would work just fine. Inductive loads, like your microwave oven, require a lot more juice. Running a 750 Watt microwave may require a 2000 or 2500 watt inverter for it to get the amount of electricity it really needs.

As for the two reset breakers and whether the there is one 1500 watt circuit or two 750 watt circuits, that would depend on the specific inverter. Since you haven't included which Xantrex it is, it could be either. You'd have to call Xantrex or look it up in the owner's manual.

BTW, is the outlet on the Inverter GFCI protected? If not, it really should be IMHO.

To use a 1500 watt inverter, you really need to have a pretty serious battery bank. It will draw about 125 amps from the battery bank when in full power use. What size batteries make up your house bank? Are they Group 31, 24, 27, 4D or 8Ds?? They' renot golf-cart batteries, if you've got three of them, since you'd either have two or four.

 

[Bill Roosa]

inverters and microwaves

If the inverter is sounding an alarm (low voltage is my guess) then it is not going to be putting out full output because the input voltage is low. Check the battery terminals and connections at the inverter (the 12 volt ones) for clean and tight connections. A down and dirty way of testing these is to run the microwave with the inverter then immediately feel all the 12 connections. The one(s) that are the problem will be warm hot from resistance.
It could also be that the wiring to the inverter from the batteries is not up to size. 750 watts is around 750/12=62 amps. They should be as big as starter cabling.

Then you could have a waveform problem. Microwave ovens use electronics and they where designed to operate off true sine wave AC current. Most inverters have modified sine wave wave forms and that can cause some pretty weird stuff to happen. My 750 microwave is driven by a 3000 w inverter and she seems to only operate at half power. It takes twice as long to heat a cup of coffee. Oddly the timer clock seems to run at twice speed.

As for the innards of the inverter and how it is wired I'd say the manual is your best bet. The power output of the inverter outlets may be on a placard on the inverter. It will be on the back side where you can't read it thought. That is just the way these things work .

 

[alexco38]

Run with Engine

I always run the invertor - microwave with the engine on. When the engine is warm, running it for a few minutes won't hurt her.

 

[Paul F]

Can you test it?

If you can unplug the boat from the inverter and just plug in the microwave directly to the inverter to see if it works. If it does the wiring in the boat is drawing down the inverter to a level where it no longer can run the microwave. I run a microwave on a 700 watt inverter with the microwave plugged in directly.

 

[Rick2413]

Inverter-Variety of Responces

Thanks to all for such prompt input. To add, the label on the batteries is 27DC 850 Marine Cranking Amps; they are 2 years old. All wiring on the vessel was replaced two years ago by the same Certified Marine Electrician. The inverter will run everything else (including the 26" plasma tv) until the battery voltage drops and the inverter alarm goes off which is normally 4-5 hours. All AC outlets are on a GFCI Circuit.
Don has no problem with his(same inverter) running a microwave yet Bill Roosa, running a 3000watt inverter is experiencing the same problem I'm having. Takes forever to cook anything and my alarm, on most occasions, will beep a problem.
I have the opportunity to buy a 3000watt inverter but would like to understand "what is the reason" for my present deficiency, hence will the 3000watt unit solve my problem.
Bill, is it my understanding that the waveform problem you refered to is that instead of being a nice clean AC signal it's more of a square wave output causing inefficiency with the circuitry?

 

[sailaway78]

How far away are the batteries

First off three group 27's for a house bank is fairly small to be pulling that much load. If the batteries are in good condition and fully charged, they should run the microwave, but not for long. If you try to use it after a day or two of usage, probably not enough power left in the batteries. If the inverter alarm is going off, that is a signal for low voltage from the batteries. How far from the inverter are the batteries. The longer the cable run, the heavier the wire needs to be. Feel them to see if they are getting warm. Put a volt meter on the terminals at the inverter, and see how much voltage you are getting. If the wire size is to small for the length of the run, you will get a pretty good voltage drop. And check all terminals and make sure they are squeeky clean, and good and tight.

 

[Don S/V ILLusion]

Rick
It may not be your inverter or it's capacity but either a voltage issue or battery capacity - group 27 batteries are on the small side for use with an inverter.. It's not surprising the Tv or other electronics works as it doesn't create as rapid a load as does a microwave. Additionally, having an electrician do the wiring is no guarantee of quality and obviously doesn't eliminate the possibility of corrosion on any of the connections.
I also don't think it has anything to do with the wave form as the microwave should work fine, regardless of it being a mod sine wave, on this size inverter all else being equal.
The thing which almost convinces me it's a voltage drop problem is that both you and Bill have the same problem despite different inverter capacity - you getting a larger inverter still puts you in the same position Bill described. The only other variable is an unacceptable voltage drop.

Out of curiosity, what size cables run from the battery to inverter and how long is the run?

 

[Guest]

Inverter application

Our Hunter sailboat is fully equipped with the usual AC and DC stuff. Two 8D batteries deliver a total of 500 amps or 250 amps of useable power, which will last about two days on the hook. Our Xantrex Freedom 25 (2500 watt) works pretty hard operating the microwave, too. Instead I try to use the CNG stove for all our cooking needs and save the microwave for when we're connected to shore power.

We just spent a long weekend in Eagle Cove on the east side of Cypress Island, a part of the San Juan Island group. Weather was mostly clear but hovered around freezing most of the time. Our diesel furnace was on around the clock to keep the boat cozy warm. Even with the fridge and freezer on, watching a movie or two, the furnace, etc., the DC system did its usual masterful job. Later on in the second day I ran the Genset for two hours to recharge the house bank and heat water so the admiral could take a bath.

All in all a wonderful long weekend on the water with spectacular Mt. Baker views, soaring eagles, good food and loving companionship. Life is great.

Bud

 

[Ron20324]

"Cranking amps" not being particularly used in this case, what is the amp-hour rating of the batteries. These ARE deep-cycle batteries, you said?

I have the manual for the 1500 watt inverter, though it is for the model XM1800. They call for DC input cables to be NO LONGER THAN 5 feet of 2/0 AWG wire. The AC output should be 12 guage wire. For the ground wire of any length, 8 guage.

Now, I read your posting that says the "electrician" only plugged the AC output cable into an outlet of the inverter but hard wired it into the AC panel??? Not good.
The AC output should be hard wired into the inverter in the space behind the AC outlet on the inverter.

You do not mention if there is a switch to select shore power/inverter input to the AC panel. Be sure the shore power is disconnected in some way when inverter is used. Do NOT run the battery charger off the inverter! The monitor panel on the inverter can be relocated (like to the nav station) simply by using a regular 4-conductor telephone cord to extend it.

 

[Rick2413]

Inverter

Many thanks to all again. There are many things I will re-verify. I know the wiring from the batteries to the inverter is the same guage as the starter wire but the run is is slightly over 5ft(by the time it twists and turns through the engine compartment). The common factor seems to be the Group 27 batteries for the house supply. It is the only weak link I did not go "top drawer on". They are Energizers from Walmart at $100 each. I figured a marine battery is a marine battery but didn't want to get into those $400 each ones. Some have mentioned 8D?? At the time, I bought the smallest 750Watt Sylvania microwave to ensure I would not have this problem. As others have suggested, there are alternative options for cooking(run the engine, bbq etc) but this is a band-aid and not the solution to installing higher end equipment.
I'll go back into the archives and research upgrading the house bank. I went ahead and bought the 3000watt converter this morning anyway and will implement all the advice given.

 

[Tom Spohn]

Rick,
I am using the same inverter with 2 6-volt golf cart batteries in series. Works my full sized microwave with no problems. GC batteries are better for deep discharge than starter or combination marine batteries.
http://www.dynobattery.com/SpecD145.pdf

 

[Benny]

I run a 700W microwave oven with a 1200W inverter just fine. Check your input voltage and make sure the wiring is of adequate size for the round trip to battery and back.

 

[Ron20324]

You should be able to put a size 31 into the 27 battery box. That worked on my B323, which came with 24's.

 

[Rick2413]

Solution....

Looks like I'm headed in the direction of battery shopping.....Thanks to all for the input. Obviously I should have paid more attention at the time of original purchase. One last question....On 2 x 6 volt batteries(golf cart) hooked in series(12volts), how does the onboard battery charger see these? How about others: 8D etc.....My documentation for my charger is at the boat but I believe its a 30 amp 3 bank charger.(10amps per bank???) Is there a special charger required also? Rick

 

[Bill Roosa]

6 volt GC batteries

Golf cart batteries are taller than most so measure before you buy.

 

[Don S/V ILLusion]

Looks like I'm headed in the direction of battery shopping.....Thanks to all for the input. Obviously I should have paid more attention at the time of original purchase. One last question....On 2 x 6 volt batteries(golf cart) hooked in series(12volts), how does the onboard battery charger see these? How about others: 8D etc.....My documentation for my charger is at the boat but I believe its a 30 amp 3 bank charger.(10amps per bank???) Is there a special charger required also? Rick

That's my preference as well , i.e., GC batteries instead of 4D or 8Ds primarily for ease of handling. Your charger will "see" these, when connected in series, as nothing unique - the charger cannot differentiate between one battery with 6 cells or 2 batteries with 3 cells each or, for that matter, 4 GC batteries connected in series/parallel, 2 8Ds connected in parallel, etc. All it "sees" is the load so no need to buy a new charger if you go this route.

l

 

[Dennis W.]

A typical 3 bank charger will be 20 amps on primary bank and 5 amps each on the other two. When properly installed will sense and charge the separate banks with individual regulation.