Power inverter

TyBoo

TyBoo

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I have a 1500 watt Cobra branded inverter onboard that I use mainly to run a Keurig coffee maker and a small microwave.

Today I tried to power a new induction cooktop and found that until a load is placed on the AC side of the inverter the output voltage just sitting there is about 70vac and the stove shuts down before it even gets started with a low voltage error. If I start the 900 watt microwave the output voltage at the inverter goes up to 106vac and then the stove will turn back on and they will both run. That, of course, overloads the inverter if I set the stove to a usable power level. It is also kind of dumb to have both things trying to run at the same time.

I don't really understand all I know about this stuff, so - here are my questions. Thanks in advance.

Is there something wrong with the inverter I have? The smaller inverter that powers the TV and a couple of video cameras always has 107-110 volts output when idle, so why doesn't the larger one? The input voltage to it is greater than 13vdc with either the motor running or the shorepower charger on to feed the batteries. There is a good deal of voltage drop when running the Keurig but the unit (almost) always stays above the 11.5vdc cutout point.

Speaking of voltage drop... When I installed the inverter I wanted it inside the cabin so I ran heavy lines from the batteries. The first try with AWG 2 wires didn't work so I ended up using 1/0 stranded copper battery cable for both legs from the batteries located port stern to the inverter located starboard amidship. That is a run of a little over 20'. I don't get any significant voltage drop with the 900 watt microwave but the 1400 watt Keurig pushes it.

I am using two marine cranking batteries (Group 24 I think, but maybe 27) and I don't recall the CCA rating but it is pretty good. I get them at Costco and replace them every few years because I pretty much abuse them. They are cabled in parallel and have been left that way for years. The kicker has its own battery that will start the main if I need to jump it so I don't worry about it. There is a 150 fuse at the battery just for the inverter supply.

If I replace the inverter I am thinking about putting it in the compartment with the batteries using short DC cables and a long AC supply line to the cabin. That should minimize the voltage drop on the DC side and safely feed the appliances inside that are used one at a time. The hatch where the batteries sit is a semi-dry compartment under the floor and there is room in it to put a small box of some sort to protect the inverter from all but humidity. I suppose it would have to be large enough and vented so the inverter fan will be able to supply cooling as needed. Can I reasonably expect the inverter to last very long out there under the floor? They aren't all that cheap, although I could get one for less than that battery cable in there now is worth.

Just a quick glance on Amazon turns up this 2000 watt inverter that is rated pretty good and accepts a remote switch so it can be turned on and off from inside the cabin. It is priced low enough that a complete fail on my part wouldn't hurt a whole lot.

This turned out to be a long winded post. I appreciate any advice or insights you can offer.
 
Without seeing your wiring, I suspect your inverter is fine and you are using an inexpensive multimeter to take the reading? Is the inverter a modified sine ? Correction: you could be using an expensive multimeter that is not a true RMS meter, and not get an accurate reading on a modified sine inverter. My electrical background is from running a royal ton of DC cathodic protection Lines from AC sources, not residential or marine work. But I would check the meter and inverter type first. Or post here and I can look after I’ve slept and compare notes with my electrician buddy if nobody more knowledgeable than myself replies (though no doubt they will!)
 
Sorry triple posting... what I’m asking is: is your inverter a modified sine inverter, and is your meter a true RMS meter? If yes to modified sine, is the new stove compatible?
 
The meter is an older Fluke DMM. It is on the boat so I can't get the model number right now. That RMS stuff is a little beyond me so I cannot answer further.

The inverter is a Cobra CPI 1575 1500 Watt modified sine wave (now discontinued).

The output voltage reading on the meter changes from 70vac to 106vac when I switch on the microwave. At that point the induction stove will operate as it should.

The internet seems to be heavily on the side of saying the stove will work on MSW. Nevertheless, perhaps I should limit my replacement options to PSW inverters? Those are getting up there in cost and I would be hesitant to risk locating it back close to the batteries. Moving or substantially changing the battery arrangement is not a good option for me. The whole project is not worth that much effort.

Thanks! I have a cheap Klein DMM I can take down tomorrow and check the voltage again to compare with the Fluke.
 
TyBoo":1hq4y42m said:
The meter is an older Fluke DMM. It is on the boat so I can't get the model number right now. That RMS stuff is a little beyond me so I cannot answer further.

The inverter is a Cobra CPI 1575 1500 Watt modified sine wave (now discontinued).

The output voltage reading on the meter changes from 70vac to 106vac when I switch on the microwave. At that point the induction stove will operate as it should.

The internet seems to be heavily on the side of saying the stove will work on MSW. Nevertheless, perhaps I should limit my replacement options to PSW inverters? Those are getting up there in cost and I would be hesitant to risk locating it back close to the batteries. Moving or substantially changing the battery arrangement is not a good option for me. The whole project is not worth that much effort.

Thanks! I have a cheap Klein DMM I can take down tomorrow and check the voltage again to compare with the Fluke.
Click to expand...

I believe your meter is most likely not a true RMS meter and taking an improperly calibrated reading on the modified sine wave inverter. If you could borrow a TRMS meter and test the AC output of the inverter it would tell you if your inverter is working. If my first guess is correct then most likely your stove and the inverter are not playing well together. I’m sorry I don’t know how induction stoves are wired, and if they operate with simple circuitry or have some crazy computer in the in them. It sounds like they may need a good jolt of clean juice to kick in, which leads me to believe they also are more of an off/on type of battery drain than one that can be controlled? I would like to know more about them if anyone knows how the electricity is converted back to heat in these? Can they be dialed down and run at low power or are they cycling on and off at full throttle to maintain a temperature?
 
Whether the voltage is being read correctly doesn't change the fact that the induction stove won't come on unless something else is turned on first.

This is probably due to how the stove interacts with the inverter- it puts very little load on during its initial start up, so the inverter thinks it sees nothing and turns itself off.

So use the microwave or preferably a smaller load to get the stove started then turn it off.

David
 
Mike, inverters stay in an idle state with no or low output voltage until they sense a load then go to full output voltage. This is so they don’t draw high
Input current and drain your battery needlessly. Your stovetop has a smart
circuit built into it to protect it from low voltage. So these two devices have a
conflict when connected together, as you found out.
Try doing what David suggested , plug in a simple resistive load first , such as
a 60 watt light bulb, let the inverter come up to full voltage, then plug in the cooktop. You can then remove the bulb to save some power.

Mike
 
I've looked at this issue quite a bit, mostly on RV sites, and have concluded that you basically never know if an inexpensive induction burner will work with an inexpensive inverter. And if it doesn't, which to blame. I lucked out and my inexpensive burner ($50) works with my "inexpensive" ($250) inverter. I had read enough to know that I might have bought an induction burner that would end up being used at home and an inverter that was larger than I needed on board.

Most of the posts that I saw blame the inverter for being MSW "Modified Sine Wave." Electronic geeks say MSW is really am acronym for Modified Square Wave made to look like a sine wave. Okay, whatever. The fact is that some MSW inverters will power an induction burner and some don't. Some claim that certain brand names of MSW inverters are a better mimic of a true sine wave and that's why they work.

The best solution I saw was to go boat to boat (or RV to RV) with the induction burner and see whose inverter will power up the burner. The second "fix" was to borrow induction burners and try them with your inverter. Not a sophisticated electrical analysis, but might be the fastest solution.

I'm entertaining the idea right now of replacing a three burner propane oven/stove with a two burner induction cook top. The boat already has a 3KW MSW inverter. I think I'll plug in my induction burner first to see if that MSW inverter will power it. Even if it does, it probably isn't a guarantee that it will work with a newer cook top. Another "low tech" solution was to order the items on Amazon Prime and quickly try them. If they don't work, send them back within the return period. Again, not a sophisticated solution.

I also saw some interesting posts on how the burner senses whether there is a pot on it and is effected by the alloy of the pot. Common knowledge is that some pots don't work. Some even find that certain pots work better. What was surprising was that some pots work better because the induction burner draws more juice with the "good" alloys. A cast iron pot, while kind of a pain on a boat, might just pull enough juice to kick on the inverter.

Mark
 
Nice video to explain True RMS and its importance. I agree with Mike W. These less expensive inverters do need a small load to come to full power, and the "on" circuit of the induction burner (I have an identical burner) is not enough to trigger the full output output of the MSW inverter

I err on the conservative side having owned MSW inverters since the early 70's (and the electrical "noise" going with them when hooked up to many appliances). I use a PSW inverter on the boat, coupled with 180 amps usable from the Li batteries.
My Victron does fine with the induction burner alone. One of the reasons I use the PSW, is that microwaves will run on the MSW, but don't seem to put out as much power, and make a lot more noise.

It really helps to have an oscilloscope to see what the true voltage and wave form is from an inverter. Some of the newer MSW are stepped so closely to sine wave, that many appliances work perfectly with them.

When it warms up a little, I'll take my simple "Kill-a Watt" meter to the boat and see what the draw of the induction burner is on its "on" setting. There are circuits in the induction burner which keeps it from turning on if there is not a ferrous or induction type of pot on the burner. I believe the circuits for even the cheap induction burner are not simple. There are variable power levels. They don't seem to vary in power use at each level, but I have not fully assessed this when cooking.
 
It sounds like I need an exciter on the boat. Maybe Lois is up to it. We are going back down to the dock to fool with it today so we will see if that does it.

That all makes sense and I will take a small lamp with a 60w bulb to try. I know that just the microwave being powered up and not running is not enough for make the stove work. If I start the microwave the stove will then turn on but stops if I open the MW door. Maybe I just need to let the induction stove get the inverter up to speed on its own before removing the other load. Or leave the lamp on. We will see.

Thanks, and I will let you know the progress.
 
Tyboo,

Tosca has had an inverter for at least 10 years. It is mounted by hanging it under the splashwell. Water doesn't get to it there, but it is most certainly very damp in that compartment. Never had a problem running that inverter.

My only complaint is that I have to get out of the cabin and open the hatch to reach the switch to turn it on. I highly recommend getting the remote switch of which you spoke.
 
Thanks Tosca! That is just what I wanted to hear.

I found one inverter on Amazon that has both the remote switch and the ability to connect the remote it to a switched power source so I can kill it with the master disconnect I have at the helm. It is a true sine wave and more than twice what I was hoping to spend but Lois wants to cook.

Funny thing is, I discovered that the 20 year old 250 watt inverter that I could replace for nineteen bucks today will run the stove just fine. Probably not for long, but it does it like I would expect. Maybe I just have a dorky inverter. Don’t tell ‘em but I might go the try/return route with Amazon until I find the right match.
 
Not yet - the first of the Amazon inverters to try should get here with the mail in a couple hours. It's the cheap one I linked earlier.

I was going to go with the pure sine wave right off the bat but after discovering the old 250 watt inverter will run the stove on low power I figured the newer MSW one might work for a couple hundred bucks less. We will see.

Interesting how quickly electronics evolve and get better/cheaper as they do. Kind of the opposite of everything else. That old inverter was bought for my toolbox at work back in the mid '90s to run a laptop computer. I remember very well the cost of the thing because the limit at the time that a foreman could approve for direct purchase was $200, and the inverter was $199.99. I had already convinced the superintendant to buy the $2500 laptop for me even though I was just a dumb mechanic so I didn't want to push it any further. The same thing today - different brand but better specs - would cost less than fifty bucks.
 
TyBoo":2o4njnh3 said:
... Interesting how quickly electronics evolve and get better/cheaper as they do. ...
Click to expand...

Problem is that nothing today is repairable. Yeah, things are cheap enough that you can just buy a new one for just about everything, but the issue is the waste caused by people throwing all those broken things away.

Remember the days of TV and appliance repairmen?
 
So here's the latest.

The new $140 inverter was for sure more efficient than the old Cobra. It ran the coffee maker without stressing the input voltage and ran the microwave oven like a champ. It also started the induction stove without the error code it had before and allowed me to set the temp/power/timer as I wanted but it still didn't heat at all. It just sat there pretending to heat. I think that is what it was doing with the little inverter too when I thought it might've been working.

So, I dropped the inverter off at the UPS Store and the refund has already been applied to my Amazon account. Monday's mail will bring me the $234 pure sine wave inverter. If it doesn't work, the next step is the $367 model. If that one is a bust then I'm either going to have to eat cold food or find a job I guess.

Just so I am clear - Pure Sine Wave and True Sine Wave are the same, correct? As opposed to square wave or modified wave? And the PSW inverter should run without making the video feeds and the radar screen shake, correct?

Today I pulled out the Honda 2000i and plugged the induction stove into it. The motor revved right up and I had water boiling in no time at all. I think that cooktop is going to be a hit on the boat and I might even get another one for use out on the patio at home or when the power goes out. That is unless I have to get the next step up in the inverters then I'll be broke.

Check back Monday. I have to go to a birthday party for my 6 year old great grandson tomorrow.
 
I gotta say, I really appreciate you doing all the legwork for what could be my next inverter 😂. Pure = true. Bonus: you should be able to charge up any finicky laptops or tablets without over heating the power packs/cables. I am currently chasing down a loose neutral in my house, and wish I was tinkering with boat wiring. Hope you eat a lot of cake and don’t step on any LEGO’s barefoot!

Nigel
 
I think that the issue is clouded by terminology as well as what we are effectively seeing electronically. The pure sine wave, maybe a little "dirty" Some stepped wave inverters are more than the 3 or 4 steps we see in a MSW inverter, lets say 8 steps, yet are still not really "pure" sine wave as we are supposed to see from Mains power. (The reality is that sometimes the "pure sine wave" is still not real "clean" from mains power. So I suspect that the induction burner need pretty clean power. If you can put an oscilloscope it will show if the wave form is a true sine wave (smooth) or its a number of steps which many would consider representative of a sine wave. For example Aims makes a 3000 watt "pure Sine wave inverter which costs $400 and one which costs about $1000. The one which is the cheaper has multiple cooling fins, and I suspect is all solid state. The more expensive, has a cooling fan, and is considerably larger and heavier. The latter has a transformer, and more sophisticated circuitry.

I have gone with the latter type, more expensive (Magnum or Victron) pure sine wave inverters, since I have seen scopes put on them, and they have a sine wave often better than mains power....

The other issue, is the service life and durability. The Magnum in the RV would run a lot of time, since it was running a household refrigerator. In 10 years of use, I had to replace a circuit board. A friend was running a cheaper "pure sine way" unit, and his would have to be replaced every year.

Only problem is that most of us don't carry an oscilloscope in our back pocket. Another resource is "The Inverter Store". They may have a handle on what less expensive inverter will handle an induction burner. One of the reasons I went with Victron on the boat, is I had verified that it would run the induction plate from information given by some who had tried other inverters. (The Victron is large and heavy, cost was just over $1100, including a 80 amp charger. It can be profiled to run with any types of battery, and has a temperature monitor, as well as a number of other perimeters which can be programed in: such as peak load, resting voltage cutoff, powered voltage cut off, as well as the charging profile).
 
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