The case for multiple small inverters

[waterman46]

This same subject of inverter standby current came up very recently in a different thread, I believe.

I think you are complicating the issue. If you have all these 120V appliances on the boat, you obviously have a large house bank. I would guess at least 800AH.



It's hard to believe that so many of the inverters referenced in this thread have such high standby current. A very simple, low power circuit can detect the condition of no AC load and shut off everything in the inverter except for it's own sensing circuit.


The 25 year old Heart (now Xantrex) 2KW inverter/charger has a standby DC current of only 120mA at 12V, and surge power output of 4500W. Plenty to start the reefer or freezer. 120mA standby current is about how much a small LED cabin light. Notice I said LED, not incandescent. This inverter/charger is an excellent design. I hope Xantrex did not change anything - the current on-line manual is still exactly the same as my 1996 printed version. My Heart inverter/charger has been chugging along just fine since 1996.



The Xantrex 2000 is not a true sine wave machine. But it works fine on our dorm fridge, TV, washing machine, tools, etc. The only time we had trouble was when our old microwave broke down and the first replacement unit we bought, the cheapest one we could find in Zihuatenejo, did not work with that inverter. Went back to store, bought a higher priced unit and it works just fine.


Not sure what your reefer load is, but I am almost sure the 2KW inverter output will handle the reefer, freezer, microwave and TV simultaneously, as long as you house bank can keep up with it. Dishwasher and washing machine can be run at times you don't need the microwave.


If you can stay under the 2KW with no real effort, just go with a single 2KW inverter. The 120mA standby current is totally, I mean totally insignificant to your house bank.


Even if you need two such inverters, we are still talking about only one extra LED cabin light amount of standby current if you fail to switch the second inverter off. As you have a huge amount of house bank and solar to charge it I'm sure, that current disappears in the noise.

[noelex 77]

Originally Posted by waterman46

The 120mA standby current is totally, I mean totally insignificant to your house bank.

120mA is a commendably low standby current for a 2KW inverter, but is wrong to view these small continuous loads as “totally insignificant”.

It is a little over 20 Ahrs a week (@12v). Another way of thinking about this, if you have an engine alternator that is capable of a continuous 60 A, it is over 20 minutes extra run time per week . Another example is you can boil a full electric kettle of water every second day for a similar power draw to this “totally insignificant” load.

The real danger is without some care and system design these “totally insignificant” loads have a tendency to accumulate over many devices.

It is nice to have abundant electrical power, but part of the secret in achieving this goal is designing systems and choosing equipment that will use the electrical power efficiently. Don’t dismiss small power loads that are running for long periods, especially parasitic loads that are not achieving anything useful.

[wingssail]

Originally Posted by Chotu

We all make our choices and compromises.

A lacking galley is not one I’m putting up with. A 50’ cat with a 70ft air draft, currently weighing around 12,000-14,000lbs,, props that retract out of the water, Dagger boards, every possible pound saved? Yes. I already made my sacrifices. But tiny dorm fridges and pits to dig through when cooking? Hell no.

I think I’ll be plenty fast with 300-400 lbs added to have a real refrigerator and freezer, laundry and dishwasher (dishwasher is already on board).

My entire propulsion system and 6kw generator weighs a grand total of 492 lbs. 2 engines and a generator. 492 lbs.

I’ll be fast enough. Lol

I think you're fortunate to be putting together such a boat and I'd say that a little extra equipment and room for a home style galley would not be out of line. I'd do it too. (I might not do the washer dryer thing however, but that's obviously up to you).

I am surprised that you are considering what I'd call a mickey mouse electric system for the AC appliances. In the first place you won't have proper monitoring of these devices, (although you'll have redundancy if one fails). In the second place you'll have more boxes, more wires and more stuff to keep quiet when you want to use the radio.

Just get a good, high efficiency, sine wave inverter/charger 2K-3K and do a professional install and your electrical usage will be close to optimum anyhow.

[Chotu]

Originally Posted by wingssail

I think you're fortunate to be putting together such a boat and I'd say that a little extra equipment and room for a home style galley would not be out of line. I'd do it too. (I might not do the washer dryer thing however, but that's obviously up to you).

I am surprised that you are considering what I'd call a mickey mouse electric system for the AC appliances. In the first place you won't have proper monitoring of these devices, (although you'll have redundancy if one fails). In the second place you'll have more boxes, more wires and more stuff to keep quiet when you want to use the radio.

Just get a good, high efficiency, sine wave inverter/charger 2K-3K and do a professional install and your electrical usage will be close to optimum anyhow.

Yeah, the washing machine is not on my want list at all. I’ve advocated to have it installed last after we are aboard to see if we really want it. Every pound does indeed count.

I’m not settled on one path or the other yet. This thread has a lot of good pro and con posts. Lots to consider. However, it wouldn’t be Mickey Mouse nor would there be any problems monitoring it.

The proposed multiple tiny inverter setup would be downstream of the DC panel. A switch on the DC panel for Refrigerator would energize the DC circuit to the tiny inline inverter to power just the refrigerator. Ever seen people use multiple small solar charge controllers instead of a big one? Same idea. It’s easily monitored by my battery monitor as a normal DC load going through the shunt.

Any inverters will certainly be sine wave only.

But I’m not absolutely convinced of either approach at this point. It may be time for.... (gasp)

MATH! ha ha ha.

[GRIT]

The Victron 3000VA Pheonix inverter manual claims it uses 1.5w on standby.

I have this unit, and it seems to cycle "on" for about a 10th of a second, every 2 seconds or so, when on standby. You can program how much load you want it to see before coming on to power your devices.

Having said that, we use a small true sign wave inverter, to power a plug in the nav station, for computers, and miscellaneous chargers.

I see nothing wrong with having an inverter for each load, or several small loads. It does give you more backup, in case of failure.

As a side note: We're still building, and are using a bar fridge until we mount/build a permanent fridge/freezer. The bar fridge didn't work well on a 1000W inverter, it sometimes started, and sometimes not. The inverter squealed an overload alarm when the fridge didn't start. We consequently bought a 2000w inverter for the fridge, but have since relegated both of them to storage, and use the Victron for everything, but the nav station plug.

Cheers.
Paul.

[s/v Jedi]

There is another advantage: many 120V/60Hz boats buy a compact European washing machine that is 230V/50Hz. They use a small inverter to power that... i.e. you can have different voltages/frequencies

[Culwatty]

Originally Posted by Chotu

the thread is about selecting either one large inverter or multiple small ones to power given loads. In the case if refrigeration, a cyclical load. In the case if everything else, user controlled loads.

marine refrigerator pits absolutely suck in every way and are just a tad more efficient than the best land refrigerators. The galley is the focal point of my life. Digging in a pit to find all the food is wasteful in terms of time spent, aggravation and even efficiency. How much heat is absorbed by putting the whole contents of the pit on what’s left of the counter when you’re trying to find something at the bottom? More than opening a door for 5 second for sure.

12v front openers?? Maybe. If there are reasonably priced, large enough ones. Still need to run the long term storage chest freezer though.

I’m off grid. Always. No shore power. Generator is only used for HVAC purposes. The rest is 1400 watts solar. 440 (I hope) or maybe 660 AH battery bank for night time loads. The less you drain the batteries the way longer they last, so I’m trying to maximize evening efficiency given the design parameters.

Another idea might be to just knock off the power to the refrigerator and freezer from say 3AM to 7AM each night. Not sure how good the insulation is on the house units. Probably not so great I’m assuming.

I am installing small top loading freezers 60L each x2 one as a freezer one as a fridge, they are very small form factor but the extra insulation means they will cycle less. i will post some figures when they are installed i may not even bother with the freezer and have 2 fridge units. time will tell!

[CaptJPMcGuire]

If you can keep them in phase OK but out of phase you just might have an open 220 volt 30 amp circuit waiting to send you and yours to the promised land!

[ikebartlett]

The smaller inverters are much less efficient and usually not a pure sine wave. I have two smaller units installed for a while, once changed out with one larger (4kw) I noticed higher DC voltage in mornings just before sunrise. I added a switch on the shore power line so only the shore power or the inverter can supply the power but never both: a couple notes
1. To supply 15 amps at 120 AC you need 150 amps from the batteries, that’s not to say you will use all that but you must size your battery cables for the maximum draw
2. I installed a 175 amp fuse at the battery to protect the circuit
3. I used 2 x 100% cables for the dc supply as they are very large
4. I added a master switch on the inverter in a convenient place in the cabin as the inverter is not easily accessible
4. With 500 watts of solar panel the system is stand alone and I haven’t plugged into a dock in years
5. I also added additional batteries to truly balance the system out

[brianbrown3373]

I installed a 6kw inverter and have the following to report.

First of all the cabling is critical. You must follow the directions on the inverter when you install it or a fire could result. Usually its a very heavy cable like the ones that run to your battery. The longer the cable the thicker and heavier it must be. So best to install just a few feet away from your battery.

Next, the inverter will only work for a short time, even with the engine on and your alternator pumping in electricity. Why? Because the inverter will suck the battery dry in less than 10 minutes if you are putting a heavy pull on it, like a fridge. Remember the equasion: Watts=volts times amps. That's a critical one when determining what AC products you can use.

Overall, this kind of converter is not ideal. It got so bad that I installed a separate battery to work with it but that too drains rapidly. So for short sprints where you need AC its a great solution. For on going needs like a fridge, choose a DC system with AC auto switch over.

Last, if you tank your batteries below 50% you will generally damage them. The inverter will tank them to 0% if you keep it on.

Originally Posted by Chotu

I had been looking at getting a big inverter (3kw) to run a refrigerator, chest freezer and whatever else, including microwave, dishwasher, washing machine.

The more I have looked into this, the more it seems that’s not the best way to do it.

Large inverters idling can use quite a bit of power.

Instead, I’m looking at getting a few small inverters. One for the refrigerator, one for the freezer, one for the microwave and whatever else, since they don’t run simultaneously.

Anyone have any thoughts as to why this is a bad idea?

I would just wire them right in to the DC panel as DC circuits, but near the panel, there would be an inverter, which then runs an ac wire to the appliance.

The other, more general microwave inverter would run normally fully on the AC circuits with a transfer switch.

[paul2884]

Originally Posted by noelex 77

120mA is a commendably low standby current for a 2KW inverter, but is wrong to view these small continuous loads as “totally insignificant”.

It is a little over 20 Ahrs a week (@12v). Another way of thinking about this, if you have an engine alternator that is capable of a continuous 60 A, it is over 20 minutes extra run time per week . Another example is you can boil a full electric kettle of water every second day for a similar power draw to this “totally insignificant” load.

The real danger is without some care and system design these “totally insignificant” loads have a tendency to accumulate over many devices.

It is nice to have abundant electrical power, but part of the secret in achieving this goal is designing systems and choosing equipment that will use the electrical power efficiently. Don’t dismiss small power loads that are running for long periods, especially parasitic loads that are not achieving anything useful.

For someone who has a house bank capable of supplying 3KW (or something like 250amps) for some length of time 120mA is pretty insignificant.
Even if it averaged out at 250w per hour over 24 hours that is still something like 500Ah/day. Can't see you managing with a 800Ah battery bank unless you are going to run a generator every day?
Must be lithium, lead acid would have to be massive not to kill it in a few months.

[ikebartlett]

PS. The main reasons I have a large inverter is that I have a water maker that has a dc supply pump but an AC high pressure pump so I need almost 15 amps AC when I make water. My unit produces 20 gallons an hour and I have 60 gallons of tankage. So the math is 12 amps x 120 Volts divided by 12 Volts = 100 amps times 3 hours equals 300 amp hours. My solar gives me 18 amps so I make water in 2 or 3 batches. If the sun is really shining I’ll make 20 amps from the solar so I’ll run the main engine to produce 60 amps, starting out with fully charged batteries I can make 60 gallons before my batteries get down to 12 volts. The second reason is that my fridge/freezer is dual voltage and runs better on 120 AC that 12 volts dc

[Cestmoi]

Good Idea dual channel reliability!

[Cestmoi]

Great Idea dual channel reliability!

[lituya1617]

It occurs to me that sailing in the sense of using sails to propel a vessel is a pretty established activity; however, when sailors start talking about having automatic dishwashers, washers and dryers, fancy refrigerators and freezers, wine coolers, automatic anchor windlesses with remote controls, autopilots attached to chart plotters, multiple diesel engines, gen sets, ad nos, this is not sailing. Maybe it is living high on the hog - but hogs are not marine animals. I love sailing - the act of sailing. I get along fine on the rudiments.