The case for multiple small inverters

[Cheechako]

One thought might be are there small invertors of high quality compared with the big ones? It seems many small invertors are toy like construction...

[CarlF]

Many small inverters are very cheaply made - and look awfully similar to mystery brands you can buy on EBay, I expect that their published specs are often fanciful. Specifically, I would not believe either their efficiency or parasitic load specs without testing. And then there’s the added risk of fire from manufacturers cutting corners or getting by with undersized wiring.

Mastervolt and Victron, on the other hand, are very well designed and conservatively rated. When you remove the cover you are struck by the beefiness of the components. With AES enabled the Victron 3kw parasitic load is extremely low. I’m not convinced that a 500 watt “no name” inverter would do better.

And if you have more than one of your three small inverters turned on, parasitic load is likely to be quite a bit worse.

Victrons also now come with a five year warranty. Something worth considering.

[Jef & Marin, Netherlands]

I have a Mastervolt Mass Sine 2000 running full time for the fridge and laptop and everything. 230V model. It takes 6W with no load, might be the most economic one.

By going to a 10% lower voltage you can get it to 5W if I remember correctly.
It is designed for full time running, professional, with a high MTBF. It is already in production since early 2000's. Has proven Mine is from 2003. Always worked.

Multiple cheap inverters will give you multiple breakdowns.


Many modern fridges need a little bit of 230 / 110 always on because they have an electronic thermostat.

[noelex 77]

Originally Posted by paul2884

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.

We have a 2.5Kw inverter, with a 600Ahr lead acid battery bank (@24v) but this is immaterial. The important parameter is the average energy in has to exceed the energy out. We have no generator so nearly all our power is solar based.

The draw of even small continuous loads such 120ma requires the energy to be eventually replaced. This is fine if the energy is achieving something useful, but if this is a parasitic load and can eliminated, surely this a worthwhile aim?

For a generator equipped boat eliminating a continous 120ma load means the saving of perhaps 15-20 minutes of generator run time a week. Most boats have more than one load that falls into this category and of course the savings are cumulative.

Implementing these efficiencies helps preserve plenty of power for important, useful systems. In many cases good system design and the removal of inefficient and parasitic loads can help remove the need for a generator completely, even on a boat where the electrical demand is relatively high.

[Tingum]

Originally Posted by Thumbs Up

Wire the thermostat of the fridge to the on trigger of the inverter.

Good one! I was thinking about something along those lines when I saw your posts. If the inverter is off, how would the fridge get the power to send a signal to the inverter to turn on?

[transmitterdan]

Originally Posted by 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.

What size battery bank did you calculate you need to run a fridge?

It sounds like your battery bank is simply too small.

Batteries are not “damaged” by going below 50%. The total number of charge/discharge cycles they can survive decreases but they don’t die below 50% charge.

[MVDarlin]

I'd buy a good quality large inverter to power everything and replace the power source switch with a 4 position off, store, genny, inverter. Otherwise you will need to do a lot of wiring. Note, when at anchor I turn the inverter off overnight. Only thing I have in refer's freezer is ice cubes. I have a separate 5 cubic foot freezer that is 1/2 full of bottles of water. It can be left off overnight. Sun comes up and 12 solar panels kick in. Turn on inverter. Also I have a big house battery bank. 10 Optimas

[john manning]

As someone who works on marine electrical systems it has been very interesting to read about the various ways people have handled this issue.

The only point not being raised is electrical safety. Inverter power is no longer 12 or 24 V. It is a dangerous voltage. Because marine electrical systems run above earth they require a common ground point at the electrical panel. The purpose of this is to ensure fuses blow or breakers trip when there is a fault.

If you do decide to use several small inverters then connect them directly to the appliance with a new line fuse. DO NOT CONNECT THEM TO EXISTING BREAKERS ON YOUR AC PANEL. ENSURE THEY ARE DISCONNECTED FROM THE AC PANEL. If you use the panel breaker then your appliance is sharing the ground point of other devices but your power source is independent. A short circuit fault in another device can then transfer through the common ground to your inverter circuit.

[AKA-None]

Originally Posted by Tingum

Good one! I was thinking about something along those lines when I saw your posts. If the inverter is off, how would the fridge get the power to send a signal to the inverter to turn on?

You would need something other than the inverter as a trigger like a switch. Which requires zero power to function

[mikedefieslife]

Originally Posted by Chotu

I don’t think this is right.

Inverters are sold based on their continuous output oddly enough. Most can handle near double their rating for brief intervals like the LRA of a compressor.

So a 300 watt model is supposed to be able to deal with the lra of 600 watts, yes?

Wouldn’t that work just fine for the compressor startup?

Not in my experience. If you have a good inverter compressor fridge/freezer maybe. My 50l bog standard A++ fridge could not start from a 500w Victron inverter. Well, it could but would instantly cut out, then start again. Once started it was fine. Measured peak load was over 80a. The 500w Victron is rated to 900w peak. An extra 100w probably would have done it.

[Chotu]

Originally Posted by MVDarlin

I'd buy a good quality large inverter to power everything and replace the power source switch with a 4 position off, store, genny, inverter. Otherwise you will need to do a lot of wiring. Note, when at anchor I turn the inverter off overnight. Only thing I have in refer's freezer is ice cubes. I have a separate 5 cubic foot freezer that is 1/2 full of bottles of water. It can be left off overnight. Sun comes up and 12 solar panels kick in. Turn on inverter. Also I have a big house battery bank. 10 Optimas

This interests me a lot.

I’d rather store some of the excess solar energy produced during the day in an arrangement like this instead of in lead based batteries.

Does the food in your refrigerator stay properly frozen, below 10F all night?

How about the refrigerator? Below 40F all night?

Turning off the power even for 4-6 hours each night is an incredible savings on battery needs and thus, weight.

[Chotu]

Originally Posted by Tingum

Good one! I was thinking about something along those lines when I saw your posts. If the inverter is off, how would the fridge get the power to send a signal to the inverter to turn on?

I suppose an analog thermostat would work best for this.

Regular refrigerator thermostat set to enable the refrigerator compressor at 40F, mechanical thermostat set to enable inverter at 39F.

Mechanical thermostat set to disable inverter at 35F.

Something like that.

[Chotu]

Originally Posted by john manning

As someone who works on marine electrical systems it has been very interesting to read about the various ways people have handled this issue.

The only point not being raised is electrical safety. Inverter power is no longer 12 or 24 V. It is a dangerous voltage. Because marine electrical systems run above earth they require a common ground point at the electrical panel. The purpose of this is to ensure fuses blow or breakers trip when there is a fault.

If you do decide to use several small inverters then connect them directly to the appliance with a new line fuse. DO NOT CONNECT THEM TO EXISTING BREAKERS ON YOUR AC PANEL. ENSURE THEY ARE DISCONNECTED FROM THE AC PANEL. If you use the panel breaker then your appliance is sharing the ground point of other devices but your power source is independent. A short circuit fault in another device can then transfer through the common ground to your inverter circuit.

Yes, this was the only logical installation method I was thinking of.

[Chotu]

What about a single inverter with fancy battery wiring?

Is it an improvement in efficiency to wire the inverter to the battery bank in such a way as to have it see 24v or 48v on the supply side?

[Thumbs Up]

After lots of research I bought one of these. No fan, uses heat sinks. Was going to run an LG inverter fridge off of it but got my old fridge up and running. https://www.amazon.com/Morningstar-S.../dp/B008H5AQZ4