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Small Inverter


Johny London

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Just got a little 300w (continuous) modified sine inverter. The idea being to hook it up over at my tv/media centre area and run those bits without needing to switch on the Victron 3000 (which I discovered sucks 3.5a per hour). Last nite I retired with sufficient charge to run the (12v) fridge over night, thanks to this new little inverter.

I was concerned the fan would kick in and get noisy but as I was only using a relatively small part of its capacity, though it did get pretty warm the fan never ran. 

It makes me wonder if I should fit it at the stern next to the Victron and configure some kind of switching - routing one or other to the entire mains ring, as needed.

Just thought I'd share that.

 

Ps I think efficiency is more than 90% and standby current less than 300ma :)

Edited by Johny London
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17 minutes ago, Johny London said:

It makes me wonder if I should fit it at the stern next to the Victron and configure some kind of switching - routing one or other to the entire mains ring, as needed.

That's what I used to do with ours - a patch lead from the baby inverter to the shorepower socket, and flick the switch over to that one.  I only used "Big Bertha" for short bursts when running heavy duty tools or the washing machine.

 

When "Big Bertha" blew up I just replaced it with a large inverter that only sips amps when not doing much and gave the small inverter away.

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It's making me rethink my whole power philosophy. Why was your new large inverter so much more economical than the orignal? Presumably not pure sign? But then would things with motors run ok?

And do those cheapo inverters rated supposedly at 3000w actual achieve that? Why is my Victron so thirsty?

The little thing I've got was only £13, ebay special. Food for thought innit!

If I put the little one over at the stern with the other electrics I'd have the bebefit of all the mcb/rcd stuff (if a cheapo waveform doesn't screw things up).

One other annoying thing was that while I was in the marina, the inverter had to be on the whole time, to pass the 230v hook up through and provide 12v resupply. Just a waste of equipment and power again.

Edited by Johny London
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1 minute ago, Johny London said:

It's making me rethink my whole power philosophy. Why was your new large inverter so much more economical than the orignal? Presumably not pure sign? But then would things with motors run ok?

And do those cheapo inverters rated supposedly at 3000w actual achieve that? Why is my Victron so thirsty?

The little thing I've got was only £13, ebay special. Food for thought innit!

They all differ. My combi is awesome and is never switched off but when its sat not powering anything it only draws 0.3 of an amp. For a short time on a previous boat I had a stirling that used to take 4 amps doing nowt!!

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28 minutes ago, Johny London said:

It's making me rethink my whole power philosophy. Why was your new large inverter so much more economical than the orignal? Presumably not pure sign? But then would things with motors run ok?

And do those cheapo inverters rated supposedly at 3000w actual achieve that? Why is my Victron so thirsty?

The old one was a low frequency inverter (big transformer inside) and came with the boat.  It ate about 4A when switched on doing nothing.

 

When it blew up I replaced it with a Sunshine Solar 3000W high frequency inverter (small transformer and some fancy electronics, pure sine wave) that is switched on 24/7.  It's off at the moment because we are in Liverpool, so get free electric hookup - it's the first time in 2 years I have plugged the boat into shorepower, and the last time was here too!  The washing machine and the immersion heater are getting a good workout. :D

 

It's rated at 3000W continuous, and can surge to 6000W briefly for motor start.  It happily runs my 2200W electric chainsaw or my 2500W chopsaw - I don't have a 3000W load to use it with!

 

I suspect your Victron will be a low frequency inverter without fancy power management, which was all that was available a few years back.

 

https://www.sunshinesolar.co.uk/catshow/Pure_Sine_Wave_Inverters_12V/PureSineWave12V.html

 

Watch the offers on that page if you like the look of them - they always have something on offer, and it changes every month or so.  I think the 3000W was on sale at £300 last month.

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I've got a little 300W Sterling inverter that I've had for 20 years.  I keep it as a backup for the TV in case my main inverter goes down.

When I first had it, it blew up my electric toothbrush.  On complaining about this to Charles Sterling his response was "well yes, it would".   I'm saying this now as a warning that cheap inverters may not be good for items powered through  a whatchmacallit plug (the name has fallen into that memory hole that wanders randomly around my brain).

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1 hour ago, blackrose said:

What about the N-E and hull bonding of these mini inverters. Is it safe to just not bother?

 

You also need to be aware that if you have two or more small inverters feeding different things, you can get a 400 volt shock if you get across both of them because they will not be running in synchronisation.

 

If you use two or more, please ensure that they and their load are at least 2 metres apart from any others so that you cannot physically touch both at the same time.

Edited by cuthound
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(Cheap) "modified" sine wave inverters should be avoided at all costs

You can't run a 12v compressor fridge from anything much less than 1200W (because the compressor had a large startup mode.

 

Been there done it (or not as the above implies)

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2 hours ago, blackrose said:

What about the N-E and hull bonding of these mini inverters. Is it safe to just not bother?

This one has a chassis terminal, I've taken it to the earth on a 13a plug. That's what it said to do in the instructions for boats. Obviously I don't have the benefit of the rcd though.

 

The sunshine inverters look good - I found the tech spec for the 3000w, standby was quoted at <1amp, which is an improvement on 3.5a at least. The c series 3000w (which look like the best of the lot?) quoted efficiency was a little higher but I didn't find the standby current. Though I'm not sure standby is the same as quiescent (which is more relevant). Standby might just be if it's connected but switched off, I'm more concerned with the least it self consumes while switched on but doing very little.

 

Just a bit of experimentation really.

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5 hours ago, blackrose said:

What about the N-E and hull bonding of these mini inverters. Is it safe to just not bother?

No. But folk will do it anyway. 

3 hours ago, Johny London said:

I'm not sure standby is the same as quiescent

It is. 

3 hours ago, Johny London said:

Standby might just be if it's connected but switched off

If it’s switched off it will use nothing. 

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5 hours ago, dor said:

I've got a little 300W Sterling inverter that I've had for 20 years.  I keep it as a backup for the TV in case my main inverter goes down.

When I first had it, it blew up my electric toothbrush.  On complaining about this to Charles Sterling his response was "well yes, it would".   I'm saying this now as a warning that cheap inverters may not be good for items powered through  a whatchmacallit plug (the name has fallen into that memory hole that wanders randomly around my brain).

Same thing happened to me. I thought it was something to do with the non-contact induction charging of the toothbrush

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Not sure of the above, because different manufacturers use the term standby, quiescent and no load in different ways.  Victron have two 'standby' modes one with the unit switched on and connected and no load / off load, and the other the same but with the unit set to 'power saving mode' or equivalent where the unit basically shuts down and test every few seconds to see if there is a load out there, some drop the volts to 80-100V to see it there is a load.  There is a big difference in the standby currents, one is a few amps (about 0.5 - 3 depends on model) and the one with power saving enabled is smaller (10's to 100's of milliamps). A lot of equipment will not switch them out of power saving mode, and some, like digital timers get really upset and throw a wobbly. Every manufacturer of inverters uses similar but different interpretations of these options in their specifications if they publish anything at all.  So you do get a bowl of apples and pears to sort through.

Motors run on modified square wave, but do run a bit hotter (peak current for longer), which may shorten their life and in the case of fridge compressors, you should check the temperature of the motor on a hot day, as they usually have poor air circulation to cool them.  Big heavy inverters (low frequency) have more umph to start a motor with than a high frequency one, a low frequency 800 watt Victron will usually run a fridge, but you need a 1200 watt high frequency modified square wave to be sure. The no load / off load current of both will probably be similar.

I use Victron as an example because it is the one I know, other makes are available, and arguably better.

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56 minutes ago, Detling said:

Victron have two 'standby' modes one with the unit switched on and connected and no load / off load, and the other the same but with the unit set to 'power saving mode'

But they’re not two standby modes, as you yourself explain. 

 

Only one of them is ‘standby’, the other mode is ‘power save’. 

 

If an inverter doesn't offer a power save mode (and you can be sure the manufacturers will mention it if they do) then standby means just that - switched on with no load. 

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I'm wondering what's going on with my Victron then - it definitely ups the power drawn from the solar by around 3.5a when its switched on with no load. (I haven't got an actual shunt/ammeter set up yet but am looking to, so I can be more certain of what's going on). The Victron manual does say it should only take 6w on "Zero-load (economy) power" so maybe I need to switch it into economy mode. But I don't have it running unless it is actually powering something, so for small loads it would be taking the 3.5a plus whatever the load needs? It may well be that it is 93% efficient (the spec quotes) at full load but with a standing 3.5a current self consumption it's efficiency would be terrible at low loads. I may enquire at Victron but I'd like to be more sure of my figures first. What I can say is, running the telly and stuff off the small inverter uses a lot less power (as proven with sg soc and a few evenings of actual use) - about as much less as I'd expect, given these figures.

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16 minutes ago, Johny London said:

I'm wondering what's going on with my Victron then - it definitely ups the power drawn from the solar by around 3.5a when its switched on with no load. (I haven't got an actual shunt/ammeter set up yet but am looking to, so I can be more certain of what's going on). The Victron manual does say it should only take 6w on "Zero-load (economy) power" so maybe I need to switch it into economy mode. But I don't have it running unless it is actually powering something, so for small loads it would be taking the 3.5a plus whatever the load needs? It may well be that it is 93% efficient (the spec quotes) at full load but with a standing 3.5a current self consumption it's efficiency would be terrible at low loads. I may enquire at Victron but I'd like to be more sure of my figures first. What I can say is, running the telly and stuff off the small inverter uses a lot less power (as proven with sg soc and a few evenings of actual use) - about as much less as I'd expect, given these figures.

If you dont have any decent monitoring equipment how do you know when your batteries are fully charged etc etc?

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1 hour ago, Johny London said:

I'm wondering what's going on with my Victron then - it definitely ups the power drawn from the solar by around 3.5a when its switched on with no load. (I haven't got an actual shunt/ammeter set up yet but am looking to, so I can be more certain of what's going on). The Victron manual does say it should only take 6w on "Zero-load (economy) power" so maybe I need to switch it into economy mode. But I don't have it running unless it is actually powering something, so for small loads it would be taking the 3.5a plus whatever the load needs? It may well be that it is 93% efficient (the spec quotes) at full load but with a standing 3.5a current self consumption it's efficiency would be terrible at low loads. I may enquire at Victron but I'd like to be more sure of my figures first. What I can say is, running the telly and stuff off the small inverter uses a lot less power (as proven with sg soc and a few evenings of actual use) - about as much less as I'd expect, given these figures.

 

The 93% efficiency will be quoted for full load. All inverters lose efficiency at less than full load, some spectacularly so, depending on the technology used in the inverter.

 

93% efficiency suggests a modern switch mode power supply inverter so will be the most efficient type you can get.

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Mr Smelly - I don't! That's why I keep knackering my batteries! (That and advice like "just give em a good charge once a week or so"). I use the s/g, which actually may be fairly well calibrated, because when it gets to 100%, the solar would typically be putting in <1amp. (remember my 440ah battery bank is down to about 100a total capacity!).

I have a shunt to connect, but the battery access is poor so I was putting it off until I either replace them or go lithium and do a full re wire etc.

I think cuthound may be right - 93% efficiency at full load but if I am using it for small current draw that figure looks very different.

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