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Old 18-05-2011, 06:56   #1
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Small AC Power Onboard

I've finally bought an inverter for my boat -- a Victron Phoenix Multiplus 24 volt 3000 watt 70 amp inverter/charger.

This solves a couple of different problems -- I will now have enough charger capacity to charge the batteries meaningfully with the generator without ridiculously long generator runs. And I will be able to run briefly various AC appliaces (microwave, electric kettle, toaster, power tools) without cranking up the genset. Hurrah!

But I also need small amounts of AC power for charging phones and laptops, and running a small television set. I have cigarette-plug DC power supplies for my own phone and laptop, but every single guest and crew member who has ever been on board always has at least one phone and one laptop each which seems to constantly need to be charged, so that is not a solution.

I have been using an el cheapo Chinese cigarette plug 150 watt inverter for these purposes with reasonable effectiveness, but it's rather Rube Goldberg looking with several phones attached to it at once, and gets in the way.

It seems to me that the Victron inverter is not designed for such small loads -- it looks like (if I'm reading the manaul correctly) it will switch itself off if there is not a load on it greater than 50W.


Anybody come up against this problem? What did you do about it? I suppose I could install a separate 350W inverter -- the Victron pure sine wave one only costs 100 pounds -- and connect it to a power strip which would be used only for electronics. But it would be inelegant to have two inverters on board, if one could deal with all of the inverting tasks.

Thoughts?
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Old 18-05-2011, 07:05   #2
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Re: Small AC Power Onboard

We have two inverters for the reasons you describe...........inelegant.....yes....cheaper and more efficent than any of the ridiculous alternatives I could come up with......YES!!
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Old 18-05-2011, 07:20   #3
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Re: Small AC Power Onboard

Turn on a light? 50watts is pretty easy to find!
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Old 18-05-2011, 07:22   #4
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Re: Small AC Power Onboard

If you don't want to run extra AC loads you don't need, and don't want to modify the guts of the nice new Victron....

One option: Exactly what you suggest, Dockhead, and what Sailmonkey did. Add a cheap, small second inverter, connected to a power strip, for the chargers and stuff. Put a warning label on the strip "Low-power chargers only" so that nobody tries to plug the power drill into it.

The only other option I can think of: Use DC/DC converters to get the voltages your devices need, and fit them with interchangeable connectors to suit the various proprietary plugs on the gadgets. Possibly a bit more efficient, but much costlier and more time consuming.
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Old 18-05-2011, 07:31   #5
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Re: Small AC Power Onboard

Your whole generator to charger to battery to load (to toast) system is so inefficient is it reasonable to concern yourself with the tiny difference between a large inverter and a small? I wouldn't think so.

Powering more than one small device at a time will solve the 50W minimum issue, as well as probably double the efficiency.
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Old 18-05-2011, 07:50   #6
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Re: Small AC Power Onboard

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Originally Posted by capngeo View Post
Turn on a light? 50watts is pretty easy to find!
Ditto. I've never had my inverter turn off from no load. Two laptops should do it.
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Old 18-05-2011, 08:02   #7
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Re: Small AC Power Onboard

Well, I have re-read the Victron manual, and I see that it will shut itself off at 40W (not 50W) only if I have the "search" function enabled. "Search" allows you to leave the inverter switched on all the time -- it will shut down the inverter when the load is less than 40W and so cut the no-load power consumption almost to nothing.

If I disable "Search", then I can switch on the inverter and it will stay on, and people can plug their chargers into any old outlet on board. It's pretty inefficient but maybe not unacceptably so. The inverter will consume 10W with no load, plus whatever it takes to produce the AC power consumed. Maximum efficiency is 94%; I have no idea what the efficiency would be while you are using 100W or so to charge phones and laptops.

I guess it probably makes more sense than to go to the trouble of wiring up a whole separate inverter for low powered devices. I kind of fall in with Daddle on this, I think.
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Old 18-05-2011, 08:10   #8
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Re: Small AC Power Onboard

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Originally Posted by capn_billl View Post
Ditto. I've never had my inverter turn off from no load. Two laptops should do it.
FWIW,

A Laptop is not even close to the same as a cellphone charger. The laptop draws a fair amount of current.

Running a simple laptop through an inverter can draw 5-10a (high if using ac 'brick'). Unless you are talking about the netbooks that can run on 12vdc, a laptop is not a small load.

To the OP, I would suggest to your guests they bring car chargers for their phones. The small inverter works ok, but they are not efficient and can cause lots of 'noise' that may effect radio communication.
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Old 18-05-2011, 08:33   #9
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Re: Small AC Power Onboard

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Originally Posted by s/v 'Faith' View Post
FWIW,

To the OP, I would suggest to your guests they bring car chargers for their phones. The small inverter works ok, but they are not efficient and can cause lots of 'noise' that may effect radio communication.
I have too many different people on board for that to be realistic. Some of them have urgent business. I have run my generator just to charge someone's Blackberry when there was something really urgent, which of course is the height of absurd inefficiency.

I am wobbling between just leaving the inverter on and letting people plug into regular outlets, on the one hand (at least, during certain hours), and creating a charging station with a separate 350W Victron inverter and a power strip, on the other. Each variant is kludgy in its own way -- bleh.

I will save a certain amount of power with the second variant. Whether it makes any noticeable difference in the end -- enough to justify installing a whole nother device -- I don't know.

Let's say we're charging a laptop and two phones at any given time. I guess that could be around 150 watts? Thinking out loud now. Let's say the big inverter is only 60% efficient at such a low load, and it has 10W of overhead on top. That means it takes 260 watts out of my batteries to produce 150W output from the big inverter -- by the way, not such a small load. The small inverter is say 85% efficient and has 5 watts of overhead -- it will be using about 180 watts. So I'll be saving 80 watts by using a small inverter. 80 watts is 3.3 amps at 24V. 24 hours of that is 80 amp/hours or around 18% of the capacity of my 440aH battery bank.

Looking at it another way: 260 watts will use 2.5% of my battery capacity every hour, so 10% every four hours and will eat up the whole 50% practical capacity in 20 hours. 180 watts will use 1.7% every hour, and 10% will take 5.9 hours to eat up 10%.

Kind of looks like the small inverter might be worthwhile.
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Old 20-05-2011, 21:00   #10
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Re: Small AC Power Onboard

Another thing to think about if you leave your main inverter on its people plug in other things in such his hair dryer etc.
Mount your small inverter out of sight and wire it directly to your battery system, with a remote switch at the power strip appropriately labeled. But the power strip in a place that can sort of act as an office. Just my two cents, Mike.
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Old 23-05-2011, 11:05   #11
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Re: Small AC Power Onboard

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Another thing to think about if you leave your main inverter on its people plug in other things in such his hair dryer etc.
Mount your small inverter out of sight and wire it directly to your battery system, with a remote switch at the power strip appropriately labeled. But the power strip in a place that can sort of act as an office. Just my two cents, Mike.
Good point. Coming from land people tend to assume that anything that looks like a plug-in has an entire megawatt power plant behind it.
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Old 23-05-2011, 12:06   #12
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Re: Small AC Power Onboard

we have a small (350w)dedicated chart table inverter,for phones,nav computer,irridium phone etc,this stays on all the time,with its own twin socket.

the other 2000w inverter runs the house sockets and appliances and can be shut down if power conservation nessacary,the house sockets also are live when the genset is running,this allows control of power usage,very important with people used to living in houses..................
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Old 23-05-2011, 12:44   #13
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Re: Small AC Power Onboard

Why not use 12 Volt (converted) to charge the small loads? Why invert to 110 and then down to whatever the phone or other gadget needs?

Alternative: USB chargers.

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