Electrical Musings

[hellosailor]

Mike, is your parasitic load 25 milliamps? mA? or microamps? uA?

25 milliamps would really seem excessive these days. I haven't gone looking at BMS systems but there are so many circuits which sip next to nothing these days, I can't believe one would take 25mA. Unless it was designed by an old Soviet engineer who retired to start a Chinese manufacturing company.<G>

Dockhead, have you contacted Victron about your situation? If their literature is THAT wrong about the product spec, and you're stuck with a problem, most reputable vendors would either replace it at no charge to you (or nominal charge) or offer to refund your money if you returned it. Give them a chance to be heros--or not. And then tell us what happens.

[Dockhead]

Originally Posted by hummingway

I turn it on only when I want AC, which isn't very often. There's a few systems that "someday" I'll convert to 12v and then I'll use it even less unless I find myself tied to a dock again.

It's difficult to assess some of this stuff since change a variable in your life and everything changes. I've been going on two week trips mostly by myself with usually a weekend here and there with a friend and a couple of weeks with my son once a year. Two weeks by myself means the 12v mini fridge can hold enough fresh food for the whole trip. The 110 in counter freezer hasn't been run in some time. I believe it used to be 12v and I'd like to convert it back but it's been low priority. Showers aren't high priority when it's just me so the 110 water heater is fine. If I can't make a solar shower and a cockpit bath won't cut it I run the gen for half an hour. Of a sudden it seems I'm going to be sharing my boat more and being able to carry more fresh food and making the hot water more efficient seems more important so I'll probably, in time, convert them to 12v.

It sounds like you run your AC all the time you're on the boat. Are you finding a lot of applications where it is required?

Yes, the AC is on pretty much constantly when I'm on board, especially if I'm not alone. Right now I have five people on board, five laptops, unknown quantity of ipads, mobile phones, cameras, etc., etc., etc., all needing a charge all the time . . .

Besides small electronics, I use AC power for a multitude of tasks in the galley, vacuum cleaner, charge power tools, etc.

For all that, the total power consumption in amp/hours doesn't seem so bad. I run the genset twice a day at peak power consumption times (or when I need to wash a load of clothes or make hot water without turning on the heat), and that seems to cover everything pretty well. If I don't have any particular heavy loads and am not running the heat, my battery bank will support life on board without charging for about 24 hours before charge gets down towards 50%. Even if I have my non-LED anchor light on and electronics powered up overnight (as I do when at anchor).

I have changed most of my lighting to LEDs and now I have become aware that the biggest power hog on board is actually my freezer, which seems to draw about 2 amps and nearly constantly. Maybe I have it turned down too cold -- will play with that. It is a DC water-cooled unit so should be more efficient than that, it seems to me, especially given the cold water I am in. AC power used on board seems to draw an amp or less including the inverter overhead if nothing is being done with it but charge phones and small electronics.

[cfarrar]

Dockhead,

Thanks for sharing your experience. Food for thought: our home office is not quite as extensive as yours, but we run everything on DC. That's two laptops, an Ipad, multiple smartphones, iPods, Nintendos, Wifi receiver, WIFI access point, digital cameras, etc. I figure if we're going to use it regularly onboard, it's worth finding the correct DC plug / voltage transformer or wiring it directly. We fire up the inverter for specific needs - microwave, charging power tools, etc. On those occasions it only takes a flick of the inverter switch. So potentially you can save amps by idling the inverter less often plus you can save amps by skipping the inefficient inverter-transformer process.

-Colin

[s/v Jedi]

Originally Posted by cfarrar

Dockhead,

Thanks for sharing your experience. Food for thought: our home office is not quite as extensive as yours, but we run everything on DC. That's two laptops, an Ipad, multiple smartphones, iPods, Nintendos, Wifi receiver, WIFI access point, digital cameras, etc. I figure if we're going to use it regularly onboard, it's worth finding the correct DC plug / voltage transformer or wiring it directly. We fire up the inverter for specific needs - microwave, charging power tools, etc. On those occasions it only takes a flick of the inverter switch. So potentially you can save amps by idling the inverter less often plus you can save amps by skipping the inefficient inverter-transformer process.

-Colin

As much as this is true, has anyone actually calculated the Ah savings from this? If this amounts to 5 minutes generator time daily, or 20W extra solar panel, would it be worth all the effort & cost every time a gadget is bought, while being defeated every time guests arrive with their own gadgets that require the inverter on again...

cheers,
Nick.

[FlyingCloud1937]

Originally Posted by s/v Jedi

As much as this is true, has anyone actually calculated the Ah savings from this? If this amounts to 5 minutes generator time daily, or 20W extra solar panel, would it be worth all the effort & cost every time a gadget is bought, while being defeated every time guests arrive with their own gadgets that require the inverter on again...

cheers,
Nick.

How about just running the inverter in search mode, and then setting the wake up to just below the watts of the sneakers, so that they only see power when a real load demands?

Lloyd

[noelex 77]

Originally Posted by s/v Jedi

As much as this is true, has anyone actually calculated the Ah savings from this? If this amounts to 5 minutes generator time daily, or 20W extra solar panel, would it be worth all the effort & cost every time a gadget is bought, while being defeated every time guests arrive with their own gadgets that require the inverter on again...

cheers,
Nick.

The savings vary a lot with the size of the inverter etc. in general DC powered appliances use about 20-30% less than using an inverter.

I use about 35 A a day on devices that use DC to DC converters like laptops. So I save around 10AHrs a day using them. It would take about a 30w solar panel to replace the difference in an average climate between using DC to DC converters or turning on an inverter.

If the inverter is left on 24hrs a day for convieniece the inverter will use much more, it varies a lot with the different models but about 18AHrs day just to have the inverter on not doing anything is typical. Combined with the inefficiency using the inverter ( which are little less because the 10AHrs includes the idle current when the inverter is on)
So full time inverter operation will cost about 25AHrs. It would need about a 75w solar panel to replace these losses.

In practice I use DC-DC appliances for almost everything I can. So I rarely have to use the inverter.
With guests I charge their laptops cameras etc via the inverter, but try to charge everything at once, minimising the inverter time. In practice guests visit in summer when we have an abundance of solar power anyway, so there is no need to too careful.

[hellosailor]

"As much as this is true, has anyone actually calculated the Ah savings from this?"
The worth of a very personal number, masured not calculated, would be rather limited. The worth of a calculated number would vary with how well it was done.
Inverters these days all claim ridiculous numbers like a 5% loss. Pubished numbers I have read indicate more like a 10% loss is tyypical--and that loss increases if the load is not matched to the inverter's full capacity.
So if you have a thousand watt inverter and you are powering 250W of laptops and a wifi hub, your loss may be more like 20-30%.

Now, you pick a number, any number, and run that by your daily consumption. Granted, the DC-DC converters also have a loss, but they are more likely to be matched to the size of each load, and to be turned off or unplugged when not in use. Counter that with the cost of the inverters, i.e a laptop "travel" adapter often sells for $125 although the same product sometimes can be found for $50. For cell phone chargers, the price is more like two-for-$5 from outlets for the same product that sells for $15 each in a kiosk store.

But then again, if you use just one main inverter for everything and that inverter pulls a Xantrex on you and goes belly-up....everything is down. Advantage to the horde of little dedicated inverters. I suspect running at lower power and running cool allows them to live longer, too.

[s/v Jedi]

Originally Posted by hellosailor

"
Inverters these days all claim ridiculous numbers like a 5% loss. Pubished numbers I have read indicate more like a 10% loss is tyypical--and that loss increases if the load is not matched to the inverter's full capacity.
So if you have a thousand watt inverter and you are powering 250W of laptops and a wifi hub, your loss may be more like 20-30%.

so, inverter loss is 20-30% at 25% inverter load you state? And that for an inverter that has 5% efficiency in it's specifications? And tests show 5% was a lie because it is 10%? Surely you can back that up with your measurements!?

My measurements do not show this at all, but I might use honest brand x while you use crooked brand b

cheers,
Nick.

[noelex 77]

The inverter manufactures quote a high effecency usually about 95%. This sounds very good, but if you read the specifications this is only at full power. The efficiency is significantly less under more usual loads. Also they don't mention this does not include the base level operating current.

My 300w inverter has a base operating current of 1.2A. So when it's turned on it draws 1.2A even if there is no load. This current must be added to whatever draw it takes to run the load.this means for low load appliances like phone chargers its very inefficient to run them off the inverter. A DC to DC phone charger might be drawing 0.5A, the same charge via the inverter is about 1.8A.

The effeciencies of inverters and in particular the base operating current varies considerably with different models, but 1A for a medium sized inverter is typical. My second 150w inverter is slightly better with a base operating current of 0.8A.

[cfarrar]

It's easy to find cheap, 12V utility plug style chargers for the common devices - USB, smart phones, Ipods, whatever. I had to spend a little more money for the DC-DC charger for my MacBook, but it also came with different tips that handle a variety of PC laptops.

[twistedtree]

If you are looking at Inverter efficiency, check to see if the manufacturer provides an efficiency graph. Any good inverter will have one readily available.

This is just a single data point, but from what I've seen it's pretty typical. I currently use a Xantrex XW 6KW inverter to power my house (not a marine application). As an aside, this is not the crappy consumer product, and Xantrex sold this division to Schneider Electric. Anyway, the worst efficiency tends to be when the inverter is lightly loaded. This one is 80% at about 100W. From 500W through to full power, efficiency is 92% or better. Max is from 1KW to 3KW where efficiency is 95%.

[mbianka]

I agree that being able to operate various electronic devices on board directly from House DC is the way to go. Using an inverter not only wastes power if left on it is also putting all your eggs in one electronic basket. If it dies your laptop and anything else you are operating with it will too eventually.
That said I do occasionally use a small 250 watt square wave inverter for quick 120 volt jobs:
THE BIANKA LOG BLOG: WHAT WORKS ON BOARD: Powerstar DC Converter
I use it to power up a hand blender when whipping up pancake batter or in the cockpit to use a Dremel tool on a project. Even then it is only for a minute or two. For my laptops, cameras etc.... I have DC power supplies and also the 120 volt supplies that came with them. Since I also have a Honda 2000 generator on board I have options in how I want to operate them. If I find the need to charge up either my 12 volt house battery bank or 48 volt propulsion bank using the generator I will operate my laptop off of 120 volts since the generator is already on. Otherwise I operate them off of the 12 volt house bank. I have options and backups by using 12 volt as the primary source for operating my electronic devices. I don't see the need for a hefty $$ inverter for my needs when I have the Honda 2000 so readily available for my 120 volt needs.

[hellosailor]

Nick, as noelex said. If you dispute his numbers, or the ballpark numbers I've been given from so many sources over so many years, by all means, give us the numbers for your prime equipment. I don't have a variety of them around to run tests on, apparently you've got one that's already known and proven to do better.

[s/v Jedi]

Originally Posted by hellosailor

Nick, as noelex said. If you dispute his numbers, or the ballpark numbers I've been given from so many sources over so many years, by all means, give us the numbers for your prime equipment. I don't have a variety of them around to run tests on, apparently you've got one that's already known and proven to do better.

I'm not disputing noelex's numbers, I'm disputing yours I understand that you just repeated what you picked up here and there... that is often the cause of wrong info going around for ever.

There is no need for me to prove numbers as I didn't claim any. Good manufacturers post the graphs like reported by another poster here. You are correct in that prime equipment has better figures. In other words: it's easy and cheap to build gear that is not very efficient.

cheers,
Nick.

[donradcliffe]

Using small inverters that match the loads is by far the cheapest solution, for laptops, cell phones, Ipads, and such. It is much more efficient than running a big inverter. We carry three 150 watt inverters for a total cost of $75.