Working off grid

[MagicalArmchair]

I have two 24 inch monitors drawing around 50 watts each, and a tiny IBM that has a draw of around 65 watts.

Let's call that, in total, 200 watts of draw (to include inverter overhead). Mirage has 280Ah in her domestic banks, leaving 140Ah of useful usage. The batteries are 7 years old, however, have been kept topped up throughout, and have not had nearly as many cycles as I would have liked (viz, lockdown!).

The idea is to sail down with the tide at around 4am, anchor up, work, off-grid, for around 4 hours, before sailing back at lunch. I have no inverter right now, solar, or any form of lithium power station on board. I was going to go and grab one of these for the experiment this evening: RINVU500

200 watts at 240V is only 0.8 Amps? So in theory, I could work all day? Am I missing anything?

Any observations or recommendations? I do need to sort out off-grid power this winter and I do want some solar on board to keep the batteries topped up - however, that is for off-season, I am just looking for something to muddle through.

 

[Rappey]

200 watts at 240V is only 0.8 Amps?

But you will be running it from 12v so it's more like 17 amps..

 

[James_Calvert]

Electrical equation: Volts x Amps =Watts

So to get say 60W output you could have:

240V x 0.25A = 60W
or
24V x 2.5A = 60W
or
12V x 5A = 60W

Problem now becomes apparent?

(stupid error now corrected)

 

[jlavery]

A general observation - separate from detailed power calculations.

An inverter has a power drain of its own. You're going to be taking 12V DC to 240AC and back to (various voltages) DC. With losses along the way.

My approach on my boat is to source a 12V power supply for the computer, and portable monitors, again capable of running off 12V. I haven't sourced the monitors yet - but there are plenty out there. Some have dedicated power supplies, some powered off the computer.

 

[AngusMcDoon]

280Ah theoretical battery capacity when new. However well you have treated them that will be much reduced at 7 years old. So usable capacity could be down to half of new - 70 Ah.

Inverters are not 100% efficient, and cheap ones are worse. They might claim 90%, but that will be under some non realistic frigged test situation like the Germans do with their cars. There will be cable and switch/connection losses too. Let's assume 80%, so the theoretical 17 A draw becomes 21 A.

So you'll get 3-4 hours before your batteries are 50%. If you do that too often they will soon cease to be.

An alternative solution is to get a low consumption long battery life laptop instead like the Acer Swift 1. It's not got a huge screen or whizzy processor, but that's all good where battery life is concerned. You can get a genuine 12 hours out of a charge if you turn stuff down or off.

 

[[2574]]

In theory you’d get a days working out of one of these: Bluetti AC200P | Portable Power Station | 2000Wh Battery

 

[ash2020]

Not sure if I missed the start of this thread but why do you need 2 x 24" monitors? Could you not work on a laptop screen?

 

[harvey38]

In theory you’d get a days working out of one of these: Bluetti AC200P | Portable Power Station | 2000Wh Battery

At £1600 I hope the OP is on a good hourly rate, you're into electric outboard money there, but four stroke outboard weight?

 

[[2574]]

At £1600 I hope the OP is on a good hourly rate, you're into electric outboard money there, but four stroke outboard weight?

One pays one’s money and takes one’s choice! Can’t expect to work a pc and two big screens with two candles and a rubber band! The alternative of course is to go in the office……thankfully I’ve packed in doing that..

 

[dankilb]

My approach on my boat is to source a 12V power supply for the computer, and portable monitors, again capable of running off 12V. I haven't sourced the monitors yet - but there are plenty out there. Some have dedicated power supplies, some powered off the computer.

I'm working my way through options for similar...

Monitors without a 240v input seem a particular challenge, perhaps because of desired commonality with office setups (I'm sure many convert the 240v inside, but the vast majority still take a 'kettle cable' input). There are a few mainstream 24" models that take 14v or 19v. Lots of LGs take 19v. My additional challenge has been finding a monitor with sound/speakers (to occasionally act as a streaming 'TV' without additional audio). So far I've only found a couple of speaker-equippped full-HD monitors - some 24", but mostly 27" (inc. curved) - that don't take 240v.

Annoyingly, I'd prefer a 22" (just because space for a screen really isn't a priority, even on our 41'), but no luck finding one of those. I'd definitely rather have a single 27" (maybe curved?) and multi-task from that than two monitors (I use two 'at the desk', but on the boat... really?!).

There seem to be plenty of step-up converters claiming sufficient wattage to go from 12v - 19v.

 

[Concerto]

Mark, I would give it a try. Ultimately the age of the batteries becomes a problem and they are really past their useful life. If your batteries start to fade, then run your engine to add some charge. The alternative would be to get a small quiet generator from Honda, certainly cheaper than that portable power station.

 

[Bristolfashion]

I seem to recall that there is a roundup of these self contained power packs in (probably) YM - or possibly PBO current issue. I quite like the idea of this as you can use 'em anywhere - camping, shepherds hut, power cut, boat etc and for all sorts of things - power a beer fridge on the beach ! I guess that they'd also charge from the boat if motoring / plentiful renewables and, in a pinch, act as a jump starter. Also good if your boat electrics go down for any reason.

 

[dunedin]

Not sure if I missed the start of this thread but why do you need 2 x 24" monitors? Could you not work on a laptop screen?

My thought also. Rather than maximising the power supply, start by minimising the power demand.

These sorts of jobs that really need twin screens tend to be ones that also need very reliable internet and powerful PCs. If the job can be done on a decent laptop it will be much more likely to be practical.

 

[Boathook]

Electrical equation: Volts x Amps =Watts

So to get say 60W output you could have:

240V x 0.25A = 60W
or
24V x 2.5A = 60W
or
12V x 25A = 60W

Problem now becomes apparent?

I thought it was v=I × w or w ÷ v= w
So 60 watts is around 5 amps.

 

[neil_s]

Turn the brightness down!

 

[Neeves]

It will depend on the work you are doing as to how much the computer and screens will draw. If you are doing large calculations or a lot of video work your power needs will be quite high.

However there are laptops that will do much media work, big power consumption, and will last a working day add a compatible tablet and you have 2 screens supported largely by their own internal power source. Use a power bank to supplement the battery capacity of the laptop and tablet.

You are probably going tp spend money to solve your dilemma - broaden your horizon to make better use of what you have, in terms of on board power, by upgrading the computer resource (that you charge at home) and consider smaller screens. I have a an iPad Pro - because I wanted the big screen - but its only 13" - 21" is huge (to me) and my MacBook is the same size.

As mentioned your inverter uses power just sitting idle - when you use your inverter recharge everything at once - and when finished switch the inverter off.

However I have a load cell and recorder that runs off 240 volt - and I'm not going to buy another one that works of 12v (even though I know the Digital data display is 12v - I'm not willing to spend on this specific item as it is single use.

We have a decent stock of power banks - because they offer a multitude of uses, back up for iPads, some lighting, camera battery recharging - its all a question of priorities. Remember solar only works when the sun is shining - and you mention solar in winter - a gen set might be more useful, Concerto Post 11, and in winter your ideas might need to be modified with the need for heating.

Your problem is very common - many of us have the same issue - and muddle through.

Jonathan

 

[James_Calvert]

I thought it was v=I × w or w ÷ v= w
So 60 watts is around 5 amps.

So it is. Thanks.

 

[AntarcticPilot]

Not sure if I missed the start of this thread but why do you need 2 x 24" monitors? Could you not work on a laptop screen?

If it's anything like my computer work, a single screen isn't enough. You need one screen for the working document and another for administrative tools. I can work on a laptop screen, but at reduced efficiency. As my clients pay by the hour, reduced efficiency isn't really acceptable.

 

[slawosz]

I use large monitor for work, but, if forced I could work just with a laptop. Throughout my carreer I used to use 2-3 monitors, but recently found that one is enough (although sometimes its easier with 2 - then I use laptop monitor). I wonder what kind of work you are doing? There is plenty of useful tools on any operationg systems that will help you to manage your windows. For example, windows is now supporting virtual desktops, and smart windows tilling - this could help to reduce monitor requirements. Or you could buy 12 v monitors.

 

[lustyd]

Indeed, with alt+tab and Windows+ctrl+left/right it's very quick to switch, probably faster than moving the mouse accross two desktops.
My Surface Laptop runs quite happily on about 12W for normal workloads (you have to measure when the battery is full!) and uses USB-C so connects directly to a USB socket installed on the boat which can deliver 18W. With 200W solar I can run the laptop, router, fridge etc. indefinitely in the summer months.

Don't forget the above 60W = 5A that 5A is 40AH over an 8 hour day assuming you work exactly 8 hours and then turn off the laptop