Running a (powerful) laptop - will I need a generator?

chenderson1965

chenderson1965

Free Member
Joined
Aug 3, 2019
Posts
327
Likes collected
274
Location
Nottingham
Funster No
62,953
MH
N+B Arto 79R A Class
Exp
10 years with hires, Newbie owner
Hi,

My wife needs the ability to do a little graphic design work while we're away to keep her business going. On hookup, running/charging from AC power is not a problem - but we might not always be able to do this.

We have two 80Ah batteries and 300W solar via MPPT controllers. I also have a small 300w (pure sine wave) inverter.

Being a powerful machine, the battery life isn't great so we may need to charge it from 12v via a (pure sine wave) inverter. The laptop['s power brick is rated at 200W and claims to draw around 3A AC.

According to the calculator I found here https://www.batterystuff.com/kb/tools/dc-to-ac-amperage-conversion-run-through-an-inverter.html , that's about 66 Amps DC (!) - although the calculator also says that would be 750 watts. If this figure is right, running off 12v is going to be impractical for all but the very shortest periods - which clearly is no use for doing work - so we'd have to buy a generator.

If I reduce the amps to get to 200w, I get to about 0.85A, which is about 16A DC. This might be true if the 3A on the power brick is the peak draw rather than continuous. If this figure is right, on a sunny day, that would probably just about be workable for two or three hours.

Which is correct?

Thanks

Chris
 
Last edited:
While the charger will be rated at 200w, that's the power needed to recharge the battery fast, it will use nothing like that if the battery is already charged. Get hold of a 12v laptop charger rather than an inverter, the current draw will be far less and there will be less losses. You need to look at the label on the laptop not the charger to see the actual current consumption. Mine is rated at 3 amps at 19v, but that also includes the power needed for any accessories which might be plugged into the USB ports, so in normal use it will probably draw about 2 amps at 19v, or 3 amps at 12v.
 
thebriars said:
While the charger will be rated at 200w, that's the power needed to recharge the battery fast, it will use nothing like that if the battery is already charged. Get hold of a 12v laptop charger rather than an inverter, the current draw will be far less and there will be less losses. You need to look at the label on the laptop not the charger to see the actual current consumption. Mine is rated at 3 amps at 19v, but that also includes the power needed for any accessories which might be plugged into the USB ports, so in normal use it will probably draw about 2 amps at 19v, or 3 amps at 12v.
Click to expand...
Thanks. I don't think that's going to work. It's rated at 19.5v, 10.3A. Even if I can find a charger with the right connector, I don't think I'll be able to find one that powerful.
 
chenderson1965 said:
Thanks. I don't think that's going to work. It's rated at 19.5v, 10.3A. Even if I can find a charger with the right connector, I don't think I'll be able to find one that powerful.
Click to expand...
That must be one heck of a laptop to use that sort of current. Are you sure you are looking at the label on the laptop, NOT the label on the charger? If it is 200w at the laptop, nearly all that energy will present itself as heat, and you will need a mighty fan in the thing to stop it overheating.
 
thebriars said:
That must be one heck of a laptop to use that sort of current. Are you sure you are looking at the label on the laptop, NOT the label on the charger? If it is 200w at the laptop, nearly all that energy will present itself as heat, and you will need a mighty fan in the thing to stop it overheating.
Click to expand...
Yep. That's what it says on the label on the bottom of the laptop. It is a powerful machine! (and it does have a mighty fan!)

Subscribers  do not see these advertisements

 
Wow. In that case it will chew through batteries. Would have thought that whilst away it would be cheaper to have a smaller laptop with a decent sized screen although somewhat more difficult for graphics. People are none too happy with generators chugging away near them, even the quieter ones - me included.
 
I was going to start with what thebriars said.

It makes no sense to power an inverter to 240v when the laptop probably needs 19v which can be achieved with a 12v charger like we use -available in most computer shops.

Secondly, are you static for long periods when your wife is working, or do you move frequently?
If you move frequently, I suuggest you look a 'battery-to-battery'(B2B) chargers with give maximum charge rates from the alternator to leisure batteries. Sterling do them so do Votronic. Staerling have an excellent description of their function on their website. Ours charges our 2x90A batteries up in about 30 mins. driving but you may need more. Even if you were parked you would get more amps off a B2B than a generator.

B2B is fit and forget - it is always pumping in, generators take space/weight and need lugging out, plus they annoy any neighbours.

The other suggestion is to always charge the laptop while driving.

Hope this helps.

geoff
 
thebriars said:
Wow. In that case it will chew through batteries. Would have thought that whilst away it would be cheaper to have a smaller laptop with a decent sized screen although somewhat more difficult for graphics. People are none too happy with generators chugging away near them, even the quieter ones - me included.
Click to expand...
Not an option for the graphics processing work she does. I understand the noise issues for others, and I'm not keen on a generator either, but if we had one we'd be using it when wild camping etc so not disturbing others.
 
chenderson1965 said:
Not an option for the graphics processing work she does. I understand the noise issues for others, and I'm not keen on a generator either, but if we had one we'd be using it when wild camping etc so not disturbing others.
Click to expand...
Probably answered your own question then. :giggle:
 
nicholsong said:
I was going to start with what thebriars said.

It makes no sense to power an inverter to 240v when the laptop probably needs 19v which can be achieved with a 12v charger like we use -available in most computer shops.

Secondly, are you static for long periods when your wife is working, or do you move frequently?
If you move frequently, I suggest you look a 'battery-to-battery'(B2B) chargers with give maximum charge rates from the alternator to leisure batteries. Sterling do them so do Votronic. Staerling have an excellent description of their function on their website. Ours charges our 2x90A batteries up in about 30 mins. driving but you may need more. Even if you were parked you would get more amps off a B2B than a generator.

B2B is fit and forget - it is always pumping in, generators take space/weight and need lugging out, plus they annoy any neighbours.

The other suggestion is to always charge the laptop while driving.

Hope this helps.

geoff
Click to expand...
Thanks.

I'm not sure how much a B2B charger would help. The batteries are pretty well topped up most of the time by the engine and solar, it's the rapid drain whilst stationary that would be the problem. A generator isn't ideal, but it's quieter and cheaper than running the engine.

We'd obviously do as much charging while driving as possible. What sort of current will the alternator be able to produce (Ducato 3.0L 2012)?

Subscribers  do not see these advertisements

 
thebriars said:
Probably answered your own question then. :giggle:
Click to expand...
Not really. I still don't know which of the calculations in my original post is correct - and depending on which it is will determine if I need a generator.
 
How about this from Amazon?.....
1591281030634.png
 
200 watts is less than one amp from your inverter A=Watts/Volts 0.83 amps or 16.6 amps from your batteries assuming no inverter losses which there will be of cours, so round it to 20 if you like.

On a good sunny day you would get most of that from your 300watts of solar (y)

Don't get too tied up with amps and doing conversions, watts are watts whatever source they come from.

Martin
 
Depending on inverter efficiency your laptop at 10.5A at 19.5V will draw around 20A and perhaps a bit more but nothing like 66A from your batteries at full tilt, your 300w inverter will just about cope with this. Make sure your wife only uses the laptop when the sun shines and your 300w solar is nearly enough to keep the batteries charged, at least in Spain.
 
Reallyretired said:
Depending on inverter efficiency your laptop at 10.5A at 19.5V will draw around 20A and perhaps a bit more but nothing like 66A from your batteries at full tilt, your 300w inverter will just about cope with this. Make sure your wife only uses the laptop when the sun shines and your 300w solar is nearly enough to keep the batteries charged, at least in Spain.
Click to expand...
Thanks. That sounds about right.

Subscribers  do not see these advertisements

 
funflair said:
200 watts is less than one amp from your inverter A=Watts/Volts 0.83 amps or 16.6 amps from your batteries assuming no inverter losses which there will be of cours, so round it to 20 if you like.

On a good sunny day you would get most of that from your 300watts of solar (y)

Don't get too tied up with amps and doing conversions, watts are watts whatever source they come from.

Martin
Click to expand...
Thanks Martin. I've been off the forum for a while given the general situation - so I missed your trade up. I have to say it feels like you've betrayed the N&B band a little. ;) but what a van! Congratulations!!
 
Look for a 19.5 vdc car charger. Then you just plug into a 12 vdc socket in the van. You will have to google around to get the unit suitable for your laptop but here is an example. The connector to the laptop will be the thing to chase through.
Amazon product ASIN B00RAFE9DW
 
sallylillian said:
Look for a 19.5 vdc car charger. Then you just plug into a 12 vdc socket in the van. You will have to google around to get the unit suitable for your laptop but here is an example. The connector to the laptop will be the thing to chase through.
Amazon product ASIN B00RAFE9DW
Click to expand...

Far too small. The OP needs at least 10 amps at 19v, that only provides 3 amps.
 
Be careful with some of those 12v adaptors that whilst the adaptor may say it can supply the power to the laptop, your socket outlet might not be wired sufficiently robustly to provide the 12v amperage.

Laptops today come in a lot of shapes and sizes. Most won't have that much of a power use requirement having moderate sized screens and integral graphics so they can claim a good battery life of a few hours, supplied with only 60 or 90 Watt 230V chargers. But there are plenty of beasts out there that include dedicated graphics cards and 17" (or even bigger specialist) screens and those will have hefty power bricks since going full tilt they will pull a lot of juice. However the onboard battery may also help to ease out some of the peaks and troughs on loadings, for most uses when we are sat at our computers we aren't doing stuff, or powering the processor at max continuously.

For me, I think the big thing will be the capacity of the vehicle's leisure battery to also ride out peaks and troughs of use. Are you expecting every day that someone would be doing 8 hours of work, or is it really a 2-3 hour period, every couple of days. If the former, and even with solar it's a cloudy day, it's your leisure battery that will be key, or as you say a generator.
 
A high end laptop might consume about 100W of electricty which equate to a little over 8 amps at 12 volts. If you round the current consumption up to say 10 amps to allow a margin, you can work out how many Amp-hours (Ah) of current you will consume. So if it is for four hours a day then that will be 40Ah which is half your safe level of capacity of 80Ah. This assumes the solar panels aren't putting anything back - if they are and it is a nice sunny day you could run the laptop indefinitely - but only during the day. Evening work after the sun has gone down would be a non-starter I think unless you want to rapidly kill your batteries.

I think you need to up your battery capacity I think and 300Ah or more might be nearer what you need. :)
 
thebriars said:
That's 90w, the OP needs a 200W+ charger.
Click to expand...

Worth trying, I use a CAD laptop ( Dell Precision 7510) for work and it has a 180w charger. It will run on a 90w charger, but won't charge the battery whilst the laptop is on, only when the laptop is off. if the OP's laptop is similiar, the 90w may run the laptop without charging the battery. I've assumed that the larger supply is so that with a flat battery you can both power the laptop and charge the battery. I've run mine on 90w without issues, other than an initial message that the charger is to small.
 
thebriars said:
Far too small. The OP needs at least 10 amps at 19v, that only provides 3 amps.
Click to expand...
I said like this example!!!!!!! Not use this, I have no idea of the laptop manufacturer, its connector (zillions of) etc! But car chargers for laptops are very common. If you have it permanently connected you will not need so much power as you would not be charging the battery. I have used a SIMILAR unit for a 19.5 vdc laptop that I had. But I am sure your experience is far greater so you can point him to the correct unit......

Subscribers  do not see these advertisements

 
Leave it charging when its light, solar will more than cope, at 300w you will have loads of excess energy!
We kept 450AHs of batteries full with 240w so you could easily increase your battery bank size for a lot less than a genny!
 
chenderson1965 said:
Thanks Martin. I've been off the forum for a while given the general situation - so I missed your trade up. I have to say it feels like you've betrayed the N&B band a little. ;) but what a van! Congratulations!!
Click to expand...

We have but I blame N+B for not building a van we liked ;)

Martin
 
The steady state power used by the laptop will be around 200W, which is 10.3A at 19.5V, or 16A from the 12V supply, as you say. So for 4 hours of solid work that's 64 amp-hours at 12V.

Your 300W of solar will probably produce about twice that on a good long summer day, so on an iffy day you will probably just about get by. Your two 80Ah batteries will give you about 80Ah of usable storage, which is likely to be enough to last over 24 hours.

The main argument for using 12V adapters for small items like phone chargers and laptops is that a large inverter has a constant large drain that is in many cases more than the phone or laptop charger draws. Using a smaller high-quality inverter that is dedicated to the task and is just the right power will be much more efficient. You'll probably only be wasting an extra 10% or so. And as you say, you'll struggle to find a laptop car charger powerful enough. I've seen car chargers at 120W but not 200W.

You could construct one from a 12V-to-19V power supply, but you'd have to add the wires and plugs yourself.
<Broken link removed>

Looking at an inverter, a good quality one will take a surge of twice the steady state power. So if the startup surge is 750W, you need an inverter rated at least 375W. So something like this Victron 375W model is worth a try. That surge might be a bit pessimistic, and you might get away with the 250W model, but it's a gamble unless you can try before you buy.
www.es-store.co.uk

Energy Solutions | Victron Phoenix 12V, 375VA 230V Sine Wave Inverter - VE.Direct IEC Unit

Energy Solutions | Victron Phoenix 12v, 375va 230v Sine wave Inverter. Unit has IEC socket and is supplied with loose IEC plug - DC cables NOT supplied. VE.Direct unit (PIN121371100) - REPLACEMENT FOR PH12/035
www.es-store.co.uk www.es-store.co.uk
 
Last edited:
Thanks everyone. I've ordered a 90w universal 12v charger (looked everywhere and couldn't find a 120w one). For £30 it's worth giving that a try. Hopefully it'll both keep the machine running when on and charge it when it's off - even if it can't do both at once.

If that's not enough, I'll have a go at putting together a step up charger with a bigger output (thanks Autorouter and MyrtleGuru for that idea).

Both ideas are better than buying a generator so I'm grateful for the help. You can always depend on this forum for useful guidance. :clap2:🙏

Subscribers  do not see these advertisements

 
  • Like
Reactions: DBK

Join us or log in to post a reply.

To join in you must be a member of MotorhomeFun

Join MotorhomeFun

Join us, it quick and easy!

Join us

Log in

Already a member? Log in here.

Latest journal entries

Back
Top