Best way to power a laptop

[msacco]

Hi guys, hope this is the correct place to ask.

I'll need to start using my laptop in the field soon, currently have a 75 AH AGM battery, and I'm wondering what would be the best and most "efficient* way to power and charge my laptop.

This is the original wall charger:

https://fixing-tools.store/adapters/ac-dc-power-adapter/14587-genuine-65w-usb-c-lenovo-thinkpad-e580-i7-8550u-ac-adapter-free-cord.html?gclid=Cj0KCQjwh8jrBRDQARIsAH7BsXfoosER0lHVPwf0P5GGYxOwC3YMc2T3K97sba8uW--Ek0ukUu_dgFUaArJaEALw_wcB

So I believe I'd need something similar, my laptop model is lenovo thinkpad E580 15" which has a usb c type charging port.

I've seen a few options in different prices, wondering what are the main differences between them.

Here is the original lenovo car charger:

https://www.lenovo.com/us/en/accessories-and-monitors/top-tech/65W-USB-C-DC-Travel-Adapter/p/40AK0065WW

That would surely be the best, but it's also very expensive.

This also looks like a decent charger:

https://s.click.aliexpress.com/e/tuZO73Sg

No idea what would be the difference really, also thought about this:

https://s.click.aliexpress.com/e/EoRT6efW

With an adapter to usb-c.

Do you guys have any recommendations? What is the difference between the chargers, and what would you recommend me?

Thanks!

[vlaiv]

Wondered the same myself for my dell laptop.

Ideally I'd like something like a car charger but without charging capability - just powering laptop after battery is low. Issue with dell is that it won't boot if charger is not "genuine" (there is some sort of identification protocol between laptop and charger).

Another option that I considered is "dummy" battery - just empty battery slot without actual battery inside - connection to external power tank and appropriate voltage, but then again - battery is sort of "smart" battery - it reports level of charge and what not and I don't think simple connection to proper voltage will work.

[msacco]

4 hours ago, vlaiv said:

Wondered the same myself for my dell laptop.

Ideally I'd like something like a car charger but without charging capability - just powering laptop after battery is low. Issue with dell is that it won't boot if charger is not "genuine" (there is some sort of identification protocol between laptop and charger).

Another option that I considered is "dummy" battery - just empty battery slot without actual battery inside - connection to external power tank and appropriate voltage, but then again - battery is sort of "smart" battery - it reports level of charge and what not and I don't think simple connection to proper voltage will work.

Interesting! I didn't even thought about it this far...So what are you using at the moment?

[vlaiv]

1 minute ago, msacco said:

Interesting! I didn't even thought about it this far...So what are you using at the moment?

At the moment - just mains power

Still don't have portable rig. However, I've found that for Dell laptops, if you provide needed voltage and current on adapter plug - it will work but will not charge (which is good - don't need to drain current from main battery to recharge laptop).

I've found very cheap step up/step down DC/DC transformer - just need to try it out. It provides around 3A of current (my current charger is something like 4.8A - but it needs more power in order to charge laptop). I'm fairly confident that laptop will run on 19.5V / 3A (that is almost 60W of power - should be enough for just running computer). And need 7.4mm laptop power plug - don't want to cut into laptop mains adapter that I already have.

[msacco]

16 minutes ago, vlaiv said:

At the moment - just mains power

Still don't have portable rig. However, I've found that for Dell laptops, if you provide needed voltage and current on adapter plug - it will work but will not charge (which is good - don't need to drain current from main battery to recharge laptop).

I've found very cheap step up/step down DC/DC transformer - just need to try it out. It provides around 3A of current (my current charger is something like 4.8A - but it needs more power in order to charge laptop). I'm fairly confident that laptop will run on 19.5V / 3A (that is almost 60W of power - should be enough for just running computer). And need 7.4mm laptop power plug - don't want to cut into laptop mains adapter that I already have.

So if I understand correctly, it simply charges at a rate low enough to just power the laptop without charging it? And Is there any way I can check it myself? I do have a spare step up I can use.

[Star101]

Great idea 

Edited September 7, 2019 by Star101

[Cosmic Geoff]

I have wondered about this myself - my Dell laptop went low a couple of nights ago and I had to take it indoors for a recharge.  I'd rather use a 12v to 240vAC converter and the standard charger and not mess with the Dell charger control system, but 60 watts or so (+losses) is going to be demanding of any battery.  One can feel the waste heat coming out of the laptop.  Perhaps a laptop with long battery endurance would be a smarter option for field use.

An option I have used is a very long mains extension lead. 🙁

[Anthonyexmouth]

One of these might be a cheap option. If you've got a box for your battery then you could pop it in the side. 

I fitted one to my boat for charging my Nintendo Switch, probably wont charge a full fat laptop but a would do a thin low power one, but would at least prolong the running time of a fully charged one. maybe worth a punt at £15

[vlaiv]

9 hours ago, msacco said:

So if I understand correctly, it simply charges at a rate low enough to just power the laptop without charging it? And Is there any way I can check it myself? I do have a spare step up I can use.

Maybe simplest way to try it is - to try it

Read voltage from your mains adapter, and see how much amperage it is supposed to give (mine is something like 19.5V and 4.8A). You don't need as much amperage - can be a bit less, because these mains adapters are designed to both power laptop in work and charge at the same time - hopefully it won't do charging of the battery, just powering laptop. See if your step up converter can deliver enough power and set it to proper voltage that you read off mains adapter. Do be very careful about plug polarity - measure it on your current mains adapter. Get another plug like that and make a lead with it from step up (of course, again minding correct polarity).

Then plug laptop into battery instead of mains and see if it will work.

9 minutes ago, Cosmic Geoff said:

I have wondered about this myself - my Dell laptop went low a couple of nights ago and I had to take it indoors for a recharge.  I'd rather use a 12v to 240vAC converter and the standard charger and not mess with the Dell charger control system, but 60 watts or so (+losses) is going to be demanding of any battery.  One can feel the waste heat coming out of the laptop.  Perhaps a laptop with long battery endurance would be a smarter option for field use.

An option I have used is a very long mains extension lead. 🙁

You can do it via 12V DC - > 240V AC and then use regular adapter. This way it will try to recharge your battery when it drops, so maybe remove laptop battery, or tell laptop in power management not to recharge battery (I don't even know if there is option for that)

Total losses are unlikely to be better than something like 15% and can be as bad as 40% - depends on efficiency of converters. But let's use 20% losses. Mind you that using step up and doing 12V -> ~18V (or what ever lap top needs) will have similar performance, but might be smaller in size and easier for DIY.

Laptop won't draw max current all the time, but it will certainly need something like 35-40W in normal working mode (no heavy processing or such). This in turn means about 50W load on battery, and at 12V it is about 4A. 4A from 75Ah battery in principle should be able to power laptop alone for about a 18h..

On the other hand, we can look at it like this:

- mount power - 2A?

- camera cooling - 2A?

- laptop - 4A?

- gadgets (flat panel, motor focuser, .... anything that uses just a bit of power - and not continuously)  - this we won't count as others won't have continuous draw at max rating so there will be plenty of power to spare for these devices

So we have something like 8A of draw (although not continuously).

We want to be able to run 8hours in the field (should be enough for complete session together with setup and everything) - that is total of 64Ah - anything above 70Ah should be enough (providing it is deep cycle).

[skybadger]

I use a 12v to 19v DC/DC converter off my 12 battery for this. That's all the Lenovo car charger is. The real trick is finding the the right power connector.

 

[msacco]

2 hours ago, skybadger said:

I use a 12v to 19v DC/DC converter off my 12 battery for this. That's all the Lenovo car charger is. The real trick is finding the the right power connector.

 

I believe I could easily do that, but isn't there something more behind the 50$ lenovo charger for example? Safety mechanism, some measurements, anything like that?

[skybadger]

There may well be. It's up to you. I'm happy to use it with mine. 

[msacco]

On 07/09/2019 at 03:48, vlaiv said:

Maybe simplest way to try it is - to try it

Read voltage from your mains adapter, and see how much amperage it is supposed to give (mine is something like 19.5V and 4.8A). You don't need as much amperage - can be a bit less, because these mains adapters are designed to both power laptop in work and charge at the same time - hopefully it won't do charging of the battery, just powering laptop. See if your step up converter can deliver enough power and set it to proper voltage that you read off mains adapter. Do be very careful about plug polarity - measure it on your current mains adapter. Get another plug like that and make a lead with it from step up (of course, again minding correct polarity).

Then plug laptop into battery instead of mains and see if it will work.

You can do it via 12V DC - > 240V AC and then use regular adapter. This way it will try to recharge your battery when it drops, so maybe remove laptop battery, or tell laptop in power management not to recharge battery (I don't even know if there is option for that)

Total losses are unlikely to be better than something like 15% and can be as bad as 40% - depends on efficiency of converters. But let's use 20% losses. Mind you that using step up and doing 12V -> ~18V (or what ever lap top needs) will have similar performance, but might be smaller in size and easier for DIY.

Laptop won't draw max current all the time, but it will certainly need something like 35-40W in normal working mode (no heavy processing or such). This in turn means about 50W load on battery, and at 12V it is about 4A. 4A from 75Ah battery in principle should be able to power laptop alone for about a 18h..

On the other hand, we can look at it like this:

- mount power - 2A?

- camera cooling - 2A?

- laptop - 4A?

- gadgets (flat panel, motor focuser, .... anything that uses just a bit of power - and not continuously)  - this we won't count as others won't have continuous draw at max rating so there will be plenty of power to spare for these devices

So we have something like 8A of draw (although not continuously).

We want to be able to run 8hours in the field (should be enough for complete session together with setup and everything) - that is total of 64Ah - anything above 70Ah should be enough (providing it is deep cycle).

 

On 07/09/2019 at 10:38, skybadger said:

I use a 12v to 19v DC/DC converter off my 12 battery for this. That's all the Lenovo car charger is. The real trick is finding the the right power connector.

 

Do you have any DC converters to recommend me?

I currently own one of these:
https://s.click.aliexpress.com/e/lOIvfCfe

Would that do the job?

And I'm not really sure how to wire from plus and minus to usb-c, I'll try searching for tutorials.