12vdc Marine Computers

[JRM]

Originally Posted by bfloyd4445

the only way to get 19vdc is by converting to a 24vdc system or using an inverter from 12vdc....I'm confused because if you say it works from a cigarette lighter plug which is 12vdc why do you need 19V

Buck converter. More efficient than an inverter and wall wort combo. You can pick one up at most electronics stores, just search for your laptop model and "mobile adapter."

Our netbook and my laptop are both Toshibas, so one adapter works for both (well, one at a time at least). It was a cheapie "universal" that came with multiple tips and a volt selection switch.

JRM

[irwin37]

Originally Posted by bfloyd4445

the only way to get 19vdc is by converting to a 24vdc system or using an inverter from 12vdc....I'm confused because if you say it works from a cigarette lighter plug which is 12vdc why do you need 19V

Not true, the charger is a boost switching power supply instead of a buck power supply used to reduce voltage, and ups the voltage from 12 to 19 volts. I have one too and work well.

[svseachange]

Originally Posted by jkindredpdx

I took my AC converter (or you could take your computer) into Radio shack and matched up the plug... cost about $3 for two. I think you want to go through the battery though, cuz it helps smooth the flow and surge protection. I wired directly to my DC panel, but cigarette lighter plug would work fine.

I have a $10 ebay dc to dc convertor for my HP laptop. I run it battery removed and find the overall power consumption much lower. Works fine and since the the dc to dc convertor can handle 10-19v it also acts like a surge protector. Working so well I delaying my purchase of a lower power laptop.

[bfloyd4445]

Originally Posted by irwin37

Not true, the charger is a boost switching power supply instead of a buck power supply used to reduce voltage, and ups the voltage from 12 to 19 volts. I have one too and work well.

You cant boost a lower dc voltage to a higher voltage dc without first converting it to ac via a square wave generator and then convert it back to dc at the higher voltage to dc. That's basically what an inverter does, its uses a square wave generator to convert the dc into a pulsating dc which is then converted to ac. Both ways will consume more electricity< watts > than just using dc. If you had a 24v system on your boat you can eaisily get 19vdc without wasting energy. If you don't but have two 12v batts in your cabin power system you can easily make a 24v plug for your 19v equipment without any power loss. But no way you can go from 12v to 19v without stepping up the 12 which will require converting it to ac then back to dc at the proper voltage.

[svseachange]

Originally Posted by bfloyd4445

But no way you can go from 12v to 19v without stepping up the 12 which will require converting it to ac then back to dc at the proper voltage.

I am no electrical engineer, but it seeems my $10 dc-to-dc brick takes 10-19V and somehow regulates it to the 15V used by my laptop, No AC needed.The lower the voltage of the power source the more amps it draws (watts = volts x amps??).

[bfloyd4445]

Originally Posted by shanedennis

I am no electrical engineer, but it seeems my $10 dc-to-dc brick takes 10-19V and somehow regulates it to the 15V used by my laptop, No AC needed.The lower the voltage of the power source the more amps it draws (watts = volts x amps??).

Ah, so its not 19 its 15. Well your alternator puts out 14.8vdc so no conversion is needed. Some regulators will allow you to step up the voltage even higher but this will result in shortening the life of your batteries. My background was in electrical engineering technology. After graduation I worked for several different engineering companies before going to work for EPA in compliance testing and instrumentation. Much of the time I spent designing different systems to test for environmental pollutants and research until I retired in 2010.

[svseachange]

Originally Posted by bfloyd4445

Ah, so its not 19 its 15. Well your alternator puts out 14.8vdc so no conversion is needed.

My alternator is rarely running when I use this setup and it works even when my battery bank is depleted (ie: voltage is low).

The assertion that AC is needed to step up voltage is simply incorrect. I challenged this assertion because on a boat AC is extremely inefficient and expensive.

However, I do agree with you that the step up taxes batteries. On a boat everything is a compromise, I would prefer to use a battery bank than introduce AC systems. My three battery house bank (in parallel) shrugs off the load of my laptop.

[goboatingnow]

Originally Posted by bfloyd4445

You cant boost a lower dc voltage to a higher voltage dc without first converting it to ac via a square wave generator and then convert it back to dc at the higher voltage to dc. That's basically what an inverter does, its uses a square wave generator to convert the dc into a pulsating dc which is then converted to ac. Both ways will consume more electricity< watts > than just using dc. If you had a 24v system on your boat you can eaisily get 19vdc without wasting energy. If you don't but have two 12v batts in your cabin power system you can easily make a 24v plug for your 19v equipment without any power loss. But no way you can go from 12v to 19v without stepping up the 12 which will require converting it to ac then back to dc at the proper voltage.

You have a partially correct situation here

All modern DC supplies , including wall warts, dc dc converters , etc whether step up or step down or both ( SEPIC) use switched mode technology. It results in a 96-98% conversion efficiency. So it's quite efficient to either step down OR up. Further the techniques of conversion in a " invertor" are significantly more complex as waveform integrity must be maintained, whereas in SWPS , simple pwm is used.

A SMPS Wall wart stepping dc from 24v to 12v will have similar efficiencies as one stepping up 12v to 24 v, both will be significantly more efficient then a linear regulator.

Dave

[JRM]

Originally Posted by irwin37

Not true, the charger is a boost switching power supply instead of a buck power supply used to reduce voltage, and ups the voltage from 12 to 19 volts. I have one too and work well.

Yup. Brain fart. You would think that "boost up" would stand out while typing, but alas, logic failed me. It's actually a boost/buck because it'll do 5V - 20V out from 12V (more or less) in.

Do I get half credit?

JRM

[goboatingnow]

Originally Posted by JRM

Yup. Brain fart. You would think that "boost up" would stand out while typing, but alas, logic failed me. It's actually a boost/buck because it'll do 5V - 20V out from 12V (more or less) in.

Do I get half credit?

JRM

Actually that's a SEPIC convertor. Buck/boost cannot handle Vin = Vout.

Dave

[bfloyd4445]

Originally Posted by shanedennis

My alternator is rarely running when I use this setup and it works even when my battery bank is depleted (ie: voltage is low).

The assertion that AC is needed to step up voltage is simply incorrect. I challenged this assertion because on a boat AC is extremely inefficient and expensive.

However, I do agree with you that the step up taxes batteries. On a boat everything is a compromise, I would prefer to use a battery bank than introduce AC systems. My three battery house bank (in parallel) shrugs off the load of my laptop.

I'm sorry but you are wrong. Yes you are right ac is expensive energy wise to make and that's why inverters draw so much power. The fact is you cannot step up DC voltage without turning it into a square wave then with the use of inductors you can step it up to a higher voltage but at lower amps and then you have to convert it back into DC at the voltage specified. Another way is with a ramp generator but again that requires watts. Electricity isn't magic and you never get something for nothing. I'm sorry but that's basic physics.

[George64]

The concern I have on directly putting my Lenovo T510 laptop to the 12v cigarette lighter is the fluctuation in the voltage as soon as I have the engine running on my sailboat.

[svseachange]

Originally Posted by bfloyd4445

I'm sorry but you are wrong. Yes you are right ac is expensive energy wise to make and that's why inverters draw so much power. The fact is you cannot step up DC voltage without turning it into a square wave then with the use of inductors you can step it up to a higher voltage but at lower amps and then you have to convert it back into DC at the voltage specified. Another way is with a ramp generator but again that requires watts. Electricity isn't magic and you never get something for nothing. I'm sorry but that's basic physics.

I never said something for nothing.

As I said, the cost is more amps. W = V x A. See the attached picture of my $10 brick. I got my numbers a little wrong but it proves my point. The brick steps up 11-15V DC to 18V DC. Notice also 6.8 A drops to 3.5A.

Now, again, as I said I am not an electrical engineer so I don't know how the brick is engineered. Maybe there is some DC-AC-DC "magic" going on.

As a practical matter for the sailor - no AC system is needed. A practical sailor just needs a $10 DC to DC brick off eBay to run their 18-19V laptop off 12V DC. I am a software developer working off my boat and this setup has worked well for me.

I should also mention that while the brick is rate to draw as much as 6.8A it only does so when charging the laptop battery. This is why I remove the battery. Without the battery installed it uses 1-2.5A.

[s/v Jedi]

Originally Posted by shanedennis

Maybe there is some DC-AC-DC "magic" going on.

Your hunch is correct, this is how they operate. With all the parts internal and tuned to each other, the efficiency is much better than for an inverter and the AC adapter combination.

[bfloyd4445]

Originally Posted by shanedennis

I never said something for nothing.

As I said, the cost is more amps. W = V x A. See the attached picture of my $10 brick. I got my numbers a little wrong but it proves my point. The brick steps up 11-15V DC to 18V DC. Notice also 6.8 A drops to 3.5A.

Now, again, as I said I am not an electrical engineer so I don't know how the brick is engineered. Maybe there is some DC-AC-DC "magic" going on.

As a practical matter for the sailor - no AC system is needed. A practical sailor just needs a $10 DC to DC brick off eBay to run their 18-19V laptop off 12V DC. I am a software developer working off my boat and this setup has worked well for me.

I should also mention that while the brick is rate to draw as much as 6.8A it only does so when charging the laptop battery. This is why I remove the battery. Without the battery installed it uses 1-2.5A.

<smile> Not trying to be argumentive just trying to make you understand that to do what you claim the brick does it must do work which requires the further expenditure of energy< watts> above what your computer would normally use. I explained how 12vdc is made into 19vdc and that requires energy and a conversion of the 12vdc into a square wave so that it can be stepped up to 19vdc. I do nave a bachelor of science degree in engineering and have worked in the field my whole life. The "brick" if it is turning 12 into 19 is using the methods I described earlier to do so which requires wattage above what the computer needs. A "brick" is not magic and if it does what you say it does so by the methods I described which costs energy. The way to find out would be to accurately measure the current draw with the brick and without and if there is no difference then the "brick" is not doing anything. I think you are spending $10 for a device that does nothing but allow you to plug the computer into the 12vdc socket.