AC/DC or 24 volt dc to 19.5 volt dc
tomsdad
Posts: 221
Any electronic boffins out there I want to run my laptop in my truck it runs on 24 v dc and my laptop is 19.5 dc. at the moment i have to either run an invertor taking 24 to make 240 ac then plug in lap top or take 24 convert to 12 then to 19.5 all seems silly surly i can just convert 24/ 30 volt to 19.5.searched the web no one makes one.s.
Any ideas?
Any ideas?
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Comments
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All you really need is a big fat resistor. Very crude, but it would double as a cab heater as well.
You need to know the average power rating of the computer PSU.
Like I said, not pretty but it can be done.0 -
Hi Tomsdad, despite the inefficiencies involved if it was my laptop I would stick with the 24V to 240V inverter then plug the official charger in to get your 19.5V at least the charger is properly regulated and compatible with your laptop.
As you say, I’ve not seen a 24V to 19.5V converter either. You could build one, it wouldn’t be difficult to design a simple linear regulator, but if it goes wrong your laptop may end up as toast. Also the inverter can be used for other things too.I ache, therefore I am.0 -
at the moment im using my 2kilowatt invertor to charge/run lap top. im always worried about power drain using the big invertor.I normally use it for my microwave and kettle but i always run the engine whilsh doing so.
what would be involved in building a whatever it was you said.?0 -
its a dell the little box says 65wattPercy Veere wrote:All you really need is a big fat resistor. Very crude, but it would double as a cab heater as well.
You need to know the average power rating of the computer PSU.
Like I said, not pretty but it can be done.
19.5 volts 3.34 amps it what it says on the back of lap top0 -
Although it might seem like I’m trying to evade your question, I would consider buying a smaller inverter for the laptop task, say 150 to 200W. They are fairly low cost these days, Road Pro do them for £40 ish.
I agree your 2kW inverter is likely to be wasting a fair bit of energy driving such a small load.
With respect to designing your own regulator I’ve had a quick look to see what “all in one” IC packages exist to do this and in the few minutes I’ve spent searching I didn’t find one! However that doesn’t mean there isn’t one.
Just looking at my laptop charger it’s rated for 19.5V and 4.7A that’s 90W max. Let’s assume the normal running power is nearer 50W or 2.6A at 19.5V. If the truck’s 24V battery voltage gets up to 28V when charging that means we may need to drop between 4.5V to 8.5V depending on the state of charge. A simple linear regulator would drop this voltage and turn all of the energy into heat. In the worst case 8.5V x 2.6A = 22W, that’s a fair bit of heat, think domestic soldering iron, this would require a big heat sink. Going to a switch mode regulator would improve the energy loss significantly but the design is more complex. Probably not a project for the novice electronics designer particularly considering the consequences of getting it wrong. Also the environment of the cab can be hostile, damp & cold or hot & humid, electronics designers go to significant lengths to test their designs under a variety of conditions, temperature, humidity, radio frequencies, vibration etc.
I would not recommend a bespoke design to you unless I tried it myself, but this brings me back to my original point and that was, in order to protect my laptop I would want to stick with my standard laptop charger and supply it with 240V AC as the manufacture intended. A true sine wave inverter should give a good mains power equivalent.
I will have a look to see what solutions are out there though.I ache, therefore I am.0 -
I am impressed.I think i will have to go the 24 to 240 inverter 150w route and save my big one for the microwave etc.
As a ps
why does my 24 to 12 convertor not get that hot i know it has a heat sink but it dosnt get that hot?0 -
dont do what percy said. your laptop will have varying power consumption depending on what its doing, a resistor will vary the voltage a lot and get very hot, when its drawing very little power or at startup a resistor would put nearly 24v into your laptop.resistors are only any good for constant loads at low wattages. when you start your engine the voltage will climb above the battery in order to charge it, alternators also throw out voltage spikes while running and produce something called load dump when you switch things off which can cause voltages well over 100v for fractions of a second. what ever you do its safer to have the engine off unless your device is voltage spike protected, even so avoid starting the engine with it plugged in.0
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It would be fairly easy to build a small regulator to convert 24v to 19.5 or whatever voltage you needed. Unfortunately it's probably not something you could do without any experience of electronics.
Unless you know somebody who could build it for you, you'd probably be better off buying a small 24 to 240v inverter and then using the Dell transformer as other people have mentioned. I'm sure you'll find other uses for the inverter.0 -
Tomsdad
We always got asked for this type of application ( I have worked for the procurement org of 2 of the largest Laptop suppliers ) to be offered in the post sales options or spare parts catalogue but never offered them . THere were always companoes like Maplin / RS etc that wold do this tye of solution
http://www.maplin.co.uk/module.aspx?mod ... 4wod6D740g [url][/url]0 -
hes using 24v from a 2 battery setup in a lorry. that only takes 12v input.
something like this is what you need tomsdad.
http://www.amazon.co.uk/LAPTOP-NOTEBOOK ... B002DJGDDO0 -
Tomsdad, I expect your 24V to 12V converter uses switching technology and can drop the voltage without generating much heat, as does your standard laptop power supply, clever design.I ache, therefore I am.0
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I have found in the past that it takes a lot out of the 24 to 12 volt dropper i have melted a couple doing this admitedly i was using a 24 to 12 to 240Runoutofgears wrote:Tomsdad, I expect your 24V to 12V converter uses switching technology and can drop the voltage without generating much heat, as does your standard laptop power supply, clever design.0 -
rake wrote:hes using 24v from a 2 battery setup in a lorry. that only takes 12v input.
something like this is what you need tomsdad.
http://www.amazon.co.uk/LAPTOP-NOTEBOOK ... B002DJGDDO
this one like the other suggestion from maplins are both 12 volt input. i even e mailed maplin to try and get them to make one but no reply.there are a lot of us truck drivers out there all with laptops etc
( we have to get our porn from somewhere whilst we are away or check out our postings on bike rader) surly theres a market.if they can make 12v ones like the above then why not a 24v one?
I'm not an electrician but it seems logical to me
If one of you clever boys makes one i'm in for 10%0 -
Tomsdad .......
Didnt read your original correctly . Try this url it has an input voltage range 12v-24v . made by Fujitsu Siemens . Various places do it on the internet . You could do a search on the intranet and get some tech support feedback before purchasing .
http://www.amazon.co.uk/dp/B0001J02AS?m ... alocouk-21[url][/url]0 -
thats seems more like.just did a quick surf couldn't find much info.I guessing that 19v 80 watt would charge/run laptop.need to check input voltage as was stated before although its 24 v it runs at about 28 most of the time need to check input voltage.0
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I've used Maplin 12V regulator products in my motorhome and found them to be poor, cheap and usually end up issuing wisps of smoke. A friend asked me recommend a PSU to enable him to use his DAB radio in the car, I suggested he check the manufacturer for a car power supply unit, but we found that they did'nt do one. This seems to be the case for most manufacturers, they don't seem interested in producing 12V, let alone 24V power supply solutions for their products. This is particularly irritating as they it would be safer than mucking about with 240V in a vehicle cab.
One thing's for sure if they did, they'ed probably cost more than the small inverter we discussed earlier.I ache, therefore I am.0 -
Thanks for all your help on the above posting I think i'm going to go the extra inverter route I can get a 24v to 240v 600w for about £25.00
next query for you clever ones is ......
If i run this to power/charge my dell laptop and i connect it to my 2 x 100amp leisure batteries (split charging system) how long before i drain batteries if i use lap top to watch dvds etc and without the engine running.
Ps saw your posting on bristol velo runningoutofgears hope to see you sunday.0 -
After a bit or searching I did finally find a DC-DC converter that would give 19.5V DC (custom order) from 24V DC nominal. The problem is it’s from a US company and it costs $145, and would still require finishing with a fused connector, leads etc
http://www.powerstream.com/dcdc.htm
So unless anyone knows different the small inverter is probably the way to go.I ache, therefore I am.0 -
tomsdad wrote:Thanks for all your help on the above posting I think i'm going to go the extra inverter route I can get a 24v to 240v 600w for about £25.00
next query for you clever ones is ......
If i run this to power/charge my dell laptop and i connect it to my 2 x 100amp leisure batteries (split charging system) how long before i drain batteries if i use lap top to watch dvds etc and without the engine running.
Ps saw your posting on bristol velo runningoutofgears hope to see you sunday.
If you've got split batteries, are they both 12v ? If so why not get somebody to connect you a 12v convertor to one battery ?
To answer the other question - not long.
If I remember my physics from 20 odd years ago, then Power = Current x Voltage.
If power is 600W, voltage is 24 volts then your current is 25 amps, which will give you exactly 4 hours of surfing p0rn before you have to push start your truck (and I guess after 4 hr's you'd be too tired right ?).
If they're both 24v/100Ahr batteries then it will be 8 hr's as they have double the capacity.
In reality it'll be a lot less as the current that the invertor uses will be higher than the 600W and the batteries won't really last that long. I'd say you'll get about half that time.
You'd still be better off buying a much smaller invertor and using it to run your laptop as the bigger the invertor, the more current it'll use. Can your local truck supplier not help you out ?0 -
the inverter will not use the full the 600w with a laptop. its like a reverse transformer with switching to make to dc battery supply ac because we all know ac only works on transformers. i would say you could run it all night on them batterys easily. 65w is roughly 10 times less than 600w so would last about 10x longer than the above calculation minus a few conversion inefficiencies about 20 hours if it was only 50% efficient.typical square wave car inverters are 95% efficiency, that is getting on for nearly 40hours at 60w power usage.
a little info here to show im not talking off the top of my head, which does sometimes happen.
http://www.smps.us/power-inverter.html0 -
rake wrote:the inverter will not use the full the 600w with a laptop. its like a reverse transformer with switching to make to dc battery supply ac because we all know ac only works on transformers. i would say you could run it all night on them batterys easily. 65w is roughly 10 times less than 600w so would last about 10x longer than the above calculation minus a few conversion inefficiencies about 20 hours if it was only 50% efficient.typical square wave car inverters are 95% efficiency, that is getting on for nearly 40hours at 60w power usage.
a little info here to show im not talking off the top of my head.
http://www.smps.us/power-inverter.html
Fair enough. I never did switch mode power supplies !0
