Question about Inverters

UK PROFESSIONAL DRIVERS FORUMS THE UK PROFESSIONAL DRIVERS FORUM (INTERACTIVE)
1

Hello chums.

Current set up;

350w 12v Inverter plugged into the 12v ■■■ socket in the dash of the Premium I have the pleasure of driving. The cap over the socket says 10A Max and the book says something about the max watt it can handle. I can’t remember but I am sure it’s something like 230w+

The problem I have;

When I run my laptop on it with a fully charged battery everything is A-Okay. However, if I’ve been sat in Truckhaven using the wireless or something and have to charge the thing up again, the in dash wiring coming from the 12v socket gets bloody hot! It’s ok if I charge it then turn it on but if I use it while it’s charging that’s when the wires get really hot. Now I know the first thing that’s springing to mind is that I should just refrain from using the laptop while it’s charging but I was just wondering if you lot experience similar? Some guys in my place have everything but the kitchen sink plugged into the 12v socket so god only knows what heat the wires are at. Is this safe? Could what I’m doing cause a fire or something?

Possible solution;

Get a decent length of cable with croc clips on it and feed it from the truck batteries through an air vent in the cab somewhere then to the inverter. I am sure there is a way to get a 12v feed from those batteries because my mate hooked up his volt meter and we managed to get a reading of 24v one way, and 12v the other. I think he took positive from one and neg from another to get it.

Do you think it’s ok to do this? Am I going to drain one battery but leave the other stable?

Any views or information, many thanks.

Post Script;

The laptop power supply puts out 90w (way under the max that 12v socket can supply) and going by what the bottom of it says it draws a mere 1.5 and then magic happens and it spits out 4.62A (still way under 10A Max for the socket)

Steven

2

we could do with an electrician on this forum all this power supply stuff confuses the hell out of me. :confused:

3

Without rrying to sound clever mate. Do a search on inverters there’s been loads of posts on here about them.
My preferred option is a proper laptop power supply which you can get at XLB etc. But I have been told by a leccy techie guy on here, that it might not be as efficient as I thought it was. Worked fine on my premium though, straight of the 24v ciggie lighter. I think it was about 20 quid.

4

Steve-o:
350w 12v Inverter plugged into the 12v ■■■ socket in the dash of the Premium I have the pleasure of driving. The cap over the socket says 10A Max and the book says something about the max watt it can handle. I can’t remember but I am sure it’s something like 230w+

power = voltage x current so 12V at 10A is 120W maximum.

Steve-o:
Do you think it’s ok to do this? Am I going to drain one battery but leave the other stable?

I would strongly recommend against that on the ground that it will stuff up your batteries.

There are two ways of solving your problem properly. The best one in my view is to get a 24V inverter and plug it either into a 24V socket on the dash if there is one or direct to the batteries via some Fat Wire is there isn’t.

The alternative is to keep your 12V inverter and feed it with a big dropper connected to the 24V feed as above.

Steve-o:
The laptop power supply puts out 90w (way under the max that 12v socket can supply)

The 12V socket rated at 10A can means a max rating of 120W at the socket but to draw 90W out of the laptop charger you will need more than that as neither the inverter nor the charger will be 100% efficient.

Hope this helps,
Paul

5

I would get one of them but I just spent £700 on this laptop and it can tell when a Non Dell power supply is plugged into it and wont charge. I got a message on the screen one day saying so. Turned out the cable was half in half out at the back but still a proper supply for my old laptop was near £90 when the last one gave up so no way am I trusting a cheap 20 quid one. No disrespect, I just don’t want my ‘baby’ going bang when I plug something like that into it.

As you can tell, I like to be spot on with electrics. Electric blanket caught fire with me in the bed when I was 5 or something and burned half the house down. Thankfully my parents were quick enough to chuck me down the stairs when they started to smell the burning and went to investigate lol :laughing:

6

No doubt you will get an “expert” reply but I would make the following points:

  • ■■■ lighter sockets weren’t designed to run anything else but they are protected by a fuse.

  • If the wire that gets hot is the lead to your inverter then it’s just not up to the job

  • If you do run a lead from the battery get someone who knows to connect it and stick an in-line fuse in the circuit. You can buy a three socket attachment with a lead and crock clips from Halfords.

  • Taking a 12v supply from one of the batteries won’t be a problem unless you leave something on over a weekend.

7

renaultman:
My preferred option is a proper laptop power supply which you can get at XLB etc

Indeed, a proper supply is better than any solution involving an inverter. Try here.

Paul

8

Paul, Santa and Renodude, thanks for the input :wink:

9

Let me help here, as my job before i started drivng was as an electro-mechanical service engineer.

First off lets look at Wattage , Basically gives an idea as to how much power an item uses.

you say your inverter is a 350W model. that 350W will be how much power the inverter can cope with under Load. Now bear in mind that load is at 230v (Mains Voltage) . So we can work out how much the max output is in Amps now by using Ohms law.

as stated above by Repton. Power (Watts) = Voltage x Current (Amps)

so we know the wattage already which is 350 , the voltage is 230v . so to work out the Ampage we use Power divided by Voltage so 350/230 = 1.5A at 230v

so your Laptop power supply is 90w at 230v so 90 / 230 = 0.4A

Now lets look at the Power Consumption at 12v

350 / 12 = 29 A Drawn by the Inverter. Way more than the 10A that the ciggy socket is rated for. Basically with the Cable being so small and you trying to draw so much power from it, Its acting as a big Heating Element, which could potentially set fire to your Cab , maybe while your asleep if your a Night out man.

Anything electrical , even low voltage you should always get it checked out beforehand that it will be ok.
one thing to remember , The higher the Voltage the smaller the Current (Amps). The Smaller the Voltage the Bigger the Current.

Techy Rant over now :smiley:

10

All bow down to the inverter know how god that is, Big Jon :laughing: :laughing:

Look what I found

http://mdsbattery.co.uk/datasheets/inverter-size.pdf

11

Good information, and cheaper than a new dashboard :stuck_out_tongue:

12

What BigJon said is right (ish). :slight_smile:

Hmm, just had a re-think on this one. Whilst the calculations are right for a 350W output, the laptop PSU is only supposed to be pulling 90W, which would make it 7.5 A. Working on a 75%-efficient inverter, would mean that you’re running the 12 V outlet at pretty much bang-on 10A. It depends on the efficiency of your inverter.

I’d suggest getting a multimeter with a 20 A range, and putting it in series with the inverter on the 12 V output to get a proper measure of the current.

At the very least, don’t plug anything else into the inverter at the same time as the laptop…

Steve-o:
However, if I’ve been sat in Truckhaven using the wireless or something and have to charge the thing up again, the in dash wiring coming from the 12v socket gets bloody hot!

Whilst I’m risking pointing out the bleeding obvious, another good rule of thumb is “if it gets bloody hot, something’s not right”.

MrFlibble MIEE (= Member of the Institution of Electrical Engineers :wink: [1])

[1] For the pedants: yes, I know it’s called the IET nowadays, but it’s a stupid name.

13

BigJon:
Let me help here, as my job before i started drivng was as an electro-mechanical service engineer.

First off lets look at Wattage , Basically gives an idea as to how much power an item uses.

you say your inverter is a 350W model. that 350W will be how much power the inverter can cope with under Load. Now bear in mind that load is at 230v (Mains Voltage) . So we can work out how much the max output is in Amps now by using Ohms law.

as stated above by Repton. Power (Watts) = Voltage x Current (Amps)

so we know the wattage already which is 350 , the voltage is 230v . so to work out the Ampage we use Power divided by Voltage so 350/230 = 1.5A at 230v

so your Laptop power supply is 90w at 230v so 90 / 230 = 0.4A

Now lets look at the Power Consumption at 12v

350 / 12 = 29 A Drawn by the Inverter. Way more than the 10A that the ciggy socket is rated for. Basically with the Cable being so small and you trying to draw so much power from it, Its acting as a big Heating Element, which could potentially set fire to your Cab , maybe while your asleep if your a Night out man.

Ho-hum.

The inverter will not be drawing 29A with the lappy plugged in. Nowhere near. For a start the 350W refers to the maximum LOAD rating for the devices its powering. That’s 350W @ 240V, not 350W at 12V. Secondly, that’s MAXIMUM load. If you’re only plugging in a lappy charger rated at 90W output, it’ll only supply a maximum of whatever the laptop inverter is wanting. For a laptop psu supplying 90W @ ~18V, it’ll draw at most 2.5A @ 240V from the inverter. You can get away with around 150W of load on the inverter and still use the 12V socket on the truck. Any more than that and you’re really pushing it.

14

Steve I have a Sytronics DCtoAC 24v converter which I used to use in my truck for my laptop, it never let me down and I always used it whilst working on the computer. As I do not drive any more you are welcome to it. Let me know and I will send it to you FOC
Rgards
George

15

Excuse,

But what everyone appears to have missed here,

is that the Lap -Top Changer is also NOT going to be 100% efficient

Likely somewere between 75 - 60%
and there-for could be drawing 120 - 150 watts from the 240Volt supply

If you re-do the maths for the best and werse case(s) factoring in the invertor figers
The Wattage & current drawn at 12volts come out @:

Best case at 12volts = 160watts [ 13AMPS]
( Worst = 213watts [ 17.75AMPS ] )

Both well over the sockets 12V/10Amp (120 Watt) Rating

Regards Double Q

16

PS… this might be helpfull

24volt Twin Battery layout diagram

IMPORTANT // if doing the work yourself

If in any doubt at all, about correct procedure for working in close proximity
to High Current (Battery) Cells, Q recomends consulting a qualified engineer.
( remember wet’type battery cells, also contain & vent Flamable Gas’es )

Also:

New cable of suitable rating, and terminated in suitable connectors,
Will be required !!

If in any Doubt at all, as to the correct type (specification) of new cable
or connectors, or the protection fuse (at source [battery pole] end)

Q again says " consult a qualified engineer "

Also::
Remember that at some time,
The Cab will need to be Tilt’ed (to gain access to the Engine bay, etc.)

There-for any new cable(s) which enter the Cab
should be run FORWARD of the Cab Pivet Point
and should be protected from chaffing, and secured with suitable tie’s

For clues as to the optimium pathway for your new cable
Just Save time and effort. and.follow the path taken by existing cables

After all: Engineers @ Mr(s) DAF, Volvo (etc), have already worked this out for you :slight_smile:

Also::: amendment

Note:
Long term loading, and or deep uneven discharge
of just one of the twin batteries in the manner described above
Will cause extra ware to both the un-discharged battery and its partner.

If this is unexceptable then you are advised to seek another solution
( such as, profeshional fitting of a High-Power 24-12volt convertor, or 24vdc - 240Vac invertor )

Regards 2xQ

17

I have been using a 12v laptop adapter for the last 18 months without any problems and it never gets hot…

http://www.maplin.co.uk/Module.aspx?ModuleNo=44736&ModuleTitle=120W+Laptop+Car+Adaptor

18

At least now, with the smoking ban, manufacturers may drop the ■■■ lighter and start to fit DIN or Hella Sockets with substantial wiring.

If you look at the wiring behind a cigarette lighter, that should be enough to show you that standard truck wiring is not designed to run kettles, videos and microwaves.

I have been fortunate to have had my recent trucks wired properly from the workshops or manufacturer. Both of my recent Volvos were wired with 2 pin continental domestic sockets. My MAN is wired with 2 hella sockets at 12/24V

Im amazed that these haulage bosses who refuse to let you climb on a trailer, change a truck wheel or replace a bulb due to health and safety.

These same bosses then turn a blind eye to drivers using paper clips and bolts to upgrade the wiring on a 100k piece of equipment.

19

DoubleQ:
Excuse,

But what everyone appears to have missed here,

is that the Lap -Top Changer is also NOT going to be 100% efficient

Likely somewere between 75 - 60%
and there-for could be drawing 120 - 150 watts from the 240Volt supply

I haven’t missed anything. It won’t draw more than is stated on the sticker on it. There’s not many lappy bricks more than 90W.

20

Conor:
Ho-hum.

The inverter will not be drawing 29A with the lappy plugged in. Nowhere near. For a start the 350W refers to the maximum LOAD rating for the devices its powering. That’s 350W @ 240V, not 350W at 12V.

Ho-hum.
It doesn’t matter whether it’s 350 W @ 240 V or 350 W @ 12 V - it still results in the same amount of current pulled from the 12 V supply.

Of course, it isn’t going to be consuming 350 W in this case anyway.

Conor:
Secondly, that’s MAXIMUM load. If you’re only plugging in a lappy charger rated at 90W output, it’ll only supply a maximum of whatever the laptop inverter is wanting. For a laptop psu supplying 90W @ ~18V, it’ll draw at most 2.5A @ 240V from the inverter.

The current being pulled at 240 V from the inverter is irrelevant, as the inverter is more than capable of supplying what is being asked of it. It’s the amount of current the inverter uses at 12 V that’s important.

Conor:
You can get away with around 150W of load on the inverter and still use the 12V socket on the truck. Any more than that and you’re really pushing it.

Hmm. Pulling at least 12.5 A from a socket marked “10A Max”, and that assumes 100% efficiency of the inverter.

I stand by my previous statement. It’s probably pulling very close to 10A, possibly over, depending on the efficiency of the laptop PSU and the inverter.

Get yourself a suitable meter (e.g. this one), or borrow one from the workshop, and measure it yourself.

DoubleQ:
PS… this might be helpfull

24volt Twin Battery layout diagram

Sure, if you want to kill your batteries.