# 12 volt power consumption



## wakk44 (Jun 15, 2006)

Hi everybody,

I've been playing with my new all singing,all dancing,Fluke multimeter today and took current readings of the TV and decoder,the results may be of interest to anyone that uses only 12 volt without a hook-up and wants to conserve battery capacity.

The TV is a Toshiba 15''LCD which according to the manual uses 36 watts,it is powered with an amperor regulated 12 volt supply.This was taking 2.8A with volume well up,and 2.7A with volume down.On standbye the reading was 0.5A,I thought this should use around 3A at 12 volts,so more or less in line with expectations.

The decoder is the Pace 12 volt Digi 'mini'box which according to the manual takes 15 watts maximum.This took 0.8A when on and 0.75A on standbye.Not much difference at all between on and standbye.

In a 24 hour period on standbye the TV and decoder would take 30A out of the leisure battery.Probably a good idea to make sure in future that both the TV and decoder are unplugged when not in use. 

Steve and Sharon


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## ethnicall (Dec 24, 2005)

I don't understand using a multimeter except how to check the battery voltage.
Please can you explain in simple terms how I can use a multimeter to do as you have done and check how many amps an appliance is using

Thanks Mark


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## Rapide561 (Oct 1, 2005)

*12v supply*

Hi

Interesting to note just how much power is used on standby.

Good post!

Russell


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## gaspode (May 9, 2005)

ethnicall said:


> I don't understand using a multimeter except how to check the battery voltage.
> Please can you explain in simple terms how I can use a multimeter to do as you have done and check how many amps an appliance is using
> 
> Thanks Mark


Hi Mark

Using a meter to check current is always a much trickier business than when checking voltage because you need to put the meter in series with the load instead of just measuring across the terminals. This means that the full current passing through the load must also pass through your meter so be very careful which range (and terminals) you use to avoid damaging your meter.
THIS SITE has a tutorial that may help you understand the methods used.


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## 99524 (Jun 4, 2006)

Hi Steve and Sharon

Really useful info. I have thought of measuring standby currents but never got round to it. I notice that even when you switch everything off - including the control unit - there is still a drain on the system. There must be some current used feeding the control unit and power systems on our van. I disconnect the battery terminals when we lay up for over a week and have noticed that there is always a spark when I remove the second earthing connection.

Why dont they include a DC breaker in vans ? It would make life much easier.

Regards

Richard


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## wakk44 (Jun 15, 2006)

ethnicall said:


> I don't understand using a multimeter except how to check the battery voltage.
> Please can you explain in simple terms how I can use a multimeter to do as you have done and check how many amps an appliance is using
> 
> Thanks Mark


Hi Mark,
exactly the way in which Gaspode has described in his reply,by putting the meter in series with the appliance.The link he has done is actually the same multimeter as mine(Fluke 73 Series 111)which I can highly recommend,it can measure DC current up to 10A.

Steve and Sharon


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## eddied (May 9, 2005)

*12v. current measurements*

 
Gaspode, many thanks for the link to the multimeter tutorial.
I've been skipping around my Chausson wielding the red and black leads like magic wands to measure voltage here there and everywhere - no problem with that.
BUT when it come to page 5 'Current' i.e. to measure amps, I'm lost (you would probabaly say thick).
Diagram '2' - 'break the circuit'
how do I do that??
I need to check the current coming out of a solar panel regulator to the 12v. cigarette lighter plug-in.
grazie e saluti,
eddied


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## 89338 (May 20, 2005)

rrichdd

A DC isolator is very easy to fit and not expensive, fitted one on my truck it is key operated, as I used to have battery problems when ity was left standing. Now that you mentioned it I think might fit one to RV

Got mine from a caravan place, if you look for one they normally have a
a red plastic key 

Regards


Lampie


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## wakk44 (Jun 15, 2006)

good morning eddied,

I don't know your solar regulator wiring but to test the current output should be a fairly easy job.First thing is to make sure your multimeter can handle the current from the solar panel,most of the meters are rated up to 10A dc.If your solar panel can produce more current than this then don't do the test,you will blow the fuse in the multimeter and could do it permanent damage.

Having said that it is very unlikely your panel can give 10A unless it is huge or you have more than one,my solar panel is rated at 85watts and has a maximum current output of 5.5A in sunlight in the summer. 
You will more than likely have to use a different socket on the meter for one of the test leads,check your instructions for DC current testing.If your regulator is wired directly to the cigarette lighter plug,disconnect the live lead from the regulator(usually red) then put one test lead on the removed lead and the other test lead on the regulator connection where you have just removed the live lead from.

This puts the multimeter in series with the solar panel output and providing you have got some sunshine(you should have sun in Italy)there should be a current reading on your meter,if not then you may have to use the other current jack socket on your multimeter which is for detecting lower current outputs.

On my Fluke meter the lower output jack is for anything below 300ma.Again make sure that the solar panel cannot give more than this as you may blow the fuse.Hope this helps.

Steve and Sharon


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## eddied (May 9, 2005)

*12v. current testing*

 
Thanks ever so much Steve and Sharon.
We do indeed have brilliant sunshine here today, altho' a bit cool; 11.3 C as we speak.
Your explanation now makes it all clear to me.
The solar panel is in fact only a 50w. rated foldable one.
I suspected, as has been raised in other posts, that possibly instead of trickle charging the batteries, it was trickle discharging them.
Of course silly me had failed to work out at the time that if I switch everything off, then the habitation 12v. plug is not live, so there cannot (can there?) be any current going into the batteries from the solar panel.
I hadn't received your reply yet when I went down to the motor home this morning, but I did switch main control panel on, and got the 12v. habitation plug live again. At the same time however I made sure unneccesary 12v. things like aerial boosters, water pumps and suchlike were switched off.
Now that I know what you have just imparted, I can go and have another play around, can't I!
tks again and
saluti,
eddied


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## hhhh (Dec 2, 2005)

wakk44, 

How did you measure the current ? I would think it's a tough job measure from the DC plug ? 

I'm just starting to get the hang of it, but doesn't the DC ground need to be connected to the appliance and the DC positive then be disconnected to measure? How do you do it correctly with small DC plugs ?


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## wakk44 (Jun 15, 2006)

hi hhhh,

it can be tricky--- unless you've got the correct equipment you will need 3 hands  

I have the clipsal 12 volt system in our van,

pull the TV plug out of the 12volt socket,put your red lead from the meter into the live socket and black lead onto the live pin of the TV plug.Then I use another lead with a crocodile clip to probe end.Put the crocodile clip on the negative pin of the TV plug and push the probe end the into negative of the socket.

Switch the TV on and then you can check the current it is using. 

Don't forget to check your multimeter instructions and set to the correct range before doing this-the link provided by Gaspode earlier on in this thread explains it clearly.If you use the wrong setting you could blow a fuse in the multimeter or damage it permanently.

DO NOT PUT ANYTHING INTO THE 240V SOCKET!!!!!!!!!

I know it's obvious but theres always one. :roll: 

Steve and Sharon


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## G2EWS (May 1, 2006)

Having been an electronics engineer for more years than I car to mention, I think we tend to state simple things to us far too technically.

You know the sort of thing, you go to the garage and the mechanic says: 'I am sorry sir but the double ended flange valve had a bit of a problem when we connected it to the retaining socket. It's not normal but it just could not penetrate the diaphragm!,

So in the interests of making a picture state a thousand words, here is a picture of a multimeter in series!

I hope it is useful.

Regards

Chris


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## eddied (May 9, 2005)

*12V. current measures*

  
Thanks Chris, just what a simple minded soul like me needed.
No wonder my 5 yr old grandson laughs at me when I try to put his Lego thingies together!
saluti,
eddied


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## Bagshanty (Jul 24, 2005)

For measuring current without breaking the circuit, use one of these:
http://www.maplin.co.uk/module.aspx?detail=full&ModuleNo=46384&doy=31m1#more_info

You need to be able to get at the current carrying wire, so only that goes in the jaws. Putting both live and return wires in the jaws will read zero. This is the cheapest I've seen, they used to be fairly pricey.


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## 101368 (Oct 12, 2006)

Bagshanty said:


> For measuring current without breaking the circuit, use one of these:
> http://www.maplin.co.uk/module.aspx?detail=full&ModuleNo=46384&doy=31m1#more_info
> 
> You need to be able to get at the current carrying wire, so only that goes in the jaws. Putting both live and return wires in the jaws will read zero. This is the cheapest I've seen, they used to be fairly pricey.


Not to be picky but that only works for AC current measurement and the original question is about 12V systems which are normally DC.


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## olley (May 1, 2005)

Hi this is the one you want >>>HERE<<<

Not sure how accurate these are in measuring low ampages.

Olley


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## G2EWS (May 1, 2006)

Clamp on Ammeters are not very accurate at low readings and the ones that are better cost far too much.

They are only of use where you are going round taking large quantities of readings. For us amateurs the standard multi-meter as being used and recommended on a number of occasions are best.

Regards

Chris


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## 101368 (Oct 12, 2006)

olley said:


> Hi this is the one you want >>>HERE<<<
> 
> Not sure how accurate these are in measuring low ampages.
> 
> Olley


It's minimum range on DC is 0-200A it says. Not terribly useful for the sort of currents we're talking about here. Which is a pity but that's physics for you.


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## sallytrafic (Jan 17, 2006)

Bagshanty said:


> For measuring current without breaking the circuit, use one of these:
> http://www.maplin.co.uk/module.aspx?detail=full&ModuleNo=46384&doy=31m1#more_info
> 
> You need to be able to get at the current carrying wire, so only that goes in the jaws. Putting both live and return wires in the jaws will read zero. This is the cheapest I've seen, they used to be fairly pricey.


Unfortunately the one linked to will only measure ac currents.

I haven't seen a clamp meter that will measure small dc currents such as standby currents.

Regards Frank


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## olley (May 1, 2005)

Hi I bought the one in my link before xmas to check on the current drawn by my inverter, it does measure small amounts to one decimal place, but whether when it says 2.7 its 1.7 or 3.7 or worse I don't know. I assume if it says 5 amps and then the current increases to 10 the increase of 5 is fairly accurate. 

As my multimeter has gone west I have an excuse to buy a new one, so I will check it against the multimeter when I get it.

Olley


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