Multimetres, what can they tell you?

[Guest]

I'm an electrical dumbarse. I have worked out how to read volts on a multimeter but bugger all else. So I'm going to ask some questions about how to work them.....after 10 odd years of ownership

 

Q1 - Just wired into the micro eco dwelling some ammeters. I fiddled with the multimeter to see if I could work it out to see if the installed ammeter was working and calibrated.

 

My multimeter is configured as in the photo, the red lead to the battery bank (12v 400amp) side of the red positive wire and the black lead to the outlet side of the same wire (it was at a join which was unjoined at the time) and there was a small radio plugged in. The radio uses feck all and is running on 3V via a small step down somethingorother.

 

The screen on the multimeter read 29.3 to 31.5 somethings. No minus sign was showing at the time. If I changed the dial to the one that says 20m/10A or the 2 below that, the screen read OL.

 

What are those somethings it's showing me?

Would I be right in assuming that is approx 1/3 of an Amp?

[wheels 543]

I am writing this not just to you KM, but so as it might be of help to all. So forgive the sucking egg lesson.

Right firstly.

uA = micro amps = 1000th of an A or 0.0001

mA = milli amps = 1000000th of an A or 0.0000001

That's really small. When measuring Amps and you are not sure what to expect, always start with the higher input and highest setting and work down. Otherwise you will blow the very small internal fuse.

When measuring Amps, you are measuring current flowing through a circuit. So you are connecting the meter with the leads in series with the circuit, not across the Positive (phase is AC) and negative (neutral is AC) conductors. Otherwise you will fry the Meter and place a dead short on the circuit. Hopefully your breaker will trip.

Make sure you always place the lead back in the Volt/Ohm Socket and select the appropriate setting before you place the meter across a voltage. Otherwise you can do some damage to meter and maybe the circuit you are measuring.

The minus sign tells you the polarity of what you are measuring in relation the the leads. If you know there is a current draw, don't worry about if the minus sign is there or not. If it appears, it just means the leads need to be swapped, but it does not affect the accuracy of the reading at all.

The "OL" means overload. This will tell you the meter is set to a setting that is too low for what it is actually sensing. A good meter can handle that OK, cheap meters may not and the OL is actually the abreviation for Chinese "Oh Luck" where they can not pronounce F if you get my drift.

Some meters are automatic ranging and will select which scale it needs. Well worth the money if you have a regular problem with seeing the chinese "OL" flashing and nothing works again.

So what you should be measuring with the scale setting you have selected and getting a reading of say 31.5mA is 0.031 amps at the voltage the circuit is at. If the circuit is 230V, you now multiply that 0.031 x 230, you get about 7.1-7.3watts.

[Guest]

I got no eggs to suck when talking this stuff Wheels, no worries on that account.

 

Thanks all good and with all those options on the metre (a Dicky Smith) I now have doubled the ones I know all the way up too 2

 

I need something with a large draw to check my dials. Ah ha, a warm fridge should suck a fair whack. Off to the boat we goes.

[wheels 543]

Yep frdge will do it. Is it a compressor type or a three way, gas, AC/DC. Those three ways will give you ruffly 17A on DC. Hint, you won't measure anything on Gas OK

Or if you do, GET OFF THE BOAT FAST!!!!

[Guest]

Weaco portable 240 or 12V, the compressor version knot the thermo-electric. Sucks around 1amp when down to temp, surprisingly good actually. Knot sure what it sucks at warm but should be a nice easily visible amount. The only connection to gas is from what the fridge contains and then is eaten

[NevP 0]

uA = micro amps = 1000th of an A or 0.0001

mA = milli amps = 1000000th of an A or 0.0000001

 

Sorry to disagree Wheels but I think you have your micros & millis back to front. (just a typo on your part I'm sure )

 

It should be

uA = micro amps = 1,000,000th of an A or 0.0000001

mA = milli amps = 1,000th of an A or 0.0001

Refer http://en.wikipedia.org/wiki/Milli-

[wheels 543]

Yes you are right. Good catch. Damn dyslexia. Thanks, it is certainly worth checking any figures i write as that is where my problem shows up the most.

[Farrari 4]

KM, I had a 50L compressor driven Waeco portable fridge/freezer in my last vessel. From memory it drew about 4 amp's while the compressor was running. It worked really well until the ambient temperature of the cabin started to rise and then it would struggle. The compressor would need to run more than 50% of the time and that's when it really started to suck the juice.

 

From memory airflow was also a bit of a problem in my case, so no matter how long the compressor ran for the radiator wasn't efficient enough to transfer the heat. I couldn't get enough cool air flowing through it for it to work effectively.

 

I solved the refrigeration by buying a bigger yacht. In hind site it was a very expensive fix to my problem

[Guest]

Farrari, if I were you I'd be running like the wind about now. My wife thinks the 50fter I brought this morning, purely on your recommendation, is a tad over the top

 

I think ours is the CF-40. It has good airflow, we keep it out of direct sun if possible and we try knot to open if willy nilly BUT we have kids so...... Load it at home while plugged into 240V then swap to the boat when ready. On occasions it's fired up on the boat but seems to come down pretty quick. We run it at 4 degrees which does the job nicely. It will freeze things but sucks the juice doing so.

 

The book says 1 Ahr 'average over 24hrs', and while I can't check for sure I don't think it's far off that. Went 4 days at Easter with it running 24/7 plus lights, radio etc all on one 120amphr battery with nothing going back in (now sorted). The battery was sad when we got home but I plugged it into the Nat grid and all is good again. Late Jan we did a week away only getting battery input via 1 40W solar panel, no worries at all.

 

I will be able to check accurately at home so I'll let you know what I find, I'm looking forward to seeing myself.

[wheels 543]

When the compressors run, they are usually 4 to 6A. but they only run for a brief time. The real energy is used when cooling food down and everytime you open the lid. Which by the way, is not a good idea having a front opening fridge as all the cool air spills out when you open the door and you have to col all that air down again.

So if the freezer is full and cold as KM has said by cooling down while on Shore power, then the cycling of the comp should average out to a small amount of energy consumed over a 24hr period. As against those stupid 3way units that draw power or use gas all the time and don't stop at all.

The real key to a Comp fridge cycling as little as possible is insulation. You can simply not have enough insulation. If you are biulding a fridge box, go for the most insulation you can possibly get away with and then double it

[Farrari 4]

Topping ours up with warm liquid refreshments every day during the middle of summer probably didn't help in our case either

[Guest]

actually insulation isn't the main power saver, decent effective seals are, they allow the full effect of the insulation you either paid for or painstkingly added to come to full fruition, remember temperature= pressure so regardless of a vertical or horizontal opener the end result will be pretty much the same......the cold doesn't'" escape" the heat invades.

Another consideration with DC refrigeration is pressure=temperature= energy, so with a restricted or warmed airflow the head pressure on discharge will rise and the unit willl consume more amp hours

And a thought to ponder.....dont ever get anyone to hookup one of these small danfoss compressors to a cabinet that was originally engine driven.........they die

[SloopJohnB 323]

I'm an electrical dumbarse. I have worked out how to read volts on a multimeter but bugger all else. So I'm going to ask some questions about how to work them.....after 10 odd years of ownership

 

 

 

Crickey thats an old model and not a "Fluke"

[Guest]

It gets sadder, it took me a good 5 years to work out how to read the volts. I tend to buy then work out how to use stuff. Like the big flash MIG welder I brought 3-4 years ago. Turned it on once while pissed but the on/off switch is about all I know what to work on it so it sits........ and sits..... and is still sitting.

[Guest]

On a top loading box,can anyone comment on how much you lose through leaky seals.I would think not much but I wonder about an impressive ice buildup near a leaky seal.

[Guest Dry Reach]

My multimeter told me, the other day... "buy a new probe!"

 

Was testing a light switch to see if it was live! and... WHAMO!, flash!, SPARK!, Whamo again!...

 

then i looked at the -ve probe and it looked like a apprentice welder had been using it on his day off!

 

i think the meter was on the wrong setting.

 

seems to still be working ok

[Guest]

DR - you probably had the positive probe in the Current measuring connection and tried to measure voltage, so basically shorted the power grid with the meter. The current circuit probably doesn't work anymore.

Easily done.

[wheels 543]

seems to still be working ok

You might have to try it again then.

[Guest Dry Reach]

seems to still be working ok

You might have to try it again then.

 

 

I was talking about the light switch!

 

the multimeter is not to smart now.

 

and slacko. you are right i think that is what i did!

 

electrickery and me are not friends

[rigger 47]

Electricity - definition of

compressed smoke contained within a wire - often broken by prodding it with metallic components upon which the wire emits smoke and the device that was connected to the electrical circuit no longer works as all the electicity (smoke) has escaped...