Model Boat Mayhem - Forum

Technical, Techniques, Hints, and Tips => The "Black Arts!" ( Electrics & Electronics ) => Topic started by: tizdaz on November 15, 2016, 02:00:29 PM

Title: Multimeter
Post by: tizdaz on November 15, 2016, 02:00:29 PM
Hi guys,


Im looking to buy a multimeter, it will be to test voltage upto around 24v and also amps upto 50ish


Ive seen a few on ebay but not sure which one i need?
Title: Re: Multimeter
Post by: g6swj on November 15, 2016, 02:47:39 PM
A general purpose meter like this would be a good start

https://www.amazon.co.uk/d/Electrical-Tools-Testers/Pocket-Digital-Multimeter-Proster-Ranging-Multimeters-Tester/B015Z451ZY/ref=sr_1_4?ie=UTF8&qid=1479220836&sr=8-4&keywords=multimeter

The catch with most of these is that they will not measure anywhere near 50amp! - Read the small print

Perhaps get a general purpose meter and then a "current meter" from Component Shop  - see this page

http://www.componentshop.co.uk/catalogsearch/result/?q=meter&cat=0

They also have a general purpose meter @6

Or if you have deep pockets and want a Rolls Royce - Google "Fluke"

Regards
Jonathan


Title: Re: Multimeter
Post by: NFMike on November 15, 2016, 02:50:52 PM
 You won't get 50 amps on a cheap, or even expensive, standard mm. I bought one of these which does volts, etc, as well via included leads:

https://www.amazon.co.uk/gp/product/B00O1Q2HOQ/ref=oh_aui_detailpage_o04_s00?ie=UTF8&psc=1 (https://www.amazon.co.uk/gp/product/B00O1Q2HOQ/ref=oh_aui_detailpage_o04_s00?ie=UTF8&psc=1)
That's from Amazon. I tried to get the same thing from ebay first but it turned out to be one of those 'UK' sellers where even the second one never arrives but in the interim "please give us positive feedback as it will be with you soon".
I've been happy with it and it's probably my main meter now.
Title: Re: Multimeter
Post by: tizdaz on November 15, 2016, 04:46:16 PM
Hiya guys :-)


I think i may have asked for wrong info in terms of amps!


My setup will consist of 4x 12v 20Ah batterys that im going to wire up using Parallel/Series, so i want to measure the total voltage and Ah so i can make sure all is good as i should be getting around 24volt and 40Ah, hope this is a bit more clear!


Also what size AWG wire should i use to link the batterys up, im guessing 14 Awg?


Thanks guys :-)
Title: Re: Multimeter
Post by: g6swj on November 15, 2016, 05:02:13 PM
Perhaps it's worth considering a permanent fixture in your model in which case something like this would be good. This way you can monitor performance over time - it can even record min and max so you can see history when boat returns to shore.

http://www.componentshop.co.uk/150a-watt-meter-and-power-analyser.html (http://www.componentshop.co.uk/150a-watt-meter-and-power-analyser.html)  - It can measure real time, min and max - check the specs

You can only measure the current drawn in "amps" in a working circuit - i.e. the motors need to be running ( and to get a true figure boat needs to be in water, props attached etc)

You will need to protect things with strategic fuse placement

Re cable size/length/voltage drop/current capability etc etc loads of charts on the net e.g. http://www.24volt.co.uk/info/Wiring/Wiring (http://www.24volt.co.uk/info/Wiring/Wiring) - I would over spec this a little to allow some tolerance

Regards
Jonathan
Title: Re: Multimeter
Post by: Buccaneer on November 15, 2016, 05:34:18 PM
Concerning your Multimeter I think it's another case of you get what you pay for. I have blown a couple of cheap Maplins ones so moved up to the 30 range. The present one is the Uni T UT151C at 29.99. I have the predecessor UT 50 and find it excellent.
John
Title: Re: Multimeter
Post by: malcolmfrary on November 15, 2016, 05:44:55 PM
Quote
i want to measure the total voltage and Ah
Measuring voltage is easy, hook up a voltmeter with a range that maxes out at a higher voltage than expected.  Most general purpose multimeters will do this.
There is no direct way of measuring the AH figure for a battery.  With an Amp meter and a clock and a log book you can estimate how much energy the battery has been offered (some expensive chargers do this with magic electronics).  Knowing how much you can get back is a different story altogether, especially with SLA batteries, even more if they are being used at a current discharge rate greater than their stated rate.  Their capacity is usually specced at a 10 hour discharge, or increasingly often, a 20 hour rate.  The faster they discharge above that rate, the less efficient the conversion of energy.
Title: Re: Multimeter
Post by: cos918 on November 15, 2016, 05:51:52 PM
there are meters that can measure the current in a SLA battery . act make them . we have them at work. waste of time and money as they are not reliable . I can get several different reading out of the same battery . Best way is to measure your max current pull . so if thats say 10ah . you should be getting 3.5 to 4hours . as this get less and less time for new batteries


john
Title: Re: Multimeter
Post by: tizdaz on November 15, 2016, 06:50:17 PM
Oki doke, thanks guys great help :-)
Title: Re: Multimeter
Post by: grendel on November 15, 2016, 08:45:31 PM
I have a fluke and that is only capable of 10A as standard, above that you need to plug a shunt in to take the majority of the current away from the meter.
Title: Re: Multimeter
Post by: Martin [Admin] on November 15, 2016, 09:13:56 PM
 
Thinking of buying a Multimeter?

See:  https://youtu.be/uFTQxWlMGeE
Title: Re: Multimeter
Post by: tizdaz on November 18, 2016, 12:10:05 AM
hiya guys :)


ok still trying to figure out what thickness wire i need to get, my motor is a 24volt 150watt, i think ive worked out that it shouldnt be pulling more than 7amps max, looking at a chart it says for 7 amps i should use 14 AWG, does this sound correct?


Also is this the AWG i should use for connecting my batteries up in parallel/series as well as to the motor?


Thanks :)
Title: Re: Multimeter
Post by: RAAArtyGunner on November 18, 2016, 02:01:56 AM
A general purpose meter like this would be a good start

https://www.amazon.co.uk/d/Electrical-Tools-Testers/Pocket-Digital-Multimeter-Proster-Ranging-Multimeters-Tester/B015Z451ZY/ref=sr_1_4?ie=UTF8&qid=1479220836&sr=8-4&keywords=multimeter

The catch with most of these is that they will not measure anywhere near 50amp! - Read the small print

Perhaps get a general purpose meter and then a "current meter" from Component Shop  - see this page

http://www.componentshop.co.uk/catalogsearch/result/?q=meter&cat=0

They also have a general purpose meter @6

Or if you have deep pockets and want a Rolls Royce - Google "Fluke"

Regards
Jonathan

Which is what I have but was a gift.
Title: Re: Multimeter
Post by: NFMike on November 18, 2016, 09:21:34 AM
hiya guys :)


ok still trying to figure out what thickness wire i need to get, my motor is a 24volt 150watt, i think ive worked out that it shouldnt be pulling more than 7amps max, looking at a chart it says for 7 amps i should use 14 AWG, does this sound correct?


Also is this the AWG i should use for connecting my batteries up in parallel/series as well as to the motor?


Thanks :)
You should size the cable to the fuse protecting it, not the expected 'normal' current (which should be somewhat less of course).
So work out max current expected in use, pick a fuse to comfortably exceed that, select cable to handle that current.
Title: Re: Multimeter
Post by: Trawlerman-Les on December 18, 2016, 04:55:27 PM
My old Tandy moving coil meter has died after forty plus years, so I've bought one of these from Wickes. Schneider seem to be a large respected company so I took a chance.

 http://www.wickes.co.uk/Schneider-Digital-Multimeter/p/119803

Hope I've done the right thing?

Les

Title: Re: Multimeter
Post by: Tug-Kenny on December 19, 2016, 11:10:43 AM

Can't go wrong with that Sir.   Just the job.     :-))

ken
Title: Re: Multimeter
Post by: Ron Rees on December 19, 2016, 04:10:27 PM
Oh the good old days when you touched the battery leads to your wet tongue!!.....What laughs we had....!
Title: Re: Multimeter
Post by: Ron Rees on December 19, 2016, 04:11:28 PM
Or better still....got your apprentice to do it!!
Title: Re: Multimeter
Post by: Netleyned on December 19, 2016, 04:13:56 PM
Remember lighting fags by putting wire wool
across the terminals and it quickly glowed red :}
Title: Re: Multimeter
Post by: Trawlerman-Les on December 19, 2016, 04:44:49 PM
Oh the good old days when you touched the battery leads to your wet tongue!!.....What laughs we had....!

 {-) {-)

Oh that's brought back some memories from over 50 years ago! Me and my old school pal, who I still see occasionally, used to call into Woolworths on the way home from school. In those days you bought items from separate counters. The battery counter was our regular stop where we would see which of us could short out the biggest battery with our tongues, before being told to sod off! Oh happy days!   %% %%
Title: Re: Multimeter
Post by: grendel on December 19, 2016, 06:24:18 PM
just one comment, dont ever try that with an old 90v radio battery, I had a headache for about 2 days after, even though it was half dead and only managed about 40v.
Title: Re: Multimeter
Post by: derekwarner on December 19, 2016, 09:35:51 PM
Quote..............

"Oh the good old days when you touched the battery leads to your wet tongue!!" .....

OK, with AA & C & D cells etc, why does this work only with the fingers left hand touching the negative end of the battery?...... and the tongue ....it's universal  O0

Some where in the grey matter someone suggested the left hand is a shorter route [circuit] to the heart  :o

Derek
Title: Re: Multimeter
Post by: NFMike on December 19, 2016, 10:15:55 PM
Some where in the grey matter someone suggested the left hand is a shorter route [circuit] to the heart  :o
Except that the heart is actually in the middle - not on the left.
Title: Re: Multimeter
Post by: malcolmfrary on December 20, 2016, 09:06:14 AM
Except that the heart is actually in the middle - not on the left.
Probably something to do with layout of the actual plumbing and where the main artery departs the heart before it branches out. 
[/size]Blood pressure readings are invariably taken on the left arm. 
[/size]The electricity, once it has got through the (fairly insulating) layer of skin, flows best through the wet conductive stuff, and the arterial path on the left side is probably shorter.  Add to that, the right hands skin on a right handed person is probably that bit tougher due to having had more use, and insulates better.
Title: Re: Multimeter
Post by: derekwarner on December 20, 2016, 09:53:11 AM
Text quotes from Malcolm as below........

"Blood pressure readings are invariably taken on the left arm"

"The electricity, once it has got through the (fairly insulating) layer of skin, flows best through the wet conductive stuff, and the arterial path on the left side is probably shorter.  Add to that, the right hands skin on a right handed person is probably that bit tougher due to having had more use, and insulates better
"

For some unknown reason, the left arm bleeds better than the right :-))...........

Derek
Title: Re: Multimeter
Post by: RAAArtyGunner on December 20, 2016, 10:41:28 AM
Been there done that and have the tell tale scar in left arm.

Started many, many, years ago as an 18 year old when we were asked if we would like help out the Red Cross.

Dumb, dumb, never volunteer, next thing we knew, we were all blood donors.
Title: Re: Multimeter
Post by: NFMike on December 20, 2016, 02:01:26 PM
Blood pressure readings are invariably taken on the left arm.
Sorry Malcolm but that is twaddle. They use whichever is easiest, usually the side the machine is on. This year alone I've had it taken on my right arm on two separate occasions.

I'm sure all this is old wives tales stemming from the belief that the heart is on the left.
Title: Re: Multimeter
Post by: Trawlerman-Les on December 20, 2016, 02:15:22 PM
I've just done my 75th donation. Left arm didn't want to co-operate too well, so the last 74 have been from the right. The resulting scar tissue makes it blood* painful now to push the needle in! :o

Les
Title: Re: Multimeter
Post by: Netleyned on December 20, 2016, 05:01:39 PM
Amazing Mayhem :}
A Guy buys a Multimeter
and ends up with a subscription to
Blood Donors Inc. :D


Ned



Title: Re: Multimeter
Post by: derekwarner on December 20, 2016, 09:23:51 PM
Good morning Ned....but never let it be said I would stray too far off thread  :P

Yes the original post included an explanation of the performance features of the Multimeter in question

As we know, Iron [Fe] is an excellent conductor of electricity...it just so happens that the blood in our veins contains Iron [Fe] :kiss:

I have been assisting an Associate Professor in Wollongong in understanding and determining how the various Iron [Fe] levels in my blood can be accurately  measured using my specially modified $25.00 home multimeter to measure the Iron [Fe] in my blood

As we can see, three Ferritin [Fe] levels [668H, 544H & 406H] levels  in my blood were marked with an H which means HIGH, this is where the Multimeter setting 'hFE' is used to detect such abnormalities

This process is in an early stage of development and we are also using my specially modified $25.00 Stanley metal detector to establish just where the Iron [Fe] loaded blood veins are located in my left arm

Associate Professor Raj....thinks we could be on a real $ spinner here....so watch this space  :}

So from here, I rest my case in the usefulness of home multimeters here on MBM.......Derek 
Title: Re: Multimeter
Post by: Ron Rees on December 21, 2016, 07:51:51 AM
They tell me 'Old Sparkey' the first Electric chair in America used only 24 volts, but at about 1000 amps, so don't try this at home!!! :(( >:-o :police:


Ron.
Title: Re: Multimeter
Post by: Netleyned on December 21, 2016, 09:36:44 AM
Derek Warner Decoy
AKA
The Tin Man :D


Ned
Title: Re: Multimeter
Post by: AlexC on December 21, 2016, 01:22:43 PM
Hi Guy's and Gal's,

What Derek is not telling us is that these High Fe levels are being discovered after several cans of (F)osters (e)xtra Which turns him into a High Gain Semi-Conscious-Conductor.  {-)
It could lead to Thermal Runaway and damage to his multi-meter if left unchecked. <:(
Have a great Christmas Derek and everyone else.
Sandy. :}
 





Title: Re: Multimeter
Post by: RAAArtyGunner on December 21, 2016, 09:47:55 PM
Alex,

You have got it in one. O0 O0
Fosters and others, were canned in tin containers but are now, canned in aluminium containers, for the reasons you mention.
However, as mentioned it has not prevented participants still exhibiting high levels of Fe. <:( <:( <:(

 %% %% {-) {-)

Oh yes, thankfully Queenslanders are immune and unaffected, as they drink XXXX not Fosters O0 O0 :} :}
Title: Re: Multimeter
Post by: derekwarner on December 21, 2016, 11:56:37 PM
Hullo Sandy.....hope all is well in Lochgilphead and the chooks are laying %)

Associate Professor Raja Ramakrishna has suggested I trial an alternate fluid for a few days & then get my $25.00 modified multimeter and my $25.00 Stanley metal detector and use the hFE setting & check my Fe levels

Charming name :o, but I improve the character by consuming the fluid [medical purposes only] in a Stewart crystal glass  :kiss:

Best wishes to you & hope Santa is kind........... Derek

PS......I don't recommend mixing this medication when using my solar powered digital ABBACUS [with flat batteries and in a dark room :embarrassed:]