Amp/volt meter...handy for us fiddlers

hako · Guru

Amp/volt meter...handy for us fiddlers

D and D · Guru

Which one?

Dave

hako · Guru

D and D wrote:
Which one?

Dave

The one at the top:

Digital LCD Watt Meter Battery Balance 60V100A DC RC Volt Ammeter Amp Analyzer

dorian · Guru

This device appears to be similar, only in a different package:

http://www.rc-cars-planes.com/docs/wu100v2_user_manual.pdf

My first impression was that the wires looked a bit light. At 10A, the dissipation in the wires and shunt would be 0.5W, but at 50A it would be 12.5W. The voltage drop at 50A would be 0.25V.

7.2 Maximum Current Capabilities

Current flowing through Watt's Up and its supplied wires generates heat due to the resistances of the wires and of the precision internal current shunt used for current measurements. Though very low (~ 0.004 Ohms in 14 gage wires and 0.001 Ohms in shunt), these resistances are finite and at high currents the heat generated becomes noticeable.

At 75 Amps, approximately 28 Watts of heat is produced -- mostly in the Watt's Up's wires. ... The high current handing capabilities of Watt's Up will be maximized when the Watt's Up's SOURCE and LOAD wires are kept short and cool. Cut the wires as short as is convenient for high current operation. A fan blowing over the wires will help their cooling. At moderate currents there is little heating. Using a "three-wire" connection will also lower heat generation.

The idea that wires need to be cooled is scary.

-- Edited by dorian on Tuesday 11th of November 2014 06:27:46 AM

SnowT · Guru

I would Not trust that Little meter for anything but extreme low amp's....

To try measure of amp. especially once you get over 10A's with that toy's is cause the possibility danger...
- either using a calibrated shunt and a meter..[be it digital or analogue]
- or via the coil the method and a meter...

I don't see how the setup they have will doing anything in the 10's or even 100's of amp's..

Juergen

Stratman77 · Senior Member

Since you've ordered it, I suggest it will probably work OK to monitor your charge current and battery voltage but I would be cautious about adding too much load. Maybe you could add load in stages to see how it goes, but 100 amps? I wouldn't think so. Maybe play it safe and put a 20 or 30 amp fuse in the positive line to start with.

hako · Guru

I just did a Google search for:
"Digital LCD Watt Meter Battery Balance 60V100A DC RC Volt Ammeter Amp Analyzer"
and it looks like there are heaps of tests on this very device plus they seem to be very common except it seems in Australia.

Lets face it - if I put it inline on the house battery, it will give me current voltage and current going in or out no problems. I know it works because I've read a few of the reviews and for the price how can I resist. If it doesn't work or overheats then it guaranteed for 12 months and it's sold out of Brisbane (not China) by a premium Ebay seller who will not quibble to refund if I say it is no good.

I will report on it when it arrives - I'll run a 100 watt QI bulb thru it and compare readings with my old Avo still in it's leather case plus check temp of wires with an IR meter, and I will be honest.

Thanks for the comments.

Phil C · Guru

We have one of these in the new electrical dist box I put in.

http://www.ebay.com.au/itm/Digital-LED-AC-Volt-Amp-2-in-1-Combo-Meter-Voltmeter-Ammeter-0-2-99-9A-/161361280122?pt=AU_B_I_Electrical_Test_Equipment&hash=item2591e1bc7a

I dont expect great accuracy, but it does give me some idea as to the state of our current draw and volt drop.

Very neat current transformer inside the box, just had to pass an active through the device and an active neutral for the volts.. sweet but probably not approved, so far no dramas.

-- Edited by Phil C on Thursday 13th of November 2014 10:11:06 AM

SnowT · Guru

Phil I was about to jump on you and say WTF have you done..

Then I noticed that it was in 237v NOT 23.7v
If it had of been a Low Voltage range I would of Said...
" Phil that is not a Thing that you should be showing People.. "

As you will know.... Never EVER MIX low voltage with high voltage..

12v-48v should never be Mixed with 240v..

so Phil I'm not gonna jump on you and just say Well Done.... [ Please Note this partial Fix has been done By an electrician - Do not do this unless you are an Electrician ]

So a Good little fix...

Juergen..

Psst -- Phil I don't need that.. I have a Victron BMS 600 which tell me My DC loads and with My style of system I don't need to really need to worry about the high voltage stuff I'm after the Battery stuff..

Plus My inverter has all that information on it at a glance..

Cloak · Guru

dorian wrote:

The idea that wires need to be cooled is scary.

-- Edited by dorian on Tuesday 11th of November 2014 06:27:46 AM

I agree that implies an overload and fire risk.

As with all these power / current detectors they all seem to be stuck on Ohms law. Are there any using a hall effect device? I couldn't find any affordable ones.

Phil C · Guru

Thanks guys, I needed to isolate the aircon, so a full replacement of the very weak Jayco system was in order. So I thought why not a volt/amp meter as well? Ebay came to the rescue. smile

BTW This job has been designed and completed by a licenced electrician and has a full certificate of compliance with it. Dont even think about doing something like this, yourself if you are NOT an electrician!

Cheers

Phil C · Guru

Cloak wrote:
dorian wrote:

The idea that wires need to be cooled is scary.

-- Edited by dorian on Tuesday 11th of November 2014 06:27:46 AM
I agree that implies an overload and fire risk.

As with all these power / current detectors they all seem to be stuck on Ohms law. Are there any using a hall effect device? I couldn't find any affordable ones.

Im pretty sure that this has a current transformer in the guts someplace, a hall effect would be a lot more expensive. Also it is not that accurate, specs say 1%, I doubt it..

I agree about Ohm's Law.. hasnt been repealed as yet.. confuse Find a new one and make a fortune.. smile

-- Edited by Phil C on Friday 14th of November 2014 08:42:16 AM

oldtrack123 · Guru

Phil C wrote:
Cloak wrote:
dorian wrote:

The idea that wires need to be cooled is scary.

-- Edited by dorian on Tuesday 11th of November 2014 06:27:46 AM
I agree that implies an overload and fire risk.

As with all these power / current detectors they all seem to be stuck on Ohms law. Are there any using a hall effect device? I couldn't find any affordable ones.
Im pretty sure that this has a current transformer in the guts someplace, a hall effect would be a lot more expensive. Also it is not that accurate, specs say 1%, I doubt it..
I agree about Ohm's Law.. hasnt been repealed as yet.. Find a new one and make a fortune..

-- Edited by Phil C on Friday 14th of November 2014 08:42:16 AM

HI Phil

Current transformer, DC ???? smile

PeterQ

Phil C · Guru

No its AC Peter, thats if you are talking about my modification. All AC mains.

Sorry guys I didnt read the posts correctly, the DC stuff will either need a hard wired ammeter or a hall effect, I have not seen one out there, all hard wired as far as I can see (for DC)

Now im confusing myself... confuse

-- Edited by Phil C on Saturday 15th of November 2014 07:35:01 PM

-- Edited by Phil C on Saturday 15th of November 2014 07:37:52 PM

dorian · Guru

I was thinking that some enterprising tech might be able to modify the cheap wattmeter by replacing the Ohmic shunt with the signal output from Silicon Chip's Hall effect based DC current clamp meter.

archive.siliconchip.com.au/cms/A_30669/article.html

The spec for the clamp meter is "Output: 1A = 1mV for AC and DC ranges". That is, for a current of 1A flowing in the cable, the meter generates an output of 1mV.

A current of 1A flowing through the 0.001 ohm shunt in the wattmeter would also produce a voltage drop of 1mV. Therefore, ISTM that all one would need to do would be to remove the shunt and wire the SC clamp meter's output and ground pins into the same location (assuming that the clamp meter's output is reference to the same ground).

Output: 1A = 1mV for AC and DC ranges
Resolution: multimeter dependent (100mA with 0.1mV resolution on multimeter)
Maximum DC current: 150A recommended (up to 900A if core is demagnetised afterwards)
Maximum AC current: 630A recommended
Linearity: typically better than 4% over range at 25°C
AC frequency response: -3dB at 20kHz (meter reading depends on multimeter AC response)
Current consumption: 15mA

-- Edited by dorian on Saturday 15th of November 2014 07:54:55 PM

dorian · Guru

Hmm, looks like it's not going to be so easy. The clamp meter's output is not referenced directly to ground.

DeBe · Guru

Ive built one of those Silicon Chip clamp meters. They do work ok but they need to be zeroed each time you use it. They do use a Hall device to measure the current.

Cloak · Guru

Ahaa a self zero reference is easy as...

And for $400.00 / hr + expenses...... You know the drill...

dorian · Guru

If the zeroing is necessary because of drift in the opamp, then perhaps an autozero-ing opamp might work.

For example, Microchip's TC913 Dual Auto-Zeroed Operational Amplifiers are pin compatible with the jelly-bean LM358:

ww1.microchip.com/downloads/en/DeviceDoc/21482C.pdf

hako · Guru

Here is an update - I've tested the device against a digital VOM (the AVO batteries were gone) and I reckon the readings are virtually spot on. For a cheap 'toy' the innards seem good quality and as good as you get - definately not cheap junk IMHO. Anyway, I've attached some pics of the results using a headlight bulb and a small 12V battery that shows a dramatic drop in voltage and yes, the jumper cable I used did melt!
Good Luck.

Knowledge speaks, but wisdom listens.

Knowledge speaks, but wisdom listens.