amp meter wanted

[AstonHill]

If you run current thru a resistance/impedence (albiet a very small one) then if you measure the voltage across that resistance/impedance you can manually or automatically calculate the current.

Are you refering to a resistor?

Example, if you run the current thru a resistance/impedance of 0.1 ohms you can measure the voltage and therefore calculate the current and the 0.1 ohms when compared to other resistances in the circuit wiring will not really much affect the readings in many circuits.

If common on cars; could I get one from a brakers yard?

Actually in a similar way, if we use our meters to measure our earth electrode resistance

Is it 7Hz?

With Volts, Amps and Ohms, if we know two of those values we can calculate the missing value

So what is the equation for this; one of the experts in the shop told me that, volts times amps = ohms
Not when I went to school is wernt

 

[AstonHill]

I have issues with calibration houses, had a bad experience, and personally all I do is compare two devices and if they both read the same, that's good enough, but I think scheme member electricians need to get test gear calibrated with a certificate issued to say it has been done. It is just part of the paper trail they need to generate.

I personally want to know within a week if a meter has gone faulty, if the pass mark is 1.38 ohms and I have passes 5 homes then find my meter has gone faulty, and is showing lower than it should to return to 5 homes is not so bad, but if I have done 40 homes, then that's enough to bankrupt an electrician having to return to do so many, so before I retired I would test a socket in my own house which had been tested many times before to ensure the meter was still OK. Having a meter tested once a year is not really good enough.

GEC large steam turbines when I worked for them went crazy on calibration, even the crimp pliers were calibrated.

Great!
But for someone who want the amp meter to tell him how much current is going into his battery and then knowing when to switch his generator off. Is a calibrated amp meter at 100 quid plus, compered to 30 quid one on ebay neosensory or not?

 

[AstonHill]

I have issues with calibration houses, had a bad experience, and personally all I do is compare two devices and if they both read the same, that's good enough, but I think scheme member electricians need to get test gear calibrated with a certificate issued to say it has been done. It is just part of the paper trail they need to generate.

I personally want to know within a week if a meter has gone faulty, if the pass mark is 1.38 ohms and I have passes 5 homes then find my meter has gone faulty, and is showing lower than it should to return to 5 homes is not so bad, but if I have done 40 homes, then that's enough to bankrupt an electrician having to return to do so many, so before I retired I would test a socket in my own house which had been tested many times before to ensure the meter was still OK. Having a meter tested once a year is not really good enough.

GEC large steam turbines when I worked for them went crazy on calibration, even the crimp pliers were calibrated.


I showed this picture View attachment 307693the current goes through the large terminals and at the top the small plug has the very small voltage that goes to the meter, the old CAV used the same shunt to work ammeter and alternator control View attachment 307695 The metal lump shown below turned current into voltage, it could be trimmed with a hack saw.

Im now starting to understand a little of how it works; but I dont think that thing is for sale for 30 quid though!

 

[AstonHill]

If one firm has one meter (or 5) they all use and its paid for by the firm and gets thrown about in vans then one a week would not be often enough but one electrician using it solely and they`d paid for it themselves then sending away every three years might be often enough.
Actually, some wholesalers run a testing day once or twice a year, take your meters in one day and call back for it the next day and at a discounted price.

OK Im stating to see the point as why as to calibrate them. given the fact that mine I plan to run for my generator, just sits there in a case to be lookrd at

 

[ebee]

Are you refering to a resistor?

If common on cars; could I get one from a brakers yard?


Is it 7Hz?


So what is the equation for this; one of the experts in the shop told me that, volts times amps = ohms
Not when I went to school is wernt

Hi Ashton,
effectively all conductors have some resistance (impedance) therefore could be called a resistor but often if they are small then we might ignore them. We might use a higher one deliberately for some reason and we can, in this case, use a small one for our intended use.

the equation is V = I x R , V is Volts, I is current in Amps and R is Resistance in Ohms.
V x I (Voltage x Current) = Watts (Power).
so V I R W, if we know two of those values then we can calculate the other two.
we can alternatively use I squared x R to calculate Watts.
Anyway V = I x R and V x I = W are two equations we very commonly use.

7Hz, I dont think so, there are a few alternative frequencies we can use in our testers, they are used to aid in cancelling interreference to some degree and to combat polarisation effects too.

You might get one from a breakers yard.
How much are you prepared to spend? What accuracy do you need?
as I mentioned, if you introduce a 0.1 ohms resistance and measure the voltage across it with a cheap multimeter for example then for every amp of current or thereabouts you would actually see a voltage of ten volts.
Your accuracy of measuring that 0.1 ohms in the first place, the accuracy of the voltmeter and the relative temperature range you go thru will all effect your measurements.
If you have a bit of copper plate (say an old Busbar) and measure the resistance, then calculate the length you need to produce a certain resistance then you are well on your way.
Your initial 0.1 (or whatever you decide to use) does not need to be deadly accurate, aim at it then measure it and say for instance its measuring at 0.136 ohms then you can still use it and do the equations accordingly.
The reasons you need it and therefore the accuracy required for comparisons determine the costs.
Example, I buy a cheap clock it might be good enough if it tells me it is Thursday Morning or I might need to know I am within 1 second of the rest of the world, or something in between.

 

[bernardgreen]

as I mentioned, if you introduce a 0.1 ohms resistance and measure the voltage across it with a cheap multimeter for example then for every amp of current or thereabouts you would actually see a voltage of ten volts.

1 Amp through 0.1 Ohm would produce 0.1 Volts

the equation is V = I x R , V is Volts, I is current in Amps and R is Resistance in Ohms

 

[ebee]

GOOD. I was wondering which one of you would spot that one!

 

[ericmark]

I know it is called the hall effect, but as to how it works, don't really know. Even the cheapest meter I have gives a full scale deflection at 150 mA, unfortunately the holes for leads are very small and to measure the ohms of the meter is not easy, but the ohms of the shunt would be very small, the problem with analogue is normally not a centre zero, and a digital meter needs a battery.

Great!
But for someone who want the amp meter to tell him how much current is going into his battery and then knowing when to switch his generator off. Is a calibrated amp meter at 100 quid plus, compered to 30 quid one on ebay neosensory or not?

The ammeter will tell you very little, same with a volt meter, if I look at my battery chargers they have a chart

from this chart you can see the battery is considered fully charged when the current drops below 0.8 amp.

Same with the latter model, to know it has reached fully charged state number 6 on both charts the rate has dropped from 0.8 amp to 0.1 amp,

I have recorded this with a energy monitor and even when fully charged it will keep topping up, and the amount of time and energy slowly reduces.

So in real terms you would not want to run a generator long enough to fully charge the battery, this is the problem with narrow boats, they only run the engine for maybe 8 hours, so they want to cram as much as they can into the battery in the 8 hours they have, Sterling Power do special alternator to battery chargers designed to try and cram in as much energy as they can, the DC out of the alternator is turned to AC and then transformed to voltage required then back to DC and the alternator voltage is kept low enough to ensure the alternators own voltage regulator keeps the alternator producing max output.

These are very expensive, so the alternative is a shore supply once a month for at least 24 hours to top up the batteries, many canal side pubs offer charge points. Today the solar panels and wind chargers have changed what is required, but a panel ammeter or volt meter are not really going to help.

 

[Harry Bloomfield]

I know it is called the hall effect, but as to how it works, don't really know. Even the cheapest meter I have gives a full scale deflection at 150 mA, unfortunately the holes for leads are very small and to measure the ohms of the meter is not easy, but the ohms of the shunt would be very small, the problem with analogue is normally not a centre zero, and a digital meter needs a battery.

If it were me, desperate to measure charge discharge currents, in an existing DC system. I would fit a volt meter, in series with a variable resistor, in parallel with the battery to alternator cable. Also in series with the lead I would temporarily connect an ammeter, set on the 20amp range, then turn some loads on, to get the ammeter showing as close to the 20amps as possible.

Now adjust the voltmeter range, to show a value greater than 20, now adjust the variable resistor, until the voltmeter show a similar value to the ammeter. Once done, your temporary ammeter can be removed and your voltmeter now shows a reasonably accurate charge/discharge current.

 

[ericmark]

If it were me, desperate to measure charge discharge currents, in an existing DC system. I would fit a volt meter, in series with a variable resistor, in parallel with the battery to alternator cable. Also in series with the lead I would temporarily connect an ammeter, set on the 20amp range, then turn some loads on, to get the ammeter showing as close to the 20amps as possible.

Now adjust the voltmeter range, to show a value greater than 20, now adjust the variable resistor, until the voltmeter show a similar value to the ammeter. Once done, your temporary ammeter can be removed and your voltmeter now shows a reasonably accurate charge/discharge current.

I can see your point, but first onto the practical problem, where will you find a cheap centre zero volt meter? In the main if I need to measure charge and discharge with the same meter, I need to go digital read out. Even my AVO Mk8 is not centre zero. To get a centre zero meter is going to be expensive, and then after all that, it will not help work out battery condition.

 

[JohnW2]

But for someone who want the amp meter to tell him how much current is going into his battery and then knowing when to switch his generator off. Is a calibrated amp meter at 100 quid plus, compered to 30 quid one on ebay neosensory or not?

Have we ascertained exactly what sort of currents you are wanting to measure (i.e. 'how many amps').

As I think has been said, or at least implied, if they were suitable (and if yuou didn't have your problem with eBay!) there are always plenty of 'vintage' 30A-0-30A, 50A-0-50A and 60A-0-60A ones available, quite cheaply on eBay.

Kind Regards, John

 

[AstonHill]

I know it is called the hall effect, but as to how it works, don't really know. Even the cheapest meter I have gives a full scale deflection at 150 mA, unfortunately the holes for leads are very small and to measure the ohms of the meter is not easy, but the ohms of the shunt would be very small, the problem with analogue is normally not a centre zero, and a digital meter needs a battery.


The ammeter will tell you very little, same with a volt meter, if I look at my battery chargers they have a chart View attachment 307803 from this chart you can see the battery is considered fully charged when the current drops below 0.8 amp.

I am very confused by this!
there are two diffarent chars showing nealy the same amps going in, but completely the opposite resalts

These are very expensive, so the alternative is a shore supply once a month for at least 24 hours to top up the batteries, many canal side pubs offer charge points. Today the solar panels and wind chargers have changed what is required, but a panel ammeter or volt meter are not really going to help.

So as from your last chart; are you saying its more efficient to charge the batteries upto a certain point and less efficient to fully charge them. But is needed to do so to prolong the life of the batteries evey now and again with a trickle charge?

 

[AstonHill]

If it were me, desperate to measure charge discharge currents, in an existing DC system. I would fit a volt meter, in series with a variable resistor, in parallel with the battery to alternator cable.

Can you show a quick schematic of this to help the not so well know people of it

Also in series with the lead I would temporarily connect an ammeter,

but I still need to buy an amp meter to do all this right?

 

[AstonHill]

Have we ascertained exactly what sort of currents you are wanting to measure (i.e. 'how many amps').

Sorry might of slipped my mind to tell you all; anyway its an 8.3amp out put on the DC of generator

As I think has been said, or at least implied, if they were suitable (and if yuou didn't have your problem with eBay!) there are always plenty of 'vintage' 30A-0-30A, 50A-0-50A and 60A-0-60A ones available, quite cheaply on eBay.

Kind Regards, John

Good idea plenty of second hand junk on ebay, some a scam some not, but I think something like this would be OK
But BTW I have a CCJ against ebay and as of such they have banned all credit, debit cards in my name and address. So ebay no good for me!

 

[ericmark]

8.3 amp is enough, with a stage charge the first stage at high amps is quite short, the problem with the lead acid battery is it will only absorb the charge slowly, the time taken is variable and depends in the main how long it has been discharged rather than by how much, the sulphur hardens on the plates, so left discharged for 6 months it could take a couple of weeks to charge, but it also means a battery discharged for a day takes longer to recharge than one left discharged for an hour.

If the battery is not fully recharged then you have some sulphur left on the plates to harden, so going back to the 50's with dynamos, we would put on an equalising charge over night once a month. But back then we had flooded batteries so we could top them back up, the early sealed batteries were in fact still flooded, they just had a vent system designed to recycle the water, latter we went to absorbed glass mat, (AGM) but both need a battery charger that will not over charge them, looking after fork lift batteries it was not unknown to use a gallon of water to top them up, same charger with AGM would kill them.

So if we take the 5 amp charger as an example, as the chart shows there are in real terms 4 stages 5 amp, 3 amp, 0.8 amp and 0.1 amp, the switch between stages is triggered by voltage, so we have looking at basics 12.8 as lower limit and 14.4 as upper limit, and if the lower limit is reached the charger steps up a stage, and if upper limit reached it steps down a stage, and when it steps down to 0.1 amp it is considered charged, it will continue to take charge after that point, but very little.

So with a non stage charger just a fixed voltage we can use the current instead, how much depends on battery size and condition, so if it were me I would fully charge with the stage charger first so I can measure the amps when fully charged, I would think likely 0.1 to 0.2 amp, this would present a problem, to measure 10 amp, and be able to see when down to 0.1 is too much of a range. So it would need a by-pass so it only measures up to 1 amp but is not damaged sending 10 amp through it. Likely a large diode would do this, the 0.6 threshold voltage would be enough to work the meter.

The cheapest tool station multi-meter will measure 10 amp, cost £20 and is digital so can also measure 0.1 amp on same scale, it does not say much about the meter, but I note separate terminal for amps, so likely a shunt built into the meter, so seems likely it will let current flow even if meter switched off, and mA range uses the other terminal, so seems likely switching through the mA ranges will cause no problem.

Personally I would use my meter, and leave a loop of wire on dash to clamp it onto when I want to measure, I get so much more by paying the extra £15, but tool station version is £123, this is the cost of having upset ebay.