Jump to content

Ammeter - advice needed


Johny London

Featured Posts

4 minutes ago, blackrose said:

I've only got two; a cheapo and a fluke. Guess which one gets lent to neighbours?

I’m the same. My two Flukes are in very distinctive Fluke bags and it’s one of those which has been recently calibrated. As it turns out, it was a waste of £35 as it hadn’t really moved from the last time. NOBODY borrows them ;)

Link to comment
Share on other sites

1 hour ago, WotEver said:

As for multimeters, last time I counted I have nine, I think. All but two of them work, only one has a D.C. clamp, and only one of them has been recently calibrated. 

 

DC clamps are SO useful I have at least six. One in each bote, one in the van, one in the house and a spare. 

 

And totally agree with everything Blackrose said. The rule I've learned the hard way is NEVER lend people tools. The only people that ask are those who see little value in them so never buy their own. I'll offer to do the job for them using whatever tool they want to borrow but lend it? No sorry. Chances are it will come back damaged in some way or with some wear and tear from mild abuse I would not have given it. IF it comes back at all. 

 

 

  • Greenie 2
Link to comment
Share on other sites

17 hours ago, Johny London said:

If it did turn out that there really was a 5a drain I would feel rather vindicated - and possibly have been rather too hard on lead acid technology!

 

I think a clamp meter would be very useful - annoyingly, I actually have one but it doesn't do DC current. Anything else I could be missing?

On a yacht I used to own, I had to leave it connected to shore power when I left it for any length of time as there was a 0.5A discharge when the battery isolators were turned off. As far as I could tell, everything on the boat was turned off at its' on/off switch.

 

Anyway, eventually, I discovered that the NASA weather reporting gizmo was connected directly to the batteries, (cant recall why), and, when turned off at the switch, it still drew 0.5A. I fitted a switch in the supply cable, so was able to turn it off properly. Happily left the boat for weeks at a time with no connection to shore power :)

 

You might have something with a "soft" on/off switch, but it would also have to be connected to the batteries directly, rather than through an isolator.

 

Having said that, 5A is a lot! Continuously running Fridge type power.

 

My Sterling inverter charger is connected directly to the batteries, with no isolator, and draws 4A when turned on and powering nothing. Cant think of anything else that draws this kind of power continuously?

Link to comment
Share on other sites

Thanks for all the great thoughts - I think something odd is going on, I'm going to think on it for a day or two while I finish painting in the engine bay - after all if it is loosing 5a then it's been going on for ages.

 

BTW I don't spend my money on weed - and little on booze these days. And have a plethora of tools including plumbing etc.

Link to comment
Share on other sites

5A is 60W, something will be warm.

Could be a combination of things, CO alarm, gas alarm, cooker ignition, light in a cupboard, radio/stereo, nav light, TV aerial, alternator.

Would doubt its cable leakage, something would have burnt long ago.

Sam.

Link to comment
Share on other sites

That's what I thought - something warm somewhere. But now I just think it is the meter miss reading - or the shunt or problem with how it is wired.

Easiest option is to try a different meter (they all seem to use 75mv shunts?). This one only goes down to 1a so not much use for seeing what the small items use anyway.

That's what I thought - something warm somewhere. But now I just think it is the meter miss reading - or the shunt or problem with how it is wired.

Easiest option is to try a different meter (they all seem to use 75mv shunts?). This one only goes down to 1a so not much use for seeing what the small items use anyway.

Link to comment
Share on other sites

6 minutes ago, Johny London said:

That's what I thought - something warm somewhere. But now I just think it is the meter miss reading - or the shunt or problem with how it is wired.

Easiest option is to try a different meter (they all seem to use 75mv shunts?). This one only goes down to 1a so not much use for seeing what the small items use anyway.

 

That's what I thought - something warm somewhere. But now I just think it is the meter miss reading - or the shunt or problem with how it is wired.

Easiest option is to try a different meter (they all seem to use 75mv shunts?). This one only goes down to 1a so not much use for seeing what the small items use anyway.

 

Have you been taking advice from MtB ?

He didn't believe his so bought two more so as to get 'best of three'.

Link to comment
Share on other sites

8 minutes ago, Col_T said:

What happens if there is a mismatch between shunt and ammeter e.g. a 100 amp shunt connected to a device that can read up to 200 amps? Just a random thought.

The shunt creates a voltage proportional to the current. The  meter measures the voltage. A 100A shunt passing 100A will create the same voltage as a 200A shunt passing 200A. So a  200A meter connected to a 100A shunt passing 100A will show 200A.

Link to comment
Share on other sites

3 minutes ago, nicknorman said:

The shunt creates a voltage proportional to the current. The  meter measures the voltage. A 100A shunt passing 100A will create the same voltage as a 200A shunt passing 200A. So a  200A meter connected to a 100A shunt passing 100A will show 200A.

 

Already explained in Post No 2, but I don't think it went in!

 

 

 

Link to comment
Share on other sites

24 minutes ago, nicknorman said:

The shunt creates a voltage proportional to the current. The  meter measures the voltage. A 100A shunt passing 100A will create the same voltage as a 200A shunt passing 200A. So a  200A meter connected to a 100A shunt passing 100A will show 200A.

But if there is 0A flowing it should still indicate correctly. So the fact that there is a non zero reading suggests some current is flowing, whatever the shunt/meter combination.

Link to comment
Share on other sites

57 minutes ago, Johny London said:

now I just think it is the meter miss reading - or the shunt or problem with how it is wired.

I can’t see how. Meter wires removed or shorted together show 0A. Therefore 0V across the shunt. Meter wires across the shunt show 5A, so there must be a voltage across the shunt. Try measuring it with a multimeter that measures mV. 

Link to comment
Share on other sites

28 minutes ago, nicknorman said:

The shunt creates a voltage proportional to the current. The  meter measures the voltage. A 100A shunt passing 100A will create the same voltage as a 200A shunt passing 200A. So a  200A meter connected to a 100A shunt passing 100A will show 200A.

Okay, so shunts are something else I don't understand!

 

I kind of thought that 75mV shunt would send 75mV per amp to the meter, which then needed to convert the mV number received into amps e.g. 300mV translates to 4 amps (value received divided by 75(mV) = amps). If that is the case, the calculation for a bi-directional shunt might need to 'centre' the reading. For instance, a shunt measure -5 amps to +5 amps would return a voltage of 375mV at 0 amp current flow.

 

is that all total borrox???

Link to comment
Share on other sites

The mV thing was a good idea - I measured across the sense wires when they were unplugged and got 0 or 1mv, then plugged them into the meter and got 0.6mv. In both cases with minimal load (radio and laptop on) so it shows the meter is affecting its own readings.

 

Also some confusion regarding how it is wired as the online instructions in the advert show a different thing to what I have got. I had the -ve supply wire tied to the wrong side of the shunt (the not battery side) but surprisingly didn't seen to make any difference.

 

Then took the thing apart and found a multi turn pot - with the sense wires unplugged/shorted it doesn't affect the reading (always at 000) but with sense wires in I set it so it was just off 000/001 then tried some loads, which didn't show up. And it doesn't see to see the power going in from the solar :(

Waste of time. Thanks all.

 

As far as the mV / shunt thing - surely any meter would just be calibrated to whatever shunt it specified? So all things being equal (ie 75mv shunt) a 100a meter would show 100a when there is volt drop x across the shunt, a 500a meter would show the same 100a for the same x, and 5x for 500a? The thing being to make sure the shunt is meaty enough for the application (and the meter software allows it to display the relevant figures).

Link to comment
Share on other sites

43 minutes ago, Col_T said:

Okay, so shunts are something else I don't understand!

 

I kind of thought that 75mV shunt would send 75mV per amp to the meter, which then needed to convert the mV number received into amps e.g. 300mV translates to 4 amps (value received divided by 75(mV) = amps). If that is the case, the calculation for a bi-directional shunt might need to 'centre' the reading. For instance, a shunt measure -5 amps to +5 amps would return a voltage of 375mV at 0 amp current flow.

 

is that all total borrox???

Yes (it’s bollox!). A 75mV shunt sends 75mV at its maximum rating, 100A, 200A or whatever. If it were 75mV per amp, at 200A it would drop 15v, leaving not a lot for the actual circuit!

  • Happy 1
Link to comment
Share on other sites

On 18/07/2019 at 23:38, Mike the Boilerman said:

DC clamps are SO useful I have at least six. One in each bote, one in the van, one in the house and a spare. 

 

Do they all read the same on a given load or are they like your smartgauges ;)

 

  • Haha 1
Link to comment
Share on other sites

A Shunt is just a very low value resistor and follows Ohms law Volts = Current x Resistance.  As stated a 75mV shunt has 75mV across the terminals at it's rated current (100A in this case) or if a 200 A shunt the 75mV will be at 200 Amps etc.

There are also 50mV shunts used by Victron and Nasa and other western manufacturers the 75mV seems to be a Chinese standard.

 

I have a Chinese ammeter and have a 0.1 amp reading at no load but just ignore it as I know it's not real, but in my case it is electrical noise pick up in the leads to the meter (disconnect leads at meter it reads 0, disconnect leads  at shunt and short them meter still reads 0.1)

 

How long are your meter to shunt leads and are they twin wire or twisted pair wire?

Link to comment
Share on other sites

That's a really good point, 4 to 5 meters I'd say, and they are not very thick either. The way I wired it, the sense wires from the shunt go to the sense wire connections on the meter. The positive comes from its own dedicated fused wire from the batteries. This links to another pin that requires 12v on the meter. The ground supply for the meter I took a loop off the sense wire that is on the battery side, rather than running one separately.

Link to comment
Share on other sites

18 minutes ago, Johny London said:

The ground supply for the meter I took a loop off the sense wire that is on the battery side, rather than running one separately.

That’s your problem right there.

 

You’ll be passing a current down that neg to power the meter, that drops the voltage at the sense input. They give wiring diagrams for a reason. 

34 minutes ago, Detling said:

disconnect leads at meter it reads 0, disconnect leads  at shunt and short them meter still reads 0.1

That’s different to the OP. When the leads are disconnected at the shunt he slows 0. 

Link to comment
Share on other sites

I thought you'd cracked it for a minute there Wotever. I disconnected the -ve supply and the meter just still works as usual. Then I connected the -ve to a ground elsewhere (one of my 12v sockets) and low and behold... I get -49 amps!

There are two +ves, but it did say that the meter can be powered from what it is monitoring "no need different supply." Of course I have mucked around with the trim pot but that just makes things even worse.

 

The thing about the meter reading - to be clear, the last post (the meter reads 0.1) is the dvm I was using to check the voltage drop across the shunt, the op was when I was talking about "the meter" as being the installed ammeter!

Link to comment
Share on other sites

27 minutes ago, Johny London said:

I thought you'd cracked it for a minute there Wotever. I disconnected the -ve supply and the meter just still works as usual. Then I connected the -ve to a ground elsewhere (one of my 12v sockets) and low and behold... I get -49 amps!

Sounds like you’re moving the wrong -ve. You’re moving the sense -ve instead of the meter -ve. 

Link to comment
Share on other sites

It does, but I have actually got the sense wires going into the sense and the supplies for the supply, I think.

It's this meter... https://www.ebay.co.uk/itm/DC-0-200V-0-500A-Volt-Amp-Meter-Battery-Monitor-Charge-Discharge-12V-24V-36V-DS/171213089055?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

The thing is this one has a dot in the display - maybe mine should have and it doesn't work. Also mine has one terminal less...

 

 

DSC_0001.JPG

DSC_0003.JPG

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.