Ampmeter reading

[Davey-T]

So got this amp/volt meter of EBay, no instuctions so wired into my power pack, the volt reading is OK but the amps is weird, don't know if the decimal point is in the wrong place or it's just [removed word]

The reading in the pics is with nothing connected and one 300mm dew heater connected. It has adjusters for volt and amp but don't know if they're for setup or just for original factory setting.

Any thoughts ?

Dave

 

[knobby]

How is it connected? To measure amps it needs to be in series

[Davey-T]

 Connected in series on the neutral return to the battery, as I said it came with no instructions and I found a few contradictory wiring diagrams on the net.

Dave

[Kropster]

Maybe the adjusters are to set the zero readings?

Amps should be zero with no load!

[pete_l]

Hopefully that reading is Milli-Amps.

[Psychobilly]

Ebay Link Davey?

[Davey-T]

This is it

Dave

http://www.ebay.co.uk/itm/Mini-Dual-Display-Combo-Meter-Red-LED-DC-0100V-050A-/251337672307

[Gina]

Ah yes, I have a couple of those.  I used one in my pier power distribution box (now replaced by another in the warm room).  There was something funny with the amps reading - decimal point wrong I think.  Yes, you have to use the negative as common ie. put the ammeter in the negative wire.  I was intending to use these in my later distribution box but with the ammeter in the negative means that with 12v and 5v with common earth/ground/negative the amps would be the sum of both 12v and 5v loads - not very useful   If you could have the ammeter in the positive rail they would be very useful.

[Davey-T]

Mucked about with this some more, when I connect two dew heaters maxed out it reads 99.9 , as the ful scale is supposed to be 100amps  I'm not sure what this means, perhaps its marked up wrongly as they all appear to be identical except for the red mark on the label so  could it  be a 10 amp one marked up wrongly ?

Dave

 

[Gina]

Mine are 10A ones I believe.  Seems yours is too.  I reckon that should be 9.99 ie. over 10A.  Also seems to be a lot of current for dew heaters.

[faulksy]

i bought a similar seperate volt one but i had to calibrate mine to be sure, had it 12 months and its spot on

[Davey-T]

So just joined both dew heaters to multimeter,  turned up to max continuous current draw and it reads 1.6 amps, so why when I  connect to the amp/volt meter does it read 99.9 ? presumably the maximum reading it's capable of as though supposed to be 100amp I don't think it can actually display this.

Dave

[Davey-T]

When I connect one dew heater it reads the same as the multimeter except the decimal point is in the wrong place as pic, 73.9 should be .739 amps, so when I connect two the reading goes up to 99.9 so won't measure

more than dew heater . So it appears to only measure 1 amp not 100

And I thought this would only take a few minutes to fit

Dave

[AstroJOE]

This post is really interesttong to me as I havr experienced a similar issue with mine. I have a similar version although not identical. For example my laptop pulls up to 3.9A but my Ampmeter reads anything up to 0.39A. Dew tapes up to may be 1.5A but Ampmeter shows 0.15A. So the decimal is always in the wrong place. I'm no good with electrics to be honest (Im amazes I was able to build myself a 110Ah power pack in the first place). So up until now I've just left it and accepted that whatever it shows is simply a 1/10th of what it should actually read. Any tips on how to sort it would be welcomed however!

[Horwig]

When I connect one dew heater it reads the same as the multimeter except the decimal point is in the wrong place as pic, 73.9 should be .739 amps, 

Dave

Sounds to me as if there's a shunt resistor missing. 

Huw

[Davey-T]

Sounds to me as if there's a shunt resistor missing. 

Huw

According to the suppliers it only needs a shunt to measure over 10amps, at the moment it won't measure over one amp, or do they mean if you want to use as 100amp you need a shunt regardless of what you're measuring, if so why don't they supply one?

Dave

[Horwig]

As with a lot of kit, what they say, and what they sell are not often related...

Huw

[Davey-T]

Done more research on the net and it appears that the shunt is needed to alter the reading as all the meters seem to be identical, so if you want it to read 0-10amps you need 10amp shunt likewise if you want it to read 0-50 amps you need a 50amp shunt

this is supposed to have a built in 10amp shunt but appears not to have so reads 0-1 amp.

Shame the shunts only seem to be available at a reasonable price from China.

Dave 

[Horwig]

That figures Dave, have you used your dvm to measure the ammeter's impedance? should be easy enough then to work out what shunt you need, and make your own from resistance wire.

Huw

[Davey-T]

Thanks Huw, don't know if I want to spend much more time on this "five minute job" I may just order 100amp shunt and hope it covers all eventualities , trouble is I don't think I'll get a decimal point at all then.

All I really wanted to do was get an Idea of the battery load with dew heaters, mount, laptop and camera plugged in to estimate how long I could image, I had hoped that 10amps would cover it, still another lesson learned, I should know all about these meters

by the time I've finished

Dave

[Merlin66]

I bought a Turnigy Power meter - measures Watts, Amps, Voltage very reliably.....

[Kropster]

How about putting a cheap digital multimeter inline.... they usually manage 10 or 20 Amps.

[Davey-T]

How about putting a cheap digital multimeter inline.... they usually manage 10 or 20 Amps.

Thought this would be good as it had volts and amps in one unit, now waiting delivery of 20amp shunt from Hong Kong so not holding my breath

Dave