remote ammeter

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tobble

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I'm looking for an ammeter to put on my wind tub, fused at 50A, so an FSD of about the same seems sensible.

the catch is I want a remote shunt. I have found for example this but given there's lots of 'in-line (i.e. no remote shunt) on ebay etc for a few pounds I'm slightly loath to fork out £25+p&p.

Does anyone know where you can get this sort of thing? pre-loved is fine in fact would probably suit the boat better!

alternatively I was wondering how feasible it would be to butcher one of the in line ones and extend the sense wires?

thanks in advance
 
The really cheap ones may be moving iron and not 'butcherable'. Plenty of cheap multimeters you could bodge, but they tend to only go up to 10 or 20 amps.
You could make your own shunt and use a meter with a volt range, obviously you want to minimise the drop to reduce heating of the shunt. As you will be measuring a few mV, you may want to screen or filter the wiring from the shunt to the meter.
What kind of accuracy are you hoping for?
You could consider using the fuse as the shunt, perhaps with an opamp circuit around it, but fuses tend to get more resistive over time.
 
excellent, that look just the ticket, although I might see if I can find a moving coil one to butcher just for fun.

would I be right in thinking you could just set up a potential divider to give about 5V of the main 12V supply? would it be a good idea to pop a voltage regulator in there too? maybe like this: maplins VR

seeing as I'm here and a bit lazy, what sort of value resistor would you use for this scenario? I'b prob put the meter on a 'push to make' switch so long term current draw not a prob (assuming the meter will work ok like that) thanks for replies so far chaps

edit; don't need very high accuracy as am planning on getting a propper battery meter like the nasa BM, or BEP marine one, this is more for interest, so say +/- 1 amp more than good enough
 
Note the LED meter shown has its -ve signal and supply pins common, so the shunt will have to go in the -ve line, if I'm reading that right, unless you power the meter from a floating supply (you could use a battery if you're only going to use it intermittently).
Nice item though, thanks for the link!
 
As has been said the shunt would go in the battery negative lead.

I would use one of the 5 volt maplin regulators as you sugest.

You could wire it up and only have to break the line from the regulator to the +12 volts to switch it off completely and any single push on / push off switch would do for that. (remember to put a fuse in that line.

I fitted a NASA current monitor on a Contessa 32 a few weeks ago. I was quite impressed with it.

I connected it to the domestic battery.

At the same time I fitted a small panel voltmeter across the engine battery.

It is unlikely that you would want to have both the NASA thing and a panel meter on the same battery as the NASA one can measure voltage and current as well as consumed power.

I noticed that the panel meter can be set up to measure both voltage and current.

Iain
 
Do you want an accurate ampmeter or just a relative indication? Do you want real accuracy.
Unless you want a digital meter I would suggest the moving coil type with remote shunt. As suggested unless it is a moving iron type there will be a shunt inside the case and should be removable fairly easily.

If you wish you cna buy a moving coil meter of typically 50 uAmps FSD which will be ideal with a shunt. A piece of stainless steel plate works well as a shunt. Start with 20g metal one inch wide and about 2 inches between the mounting holes for the lugs to the power cable. connect the meter to seperate lugs in seperate holes in the plate but near the power lugs. You will get an indication on the 50uAmp meter which will indicate if you need less resistance (shorten the distancee between holes) or more resitance by making the plate narrower. Obviously you need an accurate meter to check your shunt accuracy. But results can be interpolated upward in a linear manner.
good luck olewill
 
thanks again for responses.

just to clarify, my current (pun intended) intention is to instal the BEP marine meter which can monitor the Ah in and out of the domestic bank, the voltage on the engine starter, plus one other voltage or a bilge pump - i.e. it can only monitor one shunt for current - if I want to look at the current coming out of the wind tub, I'll need another ammeter, as that current is likely to be different to current going into the battery, because of draw from things switched on as well as innefficiencies in the charging system/batery etc...

it is mainly for information, not exact measurements so something relatively crude would do the job. I like the idea of making up my own shunts - I guess I could also use one meter and switch between shunts to measure several different points ni the system; e.g. what's the current in the dump resistors, ah lots of spare power, now's a good time to pump the bilges etc...

cheers again guys
 
I measure ALL the current going into or out of my batteries (three off) on this.
dist1.jpg


It is 50-0-50 microamp meter and has a couple of wee potentiometers to calibrate the "shunt" which physically is unidentifiable. The negative of all batteries is commoned at the battery box. The feed* then goes to the negative for the start circuit (as normal,). All wires to the ships "bits" are fed from the engine common rather than the battery, and the feed*lead becomes the shunt with a thin wire from each end going to the meter,which indicates the millivolts drop across the main feed cable.
dist2.jpg

It is then easy to switch on say 20 amps worth of lights and set the reading to suit. ~~Using imagination,( instead of focus), you can see the components mounted on the back of the meter. Note the lighting-up faultfinding screwdriver permanently available - never been used yet.
Meter is showing seven amps charge in pic 1
 
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