Voltage cutout for analogue meter.

[Bobbywolf]

Basically, I am installing an analogue ammeter in my jeep, and want to measure the charging current, and discharge current.  The meter I have is a 150-0-150amp meter (center zero), and uses a shunt to develope +/-50mV at full scale.  In other words, when the battery is being charged at 150amps, the voltage to the meter would be 50mV, and the reverse for negative.

My issue is this.  I have a winch installed on my jeep, and under full load, it can draw well beyond 150amps.  I wish to have a circuit which will intercept the voltage from the shunt, and IF it is within +/- 50mV, allow it to reach the meter.  If it is beyond this range, I want a LED to illuminate to indicate the 'beyond-range' condition, and protect the meter by not allowing the voltage to reach it, or idealy, allow only 50mV to show the full scale, AND light the LED.

I am an electronics technologist, but am many years out of practice.  Even just a few ideas to get the ball rolling would be great, and I can take it from there.  Any input at all would be greatly appreciated.

Rob D

 

[Staigen1]

Hi Bobbywolf, welcome to this forum, nice to have you here! ;D

No no, this is not the way you should do it, the shunt is still connected, and can get damaged! Instead you should connect your currentfeeding wires for your winch to the battery directly. You wont get a correct reading on your meter when you use your winch, but do you need to have that? It is the same with your starter too! It will be correct in all other instances.

//Staigen

 

[Bobbywolf]

I had just assumed that the shunt would be able to handle the excess current, and simply give higher than 50mV readings, and it was the meter I had to worry about.  I suppose I could do it that way, but the winch draw, and then the subsiquent charging of the battery afterwards (with my upgraded 120A alternator) is really what I was wanting to see.  I am really going for the "gee-whiz" factor, and would like to have everything connected.

Also, thank you for the warm welcome!  ;D

 

[Staigen1]

Hi

Then you should get an adequate ammeter, or at least shunt.
It is usally the shunt that will broke.


//Staigen

 

[ante1]

Many shunts have a 5 times the measuring current load limit, however only for a few minutes!

 

[Bobbywolf]

Ok, I got this idea from another electronics forum.  I could actually have some sort of switch that is wired to my winch to automatically change the scale. What I have in mind is, when I am not using my winch or starter (the only things that will draw more than the 150A max rating), I'll stick with the default shunt setup. However, when power is applied to either the starter, or the winch, a solidstate switch, or possibly relay will switch in a resistor that will halve the meter sensitivity making its FS reading 300A (The website for my winch lists the max current draw of 320A at full load. And typical starters draw around 300A at most)

If I feel adventurous I could even paint on a second scale on the meter itself, but more likely, I'd put a little note, stating "x2 Start/Winch"

This could be doable 

 

[ante1]

Yes, that will probably work well. Are you running the winch with contactors (relays) or is it run through a controller (adjustable rpm)?

 

[Bobbywolf]

The winch has very simple controls.  You press a button which contracts a solenoid in the winch to draw off of the battery directly.  It spools in, and spools out under power.  There is no variability, it is either on or off.  I'm getting excited now.  I'll be sure to post my progress when I do go ahead with this, along with pics.

 

[ante1]

Good Luck.

Yeah, pictures would be nice!  ;D