One 50Mv 500A shunt, two ammeters?

I'm planning to push a 75mv 50-amp shunt to 65+amps. I'll blow in its ear with an 80 mm muffin fan. The twisted pair get SOLDERED on. If I connected them backwards I'll just flip the BORG upside down. Can't have it discharging the battery can we? I'm going to let an electronics shop solder in the 10-turn pots. Hands are getting useless. Glad I don't make nitroglycerin for a living.

I'll try a 75Mv digital Ammeter for under 6$.

Slow boat from HongKong, so, I'll update well into the future as to how it works.

MrWizard wrote:
That's not the problem
75mv shunt and meter are common
The current meter and shunt are 50mv, and he can't find another 50mv meter to put on the circuit

There is no difference between a 75 mV 750A meter and a 50mv 500A meter and shunt when you're measuring less than 500A current. You have a meter that reads 10A when it sees a 1 mV input voltage, and a 0.0001 ohm shunt. If the 75 mV standard ones are easier to find, there's no reason not to buy one and use it with the 50 mV shunt.

(There would be a difference in the maximum power rating of the two associated shunts: the 500A 50mV shunt dissipates 25W maximum, while the 750A 75mV shunt needs to dissipate a little over 55W at its full rated current.)

That's not the problem
75mv shunt and meter are common
The current meter and shunt are 50mv, and he can't find another 50mv meter to put on the circuit

dclark1946 wrote:
Use the 75 mV meter and make you a little chart that multiplies the meter reading by the scale factor. If you want to get more sophisticated you could have a simple op amp scaling circuit between the shunt and the new meter. If the input impedance of the meter is specified you should get an idea if the additional loading is impacting your 50mV meter. I would be very surprised if there was any effect at all.

****

Or simpler yet, find a 75mV 750A meter (or a 75mV 75A meter and mentally shift the decimal point).

Yep, I went through many 50/120 chrysler reman'd alternators over the years. Especially before I got solar.

It was after that I took an old set of 4awg jumper cables doubled them up in one ring terminal on both ends, and ran it right from alternator(+) to my Battery switch Common, and really let those alternator amps fly.

Grounds were upgraded too.

Frankly, I was surprised it lasted as long as it did.

I've not stressed the 'new' one yet, nor seen what it can do and compare it to old. My MeanWell has been floating my AGM when the Solar is not.

Wanna see action?

Use an AC voltmeter connected between the alternator output stud and chassis negative? Despite the poor little capacitor working it's donkey off an alternator cap whether it's .47 uf or 2.2uf does not stand a chance against shorted-stator-windings or failed rectifier Ripple Champipple. AC ripple levels will rise.

You forgot to mention your 7-year old alternator has been around the block several times before the case was roto-braded, brushes replaced and bearings re-greased. Thing originated when Ronald Reagan was in office. Even though my toad is a '95 the Bosch build date was 1793 seventeenth week of 1993. Those alternators have been around since 1986.

Thanks for the workaround ideas.

My desire to see alternator current into the battery(s) from the driver's seat is not so high that I would really expend that much effort.

Running a new set of twisted pair to the display from my existing shunt would be as far as I would go and 25$ maximum.

My last alternator recently failed, and I maxed it out often and regularly for nearly 7 years before it failed. While it was failing it was the voltage it was able to hold, along with the noise it was making, that led me to want to see the amperage from drivers seat, as its output became more and more stunted, and was not able even bring the fully charged battery above 13.2v at higher rpms at the end, and at idle I could watch voltage drop to 12.6v.

An analog meter, that would display both (-) and (+) amperage flow would be OK, but my dashboard would not accommodate it nicely, and 70$ is more than I am willing to pay for the privilege of the convenience of not looking over my shoulder and seeing what my battery monitor reads.

My Alternator was also a lifetime warranty unit, and Oreilly's honored Kragen's warranty and just gave me another reman at no cost, and it took less than 15 minutes to swap out. This latest reman was a Wilson, reman'd in Mexico, and I did not see the traditional 'charge battery first before starting engine' that previous reman'd units came with which were 'Autolite' labelled.

I did one time have a previous Reman quit working when it only had 200 miles on it and was asked to charge 3 group 27 batteries depleted to inverter alarm level. After fully charging the batteries via the grid and another 20 miles of driving, the alternator magically kicked back in.

I was south of the border and was going to attempt to make it north on battery power alone, when it started functioning again. Not sure why it kicked back in, or what caused it to give out in the first place, other than the load of 3 super depleted batteries.

I would like an alternator more capable at my 525 rpm hot idle speed. I did employ a slightly smaller pulley on my last unit but it could not be employed safely on the latest reman.

Use the 75 mV meter and make you a little chart that multiplies the meter reading by the scale factor. If you want to get more sophisticated you could have a simple op amp scaling circuit between the shunt and the new meter. If the input impedance of the meter is specified you should get an idea if the additional loading is impacting your 50mV meter. I would be very surprised if there was any effect at all.

Dick

500A, 50mV shunt will have a resistance of .0001 Ohms. If you put a 1 Ohm resistor across that shunt the voltage would only change by .01%.

Putting 2 meters across it will not change the current reading enough to see on any meter.