One 50Mv 500A shunt, two ammeters?

Nyet on a switch unless it has snap action and silver contacts. Small millivolt amounts voltage drop cause huge errors. May work OK with brand-new switch for awhile.

"Recharge battery before starting engine or warranty will be void."

TRANSLATION

This alternator was salvaged from junk parts and is designed to survive only when battery is almost fully charged.Pay NO ATTENTION AT ALL to the tens of thousands of recreational vehicles whose alternators must endure full loading of the alternator year-after-year.

Now, if your head is set in six-sack cement about this go to a Ford, or GM or Mopar new car dealer and ask to see a rebuilt alternator. Do you see that little fluorescent green or orange sticker? Of course not. Of course a person could wear a vest and carry a sign RV OWNERS DO NOT START YOUR ENGINE!

Remember my little ditty about rush hour in Phoenix in July? Got news for you. All those alternators are surviving 120F air temperatures, powering 100+ amperes and do you see thousands of failures sitting on the shoulder waiting AAA? Of course not.

"Recharge battery before starting engine or warranty will be void." is the hallmark of a junker alternator. Utter total garbage that I avoid like an EBOLA outbreak.

After seeing 10,000+ alternators disassembled and then rebuilding them with my own hands and then finding my 1-year outright warranty had less than a one-tenth of one percent comeback rate (Each customer was told if the alternator EVER failed to bring it back for an extremely liberal repair consideration. And the area was the Antelope Valley of California where summer temperatures frequently hit 110F. My customers sometimes asked "Is it necessary to recharge the batteries before I start the engine" I replied, "No I WANT you to start the engine and HAMMER that alternator, then when you're talking about alternators with friends remember that". The distributor told me dozens if not a hundred new customers mentioned this policy to him when buying a rebuilt alternator.

Today, with everything being drenched in soy sauce I do not know if heavy rated button or dish rectifiers are available. But like on Quicksilver if I were worried about rectifier loading I would employ a remote rectifier. I just purchased a 300-ampere full wave bridge rectifier in case I decide on a remote rectifier for the toad. I also purchased a new Nippondenso meaning brand new 50/120 alternator to upgrade the 40/90.

"Recharge battery before starting engine or warranty will be void."
Thank You! You put a smile on my face!

Ivylog wrote:
I'd put a on/off/on toggle switch at the current location so only one is in the system. You could switch back and forth to check accuracy of the new one...
Or for $10.33 you can buy a shunt and digital V/A meter like what I installed when I put in a home refer here.

It would be fairly easy to mount a new shunt just for the alternator output, if you can use this on a +15 volt output of the alternator. Some electric meters will rely on a grounded shunt, not able to put it inline with the 12 volt output line on the alternator.

Just a thought?

Fred.

So if you hook up the 75 mV meter, it will be in-accurate, but in a easy to calculate way. In other words, if you are getting 50 amps into the battery by the E-meter from the alternator, and the dash display says 37.5 amps, you will know that reality is 50 amps, and you are doing fine.

Your shunt is providing a 50 mV differance at 500 amps, or 0.050 volts per 500 amps, or 0.01 volts at 10 amps.

The 75 mV shunt will provide that voltage drop at it's rated amperage.

Anyway I find it is not important to know how many amps are coming out of the engine alternator. I really only use the solar system to recharge my batteries most of the time. The engine alternator 'should' not be used as a high amperage device, as that will shorten it's life. On the box of any replacement alternator, it clearly states "Recharge battery before starting engine or warranty will be void." The manufacture has seen that new alternators are destroyed by trying to charge a dead battery to many times. This can overheat the windings, diodes, and other stuff inside the alternator case, as well as put stress on the front bearing, belt, and other belt drive pulleys on the engine.

What I have is a 400 watt solar system.

I also have a e-meter (much like the Tri-Metric) with a 500 amp 50 mV shunt. It was installed in 1999, before the Tri-Metric was released. . .

My RV used 35 AH daily to run the CO detector, propane leak detector, and refrigerator. Anything else was optional power, and I could use as much as 120 AH daily total, then make it up with the solar system alone in one day. If I wanted a full charge, I could run the generator a little bit in the morning, and then have it full by night.

If you decide to go solar, check prices at several vendors, including this one. SunElec.com

I made my own mounts from 6" long 2" angle aluminum. Would recommend several 20 amp PWM controllers (at $20 each) rather than a really expensive MPPT controller. You can save the $200 on the controller price and buy another 140 watt solar panel, saving money and actually collecting more solar power than the MPPT controller could provide. The 20% 'Claimed boost' is really not there. You can increase the amperage on a 12 volt panel while using a PWM controller if the battery is lower voltage.

Have fun camping!

Fred.

Nothing like coming back on board the magical mystery tech train after taking a 25-year vacation. The analog meter I am familiar with the digital is new stuff to sort out. Couldn't imagine how 75mv max could be affected by micro amounts of impedence bit there's several ICs in the meter. The 4.75 digit voltmeter has it's own reference CPU. Supposed to have +-2% accuracy least significant digit and something seldom mentioned here: A 5Hz sampling rate. I have one 3.5 digit voltmeter whose sampling rate circuit seems to have been lifted from an egg poacher.

Chris Bryant wrote:
Remember, these meters are just (milli)volt meters. They certainly should have a high enough impedance that 2 won't make a difference- they should put no load on the shunt. If I can measure a current draw using a fuse as a shunt, it should be easy.

Agreed, plus the shunt is a pretty darn low impedance source.

I cannot find a 50Mv digital Ammeter rated for 100 amps.

I will not be plumbing another shunt inline just for a dashboard mounted Ammeter.

I wonder if there are any mountable inexpensive hall effect sensor Ammeters that can handle 100 Amps.

I've seen it done with a Magnum BMK and a BlueSky solar controller in a friends coach. He says it works fine.. The impedance of those meters have to be high to keep from loading the shunt.

I have worked a lot with shunts and meters building load boxes when I was a tech in a switching power supply lab.

I am going to speculate that it will work fine and easy to try.

If the shunt runs at near max rating you might consider a fan as higher temps will affect accuracy but not much.

BTW You can remove material from the shunt to tune it to whatever drop you need.

Lots of discussion here on how many MILLIVOLT METERS you can connect to one SHUNT...

HERE

That would be an easy way out for you if you could live with a very small inaccuracy with the two millivolt meters...

Play with two meter movements on the work bench with one shunt and see what you think about inaccuracy. I'm thinking it will be very small difference.

Roy Ken

Analog needle for looking at 3" meter from a 15' distance without searching for my glasses. When needle is really tilted to the left it means the 3-1/2 digit LED ammeter should be consulted to switch to 13.4 volt float when amperage is less than point nine. Yes there are meters with inch and a half characters. Yes they cost more than 200 dollars. Yes I am using a 6-hour wind-up timer. And no this is not a converter. It is a battery charger with adjustable setpoints. The Borg, at last is being assembled. So one shunt and two meters is going to be attempted. If accuracy takes a dump in goes the second shunt.