Been busy updating and repairing the coach electrical system. Replaced the old converter/charger with a new 35 Amp converter/ 4 stage battery charger. Installed a 12 Volt outlet for a new Magestic 12 volt color TV and power booster antenna. Did a complete rework of a very scary 12 volt outlet that could have burned the entire thing down. I am not an electrical engineer but I have done my fair share of adding circuit branches and electronic widgetry over the years. I am in the process of installing a 6-18 Volt Meter and a 30-0-30 Amp Meter with an INTERNAL SHUNT. Both meters are an analog made by VDO @ a medium price range that typically are used on the front driving dash. I thought I could use them in the coach. I want to monitor the battery voltage as it discharges/charges and measure the current going in and out as we use the appliances. We have one 12 volt 100 ohM battery. Maybe in the future we'll add another. Plain Jane - nothing fancy! Both meters are set up on a temporary test board. The Volt Meter and the lights to the meters are wire with a fused 10 AWG wire to the distribution board. They work beautifully. Here's my dilemma - no matter how I wire the Amp Meter in line to the positive or negative side of the battery it still reads zero when there is load put on it. I have tested all the wires in the circuit with my multimeter = good. What the devil! It's driving me crazy. My question is did I GOOF UP trying to install an internal shunt Amp Meter. Are the built in shunts not rated @ small/ fine enough increments to read the current resistance in the application I am trying to use it in. Should I have purchased a Blue Sea analog meter 50-0-50 external shunt rated @ 1 Milliamperes @ full scale or can I add a 30 Amp, 60 mV external shunt to the amp meter I am trying use?  VDO makes a really nice 30-0-30 external shunt gauge approx $200. Yikes it is a little bit more than what I want to spend to have a matching gauge. Am I on the right track or do I have to rethink this monitoring circuit? I am going to take an aspirin - now I really have a headach. Pamela

Views: 1406

Reply to This

Replies to This Discussion

Ok..i'll bite. Your using this between the rv coach battery and its loads? If its plugged in then the converter will handle the loads and it will not register, only when power travels to and fro from the battery. Un plug the coach and try all the lights and the water pump. Your going to have to put quite a load ( in comparison to a automobile system) to see it at the meter. Ammeters are old school. If it reads negative while driving, your alternator is not keeping up with the load. If its positive then your battery is drawing current all the time and its prolly got a bad cell. Now the volt meter has pretty much taken its place. If its over 12.8 volts, its charging. If the key is on, one can read the voltage at the battery. If it starts reading below the 12.8 before cranking or below 9.6 while cranking, then the battery is suspect.
Thanks David. Just got back inside from finishing outdoor chores & some final testing. Last night my better half asked a legitimate question " have you tested the meter itself, maybe it's defective"?
I am going to have to call Santa's workshop. His quality team is sleeping on the job. The meter itself IS defective.
I did some basic testing of the meter. Put a small AAA battery then stepped up to a AA battery on the positive end ("B" terminal)on the meter then a wire to the negative ("L" terminal) and quickly touched the negative side of the battery. I wanted to gently peg the the meter to see if there was any deflection on the indicator needle. NOTHING. Mmm next test. Put "B" lead on the positive side of the 12 volt house battery nothing else attached, the converter unplugged and "L" to the positive side of the distribution board. Turned on the stove exhaust fan and the H2O pump, I think those items would be an adequate load approx 8 to 10 amp draw if not more. They both ran just fine. Disconnected one wire from the circuit and they stopped working. There is current going through the meter but the meddle is not indicating that.
Seems to be a faulty deflection mechanism in the needle.
Poop. I am disappointed. So I have make a decision which meter do I want to try next.
I did get a chuckle on your remark "this so olde school"! I agree it is. I am trying to keep true to the vintage look by adding some bells and whistles with some modern sensibilities. Analog works just fine. Digital is more percise but do ya really need it. It is a plain Jane set up. How fancy is fancy.
Your probably right. I found a load for a shurflo pump at 4.2 @ open flow no pressure. Shutting that faucet off to cause the pump build pressure to shut off should spike amp draw pretty good. The pump with no water may not draw much. Those automotive ammeters deal with quite a bit of amperage compared with typical rv loads. Are we onthe dash? How about water temp or oil pressure? Engine vacuum might help with fuel

Dave- thanks for feedback. I hope to clear up some confusion. All of our gauges in the cab dashboard work just awesome; as old as they are. The gauges we are adding in the coach will go on the wall over the thermostat by the refrigerator. These will monitor the state of the HOUSE battery not the starter battery.  I included the schematic below. Option 1 or 2 will work just fine for our application.

Pretty cool! I placed an order for the amp meter with the external shunt from Blue Sea. It should be here by next weekend. I will post on the final results. Pamela

s the VDO install, the alternator is paired with the load, indicating amperage flow in and out of the battery, a classic ammeter install. in the blue sea install, the alternator and battery are paired, indicating the amperage flow between the load and the battery/alternator combo. the latter is probably the best for what I assume your trying to do. ( i.e. measure power to loads and power back to the battery from solar or wind.). I wish Mr."T" would weigh in on this and tell me if i'm seeing this right and expound on the benefits/deficits of either install...
Now your following my thoughts Dave! Your right I was also hoping for John T comments. He has an abundance of knowledge on this kind of stuff. Adding some monitoring gauges to build towards a better, safer dry camping experiences for the fair weather to come. I can't help myself. I am a perpetual puter. This renovation project is a labor of love and an excersize in patience. Pamela

  Sorry, I just don't know the problem that ammeter/shunt has... The only thing I can think of is if there are different size (ohms) shunts that correspond with different range values of the ammeter. The analog ammeter I installed was a straight in/out 30 amp with no external shunt so I have no idea about your problem other then the needle should surely deflect. An "ideal" ammeter would have ZERO resistance and an external shunt resistor in parallel serves as a current divider so x% flows in the shunt while the other flows in the meter itself so it doesn't have to pass high current like a full 30 amps. I would be interested in the ohms value of the shunt itself and then the meter itself if its possible to disconnect/isolate the two. The fact remains however that the ammeter and/or ammeter plus parallel shunt should be of extreme LOW resistance. Conversely, an "ideal" voltmeter would have INFINITE resistance.

 I placed my analog in/out 30 amp direct ammeter in series between the solar charge controller and house battery bank so I can directly observe the solar charging. If I had another one and didn't have solar, then it would wire in series between the Converter/Charger output and battery bank to monitor what amp charge the batteries were receiving via the Converter/Charger. I also have a digital voltmeter on the house battery bank as their voltage provides information of their state of charge. Another ammeter could wire between the house battery bank and the loads, but that's not as important to me since my input charging ammeter along with the voltmeter tells me all I need to know.

 If you talk to the Vendor ask about shunt sizes and proper matching them with a particular ammeter movement??? Again, there's a current divider between the shunt and meter itself.

 I just cant say what your meter problem is....

 John T  Leaving for Florida TODAY

There you go...if the charge back from the alternator went to the converter side of the shunt then you could shunt between the converter and the batteries. Just put the load on the battery side. Otherwise the #1 install will give you charge minus load or "residual charge?". It will also show rate of discharge but on a 50 amp scale, I dont know how beneficial that would be.
Thanks both John and Dave. John you have done exactly what I an trying to do minus the solar panels at this point. Installing monitoring gauges at stratigic points doing the prep work when it's cold. Hopefully we will install a small array in the spring. The meter itself is defective. No deflection. Broken. I have spoken to the vendor and he seemed to be in agreement. It is on its way back to Santa's workshop. I should have a new one by the weekend to play with. It's snowing like crazy and bitter cold for the next couple of days. I'll post later

I thought I would chime in on this for what it's worth. from looking at the wiring diagram and please I'm old school but I can't see a reason the amp meter would work at all because there is no potential difference for current to flow.

here we go....John's gone and we got an electrical question. So, I'll try not to butcher this too badly. If we were measuring a change in voltage potential we would use a voltmeter. Think of a garden hose as the conduit. Potential is the pressure and amperage is the actual volumn of water.
That is an excellent way to describe it! The current flow is bidirectional (both ways). It is important to have the correct gauge and wire size for the application intended to use it in. I am still waiting for new gauge to arrive for final test. Great job Dave. P




  •         How To Links 

-Search Good Old RV's

-Start a New Group 

-Roof Repair Photos & Products

-Repair an RV Roof

-Pick Roof Sealer   

-Understanding RV Electrical Systems 

-Get RV Insurance   

-What to Look For When Buying a Used RV

-Jack Installs Fuel Injection in his Dodge 



 Artist Roads                                              



If you love classic and vintage RVs then come Join us. Come on in and have some fun. JOIN HERE NOW


Replacing controller ,? And inverter 1 Reply

Started by Dave King in Vintage & Classic RV Restoration & Purchase. Last reply by Rick Cornell Apr 27, 2023.

Sway Bar Links 2 Replies

Started by Grey Wolf in RV Repair & Maintence. Last reply by Grey Wolf Apr 22, 2023.

Help with photo album 2 Replies

Started by Pat Griffith in General Discussion Forum. Last reply by Jimco_W001 Nov 8, 2022.



  • Add Videos
  • View All


If you love classic and vintage RVs then come Join us.

 Come on in and have some fun.      

 Dedicated to a simpler, more rewarding and fun way of life in a Good Old RV... 

Vintage Travel Trailers, Vintage Campers, Camper Restoration, Bus Conversions, Vintage RV Forums, Old RVs, Tiny Homes, Boondocking

A work of art by member Paige Bridges


 Disclaimer - Please Read it

Enjoy this site and use it totally at your own risk.

By using or viewing this site YOU agree to Hold Harmless anyone associated with it including other members. Also, YOU agree that YOU are solely responsible for ANY and ALL actions, results or damages. Members "opinions" are just that and any repair or alteration comments or recommendations are by folks who are not licensed repair  or mechanical professionals. Any repairs or modifications you do totally at YOUR OWN RISK. Use licensed professionals for all work to avoid possible serious injury or damage. Use  banks for purchases.  Have fun!

Copywrite & Trade Mark Registered GoodOldRV© ,GoodOldRVs©,©,©,GoodOldRV.Com©

© 2024   Created by Jimco_W001.   Powered by

Badges  |  Report an Issue  |  Terms of Service