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MG MGB Technical - Ammeter connections
|We have covered this subject sort of, before. But I cannot recall the details. I am adding some extra instruments, one is an ammeter it has come with some ambiguous instructions. Can anyone guide me through the electrical connections please? I am given to understand that it should be placed in series between the battery feed and ignition switch? So that drawn current will show, ans well as a drain in current? Thanks for your help. Mike|
|I found the old thread, thanks Messers, Herb Adler, David Dubois, Stan Best Mike Howlett, and John Bilham and all others I have not mentioned. Your concensus, Ammeter, don't do it! Right, you've convinced me. I will go for a volt meter. ( It was going cheap thought I might try it .) Thanks though, if I am going to try hill climbs I do not want a fire!. Mike|
|You are right - "Don't do it", but FWIW an ammeter is normally connected between the battery and everything else except the starter, i.e. current from alternator as well as to ignition switch and everything else flows through it. If it is in the ignition switch feed it will only show ignition current, it may not even show lighting current.|
|I've been running a Smiths ammeter, in my '67 B, for close to 35 years with no problems whatsoever. Everything depends on using a large enough wire, with properly soldered ends, and carefully routing it so it doesn't chafe against any metal that will cause a short circuit. Many cars, up to the early '70s, came standard with an ammeter. They have received a poor reputation, as of late, due to incorrect installations. RAY|
|When a nice safe fused voltmeter can tell you exactly whats going on with your battery and the charging circuit, why add something that increases the risk of total electrical failure? Any added component will have a failure rate so I still vote for volts, well actually I abstain, with a dynamo equiped car you can tell everything you need to know from how it starts and the behaviour of the charging light.|
|So does an alternator-equipped car (and I abstain also). The voltmeter shows you much clearer than an ammeter that it *is* being charged, without any of the risks of connection failure bringing the car to a halt or shorting. But none of them will tell you if your car is going to start next morning.|
|The positive feature of an ammeter is that it will tell you exactly how much current is being produced by the charging system or mow much current is being drawn from the battery. A voltmeter is incapable of accomplishing this task. I find this to be of great value. It's seems that I am a lone voice, crying out in the wilderness. RAY|
|Its your car and you can instrument it however you like, it's down to you. Getting the car just how you like is a large part of the pleasure of owning an MGB. Some people dont like the non original stuff on my car, but I like it how it is.|
|"it will tell you exactly how much current is being produced by the charging system or mow much current is being drawn from the battery"|
In all normal use the battery should always be being charged. If it isn't there is something wrong, or you have put additional loads on the car that warrant a more powerful alternator. Voltage tells you whether the battery is being charged or not, and how near you are to a charging situation becoming a discharge, if you are loading up the alternator. Why would you want to know *exactly* how many amps is flowing in or out?
|Paul, The amount of current, going to the batteries after startup, can tell you if there is a sizable parasitic drain on the batteries when the car is turned off and sits for a while. I installed my Smiths ammeter when I had charging troubles after getting the car back from the body shop that replaced the sills and painted the car. After a year of hunting, I discovered that the grounding point for most of the car, which is under the windscreen, was loose and causing my problems. The first thing that I do after starting my B is to observe the ammeter readings to see how many amps are coming from the alternator to the batteries. I keep a Battery Tender hooked to the batteries, most of the time, and the reading is almost not enough to move the needle. If I have left the electric fan on, after turning off the engine, I will have a noticeable increase in charging, upon re-starting the engine. The second thing I do after startup is to press down on the brake pedal and watch the gauge. If the needle drops considerably, I know that the brake lights are functioning. RAY|
|A voltmeter measures electrical pressure (EMF) thereby directly measuring the charging system. When you turn the key to the on position the voltmeter will tell you the state of your battery. Go with the voltmeter. |
There is no need to route all of the current to the ammeter if you choose to install one.
Simply install an electrical shunt resistor in series with your battery. The shunt is typically one ohm so it does not waste any current. The ammeter (really a voltmeter) is wired across the shunt.
The big problem with this is if any of the wires to your ammeter short to ground your car will die a fiery death.
Adding a fuse to the wires to the ammeter will only corrupt the ammeter's reading because the fuse will introduce additional resistance.
|I don't need an ammeter to know if my brake lights are working, I simply turn on the indicators :o)|
"Simply install an electrical shunt resistor in series with your battery."
Definitely not. Any shunt for a remote meter ammeter should be installed in the brown wires that come off the solenoid and go to the alternator/dynamo and rest of the cars electrics. If you put a shunt in series with the battery it will be in series with the cranking current and prevent cranking. Even 1/10th of an ohm will drop most of the battery voltage across the shunt and leave virtually nothing for the starter - until it burns out that is.
You *can* install fuses between the shunt and a remote meter ammeter (in both wires, right at the shunt), precisely because the meter is measuring the voltage dropped across the shunt, i.e. the current is microscopic.
|Paul is absolutely correct about where to put the shunt resistor. I was thinking alternator B+ but said battery.|
This thread was discussed between 11/09/2011 and 20/09/2011
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