Ammeter Intallation

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Does anyone know if there is a simple way to fit an ammeter to a marine alternator/diesel engined electrical system.I have 2 batteries with 1-2-both isolator.Also thinking of fitting an alternator regulator.
My simple mind says fit ammeter between pos wire & battery,but worried in case unit fails and isolates alternator from battery.Also at present alternator goes to heavy lead on starter,with domestic supply frcm battery terminal.Presumably it is not wise to have starter current running through the ammeter!
Am I right to take alt output to battery and combine with domestic supply through the ammeter ?.Still however the isolation problem if ammeter fails etc.
 
Normally one side of the ammeter connects to the isolater output, and the other side "feeds" the boat electrics.
In this way you can see drain and charge.

DONT put the large starter cable through the ammeter it cant take it.

Below is basic diagram for connecting an engine using trailor light wire, cheap and tidy.

Basic.jpg


The wire not connected to the right side of the diagram feeds the boat.
Hope it helps
 
Ammeters are in fact usually implemented as a milli-volt meter wired in parallel to a shunt - so even if the meter fails it won't disconnect the battery from the alternator
 
The Blue Sea ammeter is pretty easy to fit.

It uses a shunt. Basically you collect all the negatives from everything you want to measure eg: main switch panel, alternator, battery charger, solar panel etc etc. The other end goes to your main negative point, usually on the engine block.

A couple more wires and the job is done.

I may have missed a stage or two, but I fitted it 3 years ago, on another boat!

It is a first class piece of equipment. I['ll be fitting to the new boat, once I understand her strange Danish flavour electrics.
 
The remote shunt for an ampmeter should be very reliable. Usually in the form of a piece of metal of higher resistance than copper with holes bolts and terminals at each end. Stainless steel is ideal.
I have made one from 20gauge SS that is 1.5 inches between bolt holes and wasted down to 1/4 inch wide./ This suits 20 amps for 200mv digital. The only problem being the highish volt drop at 20 amps (.2volt). So don't worry about the shunt failing. olewill
 
[ QUOTE ]
Does anyone know if there is a simple way to fit an ammeter

[/ QUOTE ] . If as you say at present the alternator output goes to the positive terminal on the solenoid (and then via the heavy starter lead to the battery) while the load (probably with the exception of the engine electrics like tacho, warning lights, other engine intrumentation and engine control panel illumination) is taken direct from the battery you are correct. (Presumably then the battery isolation switch is in the negative lead while the battery positves are commoned.)

You will have to disconnect the lead between the alternator and the solenoid competely, and also disconnect the cables that carry the domestic load from the battery, and then run a new cable the same size or a little heavier from the alternator and join that up with the cables that carry the domestic load. Then connect this new junction to the battery via the ammeter*.
The starter current must not flow through the ammeter, to call it unwise is a big undersatement.

*If your battery switch is in the positive the read battery switch in place of battery.

The sugestion of putting the ammeter in the negative side is an interesting one but unless your alternator has an insulated negative it is not possible as far as I can see.

If you want to mount the ammeter on a panel away from the battery then it is almost essential IMHO that you use one with a separate shunt. If you do that then fuse both leads going to the meter with small value fuses located as close to the shunt as possible. If you site a meter with an integral shunt remotely then still include fuses but rated to carry the maximum load or alternator ouput and wire it all the way with even heavier cable.

Halcyon's suggestion to use a system that senses the magnetic field is an elegant solution but you will still have to rewire the alternator output and domestic load connection but then connect the new juction to the battery with a wire around which the field can be sensed. I have not checked but I guess it will be significantly more expensive.

I'm afraid macnorton's diagram would not help me at all! Sorry

I bet you get the ammeter reading the wrong way! I fitted a replacement one for a friend ages ago and got it the wrong way round. I never did get round to correcting it and now that we are used to it he won't let me alter it.
 
VicS, you do not have to change anything, the sensor head would normally fit on the battery terminal, thus reading what goes into or out of the battery. Including starter, inverter loads etc, as it carries no current, it has infinate overload capability.

Brian
 
Sorry I should have read your link properly. An excellent solution especially as it requires no wiring changes. Would you care to tell us what a typical installation would cost
 
Alternative solution...

You asked about an ammeter, and it's useful to be able to see how much current is flowing. However, it's much more useful to be able to measure the amp-hours in and out of the domestic battery. For this, you need a battery monitor. The cheapest is the Nasa BM1, available for £89 inc UK delivery. As well as measuring the current, the BM1 gives you readouts of battery voltage, amp-hours, time to charge/discharge, and a useful battery "fuel gauge" display. It comes complete with a 100 amp shunt, which should be adequate for your needs, and has full fitting instructions. Shunts are very robust and reliable, so you needn't worry about failure. Lots of forum members have now fitted the BM1 monitor and are very happy with it.
 
Re: Alternative solution...

On a simple 2 battery boat system you need to decide which current you want to measure. Your choices being alternaor output or engine battery or domestic battery current. This will normally require 3 shuntsa permanently connected and a switch to selct whicyhb one you want to measure.
If you are limited or don't want complexity then measure alternator current. You can then deduce that if there is no significant load on at the timme that the alternator output is going into the batteries.
You can ssume that most is going into the most discharged (domestic ) battery. What will be interesting is to notice how the charging current falls after a while which may indicate that if you are running the enginne to charge the batteries that you are not getting much in for all the noise and fuel. A smart charger will improve this situation.

if you are prepared to fiddle and to calirate your amp meter yourself by using a multimeter with high current range then you can make your own shunt.
In fact the simplest shunt is to use the wire of the alternator as the shunt. There will be a finite volt drop between the alternator out terminal and where the alternator connects to the starter wire or to the battery switch. Just connect a wire to each end of the main wire and measure the volt drop just a few millivolts. This may be enough to drive a sensitive moving coil analogue meter. Don't have things like switch contacts in the circuit because the volt drop will be variable and unreliable. if the volt drop is not enough a small amplifier can be built to make it a usefull voltage for digital or less sensitive meters. You can use your multimeter tempoorarily in circuit to measure actual current and interpolate from there to calibrate your permanent amp meter. (very linear).

If there is not enough resistance in the existing wire then make a shunt out of stainless steel mount it on insualted block with good connections to the power wire and use fuses. PM me for more detail if anyone is interested. olewill
 
Hi,
Sorry but a belated thanks to all contributors.
Still not too sure what these shunts are all about.Heard of them before but never understood the principle and structure!

Thanks again .

Regards Michael.
 
Quick guide to shunts...

[ QUOTE ]
Still not too sure what these shunts are all about.Heard of them before but never understood the principle and structure!

[/ QUOTE ]An ordinary ammeter measures the current by passing all the current through the ammeter itself. For higher currents, this has disadvantages - the ammeter itself has to be a heavy-duty device, and the cable to and from the ammeter needs to be very heavy too.

Shunts are an easier way of measuring high currents. The shunt itself is a very low-resistance link which is inserted in the main cable where the current is to be measured. Shunts are usually heavily constructed, often of brass, and are therefore very reliable. Here's what a typical shunt looks like.
shunt3.jpg

The main current-carrying cable is bolted to each side of the shunt. The shunt has a very low resistance, so that the operation of the circuit is unaffected. However, there's just enough resistance to generate a tiny voltage across the shunt, directly proportional to the current flowing through it. This voltage (sometimes called the "signal voltage") is read by a simple meter, giving an accurate readout of the actual current flowing.

Typically, shunts generate only a few millivolts. For example, the shunt on my boat will handle 500A maximum, and only produces 50mV at that maximum current. The meter to measure the signal voltage is usually connected to the shunt separately (in the picture the screw terminals on the side of the shunt would be used).

Hope this helps to de-mystify!
 
[ QUOTE ]
Still not too sure what these shunts are all about.Heard of them before but never understood the principle and structure

[/ QUOTE ] Read some of the basic stuff at TB Training and the section on ammeters
 
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