Installing an ameter.

mickshep

mickshep

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I'm in the process of finishing off the installation of the Ignition system aboard Wraith and would like to install an Ameter, At present there is a red light which switches off once the alternator starts charging the battery bank, instead I would like to install a simple meter that will if I'm correct show charge rate, The alternator has just 2 wires, Gray and brown. Any ideas as to where I should put it? (IN THE CIRCUIT AT THE BACK THERE /forums/images/graemlins/blush.gif /forums/images/graemlins/blush.gif)
 
The Red light only shows that exciter current is required or not and is not the charge current. Therefore any meter would have to be placed in the leads back to battery switch, so that it shows charge rate back to battery system.
Probably easiest way is not actually to have a meter in the line, but to use a clamp type that reads amps based on sensing through the clamp. Otherwise you are into serious gear to register such high currents.
 
you need to put a shunt between the alternator and the battery - the ammeter is in fact a voltmeter across a shunt.

not sure what you would do with the numbers it gives you.
 
To get any meaningful readings a little rewiring might be required.

If I can explain in words.... You want to measure the amps into the battery bank(s) not the alternator output so any house power must be disregarded - this is easy to achieve by taking all house power off before the ammeter. The wiring should be alternator output to ammeter and from same terminal take off all house power then from the other ammeter terminal to the batteries either direct (as is normal) or via off-1-2-all switch.

Say your alternator is putting out 60 amps but house loading is 25 amps the ammeter will read 35 amps which is the charge goiing into the batteries. If you wire the ammeter directly into the alternator output the ammeter would read 60 amps but the hous power would account for 25 of those so the ammeter reading is useless.

With the alternator ticking over (say 5 amps) and a house draw of 25 amps the meter will read -20 amps (20 from the batteries and 5 from the alt)

Hope the above explanation helps
/sg
 
It is very difficult, if not impossible, to give detailed advice without access to your wiring diagram.

There are alternatives to consider.

If you want to monitor both the current drain from, and the charge current to, the battery you have to find, or maybe modify the wiring to create, a wire along which all current, both load and charge current, flows. Somewhere in that wire you insert either an ammeter with a built in shunt or the shunt of a remotely sited ammeter.

If you only want to monitor the charging current then the meter or shunt will have to go in a wire that carries only the alternator current to the battery.

If you want to just monitor the total system load then it will have to go in a wire that carries all the current supplied to the main switch panel but not the charging current.

The first option would be the normal choice perhaps but it would not measure the current that ship's systems are drawing directly from the alternator.

You will have to ensure that the starter motor current is not passing through your ammeter or shunt.

You might find these notes from TB training useful http://www.tb-training.co.uk/cover.html
 
What you need is a "battery monitor". This can measure amps into the battery bank and three or four different voltage positions eg - House - Starter - Bow thruster. Each can be set to alarm with under or over voltages. One of my positions is set to monitor the bilge pump, so any volts on the line greater than zero sets off the alarm.

Once you are measuring amps going in - or being taken out - then a simple calculation by the battery monitor gives you amps over time - i.e. Ampere Hours.

You input the size of your battery bank into the battery monitor and it calculates the remaining Ah charge of your batteries. This is far more accurate than monitoring battery voltage to determine battery charge, as battery voltage has to be under no load for at least an hour to give an indication of the true state of the battery charge.

Some battery monitors have a lot of setup parameters that need to be looked at carefully to ensure that the Ah reading it gives you is fairly accurate.
 
[ QUOTE ]
BLINKING HECK! Right can of worms I've set myself here. Just want to know it's charging. Mike.

[/ QUOTE ]

Did you really expect a simple answer ?
I do have a bit of difficulty understanding Cliff's post about measuring at alternator and getting 60A, measuring at battery bank and getting 35A. As I read it from all the books we have, alternator gives out what it can against the present condition of batterys, not 60A and 25A seems to evaporate of somewhere.
Anyway the whole subject is why I suggested a clamp type meter, that way no wiring is needed, you can clamp onto any section of wriring loom you want and see whats happening, no shunts or high load materials needed.
If you just want to make sure batterys are being charged, then many plotters will show voltage in the feed to the plotter. Engine off will be ~12V range, engine on will be higher and possible 13+ if near charged.
A battery check meter as we have, a simple voltmeter shows over 14V when engine running, lower when off.
Car Accessory shops do LED battery checkers that also check alternators, about a tenner.
Simple ideas, maybe not in keeping with experts, but seem to work. Once hubby explained, even I had no difficulty understanding them. /forums/images/graemlins/wink.gif
 
[ QUOTE ]
I do have a bit of difficulty understanding Cliff's post about measuring at alternator and getting 60A, measuring at battery bank and getting 35A. As I read it from all the books we have, alternator gives out what it can against the present condition of batterys, not 60A and 25A seems to evaporate of somewhere

[/ QUOTE ] Nothing wrong with Cliff's post although you are correct in your understanding that the alternator output will depend on the state of the batteries and the demand of the system.

He is just giving an example, suppose the alternator output is 60 amps.

Perhaps it would make you happier if he had said, "Suppose the ship's load is 25 amps and the batteries are taking 35 amps charge , which is shown on the ammeter, making a total load on the alternator of 60 amps."

Same numbers same arithmetic just expressed in a different way.

Then when the engine is just idling the alternator is only capable of producing 5 amps so in order to satisfy the ship's demand, still at 25 amps, 20 amps must come from the battery which will appear as a reading on the ammeter of 20 amps discharge
 
[ QUOTE ]
[ QUOTE ]
I do have a bit of difficulty understanding Cliff's post about measuring at alternator and getting 60A, measuring at battery bank and getting 35A. As I read it from all the books we have, alternator gives out what it can against the present condition of batterys, not 60A and 25A seems to evaporate of somewhere

[/ QUOTE ] Nothing wrong with Cliff's post although you are correct in your understanding that the alternator output will depend on the state of the batteries and the demand of the system.

He is just giving an example, suppose the alternator output is 60 amps.

Perhaps it would make you happier if he had said, "Suppose the ship's load is 25 amps and the batteries are taking 35 amps charge , which is shown on the ammeter, making a total load on the alternator of 60 amps."

Same numbers same arithmetic just expressed in a different way.

Then when the engine is just idling the alternator is only capable of producing 5 amps so in order to satisfy the ship's demand, still at 25 amps, 20 amps must come from the battery which will appear as a reading on the ammeter of 20 amps discharge

[/ QUOTE ]

That makes sense and is as I understand it. \The alternator regulates to the demand and at top demand to it's rated max output. If the ship system ie domestic is not demanding 25A, then alternator output will read similar to battery charge amps.

In the OP case, I would reckon that an ammeter showing alternator output is good enough, as he wants to know that alternator is providing it's best, whether it's for the domestic or battery charging. If he sets it to read of the battery bank, then he may feel he's got bad charging if sees a low figure.
It's an interesting scenario, as whats best ? At battery bank you can also meter what goes out when engine is off, but if at alternator you will not see this.
 
Ok back to the original question. You want to measure the current the alternator is producing. This will be a total of current charging battery and any being used. If it is a simple boat system you probably have an idea how much is being used. Or can switch most things off.

The current comes out of the alternator o the thick wire. This is the wire that must have the amp meter in. Or you can put a clamp type amp meter on this wire.

The amp meter can be a mechanical/ magnetic moving coil analogue meter or a digital meter. The amp meter can have a remote shunt or have all the current going up to the meter then back again to the battery switch etc.

The shunt is a piece of stainless steel or nichrome metal that has a stable electrical resistance. It is often mounted on an insulating block with bolt terminals at each end. It will also have terminals for small wires going to the meter. The shunt is accurately machined to match the meter to accurately indicate amps. There is nothing special baout the shunt, you can make one yourself but you must have an accurate amp meter to calibrate it against.

For instance I have made a shunt to give 200mv drop at 20 amps to drive a digital panel meter using a piece of stainless steel sheet 20g about 40mm long and 8mm wide with holes in each end for the 4mm bolts. You need to have separate bolts for connection to the meter. (because any resistance in the bolts will affect the accuracy.

A this shunt will drop 200mv (1/5 volt) at 20 amps and using digital panel meters the next range is 200 amps again dropping 200mv for 200 amps digital panel meters are not the best answer.

You can buy a moving coil analogue meter for few quid. Get a 50 microamp movement full scale deflection (FSD) You can open this up and using a fine pen mark the amp scale you want. ie 0-50 amps.

You then make a shunt say 50 mm of 25 mm wide 18g stainless steel with bolt holes for lugs and wires to the meter and to the current carrying wires. Don' t share the holes.

You will need a multimeter with 20 amp range or a clamp meter temporarily in the circuit and a current flow. You file down ( make a waste) in the middle of the SS bar. The thinner it is and longer the thin part is the more resistance hence more meter movement.
You can use a current around 20 amps and interpolate the readings upward as it is all linear.

Because the wires go from a heavy wire carrying battery or alternator current you MUST put fuses in the light weight wires that go to the meter. The fuses must be one on each wire at the shunt. This goes for any shunt type amp meter.

Having described how to make your own you can hopefully see how a simple shunt type amp meter works. The non shunt type will have the heavy wires from the alternator and to the battery switch going right into the meter on the switch board. This may or may not be convenient.

Lastly there is one very simple option. Especially if you are not after accuracy. You use a 50 micromap meter as suggested and put one wire on the alternator terminal and the other wire on the isolation switch. Or at the other end of the piece of heavy wire going from the alternator. The wire itself will drop a voltage due to its own resistance and may be useful as an indication of alternator current.
Again it will not be calibrated unless you open up the wire and fit a calibrated amp meter to compare. If you get too much meter reading then have one wire to the meter at the alternator and the other at a point along the wire. ie if it bridges more wire you get more reading less wire less reading. This may be especially successful if you have 2 or 3 metres of wire.
All the above applies to measuring current in any circuit. You can even have several shunts or wire taps and use a switch at the meter to measure the different volt drops.
PM me if you are confused good luck olewill
 
O.K. Here it is in pictures (as someone once said "A picture is worth a thousand words")
AmmeternormalWiring1.jpg

Above for "normal" ammeter

AmmeterShuntWiring.jpg

Above is for remote shunt type ammeter.

NOTE - For "Primary Feed" read domestic load (lights, radar, plotter etc. - feeds switch panel +ve bus)
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Artificial Intelligence is no match for Natural Stupidity
 
For reference you can also measure the current via the magnetic field around the cable, so it has no connection with the cable. Thus you do not have to cut the cable, it has no volt drop, does not get hot, and is not overloaded by engine starting. This allows measuring net amps in / out of battery without rewiring the alternator or starter motor.

Brian
 
Yes, with a "K" effect sensor however the question was how to fit an ammeter. I have such clamped on to the -ve battery leads - very handy to measure the starter motor draw - sad, ain't it - measuring how much the starter motor draws....... /forums/images/graemlins/grin.gif Though much handier for measuring the invertor load - like ~250 amp on full load - ooouch!

For "normal" people though a 100-0-100 or a 60-0-60 ammeter wired as above is more than adequate.
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hammer.gif
Artificial Intelligence is no match for Natural Stupidity
 
It was a bit of info that there are other ways other than resistive shunts.

There are over 3.500 normal people that have hall effect shunts that measure 30-0-30, or 50 - 0 -50 amp or 100 - 0 -100 amp. The shunt fits on battery positive terminal post, so you do not have to measure only invertor loading, but you can if you are digital.

Brian
 
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