Ammeter installation

[NB Alnwick]

Following on from recent discussions regarding the necessity of having a permanently mounted accurate ammeter. I am just wondering how this could be installed?

 

On our ancient MGB, the ammeter appears to be wired between the batteries (two six volt) and everything else apart from the starter motor. So if I put lights on, press the horn button (yes it is an old one without relays) or run the windscreen wipers without running the engine, I can see the power drain in amperes. Similarly, if I start the engine, I can then see the net rate of charge or discharge if everything is still switched on.

 

 

On the boat, the wiring is rather more complicated because (as advised by those who know about such matters) the battery charger is connected independently directly to the battery terminals with three separate positive leads. The cabin batteries have there own isolator after which there are separate positive cables to the respective fuse/distribution boards for 24v domestic equipment and the inverter. There is an ammeter installed in the engine alternator circuit which is also completely separate and provides charge to either bank of batteries switched via a relay.

 

So it would seem that there is no single point at which an ammeter capable of indicating the overall net power drain or charge could be installed. So do people have banks of ammeters - one for each circuit?

[ChrisPy]

there was an extensive thread on this recently. Basically you need to install a shunt in the battery negative to earth lead and then fit a remote ammeter matching the shunt - all of which is available on ebay from HongKong/Ireland, and probably from other sources as well.

[NB Alnwick]

there was an extensive thread on this recently. Basically you need to install a shunt in the battery negative to earth lead and then fit a remote ammeter matching the shunt - all of which is available on ebay from HongKong/Ireland, and probably from other sources as well.

 

I missed that - probably because I wasn't that interested in ammeters at the time. Nevertheless, the charger and engine alternator are still wired independently (separate negative leads) and there are battery banks with separate negative leads.

[John Orentas]

I missed that - probably because I wasn't that interested in ammeters at the time. Nevertheless, the charger and engine alternator are still wired independently (separate negative leads) and there are battery banks with separate negative leads.

 

 

Graham,

 

You don't need several ammeters, just wire a shunt into each circuit you are interested in then you can use a multi-position rotary switch wired to the sense conductors to select the shunt.. The wiring of course can be very light, you are only looking at tiny currents.

 

Much cheaper and more simple this way.

[David Schweizer]

The charge to my batteries runs through the ammeters, without any shunts etc. It was wired that way when I bought the boat and I have continued this practice. I still have the original Smiths Ammeters whch are nearly 30 years old which seem to function perfectly. I have heard of shunts, but do not really understand what they do, or why some people recommend them.

 

Any information would be appreciated.

Edited January 31, 2009 by David Schweizer

[PeterF]

The charge to my batteries runs through the ammeters, without any shunts etc. It was wired that way when I bought the boat and I have continued this practice. I still have the original Smiths Ammeters whch are nearly 30 years old which seem to function perfectly. I have heard of shunts, but do not really understand what they do, or why some people recommend them.

 

Any information would be appreciated.

On more modern boats the output of the alternator is often 110Amps or more and that is a lot of pwoer to feed through a simple dial ammeter and if things go wrong the resultant short circuit can be quite entertaining!!.

 

A shunt is a (hopefully well callibrated) resistor with a very low resistance which creates a small voltage drop as the current flows through it. A Voltmeter is used to measure the resistance dropped over the shunt, but the clever bit is as long as you buy the meter and shunt as a mathced pair then the votmeter dial reads in amps not volts. Depending how basic you want the explanation, the voltage dropped over a resistor is properotinal to the current flowing through it. For example in my set up I have a 140Amp alternator and there is no way I want that power flowing through simple dial ammeter so I have one of the 200Amp shunt / ammeters from ebay. I think the max voltage drop is comething like 0.075V so not very much, and to make sure it is not a problem I have the voltage sensor for controlling the ammeter on the battery side of the shunt.

 

The thread for installtion can be found below

 

Installing a shunt ammeter

 

PeterF

[NB Alnwick]

On more modern boats the output of the alternator is often 110Amps or more and that is a lot of pwoer to feed through a simple dial ammeter and if things go wrong the resultant short circuit can be quite entertaining!!.

 

A shunt is a (hopefully well callibrated) resistor with a very low resistance which creates a small voltage drop as the current flows through it. A Voltmeter is used to measure the resistance dropped over the shunt, but the clever bit is as long as you buy the meter and shunt as a mathced pair then the votmeter dial reads in amps not volts. Depending how basic you want the explanation, the voltage dropped over a resistor is properotinal to the current flowing through it. For example in my set up I have a 140Amp alternator and there is no way I want that power flowing through simple dial ammeter so I have one of the 200Amp shunt / ammeters from ebay. I think the max voltage drop is comething like 0.075V so not very much, and to make sure it is not a problem I have the voltage sensor for controlling the ammeter on the battery side of the shunt.

 

The thread for installtion can be found below

 

Installing a shunt ammeter

 

PeterF

 

Peter,

 

The explanation and the link are extremely helpful - thanks.

[chris w]

Following on from recent discussions regarding the necessity of having a permanently mounted accurate ammeter. I am just wondering how this could be installed?

 

As I said on your other post, the ammeter you purchased from Ebay is not a shunt type and therefore cannot be used with a shunt. It is an in-line version and is NOT a centre zero type so will measure EITHER charge or discharge but not both. It will also not be particularly accurate due to its being analog.

 

Chris

[NB Alnwick]

As I said on your other post, the ammeter you purchased from Ebay is not a shunt type and therefore cannot be used with a shunt. It is an in-line version and is NOT a centre zero type so will measure EITHER charge or discharge but not both. It will also not be particularly accurate due to its being analog.

 

Chris

 

Chris - I realise that. I got the message the first time but thank you for reminding me!

 

If I do install a new ammeter permanently, I will buy something suitable with a matching shunt.

[chris w]

If I do install a new ammeter permanently, I will buy something suitable with a matching shunt.

Good boy

[David Schweizer]

On more modern boats the output of the alternator is often 110Amps or more and that is a lot of pwoer to feed through a simple dial ammeter and if things go wrong the resultant short circuit can be quite entertaining!!.

 

A shunt is a (hopefully well callibrated) resistor with a very low resistance which creates a small voltage drop as the current flows through it. A Voltmeter is used to measure the resistance dropped over the shunt, but the clever bit is as long as you buy the meter and shunt as a mathced pair then the votmeter dial reads in amps not volts. Depending how basic you want the explanation, the voltage dropped over a resistor is properotinal to the current flowing through it. For example in my set up I have a 140Amp alternator and there is no way I want that power flowing through simple dial ammeter so I have one of the 200Amp shunt / ammeters from ebay. I think the max voltage drop is comething like 0.075V so not very much, and to make sure it is not a problem I have the voltage sensor for controlling the ammeter on the battery side of the shunt.

 

The thread for installtion can be found below

 

Installing a shunt ammeter

 

PeterF

 

Unfortunately that is all a bit too complicated for me, but thanks anyway. When it comes to electrical things I need to have a wiring diagram in front of me to follow the instructions.

 

I only have a 55amp alternator on my boat and the Ammeter is a Smiths +60amp/ -60amp dial type. Working on the basis that it has worked fine for the last 28 years do I need to worry about it?

 

One of my "problems" is that I do not like these modern digital instruments and much prefer the "traditional" appearence of the old dial instruments, and do not really want to re-design the instrument panel, especially as I have only just payed for a new one to incorporate the 4"dia VDO tachometer (black with Chrome Bezel) I have recently aquired.

Edited February 2, 2009 by David Schweizer

[PeterF]

Unfortunately that is all a bit too complicated for me, but thanks anyway. When it comes to electrical things I need to have a wiring diagram in front of me to follow the instructions.

 

I only have a 55amp alternator on my boat and the Ammeter is a Smiths +60amp/ -60amp dial type. Working on the basis that it has worked fine for the last 28 years do I need to worry about it?

 

One of my "problems" is that I do not like these modern digital instruments and much prefer the "traditional" appearence of the old dial instruments, and do not really want to re-design the instrument panel, especially as I have only just payed for a new one to incorporate the 4"dia VDO tachometer (black with Chrome Bezel) I have recently aquired.

David,

 

Attached is a simple diagram of a shunt installation. This is based on the ones that are linked from the guy on ebay. These can only go into the -ve lead because of how the electronics is wired up. Other more expensive systems can go in the +ve lead. Or you can put a shunt in the +ve lead and then use a good old fashioned analog dial gauge as that has no problems. The current that flows through the meter is very small and small cables can be used between the shunt and the meter. This should make it as clear as mud.

 

 

PeterF.

[Keeping Up]

I only have a 55amp alternator on my boat and the Ammeter is a Smiths +60amp/ -60amp dial type. Working on the basis that it has worked fine for the last 28 years do I need to worry about it?

Simple answer - NO YOU DON'T. If it works, don't try and fix it!

 

I have a 70 Amp alternator which, despite Chris W's repeated assertions that it is impossible, reliably provides me with about 65 Amps of charge when I start cruising in the mornings. This pins the needle of my 50-0-50 ammeter very hard against the end stop. It has been doing that for 14 years and the Adverc controller takes care of any voltage drop by just ramping up the alternator output a bit more.

[ditchcrawler]

Simple answer - NO YOU DON'T. If it works, don't try and fix it!

 

I have a 70 Amp alternator which, despite Chris W's repeated assertions that it is impossible, reliably provides me with about 65 Amps of charge when I start cruising in the mornings. This pins the needle of my 50-0-50 ammeter very hard against the end stop. It has been doing that for 14 years and the Adverc controller takes care of any voltage drop by just ramping up the alternator output a bit more.

Just pray it doesn't go open circuit.

Brian

Edited February 2, 2009 by ditchcrawler

[Keeping Up]

Just pray it doesn't go open curcuit.

Brian

If it does the battery won't charge and, the meter will read zero, and the alternator will supply as much as it can to both the starter battery (clamped to it by the diode splitter) and to the domestic circuits. No great problem as long as I spot it within a few hours (which I would) and no danger to the alternator either.

[David Schweizer]

David,

 

Attached is a simple diagram of a shunt installation. This is based on the ones that are linked from the guy on ebay. These can only go into the -ve lead because of how the electronics is wired up. Other more expensive systems can go in the +ve lead. Or you can put a shunt in the +ve lead and then use a good old fashioned analog dial gauge as that has no problems. The current that flows through the meter is very small and small cables can be used between the shunt and the meter. This should make it as clear as mud.

 

 

PeterF.

Yep, as clear as mud.

 

I actually understand the diagram supplied, but as that will not work with an analogue ammeter, where do I connect a shunt? Does the charge cable still have to go to the ammeter, or can I run the charge cable directly to the battery and instal a separate small wire through a shunt and across the ammeter to record the charge? One side will presumably come form the battery positive terminal, where does the other cable run to?

 

I am confused.

Edited February 2, 2009 by David Schweizer

[Keeping Up]

I am confused.

Then stay with what you've got, if it's working OK

[PeterF]

Yep, as clear as mud.

 

I actually understand the diagram supplied, but as that will not work with an analogue ammeter, where do I connect a shunt? Does the charge cable still have to go to the ammeter, or can I run the charge cable directly to the battery and instal a separate small wire through a shunt and across the ammeter to record the charge? One side will presumably come form the battery positive terminal, where does the other cable run to?

 

I am confused.

The diagram supplied will work with an analogue meter as long as the analog meter is rated for whatever the shunt voltage drop is. If you have a normal in line ammeter as la old car style then you can not use this with a shunt it needs the full current through it. If you have an analogue meter that works with a shunt then you can put that in the positive charge lead, it does not matter. It is shown in the -ve lead becasue the digital ones on ebay have to have a common -ve for the power feed to the meter and for the shunt, if you put them in the +ve lead they will not work.

 

I also suggest that if you are not too sure what you are doing then do not do anything if it is working OK.

[chris w]

Simple answer - NO YOU DON'T. If it works, don't try and fix it!

 

I have a 70 Amp alternator which, despite Chris W's repeated assertions that it is impossible, reliably provides me with about 65 Amps of charge when I start cruising in the mornings.

 

To correct you Allan, my repeated assertions are that it's impossible if you have a 2:1 pulley ratio as is typical on most NB's. If you have a 3:1 or a 4:1 pulley ratio then you will get much more out because the alternator is spinning faster. If you indeed do have a 2:1 pulley ratio and are getting 65A out of a nominal 70A alternator, then either the alternator is actually much more than a 70A model (closer to 100A) or your ammeter is actually incorrect.

 

How are you measuring 65A anyway on a 50-0-50 ammeter? 51A would bang it against the end-stop too.

 

Chris

[alan_fincher]

How are you measuring 65A anyway on a 50-0-50 ammeter? 51A would bang it against the end-stop too.

Estimated from how curved the needle looks, as it's flexing against the stop ?

 

 

I should laugh - I've still got a 30A-0A-30A in-line meter, despite uprating the alternator to 70A. I'm confident of "more than 30A" but not much more, unless I (eventually!) get around to changing the arrangements.

 

My preferred unit of measurement is "enough"!

[Keeping Up]

To correct you Allan, my repeated assertions are that it's impossible if you have a 2:1 pulley ratio as is typical on most NB's. If you have a 3:1 or a 4:1 pulley ratio then you will get much more out because the alternator is spinning faster. If you indeed do have a 2:1 pulley ratio and are getting 65A out of a nominal 70A alternator, then either the alternator is actually much more than a 70A model (closer to 100A) or your ammeter is actually incorrect.

 

How are you measuring 65A anyway on a 50-0-50 ammeter? 51A would bang it against the end-stop too.

 

Chris

It actually takes just under 60 amps to make it hit the end stop (the pin is well beyond the end of the scale). And if I switch on 15 Amps of load, and this puts the needle at the 50-amp point, then I know the alternator is providing 65 Amps.

 

I checked its accuracy by applying a known loads and by reversing the ammeter connection to check its accuracy in both directions. It is not particularly accurate, but it is well within 10 per cent.

 

The pulley is only a 2:1 ratio, and I get virtually full output at an engine speed of about 1800 rpm which on a canal corresponds to 4mph. The alternater is a 70 Amp Motorola, one of those old ones with the regulator in the positive supply to the rotor (fitted with an Adverc). Maybe the Motorola engineers weren't so dim after all; I don't question it too hard, while it works I just enjoy the benefits. The downside is that it tends to work itself to death, and has had to be rebuilt a couple of times.

[Gibbo]

It actually takes just under 60 amps to make it hit the end stop (the pin is well beyond the end of the scale). And if I switch on 15 Amps of load, and this puts the needle at the 50-amp point, then I know the alternator is providing 65 Amps.

 

I checked its accuracy by applying a known loads and by reversing the ammeter connection to check its accuracy in both directions. It is not particularly accurate, but it is well within 10 per cent.

 

The pulley is only a 2:1 ratio, and I get virtually full output at an engine speed of about 1800 rpm which on a canal corresponds to 4mph. The alternater is a 70 Amp Motorola, one of those old ones with the regulator in the positive supply to the rotor (fitted with an Adverc). Maybe the Motorola engineers weren't so dim after all; I don't question it too hard, while it works I just enjoy the benefits. The downside is that it tends to work itself to death, and has had to be rebuilt a couple of times.

 

Sounds right to me. I know Chris has a problem with this, reckoning alternators don't do anything until they reach 1 million RPM but most alternators reach about 85% to 90% rated output somewhere between 3000 and 4000 RPM. Most are producing serious output by 2400 RPM

 

http://www.exploroz.com/images/Articles/35...__TN180x200.jpg

 

http://www.kansasselectproducts.com/altern...nce%20curve.jpg

 

Gibbo

[David Schweizer]

Sounds right to me. I know Chris has a problem with this, reckoning alternators don't do anything until they reach 1 million RPM but most alternators reach about 85% to 90% rated output somewhere between 3000 and 4000 RPM. Most are producing serious output by 2400 RPM

 

http://www.exploroz.com/images/Articles/35...__TN180x200.jpg

 

http://www.kansasselectproducts.com/altern...nce%20curve.jpg

 

Gibbo

I gave up arguing with Chris on this one a long time ago. I have a 55 amp A127 alternator on a BMC1.5 engine, the pulley ratio is 3:1 and I get full output at normal cruising speeds, (assuming the batteries need it) The Tacho is not installed yet, but I reckon that is an engine speed of somewhere between 1500 and 1800rpm.

[chris w]

Yes but, to be fair to my views, MOST people are not cruising at 1800rpm!!!

 

If one is poodling along at say 1000rpm max or less, which is more realistic IMHO for most NB engines then, on a 2:1 ratio, the alternator is only rotating at 2000rpm and wil not be delivering its maximum output. My alternator will deliver full output if I whack my Isuzu engine up to 2000rpm (4000 rpm alternator speed) but normally its only cruising at 1000-1100rpm engine speed (2000-2200rpm alternator speed).

 

Here's the output chart for an A127 alternator (probably the most ubiquitous) vs engine speed:

 

 

On the "auxiliary position" curve (domestic batteries 2:1 pulley ratio) and at 1000rpm ENGINE speed the alternator output is just about 47A and at 1100rpm about 52A. Those figures represent about 67% and 74% of alternator output respectively.

 

However, in reality, rather than theory, I have an 80A alternator instead of a 70A version, but I find I get about 50A max when cruising at normal speed which is about 63% of nominal output. That is why I suggest people work on a figure of 60-65% of nominal output. Many boaters think that an 80A alternator will give 80A in a typical set up - it won't.

 

Chris

Edited February 3, 2009 by chris w

[Gibbo]

But isn't your engine a Barrus?

 

They're well known for not pulleying alternators up properly. Not everyone does that.

 

Gibbo