Wiring an Ammeter

[David Schweizer]

At the moment the domestic battery ammeter on our boat only shows the charge going into the battery, which is achieved by connecting the ammeter into the cable between the Alternator B+ terminal and the battery positive terminal. A separate cable runs from the Battery Positive terminal to the domestic Circuit fuse box.

 

I have seen several diagrams on the internet which show a separate cable running from the fuse box input terminal and the B+ side terminal on the ammeter. If I do this on the boat would it show the balance between charge and discharge when the enegine is running, and discharge when it is off?

 

Alternatively would it be possible to run the cable currently running betweenn the battery and fuse box directly to the B+ Side terminal on the ammeter?

 

I feel I should know how to do this but would be gratful for any advice from anyone who knowns more about boat wiring than I do. Here is a copy of the present wiring cicuit on our boat:-

 

Edited January 25, 2012 by David Schweizer

[mrsmelly]

At the moment the domestic battery ammeter on our boat only shows the charge going into the battery, which is achieved by connecting the ammeter into the cable between the Alternator B+ terminal and the battery positive terminal. A separate cable suns from the Battery Positive terminal to the domestic Circuit fuse box.

 

I have seen several diagrams on the internet which show a separate cable running from the fuse box input terminal and the B+ side terminal on the ammeter. If I do this on the boat would it show the balance between charge and discharge when the enegine is running, and discharge when it is off?

 

Alternatively would it be possible to run the cable currently running betweenn the battery and fuse box directly to the B+ Side terminal on the ammeter?

 

I feel I should know how to do this but would be gratful for any advice from anyone who knowns more about boat wiring than I do. Here is a copy of the present wiring cicuit on our boat:-

 

 

Hi David

 

Could you not just buy a shunt and wire it that way on the battery ?

 

Tim

[David Schweizer]

Hi David

 

Could you not just buy a shunt and wire it that way on the battery ?

 

Tim

You will have to be more explicit, I have heard of shunts but have no idea what they do or how to wire them.

[Chris Pink]

With your existing ammeter (I assume the old fashioned dial gauge). To do what you want would involve putting it between the battery and everything else.

 

This is usually impractical for the length of heavy gauge cabling involved - the reason such ammeters are now depreciated.

 

 

A shunt would go in the negative line.

 

I will go and draw you a diagram.

[Chris Pink]

 

a shunt ammeter would go where your battery switch s now (topologically speaking) and have two thin wires running to the gauge and two wires to the fuse box and -ve common

 

(I havent drawn it but the sterling sensing wire would go to the battery, not like shown)

[blodger]

With your existing ammeter (I assume the old fashioned dial gauge). To do what you want would involve putting it between the battery and everything else.

 

This is usually impractical for the length of heavy gauge cabling involved - the reason such ammeters are now depreciated.

 

 

A shunt would go in the negative line.

 

I will go and draw you a diagram.

 

I have just recently put a 200a shunt for a 200a digital display in the positive line but you have to use an isolation chip to supply power to the meter (Isolated Power Module DC-DC Converter In 10-16V Out 12V - on Ebay)as the default is using the negative and some commoning of the connections within in expectation .

[Keeping Up]

Fitting the ammeter in the main battery circuit doesn't necessarily need a great deal of additional heavy cable.

 

In my own setup, with the ammeter on the dashboard, the cable from the alternator to the ammeter is heavy enough to carry the full alternator current but is no thicker, so it causes some voltage drop but the alternator controller compensates for this by increasing the alternator voltage appropriately (which was one of the original purposes of a controller). The cable from the battery to the ammeter is thicker, to reduce voltage drop when discharging, but of course that cable would be there anyway, whether there was an ammeter or not. Here is a complete circuit of my electrical system; ignore the bits you aren't interested in. Alternator B+ is at the bottom right.

 

 

 

The one complication is that I have also a "Rediline" rotary converter (which is an old-fashioned electomechanical version of a 2kW inverter) which takes more current than the ammeter could handle, so it connects directly to the battery instead. The only disadvantage is that if the converter is being used while the engine is running, the increased current from the alternator registers as if it were a charge when in practice it is not the battery that is gaining the benefit of the current and may actually be discharging. But this is really not a problem.

[Theo]

 

I will go and draw you a diagram.

 

I have just bought an ammeter and have been assured that it can go in either the positive or negative line.

 

Nick

[David Schweizer]

Thanks for all the suggestions. I have just looked at the diagram for our boat and the fuse box supply is shown as already coming from the B+ side of the ammeter, but I am certain that on the boat it comes directly from the battery, bypassing the ammeter.

 

I would have assumed that if the wiring is as the circuit suggests, the drain as well as the supply would be shown by the ammeter, I will have to check, it won't be much if an alteration if the supply cable needs to be moved but I may need to double up the cable from the battery to the ammeter.

Edited January 25, 2012 by David Schweizer

[blodger]

I have just bought an ammeter and have been assured that it can go in either the positive or negative line.

 

Nick

Analogue ammeters with built in shunts can go in either but used mainly to be fitted in the positive line. Good peactice and the design of digital meters seems to be changing what was standard

Edited January 25, 2012 by blodger

[Chris Pink]

I have just recently put a 200a shunt for a 200a digital display in the positive line but you have to use an isolation chip to supply power to the meter (Isolated Power Module DC-DC Converter In 10-16V Out 12V - on Ebay)as the default is using the negative and some commoning of the connections within in expectation .

 

That's what they say but i have found the error if you just connect it to the 12V supply is pretty insignificant - they are not very accurate devices anyway.

 

I have just looked at the diagram for our boat and the fuse box supply is shown as already coming from the B+ side of the ammeter, but I am certain that on the boat it comes directly from the battery, bypassing the ammeter.

 

 

not on the diagram you posted it doesn't

[by'eck]

 

a shunt ammeter would go where your battery switch s now (topologically speaking) and have two thin wires running to the gauge and two wires to the fuse box and -ve common

 

(I havent drawn it but the sterling sensing wire would go to the battery, not like shown)

 

Putting the shunt where you suggest adjacent to the common negative battery switch will record total current to/from both batteries. Could be a bit alarming when you operate starter

 

Place shunt in the service battery negative cable before it connects to the starter battery negative.

 

Agree that the Sterling DAR sensing wire (red) should go directly to the service battery positive though.

[David Schweizer]

That's what they say but i have found the error if you just connect it to the 12V supply is pretty insignificant - they are not very accurate devices anyway.

 

 

 

not on the diagram you posted it doesn't

I am sure it does, there is a cable shown as coming from the B+ terminal on the Alternator to the Relay, then from the same Relay terminal to one of the Ammeter terminals. there are two more cables connected to the same Ammeter terminal, one to the Sterling and one to the Fuse box.

 

I am pretty certain that on the boat neither of these cables are connected to the Ammeter, but directly to the Domestic Battery positive terminal.

 

Putting the shunt where you suggest adjacent to the common negative battery switch will record total current to/from both batteries. Could be a bit alarming when you operate starter

 

Place shunt in the service battery negative cable before it connects to the starter battery negative.

 

Agree that the Sterling DAR sensing wire (red) should go directly to the service battery positive though.

See above post, I am pretty certain that on the boat it does. I am becoming increasingly convinced that the circuit diagram is wrong.

 

With regard to a shunt, I am not bothered about the Starter current to be shown on the Ammeter. I know that once the starter battery has been re-charged, it only takes about an amp. It is the domestic side that I want to be able to monitor, and if that can be done by moving a cable I will be quite happy even if there is a little bit of voltage drop, the Sterling should compensate for that.

Edited January 25, 2012 by David Schweizer

[smileypete]

With regard to a shunt, I am not bothered about the Starter current to be shown on the Ammeter. I know that once the starter battery has been re-charged, it only takes about an amp. It is the domestic side that I want to be able to monitor, and if that can be done by moving a cable I will be quite happy even if there is a little bit of voltage drop, the Sterling should compensate for that.

Any ideas what the max current you take from the cabin batts is roughly?

 

Also is the present ammeter a 'centre zero' type?

 

cheers,

Pete.

Edited January 25, 2012 by smileypete

[David Schweizer]

Any ideas what the max current you take from the cabin batts is roughly?

 

Also is the present ammeter a 'centre zero' type?

 

cheers,

Pete.

We have very little draw on power, the only items in regular use being a very (expensive) efficient fridge, a small low consumptuion 12v TV, a car radio/CD player, and lights. The maximum current at any one time will normally be less than 10 amps, with the average usage whilst moored between cruising being somewhere between 40 and 50 amps or less, as we often do not bother with the TV.

 

The present ammeter is a 60-0-60 Smiths unit.

Edited January 25, 2012 by David Schweizer

[Keeping Up]

Ours is a 50-0-50 Smiths unit. It sits pretty hard against the end-stop when we're charging at 70 Amps, but it doesn't seem to mind (after 20 years it's still OK)

 

 

P1030874 by Keeping Up, on Flickr

[by'eck]

Ours is a 50-0-50 Smiths unit. It sits pretty hard against the end-stop when we're charging at 70 Amps, but it doesn't seem to mind (after 20 years it's still OK)

 

I have to admit to a dislike of these small self contained ammeters as their range limits their use to only the most basic of boat electrics with small alternator, no inverter etc.

 

An ammeter will have a small shunt inside similar to the larger dedicated ones that drive a remote digital current display.

 

I'm sure the self contained ones with limited range (50-0-50 amp) will drop a larger voltage albeit still small when taken beyond their design range. Even it it doesn't burn out you will be loosing extra voltage, however small, to your distribution system. Then there's the issue of safety with one continuously over its mechanical limit overheating.

 

A shunt designed to take significantly more than the max current flow in or out of the batteries is going to be a better bet in every situation.

[David Schweizer]

I have to admit to a dislike of these small self contained ammeters as their range limits their use to only the most basic of boat electrics with small alternator, no inverter etc.

 

An ammeter will have a small shunt inside similar to the larger dedicated ones that drive a remote digital current display.

 

I'm sure the self contained ones with limited range (50-0-50 amp) will drop a larger voltage albeit still small when taken beyond their design range. Even it it doesn't burn out you will be loosing extra voltage, however small, to your distribution system. Then there's the issue of safety with one continuously over its mechanical limit overheating.

 

A shunt designed to take significantly more than the max current flow in or out of the batteries is going to be a better bet in every situation.

Well in our case that is OK as we have a 60-0-060 ammeter and a 55amp alternator, and any voltage drop will be compensated by the Sterling. but then as you will see from my post No. 15 we have a very basic electrical system, with no need for high perfomance electronics, and gizmos.

[smileypete]

We have very little draw on power, the only items in regular use being a very (expensive) efficient fridge, a small low consumptuion 12v TV, a car radio/CD player, and lights. The maximum current at any one time will normally be less than 10 amps, with the average usage whilst moored between cruising being somewhere between 40 and 50 amps or less, as we often do not bother with the TV.

OK sounds good, think I'd move the wire as you suggested:

 

 

Would make it easier to see when the batt charge current has dropped enough to show the batts are fully charged.

 

As with all unfused connections, the new cable would need to be well protected against chafing and damage, maybe add some spiral wrap round it?

 

Also I'd consider fitting a fuse in the alternator sense lead as shown to protect that wire. If the sense lead does get disconnected, would the alt controller default back to the internal regulator? Anyone know?

 

cheers,

Pete,

[blodger]

Also I'd consider fitting a fuse in the alternator sense lead as shown to protect that wire. If the sense lead does get disconnected, would the alt controller default back to the internal regulator? Anyone know?

 

The Stirling gives control back to the regulator for a variety of reasons. I have it switched in the line from the rg so that I can disconnect or easily check that it is still doing something from time to time.

 

ETA swiych is not in the sense line

Edited January 26, 2012 by blodger

[David Schweizer]

I am grateful for the various people giving advice. Unfortunately there now appear to be three versions of my wiring circuit on this thred which is why I got confused with Chris Pinks comment.

 

I suppose I should have looked more carefully but Chris was correct, unfortunately I did not realise he had altered my drawing to re-position the Fuse box supply cable, I have now caught up.

Edited January 26, 2012 by David Schweizer

[by'eck]

Also I'd consider fitting a fuse in the alternator sense lead as shown to protect that wire. If the sense lead does get disconnected, would the alt controller default back to the internal regulator? Anyone know?

 

cheers,

Pete,

 

The alt sense lead needs to be connected to a battery else it will see zero volts & confuse the controller with unpredictable & possibly harmful effects. I quote from Sterling manual:

 

The red is the sense wire, wherever it is placed on the Regulator, and will regulate the voltage of that spot, therefore, it is important that the end of the red cable and the alternator must never be isolated when the engine is running.

 

I wouldn't bother with a fuse in the sense lead if only for this reason.

[smileypete]

The alt sense lead needs to be connected to a battery else it will see zero volts & confuse the controller with unpredictable & possibly harmful effects. I quote from Sterling manual:

 

The red is the sense wire, wherever it is placed on the Regulator, and will regulate the voltage of that spot, therefore, it is important that the end of the red cable and the alternator must never be isolated when the engine is running.

 

I wouldn't bother with a fuse in the sense lead if only for this reason.

Doesn't seem the best bit of design, but fair enough.

 

As the sense wire shouldn't pass much current, a power resistor or even a light bulb would provide some overcurrent protection.

 

cheers,

Pete.

[blodger]

The alt sense lead needs to be connected to a battery else it will see zero volts & confuse the controller with unpredictable & possibly harmful effects. I quote from Sterling manual:

 

The red is the sense wire, wherever it is placed on the Regulator, and will regulate the voltage of that spot, therefore, it is important that the end of the red cable and the alternator must never be isolated when the engine is running.

 

I wouldn't bother with a fuse in the sense lead if only for this reason.

 

/quote]

 

Having read this I realise my switch is in the wire from the regulator, not in the sense wire.

I shall go back and edit what I said earlier

[David Schweizer]

The alt sense lead needs to be connected to a battery else it will see zero volts & confuse the controller with unpredictable & possibly harmful effects. I quote from Sterling manual:

 

The red is the sense wire, wherever it is placed on the Regulator, and will regulate the voltage of that spot, therefore, it is important that the end of the red cable and the alternator must never be isolated when the engine is running.

 

I wouldn't bother with a fuse in the sense lead if only for this reason.

 

 

Having read this I realise my switch is in the wire from the regulator, not in the sense wire.

I shall go back and edit what I said earlier

I have always understood that if you have a switch, it should be in the field (white) wire.

Edited January 26, 2012 by David Schweizer