How to wire a volt and amp meter

[Jokani]

I am hoping to install a volt and amp meter, but I am struggling to understand the wiring diagram:

My questions are:

1. What is the square box 'Load'?
2. The thin red and black wires connect to the fusebox?

 

[VicS]

The box labelled" load" represents all the bits of electrical gear connected to the system an powered from the battery /power supply

I suspect the thin red and black are an independent power supply for the meter module .... it may not be self powered from the circuits it is monitoring.

I dont understand why the connections between the meter module and the shunt are thick wires ... normally these would be quite thin ( but fused)


I suggest you tell us exaclty what this bit of kit is !

 

[Jokani]

The box labelled" load" represents all the bits of electrical gear connected to the system an powered from the battery /power supply

So would I just connect the left side of the shunt to the negative bus bar, the right side to the positive bus bar?

The thin red and black would go to the fuse board in the normal manner?

The box labelled" load" represents all the bits of electrical gear connected to the system an powered from the battery /power supplyI suggest you tell us exaclty what this bit of kit is !

Sorry, this it the item http://www.ebay.co.uk/itm/391123172269

 

[mikefleetwood]

So would I just connect the left side of the shunt to the negative bus bar, the right side to the positive bus bar?

No! Left side of shunt to negative bus bar - OK. BUT, right side of shunt to battery negative!

Thick red wire goes to positive bus bar.

The thin red and black would go to the fuse board in the normal manner?

Looks like it. By the way, the thing labelled "transformer" on the drawing isn't.

 

[VicS]

So would I just connect the left side of the shunt to the negative bus bar, the right side to the positive bus bar?

NO! that would short your whole system out/ burn your boat down to the waterline


the right hand end to the negative bus bar in place of all the other connections on it. transfer all those to the left hand end .

The thin red and black would go to the fuse board in the normal manner?

It would appear so yes but heaven knows what the box labelled "transformer is supposed to be..... is this a component also supplied ??... Connect with a suitable fuse in the +ve ... rated less that the safe working current of the thin wire so that the wire as well as the device is protected.

I'd also include a fuse in the (thick) red wire connection.

IMO you would be better off buying something similar from a reputable UK based retailer who provides decent and comprehensive fitting instructions. It might cost more but what price the safety of yourself and your boat?

 

[Jokani]

No! Left side of shunt to negative bus bar - OK. BUT, right side of shunt to battery negative!

I'm confused by this, aren't the negative bus bar and the battery negative effectively the same thing?

 

[Jokani]

NO! that would short your whole system out/ burn your boat down to the waterline

My first boat, so limited knowledge, learning all the time though, glad I checked first on this one!

the right hand end to the negative bus bar in place of all the other connections on it. transfer all those to the left hand end .

I'm still a bit confused here.

Ground/negative wise I think I have 3 different options:

1. direct to battery negative
2. negative battery bus bar (this has bits wired to it such as bilge pump etc)
3. ground bus bar that all thing connected to the fuse board connect to

So left side could be connected to either the negative battery bus bar or ground bus bar (as both are load)?
The right side would be direct to battery negative?

IMO you would be better off buying something similar from a reputable UK based retailer who provides decent and comprehensive fitting instructions. It might cost more but what price the safety of yourself and your boat?

Yes I was surprised not to get ant detailed instructions, I got the idea from this thread http://www.ybw.com/forums/showthread.php?434805-LED-voltmeter it may be my limited knowledge of all things 12v is even more dangerous. But I do check here whenever I am not sure, and people like yourself have always kept me safe.

I'd also include a fuse in the (thick) red wire connection.

Will do, what amp would you suggest?

 

[vyv_cox]

I think you may have forgotten your basic physics electrical lessons! An ammeter is actually a galvanometer that measures the potential between the two ends of the shunt. The shunt is a calibrated resistance through which passes all of the current returning to the battery. In your case the galvanometer is a digital device that requires its own power supply.

I have to say that I had a similar one to yours with a separate power supply to the meter. It seemed confused by using the same supply that it was measuring and it never worked reliably. I then found one that was self contained and presumably with better electronics, only needing connection to the shunt and a single power input. That one has been a lot better.

 

[rogerthebodger]

I am hoping to install a volt and amp meter, but I am struggling to understand the wiring diagram:

My questions are:

1. What is the square box 'Load'?
2. The thin red and black wires connect to the fusebox?

Disconnect the wire from the battery negative to the negative bus bar at the battery and connect to the left hand side of shunt on pic.

Connect a big wire from the battery negative terminal to the right hand side of the shunt.

Connect the "thick yellow" wire from the meter to the left hand side of the shunt.

Connect the "thick black" wire from the meter to the right hand side of shunt.

Connect a red wire from the positive bus to the "thick red" wire on the meter.

Connect the "thin black" wire to the negative bus.

Connect the 'Thin red" wire to the positive bus through a low amperage fuse or circuit breaker.

Hope this helps.

 

[Jokani]

Thanks Rogershaw, I am at the boat this weekend, I'll let you know how I get on.

 

[mikefleetwood]

could be heading for a "triple lakesailor" here - just need to check the rules!

 

[VicS]

Thanks Rogershaw, I am at the boat this weekend, I'll let you know how I get on.

But even Roger does not know how your boat is wired.


Make sure that all the circuits you want to measure the current flow in are connected to battery negative via the shunt.

I suggest that excludes the engine negative which will also probably mean that the alternator output is not measured either ... but the module in question does not appear to measure charge as well as discharge current. For the same reason, if that is so, i'd not make negative connection from the battery charger, solar panel or wind turbine through the shunt either. take them all directly to the battery negative

 

[Bodach na mara]

Roger's suggestion will not set your boat on fire but will not work as there is no connection to the load. You will have no voltage drop across the shunt as no current will be flowing through it. Let us take a step back and redefine some things.

Firstly, if the device is to function as a battery usage monitor, the "load" is everything that uses power from the battery. The shunt is, as has been said, a low, calibrated, resistance which causes a small voltage drop when any current is drawn from the battery. The value of this resistance will be a fraction of an ohm. For example I have an ex-WD meter with FSD 0.075 volts at 60 amps. The shunt for that has resistance of 0.075/60 or 1.25 milliohms. The negative busbar is a terminal block to which the all the negative wires for the boats circuits are connected along with the negative of the battery. There may also be a positive busbar but many boats make do with a single unit that contains the fuses and main switches to all the circuits. There will also be a main isolating switch, often located between battery negative and busbar. The engine starter is not usually within this circuitry but is wired to the output of the main isolator and to the battery positive.

Assuming you have a negative busbar, the wire from battery negative to busbar (or more likely isolating switch to busbar) is redirected to one side of the shunt and a thick wire used to connect the other side of the shunt to the busbar. Two wires connect the ends of the shunt to the meter and they should be THIN, not thick as described. One of these provides the negative sense wire for the voltage measurement.and is internally connected in the meter. Another thin fused wire connects the positive busbar to the meter positive. I have no ideawhat the "transformer" is other than an external power supply for the meter.

Finally, check whether the meter is up to the job of handling the total current used in the boat circuits. That is why the engine starter is kept outside this network.

 

[rogerthebodger]

You have a point Vic, we don't know if the amp meter displays both plus and negative current flow.

The shunt is a 100 A shunt and would be able to carry 600 amps of more (I used to have similar type of shunt in my bow thruster circuit) the meter would just show on over load. If the amp meter does not show plus and negative the usefulness would IMHO give limited info concerning the battery status.

IMHO even if all circuits currents pass through the shunt no damage would occur.

 

[VicS]

Roger's suggestion will not set your boat on fire but will not work as there is no connection to the load. .

The fist stage in Roger's instructions transfer all the load from the battery to the shunt !

 

[theoldsalt]

................... By the way, the thing labelled "transformer" on the drawing isn't.

These meters require a power supply which should not be the same as that being monitored unless an isolating transformer is used between the meter and the power supply. That is what the "DC4-30v" "Transformer" in the diagram is for.

 

[VicS]

These meters require a power supply which should not be the same as that being monitored unless an isolating transformer is used between the meter and the power supply. That is what the "DC4-30v" "Transformer" in the diagram is for.

Thats what I was afraid of. If the "transformer" is not supplied the OP will need to source one!

 

[rogerthebodger]

Thats what I was afraid of. If the "transformer" is not supplied the OP will need to source one!

Must use the old chip that was designed for battery power DVM's in stead of a PIC chips used these days .

OP could use one of the DC- DC converters from E-Bay.

 

[nigelmercier]

I'm confused by this, aren't the negative bus bar and the battery negative effectively the same thing?

Not if you have a shunt, it goes in the wire between them.

 

[halcyon]

You have a point Vic, we don't know if the amp meter displays both plus and negative current flow.

The shunt is a 100 A shunt and would be able to carry 600 amps of more (I used to have similar type of shunt in my bow thruster circuit) the meter would just show on over load. If the amp meter does not show plus and negative the usefulness would IMHO give limited info concerning the battery status.

IMHO even if all circuits currents pass through the shunt no damage would occur.

I would check my fire insurance before running 600 amps through a 100 amp shunt, @ 75mv shunt is 7.5 watt, 600 amp you get 45 watt massive overload, remember also to fit fireproof ventilated safety guard to avoid contact with shunt.

A Hall Effect shunt would solve overload and temperature problem, log reading bar graph would allow 600 amp load and 60 amp charge display, fitted with out cutting a wire.


Brian