Wiring an Ammeter

[by'eck]

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

 

Yes the white wire to the alt field when broken with a switch will take out the Sterling controller. Useful to see what its doing.

 

I would not recommend SmileyPete's suggestion of putting anything in series with the red sensing wire. Just make sure its close to the positive of the battery(s) its sensing on.

[ChrisPy]

I think this entire thread is just a ploy to tempt Gibbo back.

[Arthur Brown]

RS certainly do DC ammeters up to 300 amps that's about 3KW out via an inverter, BUT these are only one way reading so need to go in either a charge or discharge wire but not a wire carrying both conductors.,

[ChrisPy]

why do all these wiring diagrams show the battery isolation on the negative side?

 

That is very poor practice.

[David Schweizer]

why do all these wiring diagrams show the battery isolation on the negative side?

 

That is very poor practice.

Why?

[Chris Pink]

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.

 

 

Would a variable resistor in the sense line enable current control of the regulator?

[smileypete]

Would a variable resistor in the sense line enable current control of the regulator?

Well the battery voltage sense line ideally shouldn't carry any current, as current means voltage drop which affects it's accuracy. A check with the 10 amp range on a digital meter would verify this.

 

Maybe you're thinking of internal regulators with an extra field wire connected to an external regulator. Reducing the current in this wire with a power resistor would control the field current and it turn the output current, until the output voltage drops far enough for the internal regulator to take over.

 

Thinking about the other thread on a burnt out alternator, maybe this is the danger with external regulators as by driving the field current externally they can bypass the internal regulators temperature protection (if any!).

 

To avoid this, maybe a button thermostat on the alternator body connected in the field wire could help. Alternator gets too hot and it cuts the external regulator out, so the internal one takes over.

 

But I wouldn't be surprised if poor ventilation and maybe slipping fanbelts greatly increase the likelihood of a burn out.

 

While on the subject, copper has about a 0.4% per °C temperature coefficient, so going from 20°C to 120°C the resistance goes up about 40% and so heat losses double, as P=I²R. So a hot alternator pushing out 100A is creating twice as much heat in it's windings as a cold alternator pushing out 100A, give or take...

 

cheers,

Pete.

Edited January 28, 2012 by smileypete

[Keeping Up]

why do all these wiring diagrams show the battery isolation on the negative side?

 

That is very poor practice.

 

That's how it always used to be done, because you could isolate multiple battery banks with a single switch. It does have one other tiny advantage, in that once the switch has been isolated then you can short circuit either battery terminal to the hull (accidentally and with a spanner being the usual way) and there will not be any sparks.

 

On the other hand as you say it is now generally regarded as not being best practice.

[David Schweizer]

That's how it always used to be done, because you could isolate multiple battery banks with a single switch. It does have one other tiny advantage, in that once the switch has been isolated then you can short circuit either battery terminal to the hull (accidentally and with a spanner being the usual way) and there will not be any sparks.

 

On the other hand as you say it is now generally regarded as not being best practice.

As you say putting the isolation switch in the negative to hull cable is the way it aways used to be done

 

Is the current bad practice assertion beacause it the statement is continuously repeated, or is there actually a technical/ or safety reason?

Edited January 28, 2012 by David Schweizer

[Keeping Up]

As you say putting the isolation switch in the negative to hull cable is the way it aways used to be done

 

Is the current bad practice assertion beacause it the statement is continuously repeated, or is there actually a technical/ or safety reason?

 

There are two reasons that are usually quoted. Gibbo wrote them down on his website so I won't describe them here at any length

 

The first is that IF there is a path from the hull to the battery negative by virtue of everything being covered in dirt and grease, then when the switch is isolated you will get corrosion current flowing through the hull. True, but my response to this is DON'T let everything get covered in dirt and grease.

 

The second is that some equipment gets upset if it tries to start up when its negative lead is broken. Well my boat doesn't have any such equipment. Gibbo mentions that expensive control-panel/battery-monitor combinations can get damaged. Given that his company was set up to manufacture and sell expensive battery monitors, and that the website existed purely to support that purpose, then I do wonder if .... (heretical thought censored)

 

I reckon that it is nowhere near as definite as people say. It is quoted as an advantage of switching the positive that you can isolate one battery bank while the other remains connected; I personally place that capability in the "disadvantages" camp for safety reasons, which I believe makes the arguments nearer 50/50. Others here will probably disagree.