Electrics - Voltmeter/ammeter gauge advice

[Sulliy]

Hi there
Newbie to this site, so please forgive any stupid or duplicate questions!

I have recently bought a small cabin motorboat and just in the process of stripping it in and giving it a good clean/tidy up.

Question is - whilst I have access to instrument panels/battery...etc and easy to run cables, I am just wondering would it be useful to have a voltmeter or ammeter gauge (or both) fitted to show state of battery when at rest and in use? I have seen some boats with these, but not sure how necessary they are?

And at present, my automatic bilge pump is connected to battery via instrument panels, therefore when boat is moored and not it use, I will have to leave the isolater key in battery. I would like avoid this and have direct cable from bilge pump to battery (so avoiding instrument panel)

How complicated is this? I am not that great with electrics, so could ask boat-electrician to do this

Thanks for any advice.

 

[DaveS]

Seems a shame not to have any answers, and to a first post too, so...

While not essential, both a voltmeter and an ammeter can be informative. Assuming you've got a 12V battery, you'll only be interested in voltages in the 11V to 15V range, so either a limited scale analogue volt meter (vehicle type) or a digital volt meter makes sense. Wiring is simple: a pair of wires from the volt meter to the measurement point (typically positive to output terminal of main switch, negative to common negative terminal / bus bar; in line fuse at source of positive wire). If choosing a digital volt meter ensure that it is happy to take its internal power from the sense leads: earlier models needed an independent (usually dry battery) supply.

An ammeter will probably mean installing a current shunt. With a simple system with short wiring runs you could use a full load ammeter (providing the wiring is arranged so that it does not see cranking current) but, because it is connected in series, a failure of the ammeter, its wiring or terminations will result in complete loss of power and potentially endanger your alternator. A centre zero analogue ammeter makes it easy to distinguish charge / discharge; with a digital ammeter you need to establish a convention: +ve values = charging, say. In either case if it's reading the wrong way round just reverse the wires.

If you are going to install a current shunt then it might be worth thinking of installing one of the combined battery monitors - the Nasa models are probably cheapest, but there might be concerns about appearances, e.g. if the other instruments are currently round dials you will probably want to match these.

To allow your automatic bilge pump to operate with the main switch open you could move the positive supply wire to a fuse supplied either from the positive battery terminal or the supply terminal of the main switch.

 

[Stu Jackson]

Here's how ammeters and shunts work: http://c34.org/bbs/index.php/topic,6032.0.html

 

[ostell]

I had one of these on my last boat and am about to fit another onto my new (to me) boat. It does give a useful indication of the state of the batteries, though, as with any other measurements, it needs interpretation.

Ridiculous price asked by caravan places but look around.

 

[VicS]

Good simple explanations of basic electricity and circuits can be found in the "Boat Electrical Notes" on the TB training website
Perfect for someone "not great with electrics"

There is also a section on voltmeters and ammeters.

You may find the type of voltmeter Ostell mentions, with an expanded scale, more useful for assessing battery state of charge than one with normal 0-20volt scale. Known usually as battery condition meters.

 

[vyv_cox]

I bought a digital voltmeter/ammeter from an internet site a couple of years ago. It's the small rectangular meter at the bottom of the panel. The small switch to its right toggles between volts and amps. I must say it has proved to be invaluable and I wouldn't be without it. I paid about £30 for it but that company has now gone bust.

I have recently bought a similar one from one of the many Hong Kong sellers on Ebay. It was delivered promptly, no problems, and cost £25. The switch on this one is built in. It's not fitted yet but hopefully it will be just as good as the other one.

These are not the simplest of instruments to install. The shunt goes in the earth return to the engine/batteries and it took me some time to find all the earths from the various services and make sure they went through the shunt. I assume it needs an alternator with its own earth rather than one that earths through its casing. However, well worth the effort.

 

[ditchcrawler]

I bought a digital voltmeter display like the above off E bay for 9 quid.It is a simple 2 wire fixing and works very well.A friend has one for each battery but I can read either set of batteries via the 1/2/both switch.

 

[stevensuf]

there are plenty on ebay for 2-6 pounds

 

[William_H]

Instrumentation

I would say that a volt meter is your primary need. It will give you an idea of battery state and confirm alternator is charging. If you go in for deep cycling your battery with domestic loads and then running the engine to recharge the battery an amp meter will tell you when engine running for battery charge has become not so worth while. You can see when charge has diminished. good luck olewill

 

[sailinglegend420]

...... If you go in for deep cycling your battery with domestic loads and then running the engine to recharge the battery an amp meter will tell you when engine running for battery charge has become not so worth while. You can see when charge has diminished. good luck olewill

Yes it is a waste of fuel and engine run hours just to charge the last 15-20% of the battery - BUT - at least once a month you must get 100% charge back in to stop sulphation. A battery is fully charged when the charge current is 0.5% of the Ah capacity at an absorption voltage not a float voltage. So a 200Ah bank will be taking 1 amp of charge. A digital ammeter is cheap and will tell you just what is happening, but this level of charge is usually only possible with many hours on shorepower or a very large solar panel bank.

 

[Dabhand]

Thinking outside of the box, have you considered a fishfinder?
Certainly most, if not all Garmins have a digital voltage display which can be permanently shown on the screen along with all the other information about depth, bottom details, water temperature etc.
You may or may not be interested in finding fish but it is useful to see what is underneath, especially if you want to drop an anchor (or are about to run aground). A depth sounder is a valuable navigational and safety aid. I think prices for basic models are about £80 to £100.

 

[Sulliy]

Thanks for the advice and help. Loads of things to think about and many ideas kicking around in my head
Thanks everyone