Volt meter recommendation please

tudorsailor

tudorsailor

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On my last trip, I discovered that the starter battery for the generator was almost flat. It would not start the genny. I now think I would like to have a voltmeter on the electrics panel to tell me the state of the generator starter battery. Ideally I would like to press a button the show the battery status rather than have a constant read out - and therefore battery drain Can anyone recommend a voltmeter and source?
Thanks

TudorSailor
 
This one is good from Radio Spares
You could put a switch in the circuit if you wish.

R365625-13.jpg
 
You have received some rather elegant solutions to a simple voltmeter query and I doubt even Vic would put his hand in his pocket for one of those marine voltmeters, coo, how the rich live lol. They do look nice though.

I went for a simple solution personally, I wanted to be able to monitor the voltage from across the boat or via a quick glimpse at the panel, this meant analogue was my only factor. As the boat is fairly dry I could go for a none marine instrument if that suited and it did in the end...

I went to CPC and picked up a pair of these, though it appears the design may have changed as mine include numbers, it may be worth talking to them to confirm if this is indeed a change in design.

42251396.jpg
 
I have fitted a digital one from ebay across my auxillary batteries.

It is powered from the supply it is measuring and will operate on any supply of over 8 volts.
It reads to two decimal points. The actual absolute acurracy is much less relevent than the repeatability and resolution.

It is infinately better than an analogue display.

I have fitted a switch to connect it to the emergency back up battery if required.

Normaly the backlight is off but I can switch it on if required.

The voltmeter was quite innexpensive.

Iain
 
Higher resolution at lower cost, easier accurate reading by a non technical person and non mechanical nature of the display.

This is only for this specific application.

On some applications an analogue display is infinately better especially when the voltage source has some ripple on it.

Also the reading on an analogue display can be absorbed much quicker than a digital reading. If the reader can understand what he is looking at.
An analogue voltmeter does not always require a seperate power source to drive the display

But, as I have said a digital display is much more accurate reading at nuch lower cost than an analogue display

Iain
 
OK, lots of suggestions here, but from them you can see one of the basic problems of analog instruments. You can either have range or precision but not both. That is why the "battery condition monitors" have some fancy design electronics (all right, a zener diode in series) to cut off the bottom of the range. Because if the battery voltage is below 10 there is something seriously wrong, and most of the time you are only interested in readings between 12 and 15 volts.

For that reason, I prefer a digital cheapo meter set on the 20 volt scale. It gives 0.01 volt precision, whereas an analog meter covering 12 to 15 volts will be lucky to have precision of 0.2 volts. And the digital one covers the whole range down to zero. And yes, I do know the difference between precision and accuracy. I lectured on it for over 40 years!
 
The reason I ask is in this installation when is your battery fully charged, 12.75v or 12.76v is it flat at 11.57 or 11.54?

I don't think on a boat we require accuracy of the magnitude you describe, 11½v to 12½v is plenty adequate to keep a good watch over the batteries. Digital might look nice at first but pretty soon I think I would tire of having to read off the voltage and do the mini calculations in my head as to where it is within the charged band of the battery.

It is not as though I am averse to using different types of test equipment, I have used a stupid amount in my time, I suppose you might describe me as a pro, I much prefer moving coil over LCD.

*** figures above given as example only and not to infer that 11½ to 12½ are the true working band of a leisure battery, but I am sure someone will still complain......
 
The CPC analogue is ok if you check with no load, and assume a vertical pointer is your minimum battery state. This would give you a minimum capacity of approx 50%, in use it would be harder. The problem is large scale, so not accurate as 75% of the scale is not used.

Digital, gives you a accurate voltage reading, but you need to interprit them. As a battery has a voltage range for no load settled, on charge, and on load, this then varies by amperage, tempreture, age, how maintained, how charged, airpressure, etc. So though accurate, it is a approx guide again.

Brian
 
Yes I prefer analogue instruments myself. I am of the old school. Started my electronics apprenticeship around 1956.

But it is much easier teling SWMBO or other non technical crew that if the reading drops below 11.xxx then the eberspecher or hair drier cannot be used without the engine being started or shore power being connected.

It is much easier for them to understand a digital reading than reading an analogue meter.

If it was just myself an analogue meter would be fine.
 
That is really interesting as I honestly would have thought it the other way around.. yet this thread suggests that a none technical person would struggle with an analogue reading more than a digital.

I am not trying to prolong an argument, I honestly find it fascinating that I have probably wrongly assumed the simplicity issue and have it back to front. Maybe I am too close to it so can not see it from the other side.

I will certainly try to be more understanding in future and consider fitting digital to assist my very not technical mrs dogwatch. I am currently looking for ammeters to monitor my solar panels and had assumed I would fit analogue dials, now I will have to have a good think about it.
 
I can't see that myself - there's two requirements here.

The user wants a Go/NoGo with at best a third option of send for the fixit man.

Techie-man wants display that gives him repeatable, accurate information of specific parameters that he can compare to benchmarks.

So, either an accurate and precise analogue display show voltage gradations but with a red/yellow/green sector or:

A digital display which allows techie to interpret battery status and condition but which also shows Red/Yellow/Green for the Go/NoGo/GoGetaGrownUp scenarios.
 
For what you want, an analogue display is ideal. You'll possibly find that there is a connection point on your generator control panel for a meter.

However, it's all well and good knowing you have a flat battery but:

a) What are you going to do if it is too flat to start the engine?
b) Wouldn't you rather not have a flat battery in the first place?

I have taken a wire, through a resistor, from my main domestic battery to the generator battery positive (the negatives are connected). I can't remember what value I used but it was a wire-wound of several watts and I probably chose 100mA max when the genny battery is 12.0 and the house battery is 13.6. Say around 16 Ohms. Then, assume that you have a very flat genny battery for some reason, with a volts drop of 10V across the resistor, Power = V**2/R = 100/16 = 6.25W. The exact values are very non-critical, as you can see.

This will not work unless the negatives of the domestic and generator batteries are already connected. Fischer Panda generators are isolated and you should not bond them together unless you really know what you are doing as you could end up with electrolysis problems. Other gensets might be the same, I don't know.
 
My domestic system is 24 volt, so I cannot join them to the generator battery.
When the genset battery went flat, I jumped off the engine battery (with the engine running).
What I really want to know is when to run the generator to charge up its own battery. Most of the marinas in Mallorca have shore power so I rarely use the generator. When I needed it this summer, the battery had flatten just enough to crank without starting the generator. Had I known the generator battery was becoming flat I would have charged it up.
I will also buy a car battery charger so I can charge the battery when I do have shore power.
Thanks for all the posts with useful links to panel meters
TudorSailor
 
No voltmeter on my boat either but one of the display options on my Furuno GPS includes a a digital Input Volage reading. Hardly the main reason for having a GPS but the information you require is there for free. Use the battery change over switch to see the voltage output from each battery. Don't know if all GPS sets provide display of voltage input.
 
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