Best way to measure battery voltage?

[paulsmith]

I've got an analogue multimeter on the boat for simple circuit testing etc but its no good for acurate measurement of battery voltage ie its impossible to tell fractions of volts required to evaluate charge and condition of battery etc. Do I need to buy a digital multimeter
(expensive) or is there such thing as a simple meter that just measures volts digitaly as I don't need all the other functions available on a multimeter. I don't want to wire it in to the battery circuit just something with two wires I can put across the terminals when I want to check.The battery set up on my boat (a Westerly griffon) is two batteries with an off, bat1,bat2,off switch. no diodes splitters etc.Any Ideas?

 

[Steve_N]

You can get a digital multimeter in Machine Mart for £8.21 - I'm sure Screwfix et al have them at similar prices too.

 

[Anonymous]

An occasional test of battery volts doesn't help a great deal - in my Centaur (a very similar setup to yours) I installed a car-style 'Battery Condition' voltmeter across each battery bank, mounted by the companionway, where I could always see them. I could see at a glance what was happening and would highly recommend it - they do draw current, though, so put a switch in line.

 

[oldharry]

Digital voltmeters can be picked up for as little as a fiver, and are normally quite accurate enough for this purpose. Bear in mind when measuring battery condition that you will get a false reading if anything is switched on, or if the battery has been charging or discharging in the last 15 - 20 minutes. Strictly speaking a true 'quiescent voltage' reading needs the battery to have stood idle for several hours, but in practice it will have settled sufficiently within 20 minutes to give a reasonable degree of accuracy.

Altenatively fit a 5 or 6 LED 'alternator and battery tester' available from Maplins and many car stores. This will tell you at a glance if there is a problem. Many folk jumped down my throat last time I suggested this on these boards, but you know 'at a glance' whether all is well or not. If its lights are showing amber (or worse still red), then out with the DVM to find out why.....

And as I have said before, even my supremely non technical minded SWMBO (she a brilliant cook and crew though!) can warn me if the wrong colour light is showing on the panel. Last time she tried to read a DVM she told me I had 12500 volts on the battery....... hmmm!

 

[wicked]

I bought an item at a boat jumble which is ideal. It's effectively a cigarette lighter plug with a large illuminated digital voltmeter display. Does not need batteries as it is powered by the line, and you can see it in the dark. Also serves as a doubler to present two cigarette lighter sockets.

Here's a link to it on the web. It's the one at the bottom with the illuminated display.

Cigarette Lighter Voltmeter


Dave

 

[oldharry]

Know them, and have one, but find they can be quite inaccurate, because of voltage drop in the wiring and more particualrly on a worn lighter socket. Dont know who makes them though. (mine also ex Boat jumble!)

 

[VicMallows]

That's good going. Whatever the colour, I would just get ' that's your department'!

Personally I like to check the batteries at the terminals with the DVM (calibrated!) from time-to-time immediately I get on the boat after it's stood a few weeks on the mooring. I know I've currently got one nearly perfect, and the other should manage 2 years OK . Reminds me: the 'skip' battery for the bilge pump is probably due a charge.

Vic

 

[tonykerry]

Maplin sell a digital multimeter for £4.99 which should do the job. It has voltage, current and resistance ranges as well as transistor and diode tester, so covers most situations, and is often on special offer at less than this price. The description is 'Domestic Tester with Protective Holster' and the code is N20AX. Tony Kerry

 

[EdEssery]

Get a permanent view of what's going on by wiring one of these into your DC system. I have one on my domestic and my engine battery circuits - great piece of kit. Accurate to +/- 0.01V and only draws 3mA. £20+VAT from RS, part number 221-2845 and 176-4200 for the bezel if you want it.

The picture shows it as an LED but it's actually an LCD - take a look at the technical info/data sheet for the detail.

Ed

 

[gorb]

A "battery condition meter" is useful. It's just a voltmeter with a supressed zero, so that the scale goes from something like 9V to 15V. It draws negligible current, so no switch is necessary. But it would be wise to put a fuse (0.1A say) in the wire to it at the battery end to protect against faults. This solution is better than a digital meter in that it gives permanent indication and does not need an internal battery for operation.

For a double battery installation, you can either use two meters, or else one with a switch to access each battery.