How to tell how much juice is left?

[Bundyman Lurker Find all posts View Profile Close Bundyman]

Is a simple digital volt meter a reliable way to measure how much energy I have left in my auxiliary/dual battery when running my fridge?

I have dedicated 12v outlets with heavy cable in the back of my 150 D4D and would like to be able to quickly determine the amount of "juice" (not very electrically savvy!) left in the battery, especially when sitting at a camp for a few days.

Any advice/comments very welcome.

And I do have one of the Aussie voltage boosters on order!

[drivesafe Senior Member Find all posts View Profile Close drivesafe]

Hi Bundyman and good to see people supporting Australian Made.

Here is a chart you can use to get a fairly good idea of the State of Charge of your battery while you are using it.

NOTE, a voltage reading of a battery while your motor is running is useless but if while camping, and you have a small load connected to your battery, like a compressor fridge, a voltage reading can be comparatively accurate, at least enough to tell you whether you have heaps of capacity or you're are about halfway though your capacity or that your battery is low and in need of a charge.

[K & M McF Senior Member Find all posts View Profile Close K & M McF]

Used to use this till I found a cheap meter on Ebay. Worked for many years okay.

[Bundyman Lurker Find all posts View Profile Close Bundyman]

Thanks for the info drivesafe and K&M!

I am looking at a simple "plug into one of my spare 12v outlets for the fridge" devices that measures voltage and will give me a estimate of capacity of my battery.

Perhaps something like this when combined with drivesafe's voltage table:

http://www.ebay.com.au/itm/PROJECTA-...item19cc746dfa

I presume that the best measurement would be with the engine off and the fridge compressor working?

cheers

[drivesafe Senior Member Find all posts View Profile Close drivesafe]

Hi again Bundyman and anything that uses a cigarette power socket to source a voltage reading from is next to useless.

The problem is that the factory wiring to most power sockets is so thin, it causes a considerable amount of voltage drop, particularly if there is the slightest load, like your fridge, connected anywhere else to the same circuit.

The voltage drop can be as much as a volt or more, making any form of reading a waste of time.

The ONLY place to take a reading is at the battery terminals.

Sorry to be such a wet blanket but there are gimmicks and there is the correct way to do things, you just need to know what works and what just looks good without any real benefit.

[Bundyman Lurker Find all posts View Profile Close Bundyman]

Hi again Bundyman and anything that uses a cigarette power socket to source a voltage reading from is next to useless.

The problem is that the factory wiring to most power sockets is so thin, it causes a considerable amount of voltage drop, particularly if there is the slightest load, like your fridge, connected anywhere else to the same circuit.

The voltage drop can be as much as a volt or more, making any form of reading a waste of time.

The ONLY place to take a reading is at the battery terminals.

Sorry to be such a wet blanket but there are gimmicks and there is the correct way to do things, you just need to know what works and what just looks good without any real benefit.

Thanks for the info.

I was planning to plug it into one my my dedicated fridge outlets that are wired with heavy cable directly from my auxiliary battery.

If this cable minimizes voltage drop to run my Waeco correctly could the volt meter then give me more useful data?

Or should I just pop the bonnet and use a multimeter on the aux. battery?

cheers

[drivesafe Senior Member Find all posts View Profile Close drivesafe]

Hi Bundyman, I know the amount of voltage drop sounds a bit far fetched but while your fridge is running, try measuring your battery’s voltage and then measure the voltage at your fridge.

Even with thicker wire, you still get a decent voltage drop between the battery and the fridge, and the further the fridge is, cable wise, from the battery the greater the voltage drop.

Again, try measuring your own set up and then decide if the amount of voltage drop is with in your expectations.

[Bundyman Lurker Find all posts View Profile Close Bundyman]

Thanks Drivesafe,

Looks like I have a bit of experimentation to do. Hopefully with the voltage booster and a decent meter I might be able to determine how much juice my aux. battery has when running my fridge.

I hate warm beer!