Voltmeters

Submitted: Saturday, Oct 27, 2007 at 12:19

ThreadID: 50947 Views:3525 Replies:8 FollowUps:4

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Steve from Top End Explorer Tours

I am building a battery compartment in my CT and would like to install voltmeters as there will be 2 batteries in parallel.

My question is if I want to know the volts of the batteries individually do I need one or two meters EG: one meter on one and one on the other, or will one meter be enough.

Thanks in advance.

Steve.

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Reply By: Footloose - Saturday, Oct 27, 2007 at 12:38

Saturday, Oct 27, 2007 at 12:38

Do you have an isolator or just in parallel full time ?

AnswerID: 268613

Follow Up By: Steve from Top End Explorer Tours - Saturday, Oct 27, 2007 at 12:48

Saturday, Oct 27, 2007 at 12:48

I will probably isolate them.

Steve.

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Follow Up By: Geoff M (QLD) - Saturday, Oct 27, 2007 at 19:15

Saturday, Oct 27, 2007 at 19:15

If you isolate them, you will need either 2 voltmeters or 1 voltmeter and a 3 way (on/off/on) switch..

Geoff

FollowupID: 531338

Reply By: Member - John T (NSW) - Saturday, Oct 27, 2007 at 12:39

Saturday, Oct 27, 2007 at 12:39

Afternoon Steve,

I'm no auto electrician but I think you should be able to get away with just 1 meter - wiring it via an "on - off - on" 3 way type switch. Switch is wired to both batteries and the meter can be switched between the two.

I've got 2 batteries in parrallel in my CT and I'm going to do the same thing eventually - but will use a multifuction meter - sorta thing Derek from ARB has in his shop.

I trust someone more knowledgable than me gives some advice too.

Cheers

John T (Lifetime Member)
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AnswerID: 268614

Reply By: Member - Franga (QLD) - Saturday, Oct 27, 2007 at 12:41

Saturday, Oct 27, 2007 at 12:41

Steve you could use one volt meter and a double pole switch to switch from one to the other.

Regards Franga

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AnswerID: 268616

Reply By: Footloose - Saturday, Oct 27, 2007 at 12:51

Saturday, Oct 27, 2007 at 12:51

Whatever you use and however you do it , remember to fuse both wires at the battery. Nasty to be seeing smoke as you bounce along the corros :(((

AnswerID: 268619

Reply By: glids - Saturday, Oct 27, 2007 at 13:54

Saturday, Oct 27, 2007 at 13:54

Hi Steve,

You will need to isolate the batteries before taking your reading, otherwise you will take voltage of the parallel pair - not necessarliy individual voltages.

Depending how you wire it up, you may or may not need the on-off-on switch referred to by others, but that is most likely the easiest way.

Also, it is my understanding from other references that when you isolate the batteries (ie separate them) you need to allow the voltage(s) to stabilise for 20 to 30 minutes before taking your readings. Without doing this, your volt readings will tend to be the combined (parallel) voltage. You could test this by taking the reading while connected in parallel, then immediate readings on the individual batteries after disconnection, then repeat individual readings after 5 min, 10 min, 20 min etc - Note: the batteries must not be under load or charge when you do this. Any change in voltage could indicate one of the batteries is suspect - the more the two battery voltages remain the same, the closer the 2 batteries are matched in state of charge.

Remember that the voltage reading is only an indication of state of charge. A hydrometer reading of the electrolyte is more accurate.

Hope this helps.

cheers,
glids

AnswerID: 268624

Reply By: Member - Jim S (NSW) - Saturday, Oct 27, 2007 at 14:54

Saturday, Oct 27, 2007 at 14:54

Hi

If the batteries are permanly connected in parallel then there is no way you can measure the voltage of each as they act as one battery in this mode .... If you install an isolating switch between the batteries then you can use a change over switch to measure each battery voltage with only one voltmeter ...

Hope this is of help.
Cheers
Jim

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AnswerID: 268628

Reply By: Mainey (WA) - Saturday, Oct 27, 2007 at 16:22

Saturday, Oct 27, 2007 at 16:22

Steve
If the 12v batteries are permanently connected in parallel .... they are technically only ONE large battery.

They deliver the same voltage (12v) but obviously double the Amps, no longer being two individual batteries.

To check them individually you would have to "totally" disconnect them from each other, and all their electrical connections, and wait at least '3' hours to allow each battery to return to it's own individual State of Charge, with-out any assistance or interference from the other battery, or their electical loads and also the chemical reaction with-in the two batteries to subside.

Would only be doing this check if I thought there was a definite problem...
I use 2 x DC AGM's attached in this way, but they are charged by Solar and the Solar reg shows all the Amps & Voltages, there is also a 10 Amp ->Ammeter link: <- MA-1010 Ammeter installed between the "battery" and the Reg, it shows ALL Amps going both directions, into or out of the "battery" at all times as well as a 12v Voltmeter installed as follows

attach the (+) lead to the (+) terminal of FIRST battery
then the (-) lead to the (-) terminal of the SECOND battery
wiith THICK cable & solid connections between the two batteries

How will this "battery" be charged ??

AnswerID: 268635

Follow Up By: Steve from Top End Explorer Tours - Saturday, Oct 27, 2007 at 16:52

Saturday, Oct 27, 2007 at 16:52

Hey Mainey

I can only charge with a 14 amp charger with either mains or gen-set, this is all I have.

I have a New 130 ah US battery, a generic 75 ah (old) and a New 55 ah generic battery all Deep cycle.

I was going to put 2 in parallel as I have an Old 47 lt Engel to use as a Freezer and a brand new Eva Kool 68 lt as a Fridge.

Now while they were in the car I will run them of a duel battery system joined to the old 75 ah battery while driving and when the car is stopped they can still run with out fear of a flat battery the start battery being isolated.

They should for an over night stay keep running.

When I am stopped for more than a day and set up, I would run them on the ones in the camper over night as they would be removed from the car, when able to run them on 240V mains or Gen-set while charging the batteries from the mains or gen-set.

The main reason for the Voltmeter was to check that they were fully charged, as of this afternoon I also have a Hydrometer.

They will be hard wired.

I hope someone can make sense of this as I am only guessing.LOL

Cheers Steve.

FollowupID: 531301

Follow Up By: Mainey (WA) - Saturday, Oct 27, 2007 at 22:24

Saturday, Oct 27, 2007 at 22:24

Steve,
Like you I also hope someone "can make sense of it" for you lol
So let's assume I understand . . .

You have a dual battery system with an 'old' 75ah DC battery ?

If you run a fridge in the vehicle, replace the 'old' 75ah with the 'new' 130ah DC battery, run thick cable via an Anderson plug and a fuse 'system' each end to the two smaller DC batteries both wired together in Parallel in the Camper.

That way the new 130ah DC always gets charged from the Alternator when driving, when the other two are connected via the Anderson plug, all batteries will be charged as one (1) battery by the Alternator.

If nothing of high Amp drain is used in the vehicle, leave the 'old' 75ah battery in the vehicle and put the 'new' 130ah wired in parallel with the 'new' 55ah battery in the Camper.

If the 75ah battery is in good condition and holds it's charge ok you will have no hassles, if not, then dump it, if in doubt get it tested.

Just because a battery is 'old' does not make it bad or no good, my present Cranker was originally my Calcium Deep Cycle storage battery for 4 + years, and it's now well over 5 years old.

You should have the higher battery capacity where the highest drain fridge/freezer is situated, so it can be supplied adequately.

FollowupID: 531383