Volt and amp metre connection

Submitted: Monday, Dec 26, 2005 at 13:41

ThreadID: 29170 Views:11277 Replies:5 FollowUps:1

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JB Patrol

Hi,

I have a camper trailer with two 6 volt batteries coupled to produce 12 volts. I have a volt metre and an amp metre I wish to install to monitor the voltage and amps.

I am not sure how to install these. I believe the volt meters connects eith side of the battery, + & -.

The amp metre I am not sure of, it has a bridge on ther back of the gauge connecting positive and neg. it then has a positve cable and a negative cable connected to the rear of the metre as well.

I am guessing i need to break the positive cable leading to the battery and insert the positive side of the amp metre and the negative side straight to ther battery. Is this correct. If so How do i connect the positive side. When I break the positive side to the battery, do i then connect it to the positve side of the metre, then from the metre back to the battery.

I hope this makes sense

Thank You

John

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Reply By: MartyB - Monday, Dec 26, 2005 at 14:50

Monday, Dec 26, 2005 at 14:50

Hi John,
You are right with the voltmeter.
With the ampmeter, take the cable off the pos battery terminal that leads to your outlets. Connect this cable to the neg side of the bridge on the back of the ampmeter. Connect the pos bridge of the ampmeter to your pos battery terminal. In other words all the load runs from the the pos battery terminal through the ampmeter to your outlets. Also you need to have a fuse or circuit breaker on all pos cables from your battery. A good place to have this is between the battery & the ampmeter.
from Marty.

AnswerID: 145603

Reply By: JB Patrol - Monday, Dec 26, 2005 at 17:05

Monday, Dec 26, 2005 at 17:05

Hi Marty,

Thank You for your prompt responce. If I may ask, The Positive lead going to the battery is the + line feeding from my trailer plug to charge the batteriess in the camper trailer. Do I run this positive wire to the negatie bridge side of the amp metre and another positve wire from the postive side of the metre to the + side of the battery.

Thank You
John

AnswerID: 145608

Follow Up By: Member - Roachie (SA) - Tuesday, Dec 27, 2005 at 09:15

Tuesday, Dec 27, 2005 at 09:15

John,
I would say that the power input cable from the vehicle should still go directly to the trailer battery terminal. You are trying to monitor the amps which the various accessories are using (which has nothing to do with what the car is putting in).
So, on the + battery terminal you should have

(a) the car's input cable and an output (via a self resetting fuse...aka "fusible link" or "circuit breaker") then onto

(b) the + post of the amp meter.....with neg leading onto the accessories (if you have quite a few things to run, it would be adviseable to use a multi-post fuse block here too).

(c) the voltmeter

In practice (in my camper trailer's case), I have not bothered with the amp meter as I don't believe they are really necessary to have. Also, in my particular case, I have a Narva 6 post fuse block and use one of those posts to get power for the voltmeter, rather than hooking it straight up to the + post of the battery. I also have an on-board 240v battery charger, so the + terminal of my batteries (I have 2 x 12 volt in parralel) have the + cable from the charger, the + cable from the truck, and the + cable going directly to the fuse block. From the fuse block, I have cables going to the voltmeter, the fridge, the various 12 volt appliances (CD, water pump, lights etc), and another one to a double 12 volt socket in the battery compartment. That way everything is "fused".

Hope this helps; not confuses you even more...hehehe

Cheers
Roachie

FollowupID: 399186

Reply By: geocacher (djcache) - Monday, Dec 26, 2005 at 22:03

Monday, Dec 26, 2005 at 22:03

Bit of a diagram I just knocked up. I think it's self explanatory but if you have any questions please ask.

A moving coil volt meter and ammeter are the same thing essentially. Both measure a minute amount of voltage and have been modified to do what it says on the box.

The volt meter has had a higher value dropper resistor inserted inside the case to drop 12v to what ever is required to reach FSD (Full Scale Deflection) on the scale on the front.

The current meter has had a very low value resistor placed across the meter for the current to pass through. The maximum current creates a miniscule voltage drop across the resistor that corresponds to the minute voltage required to get the meter to go to FSD. Typically the voltage drops we are talking about are measured in microvolts and as such do not affect what ever you are charging or running off the setup.

Any questions please ask.

Dave

AnswerID: 145646

Reply By: Grungle - Tuesday, Dec 27, 2005 at 09:59

Tuesday, Dec 27, 2005 at 09:59

The bridge on the back of the ammeter is also refer to as a 'shunt'. Just be mindfull of its current limitation. Normally you do not see the shunt on high amperage meters mounted to the meter itself as it is difficult to route heavey duty cabling from the battery to the meter to the load. They can also generate some heat in high current situations.

Do a search on the type and model of meter you have to find out is specifications.

Normally the shunt is a stand alone device which is mounted in the -ve lead close to the battery. Battery on one side and all the -ve leads for the accessories on the other (won't give accurate results if the battery and accessories are chassis earthed). The meter is then connected to either side of the shunt and measures the millivolt changes that corresponds to different amperage flow (ammeter is just a millivolt meter). The current / millivolt relationship depends on the specs of the shunt and how accurate it is. Can be 5A/50mV, 50A/50mV (as mine is) 100A/100mV, 200A/200mV etc (check Jaycar - http://www.jaycar.com.au/index.asp search for 'current shunt')

Regards
David

AnswerID: 145684

Reply By: JB Patrol - Monday, Jan 02, 2006 at 21:29

Monday, Jan 02, 2006 at 21:29

Hi All,

I would just like to say thank you to everone that answered my posted question about ammetres.

I think I have the idea now. I need to connect ther positive side of the ammetre to the positive side of the battery and the other side to the negative side of what ever load or appliance used.

Thank You very much

John.

AnswerID: 146350