volt/amp meters

Submitted: Monday, May 02, 2016 at 10:27
ThreadID: 132292 Views:2288 Replies:6 FollowUps:8
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Hi Folks

Just wondering what people are running to measure their battery voltage at a glance without the need to pull out the meter?
Installed a dual battery system in a mates Hilux 2 years ago, works great. However he noticed the battery voltage was dropping very quickly.
We had installed a Baintech volt meter in the back left corner of the roller draws, this could be turned off via an adjacent switch. Putting my fluke meter on the battery showed the reading was out by .3 of a volt. Now there's a big difference between 12.5 and 12.2V. Seems the gauge had become inaccurate.
The gauge of the wire on the back of this panel if described in MM2 would require the use of powers to the -10. A true joke, the thinnest wire I have ever seen.
So just wondering what you folks that use a gauge are using?
Volt Meter

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Lyndon
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Reply By: HKB Electronics - Monday, May 02, 2016 at 10:39

Monday, May 02, 2016 at 10:39
A volt meter should ideally place no load on the circuit it is measuring, the gauge of wire used on the volt meter no doubt would be more than is required assuming the meter is located fairly close to the battery being measured. If it is mounted a fair distance away then you could use a slighlty heavier gauge of wire to connect it. Keep in mind that a suitable fuse should be installed for protection purposes, generally the manufacturer would argue that being a very light gauge wire that a fuse is not required as the wire itself will fuse, and that is ok if the wiring is installed so that it is not in contact with any flamable surface.

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Follow Up By: Member - lyndon NT - Thursday, May 05, 2016 at 07:55

Thursday, May 05, 2016 at 07:55
yes, it quite close.

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Reply By: Zippo - Monday, May 02, 2016 at 11:25

Monday, May 02, 2016 at 11:25
This under the dash. Wiring from each battery is fused.

Note I went for the extra digit, and have checked its calibration against my quality DMM's - it varies between spot-on and out by 0.01V. Switch selects cranking/auxiliary/off.
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Reply By: Frank P (NSW) - Monday, May 02, 2016 at 13:19

Monday, May 02, 2016 at 13:19
I use a Hummingbird Bluetooth battery monitor to monitor my van battery. This was installed to satisfy NSW's requirement to be able to monitor the breakaway battery.

The second battery in the tug is charged with a Ranox dc-dc charger which uses Bluetooth and an app to duplicate its display (volts, amps) on any Android device.

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Reply By: Allan B (Member, SunCoast) - Monday, May 02, 2016 at 13:43

Monday, May 02, 2016 at 13:43
Hi Lyndon,

You say that you compared the 'fluke meter on the battery' with the Baintech in the drawers and got an error.
I would bet that the Fluke was reading the higher voltage.

The question is, where is the Baintech wiring connected. Is it right on the battery where you put the Fluke or onto the vehicle wiring behind the dash or elsewhere?
To compare the meters the measurement must be taken from exactly the same point.

If the Baintech is connected to the vehicle's wiring away from the battery there could well be a small difference in the voltage at that point. If you want to accurately measure the battery voltage then you must measure it right at the battery.

The gauge of cable supplying the Baintech should not introduce an error provided that there is no other load connected to that same cable. And it should be fused with a fuse rated appropriate to the current rating of the cable. Relying on the wire itself to fuse to limit the fault current is not good practice.
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Allan

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Follow Up By: Member - lyndon NT - Thursday, May 05, 2016 at 08:01

Thursday, May 05, 2016 at 08:01
Hi Allan

The volt meter is very close to the batteries. We are minding the car for our mates at the moment but as it is full of stuff I haven't been able to measure direct off the batteries. Just from a Anderson outlet.
Only the cable supplied with the unit was used. I don't think we fused it due to the very short length, how would you fuse wire that is .1 mm2 anyway?
I guess the cable length is about 30 cm. I will do a direct battery test when he empties his car but I'm not expecting much difference in the results.
Thanks for the feed back.

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Lyndon
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For the clock may then be still

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Follow Up By: Allan B (Member, SunCoast) - Thursday, May 05, 2016 at 13:26

Thursday, May 05, 2016 at 13:26
-
0.1mm2 wire is very small indeed. It is OK if nothing more than a voltmeter is connected but very frail mechanically. Sure to break sooner or later.
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Allan

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Reply By: Peter_n_Margaret - Monday, May 02, 2016 at 13:46

Monday, May 02, 2016 at 13:46
Unless the battery has had all loads and charge sources disconnected for a while, a voltmeter is pretty useless for telling you its state of charge.

Cheers,
Peter
OKA196 Motorhome
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Follow Up By: Allan B (Member, SunCoast) - Monday, May 02, 2016 at 13:52

Monday, May 02, 2016 at 13:52
That wasn't the OP's question Peter, however what do you suggest for gauging the battery's state of charge "at a glance"?
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Allan

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Follow Up By: Peter_n_Margaret - Monday, May 02, 2016 at 15:44

Monday, May 02, 2016 at 15:44
Some solar controllers count power in and out. Our Plasmatronics is pretty good at showing a current SOC. It also displays charge/discharge rates and voltages of the battery and panels too.
Otherwise, there are battery monitors that will do that job.

Cheers,
Peter
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Follow Up By: Sand Man (SA) - Monday, May 02, 2016 at 16:55

Monday, May 02, 2016 at 16:55
I use this Nasa BM-1 Battery Monitor from ABR.
Shows either volts and amps, or Ah capacity, by the push of a button.
Have it mounted in the Van's front boot to show me at a glance what the battery condition is, whether everything is running off the battery, or confirmation of charging if connected to 240v supply.

Bill


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Follow Up By: Allan B (Member, SunCoast) - Monday, May 02, 2016 at 18:21

Monday, May 02, 2016 at 18:21
Certainly Peter, coulomb counting instruments are likely somewhat better than voltage observations but still not perfect. Those marketed to the leisure consumers do not incorporate compensation for factors such as Coulombic efficiency of the battery and internal discharges which progressively degrade the integrated reading unless regularly corrected by manual resetting. What goes in is not what you get out!
Considerably more expensive and more involved to install than a basic voltmeter which provides a reasonable indication of battery condition if interpreted with some insight. After all, voltage measurement is the parameter that "intelligent" chargers employ and it works well enough for the purpose.

I'm sure that if continued, we will confuse the OP and others as is usually the way with electrical subjects on here.
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Allan

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Follow Up By: Peter_n_Margaret - Monday, May 02, 2016 at 19:27

Monday, May 02, 2016 at 19:27
As I said Allan, the Plasmatronic unit I use is pretty good. It does include a charge/discharge inefficiency factor and the SOC read out is re set automatically, from time to time.
I mentioned it because all solar systems need a solar controller, so it may make some sense to buy something that avoids some add-ons later. The Plasmatronics units are not the only ones, but they have great back up and they are an Australian product.

Cheers,
Peter
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Reply By: vk1dx - Thursday, May 05, 2016 at 09:31

Thursday, May 05, 2016 at 09:31
Nothing extra. The meters in the dash are very easy to read with just a quick glance when moving and accurate enough to properly read when stopped. I have an old reliable multimeter in the console and if it does't "look right" in the dash then I will check it with the meter.

I really feel that there is an element of "gotta have the bling" with some people who need a cabin full of meters, dials and switches. Not all, but certainly some.

Now OT:
We did with the Kingswood back in the 60's and 70's (it was a HK) but no car after it. I basically never referred to them after a while. But they looked good and especially at night with all the different colours.

Phil
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