MICTUNING double voltmeter

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Ok, seemed cheap, ordered one on Ebay to test and open up. Arrived today.

So, open it up and here's some observations.

1) Draws about 7mA (depending on combination of segments on the leds, e.g. 13.8 will draw more than 11.1, less segments lit on 11.1).

2) Accuracy is decent, if voltage is say 12.44V it will display 12.4V, if voltage is 12.46V it will display 12.5V. Same accuracy both channels. This measured with a precision powersupply/meter.

3) Not particularly bright since the 'frosted' lens does attenuate the light output, but then it also improves segment contrast.

4) The unit stock will operate if either MAIN or AUX has power connected. It uses a simple Diode-OR circuit to combine either battery to run the regulator in the unit. Easy to remove the Aux diode if desired and then the unit will only operate if there is power on the Main input (i.e. ignition switched Main input).

5) Benefit of removing the Aux diode is that if you feed the Main input from ignition switched, then the display/unit will turn off when you turn the key to off. Current draw from the Aux battery in that case is only 0.2mA, and obviously 0mA from the main since there is no power with ignition turned off.

So, here's the modification process. The unit can easily be opened by pushing 2 clips on one side in and then 2 clips on the other side in and the back cover slips off. NOT ultrasonically welded close etc - so 'mod' friendly.

Pictures:

vm_stock.jpg


vm_dioder.jpg


vm_drm.jpg


vm_drmb.jpg


To remove I just added a little solder to the soldering iron tip, heated one end of the diode then the other, then back again and then it slipped off the board. Easy to add back in if ever desired.

Overall picture:

vm_all.jpg


cheers,
george.
 
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George could this be used to monitor the individual batteries in a 24v bank?
 
cruiserdan said:
George could this be used to monitor the individual batteries in a 24v bank?
Click to expand...

Well, sorta/kinda :)

The mictuning type product has a single 'ground' so all measurements are common to that ground.

You could wire the MAIN input lead to the 24V side of the 2 battery stack. Wire the AUX to the 12V 'center' tap.

The unit would then display the total pack voltage on the MAIN display and the low 12V battery on the AUX display. You would then need to do mental arithmetic to subtract the 2 readings to know what the high 12V battery is at... Though you're a similar vintage wine as me - and we preceded all these new fangled calculators/smart phones and can do simple arithmetic in our head unlike many of the young'uns... :lol:

cheers,
george.
 
I kan indeed math stuff like that on the fly...:lol:

I have noticed that when I use my digital diagnostic meter the individual battery voltages when added together do not reflect the same voltage the combination reads. IE battery A may read 12.65 and battery B may read 12.86. This adds up to 25.51 volts and the combined voltage read by the same meter may be 25.2 volts. Odd.
 
cruiserdan said:
I kan indeed math stuff like that on the fly...:lol:

I have noticed that when I use my digital diagnostic meter the individual battery voltages when added together do not reflect the same voltage the combination reads. IE battery A may read 12.65 and battery B may read 12.86. This adds up to 25.51 volts and the combined voltage read by the same meter may be 25.2 volts. Odd.
Click to expand...

What kind/brand/model of meter are you using? A HF unit or something a 'bit' better :)

I assume these are static/no-load readings (no engine running/accessories etc)?

If you have stuff running then the 'combined' voltage is including voltage drops in the wiring (predominately the cable runs from the + of the 12V low battery and the - of the 12V high battery). This would lead to a lower voltage displayed across the two batteries + wiring versus the sum of the two direct readings right at the +/- posts of each battery....

cheers,
george.
 
My "kick-around" meter is in beter than HF and it's no Fluke :). My measurements have been with the vehicle at rest and the only load I know of is the OEM clock. The battery-to-battery cable is new OEM with pretty red covers.:hillbilly:

Note, no evil center-tap present.:wrench:
20170518_191541.jpg
 
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Very pretty hookup. Nice short cables between the 2 bats. Yep, center taps on 24V systems are evil. But then I hate 24V systems and spent several weeks and some $ converting my old 24V patrol to 12V. I'm a much happier fellow now - simplifies my universe a lot when out bush...

Anyhow, with no load an measuring across the 2 bats as a 24V readying versus measuring each 12V and adding should give the same results. I would highly suspect your meter having a non-linearity between a lower voltage reading of ~12V versus higher ~24V readings... Or your arithmetic has had a hickup :)

cheers,
george.
 
My math is solid as a kidney stone so my meter needs an up-grade:hillbilly:
 
Does the switch still work with the aux diode removed? With normal operation before the mod, is there a middle position on the rocker?
 
^ There is no 'switch'. It looks like a switch, but it is just 2 LED displays - you can see from my photos the LEDs etc - that is what you see on the front of the unit.

Basically IF there is voltage applied to MAIN/AUX/GND it will display that voltage, no voltage applied and the unit is obviously off.

The diode removal mod just stops the unit from running if there is no MAIN/GND applied voltage (i.e. it is fed from after the ignition switch).

cheers,
george.
 
Ah, ok. The link I provided described it as a rocker. That sucks. It would be great if it was so you can switch it up to see the main then down to see the aux. The search continues...
 
^ huh? The unit can display both the MAIN and AUX battery at the same time. It has a top row LED and a bottom row LED (each displays xx.y) for the voltage of each battery simultaneously. They are also labeled MAIN and AUX on the front of the unit.

Better than having the extra complexity of a rocker switch to select on or the other...
vm_full.jpg


cheers,
george.
 
The "rocker" description comes from the manufacturer calling the hole it fits in a "rocker switch opening".
 
george_tlc said:
^ huh? The unit can display both the MAIN and AUX battery at the same time. It has a top row LED and a bottom row LED (each displays xx.y) for the voltage of each battery simultaneously. They are also labeled MAIN and AUX on the front of the unit.

Better than having the extra complexity of a rocker switch to select on or the other...
vm_full.jpg


cheers,
george.
Click to expand...
yes, got that but what I was talking about is and actual rocker switch. up is main middle is off and down is aux. that way its not on all the time and you can see it when you want to...
 
Well, do the mod I described and wire the MAIN input to ignition switched +12V. Then it only operates when the ignition is on/engine running. All automatic and you don't need to remember to switch it off or which position the (non-existent) rocker is in.

Anyhow, I think it's quite good as is once you've done the mod.

cheers,
george.
 
George can we revisit the 24v bank usage. If I have digested correctly everything you have outlined I think it sums up something like this:

Pull the diode out.
Ground the gauge to the chassis.
Feed the gauge aux + leg with a center-tap.
Feed the gauge main + leg with switched 24v bank power.

Powered up the "main" reads total bank and the "aux" reads the lower battery.

I understood you to say that there is a continuous, albeit slight, current draw on the aux battery. Is that still the case here?
 
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