'floating' DC supply design needed

In summary, a digital panel meter needs a power supply with a negative voltage to work, and there are many options available on the internet.
  • #1
sophiecentaur
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I am going to put a digital panel meter on my boat to measure the battery volts and a few other things. For this, I need a DC power supply for the meter with a negative which is below the boat ground.

I could easily use a 9V battery and a push button to keep it on just for taking readings.
But it would be better and more satisfying to provide a supply, using the boat's 12V power. I have looked for something on the web which can give me 7 to 12V, which is what the meter needs but I only seem to find unsuitable voltages.
Has anyone any ideas, please, about a suitable chip for the job (I only need a few mA!)? I am a bit out of touch with this stuff and there must be plenty of solutions if only I could get to them.
 
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  • #2
Digikey carries a huge varety of this sort of DC-DC converters.
http://www.murata-ps.com/data/power/ncl/kdc_nke.pdf

some will operate right off 12 volt battery, but they tend to need around 10.8 volts minimum.

"""something on the web which can give me 7 to 12V, """
is that what you want to hand the meter for power, or the range you want to track battery?

a lower volt isolator and 3 terminal regulator would let it follow the battery clear down into deep discharge..
 
  • #4
Thanks for those posts, chaps.
There is a fair bit of choice there, altogether.
I'll see how I get on with the mini project. It's a bit more hi tech than most of the varnishing, cabling and drilling I seem to be doing all the time! Electronics is pretty predictable most of the time- unlike the wind (or even the tide, actually).
 
  • #5
""It's a bit more hi tech than most of the varnishing, cabling and drilling I seem to be doing all the time! ""

in S Florida i grew to like white teak and green bronze...
 
  • #6
I like to show her I love her.
 
  • #7
Older LCD voltmeters needed a power source that had a floating ground. I have one of these that works OK but it has remained unused for 20 years because of this peculiar power requirement.

You can get meters now that do not require this.

Just as an example, I have some of these :
http://www.ebay.com.au/itm/4-Digit-Digital-Panel-Voltmeter-0-33V-Red-LED-Voltmeter-/120751739881?pt=AU_B_I_Electrical_Test_Equipment&hash=item1c1d5d53e9

They are about 4.2 pounds delivered.

They run off any power source from 7 to 30 volts (so they probably use 5 volt regulators internally), and they measure from zero to 33 volts with 2 decimal place precision. Seem pretty accurate.
The power source and the measured voltage have to have the same ground. There are 3 wires that come out of the device, ground, measured voltage and positive power.
The measured voltage can be greater than the supply voltage.

They have a bright red display and take about 22 mA supply current, depending on the displayed digits.

Possible disadvantages are that they do not come with a mounting box and they can't measure negative voltages.

The same company have lots of other meters as well as a lot of cheap power supply modules.

You can get other meters that would be OK for a boat where the voltage should never go to zero:
http://www.ebay.co.uk/itm/Blue-LCD-Digital-Voltmeter-Battery-Monitor-Panel-Meter-/270911120283?pt=UK_BOI_Electrical_Test_Measurement_Equipment_ET&hash=item3f138fa39b
This one works from 7 volts upwards. Looks easy to mount.
 
  • #8
I'm fixed up now, thanks.
 

1. What is a "floating" DC supply design?

A "floating" DC supply design refers to a power supply that has no direct connection to ground or any other reference point. This means that the voltage output of the supply is not referenced to any specific point, allowing for more versatility in its use.

2. Why is a "floating" DC supply design needed?

A "floating" DC supply design is needed in certain applications where a ground reference is not available or is not desirable. This can include medical equipment, high voltage systems, and some industrial equipment.

3. How does a "floating" DC supply design differ from a grounded one?

A "floating" DC supply design differs from a grounded one in that it does not have a direct connection to ground. This means that the voltage output is not referenced to ground and can be set to any desired level within the supply's voltage range.

4. What are the advantages of using a "floating" DC supply design?

One advantage of using a "floating" DC supply design is that it allows for more flexibility in its use. The lack of a ground reference means that the voltage output can be set to any desired level, making it useful in a variety of applications. Additionally, it can provide isolation between the power supply and the rest of the circuit, providing protection against ground faults.

5. Are there any drawbacks to using a "floating" DC supply design?

One potential drawback of using a "floating" DC supply design is that it may require additional safety precautions, as there is no direct connection to ground. In some cases, it may also be more complex and expensive to design and build a floating supply compared to a grounded one. Additionally, it may not be suitable for certain applications that require a ground reference for proper functioning.

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