+-15V Split Rail from 12V Battery

Thread Starter

qrb14143

Joined Mar 6, 2017
112
Hi all,

I am working on a remote monitoring project, gathering voltage and current measurements from an off grid Photovoltaic system.

In order to measure current flow, I have selected an LEM HAIS 50s current transducer which needs a +-15V and ground supply to operate. However, the only power available to us is a 12V battery. I'm hoping someone will be able to point me in the direction of a suitable converter.

The only thing I can think of is to have two switch mode converters side by side, one converting +12V to +15V and one converting +12V down to -15V. I would prefer not to go down the road of building these from scratch! I have had a look at TIs range of converters as I thought there was bound to be an off-the-shelf solution but I've come up empty so far.

Likewise, if anyone could recommend an alternative Hall Effect sensor to the one mentioned that may be another option.
 

Dodgydave

Joined Jun 22, 2012
9,306

Thread Starter

qrb14143

Joined Mar 6, 2017
112
Hello,

Have a look at the LTC3265.

Bertus
That looks like just the thing for the job. I would be pushing it out of its comfort zone driving four transducers but I could always use two of them.

I have to say, Linear Technology know how to put together a decent datasheet :)

Thanks
 

Thread Starter

qrb14143

Joined Mar 6, 2017
112
You need an Isolated DC to dc boost converter, search ebay or other web sites for similar, choose the current limit that you need.


http://m.ebay.co.uk/itm/DC-DC-8-32V-to-9-46V-MAX-15A-150W-Boost-Converter-Step-Up-Voltage-Regulator-New-/251748599021?hash=item3a9d62c4ed:g:pKYAAOSwuMFUhQWe&_trkparms=pageci%3A1d676c5b-3caf-11e7-8bcd-74dbd180f675%7Cparentrq%3A2182ea3315c0a9c518c948f6ffffba61%7Ciid%3A5

Isolated means you can put them in series without it affecting your power supply.
So do you mean put two in series then take the middle point as "ground"?
 

Thread Starter

qrb14143

Joined Mar 6, 2017
112

Thread Starter

qrb14143

Joined Mar 6, 2017
112
Is there a specific reason you need to use a closed-loop hall sensor? They are great for high accuracy applications.

https://www.digikey.com/en/articles/techzone/2012/sep/the-basics-of-current-sensors
The sensor was selected for a few reasons....
1) It is important to us that the sensor is non invasive and can be easily retrofitted to existing systems].
2) The molex connector on the sensor is an attractive feature as it makes it easy for us to place the sensor anywhere in the system and run a cable back to the microcontroller ADC.
3)The sensor has good mechanical fixing points and is ideal for bolting onto our system.
4)We have used these sensors on a number of applications with good results, admittedly we've always powered them using a mains powered lab supply.
5) Possibly most importantly.... We have ten of them lying around!
 

nsaspook

Joined Aug 27, 2009
7,469
The sensor was selected for a few reasons....
1) It is important to us that the sensor is non invasive and can be easily retrofitted to existing systems].
2) The molex connector on the sensor is an attractive feature as it makes it easy for us to place the sensor anywhere in the system and run a cable back to the microcontroller ADC.
3)The sensor has good mechanical fixing points and is ideal for bolting onto our system.
4)We have used these sensors on a number of applications with good results, admittedly we've always powered them using a mains powered lab supply.
5) Possibly most importantly.... We have ten of them lying around!
#4&5 works for me.:D

There are many module level DC-DC converters that can handle the job, just check the power requirements.
http://www.newark.com/w/c/power-line-protection/power-supplies/dc-dc-converters/isolated-board-mount-converters-dc-dc?no-of-outputs=2-output&input-voltage-dc-min=10.8v&output-voltage-output-1=15v&output-voltage-output-2=neg15v
 

ian field

Joined Oct 27, 2012
6,539
You need an Isolated DC to dc boost converter, search ebay or other web sites for similar, choose the current limit that you need.


http://m.ebay.co.uk/itm/DC-DC-8-32V-to-9-46V-MAX-15A-150W-Boost-Converter-Step-Up-Voltage-Regulator-New-/251748599021?hash=item3a9d62c4ed:g:pKYAAOSwuMFUhQWe&_trkparms=pageci%3A1d676c5b-3caf-11e7-8bcd-74dbd180f675%7Cparentrq%3A2182ea3315c0a9c518c948f6ffffba61%7Ciid%3A5

Isolated means you can put them in series without it affecting your power supply.
The old 8 bit PC network cards had a block mounted on them which contained a +/- inverter. I forget what the output voltage was and they ran off 5V, but they're probably not the only product in the range.

Modern network gear has smaller inverters that look similar to DIL relays - probably also in a range of specifications.
 

AnalogKid

Joined Aug 1, 2013
8,534
Talk with LEM about how the part will perform on +/-12 V. If they hold to +/-15 V, then one non-isolated boost converter will turn the battery into +15 V, and another one will turn it into +15 V. If the switcher noise is a problem, then boost to +/-18-20 V and linear regulate it down.

What are the current requirements at +/- 15 V?

The buck-boost or inverting or inverting-boost configuration is a non-isolated switching stage that boosts the input 12 V to an output of 27 V, but the output is referenced to the +12 V so the output - side is at -15 V. Yes, this actually works. Several of the National Semiconductor Simple Switcher parts have the circuit in the data sheet.

ak
 
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