Author Topic: 5V isolation  (Read 4160 times)

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Offline niekproductions

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5V isolation
« on: October 08, 2013, 01:02:03 am »
I have a panel current meter that requires 4-10V DC and an isolated ground. I'd like to power it from the battery it's measuring, how would I go about isolating it?

I thought about using a 1:1 transformer, but I couldn't find one in my junk bin.
 

Offline Simon

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Re: 5V isolation
« Reply #1 on: October 08, 2013, 01:10:45 am »
you can't use a transformer on a battery or any DC current. why must the ground be isolated ? are you sure about this ?
https://www.simonselectronics.co.uk/shop
Varied stock of test instruments and components including EEVblog gear.
Also, if you want to get ripped off: https://www.ebay.co.uk/usr/simons_electronics?_trksid=p2047675.l2559
 

Offline niekproductions

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Re: 5V isolation
« Reply #2 on: October 08, 2013, 01:24:59 am »
why must the ground be isolated ? are you sure about this ?

I am sure about it. The meter uses a shunt. When I power the meter from the same battery I'm measuring, it shorts out.
 

Offline Rigby

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Re: 5V isolation
« Reply #3 on: October 08, 2013, 01:35:37 am »
Back up.  What are you trying to do?  What's your goal?  You're trying to measure the battery with a device powered by that same battery.  Why?
 

Offline niekproductions

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Re: 5V isolation
« Reply #4 on: October 08, 2013, 02:38:11 am »
Back up.  What are you trying to do?  What's your goal?  You're trying to measure the battery with a device powered by that same battery.  Why?

Okay,
I have a robot. Inside, it has one 7V lead acid battery. I purchased a panel current meter with four wires: two for high-side current measuring and two for the meter's power. Because the grounds are connected together and it's on the high side of the battery, it will short out via the shunt.

I don't have enough space to fit a second (small) battery.
 

Offline MinK

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Re: 5V isolation
« Reply #5 on: October 08, 2013, 02:39:08 am »
Try to power your measurement gadget from separate battery or you can use insulating DC-DC converter. I guess nn2-05s05s might work.
or maybe you can use other measurement device, some sort of analog-digital converter. Micro controller typically has analog digital converter embedded.
« Last Edit: October 08, 2013, 02:42:22 am by MinK »
 

Offline andtfoot

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Re: 5V isolation
« Reply #6 on: October 08, 2013, 02:45:14 am »
You can't just connect the shunt on the other side of the load so the grounds are common?
 

Offline zapta

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Re: 5V isolation
« Reply #7 on: October 08, 2013, 03:05:29 am »
Can you provide a link to the datasheet of that panel meter?
Drain the swamp.
 

Offline niekproductions

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Re: 5V isolation
« Reply #8 on: October 08, 2013, 03:31:06 am »
You can't just connect the shunt on the other side of the load so the grounds are common?

Doh!  :palm:

Can you provide a link to the datasheet of that panel meter?

It's this meter http://www.adafruit.com/products/574.
I don't know why I decided to wire it on the high side.. Probably why I posted it in 'Beginners'  ;D
 

Offline WarSim

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5V isolation
« Reply #9 on: October 08, 2013, 03:35:48 am »
Relay
 

alm

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Re: 5V isolation
« Reply #10 on: October 08, 2013, 05:22:49 am »
It's this meter http://www.adafruit.com/products/574.
I don't know why I decided to wire it on the high side.. Probably why I posted it in 'Beginners'  ;D
From that page:
Quote
Another option is to have one circuit power the meter while it is sensing the same circuit. To do this, you'll need to make sure that you are low-side sensing. This is because the ground power wire is connected to the black current sense wire.

Relay
???
 

Offline Janaha

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Re: 5V isolation
« Reply #11 on: October 08, 2013, 07:52:30 am »
Hy.

Sorry, you already buyed that pannel meter like me. I felt in the same bug hole and i also have some of the lying around here.

I learned that i must search for a pannel meter that supports a common ground. I found some on ebay, but they a a bit pricier than those simple pannels without the ability to share a common ground. ( The searchterm i used to find these is : panel meter common ground )

I just locked on ebay and found those here as an example. eBay auction: #220918151290

Those pannels are working even in those situatios where you whant to have them sharing a common ground with the "power" you want to measure.

Greetings
Janaha
 

alm

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Re: 5V isolation
« Reply #12 on: October 08, 2013, 07:57:14 am »
Did you actually read the Adafruit page?
 

Offline niekproductions

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Re: 5V isolation
« Reply #13 on: October 08, 2013, 11:25:54 pm »
Did you actually read the Adafruit page?

I bought the thing from a reseller, so I didn't see that  |O

Relay
???
:-//
« Last Edit: October 08, 2013, 11:27:53 pm by niekproductions »
 

Offline zapta

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Re: 5V isolation
« Reply #14 on: October 10, 2013, 04:13:00 pm »
The adafruit page has this schematic that shows how to measure low side current while powering the meter and the load from the same DC supply.



It is similar to these kind of in series meters that are popular with remote control models.

http://www.rcgroups.com/forums/showthread.php?t=311574
Drain the swamp.
 


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