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is it OK to use the FMA PowerLab 8 v2 with common ground for input DC and output?

Old 03-30-2011, 08:30 PM
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miernik
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Default is it OK to use the FMA PowerLab 8 v2 with common ground for input DC and output?

Is it OK to use the FMA PowerLab 8 v2 with the negative terminal of the DC input connected to the negative terminal of the charged battery?

The reason I ask is that I want to use it in a car to charge an A123 battery from the main car lead-acid+alternator circuit. Both batteries and the PowerLab will be permanently installed in the car and running permanently.

Should I connect both batteries negative terminals to the car's chassis, i.e. have a common ground, will it all function correctly?

Or should I completely isolate the secondary DC installation with the A123 battery from the main car DC circuit?

More details about the scenario: www.google.com

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Old 03-30-2011, 08:34 PM
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Thats the preferred way to use it.

You get a better contact directly to any battery, versus a common ground.

Sharing a ground would not be reccomended for dissimilar batteries.


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Old 03-30-2011, 09:04 PM
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Originally Posted by Nitro Blast View Post
Thats the preferred way to use it.

You get a better contact directly to any battery, versus a common ground.

Sharing a ground would not be reccomended for dissimilar batteries.
Well, now I am confused, because the last sentence contradicts with the first two.

So sharing ground is a good idea, but only if the source and charged battery are similar batteries? How do you define similar? Similar in size or chemistry or ...?

And what in multiple-source scenario, i.e. car alternator + lead acid battery + rectified mains power through an AC-DC power supply - I would sometimes have all three connected together as a source (+ maybe even a solar panel as a 4-th source). The destination will be always a A123 battery which will be used to power everything in the vehicle, lights, computers, even the vehicle itself after I convert it to a electric hybrid vehicle.

In that case should/can/may/rather-not/must-not have common ground on both sides of the FMA PowerLab 8 v2?

What are the pros and cons of common/isolated ground on that scenario?

If it should be separate ground - which ground should be on the car chassis - source ground or A123 pack ground?
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Old 03-30-2011, 10:12 PM
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Originally Posted by miernik View Post
Is it OK to use the FMA PowerLab 8 v2 with the negative terminal of the DC input connected to the negative terminal of the charged battery?


Yes, that is the preferred way. Connect direct to battery.
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Old 03-30-2011, 10:25 PM
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I dont know if I agree with that. Notro - I think you are misunderstanding what he is asking about. he is connecting the battery being CHARGED back to the input side of the chargers ground.

Your creating a direct connection from the chargers input to the chargers output. That may or may not be good. Remember the charger steps UP or down the voltage from the car battery to match the battery being charged.

The output ground may not be at the same voltage as the input depending on how the circuitry is designed.

I would e-mail FMA support before trying that. Might save you sending the unit back in for a service call.
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Old 03-30-2011, 10:44 PM
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Larry, indeed I misunderstood his question.
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Old 03-30-2011, 10:47 PM
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Originally Posted by Larry3215 View Post
I dont know if I agree with that. Notro - I think you are misunderstanding what he is asking about. he is connecting the battery being CHARGED back to the input side of the chargers ground.
Yes, but only the negative terminals (black wires), not the red wires of course!
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Old 03-30-2011, 10:51 PM
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Originally Posted by miernik View Post
Yes, but only the negative terminals (black wires), not the red wires of course!
I understand, but I would still contact FMA support before trying it.
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Old 03-30-2011, 11:05 PM
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Originally Posted by Larry3215 View Post
I understand, but I would still contact FMA support before trying it.
I thought this forum is FMA support. I got here through a link in the lower left corner of http://www.fmadirect.com/
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Old 03-31-2011, 12:32 AM
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Originally Posted by miernik View Post
I thought this forum is FMA support. I got here through a link in the lower left corner of http://www.fmadirect.com/
Hi:

You're in the right place. Give me a little while to get you an answer.

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Old 03-31-2011, 02:15 AM
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Originally Posted by Tim Marks View Post
Hi:

You're in the right place. Give me a little while to get you an answer.

Tim Marks
Hi:

Asked the chief engineer about this. He says no. You can't connect the output battery ground to the input supply ground. The charger won't be able to read current.

Tim Marks
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Old 03-31-2011, 02:35 AM
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Originally Posted by Tim Marks View Post
Hi:

Asked the chief engineer about this. He says no. You can't connect the output battery ground to the input supply ground. The charger won't be able to read current.

Tim Marks
Ah ha
The Cellpro charger looks like its current sensing resistor is located in the negative lead for the battery under charge.
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Old 03-31-2011, 02:39 AM
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Originally Posted by Tim Marks View Post
Hi:

Asked the chief engineer about this. He says no. You can't connect the output battery ground to the input supply ground. The charger won't be able to read current.

Tim Marks
Another question for Cellpro.

My new Cellpro Prolab 8 has what looks to be a clear plastic protective sheet covering the complete top of the unit. (A little corner is lifting off.) The two binding posts for power output are installed over the plastic sheet.

I hesitate to pull it off, and have all the labels come with it! If it is a protective covering, might just leave it on until it falls off, but would be nice to know exactly what it is.
Thanks!
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Old 03-31-2011, 05:51 AM
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Originally Posted by kyleservicetech View Post
Another question for Cellpro.

My new Cellpro Prolab 8 has what looks to be a clear plastic protective sheet covering the complete top of the unit. (A little corner is lifting off.) The two binding posts for power output are installed over the plastic sheet.

I hesitate to pull it off, and have all the labels come with it! If it is a protective covering, might just leave it on until it falls off, but would be nice to know exactly what it is.
Thanks!
Hi:

This is protective material. It is intended to be removed. The label will not come off when you remove this. The label adhesive is very aggressive. Whether you elect to remove or not, the choice is yours.

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Old 03-31-2011, 06:32 AM
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Originally Posted by Tim Marks View Post
Hi:

This is protective material. It is intended to be removed. The label will not come off when you remove this. The label adhesive is very aggressive. Whether you elect to remove or not, the choice is yours.

Tim Marks
Hi Tim
Thanks, your quick response is very much appreciated. Have a good day!
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Old 04-01-2011, 03:01 AM
  #16  
miernik
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Originally Posted by Tim Marks View Post
Hi:

Asked the chief engineer about this. He says no. You can't connect the output battery ground to the input supply ground. The charger won't be able to read current.

Tim Marks
Thanks. That makes me ask another question: are the input and output sides of the charger electrically isolated from each other (i.e. the high frequency transformer of the SMPS inside is the only link between the input and output sides), or are there direct wire connections, which would mean they are not isolated?

To rephrase it in more directly: is the charger an isolated or a non-isolated DC to DC converter?

I ask from a safety perspective in a permanent installation.
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Old 04-05-2011, 06:10 PM
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Originally Posted by miernik View Post
Thanks. That makes me ask another question: are the input and output sides of the charger electrically isolated from each other (i.e. the high frequency transformer of the SMPS inside is the only link between the input and output sides), or are there direct wire connections, which would mean they are not isolated?

To rephrase it in more directly: is the charger an isolated or a non-isolated DC to DC converter?

I ask from a safety perspective in a permanent installation.
Hi:

The power section topology is buck/boost. It is not isolated. Isolation can be achieved with an external flyback topology DC to DC converter at the charger input. The PL8 input current limit can be set to match the DC to DC converter. The FUIM3 PC interface is opto isolated to 2000 VDC.

Tim Marks
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Old 04-06-2011, 03:44 AM
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Originally Posted by Tim Marks View Post
Hi:

The power section topology is buck/boost. It is not isolated. Isolation can be achieved with an external flyback topology DC to DC converter at the charger input. The PL8 input current limit can be set to match the DC to DC converter. The FUIM3 PC interface is opto isolated to 2000 VDC.

Tim Marks
Check out this power supply.
http://www.mpja.com/prodinfo.asp?number=18404+PS

I've got one, they are not cheap, but they are rated for 24 VDC, 25 Amps output. And their output is isolated from the 120 VAC input.

So, if you've got 120 VAC available, an extra few hundred dollars, and a pair of the Cellpro 8's this would do it. Putting this all together will require a dedicated 15 Ampere circuit breaker on your 120 VAC outlet.
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