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TejanoBob
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Join Date: Feb 2007
Location: Allen, Texas (north Dallas)
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Dissimilar Parallel Voltages

11/18/2008 10:51 AM

This is probably an embarrassingly simple question, but what is the resultant voltage if a 6VDC source is connected parallel with a 5VDC source to feed a single load? Does the 6V source also treat the 5V source as if it is in need of charging?
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TVP45
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#1

Re: Dissimilar Parallel Voltages

11/18/2008 10:57 AM

Yes. It will try to charge the 5V battery to 6 V and will usually rupture the 5V battery if it has enough oomph.

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TejanoBob
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#2
In reply to #1

Re: Dissimilar Parallel Voltages

11/18/2008 11:01 AM

Thanks for the quick reply - appreciate it.
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Sparkstation
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#3

Re: Dissimilar Parallel Voltages

11/18/2008 8:52 PM

Hello TejanoBob

It does depend on the relative impedances of each source.

There are not many 5Volt batteries around.

So I am thinking that if the both sources are from Voltage Regulators, then the 5V Regulator will not supply and the total connected voltage becomes 6Volts.

If both the supply impedances are very low = Large batteries, then as TVP45 has said above, the higher voltage supply (6V) will charge the (5V) battery, and the charging current may be very large, causing the (5V) battery to heat up and/or be damaged.

Kind Regards....

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cnpower
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#4
In reply to #3

Re: Dissimilar Parallel Voltages

11/19/2008 4:53 AM

So I am thinking that if the both sources are from Voltage Regulators, then the 5V Regulator will not supply and the total connected voltage becomes 6Volts.

Hi, sparkstation,

Is this your words? Im afraid you are misleading reader.

pls check and amend it. refer to tvp45.
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TVP45
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#6
In reply to #3

Re: Dissimilar Parallel Voltages

11/19/2008 2:36 PM

Sparky,

I understand your point and agree if we're talking regulators. I based my answer on the word "charged". You can even do it with batteries and diodes, but I didn't want to go there.

I didn't blink at the 5V battery since we used to use ~5V reference cells.

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Haajee
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#10
In reply to #3

Re: Dissimilar Parallel Voltages

11/19/2008 9:37 PM

Sir a good answer.

But BOOM is too fast !

Regards
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Anonymous Poster
#5

Re: Dissimilar Parallel Voltages

11/19/2008 1:51 PM

Blowed up sir...
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Akihito Shigeno
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#7

Re: Dissimilar Parallel Voltages

11/19/2008 8:08 PM

Dear all,

If two DC power sources are required to be connected to parallel, use a blocking diode to avoid current backflow. With a blocking diode, only higher voltage power source will supply the power, while lower voltage one will not supply power but remains as a stand-by.

Regards

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StandardsGuy
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#8

Re: Dissimilar Parallel Voltages

11/19/2008 8:17 PM

Hi TejanoBob,

If you put a forward biased rectifier on each output, then you can parallel the voltage sources. A heavy load will load down both sources, and you will get current from both. The output voltage will be less than 6V because of the voltage drop of the rectifier. At heavy loads it will be less than 5V. This is not a good way to design a power supply.

Regards,

S

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whyme
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Join Date: Mar 2008
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#9

Re: Dissimilar Parallel Voltages

11/19/2008 8:36 PM

Forget about the 5 volt source. The only way it might help would be if the load pulled the 6 volt supply to below 5 volts at which point the 5 volt supply would become helpful. The problem is if the 6 volt supply is that overloaded your are in trouble anyway.
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Users who posted comments:

Akihito Shigeno (1); Anonymous Poster (1); cnpower (1); Haajee (1); Sparkstation (1); StandardsGuy (1); TejanoBob (1); TVP45 (2); whyme (1)

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