Add Not: Parallel ???

[Randy Gross]

This question has to do with the wiring of 2 12vdc batteries in parallel. I
know the voltage remains the same. The question here arises with the
current:

Does the current add at some point or,

Does it just mean that the setup is capable of supplying a certain current
for a longer period of time? (Increase the Duty)
--

An Inquiring Mind
Randy Gross
----------------------------------------------------------
<') >< Homebuilt Arc Welders >< ('>
http://www.gomedia.ca/~aaawelder/
Chance favors the prepared mind whose hands do the work!

 

[John Popelish]

Randy Gross wrote:

This question has to do with the wiring of 2 12vdc batteries in parallel. I
know the voltage remains the same. The question here arises with the
current:

Does the current add at some point or,

Does it just mean that the setup is capable of supplying a certain current
for a longer period of time? (Increase the Duty)

Batteries have an internal resistance that uses up some of the voltage
when current passes through the battery. This resistance limits the
maximum current the battery can deliver into a short circuit. The
internal resistance effectively is the load resistance under that
condition.

Paralleling two batteries effectively parallels their internal
resistances. This allows both higher peak current for a given amount
of voltage sag, and also allows longer delivery of all currents
because the total amp hour capacity of the two batteries are combined
to deliver the load current.

--
John Popelish

 

[K Wind]

"John Popelish" <jpopelish@rica.net> wrote in message
news:3F4C379C.1D1E526F@rica.net...

Randy Gross wrote:

This question has to do with the wiring of 2 12vdc batteries in
parallel. I
know the voltage remains the same. The question here arises with the
current:

Does the current add at some point or,

Does it just mean that the setup is capable of supplying a certain
current
for a longer period of time? (Increase the Duty)

Batteries have an internal resistance that uses up some of the voltage
when current passes through the battery. This resistance limits the
maximum current the battery can deliver into a short circuit. The
internal resistance effectively is the load resistance under that
condition.

Paralleling two batteries effectively parallels their internal
resistances. This allows both higher peak current for a given amount
of voltage sag, and also allows longer delivery of all currents
because the total amp hour capacity of the two batteries are combined
to deliver the load current.

Isn't it true that batteries above ~6V should not be wired in parallel
unless a diode is used for each, so current from one battery can't flow into
the other? It's my understanding that the terminal voltage will never be the
same.

I wrote Duracell and asked the question. Here is their response:

<quote on>

Yes, batteries can be wired in parallel to increase capacity. It is not
recommended that batteries be wired in parallel to increase current
capability. If batteries are to be wired in parallel they should be from
the same date code/lot code to insure that they are matched. We recommend
that no more than 2 batteries be wired directly in parallel however,
series/parallel combinations are generally OK up to 4 cells in series with
two series strings in parallel. Beyond that, diodes are recommended.

<quote off>

Ken

--
John Popelish