Tuesday, October 16, 2018

Today's Electrical Question

I suspect that I learned this in high school physics 1973-74.  But Nixon was President, so I likely forgot.

You have a 3VDC source (two AAA batteries); you add another 3VDC source to the same wires.  Do they add, or do you only get 3VDC?

STOP!  I have more evidence of how smart my readers are, dozens of answers in agreement.  Alas, mechanical issues rendered my idea impractical.  The Crossbow Equatorial Platform  runs on two AAA batteries (remarkable since it is moving more than 100 pounds of telescope at one revolution per day.  It is good for 120 hours, but you must remember to turn it off when you are done.  The switch is in an awkward position, so easy to forget at the end of the evening. 

I was thinking of hooking up the 12 VDC power source that I use for the Sky Commander through a 12 VDC to 3 VDC gadget that I assembled from parts.  Turn off  the power source when closing up for the night, and the switch does not matter.  But the problem with both cables is that as the telescope turns it winds the cables around the base.  I even thought of bungee cording the power pack to the side of the telescope base so it rotates with the telescope and the Sky Commander, but the platform does not rotate, so the cable to the 12 VDC to 3 VDC converter will wind instead.  Besides, the power pack is very heavy and affects operation of the platform.  I may consult with my wife, who is very good at spatial conception.

I can live with batteries on both electrical parts; replacing 12VDC and AAA batteries after forgetting to turn them off isn't really that hard.

32 comments:

rick said...

If they are stacked end-to-end (series), then the voltage adds. If they are next to each other (parallel), the voltage stays the same but the capacity adds.

w rorke said...

In series the volts add, amps stays constant. In parallel amps add, volts stay constant. Series is when plus of one feeds minus of other Parallel is where both pluses connected together and both minuses are connected together Picture each battery as a flight of stairs.

StormCchaser said...

If you put them in series, you get 6V. If you put them in parallel, you get 3V but with more current capacity.

Series: the positive of one is tied to the negative of the other. The remaining positive and negative terminals have 6V between them.

PhaseMargin said...

If you add to the same wires without removing the connections to the original battery it's a parallel configuration and the voltage is the same 3V, but your amp-hours and endurance should roughly double.

Add the new battery in series with the old one and you add the voltages to 6V. More voltage, but amp-hours should be mostly unchanged.

(Vastly simplified because real batteries have secondary effects that vary based on type, load, etc. Designing battery chargers correctly is a royal pain.)

Random #57 said...

Parallel, you get more amps and thus watts and watt hours at 3VDC. Series, you get 6VDC. Think of all the gadgets where you put at least 2 nominally 1.5VDC batteries in series to get up to 3VDC for standard lower voltage CMOS circuitry. Only gadget I've ever come across that had batteries in parallel was a game camera, that was to give it a longer life in the field.

Wayne & Maria Johnson said...

Clayton:

How are you connecting the sources:

If you are connecting them in series (wire from the positive terminal of one source to the negative terminal of the other source, power taken from the other two terminals), you add the voltages.

If you are connecting them in parallel (connect wires from both positive terminals to the load and from both negative terminals to the load) then the voltage stays the same, but the ampacity goes up.

If you simply need more capacity, try using 2x AA or 2x C cells. It is a far more efficient way of adding capacity than paralleling 2 sets of AAA.

Wayne

KCSteve said...

In parallel, 3V with more current available, in serial 6V.

John Roberts said...

If you wire them in series the voltages add to 6V. If you wire them in parallel the voltage remains 3V.

To be extremely clear, if you put all four batteries end-to-end (positive pole of one touching negative pole of the next), with one wire touching the negative pole at one end, and the other wire touching the positive pole at the other end of the four batteries, you'll measure 6V between the wires.

If instead you have one wire touching the negative poles of two batteries, have the positive poles of those batteries touching the negative poles of two more batteries (i.e. two pairs of two batteries each), and have a second wire touching the positive terminals of the second two batteries, you will measure 3V across the two wires.

Rich in NC said...

connected in parallel - 3v
connected in series - 6v

Ed H said...

Adding another source across the wires will result in the same 3 volts. Putting the new source in series will give you 6 volts.

Tony Ross said...

Hooked up in series, wire + - + - wire, you would have 6 volts. Hooked up in parallel, + - 3v 3v 3v
+ - 3v
wire wire
it would stay at 3volts and would last longer than just one set of batteries.

Left Coast Conservative said...

If you connect the negative terminal of the new 3VDC source to the positive terminal of the first 3VDC source you have wired the sources in series, and the voltages add. If you connect the positive of the new 3VDC source to the positive terminal of the first 3VDC source, you have wired the sources in series, but of a way that they cancel out, so you have 0VDC.

Connect the negative terminals of the first and second sources, and the positives terminals of the first and second sources, then they are wired in parallel. You get the same voltage, twice the current, and faster battery death.

Will said...

If added in series, you'll have 6 volts (+ to - to + to -)
Parallel (+ to +, - to -) you get beefier 3 volts (heavier current capability).

ErolB1 said...

It depends on whether you connect them parallel or serial. If you connect them serial (plus end of the first source connected to the minus end of the second) then you get voltages adding. If you connect them parallel (plus ends together, minus ends together) then you only get 3VDC but more amperage.

Jumped Up NeoBarb said...

See https://www.batterystuff.com/kb/articles/battery-articles/battery-bank-tutorial.html

Pete said...

AAA batteries individually are 1.5 Volts, so in your example, they are wired in series to get 3 volts. Adding another battery in series will yield 4.5 Volts. If the two original batteries were wired in parallel, they would yield 1.5 volts, and adding another battery in parallel, would just give a longer-lasting 1.5 volts.

Pete said...

Oops, that wasn't your question. The answer is still much the same, though--added in series will yield a 6 volt source, and in parallel a 3 volt source.

Fidel said...

Depends if the additional source is parallel or serial

Rod Spade said...

If they are in series (the same way the two 1.5 V batteries are connected to get 3 V - the positive terminal of one connects to the negative of the other, and the current runs serially through them) then the voltage adds together.

If they are connected in parallel, it remains 3 V. You get additional current capacity and run time.

Rick C said...

Connecting in series adds the voltage. Connecting in parallel adds the current (amps).

James Gibson said...

Did you add them in series, or in parallel? If you did it in series the voltage is added to 6 VDC. But the current from the batteries is not, to double it the batteries should be attached in parallel.

Jim Horn said...

If the added source is connected to the same wires, i.e. in parallel with the 2 AAA batteries, it's still 3VDC. Such an arrangement will continue to work without the batteries if the added source can handle the load by itself.

If the added source is connected by disconnecting one of the wires from the two AAA batteries and hooking it up to the two loose ends, that's a series connection that adds up to 6VDC. Both supplies - the two batteries and the added supply - have to be there for power to reach the load.

Eighteen minutes of blank tape is optional in either case...

augustrrr said...

in sequence +-+-+- additive 3+3+3= 9v same amps
in parallel more amps

Shawn Snyder said...

If you are adding the other 3VDC in parallel, you get more amp hours, but still 3 volts. If inline, you double the voltage.

Curtis Cook said...

If you add an additional battery in parallel then it's still 3VDC. In series 6VDC.

Jeff Dege said...

Add in parallel and you still have 3V.
Add in series and you have 6V.

Eskyman said...

If you add the additional 3v voltage source in series with the other one, then you'll have 6 volts (nominal voltage.) If you put the two voltage sources in parallel you'll have only 3 volts but more current will be available to your project.

Unknown said...

If connected in series, the voltage will add. If in parallel, the amperage will add while the volts stay the same.

Jim Dunmyer said...

If you connect the additional 3 volt supply in parallel, + to + and - to -, it's still 3 volts. Connect the "new" supply's - to the original's + and you have a total of 6 volts.

Karl said...

Depends on how you add them.

If you put them in series, you'll get the sum of the two voltages.

If you put them in parallel, you'll get the same voltage, but twice the battery life.

Windy Wilson said...

Serial or parallel?
Connecting all the batteries front to back,
-~+ -~+ -~+ -~+ gives six volts
Connecting the batteries parallel to each other,
-^+
___ /-^+ \____
\-^+ /
-^+
gives 1.5 volts but (IIRC), more amps

Will said...

Rotating contact plate like that inside your steering wheel: two circular tracks with contacts or brushes that rub on them.

Alternative would be on a central shaft like a motor with commutator and brushes.