Let's Make Robots!

Batteries Series Parallel

A few questions to make sure I don't burn something up. I am playing around with different batteries and ways to make my bots last longer between charges. I want to ensure I have this right before I hook anything up.

First off lets assume I have 5 volts hooked up to a LED (max rated current of 30milliamps) using a 150 ohm resistor (5 volts divided by .03 amps = 166 resistor to keep LED from burning out).

Series: Lets say I take a 5 volt battery pack and hook it up in series making the total voltage 10 volts.

Assumption: The LED will burn out due to the increased voltage. I need to use a 330 ohm resistor to keep ir from burning out (10 volts divided by .03 amps = 333 ohms).

Parallel: Lets say I hook up a 5 volt battery pack in parallel making the total volts still 5 but doubling the amperage (also how long the LED will stay lit until the battery can no longer keep the LED on.

Assumption: No change required the 150 ohm resistor will keep the LED on and it will stay lit approx twice as long as the first scenario with the one 5 volt battery.

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Did we ever answer the question you had?
In a round about way. After I finish the project I'm currently working on I will need to use this info to make my next one. Everything has been delayed with everyday life crap.

I forgot about the re-wire. Yes, when I changed the tool from 110 to 220, I did have to change some wires going to the motor. Windings, yadda yadda.

At any rate, the all things being equal thing is right on and I sorta missed the point on this one. 

I'm sticking with, You can suck amps, not shove them.

That kind of reasoning would lead to renaming a "resistor" to "allower". I think the property of "Allowance" ought to be measured in Ampere per Volt.

I'm sticking with ya bro!

or more strictly speaking: a "Conductor", Symbol G, unit Siemens (S).

I can see why that never caught on outside of universities. Does not surprise that someone beat me to it.

Conductor vs Resistor is kind like Voltage vs Current Supplies, isn't it, lingo-wise?

I'll subscribe to that view.

Of voltage and current sources being close to logical inverses of each other. Perhaps not entirely correct, but it helps me keep my sanity ;)

I dunno man,

My dust collector for my shop pulls almost a full 20 amps at 110-120vac. I rewired it for 220v and it draws 10amps. Double the voltage, 1/2 the current. Is this an AC/DC thing?

If you just plug a 110vac motor into 220V (single phase to two pase) then assuming the insulation could handle the increase in voltage the motor would most likely draw close to twice the current and fried.

Since your house hasn't burned down (is that smoke I smell?) I'm assuming that the dust collector is designed to be changeable between different voltages.

In that case twice the voltage and half the amperage = 2x0.5 = 1 = the same power used as before.

Presumably when you rewired it it had two windings that you changed from parallel to series or else it has two sets of windings and you changed from one to the other.


In jklug's description there was no rewiring. The experiment there was all about "all things being equal...".

When you rewired the machine for a higher voltage, you did purposily (albeit unwittingly) prevent what Oddbot is describing: doubling the current, quadrupling the power dissipation.