Series V Parallel Question

[tyebud]

First off, thank you for entertaining my ignorance.

I've got this dual LED bicycle light design turning over in my head. I'm still having a hard time grasping the fundamentals of how the draw works wiring series compared to parallel.

If I have two SSC P7 emitters connected in series, and the driver is driving 1400mA, does that 1400mA get split between the two LEDs or is it 1400mA per emitter? How would this work wired in parallel?

I haven't been able to find a good understandable source for figuring this out, so if you all have any links, or want to share your understanding, I'd really appreciate it.

Thanks
T

 

[LukeA]

With a 1400mA driver and 2 emitters in series, each emitter will see 1400mA. The whole thing wil work as long as the voltage remains high enough to satisfy the total voltage drop of the string. In parallel, each emitter will see approximately 700mA. Resistors should be used to make sure that the current is spread evenly across both emitters.

Some drivers are capable of handling series of LEDs. One such driver is the Kennan from Kaidomain. However, that driver is intended for use with single-junction power LEDs, of which the P7 is not one. It would work, but the P7 would be very underdriven.

Some very helpful information would be the source voltage and type of the intended battery.

 

[half-watt]

for the purposes of your question regarding current flow in series v. parallel ckts, just think on the following analogy:

current flowing through a wire (and electrical/electronic devices) is similar to water flowing through a pipe.

given your series emitters, if they were, for the purposes of illustrative analogy, hydraulic devices (valves, turbines, etc) in series would the water split between them, or would the same water that passed through the first hydraulic device in series also pass through the second one?

obviously, it would NOT split in this analogy. however, if the pipe forked or had a 'T' section (to service hydraulic devices in parallel, for instance), then the water would split in some fashion (i.e., equally or unequally) and each device would only see a portion of the water passing through the main pipe leading up to the 'T'.


for the purposes of your question, it's as simple as that.

hope this illustrative analogy helps some.

 

[tyebud]

Thank you for your response.

So if I have a driver pushing, say 1 amp, to the two LEDs in series, each LED will be getting about half of that amp, correct?

If I had the LEDs wired in parallel, would the LEDs be receiving 1 amp each but at half the voltage?

 

[TMorita]

First off, thank you for entertaining my ignorance.

I've got this dual LED bicycle light design turning over in my head. I'm still having a hard time grasping the fundamentals of how the draw works wiring series compared to parallel.

If I have two SSC P7 emitters connected in series, and the driver is driving 1400mA, does that 1400mA get split between the two LEDs or is it 1400mA per emitter? How would this work wired in parallel?

I haven't been able to find a good understandable source for figuring this out, so if you all have any links, or want to share your understanding, I'd really appreciate it.

Thanks
T

Imagine each LED as a little water turbine that spins and generates light.

If you wire the two turbines to a water source in parallel, then half the water (current) flows through each turbine. Each one gets the full water pressure (voltage) though.

If you wire the two turbines to a water source in series, then all the water (current) goes through each turbine, but each turbine only receives half the water pressure (voltage) .

Toshi

 

[tyebud]

Imagine each LED as a little water turbine that spins and generates light.

If you wire the two turbines to a water source in parallel, then half the water (current) flows through each turbine. Each one gets the full water pressure (voltage) though.

If you wire the two turbines to a water source in series, then all the water (current) goes through each turbine, but each turbine only receives half the water pressure (voltage) .

Toshi

Ok that makes a little more sense to me.

So if I want to run 2 of the P7s - supposedly 4.2V, 740 Lumen @ 2.8A - in series at 50% (370ish lumen), I would need a driver that pushes 1.4A @ 8.4V?

 

[TMorita]

Ok that makes a little more sense to me.

So if I want to run 2 of the P7s - supposedly 4.2V, 740 Lumen @ 2.8A - in series at 50% (370ish lumen), I would need a driver that pushes 1.4A @ 8.4V?

No.

When the water turbine is in series, each one receives only 1/nth the water pressure (due to back pressure), but all the water needs to go through each water turbine.

Toshi

 

[steve6690]

Ok that makes a little more sense to me.

So if I want to run 2 of the P7s - supposedly 4.2V, 740 Lumen @ 2.8A - in series at 50% (370ish lumen), I would need a driver that pushes 1.4A @ 8.4V?

Actually I think that's right. You want to supply 1400ma to each Led. If you wire them in series then the current will be the same at any point in the circuit so you need a driver that will output 1400ma. In series though, the voltage drop across each device would be added together so the voltage provided by the driver in your example would be 4.2 x 2 = 8.4

 

[Calina]

Ok that makes a little more sense to me.

So if I want to run 2 of the P7s - supposedly 4.2V, 740 Lumen @ 2.8A - in series at 50% (370ish lumen), I would need a driver that pushes 1.4A @ 8.4V?

Yes, that's exactly it.

 

[Gomer]

No.

When the water turbine is in series, each one receives only 1/nth the water pressure (due to back pressure), but all the water needs to go through each water turbine.

Toshi

You forgot frictional losses

 

[tyebud]

Thank you everyone!

I spent all day trying to get my head around the basics of series v parallel, and thanks to you guys, I've got it now.

I've also realized that the P7s are NOT what I want, but that's neither here nor there.

T

 

[TMorita]

Yes, that's exactly it.

Ah, sorry...he is right. I missed the "at 50%" part of the original message.

Toshi