wiring 2 loads up in in parallel to drop voltage (ed: he means in series)

[ebee]

We are discussing two (or, possibly, more) strings
in each 6 V "device"
with the "strings" in each 6 V "device" connected in parallel
but
with the two 6 V "devices" connected in series,
across 12 V .

One may have a "failure" of one "string", causing the problem.

Consider the situation below

If there are Four equal "Resistance" Strings
connected in "Series/Parallel"
with R1 and R2 being the "LED Strings" in one Lamp
and
R3 and R4 being the "LED Strings" in the other Lamp.

Normally, there will be 6 V across all resistors.

However. if R1 "fails" (Open Circuit)
the Voltage across R2 will increase (to 8 V)
and
the voltage across R3 and R4 (in parallel) will decrease (to 4 V.)


View attachment 311172

I once did something like that in a factory - The "Resistors" were actually 32ohm impedance speakers for an intruder alarm system. The factory was usually occupied by 1 to 5 staff at varying times of the day. There were 4 speakers scattered about to ensure that the "Door chime" facillity was audible throughout the factory and the equipment manufacturer had specified 16ohm speakers x 2 maximum (in parallel) for the system. So if there was a failure in any speaker or its wiring either short circuit or open circuit then the remaining 3 speakers should still work acceptably and not put undue stress on the system. I did run this past the equipment "technical department" first ( you soon learn that the "Technical Department" of many big firms nowadays is not actually an engineer who did or could design things but merely somebody who is trained up to read from a card or flow chart.
A neighbour of mine was a Plumbing and Heating Engineer and wanted to operate the controls in a slightly non standard manner. As I was at the same premises doing the electrics he asked my opinion. I gave him a few pointers. He then contacted the equipment tech dept and I could hear him getting into a confused conversation.
He was talking to a lady, after a while he said something not PC - "Please can I talk to the Technical Bloke?" . I heard her reply as she had raised her voice to him "I AM the TECHNICAL Bloke!" was the reply.
Oh dear, she obviously had quite a good knowledge of the many technical aspects of the systems and common problems and solutions but not sufficient insight to vary from what is written on a card, I thought.
"Oooh Derek, you should not quite have said that!" I said to him after the call ended.

 

[Harry Bloomfield]

I though Diodes where there to force electricity in one direction only

Better to think of a basic diode, as a one-way valve, allowing current flow in only one direction. Zenor diodes, are a special type of diode, which begin to conduct at a set voltage. Thus they can be used as a low current voltage regulator.

 

[bernardgreen]

are a special type of diode, which begin to conduct in the opposite direction at a set voltage.

 

[Harry Bloomfield]

Obviously, I was trying not to over-complicate explanations.

 

[JohnW2]

Do you mean if one load has more amps then the other?

How exactly can two loads in series have 'different amps' flowing through them?

If you have two resistances in series then put a voltage across them they will draw current according to the total resistance of those resistors combined.
If those resistances have quite similar values then they will quite similar voltages across each one (approx equal to half the total voltage applied across them).
If, however, their resistances are more unequal then the voltages across each one will be more unequal too but the current drawn by them will be the same as each other.

That's exactly what I've been saying.

So engineering tolerances and other variables make each resistance not quite the same but when doing calculations we might ignore those differences if we consider them to be quite small depending upon how we want to use them. If the differences are relatively not quite small we might want to re-evaluate the voltage differences produced. It just depends on how much difference we might expect it to make to our finished result and what effect it might have.

Exactly. Again, I have essentially implied that.

If two resistances are connected across the voltage in parallel then the opposite happens ....

Yes, we know that, but it's not what we're talking about.

I think I must be missing something, since you don't seem to be saying anything that I (and others) have not already said and/or implied.

Kind Regards, John

 

[ebee]

Yes John we were saying the sane thing. I was merely trying to explain it slightly differently.
Ps - the first bit about the amps was AstonHall not me

 

[JohnW2]

Yes John we were saying the sane thing. I was merely trying to explain it slightly differently.

Fair enough.

Ps - the first bit about the amps was AstonHall not me

Ah - that hadn't really occurred to me. It would have helped if you'd used the forum's quoting facility, because I thought you had written that yourself and (in view of what you had quoted), I thought it was directed at me

Kind Regards, John

 

[LeeJC]

Couple of guys called Kircchoff and Thevenin did some work on this kind of stuff a little while ago now I think.
They both confused the hell out of me so I ended up using superposition and then chopping it up to fit the chaps above theories.

 

[JohnW2]

Couple of guys called Kircchoff and Thevenin did some work on this kind of stuff a little while ago now I think

They did, and others.

They both confused the hell out of me so I ended up using superposition and then chopping it up to fit the chaps above theories.

None of it is really much more than 'applied common sense'. People often find analogies with hydraulics (i.e. water, pressure, flow, pipes and pumps) quite helpful.

Kind Regards, John

 

[AstonHill]

What you say is strictly true but, as I've implied, if it were me I'd probably first try the simpler/cheaper approach of just putting the lamps in series - and I strongly suspect that that would work fine.

Kind Regards, John

Forgot to say; I only bought the one lamp. But there where lots in stock so when I go to Aldi Friday I will buy the other, if there are no objections to this not working

 

[ebee]

Nobody has mentioned the age old "Which lamp grows brighter" (You put bulbs in gardens. You put lamps in lampholders) .
Variations of the question use two "bulbs" or four bulbs etc etc.
Ok so you take some mains bulbs of 40W, 60W and 100W and wire them in series, which will glow brighter (if at all), if it helps you can increase the voltage.

 

[blacksheep]

Excuse to play around with regulators ie https://cpc.farnell.com/stmicroelectronics/l7806cv/v-reg-6-0v-7806-to-220-3/dp/SC08342

 

[ebee]

Yep good old regulators 12V, 9V, 5V and 1.25V in my armoury, all of those you can boost voltage up a bit or use as current regulators too.

 

[blacksheep]

Used to find them on old boards years back lol

 

[JohnW2]

Nobody has mentioned the age old "Which lamp grows brighter" (You put bulbs in gardens. You put lamps in lampholders) .

So some people now say!

However, as I often point out, as a result one now sometimes has to "put lamps in lamps" - and that tends to totally confuse the staff in retail establishments

Kind Regards, John