# How to split a voltage source into two

1. Sep 1, 2014

### Mniazi

Suppose I have a 10kW input. I want to divide the 10kW into two separate sources, like 1kW and 9kW. What can I do to separate the input into these different ratings?

2. Sep 1, 2014

### milesyoung

What will you use it for?

3. Sep 1, 2014

### davenn

Hi Mniazi

firstly you need to understand the small error in your subject

your thread title was OK How to split a voltage source into two"
but your diagram doesn't support that

you don't have Wattage sources. You have a voltage source capable of a given amount of current

You then have 2 loads, one that requires up to 9kW (output1) and another of up to 1kW ( output2)

So my questions to you now is...
WHAT is your voltage source and how many Amps can it supply ?
can it supply a total of 10kW ?

examples may be .... 10kV @ 1A; 1kV @ 10A; 500V @ 20A

see where this is going ?

all of those sources can supply loads totally 10kW

Dave

4. Sep 1, 2014

### davenn

OK whilst awaiting your response .....

lets assume your 2 loads require the same voltage, for example lets say 500V

that means load 1 will draw 18A for a full 9kW output
and load 2 will require 2A for a full 1kW output

Having the same voltage requirement means they can be fed off the same BUSS rail
and you main concern is that the cabling supplying 18 Amps @ 500V to the 9kW load is capable of doing that
and of course likewise for the 1A @ 500V cabling

Dave

5. Sep 1, 2014

### Mniazi

Ok right now im going to school, ill come back and redefine my diagram to make everything clear! :)

6. Sep 2, 2014

### Mniazi

Ok so I have a 500 volt and 20Amp source, So if I put say an object requiring 18A and 9kV and another object requiring 2A and 1kW so can I put those two objects on the same output wire which takes 10kW without overloading either objects?

7. Sep 2, 2014

### Staff: Mentor

Probably, possibly, maybe. I'm hesitant. Your source is 500V, so whatever you connect to it must also be rated for that voltage. Are they? Your figures suggest so, but maybe they are only approximations/estimates? Is this DC or AC you are talking about?

I would encourage you to get the assistance of a properly qualified professional. 500V is not a safe area for you or anyone to experiment with electricity.

Incidently, too, it is unusual to hear an electrical device referred to as "an object". http://physicsforums.bernhardtmediall.netdna-cdn.com/images/icons/icon6.gif [Broken] Just saying.

Last edited by a moderator: May 6, 2017
8. Sep 2, 2014

### Mniazi

Sorry, im new here, im assuming it can be any voltage rating, just tell how can I split voltages into two different sources of different rating. Is that possible?

9. Sep 2, 2014

### Mniazi

Its DC voltage

10. Sep 2, 2014

### Mniazi

I am just asking a theoretical question :P

11. Sep 2, 2014

### sophiecentaur

Hang on a minute. Your posts are not quite consistent and your quantities are muddled. Do you want to add two sources of Voltage, to get a higher voltage or do you want to add the outputs of two power supplies and feed a load that works on the voltage of each power supply? Tell us the precise requirement and you may (or may not) get a feasible solution to the problem.

Without an awful lot of trouble, it is often not feasible to mix sources or loads which operate at different voltages.

12. Sep 2, 2014

### Staff: Mentor

Let's pretend you have a 10kW-rated diesel generator, supplying 500V. You wish to operate a few house lights totalling less than 1kW (rated at 500V, of course, so the bulbs don't explode), and you also want to power your custom-built 9kW air-conditioning plant (rated to operate at 500V, too). Does this resemble what you have in mind? Theoretically.

13. Sep 2, 2014

### jim hardy

A question well stated is half answered.

I cannot tell what kind of apparatus you have in mind or what you want to do with it.

I would guess from the way this one's stated that perhaps you have a 10Kw steam boiler and two small steam engines.
If that's so, just connect two pipes , one 3X the diameter of the other. Larger one goes to the 9kw steam engine and smaller to the 1kw steam engine.
If this is homework, can you answer why the 3X ratio of diameters?

..................................

Does this demonstrate the importance of investing a few minutes to clearly formulate your question ?

This is not a personal attack. Just pointing out it's a two way street - if you want help, pitch and do some of the work. Here in US we call that "Priming the pump" .
From "Global Guidelines " under Site Info at top of every page:

Well, 18A at 9KV is 162KW. That's a lot more than 10KW.
So this question is also not clearly stated .
Slow down and think before you type. It'd be a good idea for you to write your questions out longhand before going to the keyboard.

old jim

14. Sep 3, 2014

### Kavik

I'm going to assume you meant 9kW instead of 9kV here.

Are you asking if you should use something like a circuit breaker or fuse (overcurrent protection)? Here's what I would do if this was a factory power supply and not some independent generator:

A 10kW supply to me means it can provide up to 10kW of power. So you can run your 1kW device off of this supply on it's own and the supply will just provide that 1kW of power. Same deal with the 9kW device. If I wanted to run both, and they were at the same voltage, I would do what davenn suggested: Attach both devices to the main power supply bus rail with properly rated wires running to each device. I would also place a circuit breaker at the main power supply for each device. It would look something like this:

This assumes that the supply also has some type of overcurrent protection, probably ~ 20 Amps. I would also get help from an electrician or electrical engineer in person and not get anywhere near 500 Volts.

15. Sep 3, 2014

### davenn

Nice post kavik

good info, and to the OP, particular reference to your last suggestion to him .....

I would also get help from an electrician or electrical engineer in person and not get anywhere near 500 Volts.

cheers
Dave

16. Sep 3, 2014

### mp3car

Yes, Kavik's and Davenn's posts summed it up well. If you have a source capable of supplying 10kW of POWER, and you want to run two devices from this, one requiring 1kW of power and one requiring 9kw of power, then all you do is hook the two devices in parallel, each device will pull the respective wattage. If the devices have different voltage requirements, then you'll need to bring in transformers to place between the source and the device, but then of course your have loss in the transformers - a whole different discussion. Also, just like a 15A breaker at 120V can supply fractions of a watt, it can also provide all the way up to around 1800W. You can wire ten 100W bulbs and twenty 40W bulbs, all in parallel. 120V will go to each bulb, with approximately 40W to the 40W bulbs, and 100W to the 100W bulbs. if you want to say only two devices, then suppose it's a device needing 1kW and a device requiring 800W, same thing, wire them in parallel.

Bottom line, a source only provides as much wattage as the device needs, up to the current limit of the source (I won't go into what determines the limit). For example, even though a car battery can provide hundreds of amps of current, it would only "provide" 55W for a single halogen headlamp. but if you hooked up 10 of these bulbs, the battery would "provide" 550W of power. You're generally only concerned with the maximum amount of power a source can provide without having too much of a voltage drop below the required voltage (because then you end up having a drop in power as well, for example, a car battery couldn't provide nearly enough POWER in kW to run (10,000) 55W car headlamp bulbs in parallel (this would be over 45,000 amps). If you connected 1,000 55W bulbs, the voltage would drop well below 12V and you would not get the power required through the bulbs to make them come on. You would essentially be placing a "dead short" across the battery.

Power (wattage) that "comes out of" a source is all dependent on the device connected to that source. Another example is with dry hands, touching 120V house mains (i.e. voltage from a single "hot" wire to either ground or neutral) on a 15A (single) breaker vs. a 40A (also single pole) circuit breaker will give you the same exact shock, because the dry resistance is low enough that it doesn't even come close to exceeding the 15A current limiting device, which is really only there to protect wiring - YES, CBs are to protect the WIRING in your house, (to limit the wiring from becoming heaters!) and are not intended to protect anything you're plugging into it, and definitely not to protect a person. However, having a 240V shock WILL be worse because it would be roughly double the amount of current through your body because the resistance of your skin is the same whether it is 120V vs. 240V (the same for this example anyhow, different things come into play in theoretical problems and much higher voltages). Since it's your body's resistance that determines how much current goes through you - until your body gets to be a low enough resistance that you're approaching 15A through your body, then the CB would trip (theoretical differences could actually come into play, but I'm ignoring those as they are not relevant in my example).

I have rambled long enough, but if it causes any light bulbs to come on in your head (without being shocked of course :) ) or if it prompts you to ask another question, then my rambling was worth it :) It is a wonderful thing (I think) when answers to science questions raise more questions from the person asking the question!

P.S. BUT, do be very careful if you're doing anything with 500V... Doing anything that could remotely result in you being shocked should be treated like a loaded gun without the safety on, and knowing very little about guns either. 500V is easily enough to cause a severe shock even even with dry hands, enough to kill you, and if you had sweaty hands and grabbed bare large conductors, you can almost certainly say goodnight... I have been shocked with 600V with dry skin and my vision went out for a split second, I am not exaggerating and I was very lucky!!! Your body's resistance depends on things such as perspiration, gender, age, body size, AND how hard you grip and how large of a surface area. Once you get to higher voltages, burns come into play, and once your skin is burned, you've lost the skin resistance which is considerably higher than "internal" resistance (skin resistance can be thousands of times higher than internal, or "blood to blood" sort of thing). If your 500V source is current limited and can only provide less than a few milliamps, then you might be okay, but I still wouldn't try it on purpose! Where I work (aerospace), we have devices that run on something like 13,000V at >3A, and would easily kill you.

Last edited: Sep 3, 2014
17. Sep 3, 2014

### jim hardy

great explanations, all.

old jim

18. Sep 4, 2014

### sophiecentaur

Absolutely. Don't go near this until you can state your question in a totally understandable way. 'Electrical things' do exactly what you tell them to do and not what you 'want' them to do. You have to be very precise. Better still - let someone else handle your 500V until you have all the necessary susstificates.

19. Sep 4, 2014

### psparky

I gotta call you out on that word.....huh?

20. Sep 4, 2014

### sophiecentaur

You pin em up on the wall to show yer qualifications.