Connecting electrical devices into DC grid - polarity

[Maris]

Hello!
I have a very simple question: How do I connect DC electrical devices into DC grid regarding polarity? I know that current flows from "+" to "-". So when you connect batteries, you connect "+" with "minus" same goes when you connect solar panels. However, lately I have noticed that sometimes you connect "+" with "+" . For example when connecting Electrolytic capacitor into DC grid. Or when connecting solar panel array to charge controler or inverter as in picture below:

So how is it? I have been working with solar panels and can't seem to understand why you connect "+" with "+"? It's quite confusing to see that sometimes you connect "+" with "-" but sometimes "+" with "+" or "-" with "-".
Can anyone explain this?
Thanks.

 

[Terry01]

I think what your asking is...

Batteries can be connected in series + to - or in parallel + to +,this either gives more volts (series) or more Ah or current available (parallel).
When you connect a device to a battery most things are polarised so your just completing the circuit so connect + to + and - to - so the electrons flow the correct way, + to - . No sparks or smoke!

Google batteries in series and parallel and polarised devices.

 

[Maris]

I do understand how voltage and current sources work when they are connected in series or parallel. And I have zero questions about that. The question is about connecting electrical devices. Why you connect Solar panel with Charge Controller (Image above) by connecting + with + and - with -.
So as I understand you basically connect all DC devices by connecting + with +, right?

This is so confusing as it seems to be a very simple and basic thing and should be easily explainable. So in few words when connecting dc devices you always connect same polarities and connect + with - only when connecting voltage or current sources?

 

[Terry01]

An ok the simple answer is for electricity to work the electrons flow in a complete circuit + to - dumping their charge as light,heat or whatever as they flow through. For them to flow you have to have a complete + to - circuit. Think of a simple battery and bulb,connect it up + to + and - to - and the electrons flow through the circuit light the bulb as they pass through and the flow continues. Turn the connections the other way and the flow stops. Polarity is what you need to understand. To make things worse I think they found out after years of thinking electrons flow + to - they actually flow - to + but since everything was set up for flowing + to - they just kept going with that as it would be too much of a PITA to fix it!

Maybe someone with more knowledge than me will be along soon and can make a better explanation for you.

I'm still learning but the guys here are very patient and don't mind explaining a couple times if the know you want to learn. I do!

 

[Harald Kapp]

I do understand how voltage and current sources work when they are connected in series or parallel. And I have zero questions about that.

But you sure seem to have questions about that.

So when you connect batteries, you connect "+" with "minus" same goes when you connect solar panels.

Only if you want to make a series connection to increase the voltage, as @Terry01 rightly stated.
This is not a requirement, however. You are free to connect such power sources in parallel, provided the output voltages match, to increase current capacity while maintaining the output voltage at a lower level than in series connection. In that case (parallel) you also connect + to + and - to -.

When operating from a voltage source (battery, dc power supply etc.) which is the common way to do it you always connect + to + and - to - The load (device) is connected in parallel with the source (battery). This again is regardless of the number of batteries, solar cells etc. that may (or may not) be connected in series or parallel to increase the power output.

 

[Terry01]

Thanks Harald.

 

[Maris]

Thanks to both of you. So as far as I understand right out of voltage or current source you have to connect + with + and - with -. Afterwards, it depends whether devices are connected in series or parallel? Am I right?

 

[Cannonball]

This is the way I understand it. If you have 2 9v batteries and a device that draws a lot of current you connect the batteries + to + and - to -. This will double the capacity of the batteries.

Now you may have a device that requires 18 volts. You can connect the - terminal of one of the batteries to the device and the + terminal to the - terminal of the other battery and the + terminal to the device.

It works for me.

 

[Maris]

This is the way I understand it. If you have 2 9v batteries and a device that draws a lot of current you connect the batteries + to + and - to -. This will double the capacity of the batteries.

Now you may have a device that requires 18 volts. You can connect the - terminal of one of the batteries to the device and the + terminal to the - terminal of the other battery and the + terminal to the device.

It works for me.

I do understand all of that. The question wasn't about how to connect batteries but about connecting a DC device to DC circuit. The key here seems to be that wires coming straight from voltage source have to be connected to the same polarity terminals of DC device. All wiring(polarities) after the first device relies on whether devices are connected in series or parallel. Just want an approval.

 

[Harald Kapp]

All wiring(polarities) after the first device relies on whether devices are connected in series or parallel. Just want an approval.

It is comon to wire loads in parallel to a source. Compare this to your mains installation (although being AC the principle is the same): The power source is primarily seen as a voltage source which means the source impedance is very low and the output voltage is more or les fixed regardless of the load. In your mains installation all outlets are in parallel, wired to the same source: the main distribution which in turn is powered by your energy supplier. Therefore any load (lamp, regrigerator, you name it) is connected in parallel. That's because all devices are designed to be used with the same voltage whcih can only be achieved by a parallel connection.
If you were to put loads in series, any load turned on or off would have a profound influence on the other loads (imagine a 1000 W kitchen appliance in series with a 5 W LED lamp for a e.g. a closet)...

The same reasoning is true for DC.

 

[Harald Kapp]

So as far as I understand right out of voltage or current source you have to connect + with + and - with -.

Be careful with your slection of words. A voltage source operates as described above (post #10). A current source is another beast. A current source is something you will not find in your everday experience. A current source is a power source that provides a fixed current, not voltage (whereas a voltage source provides a fixed voltage, not current). When you connect a single load to a current source you also connect + to + and - to -. But if you were to connect multiple loads, you'd connect them in series, thus ensuring every load sees the same current. If you were to connect loads in parallel to a current source, the fixed current would be split among the loads (current sharing) and each load would receive less power than it was designed for.
This is a fundamental difference.

The term current source is colloquially used synonymously to voltage source, but technically this is not correct. As this is a technical forum...

 

[hevans1944]

@Maris: It appears that you have some misconceptions about how electricity works. Please do your homework and exercise due diligence and research before posting questions in this technical forum. I would recommend that you visit this Google results page for starters.

 

[Maris]

@Maris: It appears that you have some misconceptions about how electricity works. Please do your homework and exercise due diligence and research before posting questions in this technical forum. I would recommend that you visit this Google results page for starters.

There are no misconceptions. Most of the awnsers here are offsubject explaining things that are clear. There wasnt a single direct awnser to my question or statement of my tought aproval.

 

[Cannonball]

I have a very simple question: How do I connect DC electrical devices into DC grid regarding polarity?

Simple question, Simple answer. You connect + to + and - to -. I am sorry, I didn't understand your question.

 

[Terry01]

That's a bit rude Maris. Why? We were only trying to help you but....

If you want a single direct answer on the subject " I think your a bit thick and full of BS and quite cheeky"

You say you understand voltage and current sources and series and parallel but yet not how to connect a device!

Take the sound advice given to you and do some homework and learn a wee bit. If you want people to help you don't throw insults when it's you who can't understand simple descriptions.

I know because I knew even less than you a few months ago and the same guys who you say don't explain things well enough (me included) took the time to help me.

You are wrong on this one.

 

[(*steve*)]

Simple question, Simple answer. You connect + to + and - to -. I am sorry, I didn't understand your question.

In general you connect things in a way such that that terminal marked +ve is always more positive than the terminal marked -ve.

This works for batteries, capacitors, radios, cars, and small furry creatures from Alpha Centauri.

Given that you understand current and voltage sources, pretty much everything follows from that and the general statement above.

 

[Maris]

Thanks, @(*steve*), that's the answer I was looking for

@Terry01 I'm sorry if I did sound a bit rude, but that was not my intention. However, you're starting to sound rude. Until now, all I had done is some circuit calculus where polarities don't matter, just the direction of the current. But now when I'm dealing with real devices, it was just a bit confusing that you connect + with + for the first device that comes after battery but now I get it. And if you ask me, it is a bit disappointing if you ask one thing and get a completely different answer.

 

[Harald Kapp]

polarities don't matter, just the direction of the current

Direction of current implies polarity, therefore polarity does matter.

 

[Maris]

Direction of current implies polarity, therefore polarity does matter.

Yes, but by saying this I meant that in calculus I dealt only with current direction.

 

[Harald Kapp]

but by saying this I meant

Then please say what you mean, do not expect others to derive the implications from your words. This can go awry as you can easily see from your 1st post and the reactions:

So when you connect batteries, you connect "+" with "minus" same goes when you connect solar panels. However, lately I have noticed that sometimes you connect "+" with "+" .

In your initial post you were implying that you think you have to connect + to - because you do this (I have to add "sometimes"). People here have been trying to correct this implication.

It may seem to you that a simple yes or no answer might have been sufficient. Maybe for this case. But: Sometimes (not too rarely) people jump to the right conclusion by the wrong reasoning (line of thoughts). This may work for a special case being considered at that moment, but the same line of thought may lead to completely wrong conclusions in other cases. Therefore it is necessary to understand not only the solution but the way leading to it. All the kind people on this forum have been trying to was to show you this way.