DC Supply Question

The first several times I looked at the image, I didn't see Bozo. Once I saw him, it is quite striking. Now I can't look at it without seeing him...

I still don't find the image appropriate for this thread. Rather than trying to scare the OP, I think it much more appropriate to show him/her how to do the connections properly. There is no reason it can't be done, if connected correctly with appropriate diodes and fuses.

It depends entirely on the circuit protection equipment, which you say nothing about. So how am I supposed to know?

It depends on whether the two sources are properly matched in voltage and polarity.

polarity is same and the voltage is 110 v then?

Still stuff-all about the circuit protection arrangements, though.

Why would you want to?

keep it all on the same wave

That depends on the output impedance of your two DC power supplies and the impedance of the wires doing the connecting. Please review the chapter in your textbook on electric circuit analysis.

Wait a minute, you never said that you had two different power supplies. You say that you have two different undefined sources. This implies that the two undefined sources are connected in parallel to power the d.c. supply. Well the same answer applies. Once the power sources are defined you should apply the superposition principle described in your textbook.

Let us just say increase energy capacity/availability. The OP might misunderstood the concept, he might think adding another source will double up circuit current. Nope.

The OP could make this type on configuration with DC, but for AC, having two source is only applicable only when the two sources is at the same phase. Otherwise, it will either cancel out potential difference at the source, potentially defecting both sources.

This assumes that both batteries (or other sources) have exactly the same voltage. If not, the one having the higher voltage will send current to the source having lower voltage, unless diodes are installed to prevent the back current, as mentioned by Kilowatt0.

Sorry to ask a question...In parallel connection, the voltage remains the same and the AH adds up as it shown in your diagram....But I ain't sure about the rating of each 12 V battery to have 400 Ah? (1) Is that from manufacturer or you just assumed it? (2) How to find the number of cells in each battery of 12 V? (3) How to find the Ah of each cell? Like 1.67 Vdc per cell etc.? (4) How to find a battery backup time? I know the equation but please put a through example. I read some old threads about designing or sizing the right UPS system (standby) but mostly not enough or wrong calculations. I need simple calculation to compare it to mine. Battery charger sizing and calculation is needed too.Take for example a simple load of 1000-1500 W. And don't just use rule of thumb to say use 2000 VA or 2 KVA rated UPS system...blah,blah...I need to size inverter to DC/AC of 220 V single phase system...I kind a know it but not my specialty...Do I need an AVR or AVS or any other form of stabilizer to main since always the main AC line has low voltage input i.e lower than rated 220 V due to utility equipment or distribution....Some type of control circuit too...I see some UPS are having modem system to switch between....I would prefer a Static transfer switch over Automatic transfer switch due to electro-mechanical problems occuring...Need I say more? I guess I am bluffing to be here on this forum...

1. generally speaking a small battery of lead acid type ( AGM, wet cell, gel ) will have a lower Ah than a bigger one. The seller should be able to tell you the Ah.

2. Number of cells doesn't matter but a lead acid cell is 1.5v a NiCd is 1.2v a NiMH is 1.2v etc Google is your friend.

3.See 1.

4. Divide your bank of batteries total Ah by your consumption in Ah ( You said 83 to 120Ah You actually said 1000 - 1500 watts divide by 12v and assume you use this for 1 Hr = 83 - 120Ah) then allow for the level you want to drain your TYPE of battery down to. Again the seller should be able to tell you the optimal range for the type and brand of battery you buy. A wet lead acid should not be drained very far but a deep cycle one can be, for example. Lets say down to 85%. This means your max usage rate of 120Ah can only be used for 15% of the bank's total capacity in Ah.

I can help no more as I know nowt about UPS systems.

Jim

Amperage will increase as the total of both systems. If one system is designed for a lower amperage, then, that would burst.

Depends a bit on what is supplying the 110Vs. If there were two batteries you would increase the amp/hour rating eg if one was capable of 20Ah and the other 10Ah then you would have a capacity of 30Ah when connecting these two supplies in parallel. If they were DC power supplies a similar situation would arise as long as the current draw doesn't exceed the total available otherwise damage could occur to both supplies.

As soon as I can remember my basic circuit theory I will try to work this out for a resistive circuit when the two AC sources (110 volts 50 Hz) are in phase and 90 degrees out of phase. If the sources are DC then they must be of the same voltage and have the same source impedance for full efficiency. Off the top of my head (after 4 cans of Carlton) AC sources with 90 degree phase difference will give zero voltage and max amps. This could destroy both sources. As I say, I will have to do an analysis of the situation to be sure. For DC how often do you connect a 12 Volt battery to the 12 volt battery in parallel (+ to + and - to-) on your car when you have a flat battery. Your question should work on the same principal.

Check the voltage profile of both the sources ie. +ve wrt ground & -ve wrt ground, if the profiles match which they should then go ahead and parallel them without any hesitation. If the voltage profile do not match then check for any earth leakage in the system with a skewed profile and eliminate it. Later, you can parallel them.

Ideally and the available current capacity is supposed to increase or doubled up if they are of similar type of DC source as in 2 Double A batteries.

In this real world, No two perfectly identical - balanced sources can be found, they do not exist nor are available. Due to electrical, physical differences an imbalance will prevail. One of the DC sources will always become a load extracting energy from the other! This oscillating action will continue due to the differences in their impedances!

It depends upon "how" you connect them, there are other posts here that explain it.

Answers:- One, nothing bad happens (as long as you don't touch a live connection!) and the other is a big bang - hopefully fuses!!.......

Find out which!

Lots of answers, but which one is right and will let you keep your eyebrows?

Can you please explain exactly what the sources are you are trying to connect before you potentially kill yourself?

No, they cannot explain the difference because they do not even comprehend, let alone can they communicate the critical attributes of a difference between the poorly specified power sources of this thread. The advantage of this is that they can do anything at all, collect a result and then feel superior to all those that guessed wrong what they were trying to do.

Is your power supply;-

1. rectified A.C.

2. dynamo generated D.C.

3. battery bank. ?

P.S. Isn't a battery already a 'bank' of cells? Maybe I should just say two batteries.

Jim

Interesting point, and a nice analogy with self-balancing piping loop designs.

thank u very much sir,you cleared my doubts.it was 110 v dc supply from two battery banks(ni cd cells of 90 nos connected in series)

Now we know. You need to do a lot of research into NiCd cells. For instance they have a low internal resistance and they can act like capacitors in a short circuit. They also develop "memory' which will make them useless when you need them the most. Don't go away as I think more people will add comments now that we know the setup.

Jim