Hi All, is this possible, I have a bunch of 18650s all doubled up making 7.2v, reg'ed down to 5v volts, what I need to do is have 2 x 5v outs but if one gets shorted or overloaded it wont pull the other one down, can it be done ?

Thanks

 

is this possible

Yes. As long as the regulator that gets shorted doesn't make the battery voltage drop low enough to affect regulation of the other regulator.

 

Is there no magic IC's I can put inline to protect the other side?

 

Is there no magic IC's I can put inline to protect the other side?

There's nothing you can do if the shorted regulator makes battery voltage drop too low for the regulator to function.

Depending on the regulators you use, they may have built-in current limiting. You could add your own e-fuse circuit that would open for high current. But nothing will make the other regulator function if battery voltage drops too low.

 

Is there no magic IC's I can put inline to protect the other side?

There is no crying in baseball, and there are no magic integrated circuits. Too bad -- so sad.

 

Would any of these 3 be any help to me?

 

What do you imagine they will do for you?

 

What do you imagine they will do for you?

I dont know, that is why I am here asking questions and trying to get help, if you dont want to help me as I am not an electronics specialist then no problem I'll wait and hope someone else can guide me along

Thanks for all what youve done up to now

 

I dont know, that is why I am here asking questions and trying to get help, if you dont want to help me as I am not an electronics specialist then no problem I'll wait and hope someone else can guide me along

Thanks for all what youve done up to now

I'm sorry, I thought you knew what the purpose of those schematics was. I want to help you, but I don't know how. Throwing spaghetti against a wall to see if something sticks is not a very efficient way to go about solving a problem. As has already been mentioned, it is not clear that a solution exists for you particular problem. It all depends on the regulators that you use. Without more details, which are still lacking, we cannot even analyze the situation.

 

I dont know, that is why I am here asking questions and trying to get help, if you dont want to help me as I am not an electronics specialist then no problem I'll wait and hope someone else can guide me along

I'm not inclined to analyze a bunch of circuits when you don't know what you want.

1. What do you think can short the regulators?
2. What will the load be?
3. What is the AH rating of the batteries?
4. How long do you expect to operate the circuits?
5. What regulators will you be using?

There are too many variables and too little information. Even if you don't understand electronics, you have to be able to describe what you want clearly if you want members to take the time to help you.

 

1. What do you think can short the regulators?...............One of the outs will have a fly leads like DMM lead for testing
2. What will the load be?...........................................................No more than about 500ma
3. What is the AH rating of the batteries?..........................2000mha
4. How long do you expect to operate the circuits?.......Max 2 hous, norm use, 10-20 mins
5. What regulators will you be using?...................................I dont know yet, regs, buck converters or something that will do the job

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Thanks

 

You could install a current limiting circuit or fuse on the input side of the regulators.

Without knowing the regulators you're going to be using, we don't know the dropout voltage requirement. That may have some impact on the current limiter or fuse. You could use a regular one time fuse or a PTC, which would be self resetting. Both will introduce a voltage drop between the battery and regulator, hence the need to know the dropout voltage at the desired maximum operating current.

A 2AH 2Ah battery isn't likely to provide 1A for 2 hours.
EDIT: corrected typo to avoid future digs

 

You said you have two 18650 Lithium battery cells producing only 7.2V. Then they are nearly dead.
They produce 8.4V when fully charged and they should be disconnected when their voltage drops to 6V or 6.4V.

 

You could install a current limiting circuit or fuse on the input side of the regulators.

Without knowing the regulators you're going to be using, we don't know the dropout voltage requirement.

That's why Im here, I used normal old 5v regs like lm7805 but they've been hard-wired so to speak so no fear of shorts \ shorting, what reg\s would you guys recommend

A 2AH battery isn't likely to provide 1A for 2 hours.

You said you have two 18650 Lithium battery cells producing only 7.2V. Then they are nearly dead.
They produce 8.4V when fully charged and they should be disconnected when their voltage drops to 6V or 6.4V.

Sorry the info on the batteries says: 3.6v 2000mAH, they will be fully charged so yes the output voltage will be a little higher, I have 8 of these cells all doubled up

 

What are You building ?, and what will it be expected to do ?
What problem are You trying to solve ?

You can simply double-up on the number of Batteries and a multitude of problems will be solved.
.
.
.

 

You still haven't answered my questions.

Sorry the info on the batteries says: 3.6v 2000mha

That can't be right. It should be 3.6V 2000mAH mAh. In electrical engineering, capitalization matters.
EDIT: corrected typo to avoid future digs

I have 8 of these cells all doubled up

What does that mean? We usually refer to battery configurations as series, parallel, or series and parallel.

 

Sorry the info on the batteries says: 3.6v 2000mha, they will be fully charged so yes the output voltage will be a little higher, I have 8 of these cells all doubled up.

All older lithium-ion-cobalt batteries are sold at a 3.7V "storage" voltage so that they can last a long time on a store shelf.
Maybe yours are the newer ferrous lower voltage type or its seller does not know anything about its voltage.

 

You still haven't answered my questions.
That can't be right. It should be 3.6V 2000mAH. In electrical engineering, capitalization matters.
What does that mean? We usually refer to battery configurations as series, parallel, or series and parallel.

Sorry I have corrected my typing error

All older lithium-ion-cobalt batteries are sold at a 3.7V "storage" voltage so that they can last a long time on a store shelf.
Maybe yours are the newer ferrous lower voltage type or its seller does not know anything about its voltage.

I dont know, I know I CAN NOT mix before anyone chips in, as the samsungs have a higher "mAH" but looking at the data sheet for the samsung's and what is on the other cells, Ive got 3.6v so the manufactures must have all got it wrong

 

So they call it 3.6 to get a few more maH than others that call it 3.7.

 

Sorry I have corrected my typing error

Apparently I got it wrong too. I thought the abbreviation for hours was capitalized.

EDIT: corrected typo in previous posts to avoid future digs

When describing series or parallel combinations, it's conventional to use 's' and 's'. Two batteries in series would be called 2s. Two batteries in parallel would be called 2p. That's clearer than saying doubled.

2 strings of 3s in parallel would be called 3s2p.