How to prevent increasing current above a certain level?

[meBigGuy]

It is not completely clear to me yet what you really want to do.

1. Limit the current to 10A "cleanly". That is, drop the voltage smoothly such that the max load current is always 10A. (that also means the voltage will naturally increase to maintain 10A as the load reduces)
OR
2. Cutout at 10A (seems to be what you are suggesting, but not what I think you really want). If you do this, how will decide when to turn back on.

I think old 3-relay style voltage regulators increased/reduced the field current quickly, which the battery smoothed.
But, you don't have a field winding or a battery.

The rest of this assumes scenario 1, a clean current limit:

I'm assuming you cannot vary the RPM or the field, so you are limited to something in series with the generator to limit the current.

A buck converter would be the most efficient. but it isn't a trivial design for 70V input and 10A current limit. If you were 80% efficient, limiting at 30V @ 10A out (300W) would require 360W in, so you would dissipate 60W. If it was 60V @ 10A = 600W out then at 80% efficiency you need to dissipate 120W. You may be able to get much better than 80%. I just chose 80% to illustrate the basic principles.
There may be commercial units that will do what you want, but I have not searched.

A linear current limit (of any kind) would need to dissipate "a bit" of power. Say you have 70 volts at the generator and you need to linearly reduce the voltage to 30V to keep the load at 10A. That would mean you need to dissipate 40V @ 10A which is 400 watts. That's a pretty hefty design. (if you need 60V @ 10A it would only dissipate 100W).
With a linear approach, the more you need to drop @ 10A, the more power you need to dissipate.

 

[benofer90]

It is not completely clear to me yet what you really want to do.

1. Limit the current to 10A "cleanly". That is, drop the voltage smoothly such that the max load current is always 10A. (that also means the voltage will naturally increase to maintain 10A as the load reduces)
OR
2. Cutout at 10A (seems to be what you are suggesting, but not what I think you really want). If you do this, how will decide when to turn back on.

I think old 3-relay style voltage regulators increased/reduced the field current quickly, which the battery smoothed.
But, you don't have a field winding or a battery.

The rest of this assumes scenario 1, a clean current limit:

I'm assuming you cannot vary the RPM or the field, so you are limited to something in series with the generator to limit the current.

A buck converter would be the most efficient. but it isn't a trivial design for 70V input and 10A current limit. If you were 80% efficient, limiting at 30V @ 10A out (300W) would require 360W in, so you would dissipate 60W. If it was 60V @ 10A = 600W out then at 80% efficiency you need to dissipate 120W. You may be able to get much better than 80%. I just chose 80% to illustrate the basic principles.
There may be commercial units that will do what you want, but I have not searched.

A linear current limit (of any kind) would need to dissipate "a bit" of power. Say you have 70 volts at the generator and you need to linearly reduce the voltage to 30V to keep the load at 10A. That would mean you need to dissipate 40V @ 10A which is 400 watts. That's a pretty hefty design. (if you need 60V @ 10A it would only dissipate 100W).
With a linear approach, the more you need to drop @ 10A, the more power you need to dissipate.

1. Limit the current to 10A "cleanly". That is, drop the voltage smoothly such that the max load current is always 10A. (that also means the voltage will naturally increase to maintain 10A as the load reduces)
ANSWER: yes i will use this option with a "DC to DC Step Down Constant Current Voltage Power Regulator Buck Converter Module" so that i have covered. 2. Cutout at 10A (seems to be what you are suggesting, but not what I think you really want). If you do this, how will decide when to turn back on.
ANSWER: I also need this to prevent the "DC to DC Step Down Constant Current Voltage Power Regulator Buck Converter Module" from getting too much current then the specs allow .

If you do this, how will decide when to turn back on.
ANSWER: if i have a device who is pre set let's say to 10A then bellow the switch will be ON position if above the Switch will be OFF.

I'm assuming you cannot vary the RPM or the field, so you are limited to something in series with the generator to limit the current.
ANSWER: yes i can control the RPM . that is what i need an ON OFF switch to know when its to much power. I don't want to do it with an RPM sensor at this point

A buck converter would be the most efficient. but it isn't a trivial design for 70V input and 10A current limit. If you were 80% efficient, limiting at 30V @ 10A out (300W) would require 360W in, so you would dissipate 60W. If it was 60V @ 10A = 600W out then at 80% efficiency you need to dissipate 120W. You may be able to get much better than 80%. I just chose 80% to illustrate the basic principles.
There may be commercial units that will do what you want, but I have not searched.
ANSWER: 10A is just an example i might go with lower. but still i need to make sure the buck convertor doesn't get too much for safety.

any ideas? have u seen he links i posted with my last answer to axemaster?

 

[meBigGuy]

ANSWER: yes i can control the RPM . that is what i need an ON OFF switch to know when its to much power. I don't want to do it with an RPM sensor at this point

OK, we are learning what you need little by little. Still not totally clear though.

If you can control the rpm electronically, then there is no need for a series current limiting circuit.

You need to sense the current and use that information to control the RPM. Say you turn on the system and the current ramps up. As the current approaches 10A you slow the RPM and do not let it go above 10A.

Essentially an industrial PID controller can do what you want. But, we need to understand more about how to specifically control the RPM electronically.

any ideas? have u seen he links i posted with my last answer to axemaster?

I saw those, but I still don't understand what you need them for.

1. How do you control the RPM of the generator? Can we use that to control the current?
2. If you decide you need a buck, figure it out before you decide you need some sort of relay to protect it.
3. It may be hard to find a commercial buck unit to do what you want.
4. Regarding your switch, it has been noted before that this has an issue. If you sense 10A and turn off, the current drops to 0 amps, and it turns back on, draws 10A and turns back off, on and off forever. How do you plan to stop that from happening?

I think we are at the point now where you could draw a diagram of what you are trying to implement.

 

[benofer90]

OK, we are learning what you need little by little. Still not totally clear though.

If you can control the rpm electronically, then there is no need for a series current limiting circuit.

You need to sense the current and use that information to control the RPM. Say you turn on the system and the current ramps up. As the current approaches 10A you slow the RPM and do not let it go above 10A.

Essentially an industrial PID controller can do what you want. But, we need to understand more about how to specifically control the RPM electronically.I saw those, but I still don't understand what you need them for.

1. How do you control the RPM of the generator? Can we use that to control the current?
2. If you decide you need a buck, figure it out before you decide you need some sort of relay to protect it.
3. It may be hard to find a commercial buck unit to do what you want.
4. Regarding your switch, it has been noted before that this has an issue. If you sense 10A and turn off, the current drops to 0 amps, and it turns back on, draws 10A and turns back off, on and off forever. How do you plan to stop that from happening?

I think we are at the point now where you could draw a diagram of what you are trying to implement.

There are two elements to what i need and they don't go on the same circuit (two separate circuits).
1) limit the current from going above X amps. if it does go above X amp the switch should go off and if below switch should go on and allow the current flow .
2) i am planing on using the buck convertor parallel to #1 and use it to set up output for various devices .

QUESTIONS
1. How do you control the RPM of the generator? Can we use that to control the current?
ANSWER: that is element #1 above . i want to cut the current at X Amps, if drops below X Amps then should automatically allow current to flow .
2. If you decide you need a buck, figure it out before you decide you need some sort of relay to protect it.
ANSWER: yes i want a buck cuts the current and the Voltage are changing with RPM (i will keep the RPM in rage but it will fluctuate and i want to try it in different RPMs while testing)
3. It may be hard to find a commercial buck unit to do what you want.
ANSWER: I am planing on using a simple one . i will not go to high with amps
4. Regarding your switch, it has been noted before that this has an issue. If you sense 10A and turn off, the current drops to 0 amps, and it turns back on, draws 10A and turns back off, on and off forever. How do you plan to stop that from happening?
ANSWER: I want it to go on off forever , it need to be a switch that can handle that kind of operation

 

[benofer90]

Hi meBigGuy, axemaster, Jeff Rosenbury and to whom it may concern :

can i use any of the bellow ideas("Auto Reset Circuit Breaker") to " limit the current from going above X amps(i will pre determine X in advance). if it does go above X amp the switch should go off and if below switch should go on and allow the current flow ."?

1) https://www.google.com/shopping/pro...0CN8CEPMCMA04KGoVChMIxtGMmZTexwIVQlg-Ch0gegfS

2) http://www.delcity.net/store/Mid!Ra...p_kw=&mp_mt=&gclid=CLL8mt-S3scCFYeRHwodSFwLPg

3) https://www.google.com/shopping/pro...d=0CP4CEPMCMAtqFQoTCOKf7dOS3scCFUw3Pgod6CoLIg

4) http://www.delcity.net/store/Maxi-F...p_kw=&mp_mt=&gclid=CJzThv2T3scCFZKRHwod_GILzg

5) http://www.davis.com/Product/Curren...=51664355285&gclid=CIvGvtiZ3scCFZcYHwodIAUErQ

 

[JBA]

One question that has not been asked is "what are you planning to use to drive your generator?"

This is critical for determining the method to control its rpm.

 

[meBigGuy]

It's kind of discouraging to go through this much discussion and still not have answers to the basic questions. There seems to be a comprehension problem.
I ask:

1. How do you control the RPM of the generator? Can we use that to control the current?

And the answer is:

ANSWER: that is element #1 above . i want to cut the current at X Amps, if drops below X Amps then should automatically allow current to flow .

Which has nothing to do with controlling the RPM of the generator. You said you can control the RPM of the generator. Please describe HOW!

 

[jim hardy]

4. Regarding your switch, it has been noted before that this has an issue. If you sense 10A and turn off, the current drops to 0 amps, and it turns back on, draws 10A and turns back off, on and off forever. How do you plan to stop that from happening?
ANSWER: I want it to go on off forever , it need to be a switch that can handle that kind of operation

"on and off forever ? "
Isn't that a PWM series regulator ? Interesting approach.

We learn more by by doing than by reading about doing. ( anyone old enough to remember Fanny Hill?)

It seems to me Benofer's idea is not clearly thought all the way through.
He needs to build something and figure out why it didn't work, climb up the learning curve as he gets it working piece by piece.

old jim

 

[benofer90]

One question that has not been asked is "what are you planning to use to drive your generator?"

This is critical for determining the method to control its rpm.

why ?

put aside the generator or anything . just looking for a method to cut current at x amps and allow current flow below (automatically) .

for the rest i will use buck convertor as suggested .

 

[benofer90]

It's kind of discouraging to go through this much discussion and still not have answers to the basic questions. There seems to be a comprehension problem.
I ask:

And the answer is:
Which has nothing to do with controlling the RPM of the generator. You said you can control the RPM of the generator. Please describe HOW!

put aside the generator or anything . just looking for a method to cut current at x amps and allow current flow below (automatically) .

for the rest i will use buck convertor as suggested .

 

[benofer90]

"on and off forever ? "
Isn't that a PWM series regulator ? Interesting approach.

We learn more by by doing than by reading about doing. ( anyone old enough to remember Fanny Hill?)

It seems to me Benofer's idea is not clearly thought all the way through.
He needs to build something and figure out why it didn't work, climb up the learning curve as he gets it working piece by piece.

old jim

Hi Jim , i can have a range as specified before but was deviating from it . it can be a range . for example : detect either overcurrent of 10 Amps and undercurrent of 5Amps so at 10 it will cut flow and below 5 it will allow current .

 

[meBigGuy]

That makes no sense at all. If you open the circuit at 10 amps, you then instantly have zero amps. Where will the 5 amps come from.

What are you getting from the buck converter? Why are you using it? What do you expect it to accomplish? We had something in mind when we suggested a buck, but I think you missed the point entirely. Do you understand what a buck converter does?

 

[JBA]

The best answers to problems are obtained when all elements of the problem are known. When you limit your input to how do I do this single element in your design, you limit the ability of the respondents. For my part, in order for me to spend time on the subject I would prefer to know whether or not the whole system is logical; or, is not simply reinventing the wheel. For example, if you were to state "I want to build my own electric welding machine" then I would suspect that there is a lot more information you require than simply how to "limit the current to 10 amps".

 

[JBA]

The reason I am asking about your driving method is that varying circuit loads result in varying loads on the generator driver; so, if you want to have any type of a stable generating system you will require a feedback system that respond to those load variations and maintain a stable rpm rate to the generator. Every type of electrical power generator has a governing system to achieve this goal; otherwise, you can end up with an uncontrolled power oscillation in your system.

 

[benofer90]

The reason I am asking about your driving method is that varying circuit loads result in varying loads on the generator driver; so, if you want to have any type of a stable generating system you will require a feedback system that respond to those load variations and maintain a stable rpm rate to the generator. Every type of electrical power generator has a governing system to achieve this goal; otherwise, you can end up with an uncontrolled power oscillation in your system.

Hi JBA,

"you can end up with an uncontrolled power oscillation in your system." which i am ok with having power oscillation in the system.
all i want is a self powered adjustable DC device to detect both overcurrent of X Amps and undercurrent of Y Amps so at X it will cut flow and below Y it will allow current . where X>>Y. where the Voltage can be from 0-30 (I'm flexible on the voltage upper limit )

thanks

 

[benofer90]

That makes no sense at all. If you open the circuit at 10 amps, you then instantly have zero amps. Where will the 5 amps come from.

What are you getting from the buck converter? Why are you using it? What do you expect it to accomplish? We had something in mind when we suggested a buck, but I think you missed the point entirely. Do you understand what a buck converter does?

Buck convertor is for another circuit which will be part of the entire system . that is why i divided my answers.

as i answered to jim and JBA above:

"Hi Jim , i can have a range as specified before but was deviating from it . it can be a range . for example : detect either overcurrent of 10 Amps and undercurrent of 5Amps so at 10 it will cut flow and below 5 it will allow current ."

"all i want is a self powered adjustable DC device to detect both overcurrent of X Amps and undercurrent of Y Amps so at X it will cut flow and below Y it will allow current . where X>>Y. where the Voltage can be from 0-30 (I'm flexible on the voltage upper limit )"

 

[jim hardy]

"Hi Jim , i can have a range as specified before but was deviating from it . it can be a range . for example : detect either overcurrent of 10 Amps and undercurrent of 5Amps so at 10 it will cut flow and below 5 it will allow current ."

look up "foldback current limiter circuit"

 

[axemaster]

I'd like to jump in an quickly mention 2 things:

1. Relays have a finite lifetime. If you have one toggling on and off constantly, it will wear out. If it's switching a large current, it may burn out very quickly.

2. I strongly recommend that whatever you do, you test it out on a low power circuit first. This is doubly true given your inexperience. As I said before, your system has 100's of watts available, and that means it has explosive potential.

 

[meBigGuy]

Hi Jim , i can have a range as specified before but was deviating from it . it can be a range . for example : detect either overcurrent of 10 Amps and undercurrent of 5Amps so at 10 it will cut flow and below 5 it will allow current ."

Can't you see the problem with that statement? How can it conduct 5 amps if it is shut off? Once you cut flow there is no current to detect.

You need to make a functional drawing of what you would like to implement. Show the source of generator RPM, how it can be controlled, how the buck is connected, what its output voltage is, where you want to sense current, and where you want to switch it off, and where the load is, and its nature. Without such a top level drawing we will keep going in circles as we have been doing.

It doesn't have to be a real schematic. Just a symbolic drawing that describes the system architecture. I think when you try to draw it you will begin to see the issues that have been raised.