#### daz E

Joined Nov 7, 2017
47
What options are there for a novice such as me, to design (or take existing design) and build a power control box module with current limiting.

The power will come from a 12V led acid battery 8Ah
I would like to control (limit) 5 different loads on the same battery, each load being a 12V device of either 1, 2, 5, 7 or 10A draw.
All 5 loads might be connected at the same time. Not sure what this is called exactly, but a "5 way" or "5 channel" limiter ??
So 5x current "I" limits of 1,2,5,7,or 10. Not sure what you call these so I will refer to them as I1, I2, I3, I4, I5
Each limiter needs to open the circuit (circuit break / electronic fuse) if that circuit is drawing more current than "I", e.g. I1 or I2 or I3 - whichever.

When the circuit is open/cut/break, then a switch will reset the circuit. If the load is still connected and drawing too much current, then the circuit is opened again automatically.

Please can you provide diagrams/examples/links and all important narrative because whilst I understand to a beginner level, I am new to project build and Autodesk and alike.

By the way, is Autodesk the best for beginners to design circuits, PCB layout and enclosure hardware positioning.

#### Picbuster

Joined Dec 2, 2013
1,025
A micro chip plus a number of P mosfets (5) will do the trick.
Or look at multi fuse (Bourns) but I am not sure if available above the 5Amps.

Picbuster

#### Picbuster

Joined Dec 2, 2013
1,025
What options are there for a novice such as me, to design (or take existing design) and build a power control box module with current limiting.

The power will come from a 12V led acid battery 8Ah
I would like to control (limit) 5 different loads on the same battery, each load being a 12V device of either 1, 2, 5, 7 or 10A draw.
All 5 loads might be connected at the same time. Not sure what this is called exactly, but a "5 way" or "5 channel" limiter ??
So 5x current "I" limits of 1,2,5,7,or 10. Not sure what you call these so I will refer to them as I1, I2, I3, I4, I5
Each limiter needs to open the circuit (circuit break / electronic fuse) if that circuit is drawing more current than "I", e.g. I1 or I2 or I3 - whichever.

When the circuit is open/cut/break, then a switch will reset the circuit. If the load is still connected and drawing too much current, then the circuit is opened again automatically.

Please can you provide diagrams/examples/links and all important narrative because whilst I understand to a beginner level, I am new to project build and Autodesk and alike.

By the way, is Autodesk the best for beginners to design circuits, PCB layout and enclosure hardware positioning.
oops you need this as well http://www.bourns.com/docs/Product-Datasheets/mfusmf.pdf
Picbuster

#### daz E

Joined Nov 7, 2017
47
A micro chip plus a number of P mosfets (5) will do the trick.
Or look at multi fuse (Bourns) but I am not sure if available above the 5Amps.

Picbuster
Could you elaborate please , perhaps a link to a schematic or a project I can follow? Don't really want to re-invent what surely must be a lot of wheels ??? many thanks by the way

#### daz E

Joined Nov 7, 2017
47
wow.

but

I am a novice beginner who has built a few simple projects , which worked, and looking for some help/tutorial/guidance. Reading up on electronics as I go, building then understanding what I have built. we all started somewhere

That datasheet might as well be in Chinese

#### AnalogKid

Joined Aug 1, 2013
8,806
Polyswitch fuses are not a good choice for this project:
They cannot be reset manually. You must wait for the device to cool down.
With each trip cycle the device trip point becomes less accurate and it's "on" resistance increases.
The trip point accuracy is very poor.

The general term for a circuit that does what you want is an electronic circuit breaker. Several companies make chips specifically for this application, or you can whip up one (per output) with a comparator/opamp and power transistor. The circuit is based on a very low value resistor (called a current shunt) placed in series with each load, and sensing the voltage drop across the shunt to determine the current.

ak

#### daz E

Joined Nov 7, 2017
47
Polyswitch fuses are not a good choice for this project:
They cannot be reset manually. You must wait for the device to cool down.
With each trip cycle the device trip point becomes less accurate and it's "on" resistance increases.
The trip point accuracy is very poor.

The general term for a circuit that does what you want is an electronic circuit breaker. Several companies make chips specifically for this application, or you can whip up one (per output) with a comparator/opamp and power transistor. The circuit is based on a very low value resistor (called a current shunt) placed in series with each load, and sensing the voltage drop across the shunt to determine the current.

ak
Ok,
I found this.

Now, I get the Stepdown using windings to reach 12v DC through a full bridge diode rectifier, and waveform smoothed with the smoothing capacitor

But, what I don't understand is how 5v is at 7805 Vi. Why is this not 12v? Please can you explain

#### Attachments

• 16.2 KB Views: 53

#### crutschow

Joined Mar 14, 2008
26,008
But, what I don't understand is how 5v is at 7805 Vi. Why is this not 12v? Please can you explain
Because that's the power supply to the breaker, not the breaker itself

Below is the LTspice simulation of an electronic fuse circuit using two BJT's and a P-MOSFET.
The current limit is determined by the value of the sense resistor Rlim.
The simulation shows the trip point varying from 1A to 10A as the value of Rlim changes from 0.7Ω to 0.07Ω.
SReset is a push-button switch that resets the circuit (shown being pressed at 42ms).
(Note that one reset switch can reset all the circuits by connecting the switch in parallel to all the R1 resistors.)

The P-MOSFET can be just about any with an ON resistance of ≤10mΩ.

You would need one of these circuits for each output.

#### Attachments

• 2.8 KB Views: 2

#### daz E

Joined Nov 7, 2017
47
Sorry

I have no idea what you are talking about. Just acronyms to me.

I looked at the 7085 data sheet and noted In is 7 to 35v so yes, you are of course right. My bad

Am I right in calculating that the current voltage (top of diagram) is between 0.001 and 0.023 Amp

Because that's the power supply to the breaker, not the breaker itself

Below is the LTspice simulation of an electronic fuse circuit using two BJT's and a P-MOSFET.
The current limit is determined by the value of the sense resistor Rlim.
The simulation shows the trip point varying from 1A to 10A as the value of Rlim changes from 0.7Ω to 0.07Ω.
SReset is a push-button switch that resets the circuit (shown being pressed at 42ms).
(Note that one reset switch can reset all the circuits by connecting the switch in parallel to all the R1 resistors.)

The P-MOSFET can be just about any with an ON resistance of ≤10mΩ.

You would need one of these circuits for each output.

View attachment 138927

#### crutschow

Joined Mar 14, 2008
26,008
I have no idea what you are talking about. Just acronyms to me.
What acronyms?

#### daz E

Joined Nov 7, 2017
47
Can someone explain the above LTsense circuit please

I've no idea where to start working things out

#### daz E

Joined Nov 7, 2017
47
lTspice I mean

Where do I start, how do i Work through the components and trace the flow. How are the values of resistors determined. A mosfat? Huh

#### daz E

Joined Nov 7, 2017
47

#### crutschow

Joined Mar 14, 2008
26,008
lTspice I mean

Where do I start, how do i Work through the components and trace the flow. How are the values of resistors determined. A mosfat? Huh
It's LTspice, which is an electronic simulation program based upon the SPICE (Simulation Program with Integrated Circuit Emphasis) engine, and is a free download from Linear Technology.
A MOSFET is a Metal Oxide Semiconductor Field Effect Transistor.

So it would appear you are indeed a complete novice with little knowledge of electronics and electronic parts.
That would make it rather difficult for you to build the circuit I posted and get it working.
And without an understanding of the basics, I can't explain its operation here in the limited time and space available.
You should first read through the electronic tutorials at the top of the page (Textbooks) for help in understanding the circuit before you attempt to build such a circuit.

#### daz E

Joined Nov 7, 2017
47
Wrong

I am an aircraft fitter , so understand electronics. We use various rigs and benches , scopes,, relays, and ICs mostly. I just do not understand THIS circuit. Please explain , let's go from there .

It's LTspice, which is an electronic simulation program based upon the SPICE (Simulation Program with Integrated Circuit Emphasis) engine, and is a free download from Linear Technology.
A MOSFET is a Metal Oxide Semiconductor Field Effect Transistor.

So it would appear you are indeed a complete novice with little knowledge of electronics and electronic parts.
That would make it rather difficult for you to build the circuit I posted and get it working.
And without an understanding of the basics, I can't explain its operation here in the limited time and space available.
You should first read through the electronic tutorials at the top of the page (Textbooks) for help in understanding the circuit before you attempt to build such a circuit.

#### crutschow

Joined Mar 14, 2008
26,008
Wrong

I am an aircraft fitter , so understand electronics. We use various rigs and benches , scopes,, relays, and ICs mostly. I just do not understand THIS circuit. Please explain , let's go from there .
You may understand basic electrical circuits but, if you don't know what a MOSFET is, you don't know electronics.
Get back to me when you have a basic understanding of what BJTs and MOSFETs are and how they work.

#### daz E

Joined Nov 7, 2017
47
You may understand basic electrical circuits but, if you don't know what a MOSFET is, you don't know electronics.
Get back to me when you have a basic understanding of what BJTs and MOSFETs are and how they work.
I understand all switches
Comning from a university degree in London studying computer science, oh I understand
My hunch is YOU are incapable of conveying the circuit behaviour because YOU do not understand the circuits you are posting .

Get back to you...

No, I think I'll ask someone who is more able but thanks for the picture

#### crutschow

Joined Mar 14, 2008
26,008
I understand all switches
Good for you.
But Q1 is not being used as a switch but as an analog component.
Comning from a university degree in London studying computer science, oh I understand
Really?
Did you study analog electronic circuits as part of your "university degree"?
And how could you not know what a MOSFET is if you understand electronics?
My hunch is YOU are incapable of conveying the circuit behaviour because YOU do not understand the circuits you are posting .
I was involved in analog and digital circuit design for over 40 years and quite understand the circuit, as I designed it.
But I can't explain how it works to you until you understand how BJTs work as analog devices.
It's not apparent that you do.

#### daz E

Joined Nov 7, 2017
47
Didnt study electronics as in component electronics. We studied the science of computing. If you dont know what that is then perhaps you should not cast dispersions.

This is the 2nd time you have "supported" me on these forums, and the second time I have become frustrated with you. I mean I am asking for help , an explanation as one might give a student. If you dont - or rather cannot - provide the requested information , then I politely ask you to refrain from posting to my threads and go and "help" someone else. Your kind of help is not what I seek. Thank you all the same, but please help elsewhere

#### crutschow

Joined Mar 14, 2008
26,008