### Author Topic: how do i limit current?  (Read 6399 times)

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#### dmkmedia

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##### how do i limit current?
« on: January 14, 2017, 01:39:51 pm »
i am using a load on a 3.7 volt battery and the battery is connected to a charger circuit to allow it to charge
http://www.hotmcu.com/tp4056-micro-usb-5v-1a-lithium-battery-charger-with-protection-p-176.html

but when i use the load the current drain make the charging unit the battery is empty so it cuts it off after a few seconds

is there a way to smooth or limit the current used so its not so demanding on the power and the charging curcuit will not cut off

#### jeroen79

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##### Re: how do i limit current?
« Reply #1 on: January 14, 2017, 01:45:57 pm »
Can you give some more details?
You have a 1A charger and a load connected to the battery at the same time.
What kind of load is this? How much current does it draw?
If it draws more than the charger can provide the excess will have to come out of the battery.

#### Seekonk

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##### Re: how do i limit current?
« Reply #2 on: January 14, 2017, 03:45:08 pm »
Pretty confusing.  You don't have to use the current limiting if your load is higher. If under 1A the battery may be bad.

#### danmcb

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• if it ain't bust, I didn't test it yet.
##### Re: how do i limit current?
« Reply #3 on: January 14, 2017, 03:56:12 pm »
with a resistor. But that's probably not the answer you want. Can you maybe sketch a schematic and explain exactly what you are trying to do?

#### Audioguru

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##### Re: how do i limit current?
« Reply #4 on: January 14, 2017, 04:15:14 pm »
Since you do not say the current used by the load then maybe most of the 1A of charging current is powering the load and hardly any of the charging current is charging the battery cell.

#### dmkmedia

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##### Re: how do i limit current?
« Reply #5 on: January 14, 2017, 05:00:46 pm »
i am making a rechargeable taser powered by a 3.7 volt battery the coil can take anything from 3.5 to 6,5 volts and outputs anything from 400 to to 600Mv

now i thought i was going to power the coil direct from teh battery but it says i use the Power out on the board so it stops the battery from draining too much

but if i do that the draw on the charger board is too much and it shuts off. but the coil works fine on my bench power supply using 3.6v and 1 amp i just need to limit the pull from the charger board to the coil as if left unlimited it will pull all 3 amps of my bench power supply under 3.5 volts

#### shteii01

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##### Re: how do i limit current?
« Reply #6 on: January 14, 2017, 10:35:47 pm »
Use current divider, maybe.
This way voltage remain the same, the current is split between the two loads.  You, the designer, then can determine what fraction of the main current gets to your target load.

#### Rick Law

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##### Re: how do i limit current?
« Reply #7 on: January 14, 2017, 11:27:20 pm »
i am making a rechargeable taser powered by a 3.7 volt battery the coil can take anything from 3.5 to 6,5 volts and outputs anything from 400 to to 600Mv

now i thought i was going to power the coil direct from teh battery but it says i use the Power out on the board so it stops the battery from draining too much

but if i do that the draw on the charger board is too much and it shuts off. but the coil works fine on my bench power supply using 3.6v and 1 amp i just need to limit the pull from the charger board to the coil as if left unlimited it will pull all 3 amps of my bench power supply under 3.5 volts

If I understand you right, you want it to power by the battery, and also have the battery connected to the charger so you can charge the battery; you will also want to use your load (taser) while it is charging?

If so, you can always have a by-pass.
- Have power-in connected to the TP4056
- The 4056 board output connects to the battery and also to the load via a diode
- Have power-in also connected to another voltage regulation circuit (at 4.3V to 6volt), say we choose 4.3V
- The voltage regulation circuit (which is connected to power-in) power-out connect to the load via a diode

The battery will never go beyond 4.3V.  So, whenever power-in is on, power to the load comes directly from your voltage regulation circuit.  At the same time, the 4056 board is charging the battery.  When power-in is off, the voltage from your voltage regulation board is 0V, so power to the load comes from the battery.

Now you can control how much current the load and battery get.
- To control charge current, the Rs on TP4056' pin2 selects the current.  I=1200/Rs, so Rs=1.2K for 1Amp, Rs=2.4K for 0.5Amp, so on.
- To control voltage-regulation circuit current, that depends on how you design the regulation circuit.  There are zillion of examples out there.  Or, you can just buy a cheap Chinese buck board that has both voltage and current control.

For the diodes, I would use Schottky diode like 1N5817 (1Amp or less) or other Schottky diode if larger current is needed.
« Last Edit: January 14, 2017, 11:35:23 pm by Rick Law »

#### Brumby

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##### Re: how do i limit current?
« Reply #8 on: January 15, 2017, 04:05:24 am »
i am making a rechargeable taser powered by a 3.7 volt battery the coil can take anything from 3.5 to 6,5 volts and outputs anything from 400 to to 600Mv

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#### Rick Law

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##### Re: how do i limit current?
« Reply #9 on: January 15, 2017, 04:19:46 am »
i am making a rechargeable taser powered by a 3.7 volt battery the coil can take anything from 3.5 to 6,5 volts and outputs anything from 400 to to 600Mv

I thought he made a typo!  Since he was running it off a 3.7V LiIon, I mentally adjust the number as 4000 milli-volt 6000 milli-volt. (4.00V to 6.00V).

If that is M as in mega volt and taken the number as is, he is going to need a hell of a boost converter.

#### Cupcakus

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##### Re: how do i limit current?
« Reply #10 on: January 15, 2017, 08:33:08 am »
i am making a rechargeable taser powered by a 3.7 volt battery the coil can take anything from 3.5 to 6,5 volts and outputs anything from 400 to to 600Mv

I thought he made a typo!  Since he was running it off a 3.7V LiIon, I mentally adjust the number as 4000 milli-volt 6000 milli-volt. (4.00V to 6.00V).

If that is M as in mega volt and taken the number as is, he is going to need a hell of a boost converter.

I'm a bit confused as well, a typical taser is high voltage low current, neither of those voltage ranges seem reasonable for the purpose, 40 to 60kV maybe.

#### Gyro

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##### Re: how do i limit current?
« Reply #11 on: January 15, 2017, 10:10:29 am »
Quote
I'm a bit confused as well, a typical taser is high voltage low current, neither of those voltage ranges seem reasonable for the purpose, 40 to 60kV maybe.

Apart from being illegal in the UK.

« Last Edit: January 15, 2017, 10:25:00 am by Gyro »
Chris

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#### Rick Law

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##### Re: how do i limit current?
« Reply #12 on: January 15, 2017, 06:44:29 pm »

i am making a rechargeable taser powered by a 3.7 volt battery the coil can take anything from 3.5 to 6,5 volts and outputs anything from 400 to to 600Mv

Be it Kilo V or Mega V or the typo I assumed, his coil's input is 3.5 to 6.5V.  So, the input to his taser is 3.5 to 6.5V.

So, a charger-bypass with two diodes could work.  Actually, the bypassing second volt-regulator doesn't even need to regulate volts, it just needs to regulate current and ensure it is above 4.3V so the battery side doesn't cut in.

But KV or MV, there is a lot of energy somewhere in that circuit.  Given the question asked, the OP probably is of limited experience.  Messing around in a circuit like that is not a good idea.

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#### dmkmedia

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##### Re: how do i limit current?
« Reply #13 on: January 15, 2017, 08:06:13 pm »

i am making a rechargeable taser powered by a 3.7 volt battery the coil can take anything from 3.5 to 6,5 volts and outputs anything from 400 to to 600Mv

Be it Kilo V or Mega V or the typo I assumed, his coil's input is 3.5 to 6.5V.  So, the input to his taser is 3.5 to 6.5V.

So, a charger-bypass with two diodes could work.  Actually, the bypassing second volt-regulator doesn't even need to regulate volts, it just needs to regulate current and ensure it is above 4.3V so the battery side doesn't cut in.

But KV or MV, there is a lot of energy somewhere in that circuit.  Given the question asked, the OP probably is of limited experience.  Messing around in a circuit like that is not a good idea.
thanks fir the info im not really messing around inside the coil is already made i was given 2 of theses https://www.amazon.co.uk/gp/product/B01MF4RMC6/ref=oh_aui_detailpage_o02_s00?ie=UTF8&psc=1
and wondered what i could do with them

im sure there is a better use for them

#### Vtile

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##### Re: how do i limit current?
« Reply #14 on: January 15, 2017, 11:36:50 pm »

I suggest that you put them a drawer and return to the highvoltage subject when you have the basics sorted out (that is a few years from now, when you know what you don't know). No offence, but people actually die playing with those contraptions without proper knowledge what they are doing.
« Last Edit: January 15, 2017, 11:41:57 pm by Vtile »

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#### janoc

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##### Re: how do i limit current?
« Reply #15 on: January 16, 2017, 01:37:03 am »
thanks fir the info im not really messing around inside the coil is already made i was given 2 of theses https://www.amazon.co.uk/gp/product/B01MF4RMC6/ref=oh_aui_detailpage_o02_s00?ie=UTF8&psc=1
and wondered what i could do with them

im sure there is a better use for them

No offense, but the best use for one of those things is the trash bin, especially with your level of knowledge. Otherwise you are literally asking for the Darwin award.

Judging from the auto-translated chinglish in the description on Amazon, that boost converter is likely built to the rock bottom price using the cheapest components available. It most likely delivers only 1/10th of the rated voltage (aka ~60kV instead of the 600kV) but do you want to entrust your life to such black box, with unknown parts and build quality inside? It won't deliver a whole lot of current at that voltage, but likely still enough to be lethal if you do something dumb.

Also do you have an idea how much isolation distance something producing 600kV actually requires before it arces over (and blows up)?? That's the voltage commonly used in the long distance electricity distribution lines.
« Last Edit: January 16, 2017, 01:46:02 am by janoc »

#### edy

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##### Re: how do i limit current?
« Reply #16 on: January 16, 2017, 08:00:15 pm »

As few as 100 mA and up to 2000 mA across your arms. Let's see... 60,000 V, the resistance you need to have in your body to keep under 100 mA is 600,000 ohm, which is 600 K-ohm or 0.6 M-ohm.

https://en.wikipedia.org/wiki/Electric_shock

Quote
The resistance of human skin varies from person to person and fluctuates between different times of day. The NIOSH states "Under dry conditions, the resistance offered by the human body may be as high as 100,000 Ohms. Wet or broken skin may drop the body's resistance to 1,000 Ohms," adding that "high-voltage electrical energy quickly breaks down human skin, reducing the human body's resistance to 500 Ohms."[15]

So basically under dry conditions your skin may have 100,000 ohm resistance and you are playing with 60 kV which is enough to produce  600 mA, or 6x the amount of current likely needed to kill you. But wet or broken skin and that drops 1000 ohms, giving you 60 A, definitely will fry your internal organs.

Is it really worth building something like this? It not only sounds dangerous to you but also to any victim you intend to use it on. And the poorly-worded grammar in the Amazon listing also makes me wonder. I wouldn't touch this thing with a ten-foot grounded isolated ceramic-insulated rubber handled pole.

This is not the same thing as static electricity... Yes I know we are talking 20-25 kV when you rub your socks on the carpeted floor and zap yourself on a grounded copper pipe. A static discharge lasts on the order of milliseconds and there just isn't enough charge there to continuously pass through. But that high voltage converter could last much longer, enough to deliver sufficient power to definitely do damage.

I wonder if this site is contributing to the interest:

http://www.electroboom.com/?p=484

« Last Edit: January 16, 2017, 08:11:37 pm by edy »
"Ye cannae change the laws of physics, captain" - Scotty

#### ziplock9000

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##### Re: how do i limit current?
« Reply #17 on: January 16, 2017, 08:03:43 pm »
Quote
I'm a bit confused as well, a typical taser is high voltage low current, neither of those voltage ranges seem reasonable for the purpose, 40 to 60kV maybe.

Apart from being illegal in the UK.
Didn't stop me taking relevant parts out of an old telly and making a jacob's ladder. Those 555 timers have some use! ha

#### janoc

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##### Re: how do i limit current?
« Reply #18 on: January 16, 2017, 08:27:31 pm »

The gizmo won't deliver that much current - it has rougly 30W on input, give or take judging from the 7.2V battery and the 4A current. With 80% efficiency that leaves 24W, at 60kV that gives some 400uA maximum it will be able to deliver.

However, the shock and the resulting muscle spasm will throw you across the room, no problem. Also the resulting nice high frequency burns are "fun" to heal.

#### Gyro

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##### Re: how do i limit current?
« Reply #19 on: January 16, 2017, 08:59:28 pm »
Quote
I'm a bit confused as well, a typical taser is high voltage low current, neither of those voltage ranges seem reasonable for the purpose, 40 to 60kV maybe.

Apart from being illegal in the UK.
Didn't stop me taking relevant parts out of an old telly and making a jacob's ladder. Those 555 timers have some use! ha

Sure, but you were making a Jacob's ladder not a "rechargeable taser". Bit of a usage difference there!
Chris

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#### Audioguru

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##### Re: how do i limit current?
« Reply #20 on: January 16, 2017, 09:49:36 pm »
The Electro BOOM guy is very funny. His videos of the car ignition coil and an electric guitar almost killed him and made him jump high and swear.
The electric guitar had 4 strings connected to 120VAC electricity and when he played it I laughed for an hour.

#### Vtile

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##### Re: how do i limit current?
« Reply #21 on: January 16, 2017, 11:16:19 pm »

The gizmo won't deliver that much current - it has rougly 30W on input, give or take judging from the 7.2V battery and the 4A current. With 80% efficiency that leaves 24W, at 60kV that gives some 400uA maximum it will be able to deliver.

However, the shock and the resulting muscle spasm will throw you across the room, no problem. Also the resulting nice high frequency burns are "fun" to heal.
If you trust that chinese PoS, I wouldn't.

Smf