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betwixt said:
Certainly - all you need is a 1M resistor and a 12V Zener diode.

Brian.
Click to expand...
Hello I am new in electronics can you suggest to me the best circuit to convert 100V to 12v my circuit needs 12v 1A current and I have an Electric forklift which gives 95v output which I need to convert to 12v for my circuit
 
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Some questions :

1) 95V is DC or AC ?
2) The 12V, what is its load ?
3) What is allowable range / tolerance of 12V supply output V and current ?
4) Minimum load current that will always exist ?
5) Does 95V supply have load dump transient V generation issues ?
6) 95V supply, what is its absolute min / max V ?
7) What is ambient temperature range the Fork Lift has to operate in ?
8) If 95V is DC, supplied by series connected 12V batteries, can you tap off
at a lower voltage point in the series connected battery chain ?

Regards, Dana.
 
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danadakk said:
Some questions :

1) 95V is DC or AC ?
2) The 12V, what is its load ?
3) What is allowable range / tolerance of 12V supply output V ?
4) Minimum load current that will always exist ?
5) Does 95V supply have load dump transient V generation issues ?
6) 95V supply, what is its absolute min / max V ?
7) What is ambient temperature range the Fork Lift has to operate in ?

Regards, Dana.
Click to expand...
1) 95V-100V DC
2) A small ble scanner circuit which contains esp32 and some components my whole circuit consumes approx 1A current on 12V
6) min 36V - max 100V
7) 35-degree centigrade
 
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So basically you have to drop, worst case, 100 - 12 V = 88 V.

So pick a 30V DC DC module to gen the 12V, then drop the rest arcoss
a series of zeners.

So lets pick a DC DC thats 80% efficient, output load = 12W, so input power =
12 / .8 = 1.5W. So Input current = 1.5 / 30 = 50 mA.

So we have to drop 100 to 30 with a current of 50 mA. So Pz = 70 x .03 = 2.1W
So use a 5W (margin over 2.1WW) = ~ 70V zener.

Zener must have a heat sink.

DC - DC module : https://www.banggood.com/LM2596-DC-...-p-1005123.html?cur_warehouse=CN&rmmds=search

You can trade off input V to DC to DC with zener ratings, just make sure you always use margin
worst case for design, say 50%. Asd you raise Vin of DC to DC the Pz drops.


Regards, Dana.
 
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danadakk said:
So basically you have to drop, worst case, 100 - 12 V = 88 V.

So pick a 30V DC DC module to gen the 12V, then drop the rest arcoss
a series of zeners.

So lets pick a DC DC thats 80% efficient, output load = 12W, so input power =
12 / .8 = 1.5W. So Input current = 1.5 / 30 = 50 mA.

So we have to drop 100 to 30 with a current of 50 mA. So Pz = 70 x .03 = 2.1W
So use a 5W (margin over 2.1WW) = ~ 70V zener.

Zener must have a heat sink.

DC - DC module : https://www.banggood.com/LM2596-DC-...-p-1005123.html?cur_warehouse=CN&rmmds=search

You can trade off input V to DC to DC with zener ratings, just make sure you always use margin
worst case for design, say 50%. Asd you raise Vin of DC to DC the Pz drops.


Regards, Dana.
Click to expand...
Thanks, Dana

Can you suggest me another thing I have a 72V Dc to 12V DC converter can I use a series of zener diodes for the input to drop 100-70V=30V for my converter input please also mentioned the zener diode which is useful in this case?

This converter which I am using
 
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You have to go thru the calculations, to get at Zener power just as I showed you.

Regards, Dana.
 
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danadakk said:
So lets pick a DC DC thats 80% efficient, output load = 12W, so input power =
12 / .8 = 1.5W. So Input current = 1.5 / 30 = 50 mA.
Click to expand...

I think there is a mistyping here, 1.5W instead of 15W:
... so input power = 12 / .8 = 15W. So Input current = 15 / 30 = 500 mA.
 
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@KerimF
Thanks for picking this up.

@MuhammadAnas
So in post # 7 this :
So we have to drop 100 to 30 with a current of 50 mA. So Pz = 70 x .03 = 2.1W
So use a 5W (margin over 2.1WW) = ~ 70V zener.
Click to expand...

Should be changed to this :

So we have to drop 100 to 30 with a current of 500 mA. So Pz = 70 x .5 =35W
So use a 50W (margin over 35W) , 70V zener (68V seems closest).
Click to expand...
Click to expand...



Regards, Dana.
--- Updated ---

Notes on heatsink design for Zener :



Heatsink Calculations – Renewable Energy Innovation

www.re-innovation.co.uk www.re-innovation.co.uk


Regards, Dana.
 
Last edited:
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danadakk said:
@KerimF
Thanks for picking this up.

@MuhammadAnas
So in post # 7 this :


Should be changed to this :





Regards, Dana.
--- Updated ---

Notes on heatsink design for Zener :



Heatsink Calculations – Renewable Energy Innovation

www.re-innovation.co.uk www.re-innovation.co.uk


Regards, Dana.
Click to expand...
Hey, Dana thank you for your reply actually this zener diode is not available in my country can you please suggest me an alternative circuit to drop 100VDC to 70VDC whose components are easily available?
 
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If 100 to 70 then split the V over whatever diode you can get.
Say you can get 10V, then 3 in series will do the job. Then calc
Pzener as we did before and split that power, with margin,
over the 3 zeners.

You can always do this with a zener and a R :

1687513711124.png


So 70V Zener insures max in to DC/DC never exceeds 70 V, and R
drops most of the power. Design here (juggle the values in alignment
with what you can get for components) -

Zener Diode Calculator

calculators, engineering calculators....
www.calculatoredge.com

or https://www.electricaltechnology.org/2014/03/zener-diode-voltage-regulator-calculator.html

or https://www.petervis.com/electronics guides/calculators/zener/zener.html

Remember the calc will give you max Pzener, so you split that across the series zeners
with margin.


Regards, Dana.
 
Last edited:
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