Go Down

Topic: Diode voltage drop (Read 6180 times) previous topic - next topic

septillion

@Mark, that's cool but dropping 8-isch volt or so with that @ 5A will generate 40W! That is A LOT!

If you really want to try you can open one up and look for the feedback loop inside. Sometimes it obvious but sometimes it's not. But if you can find it (most of the time some sort of resistor diver) you can change it to lower the voltage.

If you don't want to do so I think the best/easiest option remains a new PSU. Dropping that kind of voltage with that kind of currents in a linear fashion is just making a heater (and asking for trouble).
Use fricking code tags!!!!
I want x => I would like x, I need help => I would like help, Need fast => Go and pay someone to do the job...

NEW Library to make fading leds a piece of cake
https://github.com/septillion-git/FadeLed

Domino60

I found a solution using this module :



To be or not to be? Read a book and you will see.
Join Discord Free_World (Arduino_Room) Live chat
https://discord.gg/bBXEuKQ

septillion

Yes, that will work (it's a switch mode step down converter as I suggested in my first post) but be aware the 3A out is the absolute max current (and probably isn't to happy to run @ 2A+ for long). So if you set the charger to charge to fast it will fry the converter. (Charger is speced @ 5A)
Use fricking code tags!!!!
I want x => I would like x, I need help => I would like help, Need fast => Go and pay someone to do the job...

NEW Library to make fading leds a piece of cake
https://github.com/septillion-git/FadeLed

Domino60

Quote
Yes, that will work (it's a switch mode step down converter as I suggested in my first post) but be aware the 3A out is the absolute max current (and probably isn't to happy to run @ 2A+ for long). So if you set the charger to charge to fast it will fry the converter.
It's working really well, i start charging at 2A after 35min the module reached +85C` and start shuting down itself so i added a kinda big heatsink above and a 12v fun to cool down and works another thing is that the power supply start getting hot too so in the future if i will keep this setup i need to make a box to put them all inside.  Power supply, drop down module, heatshik and fun. At least it's working.


ps (after 25min "without fun" i start smelling burning plastic i was like wtf :D put my finger on the module and it was hot as hell).


To be or not to be? Read a book and you will see.
Join Discord Free_World (Arduino_Room) Live chat
https://discord.gg/bBXEuKQ

septillion

Yep, that's what I suspected ;) What kind of battery were you charging? Because the charge current isn't important but the charge power ( I x U = P).

If you charge a single NiMH cell @ 2A you have +- 3,2W (2A x 1,6V). At the 12V input of the charger (and so the output of your step down converter) this only gives a current of 267mA (3,2W / 12V).

But if you charge a pack of 6 LiPo's with 2A you put 50W!!! (6 x 4,2V x 2A) into the pack. At the input of the charger/output of the step down this is 4,2A (50W / 12V). That's to much for the step down converter, even with a fun :p (I guess you mean fan but it looks funny :p). And I don't even take in account the losses in the charger etc. So be aware of your settings when charging with this setup. Setting it just to 2A for charging isn't a guarantee you don't overload the step down module.

And to be able to charge as fast as you can, set the output of the step down module to 18V. This way you have 54W (3A x 18V) (assuming it can handle 3A constant wich I doubt and without losses) instead of 36W (3A x 12V)
Use fricking code tags!!!!
I want x => I would like x, I need help => I would like help, Need fast => Go and pay someone to do the job...

NEW Library to make fading leds a piece of cake
https://github.com/septillion-git/FadeLed

elac

Link to your LM2596 module?
Most of those small switching modules handle around 10W - 15W, over 10W use heatsinks. They will handle a max of 3A @ 5v or less.
It's all about the skills

Domino60

To be or not to be? Read a book and you will see.
Join Discord Free_World (Arduino_Room) Live chat
https://discord.gg/bBXEuKQ

septillion

3 lipo cells charged @ 2,2A gives 27,72W. If you set the step down to 12V this means you have a current of 2,31A not including losses!. If i include losses and say the charger is +-80% efficient your up to 35W so @ 12V gives you 2,9A, very close to the max of the step down.

If you go to 18V output of the step down you only have 1,54A without or 1,94A with losses.

And now about the losses in the step down (chip only, losses in the coil not taken into account). At an input of 22V and an output of 12V to 18V it's 90% efficient max under full load. If it has to supply 35W it is still burning about 4W in the converter already which can get hot.

So set the step down to 18V and indeed cool the step down. Also don't charge faster then 2,2A or more then 3 LiPo cells with this setup because the step down is just to light for that.
Use fricking code tags!!!!
I want x => I would like x, I need help => I would like help, Need fast => Go and pay someone to do the job...

NEW Library to make fading leds a piece of cake
https://github.com/septillion-git/FadeLed

Domino60

#23
Jul 26, 2015, 03:37 pm Last Edit: Jul 26, 2015, 03:38 pm by Domino60
Quote
So set the step down to 18V and indeed cool the step down. Also don't charge faster then 2,2A or more then 3 LiPo cells with this setup because the step down is just to light for that.
I charge the LiPo at 1C so it's normal for the lipo and B6 about the step down "let it burn" :D I'm joking, it's working fine, yes it heats up a lot but with a 5cm x 5cm fun it gets in a normal temperature (under 40C`).

btw the step down i got it at +12v or i can put it 12~18v i don't really care :D it works.
To be or not to be? Read a book and you will see.
Join Discord Free_World (Arduino_Room) Live chat
https://discord.gg/bBXEuKQ

septillion

Yeay, I know it's normal. But that doesn't mean you don't blow the step down if you charge faster/more. @18V the step down will be cooler / capable of charging more LiPo's etc
Use fricking code tags!!!!
I want x => I would like x, I need help => I would like help, Need fast => Go and pay someone to do the job...

NEW Library to make fading leds a piece of cake
https://github.com/septillion-git/FadeLed

MarkT

Its an emitter-follower driven from a zener, so its basically a high-power zener in function.

Of course you have to waste all the power, whereas using the right power supply in the first
place would avoid that.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

Domino60

Quote
Of course you have to waste all the power, whereas using the right power supply in the first
place would avoid that.
I got as well a 12v 800mA power supply which i charge my battery drill but when i tested the output of that
power supply i got over 19 volts so i can't understand why the hack do that.
To be or not to be? Read a book and you will see.
Join Discord Free_World (Arduino_Room) Live chat
https://discord.gg/bBXEuKQ

raschemmel

#27
Jul 27, 2015, 01:50 am Last Edit: Jul 27, 2015, 01:51 am by raschemmel
Quote
is there any other kind
of diode that i can drop it more but with a single diode not more ?
Well, not to state the obvious, but if it dropped 7V instead of 0.7, it wouldn't be a diode drop now would it ?

FYI, any linear power supply is going to consist of an input voltage and a regulator circuit.
You already have your input voltage (19V). All you need is the regulator circuit.
12V regulator circuit

Of course if that's too complicated you can go with the 10 diodes in series...
Arduino UNOs, Pro-Minis, ATMega328, ATtiny85, LCDs, MCP4162, keypads,<br />DS18B20s,74c922,nRF24L01, RS232, SD card, RC fixed wing, quadcopter

Domino60

Quote
Quote
You already have your input voltage (19V). All you need is the regulator circuit.
If you look few comments above you will see that i got one :D
To be or not to be? Read a book and you will see.
Join Discord Free_World (Arduino_Room) Live chat
https://discord.gg/bBXEuKQ

raschemmel

Those LM2596 modules are cheap enough that you can put two of them in parallel. to eliminate your overheating problem.
Arduino UNOs, Pro-Minis, ATMega328, ATtiny85, LCDs, MCP4162, keypads,<br />DS18B20s,74c922,nRF24L01, RS232, SD card, RC fixed wing, quadcopter

Go Up