Diode with very low voltage drop... 0.3v or less? For solar applications...

Clarkdale44Clarkdale44 Registered Users Posts: 17 ✭✭
As my title says...

Is there such a diode with very low forward voltage drop... 0.3v or less.. for higher current such as 60A and 50V?

I will be using it on 12V battery, the max i will be drawing is about 20Amps constantly and might go up 28 to 30A in rare occasions.
I need a very less voltage drop otherwise my inverter may fail to recognize the battery also less dissipation.

Is there such a diode exists?

Comments

  • mike95490mike95490 Solar Expert Posts: 7,357 ✭✭✭✭
    Huh ?   Why do you need a diode on your inverter line ?  Does your inverter trip offline from too high of voltage ?

    The last couple months, I've seen many neophyte questions about using a magic diode somewhere.
     Is there some blogger trying to sell diodes ?   No modern PV system needs any added diodes.

    If you need a diode action, with little Vf drop, a FET biased ON has less drop and loss than even a Schottky Diode.

    Here's 2 articles you can read about diodes and FETs
    http://www.digikey.com/en/articles/techzone/2012/dec/active-bypass-diodes-improve-solar-panel-efficiency-and-performance
    http://www.radio-electronics.com/info/data/semicond/schottky_diode/schottky_barrier_diode.php

    Read, learn, and no need to buy anything, unless you have VERY unusual circumstances,



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  • Clarkdale44Clarkdale44 Registered Users Posts: 17 ✭✭
    edited October 2016 #3
    mike95490 said:
    Huh ?   Why do you need a diode on your inverter line ?  Does your inverter trip offline from too high of voltage ?

    The last couple months, I've seen many neophyte questions about using a magic diode somewhere.
     Is there some blogger trying to sell diodes ?   No modern PV system needs any added diodes.

    If you need a diode action, with little Vf drop, a FET biased ON has less drop and loss than even a Schottky Diode.

    Here's 2 articles you can read about diodes and FETs
    http://www.digikey.com/en/articles/techzone/2012/dec/active-bypass-diodes-improve-solar-panel-efficiency-and-performance
    http://www.radio-electronics.com/info/data/semicond/schottky_diode/schottky_barrier_diode.php

    Read, learn, and no need to buy anything, unless you have VERY unusual circumstances,



    "VERY unusual circumstances".. It is indeed as you have said..

    My ups/inverter has a low battery cut off voltage of 10.4v, which i think is pretty damn low for a 12.0v battery.
    At first i thought only 0.3 is necessary but now i think 0.7 is not bad but more on the safe side.

    So by using a diode here between the charging cable and battery terminal, and using a diode's voltage drop, i think i can make my ups think that it is disconnecting the battery at 10.4 in reality it will be cutting off at 11.1v if the voltage drop of diode is 0.7v.

    Did you get what i am trying to do here?
    10.4v + 0.7 = 11.1v, so when battery voltage reaches 11.1v ups would think it is 10.4v and will disconnect the battery.

    I have a small solar panal which efficiently charges the battery so i don't need the charger inside ups.

    So is there such a stud diode with 0.7 or less voltage drop with current capability for handling about 30 to 40Amps?
  • AguarancherAguarancher Solar Expert Posts: 267 ✭✭✭
    edited October 2016 #4
    If you are drawing your battery down below 12.0 on a regular basis, you are sending it to an early death. 12.1v is 50% drained on a 12v battery and about the max you want to discharge it.. 11.51v is 90% discharged..
  • BB.BB. Super Moderators Posts: 26,951 admin
    11.5 volt under significant loading--Is probably not a bad cutoff... But remember that your diodes are dropping voltage which is a waste of energy.

    A 1.2 kWatt load at 12 volts is around 100 amps... 100 amps * 1.0 volt drop = 100 Watts of wasted energy.

    Your better bet--Setup an alarm system when you hit low voltage (say 10.5 volts for 20 seconds, 11.5 volts for 5 minutes, 12.0 volts for 1 hour)--Or get a different inverter with programmable cutoff voltage.

    Alternatives include using a battery monitor with a low battery output contact such as:

    https://www.victronenergy.com/battery-monitors/bmv-700

    But battery monitors have their own issues (there readings can drift over time).

    Are you trying to create a system to protect your battery bank for a remote system (nobody living there)? Adding devices to turn off loads to protect your battery bank automatically (and/or adding an automatic start genset) adds complexity and the chances for more ways for something to fail.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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