# Discharge circuit, dump circuit

#### Mrusten

Joined Dec 23, 2015
60
hello

im looking for a circuit that can remove access power from a battery, but i can not find it anywhere.
im not that competent in designing circuits so i wil try in forum.

maybe someone have a circuit that i can use.

ok i have a few "requirements" for way of function
no programming
pwm based discharge
pwm 0-100% (not critical can be for example 10 - 90%)
pwm start voltage adjustable if batteryvoltage 5v over start voltage =100% pwm
pwm start voltage adjustable dc240v - dc265v (example start 265,05=1%pwm 270=100%pwm
pwm ramp up and down slowly
pwm is limited by a current shunt adjustable from 1A to 100A
pwm frequency not critical about 3khz

explaining of circuit work:
current limit set to 10A

voltage increase to 240,1vdc
pwm start 2%

voltage increase to 241vdc

voltage increase to 242vdc
pwm try to adjust slowly to 40% but the current limit stop and hold the pwm at 30%

voltage increase to 243vdc
current limit still hold the pwm at 30%

voltage decrease to 240,5

voltage decrease to 240
pwm stop

#### crutschow

Joined Mar 14, 2008
24,724
im looking for a circuit that can remove access power from a battery
What is "access power", or assuming you mean "excess power" what is that?

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#### Mrusten

Joined Dec 23, 2015
60
haha englich is not my native language so i miss spell a lot.
i mean power witch is extra or to much

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#### MrAl

Joined Jun 17, 2014
7,491
You can get battery chargers that will drain a cell and tell you the ampere hours measured while it is discharged. I dont know what kind of battery you care talking about here though did you mention taht yet?
The small cells like 1.5va and the Li-ion type can be done with those kinds of battery chargers.

You know you can use a power resistor if you are not in a hurry.

#### crutschow

Joined Mar 14, 2008
24,724
i mean power witch is extra or to much
How can a battery have extra or too much power?
That maximum energy stored in a battery is when it is fully charged.
There's usually no reason to discharge it from that point.
Why do you think you need to do this?

#### Mrusten

Joined Dec 23, 2015
60
How can a battery have extra or too much power?
That maximum energy stored in a battery is when it is fully charged.
There's usually no reason to discharge it from that point.
Why do you think you need to do this?
to keep the battery working for a long time i use only 60% of the total avalible storage.
to prevent solar charger to shut off when battery is full i want to drain the top off the battery to use the free energy for something useful

thats why i want to drain all power above sertain voltage

#### Mrusten

Joined Dec 23, 2015
60
You can get battery chargers that will drain a cell and tell you the ampere hours measured while it is discharged. I dont know what kind of battery you care talking about here though did you mention taht yet?
The small cells like 1.5va and the Li-ion type can be done with those kinds of battery chargers.

You know you can use a power resistor if you are not in a hurry.
battery is 90kwh
i want to drain the top of the battery to prvent the solar charger to shut off when the battery is full

i do not know where you got a single sell from, in my example i wrote 240vdc i do not know about any cell that is 240vdc
i also didnt mention any measurements only to have a limit for the discharge current

#### nsaspook

Joined Aug 27, 2009
7,181
What you want is a dump/diversion load circuit.

The function can be built into the charge controller or system monitor. For my 12vdc solar monitor I designed in a diversion load system to transfer excess solar power to a AUX heat load when the battery is fully charged and the inverter load is low. Usually there's little excess power to divert.

Status report line:

System Status:
PV Voltage 13148mV, Charging Voltage 13206mV, Controller Voltage 11823mV, Charge Cycle Time Left 9:18, Absorp Current 000mA, End-Amps 3000mA
PV Current sensor 11200mA, Inverter Battery Current sensor -4900mA, Inverter Load Current 6300mA, Current Power IN 147W, OUT 83W
AC PWR Inverter 0, Utility 0, Glitch Count 0: Power Diversion enabled: DIPSW7, Diversion Status Off: PWM 0%
Todays Power Q level: 8, Yesterdays Power Q level: 27
Total Charger Energy 20695Wh, Todays Charger energy 895Wh, Prev Charger Energy 2105Wh, Diversion Energy: Total 0Wh, Todays 0Wh
Total PV Energy 6261Wh, Todays PV energy 205Wh, Prev PV Energy 634Wh, Total Usage 23087Wh, Todays Usage 1698Wh, Dayclock 0:

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#### Mrusten

Joined Dec 23, 2015
60
What you want is a dump/diversion load circuit.

The function can be built into the charge controller or system monitor. For my 12vdc solar monitor I designed in a diversion load system to transfer excess solar power to a AUX heat load when the battery is fully charged and the inverter load is low. Usually there's little excess power to divert.

Status report line:

System Status:
PV Voltage 13148mV, Charging Voltage 13206mV, Controller Voltage 11823mV, Charge Cycle Time Left 9:18, Absorp Current 000mA, End-Amps 3000mA
PV Current sensor 11200mA, Inverter Battery Current sensor -4900mA, Inverter Load Current 6300mA, Current Power IN 147W, OUT 83W
AC PWR Inverter 0, Utility 0, Glitch Count 0: Power Diversion enabled: DIPSW7, Diversion Status Off: PWM 0%
Todays Power Q level: 8, Yesterdays Power Q level: 27
Total Charger Energy 20695Wh, Todays Charger energy 895Wh, Prev Charger Energy 2105Wh, Diversion Energy: Total 0Wh, Todays 0Wh
Total PV Energy 6261Wh, Todays PV energy 205Wh, Prev PV Energy 634Wh, Total Usage 23087Wh, Todays Usage 1698Wh, Dayclock 0:
yes thats what im looking for, but i would like to build a circuit to drive a SCR to do that job, thats why im asking if someone have voltagecontrolled pwm and tell what to modify to make it work with 240vdc ++
my solar is 18kw and 7kw of wind, house can not use it all so i would like to devirt the power when battery is full.
my controllers do not have that function built in, my controllers just shut off when battery is full

#### nsaspook

Joined Aug 27, 2009
7,181
What type of load do you want to divert that 240vdc to?

#### Mrusten

Joined Dec 23, 2015
60
What type of load do you want to divert that 240vdc to?
heating element
i wil use scr or igbt to do the job but need the pwm circuit

#### nsaspook

Joined Aug 27, 2009
7,181
One of your requirements is no programming but your list of features require feedback loops and set-point programming of some type (analog and digital) so good luck with your pwm circuit.

#### Mrusten

Joined Dec 23, 2015
60
One of your requirements is no programming but your list of features require feedback loops and set-point programming of some type (analog and digital) so good luck with your pwm circuit.
by programming i ment microcontroller.

feedback circuit with potentiometers is what i would like to have

#### nsaspook

Joined Aug 27, 2009
7,181
by programming i ment microcontroller.

feedback circuit with potentiometers is what i would like to have
What you would like and what's practical with your specifications using simple controllers are two different things.

#### Mrusten

Joined Dec 23, 2015
60
What you would like and what's practical with your specifications using simple controllers are two different things.
here is a drawing to show what i was thinking,
offcorse it do not work bechause i do not have the knowlege to make it correct but the design or how to do should be possible this way.
240v is stepped down to 0v and 245v wil then be 5v, potentiometer is there to adjust the 0v from 240 to 265v and the 5v wil be 5v higher as in the first example.

0-5v is amplified by opamp, zener is there to pull down the voltage if the 0-5v should be higher than 5v.
0-5v pwm circuit 0v=0%duty 5v=100%duty.
pwm output have a pull down resistor to shut the SCR off when pulse is low.

shunt feedback the current via transistor and pull down the 0-5v if current is over setpoint by the potentiometer close to the shunt

then finally the battery and load is connected to the SCR input and output.

SCR is a NKT110-16A

#### Alec_t

Joined Sep 17, 2013
11,144
A problem with using an SCR in a DC-only circuit is that once triggered on it stays on (unless the current through it or voltage across it is reduced to near zero), so trying to control it with PWM becomes complicated. A power MOSFET would be more suitable.

#### Mrusten

Joined Dec 23, 2015
60
A problem with using an SCR in a DC-only circuit is that once triggered on it stays on (unless the current through it or voltage across it is reduced to near zero), so trying to control it with PWM becomes complicated. A power MOSFET would be more suitable.
so the pulldown resistor to the scr gate wil not work?

#### Mrusten

Joined Dec 23, 2015
60
A problem with using an SCR in a DC-only circuit is that once triggered on it stays on (unless the current through it or voltage across it is reduced to near zero), so trying to control it with PWM becomes complicated. A power MOSFET would be more suitable.
i have a large igbt in my shelf somwhere too so could use that

#### MrAl

Joined Jun 17, 2014
7,491
Hi,

Yeah you can not turn off an SCR via its gate once on when it has a DC current flowing through it. You have to reduce the current to below the holding current which is typically quite low.

What are you going to use for the discharge load?
I ask because some people think you can use a 10 watt resistor to handle 100 watts just because they are PWM'ing it. The resistance must be able to handle the power being delivered to it PWM or not.

At 200 volts the power can be quite high unless the resistance is also rather high.
for resistances of:
200,500,1000,2000,5000,10000
Ohms

the power respectively is:
200,80,40,20,8,4
watts.

so you need about double that power rating for the dump load.

Note that for example if you use a 200 Ohm resistor and PWM it at 50 percent, the power is 1/2 of that above which is 100 watts, so a 200 watt resistor would do it although it will get hot.
If you PWM it at 25 percent duty cycle it will be 50 watts so a 100 watt resistor would handle it although get hot. If you PWM it at 10 percent duty cycle it will be 20 watts so a 40 watt resistor should handle it although get hot.

#### Mrusten

Joined Dec 23, 2015
60
Hi,

Yeah you can not turn off an SCR via its gate once on when it has a DC current flowing through it. You have to reduce the current to below the holding current which is typically quite low.

What are you going to use for the discharge load?
I ask because some people think you can use a 10 watt resistor to handle 100 watts just because they are PWM'ing it. The resistance must be able to handle the power being delivered to it PWM or not.

At 200 volts the power can be quite high unless the resistance is also rather high.
for resistances of:
200,500,1000,2000,5000,10000
Ohms

the power respectively is:
200,80,40,20,8,4
watts.

so you need about double that power rating for the dump load.

Note that for example if you use a 200 Ohm resistor and PWM it at 50 percent, the power is 1/2 of that above which is 100 watts, so a 200 watt resistor would do it although it will get hot.
If you PWM it at 25 percent duty cycle it will be 50 watts so a 100 watt resistor would handle it although get hot. If you PWM it at 10 percent duty cycle it will be 20 watts so a 40 watt resistor should handle it although get hot.
i wil use water heater elements and i wil limit the current by the current shunt feedback to prevent melting of the heating element, i explained it in the text above

typically heating element is 2000w, its a resistive load so it wil work fine with dc.
i need to experiment with how many heating elements and i need to limit the current according to the ammount of heating elements. that stuff i understand, what i can not do is designing circuit, i understand only the basic functions

we are talking about 90kwh battery and high voltages and powers up to about 27kw, its no joke, 10w resistor is not going to work

scr or igbt wil see between 240 - 270v and 0-100A

thats in the extreme end of the scale. normal operation wil be to divert access power when battery is full minus loads = 6kw

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