Problems when shortcutting a solarpanel

Hi all,

I don't know if this is the right place for the topic. Anyway

I have made a charging circuit to charge a 6V lead batteri from a 5W solarpanel.

The batteri will 3 times a day drive a motor. When the motor is running it draw current from the batteri of corse but it will also try to take current from the charger and in the end the solar panel.

Now the panel is very small so the voltage wil just drop to 0V and the charger wont be damaged. But will the solarpanel? I think no, because there is very little current being drawn from the panel, as the voltage on the panel is close to - if not 0... But what is your opinion?

Kind Regards
Michael

Re: Shortcutting solarpanel

Short circuit of photovoltaic panel is used in current test, also this cant make harm to panel, but we speak about panel not about system with several panels in serie that will give huge sparks even fire. I think that panel should not be stayed in this short circuited condition for longer time, I think this can shorten life of panel.

Re: Shortcutting solarpanel

tpetar said:

Short circuit of photovoltaic panel is used in current test, also this cant make harm to panel, but we speak about panel not about system with several panels in serie that will give huge sparks even fire. I think that panel should not be stayed in this short circuited condition for longer time, I think this can shorten life of panel.

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Thanks for your reply,
Well it is a rather small solar panel: 18V 5W

the issue is that the panel with charging circuit is connected to the battery at all times. As mentioned before, the battery is driving a dc motor witch is turned on 3 times a day for about 5 sec.

What ytou recommend some kind of protection circuit to avoid that the motor will draw current from the charger/solarpanel when it turns?

I was hoping that it didn't matter as the solar panel is quite "weak"

Kind Regards
Michael

Re: Shortcutting solarpanel

You can make some simple low voltage detection and disconnection circuit, but there is another problem.

1. We have Sunlight, panel charge battery, motor running.
2. Sunlight is over, motor running, battery discharging.
3. Motor running, battery dont have energy its empty.
4. Motor stays connected on battery and panel.

5. Sunlight back, panel produce power but is this power enought to power motor to run, and charge battery ?

Re: Shortcutting solarpanel

I understood your problem,when the motor turns on it should only draw the current from the battery.But tell me the ratings of your DC motor(voltage/current/power) and the ratings of your lead acid battery(voltage/AH rating) if you connect the solar panel always with the battery this may overcharge your battery

Re: Shortcutting solarpanel

I don't understand which problem you are imagining. You'll need a charge controller, that stops battery charging at about 7.2 V. You should also implement protection against deep discharge, the motor must not run when the battery voltage is below a certain level, e.g. 5 V. The solar panel will be connected through a diode to avoid battery discharging. Because the voltage is buffered by the battery, no other protection means are required.

Re: Shortcutting solarpanel

I don't know the specs on the dc motor. I only have the battery wich drives it. The battery is 6V 1.3Amp. The system is not for me....

I use a LM317 wich is set up as a current limiter, to charge the battery. The maximum charge current is 390mA. As you probaly already know the current will decrease when the voltage on the battery increase. And when it is fully charged the charging current is almost 0.

The battery can operate the motor for several months without a charger on it. So the highlighted scenarios below should not ever be the case:

1. We have Sunlight, panel charge battery, motor running.
2. Sunlight is over, motor running, battery discharging.
3. Motor running, battery dont have energy its empty.4. Motor stays connected on battery and panel.
5. Sunlight back, panel produce power but is this power enought to power motor to run, and charge battery ?

Re: Shortcutting solarpanel

DC motor runs only 15seconds (3times*5secs/day) per day so battery dont need to be charged always because after the load is disconnected then the battery's voltage will regain to its full voltage after few minutes.if battery is continuously charged/discharged the life of the battery would reduce(so battery need to be charged after it reaches its minimum voltage(Deep discharge cut-off voltage))

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you are using constant current method to charge the 6V/1.3AH lead-acid battery its not advisable to charge the lead-acid battery using constant current method instead you have to use constant voltage method(check your battery for the charging details) then you can check the state of charge by monitoring the battery charging current.i think you have to concentrate about designing a battery charger.

Re: Shortcutting solarpanel

yogece said:

DC motor runs only 15seconds (3times*5secs/day) per day so battery dont need to be charged always because after the load is disconnected then the battery's voltage will regain to its full voltage after few minutes.if battery is continuously charged/discharged the life of the battery would reduce(so battery need to be charged after it reaches its minimum voltage(Deep discharge cut-off voltage))

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Hmm, anyone know of a circuit that can handle that?

But should I have some kind of protection circuit to avoid the motor to draw current from the charger and panel when it is running?

Re: Shortcutting solarpanel

yogece said:

DC motor runs only 15seconds (3times*5secs/day) per day so battery dont need to be charged always because after the load is disconnected then the battery's voltage will regain to its full voltage after few minutes.if battery is continuously charged/discharged the life of the battery would reduce(so battery need to be charged after it reaches its minimum voltage(Deep discharge cut-off voltage))

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This is not true, battery cant recharge itself, but chemical will stabilize inside battery and this will also stabilize voltage, but will not bring battery to full of charge. Lead Acid can be on float charging for long time, and lead acid should not be on minimum ever (if starter),.... but this you can read in other threads, this story is repeating 1000 times...

you are using constant current method to charge the 6V/1.3AH lead-acid battery its not advisable to charge the lead-acid battery using constant current method instead you have to use constant voltage method(check your battery for the charging details) then you can check the state of charge by monitoring the battery charging current.i think you have to concentrate about designing a battery charger.

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First phase of charging lead acid can be constant current, later goes float charging,......




You need good solar controller, what FvM says, if you charge that battery from small battery you dont have lots of options for charging.

Other timing circuits which controls motors working time is on your will.


Never get lead acid discharged below 11,9V (1,98-1,99V per cell) if starter type, 10,5V if deep cycle type (1,75V per cell).

Your answer is in post #6.

Re: Shortcutting solarpanel

i am suggesting you to disconnect the charger from the battery when the battery doesnt require charging because you dont need to charge the battery often if the battery voltage reached the deep-discharge cut-off point then you turn on the changer and disconnect the charge once your battery attains the full charge.for accomplish this you have to design a battery voltage monitor circuit(Design battery voltage monitor by using LM324) and charger turn-on circuit(if you charge the battery using the constant voltage method then you can easily cut-off the battery and charger by simply inserting a 1N4007 diode and in addition the LM317 must produce the output voltage less than the deep-discharge cut-off voltage once the battery monitor detects that battery attains the cutoff point then the output voltage of the LM317 should be increased to battery charging voltage+0.7V(for eg: if battery charging voltage is 7.5V then the output voltage of regulator should be equal to 8.2V) once the battery attains full charge then the voltage of LM317 should be lowered below the cut-off point voltage of the battery).

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Dear tpetar i dont say the battery would recharge itself.But when you connect a battery with a load for very short time(if battery drives a load for a short duration) here it needs to work only 15 Seconds/day.wont the battery reach its maximum voltage after the load is removed,it will take few seconds or minutes to regain its maximum voltage.Do you agree with this or not?

If you want to recharge the battery quickly first you should use constant current charging(you cannot use constant current charging until your battery gets charged fully) and if your charger is not intelligent enough to detect the state of charge(SOC) of your battery it will immediately deliver constant current to charge the battery(this frequent charging/discharging of battery would considerably reduce the battery life) the battery charge should decide whether to use constant current/constant voltage according to the battery usage cycle i.e standby(moderately discharged battery) use or cycle use(Deep discharged battery) for charging the cycle use constant current charging is used for standby use charging constant voltage charging is used.
after the CC,CV (Topping charging) charging finally the battery would be trickle or float charged.
The trickle or float charging method is used to keep the rated battery terminal voltage due to self discharge the terminal voltage of the battery's would be reduced(this method is can be used for higher AH battery's) these three charging methods are used by the intelligent chargers.

Re: Shortcutting solarpanel

@ yogece

well the alternative to remove battery from charger is of no use as it becomes cumbersome to repeat it day in and day out

this may also lead to prob if manual error of replugging is over looked many aspects are to be considered before we try this out

Re: Shortcutting solarpanel

The standard charging method for lead-acid batteries used as power supply backup is constant current/constant voltage. There's no need for or advantage in disconnecting the battery charger. An additional low-voltage cutoff circuit will prevent from deep discharge, as discussed by tpetar in post #10.

Operating the battery this way achieves maximum battery lifetime. The simple charge method is specific to lead acid batteries and doesn't work in the same way for NiMH or Li-Ion.

(I noticed a strange behaviour of the board software. I found this post doubled, after deleting a copy, both instances disappeared).

Re: Shortcutting solarpanel

I have been reading a lot about charging lead batteries, because of this discussion
I used to believe that the general "rule" is to charge a battery with a 1/10 of its capacity.

So when I made my charger with the LM317 regulator I adjusted the charging circuit to charge with 130mA.
But when I looked at the specs of the battery it said that max charging current is 390mA. And the voltage for cycle use is 7,2-7,5V

With that in mind I discharged the battery a bit at adjusted the charging current to 390mA. And then I waited for it to start trickle charging.
When that happend I could only measure about 6,2-6,3V over the battery. Then I tried to adjusted the charging current while measuring the voltage over the battery. If I adjusted it to the 7,2V the current is way over 390mA!

Is my charging circuit not suitable after all?
When I recieve the batteries the only measure 6,3V. Should they measure 7,2V to be fully charged?

The batteries is a ultracell UL 1,3-6
www.ultracell.co.uk

Re: Shortcutting solarpanel

AS I recall optimum load is about 70% of open cell voltage, so you may want to consider rewiring array from 18 to 9V array to charge 6V Pb acid cells to 7.1 V max.

Put UVP and OVP into your system design to protect the battery.

I have made some changes to my circuit today. I before it could handle charging current way above 1 amp. I have now limited it to 300mA.

Before I connect the battery I adjust til voltage to 7.2V
According to the battery specs, cycle use voltage is 7.2V

It seems to function perfectly this way. Though I had to decrease the charger input voltage
from 18V to 10V as the heat dissipation in the LM317 has increased after the changes.

Can you change your solar panel from 18V to 9V?

Can you post your setup photo and schematic?

Can you change LM317 to an LDO regulator?
This way you can drop the charger voltage and increase the current to C/4 or Amp-hr rating /4h to limit this result to the current without significant temperature rise in regulator.