Hi, do you guys mind explaining a little about this?

What are the consequences of applying a solar panel which has the output voltage of 20V to a 6V sealed lead acid battery for charging purposes?

Will doing so reduce the life-time of the battery?

Thanks in advance

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Lord Robert Stephenson Smith Baden Powell\'s last message : -BE PREPARED-

 

hi devonsc
no because the battery will bring down the solar panel voltage to a little above the battery voltage..
the solar panel kind of 'self adjusts' to the battery it is charging, due to the internal resistance of the battery..
just because the solar panel has an open circuit voltage of 20V , does'nt mean that it will charge the battery at 20V

 

I disagree with WilliB. If the solar panels have the capability of taking the charge voltage above 7.2 to 7.35 volts the battery can be overcharged. Most manufactures recommend that when the charge voltage reaches this level that the charger should be removed or the charge voltage be reduced to 6.75 to 6.9V.

As a side note I have 3ea 75 watt solar panels that charge some 12 volt batteries. The open circuit voltage is around 20 Volts. When the sun hits these panels and they are charging at maxium current (about 12 amps) the voltage output is 18V. I use a charge controller so I don't overcharge the batteries.

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very true but devon is talking about a single solar panel , which doesnt have the current to push the battery that far..
he is doing a school project and i guarantee his panel isnt putting out 75W..sorry Devon :wink: My two solar panels dont even put out one watt combined.. ops: :lol:

 

Thanks, k7elp60 and williB...

Actually, williB guided me in developing a boost DC/DC converter before this, that is the reason why he knows the exact panel that I'm talking about. Would like to clarify my question again, help needed from you guys Sorry for not making myself clear...

I understand that one of the main requirements to charge a battery would be having a higher voltage from the source to allow the flow charge or current to the battery, is this right?

I was trying to know if there would be any negative consequences to the battery if I were to apply a...for example, a 20V solar panel to charge a 6V SLA battery.

I've developed a buck-boost converter (williB? I've changed my design from boost to a buck-boost, thanks) to charge SLA battery of 12V and 6V. I have overcharge protection by controlling the the MOSFET switching through a PIC microcontroller, where I will turn on and leave the MOSFET under on state if the battery level feedback is 14V for 12V SLA battery and 7V for 6V battery, is this okay? Any comments?

I was just trying to understand in depth regarding the necessitiy for me to buck the voltage level of the solar panel if it is way too high. Is there any? As in, is it a must to buck before I charge? Will I somehow spoil the battery if I didn't buck the output voltage of the solar panel to a lower level?

Thank you very very much in advance...

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Lord Robert Stephenson Smith Baden Powell\'s last message : -BE PREPARED-

 

It depends on the current output of the panel, a lead acid battery requires charging current - it will pull the incoming voltage down to what it wants.

In doing so it obviously draws current from the charging source, and if the source can provide high currents it 'could' overcharge and damage the battery.

However, this is extremely unlikely with solar panels, unless you have a huge great array of them!.

But your question leaves out the important information, such as the maximum output current of the panel, and the AH rating of the battery.

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I do not have any of the mentioned parameters in-hand, Nigel. It was just a question that I suddenly thought of:

Just like, why do we need a buck converter when we have proper overcharge protection? So, for instance, a 6V 3AH battery being charged by a solar panel that has the output of 20V, 40mA charging current

"Why do we need a buck converter?" as in, we will still be able to perform proper charging even though my solar panel outputs a very very high output voltage with 40mA charging current.

Like the mentioned example, charging the 6V battery after stepping down the output voltage of the solar panel to a level of...say, 10V better than not having the output of the solar panel being stepped-down?

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Lord Robert Stephenson Smith Baden Powell\'s last message : -BE PREPARED-

 

I suggested a LONG!! time ago, feeding the panel directly to the battery, with a reverse blocking diode, if your panel can only supply a maximum of 40mA it's NEVER going to overcharge anything!.

Try it and see what results you get!.

The point behind using a switchmode converter is to better utilise the power - for example converting it to 10V at 80mA - but it all depends on losses etc.

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so did I......!!! :roll:
the panel probably allready has a reverse current diode built in!! :roll:

 

Okay, okay Thanks thanks Sorry for my stupidity ops:

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Lord Robert Stephenson Smith Baden Powell\'s last message : -BE PREPARED-

 

A 20V 40 mA panel will charge a 6V battery at basically 40mA. It has just as much potential to overcharge the battery as a 10V 40mA panel. If you shut off the current when the battery voltage reaches a full charge, you are fine. It will not damage the panel to operate like this.

The buck converter will allow a 20V 40mA panel to put out a charge current of nearly 3x, like 120mA. The battery will charge much faster.

It is unlikely that a 40mA charging current will have much ability to overcharge an SLA battery unless it's a really, really tiny battery. You will only see the full rated 40mA current under strong sunlight, only a few hours a day. I doubt this would substantially affect the overall battery life.