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solar panel.

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Gregory

Member
I am looking at buying a solar panel The Informaion is below.
I would like to keep two 12V battery's charged when I am not using my boat.
Would the panel below do the job .
Would I require a voltage regulator.
Can it be a basic 12V regulator or dos it have to be a special regulator for a solar panel.
Would the sola panel have to be isolated befor starting the engin which has a alternator,

Specification:

Model No.: SP20

Watts peaks: 20w

Short Circuit Current: (Isc) 1.21A

Open Circuit voltage: (Voc) 22.5V

Optimum Operating Current: (lmp)1.11A

Optimum power voltage: (Vmp) 18V

Dimension: 630x290x25mm

Weight: 3kg
 
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audioguru

Well-Known Member
Most Helpful Member
Make a regulator with an output voltage of 13.8V for the batteries plus 0.7V for isolation diodes= 14.5V total. An LM317 adjustable regulator set to 14.5V with two resistors and two capacitors can be used. It will need a medium size heatsink to dissipate 5.5W.
The LM317 needs two resistors and two capacitors as shown on its datasheet.
 

Hero999

Banned
It depends on the size of the battery.

A large battery probably won't need a regulator, a smaller battery will.
 

bailey45

New Member
The LM317 will cost you some of your operating range. The drop out voltage for a 317 is 3 volts meaning your solar cell will need to output more than 17.5 volts to charge the battery. A LT1084CT or other LDO type regulator may be a better choice.

In applications with larger batteries > 100AmpHr a regulator may not be required as this solar cell would take 12-14 days to charge up a 100 Amphr battery. A blocking diode would be the only requiment.
 

MikeMl

Well-Known Member
Most Helpful Member
It depends on the size of the battery.

A large battery probably won't need a regulator, a smaller battery will.

I disagree. The OP's panel's average current over the solar day will be about 0.4A. To a 12V battery, the solar panel looks like a constant-current source, meaning that after the battery is charged, the battery voltage will be driven to a terminal voltage into the gassing range above 14.5V. Even a 100Ah battery will be driven into the gassing range; it just takes a few days longer.

Try connecting a current-controlled lab supply set to 0.4A (output voltage set to ~20V) to a flooded-cell lead-acid battery. The battery will be destroyed in about week due to grid corrosion!

Voltage regulation is absolutely required for long term float charging. The float voltage is the most important parameter. Setting the Long-term float voltage is somewhat of an art. Too low, and you don't prevent self-discharge. Too high, and the constant gassing depletes the electrolyte and the cranking capacity is destroyed due to chemical erosion of the lead grid.

I have researched this extensively, and I float my flooded-cell lead-acid batteries at 12.9 to 13.2V, depending on ambient temperature.

After the battery is fully charged, the steady state current into the battery kept at a regulated 12.9 to 13.2V will settle to a value which just equals internal leakage (self-discharge). I routinely see float currents of between 35mA to 120mA on large (Group 75 size). If you force 400mA into a battery long-term, the excess current goes in to electrolyte gassing, and plate corrosion.
 
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bailey45

New Member
I think we are talking about two different applications. For a solar powered system described I would use gelled Lead Acid (SLA) batteries not flooded cells. The gelled product has a better characteristic for long discharge periods. With this type of battery 400mA would not shorten the life the battery as the current required to keep the battery fully charged is 2-4 mA / AmpHr.
By comparison a 100 AmpHr SLA is the size of approximatly 3 group 75 size batteries
 

MikeMl

Well-Known Member
Most Helpful Member
Bailey,

I maintain a total of 8ea 100AH Sealed Lead-Acid batteries, four in an industrial scissors lift, and four to run my ham station on.

The correct float voltage (printed right on the battery) is 13.6 to 13.8V, about 700mV higher than for a flooded-cell lead-acid battery. You are right, the self-discharge rate of a SLA is about 1/3 to 1/2 of what it would be for a comparable size flooded-cell. On float, after they are fully-charged, I see a long-term leakage current of 35-85mA on the 100Ah SLAs at room temperature. As they age, this current keeps increasing. By the time the leakage current is over 120mA, the battery is ready to be replaced.

SLAs are even more prone to damage due to chronic overcharging than flooded-cell batteries. You cannot replace the electrolyte, and their grids are also subject to corrosion.

Read the warnings about overcharging on the SLA maker's spec sheet. They are very emphatic about it, and they will not honor their warrantee if they inspect a battery, find the plates corroded due to overcharging. (Ask me how I know) :mad:

An unregulated 0.4A(ave) constant-current solar panel will overcharge even a large SLA if you are relying on the self-leakage of the battery to consume the available current, precisely because the leakage current is so low to begin with.

Get some of these:
 

Hero999

Banned
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Gregory

Member
What you have writen abou the float voltage , Dos that men I cn go ahead and buitl the Voltage regulator thet Udioguru Has described or is there more to be added to this Circuit.
 

audioguru

Well-Known Member
Most Helpful Member
What you have writen abou the float voltage , Dos that men I cn go ahead and buitl the Voltage regulator thet Udioguru Has described......
Please write replies in good English with proper spelling.
 

Gregory

Member
I apoligise about the spelling and grammar as I was in a hurry and did not check the post

What you have written about the float voltae., Dose this mean I can go ahead and build the voltage regulator that Audioguru, has described or is there more to be added to the circuit.
 

MikeMl

Well-Known Member
Most Helpful Member

Hero999

Banned
I apoligise about the spelling and grammar as I was in a hurry and did not check the post

Get Firefox, it has a built-in spell checker so you don't have to worry about spelling again.

Opera also has a built-in spell checker and you can get a spell checker for Internet Explorer but it's not free.
 

chuck

New Member
I'm slow on a lot of things, but a light bulb just went on. I read:
Make a regulator with an output voltage of 13.8V for the batteries plus 0.7V for isolation diodes= 14.5V total. An LM317 adjustable regulator set to 14.5V with two resistors and two capacitors can be used. It will need a medium size heatsink to dissipate 5.5W.
The LM317 needs two resistors and two capacitors as shown on its datasheet.

The LM317 will feed the battery until the voltage is 13.8 and this will keep the battery at optimum charge and happy? Can I do this same sort of thing using solar panel to charge ni-cad? Thank you for your time.
 

MikeMl

Well-Known Member
Most Helpful Member
...
The LM317 will feed the battery until the voltage is 13.8 and this will keep the battery at optimum charge and happy? Can I do this same sort of thing using solar panel to charge ni-cad? Thank you for your time.

Yes, an LM317 set to ~14.5V, - the forward drop of a Si rectifier will "float" just fine. This method will not recharge an SLA in the shortest possible time, however. To do that takes a "two-cycle" or "three-cycle" smart charger.

NiCad charging is altogether different from charging Lead-Acid batteries. NiCad charging requires constant-current; not constant-volktage. The end-of-charge determination is totally different, too. Read up on the differences between Lead-Acid and NiCad charging here.
 

Hero999

Banned
If the battery will be charged regularly and the solar panel has a built-in protection diode, a separate blocking diode is not needed and just wastes an extra 0.6V to 0.8V.

Setting R1 and R2 to high values reduces the current sucked back from the battery to a negligible amount.

I used 2k4 for R2 and 43k for R2 which meant only 520µA was drawn from the batteries when dark.

8571-lm317t-voltage-regulation-circuit.gif

https://www.electro-tech-online.com/threads/inexpensive-solar-panels.86770/#post711703
 
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