Trickle Charge Battery

Deep cycle batteries are more expensive than starting batteries. The advantage to them is that they are designed to endure many charge/discharge cycles, where the level of discharge is high, compared to what a starting battery endures.

If you size the solar cell correctly, you can just hook it up to the battery with no other circuitry. The way this would work is that when you have power, you keep the battery charged with a charger, and leave the solar cell circuit open.

When the power goes out, open the charger circuit, and close the solar cell circuit. There may be some danger of overcharging the batteries with the solar cell if it is very sunny and/or you don't use the equipment.

If you are only trying to keep the batteries topped off, and not trying to run indefinitely, then you can just use a very small solar cell, and there will be no danger of over-charging under any circumstances.

Good luck.

--Mac

I know this question has probably been beaten to death, nevertheless I hope you will still indulge me.

During a power outage, which occurs frequently in Florida, I would like to use a battery to power some communication gear. Although the battery is 12v and not 13.8v, I think that the gear will still work OK (hopefully).

Question 1. I believe that car batteries have a low internal resistance because their primary function is to provide a lot of current for a short time. There are other 12v large battery types that will last as long as a typical car battery. They are designed not to provide peak current, but to supply steady state current for a long time. For the life of me, I can't remember the name of those type batteries so I can't do a google to find a supplier. I hope this is making some sense.

Question 2. Where can I find articles & schematics for a solar cell to provide a trickle charge for the aforementioned battery?

Thank you very much.

Cordially, west

hope

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is 12v

The voltage of a fully charged battery will be over 12V, somewhere around 13ish.

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sense.

You are talking about a "deep cycle" or marine battery.

Google

Even if such batteries exist, they won't have a cost-effectiveness advantage over car batteries. You are thinking that by trading in peak current you are going to gain in overall amp-hours. It just isn't true. You won't find a cheaper way to store X amp-hours than a car battery.

-Robert Scott Ypsilanti, Michigan

It's probably best to get one from a specialist rather than try to roll your own.

Eg...

Graham

You will need a blocking diode to prevent the solar panel from becoming a load at night.

--
James T. White

load

Some panels will eat when unilluminated, some dont.

NT

other than using something from the junkbox.

NT

See...

"PerfectDiodeForChargerIsolation.pdf"

on the S.E.D/Schematics page of my website.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

"Robert Scott"

** Nor a cheaper way to obtain a trickle charger to use with the solar panel than to buy one from the same store that sells the panels. That panel is going to be the big expense.

........ Phil

AIUI, the diode consumes more power than the solar cell. I don't think you need the diode.

I lived on a boat with solar cells for 2 years, and I had no diodes. It didn't seem to be a problem.

--Mac

Nominal voltage is 13.8 fully charged. "12V" is just the sticker value.

Deep cycle.

Generally from who you buy the solar cell.

Please explain how they can output 20V when loaded with a lead-acid battery.

Graham

The household breakers use thermal trip for overload and magnetic trip for short circuits. The rating specifies the current that is *passed* and not the trip level. It may take several minutes to trip on 25A for example. And it is not enough to test for trip point, the response time also must be measured. The most commonly employed technique is "primary current injection," and the most commonly used, if not only, method is with a high current step-down transformer. This spells weight and cost. You can see an example of a modestly sized one and how it used here:

and when you start dealing with the newer arc-fault type of relays or others with internal electronics, you have to add provisions for keeping it powered during test. Complex arc fault relays are beyond the reach of the non-specialist for actual arc testing, but you still can test the basic trip mechanism for conventional faults.

A solar cell can be modelled as a current source with a current proportional to the amount of light falling on it, in parallel with a silicon diode.

As such it tends to have an output voltage that is proportional to the logarithm of the solar intensity that drops with increasing temperature (~2mV per degree). The individual cell voltage will be a maximum of about 0.5V and because of the logarithmic effect of the diode does not drop greatly as the intensity reduces.

A typical solar array will consist of 36 cells in series giving an open circuit voltage of about 18V. When this is fed to a 12V lead acid battery through a diode the voltage will drop to about 13-14V depending on charge level - it will act as a constant current generator so the series diode will have little effect on charging current except at low intensity levels or high-temperatures.

At nighttime the solar panel will act act like 36 forward biased silicon diodes in series - with ~13V from the battery each diode will only have about 360mV across each and the current will be pretty low, usually the array temperature will be lowest at night so this increases the voltage required for the diodes to conduct helping reduce the current.

So it is usually acceptable to not have a reverse blocking diode but it will not significantly affect the charging current except when the array temperature is high (under midday sun).

I like to have a blocking diode as a safety measure to avoid dangerous currents from the battery if the array wiring that is exposed to the elements has a short ( you should put a fuse in series with the battery physically close to the battery as well - even a small battery can have short-circuit currents of hundreds of amps).

Some solar arrays do have diodes included in the array but they are usually in parallel rather than series - this is to avoid problems when arrays are placed in series and one array gets shaded while the others don't. Without the diode the shaded array would be reverse biased by the voltage from the other arrays and be damaged (a similar problem can occur with series cells in a battery when one is discharged before the others.)

It is usually advisable to have a charge controller - if the voltage goes above ~14V the electrolyte in the battery will be electrolyzed away pretty quickly - in the case of sealed lead acid batteries there is no way of replacing it and so the battery will be damaged.

There are some solar arrays available with fewer cells that claim to be self regulating - these usually just have fewer cells (33 rather than

36) so that the charging current drops off as the battery is charged. These are not usually completely effective.

These days small charge controllers only cost $20-30 and are easily available - my local Fry's has them.

kevin

"Mac"

** Then you don't understand much. ** A series Schottky diode is often built into the solar panel itself.

There is a 0.5 volt loss during charging, but this is trivial as panels typically output 20 volts in bright sun.

........ Phil

are those cells connected directly to the battery?

Bye. Jasen

yes, or what remains of it

NT

They do, and they do, and they do.

They're called "deep-cycle" batteries, or "marine", or sometimes "golf cart" batteries. They're designed to provide moderate current for a long time, whereas car batteries are designed to stay at the ready on float while in use, and provide hundreds of amps of starting current when needed.

Please don't mislead the children.

Thanks! Rich

You are thinking that by trading in