Same regulator for solar panels and other battery chargers?

[Argie]

Could anybody enlighten me about the possible problems of using the same (oversized) solar panel regulator to also charge the batteries with a very simple transformer (15 volts) and full rectification?

Should I only be careful about not exceeding the current ability of the regulator when using the two systems at once, which is most unlikely anyway?

[Dreadstar]

a smart charger style charger after the solar panel charge controller will work better. won't burn out the solar charge controller. and will allow the panels to work at optimum voltage with the controller.  I have done so with a remote site with 2 80 watt panels to augment the solar when not enough sunlight to run the site. it has grid power but i wanted to make the site as independent as possible. because power there is off more than it is on.

I assume that is why you want to use a ac charger in conjunction with the solar charger. good luck

[Argie]

Either I didn't understand your response or you didn't understand what I meant with my question.

I have two solar panels (75 and 85 watt monocrystalline) mounted on the roof of my RV charging three battery banks (all gel cells, including the starting battery) via a Solarex SC18 controller which can handle 18 amps.

This solar controller has a boost and float stage and it's quite suitable for the job of charging these gel cells, (as soon as I manage to finally adjust those voltages properly since it wasn't really designed for anything other than standard batteries)  which is what brings me to the question; why spending money on another electric battery charger, which would be rarely used anyway, when I already have most of what I need (I think) in that solar controller?

Or don't you believe in saving money, weight, bulk, and number of items stored or mounted in a small and already overcrowded room on wheels?

Can I get into any troubles by paralleling the solar panel output with the rectified but not filtered or regulated output of a 15 volt transformer?

This solar controller has a series switching input system, I believe, and my next question, (before I ask about what would be involved in using an old PC power supply instead of that transformer - I'm VERY cheap ) is; does anybody know what's the best way of adjusting the boost and float voltages in this solar panel?

Can I load it with resistor so I can at least adjust the boost voltage without any "voltage back-feed" from the battery?

I already have a list of the temperature compensated voltage values for gel cells but I don't even know what I'm doing with those two voltage adjusting pots because they don't have a rotation limit (which means I don't know what's their minimum or maximum setting) and the voltage responses change so much without any apparent reason.

[Nando]

Argie:

Yes, you can add them in parallel, making sure that the overall current sources do not add to the controller current capabilities.

Make sure, as well, that the power source that is not a current source ( panels are current sources) have enough impedance to be able to share part of the current and not all the current otherwise it may "short circuit", in this case the transformer rectifier.

Isolate each source with a power diode.

A better circuit would be one that detects the panel voltage and/or current and switches the transformer to the charging circuit.

LASTLY:

YOU SAID:

>Either I didn't understand your response or you didn't understand what I meant with my question

You like to include highly superfluous or unnecessary data THAT CLOUDS YOUR QUESTION like :

>This solar controller has a boost and float stage and it's quite suitable for the job of charging these gel cells, (as soon as I manage to finally adjust those voltages properly since it wasn't really designed for anything other than standard batteries) - which is what brings me to the question; why spending money on another electric battery charger, which would be rarely used anyway, when I already have most of what I need (I think) in that solar controller?

>Or don't you believe in saving money, weight, bulk, and number of items stored or mounted in a small and already overcrowded room on wheels?

~~~~~~~~~~~~~~~~

Do I need to include more superfluous information --

Nando

[Argie]

Nando:

You said: >>>Make sure, as well, that the power source that is not a current source ... have enough impedance to be able to share part of the current and not all the current otherwise it may "short circuit", in this case the transformer rectifier.<<<

You lost me already, and I'm not saying that's your fault.

I already have a solar current source, each one of the  solar panels has an isolating diode so that shade on one doesn't kill the other, and my intent was to use a 15 volt a.c. transformer with full wave rectification, most likely four diodes in a bridge configuration but without filtering; how do I make sure these two current sources have "enough impedance to share part of the current and not all of the current"?

Wouldn't the solar panel diodes and the rectification diodes in the transformer take care of everything?

>>>Isolate each source with a power diode.<<<

Understood.

>>>A better circuit would be one that detects the panel voltage and/or current and switches the transformer to the charging circuit.<<<

If it can be helped in some other way I'd rather keep the circuit simple and cheap.

>>>You like to include highly superfluous or unnecessary data THAT CLOUDS YOUR QUESTION<<<

Hey! I kept my first post very clear and simple until the first response led me to believe that my purpose wasn't entirely clear (I didn't want just a second battery charger in parallel with the batteries), which is why I then "went wild" with all the details, but I'll take the hint and save those other questions for other threads if I'm still welcome here.  

[Nando]

If you are going to have the rectifier bridge unfiltered then this voltage will assist in the charging when the rectified voltages goes above the battery voltage plus the charge controller drop voltage, and if the rectified voltage is greater than the panels voltage, only the rectified voltage will supply energy to the panel, which is one thing that I think you do not want --

I thing that you want the panels to supply all the energy and only when the panels are low the rectified voltage will feed power .

In this case the rectified voltage will supply energy just during the sine wave peaks and the width depends on the battery voltage and the rectified voltage with the current depending on the impedance of the transformer.

Is that what you have in mind ?.

Otherwise another arrangement has to be made.

Nando

[Argie]

>>>In this case the rectified voltage will supply energy just during the sine wave peaks and the width depends on the battery voltage and the rectified voltage with the current depending on the impedance of the transformer.

Is that what you have in mind ?.<<<

Yes, whatever current the solar panels can provide when the sun's up PLUS whatever current the transformer can provide when plugged in will do fine as long as their added maximum current doesn't exceed the maximum capabilities of the controller and  the solar panel/s and the transformer don't drain each other's current when the transformer is not plugged in or the RV's parked under cover.

Everything automatic and fool proof would be nice.

[Nando]

In this case, the full wave rectified voltage, should be set to be equal to the Solar Panels unloaded voltage and the impedance of this source to be equal to the the

SOURCE IMPEDANCE = [(Rect-volt)-(battery-voltage)]/[(charger Current limits)*0.5]

so this way the solar panel will be able to supply 1/2 of the current and the rectified voltage to supply 1/2 of the current.

Alternate solutions will be to detect the solar voltage and power and supply additional current with the rectified voltage I.E. to reduce the impedance by 1/2 or increase the rectified voltage.

This is a touchy situation that really needs good electronic/electrical knowledge, preferable would be a PWM supply set to a fixed voltage, high enough to produce the necessary current and low enough to allow the panel to supply all the available current..

Nando

[Argie]

The part I cannot understand is why it should be so important that the transformer and the solar panels give exactly half of the total current to the regulator.

As long as their maximum combined current output doesn't exceed the 18 amp rating of the regulator why should it matter if the solar panels are producing only one amp instead of ten in a cloudy day, or the transformer is producing 17 volts while the solar panel is producing a higher voltage.

Wouldn't it work the same way as one strong man, one woman and one small child pushing a car together, with the total force being the sum of the three forces?

Or doesn't it work the same way when a 17 volt 8 amp DC source is paralleled with a 21 volt 10 amp source?

I understand how *at* 21 volts the two of them paralleled can still only supply 10 amps but don't they still add up to 18 amps once the voltage has been pulled down under load to at least 17 volts, which it will when under even medium load?

And wouldn't this difference in their output voltages work to my advantage when the batteries are full and I have forgotten to switch off the transformer because then only the solar panel will be providing the (FREE) little current they need to keep at float voltage?

There *is* some method to my madness.

[Nando]

Let's try it.

The panel voltage is limited to Voc and also, under load needs to go down to Vmp and to the best current setting for maximum power transfer.

So you have a narrow window that if the second power source has a wider voltage and current range and the controller is like a MX60 that sets the current with the best power transfer curve the second source may be the one supplying all the power because the input voltage could be higher than the panel voltage and the diodes isolate one source from the other source.

>Or doesn't it work the same way when a 17 volt 8 amp DC source is paralleled with a 21 volt 10 amp source?

The winner here would be the 21 volts 10 amp source and the 17 volts, 8 amps will be floating and isolated.

Do you need further assistance ?

Nando

[Argie]

Are you doing that on purpose?

I cannot even follow you.  

Oh, well,.. I should say "thanks" I suppose.  

[Nando]

LET'S TY AGAIN

It is not my intention to miss lead you or trying to use "jargon" unknown to the group.

Voc= Voltage @open Circuit

Vmp= Voltage @maximum power

The Solar panel generates a Voc at maximum solar Insolation that is the highest possible and it is defined by the Diode formed in the Silicon junction with certain "additives" = Voc

When the panel is loaded at certain defined current and the voltage is the highest it is Vmp

The difference between Voc and Vmp is around 0.1 volt ( not exactly) it varies with the process, as well as, the number of junctions ( Cells) in series.

When two sources are ADDED in parallel, via Diodes, there is a needed relationship of voltage levels that allow that both supply current to the load ( in this case a battery bank), and many times defined by the controller way of doing the charge to the battery.

Controllers like the C60 are in reality just switches ON/OFF with a voltage level detector and some with current limiting capabilities to make sure that the battery is not OVER voltage and current limited to protect the controller and/or the battery.

Reason why they are so in-expensive.

Since it is a switch the source with the highest voltage and current capability will take over and the other will be "cut OFF" because it would be at lower voltage.

For both to supply current the voltages need to be close and the impedance more or less equal for both to share in the current sourcing -- this is just basic electrical/electronic principles.

If using a MX60 or like, there is another problem and it is the MX60 IMPEDANCE conversion ratio between the input to the output, which sets the input voltage range depending on the source impedance that with the output current (in reality the battery impedance ratio) -- not the battery internal impedance --- that forces the input power to go up or down at will by the MX60 and if one has higher voltage capabilities and a bit lower impedance, than the other, becomes the winner supplying power and isolating the other that can not go high enough in voltage to share the current.

It is a marriage of wills.

I hope that this is a bit clear !!

Let me know

Nando

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nando

was just lurking around when I saw this thread...

 helped me a bit to understand a bit more about one of the many things that elude my grasp<l>

thanx

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