12 V 10 watt solar panel questions

[99yam40]

picked up a 12v 10 watt panel online to hook to tractor battery when not used (sitting for months) and the instruction page that came with it said to cover all modules before making or breaking electrical connections.

Could it harm the panel if that is not followed?
Or is it just an electrical shock safety thing?
would it hurt to have the solar panel sitting open circuit( not hooked to battery, but exposed to the sun) for long periods of time, when I go up every week or two? or just when running the tractor around on the land?

I have also read it is not good to start the tractor while panel is hooked the battery, is that a real problem if it happens?
I do not think I would do that but someone else might. and I might forget as I am getting older

I plan on installing a blocking diode in the pos + lead as it leaves the panel to keep the battery from discharging into the panel when no sun shine is on the panel but probably not going to install a solar con*****er.
the panel will be mounted on a wood board at the edge of tin roof so it would not be easy to cover the panel when connecting or disconnecting.
Plan on just rigging wiring so I can plug into a set of wires on tractor to battery that I have installed for running a 12 v spray pump

plate on panel
Pmax - 10W
Vpm -18V
Ipm - .55 A
Ocv - 21.5V
Isc - .61A

what does the Vpm & Ipm stand for?
Volt and Current at power max maybe

Ocv should be open circuit voltage
is Isc current short circuit?

[boscoe99]

Just because I am crazy does not mean that I cannot love this stuff. If I had my life to do over I would be an electrical engineer.

Don't know what the covering the modules is about. Probably based on one out of ten billion doing something stupid so the manuals include unnecessary garbage IMO.

I suspect that a solar panel is like a PMA. If nothing is connected then no harm no foul. Nothing connected to my wall outlet most of the time and it is perfectly fine.

Starting the tractor with the battery connected to the solar panel should not hurt a thing. The panel can only output so much current. Won't be as much as the closed circuit current. Which is small.

I would not install a blocking diode. Cuts down on current flow and should not be needed. You can test by connecting the battery to the panel with the panel being covered so that no light hits it. Test for current flow. Don't think there will be any.

Open-circuit voltage (abbreviated as OCV or V_OC ) is the difference of electrical potential between two terminals of a device when disconnected from any circuit. There is no external load connected. No external electric current flows between the terminals.

Isc: Current under short-circuit conditions. The peak current a solar panel can produce with its output shorted. Used for calculating wire size and circuit protection ratings. The "I" comes from an old term for current; Intensity.

Vmp: Voltage at Maximum Power. The output Voltage of a PV when it is at its maximum current.

Imp: Current at maximum power. The most Amps a solar panel will produce under normal operating conditions. The "I" comes from an old term for current; Intensity.


https://forum.solar-electric.com/dis.../5001/glossary

[99yam40]

thanks for that info.

I was thinking maybe some kind of surge or spike when connecting or disconnecting could be a problem. or when hitting the starter(large current draw and drop in voltage)
or when dropping out the starter could cause voltage spikes.

seems we ran into some strange things happening out at the plant from some spikes on 125 V DC control circuits. Do not remember what all was involved, but it may have been from a DC to DC con*****er or some contacts opening and closing sending heavy duty(high) voltage spikes into something.
it was a long time ago

I am not sure if the diode would also give some reverse polarity protection also if someone hooked battery up backwards, but not sure if that would need a diode on both legs.

I tried playing with it some when it came in this weekend, but cloudy and drizzel has limited testing.

I did fire up a 500W quartz light and held the panel in front of it Sat. to see voltage and some current.
hooked it to a small sealed 12 v battery, but its voltage was over 13 and could not get any current to flow from the panel
waiting on the sun to come out so I can hook it up to battery in boat or the lawn mower to see how it works

I also saw a video about solar panels loosing a lot of its current/volts output if part of the panel is not exposed to the sun.they talked about adding shorting diodes.
maybe I had my hand shading part of the panel when trying that

[99yam40]

walked outside to pick up the paper and heard a humming noise.
turned out it was the bilge pump on my boat running.
no idea how long that was going on, but the switch was in the off position.
I disconnected the pump wiring.
ended up finding the switch to pump full of water so I replaced it.

figured this would be a good time to see what the solar panel would do on a battery that was not fully charged.
hooked it up and even with overcast sky it was putting out 40 miliamps into the battery,
put the diode in the circuit and it dropped only 1 ma.
when the sun did pop out once I set the panel where it would catch full sun and I was getting 300 ma for a few minutes until sun went away again.

Hooked up my small 6 amp 12 v charger to the battery also and the solar panel still was putting out 39 ma to the battery.
voltage was 15 v+ when measured at battery while charger was on.

Took a 12v4.5 AH gelcell that was fully charged reading 13.5V( just off a charger) and hooked it into the solar panel and it kept on putting out 30+ ma.
I just went out to check it again and voltage was up to 14.59V .
then measured the current and it was 50ma( depends on how much sun is hitting it)

Looks like it would be a good idea to get a con*****er to make sure the voltage keeps in the proper float voltage range if I plan on leaving the panel hooked up for months at a time.

Oh yea, I put my thumb over just one of the cells and the ma dropped from 56 to 36.
covered another and it dropped to 16ma.
there are 4 rows of 9 cells on the panel

[boscoe99]

Wish I knew if it is really excessive voltage or current that can harm a battery.

I am in the excessive current camp. Reason why is years ago I had a constant current battery charger. I left it on and it cooked a battery dry of electrolyte.

I suspect that 16/17/18 volts to a 12 volt battery, at a current rate of much less than half an amp, for a long period of time, won't hurt a thing. Particularly if the battery is large.

[99yam40]

I do know there are different float voltages for different types of cells/ batteries.
even the cheap con*****er I am thinking about getting has different setting for different types of batteries

You would think for current to flow into a battery the impressed voltage has to higher than the battery voltage, unless there is something different to all of this charging batteries than I have ever read about.

the only way i know of to have a constant current charger would be to either start out at a low voltage to meet the current setting and then slowly increase the voltage as current dropped until it hits the maximum voltage set point.

the battery voltage and the solar panel voltage has to be straight DC.
battery chargers tend to be rippled, but the better large ones have lots of caps to help smooth the ripple out
we had battery banks from 24, 48, & 125 v to run things and they each had a set voltage we kept them at at all times with chargers on 2 different feeders into the plants. if you lost both feeders the whole plant was down anyway so the batteries just let you control all of the switch gear , valves, and other instruments to do a con*****ed shut down.
but then we would do an equalizer charge if some of the cells got out of spec. lots of PPM checks to keep an eye on it all
they lasted for many years( thinking 15 to 20 years)
if my memory still works OK
a good scope would be nice to look at some of this stuff

[boscoe99]

My understanding is that for current flow to occur the source voltage has to be higher than the battery voltage. Just like water.

Battery voltage and solar panel voltage are always DC.

I also wish that I had a scope. Maybe in the new year I can find a good used one. Think my neighbor has two. Maybe he will part with one. Or just load it.

[99yam40]

also wanted to report that without the diode in the + between the panel and battery and the panel turned upside down so not light could hit it,
it did show 5 or 6 ma heading to the panel from the battery.
so it would discharge the battery a small amount at night when no power was being generated by the solar panel

I actually watched the ma go from a Negative(-) number to a positive (+)one as I lifted the panel off of the counter and pointed it toward a light bulb

and I read that the con*****er I was looking at said that disconnecting and connecting the battery and panel out of proper sequence could harm the con*****er.
So just unplugging the battery to run the tractor and then hooking it back up is a no no.
so I would have to disconnect both the battery and panel in proper sequence each time.

I think I will mount the panel and hook it up to the tractor battery with the diode installed and then monitor it for awhile before deciding on a con*****er

[TownsendsFJR1300]

So the panel itself is NOT a battery charger specifically?

I suspect, one made for batteries would have all the safety features, diodes, etc, no?

[99yam40]

it is just a 12v 10 watt solar panel I paid $18.99 for
yes you can find complete set ups with all sorts of stuff that comes with it for more money.

I just bought this because it was 10 watt and not a 5 watt like a lot of stores sell for a little more.
some of which showed only .03 amp out put to battery.
I figured .5 amps would be better. maybe not for long term upkeep of a tractor battery.
may put too much into battery over months with plenty of sun without a con*****er to limit the float voltage.

I bid $5.00 on a con*****er with free shipping, will have to wait to see if that wins me something to play with.

Son sent me a message he wanted to take his daughter up to the farm this week while she was out of school, will have to see if the rain will go away Thursday about noon as they predict it to. She has never been there before, and it will be in the 40s. Not much for her to do there except look around some.
I did install a wood stove and a TV for those long dark cold nights.

I am trying to come up with a mounting system for the panel now ,so we can get it mounted on the building.
thinking of just a 1/2" pipe flange screwed to a board on edge of tin roof, with a piece of 1/2" pipe screwed into it and 2 two hole conduit clamps clamping around the pipe to the aluminum frame so you can tilt the panel to the south a little.
may have to bend some conduit to get it done properly to catch more sun, we shall wait and see.

[99yam40]

here is something I think is strange I found on a 25W panel output on the web.
this pic shows something between the P and N terminals on the back of the panel that you hook up to to head to the con*****er or battery.
can you identify what it is?
A resister maybe to keep a small load on the panel when it is disconnected?
or maybe a zener diode to short out if voltage goes too high?

[boscoe99]

I am guessing a zener diode. To short excess current to ground to keep the voltage in check. A regulator of sorts.

A fairdeal type might measure the voltage with and without the diode in the circuit to see what the difference is.

[boscoe99]

looks like this one

[boscoe99]

[99yam40]

It is just a picture, It is not on the panel I bought.

Just trying to figure out what it was without getting to play with one in person, and why it would be put across the output like that.
does your reply about taking excess voltage to ground also mean taking it back to neg since the panel circuit is not referenced to ground.

I did read something about following guide line and grounding the = side of a system, but 12V systems were exempt from that.

reading some today. I ran across someone saying to just install some blocking diodes in series to lower/limit the voltage out to battery( each diode will drop voltage some)
had not thought of that before, but then I am sure it will also limit current some too by adding resistance.

I will have to be taking some readings once hooked up to the big battery over weeks or months to see if that would be needed.
Loosing the radio Shacks around he makes things a lot slower to get you hands on needed supplies.
I pulled some diodes out of an old computer power supply the other day, but the one I tested hooked to the panel dropped the voltage from 10VDc to 2 v , while not in any sunshine I have no idea what that diode was so I stuck with the new 600V 1 amp I had .


there was talk of internal resistance on one place I was reading
I thought by adding a resister across the + & - , it would still load the panel some when disconnected from battery.
seems they talked about if some of the cells were shaded while open circuited but panel in sun it could cause reverse bias to those cells causing current to flow in the shaded cells causing heating reducing life span.
I guess I need to make sure where I mount this panel is not going to be partially shaded during the day.

can't move the building or the big Live Oak and they say to keep the wiring as short as possible