Does anyone run a solar panel with a digital controller?

[mikeschn]

Does anyone run a solar panel with a digital controller? I'm curious what kind of amps you get out of it.

I hooked my battery up again today, and the controller shows that I am getting between 0.3 and 1.5 amps out of it.

For reference, it's a 65 watt panel, and should be getting 5.4 amps, per this calculator.
http://ourworld.compuserve.com/homepage ... hmslaw.htm

Any thoughts?

Mike...

[brian_bp]

I think that there are too many possible designs of controller to generalize, but I do have a few questions to help the diagnostic process along:

What is the sun condition? The 65 watt rating is for ideal conditions, and in the actual test condition there may not be enough solar power hitting the panel to reach rated results.

What is the load condition? If the panel is trying to push current through a charged batter, the battery might be at higher than 12V, and thus the panel will not be capable of pushing as much current. We know the current which has been measured, but not the corresponding voltage.

How about the panel orientation? Even in ideal sun conditions, a panel tilted so that it is not directly pointing at the sun is effectively a smaller panel.

What type of regulation is used?

• My simple controller is an on/off switch like the one in a basic automatic battery charger: it is just a switch which is on (as if there were no controller at all) until the voltage gets to some set point, then it switches off (as if the panel were completely unplugged) until the voltage gets down to some much lower point. I don't see how a simple controller could cause this problem of too little current - it will be all or nothing.
• A pulse-width modulation (PWM) controller will rapidly switch on and off so that output current or voltage meets some target condition, so it's hard to say what it should be doing unless you know what it's trying to do. If the panel is charging a battery and the battery is nearly fully charged, this type of controller could just be "throttling" the current to maintain the target voltage.
• A maximum power point tracking (MPPT) controller actually does a voltage conversion between the panel and load, attempting to keep the panel in it's most effective condition (whatever balance between voltage and current gives the most power). With this type of controller, both voltage and current would need to be measured on both the panel side and the load side to understand what is going on.

[mikeschn]

First a photo of the orientation:


Then a picture of the charge controller:


The sun is a weak winter sun, and while I certainly expect some degradation, I didn't expect it to drop that low.

But in the fall when the sun was stronger, I didn't seem to get much juice out of it either. But I didn't have time to analyze it then.

I don't know much about the controller, but you can see it here:
http://www.northerntool.com/webapp/wcs/ ... _200365189

This is the second controller from Northern Tools. The first one was defective, and they replaced it. Do you suppose I could have damaged the panel with a defective controller?

Mike...

[emiller]

I'm using a 33 watt solar panel from Northern Tool and get 1.4 to 1.5 on a sunny day. The controller is a Mark 15
http://www.specialtyconcepts.com/SPECIA ... _SHEET.PDF

Next picture shows the panel

[brian_bp]

First a photo of the orientation...

Well, that looks pretty nicely lined up... I guess it's not an orientation issue!

The sun is a weak winter sun, and while I certainly expect some degradation, I didn't expect it to drop that low.

But in the fall when the sun was stronger, I didn't seem to get much juice out of it either. But I didn't have time to analyze it then.

Sun strength by itself doesn't seem to me like a likely cause by itself of such low output in this case, because (at least in the photo) it's in strong direct light.

I don't know much about the controller, but you can see it here:
http://www.northerntool.com/webapp/wcs/ ... _200365189

The Northern Tools page doesn't say much, but it does give the brand and model number, which lead to a better source of information: SunForce Products. I couldn't find the 10-amp controller, model #600311, on their site, but...

Then a picture of the charge controller...

This doesn't look quite like the Northern Tools image. It has more indicators, and does that text say 30 amp? If it's the 30 amp model, then perhaps its model #60032.

You have to dig way into the manual to get any indication of how this works, but in section 6 (page 2 of the owner's manual) it finally says that he is a three-stage charge controller using a PWM design - once the battery has gone through the bulk-charging state, the controller will throttle back to maintain a specific voltage (14.1 to 14.9 V), which may mean very little current; after that, is goes to float mode, which again is a constant voltage, but even lower (13.0 to 13.8 V). The controller would only allow the panel to push out as much current as it can in the bulk charging stage.

If the controller is set for gell cells, and you have a flooded lead-acid battery, the constant charging voltage will be 0.4 V lower than it should be, cutting back on charging current too early.

The 65 watt panel rating is under the ideal loading conditions: if the load is infinitely hard to push current through, that's an open circuit, for which you get lots of voltage but zero current and thus zero power; if the load is very infinitely large (like a short circuit) a fair amount of current flows but at zero voltage so there's essentially no power delivered. The only way to get 65 watts, even in ideal sun, is if the voltage across the load is at some ideal point in between, e.g. perhaps 4.3 A at 15 V... that ideal voltage may never be reached in the bulk charging state, so my guess is that the panel will never quite put of 65 watts.

This isn't a criticism at all - this type of setup should be exactly what the battery needs, and there's only a problem if there isn't much power produced in the bulk charging stage.

There seem to be status lights on the controller - Mike, what do they say? There is a current/voltage selection switch for the meter: what is the voltage when these low currents are seen?

This is the second controller from Northern Tools. The first one was defective, and they replaced it. Do you suppose I could have damaged the panel with a defective controller?

Mike...

I suppose it's possible, but at a guess it seems unlikely to me. The worst that most controllers could do is to short-circuit the panel's output leads, which isn't great for it but should be tolerable as long as the panel isn't allowed to get too hot in the process.

[mikeschn]

There seem to be status lights on the controller - Mike, what do they say? There is a current/voltage selection switch for the meter: what is the voltage when these low currents are seen?

The voltage is 12 volts maybe just a touch more than 12.

The switches, and the lettering can be seen in this closeup.



Mike...

[Micro469]

I'm using a 33 watt solar panel from Northern Tool and get 1.4 to 1.5 on a sunny day. http://www.specialtyconcepts.com/SPECIA ... _SHEET.PDF

Next picture shows the panel

Your second pic just blew the heck out of my controller...
Nice looking tear....

[Steve F]

WOW, that does seem low for a 65w panel, I measured mine with a digital meter when I first hooked it up and was getting a touch under 2A in full sun on a September day here in Sydney Australia (so first month of spring) with the panel flat on the ground. My panel is a 35W monocrystalline panel.

Cheers
Steve

[brian_bp]

There seem to be status lights on the controller - Mike, what do they say? There is a current/voltage selection switch for the meter: what is the voltage when these low currents are seen?

The voltage is 12 volts maybe just a touch more than 12.

The switches, and the lettering can be seen in this closeup...

The switch does appear to set for "gel"; if the batteries are the conventional flooded type then the controller will quit charging earlier. If they are AGM... I would check the battery manufacturer's charging spec to see what the later stage voltages should be (I'm guessing "flooded", not "gel"). Sorry Mike, I don't remember what you have for a battery.

The top indicator (which looks like a dot in circle but I suppose is supposed to mean "sun") appears to be on, shows that there is power available from the panel.

The next indicators are for "charging" (lightning bolt) and "charge complete" (filled battery); I can't tell if either one is on, so I can't tell where it is in the charging cycle.

The bulk charge would have "charging" on and "charge complete" off - as the manual says this "Indicates the battery is charging, virtually all the
power from the solar array pass through to the battery"... and that's the only condition in which all of the available power is passing through. At not much more than 12V, this is the condition which I would expect... and if that's what's happening, there appears to be a problem with panel output.

If "charging" flashes and "charge complete" is off, the controller is saying that there is not sufficient output from the panel to work properly in bulk charge mode. Again, something may be wrong on the panel side.

If "charging" is off and "charge complete" is on, then this "Indicates fully charge reached, a small “Float” charge continues to optimize battery when you need"... this is the state which I thought the controller might be reaching, but at only 12V this shouldn't be the case. If this is happening, it suggests a bad controller to me.

By the way, just to eliminate battery issues, I would try connecting a battery which I know to be good but nowhere near fully charged, to see what the panel and controller do - that should allow maximum power throughput.

[Rock]

I think that all solar panels are rated at maximum solar "flux" or power. That's about 1000 watts/meter^2. But only at high noon on the equator. (seriously)

Mike - the sun looks real low in the sky based on the shadows. Plus I assume it's a recent photo at about 42.5 degrees N latitude. So if you're seeing 1.5 amps that a little better than 25% of the max output of 5.4 amps. This may be as good as you're going to get under these conditions.

Next sunny day (Turkey Day?) go outside and play around and tilt it as much as you can right into the sun at noon. You'll do better then.

So at high noon on June 21 the sun's rays come down like this:

||||||||||||||||||||||||||||||||||

But late in the evening in November they're like this:

/ / / / / / / / / / / / / / / / / / /

Basically all spread apart.

Don't know if this is all of your problem. I doubt you damaged the panel in any way. Maybe I'll play around with my HF 45 watt panel this weekend and report out.

[emiller]

That really doesn't look like a 65 watt panel. It looks small like a 10 or 12 watt.

[mikeschn]

This is my panel...

http://www.affordable-solar.com/kyocera ... .panel.htm

Electrical Specifications
Model: KC65T
Maximum Power: 65 watts
Tolerance: +10% / -5%
Maximum Power Voltage: 17.4 volts
Maximum Power Current: 3.75 amps
Open Circuit Voltage: 21.7 volts
Short-Circuit Current: 3.99 amps

So maybe 1.5 amps is right for the autumn sunlight?

Another question: Does your digital controller look like the solar panel is sending 1.5 amps in bursts? Let me explain. The controller display changes 2 or 3 times a second. Most of the time it displays 0.3 amps. Then once every couple seconds or so it jumps up to 1.5 amps, and then right back down to 0.3. Does that sound normal?

Mike...

[brian_bp]

...
Another question: Does your digital controller look like the solar panel is sending 1.5 amps in bursts? Let me explain. The controller display changes 2 or 3 times a second. Most of the time it displays 0.3 amps. Then once every couple seconds or so it jumps up to 1.5 amps, and then right back down to 0.3. Does that sound normal?

Mike...

Pulse-width modulation means that the controller is on for a while, then off, in a cycle. The fraction of the time it is "on" is the width of the pulse, which can vary from zero to the full cycle time. The description could be a controller which is cycling every "couple seconds or so", and is on for a small amount of this time, because it is trying to throttle the power to the battery down.

Four things seems strange about this to me:

• I would have guessed that the cycle time would be much shorter than a couple of seconds
• the meter should average voltage and current readings over the whole cycle, so the cycling doesn't confuse things
• at around 12V, the controller should be on full-time (the pulse should be the whole duration of the cycle, not just a bit of it)
• during the off part of the cycle, current should be much less than 0.3 A

Perhaps the PWM cycling is much more rapid than a couple of seconds, and the controller is having some problem so it is switching between running at a controlled output of 0.3A for a while, then occasionally "waking up" to the fact that it should be in bulk charge mode and letting the full panel output (1.5A) through, but then falling back into this throttling mode again... and repeating the whole cycle every couple of seconds.

I'm still interested in what the "charging" and "charge complete" lights are showing.

[brian_bp]

...So if you're seeing 1.5 amps that a little better than 25% of the max output of 5.4 amps. This may be as good as you're going to get under these conditions.

I'll buy that.

But I was reading this:

... the controller shows that I am getting between 0.3 and 1.5 amps out of it...

and thought that we were talking about continuous output (for which 1.5 A is fine but 0.3 A would be too low)... but it appears to be a rapid cycle:

...The controller display changes 2 or 3 times a second. Most of the time it displays 0.3 amps. Then once every couple seconds or so it jumps up to 1.5 amps, and then right back down to 0.3.

Here's my guess:
1.5 amps is fine for the available sunlight, but...
the controller is cycling to something other than the expected bulk charge state for some reason.

I suspect that the panel is fine, and would hook the panel to the battery without the controller, but through an ammeter. If the panel maintains some reasonable current, there's nothing wrong with the panel, and I would want to confirm that.

[brian_bp]

Electrical Specifications
Model: KC65T
Maximum Power: 65 watts
Tolerance: +10% / -5%
Maximum Power Voltage: 17.4 volts
Maximum Power Current: 3.75 amps
Open Circuit Voltage: 21.7 volts
Short-Circuit Current: 3.99 amps

That makes sense... in full blast sunlight:

• at its best operating point the panel puts out 3.75 A at 17.4 V (which is 65 watts)
• if shorted out it puts out 3.99 amps, but at no voltage (and thus no useful power)
• if not connected to anything it puts out 21.7 V, but no current (and thus no power)

12V is well below the max power voltage, so at that point is should ideally put out more than 3.75 A of current, but less than 65W of power... the current at 12V in perfect sun would be between 3.75 A (the 17.4 V current) and 3.99 A (the zero volt current). The observed 1.5A is about 40% of ideal, and may be just fine for the season and location.