Low voltage output in full sun

[free01]

Hello,

I have a 100watt 18v / 5.56 amp hard sided portable solar panel and in full sun I only see a maximum of 14.3 - 14.5 volts. I can see upwards of 5.x amps when in good sunlight but no matter what I do I never see over 14.3'ish volts - without any load, I have tested using a volt meter via 1ft pig tail direct connected to solar on 14 gauge SAE quick connect. I understand it is only a basic PWM controller, but I would think it should be capable to output more than 14.5 volts. The manual says it is a full 4-stage charge controller (I LOL at this). At 14.5v with 5amps this is only 72.5 watts even without any load. I am not expecting to see the full 100watts but shouldn't I see at least 80-90 watt'ish? I also do not see a way to increase the bulk charge voltage output in the manual. I do see a way to set the float but that is it. Or is this normal?

In this testing scenario I have not including the batteries, I am just trying to troubleshoot why the panels (or PWM) is not outputting more than 14.5

Any tips or guidance would be appreciated.

 

[sunshine_eggo]

Hello,

I have a 100watt 18v / 5.56 amp hard sided portable solar panel and in full sun I only see a maximum of 14.3 - 14.5 volts. I can see upwards of 5.x amps when in good sunlight but no matter what I do I never see over 14.3'ish volts - without any load, I have tested using a volt meter via 1ft pig tail direct connected to solar on 14 gauge SAE quick connect. I understand it is only a basic PWM controller, but I would think it should be capable to output more than 14.5 volts.

14.5V is a common charger output voltage. Very few "12V" systems charge to much higher. Rolls batteries charge to 15.0V, but most charge to 14.4-14.8V. You might be able to change that based on the PWM settings.

The manual says it is a full 4-stage charge controller (I LOL at this).

Why? What's funny about that? Does it offer bulk/boost/absorption, float and equalization options? If so, it qualifies as a 4 stage charger. Most do.

At 14.5v with 5amps this is only 72.5 watts even without any load. I am not expecting to see the full 100watts but shouldn't I see at least 80-90 watt'ish? I also do not see a way to increase the bulk charge voltage output in the manual. I do see a way to set the float but that is it. Or is this normal?

You've just learned an important lesson concerning PWM. PWM works by shorting the panels to the battery thus forcing the panels to operate at slightly above battery voltage. Thus, you lose ~25% of your potential output right off the bat. You're measuring < panel Vmp because the unit is opening and closing the circuit thousands of times a second to effectively provide 14.5V at the output terminals.

The ~25% loss is actually less severe in hot weather as hot panels produce less voltage. Even on an MPPT, the panel might only deliver 16-16.5V instead of 18V due to heat. In this case, the PWM might only be 10-15% worse.

 

[free01]

14.5V is a common charger output voltage. Very few "12V" systems charge to much higher. Rolls batteries charge to 15.0V, but most charge to 14.4-14.8V. You might be able to change that based on the PWM settings.

Thank you for the reply, I thought so that makes sense. My 3-stage RV battery charge has a bulk charge of 14.82, so the PWM outputting 14.5 is not too far off.

Why? What's funny about that? Does it offer bulk/boost/absorption, float and equalization options? If so, it qualifies as a 4 stage charger. Most do.

I do not see any additional technical specs on what the voltage output is on any of the 4 stages of charge (bulk, boost, absorption) the only setting that I see where I can modify is the float charge which I have set to 13.5, same as my RV charge controller as well as the Trojan T-105 specs recommend.

You've just learned an important lesson concerning PWM. PWM works by shorting the panels to the battery thus forcing the panels to operate at slightly above battery voltage. Thus, you lose ~25% of your potential output right off the bat. You're measuring < panel Vmp because the unit is opening and closing the circuit thousands of times a second to effectively provide 14.5V at the output terminals.

The ~25% loss is actually less severe in hot weather as hot panels produce less voltage. Even on an MPPT, the panel might only deliver 16-16.5V instead of 18V due to heat. In this case, the PWM might only be 10-15% worse.

 

[free01]

Thank you for the reply, I thought so that makes sense. My 3-stage RV battery charge has a bulk charge of 14.82, so the PWM outputting 14.5 is not too far off.

Re: 4-stage controller question. I do not see any additional technical specs on what the voltage output is on any of the 4 stages of charge (bulk, boost, absorption) the only setting that I see where I can modify is the float charge which I have set to 13.5, same as my RV charge controller as well as the Trojan T-105 specs recommend.

I think your reply has answered my question, the primary reason why I started with a suitcase solar panel is to learn about the basics of solar charging. I think I've got a much better grip now and as far as my current setup I am maximizing the potential of the Dokio panels. Very much appreciated, again @sunshine_eggo!

 

[RCinFLA]

Need to know battery type and AH size to set charge controller parameters.

Bulk current is maximum battery charge current allowed.

Float voltage (what they are apparently calling 'boost') is battery maintenance charge complete idle voltage.

Absorb voltage is charge top off voltage. Held for a given time period or until charge current drops off. Then voltage drops to float voltage.

The 4th stage is equalize over-voltage. Only used once in a while for lead acid batteries to equalize state of charge between cells. It is hard on battery and consumes water in electrolyte of lead acid battery. Not used for sealed lead acid battery that cannot vent the hydrogen and oxygen gas from split up water in electrolyte. If you cannot add water to cells to replace burned off water do not do equalize cycling.

 

[free01]

Need to know battery type and AH size to set charge controller parameters.

Bulk current is maximum battery charge current allowed.

Float voltage (what they are apparently calling 'boost') is battery maintenance charge complete idle voltage.

Absorb voltage is charge top off voltage. Held for a given time period or until charge current drops off. Then voltage drops to float voltage.

The 4th stage is equalize over-voltage. Only used once in a while for lead acid batteries to equalize state of charge between cells. It is hard on battery and consumes water in electrolyte of lead acid battery. Not used for sealed lead acid battery that cannot vent the hydrogen and oxygen gas from split up water in electrolyte. If you cannot add water to cells to replace burned off water do not do equalize cycling.

Thanks, I think sunshine_ego answered, and gave a pretty good technical explanation that fully answers what I was looking for. In my initial question, I stated I was testing max voltage output and did not have any load or batteries connected so the batteries in this example is not part of the equation. However, also as I mentioned to sunshine_ego, my two Trojan T-105s like a bulk charge of 14.82v, so if the max my current solar panel can output is 14.5, I am really not that far off. And with my 14 gauge wires, my voltage is not the issue I would need to add more solar and an MPPT if I wanted to see higher AMPs.. But, that isn't my issue I do not expect more than 5amps on 100 watt I was really just trying to better understand why I could only see a max of 14.5v output which Mr Sunsine answered.. Thank you for your reply!

 

[free01]

14.5V is a common charger output voltage. Very few "12V" systems charge to much higher. Rolls batteries charge to 15.0V, but most charge to 14.4-14.8V. You might be able to change that based on the PWM settings.



Why? What's funny about that? Does it offer bulk/boost/absorption, float and equalization options? If so, it qualifies as a 4 stage charger. Most do.



You've just learned an important lesson concerning PWM. PWM works by shorting the panels to the battery thus forcing the panels to operate at slightly above battery voltage. Thus, you lose ~25% of your potential output right off the bat. You're measuring < panel Vmp because the unit is opening and closing the circuit thousands of times a second to effectively provide 14.5V at the output terminals.

The ~25% loss is actually less severe in hot weather as hot panels produce less voltage. Even on an MPPT, the panel might only deliver 16-16.5V instead of 18V due to heat. In this case, the PWM might only be 10-15% worse.