Solar panel, MPPT, Battery switching

[goboatingnow]

Originally Posted by thomm225

I was making a point about the lack of current flow on the panel side when not hooked up to the controller or if the batteries are fully charged.

Basically agreeing you don't need to fuse the panels.

Also I wasn't looking at waveforms as I didn't need to. Why would I use a scope to check a DC Voltage level?

I do miss using O'Scopes though, but they are usually just collecting dust these days

As far as turning the panels off, one of my controllers was acting up so I would disconnect that panel at the panel with one lead when I wasn't on the boat to monitor it leaving just my 65 watt panel to charge the batteries.

Other times, I'd unhook everything for a couple weeks in Winter.

I didn't see the need to constantly charge the batteries.

They would still be at about 12.5 -12.6 volts when I plugged the controller and panels back in.

Because theoutput of a pwm controller isn’t dc ( even though the battery acts as a giant filter )

[thomm225]

Originally Posted by goboatingnow

Because theoutput of a pwm controller isn’t dc ( even though the battery acts as a giant filter )

I think you missed the point and went off on a tangent.

I was showing that the batteries got fully charged with my old, cheap PWM controllers by checking voltages on either side of the controller.

On the battery side of the controller, I was seeing battery voltage.

On the panel side, panel voltage.

As I said, when the PWM Controller went to Float (or stopped at a certain voltage) the battery voltage was for example 13.5 Volts. The Panel side was also 13.5 volts.

After a day or so as the battery got fully charged the panel side of the controller increased toward panel VOC while the battery side remained at 13.5 Volts so these controllers were still allowing enough current thru to charge the battery up fully

These old PWM's I had didn't have an Absorption Phase. They also didn't have a display and may be off the market today. These controllers sort of clamped the voltage at a certain level.

If memory serves, I have seen that panel side voltage nearing 20 volts. (VOC is like 21.2 or so)

Now with the Victron and probably newer PWM Controllers, when they drop to float they have completed the Absorption Phase and there is little current still going into the battery so when these controllers drop to Float the Panel Voltage is close to VOC.

Mine was 19.6 or so during the first charge cycle after I hooked up the Victron. This voltage may go higher (closer to VOC) on a different day under different conditions)

It's all about the lack of current flow allowing the panel voltage to increase to near VOC.

I used to troubleshoot failed circuits in a similar way back in the day. If you found an area in a circuit that was at supply voltage you knew you have an open component close by.....

[hzcruiser]

Originally Posted by donradcliffe

My experience with cheap PWM controllers is that there is about a 30% chance of frying the controller by disconnecting it from the battery and leaving it connected to the panels during the day. I don't try this with more expensive controllers.

maybe that's separating the wheat from the chaff?

[hzcruiser]

Originally Posted by StuM

WARNING! Connect the battery terminal wires to the charge controller FIRST, then connect the solar panel(s) to the charge controller. NEVER connect solar panel to charge controller before the battery.
.[/I]

That's the 12/24 V auto sensing SCCs?

[goboatingnow]

Originally Posted by thomm225

I think you missed the point and went off on a tangent.

I was showing that the batteries got fully charged with my old, cheap PWM controllers by checking voltages on either side of the controller.

On the battery side of the controller, I was seeing battery voltage.

On the panel side, panel voltage.

As I said, when the PWM Controller went to Float (or stopped at a certain voltage) the battery voltage was for example 13.5 Volts. The Panel side was also 13.5 volts.

After a day or so as the battery got fully charged the panel side of the controller increased toward panel VOC while the battery side remained at 13.5 Volts so these controllers were still allowing enough current thru to charge the battery up fully

These old PWM's I had didn't have an Absorption Phase. They also didn't have a display and may be off the market today. These controllers sort of clamped the voltage at a certain level.

If memory serves, I have seen that panel side voltage nearing 20 volts. (VOC is like 21.2 or so)

Now with the Victron and probably newer PWM Controllers, when they drop to float they have completed the Absorption Phase and there is little current still going into the battery so when these controllers drop to Float the Panel Voltage is close to VOC.

Mine was 19.6 or so during the first charge cycle after I hooked up the Victron. This voltage may go higher (closer to VOC) on a different day under different conditions)

It's all about the lack of current flow allowing the panel voltage to increase to near VOC.

I used to troubleshoot failed circuits in a similar way back in the day. If you found an area in a circuit that was at supply voltage you knew you have an open component close by.....

Ultimately if you have enough sun , and enough time everything gets charged. If you have big solar power and small loads any junk charging controller will work

That’s all irrelevant

When you have marginal systems it’s then the better power conversion processes come into play


again pwm controllers don’t have power conversion ability. They don’t really have a constant current ( bulk ) or constant voltage ( absorption ) modes. They “ simulate “ this by changing the mark space ratio of the pwm signal

If the battery is full then the pwm is only briefly connecting the panels to the battery ,with a multimeter what you see is a panel voltage close to Voc.

If you look at it with a scope is you see a waveform where the panel voltage drips to the battery voltage briefly when the pwm cycle turns on the mosfets and then jumps back to Voc when the mosfets are turned off.

Your meter “ averages “ this pulse train onto a voltage. But it’s not actually what’s there.

This is why high voltage panels and pwm controllers can be very inefficient as every time the pwm signal connects the panels to the battery the operating point of the panel is pulled down to the battery, this results in a very inefficient transfer of power from a higher voltage panel ( 50% less or even more )

Hence where the PV panel had an operating point close to the battery voltage pwm delivers efficiencies close to mppt. Away from that point they can be very inefficient

[thomm225]

Originally Posted by goboatingnow

Ultimately if you have enough sun , and enough time everything gets charged. If you have big solar power and small loads any junk charging controller will work

That’s all irrelevant

When you have marginal systems it’s then the better power conversion processes come into play


again pwm controllers don’t have power conversion ability. They don’t really have a constant current ( bulk ) or constant voltage ( absorption ) modes. They “ simulate “ this by changing the mark space ratio of the pwm signal

If the battery is full then the pwm is only briefly connecting the panels to the battery ,with a multimeter what you see is a panel voltage close to Voc.

If you look at it with a scope is you see a waveform where the panel voltage drips to the battery voltage briefly when the pwm cycle turns on the mosfets and then jumps back to Voc when the mosfets are turned off.

Your meter “ averages “ this pulse train onto a voltage. But it’s not actually what’s there.

This is why high voltage panels and pwm controllers can be very inefficient as every time the pwm signal connects the panels to the battery the operating point of the panel is pulled down to the battery, this results in a very inefficient transfer of power from a higher voltage panel ( 50% less or even more )

Hence where the PV panel had an operating point close to the battery voltage pwm delivers efficiencies close to mppt. Away from that point they can be very inefficient

Again I didn’t need a scope to verify the batteries had charged up completely.

The fact that the voltage on the panel side was near VOC told me that. This did occur though for a day or so after the controller got to a certain voltage which you could call it’s Float Voltage

Also since the old PWM’s I was using didn’t have displays I took voltage checks with the meter to confirm the batteries were charged and not just clamped at a certain voltage

[goboatingnow]

Originally Posted by thomm225

Again I didn’t need a scope to verify the batteries had charged up completely.

The fact that the voltage on the panel side was near VOC told me that. This did occur though for a day or so after the controller got to a certain voltage which you could call it’s Float Voltage

Also since the old PWM’s I was using didn’t have displays I took voltage checks with the meter to confirm the batteries were charged and not just clamped at a certain voltage

You can’t actually see what’s going on with a multimeter , and you miss my point , an PWM controller cannot match a PV panel to a battery whereas an mppt controller can. This means for pv panels with a high Vmp , the panels will be very inefficient using a PWM controller and considerably more efficient with an mppt one.

Of course both will get you charged given enough time and sunlight. But the mppt one will do it sooner and better in less optimal conditions

Note the controller didn’t get to the float voltage , the batteries did and the panels will be clamped to that voltage during the PWM on time.

[thomm225]

Originally Posted by goboatingnow

You can’t actually see what’s going on with a multimeter , and you miss my point , an PWM controller cannot match a PV panel to a battery whereas an mppt controller can. This means for pv panels with a high Vmp , the panels will be very inefficient using a PWM controller and considerably more efficient with an mppt one.

Of course both will get you charged given enough time and sunlight. But the mppt one will do it sooner and better in less optimal conditions

Note the controller didn’t get to the float voltage , the batteries did and the panels will be clamped to that voltage during the PWM on time.

You can see what's going on just fine with a multimeter.

The meter reads the same as the voltage display on my later "true" PWM's.

I wasn't comparing PWM controllers to MPPT's except to say that there is little difference with my system probably since I only have 115 watts going with the MPPT controller and 115 watts to 155 watts with the PWM's except that 40 watts worth of panels are hooked directly to the batteries and 115 watts through the PWM Controller.

My whole point was the early PWMs did not have a true Absorption Phase the voltage just stopped at a certain point/level which you might call Float and the panel side of the controller voltage was the same as the Battery side.

Hours later the panel side was closing in on the panel's VOC as the batteries continued to get a small charging current thru the "controller" .....

The Victron MPPT does this with a proper Absorption Phase so when it drops to Float the panel side is already close to VOC.

You can see all this with a meter.

Today for example the panel side voltage was almost 21 volts, (which is very close to the panel's VOC) batteries a little over 13 volts.

Below are a few of the types of solar controllers I've had on my boat over the years. The Victrons are one with Bluetooth and one without. The rest are PWM's or PWM wannabe's. (regulators)

I have been experimenting with them since 2012 and just last weekend mounted my first controller the Victron 75/15 MPPT (Bluetooth). All the rest were never mounted because I was still testing. One day I'll mount the panels also. (maybe)

My first one the CMTP02 is the one I was talking about mostly. It's actually called a Solar Regulator and you used to be able to get them for $10 ea.

You have to stay on top of it though or it might over charge your batteries. I would unhook it after the panel side closed in on VOC. This in 2012-2014 or so.

https://www.aliexpress.com/item/3256...apt=4itemAdapt

[OS2Dude]

On our boat the panels stay connected 100% of the time. (Rare exceptions when doing maintenance.) I can see no reason to disconnect the panels or controller that often. Controllers have circuits to keep from over charging the batteries, no need to disconnect the charger from the batteries manually. We do have in-line fuses between panels and controller, as well as between controller and battery.

[thomm225]

Originally Posted by OS2Dude

On our boat the panels stay connected 100% of the time. (Rare exceptions when doing maintenance.) I can see no reason to disconnect the panels or controller that often. Controllers have circuits to keep from over charging the batteries, no need to disconnect the charger from the batteries manually. We do have in-line fuses between panels and controller, as well as between controller and battery.

The "controller" I had first held the batteries at 14.4 volts so after the panel side voltage neared panel VOC showing a decrease in current flow I would disconnect that controller. This usually took a day or so. It was the absorption phase.

Some of the other low cost PWM's I had did various other things I wasn't sure of so I'd disconnect them as well.

Also I was experimenting some.

I was also connecting panels directly to the batteries with no controller when needed

In Winter I'd disconnect for a complete weeks at a time. Didn't see the need for a constant charge since the boat wasn't being used.

Battery voltage never dropped below 12.5-12.6 volts depending on which meter I was using.

Photo is of my early Controller / Regulator which I still have. Cost was $10. Regulates voltage to 14.4 volts.

CMTP02 30A 12V 24V Black Safety Solar Controller Automatic Solar Charge Regulator

https://www.aliexpress.com/item/3256...apt=4itemAdapt

[jo_sail]

Originally Posted by hzcruiser

That's the 12/24 V auto sensing SCCs?

Yes!

That‘s it for many solar battery controllers which can work for either 12 V or 24 V.

Most of them switch automatically and need a stable voltage information for doing it correctly. If the battery is not connected but the 14.4 V PV is connected sometimes having 20-27 V without load, the unconnected battery terminals could go floating anywhere and deliver false info to the controller. Not necessarily, but there is a risk. Especially if a 12 V battery would be charged at somewhere above 24 V it‘s a risk of battery explosion.

Furthermore,
in a controller connected to only PV without load nor battery, there is no significant current through the controller. Some simple voltage controllers are completely unable to control anything without at least a very small current. Then potentially also the overvoltage protection is ineffective. If now PV is connected and disconnected (or intermittend in the moment of tuching cables), its high initial voltage may go through the electronics of the controller without control and destroy parts of the circuit.

Again, often things might go well without damage to the electronics. Especially if the controller circuit is built sufficiently robust taking into account such undefined connection states. But lack of stable battery voltage supply and lack of any load places a risk to the electronics.

Both are good reasons to always connect battery first and disconnect it last as effective protective measure, which allows the controller to always do its job properly.

So it is written in many user manuals of solar controllers without telling the reasoning.

[jomoman]

if you have a victron charge controller, the connect/ disconnect sequence is correct. connect batts first then the solar via a breaker. opposite when disconnecting.
leave your breakers on all the time.

[goboatingnow]

You can see what's going on just fine with a multimeter.

The meter reads the same as the voltage display on my later "true" PWM's.

You cannot see the PWM action , what you see is the meter averaging the results ( as is the PWM controller display )

My point was the fundamental weakness of PWM , especially where the panel optimum voltage point is significantly different from the battery voltage is that the panel is directly connected to the battery anytime the PWM duty cycle demands. At that point the operating point of the panel is moved to the battery voltage ( you cannot see this without a scope ) this can cause significant loss of power , especially with high voltage panels. PWM is not really suitable for this type of application

[thomm225]

Originally Posted by goboatingnow

You cannot see the PWM action , what you see is the meter averaging the results ( as is the PWM controller display )

My point was the fundamental weakness of PWM , especially where the panel optimum voltage point is significantly different from the battery voltage is that the panel is directly connected to the battery anytime the PWM duty cycle demands. At that point the operating point of the panel is moved to the battery voltage ( you cannot see this without a scope ) this can cause significant loss of power , especially with high voltage panels. PWM is not really suitable for this type of application

I didn't care about the PWM action, the MPPT action, or the regulator action, I simply cared about the voltage to check my batteries charge.

When you put your meter leads on the battery terminals, you get battery voltage!

When the wires attached to the battery terminals are hooked to the controller and you read the voltage there, you get battery voltage! Same on Panel side. You get panel voltage.

And on the small 20 watt panels I had hooked directly to the batteries without a controller you also get battery voltage

I guess we techs have more real world experiences with systems as compared to some engineers......this wasn't an analysis but data gathering.

I wasn't analyzing controllers but simply checking the charge on my batteries. (since I was using $10-$15 controllers)

This from a tech that almost always used an O'scope or logic analyzer to troubleshoot with....

but that's all old school now as the speeds are so fast and most everything runs on a bus.

At present though, we are switching over to VM's (virtual machines) to replace real computers ....

Not sure what's next but whatever it is it will come fast.....

Photos from around 2017 or so.

[goboatingnow]

Originally Posted by jo_sail

Yes!

That‘s it for many solar battery controllers which can work for either 12 V or 24 V.

Most of them switch automatically and need a stable voltage information for doing it correctly. If the battery is not connected but the 14.4 V PV is connected sometimes having 20-27 V without load, the unconnected battery terminals could go floating anywhere and deliver false info to the controller. Not necessarily, but there is a risk. Especially if a 12 V battery would be charged at somewhere above 24 V it‘s a risk of battery explosion.

Furthermore,
in a controller connected to only PV without load nor battery, there is no significant current through the controller. Some simple voltage controllers are completely unable to control anything without at least a very small current. Then potentially also the overvoltage protection is ineffective. If now PV is connected and disconnected (or intermittend in the moment of tuching cables), its high initial voltage may go through the electronics of the controller without control and destroy parts of the circuit.

Again, often things might go well without damage to the electronics. Especially if the controller circuit is built sufficiently robust taking into account such undefined connection states. But lack of stable battery voltage supply and lack of any load places a risk to the electronics.

Both are good reasons to always connect battery first and disconnect it last as effective protective measure, which allows the controller to always do its job properly.

So it is written in many user manuals of solar controllers without telling the reasoning.

These reasons are not really the reason for connecting battery first ,

Firstly battery voltage sensing will begin immediately a stable voltage is detected , until that point PV panel voltage will be connected. In Victron the battery voltage is then memorised so that this is the default for subsequent restarts

Nor is the need for a small current the issue either , most decent controllers don’t need a small current , nor is the lack of load an issue in itself


The primary reason is the nature of the circuit design , the power to the electronics is derived from the battery voltage , whereas the panel voltage is merely an “ input “ voltage to the electronics

For internal protection devices to be activated , including protection diodes built into the micro controller and other ICs , the power needs to present before the inputs go “ live “ other wise input protection is weak , and errant operation of certain ICs can occur. ( there is typically latch up protection but it isn’t always sufficient )

Hence the stipulation that the “ power supply “ is connected first , ie the battery then followed by the inputs. ( pv panel). This is good advice in any electronics which has inputs powered separately from the power supply.