MPPT or PWM solar controller?

[p38arover]

I've wondered what was meant by MPPT and why they may, in some situations be better than the el cheapo PWM controllers supplied with portable solar panels.

This White Paper by Victron explains a lot: https://www.victronenergy.com/upload/documents/White-paper-Which-solar-charge-controller-PWM-or-MPPT.pdf

Just changing to MPPT may not necessarily be better but it could be. I must get my infrared thermometer out and measure the panel cell temperatures this week when the ambient is in 40s C. I'll do that tomorrow and update this thread.

If I went MPPT, I could reconfigure my panels to be in series instead of parallel for better performance in (a) partially shaded conditions, (b) cloudy weather, or (c) high panel temperatures.

When I went camping a couple of weeks back I was struggling to keep my 2 x 45Ah AGM deep cycles charged with my 120w solar panels and I was only running the 29 litre Engel fridge. However, having said that, I had inadvertently isolated the connection between the main and aux batteries and only remembered 40km from my destination. The fridge had been running for a couple of hours at that point so my aux batteries were not fully charged to start. Then a couple of days of cloudy weather and the sun not getting into the valley until about 11am reduced the charging time. At peak, the panels were putting about 6-7 amps into the batteries. I did look at the power meter on the cable and was only getting about 30Ah into the battery on a good sunny day.

[DiscoMick]

I think you may need more solar and bigger batteries.
Another trick is to put the regulator close to the battery, rather than on the back of the panel. That way the full output of the panel can flow all the way down the cable, reducing voltage drop, and is only regulated just before reaching the battery.
From what I can figure as a non-expert, Maximum Power Point Tracking may give a slightly higher input than Pulse Width Modulation in some situations when the panel is performing at maximum output, but often there is little difference, despite the much higher price.
Here's another explanation :
MPPT vs PWM Solar Controllers - Enerdrive Pty Ltd (http://www.enerdrive.com.au/mppt-vs-pwm-solar-controllers/)

[DiscoMick]

Solar Regulators - Solar Charge Controller - MPPT Solar Charge Controller - 12v Solar Regulators (https://www.aussiebatteries.com.au/solar-regulators/solar-charge-controllers/)

[p38arover]

I think you may need more solar and bigger batteries.
Another trick is to put the regulator close to the battery, rather than on the back of the panel. That way the full output of the panel can flow all the way down the cable, reducing voltage drop, and is only regulated just before reaching the battery.

2 x 45Ah are as much as I can fit in the space available under floor. I replaced the original cables with much heavier wire a few years back to reduce voltage drop. I'll check the voltage drop today, at 7A, I'm expecting less than 0.1V

[p38arover]

Ambient temp 39 deg C and the panel temp was 50 deg C after stabilising in full sun for an hour.

Voltage drop was a difficult to measure, it peaked at about 160mV in each cable leg at just over 5A - the current would rise and fall as the charge rate changed.

So I measured the cable resistance with a special ohmmeter (ESR Meter) that will measure very low resistance.

The measuring leads on the ESR meter measured 0.07 ohms and each solar panel cable measured 0.1 ohms (including the meter leads). So each cable leg has a resistance of (0.1 - 0.07) ohms = 0.03 ohms for a total cable resistance of 0.06 ohms.

At 7 amps that would be (7 x 0.03) volts, i.e., 0.21 volts or 210mV in each cable leg. That tallies with the measured 160mV at approx 5A mentioned above.

When it cools off in my electronics workshop, I'll put a power supply onto the cable and a load on the other end and measure voltage and current to check the measured resistance.

To be honest, I don't think it's an issue based on this sentence from the Victron White Paper:


Assuming a discharged battery the initial charge voltage will be around 13 V, and assuming a voltage loss of 0,5 V over the cabling plus controller, the panel will be at Vpwm = 13,5 V.

So the panel will make up for that voltage drop on the cable - the panels have an open circuit voltage of about 18V.

As an aside, what I did notice when camping was that angle of incidence to the sun made a marked difference in output. The legs on my panels put the panels at about 50 deg tilt (measured with an inclinometer). If I lifted the lower edge of the panels onto a camping step to reduce the angle to about 30 deg (I was camped at approx 34 deg south), the output rose nearly 15%. I will be modifying the supports to lower the angle. I believe that, in summer, they should be at the same angle as our latitude but in winter the angle should be about 15 deg more.

[austastar]

Hi,
March and September, panels at latitude, December tilt up 23 degrees, June tilt down 23 degrees.
Cheers

[p38arover]

Who do you believe? Some say 15 degrees up/down. Others say no change for summer, only for winter.

My house panels (33.75 deg latitude) are at 22.5 deg (the pitch of the roof).

[austastar]

Hi,
Ideally the panel should be fully facing the sun. Practicality however means as close at is possible without indulging in full xy tracking.
Cheers

[weeds]

For my portable panels I just face them to the north at 30 ish degrees...

at the end of the day I do face them east to catch the moon than the morning sun.

[p38arover]

Hi,
Ideally the panel should be fully facing the sun. Practicality however means as close at is possible without indulging in full xy tracking.
Cheers

I use the shadow cast by the panel to orientate the panel.

[austastar]

Hi,
Yep, precision is wasted effort. 10 or 20 degrees out makes such little difference it is of academic interest only.
Even on a house it is cheaper to put in extra panels facing East or West to catch the lower sun than to put in the mechanics to track the sun.
Cheers

[p38arover]

Jaycar had a clearance sale on over the last weekend.

I dropped in to buy a simple voltage switch kit ($7.50 vs usual $25) and noticed they had an MPPT Controller kit marked down from $140 to $80. When I asked at the checkout, the priced was halved to $40 - so I bought it. It's a design from Silicon Chip magazine - meaning I can probably repair it should it fail.

[weeds]

Jaycar had a clearance sale on over the last weekend.

I dropped in to buy a simple voltage switch kit ($7.50 vs usual $25) and noticed they had an MPPT Controller kit marked down from $140 to $80. When I asked at the checkout, the priced was halved to $40 - so I bought it. It's a design from Silicon Chip magazine - meaning I can probably repair it should it fail.

I hope it doesn’t end up in your under thread as failed to work.

[p38arover]

Sshhhh! :bat:

[trout1105]

I have just bought a couple of MPPT controllers to replace the PWM controllers on my boat and on my Navara and I am wondering what the "Load" connection is used for.

[pop058]

I have just bought a couple of MPPT controllers to replace the PWM controllers on my boat and on my Navara and I am wondering what the "Load" connection is used for.

Fridge ??

[Red90]

The stuff using the power.

[trout1105]

So do i run the fridge/fridges from the batteries or from the load outlet on the MPPT controller?

[Red90]

Read the instructions.

[101RRS]

It is just a spot/outlet to run something direct from the solar panels/controller while the sun is still making enough power - is something that is there but never used it - simply easier to let all power from the panels go to the batteries and provide power for you gear from there. If the sky clouds over the batteries still provide a buffer where power at the load point will drop off.

Garry

[austastar]

Hi,
How many connections?
Minimum needed is 2,
1) solar panel
2) battery

If you have 3, the third one should be for the load, and it will probably have a low voltage protection built in to protect the battery from drawing down too far.
You may like to wire at least one light directly to the battery so you won't suddenly be in the dark.
As mentioned above, the instructions should explain it.
Cheers

[trout1105]

Hi,
How many connections?
Minimum needed is 2,
1) solar panel
2) battery

If you have 3, the third one should be for the load, and it will probably have a low voltage protection built in to protect the battery from drawing down too far.
You may like to wire at least one light directly to the battery so you won't suddenly be in the dark.
As mentioned above, the instructions should explain it.
Cheers

I have installed the new MPPT controllers on the boat and the Nissan and the fridges will run directly from the battery or from the "Load" outlet.
I disconnected the solar panel to replicate night time conditions and the fridge still runs so I may leave them set up running from the "Load" outlet for now[thumbsupbig]

[DeanoH]

So do i run the fridge/fridges from the batteries or from the load outlet on the MPPT controller?


The 'load' connection on the solar controller is in most cases irrelevant and all you need to do is connect the solar panel and battery with your load distribution connected to the battery, leaving the 'load' connection unused. This is what most people do.

What the 'load' connection does is to allow a timer controlled output from the controller and depending on the controller the ability to measure output (load) current. A typical example of this would be to automatically switch a light on and off. eg. at night time in a toilet at an unattended solar powered site. Not particularly useful in an automotive situation but could be used for example in a campervan to automatically switch the fridge off/on at night if the compressor noise was a problem whilst trying to sleep. In some controllers load current can be displayed giving the user an 'all in one' monitoring device without the need of additional meter(s). In this scenario the solar reg is left in its (usually default) mode of 'always on 24/7'. The downside of this is if the electronics fail in the timer/current measuring circuitry then you've got no power to the load ie. fridge and your beers hot and SWMBO's ****ed cos the foods gone off.

IMO best left unused.

Deano :)

[trout1105]

The 'load' connection on the solar controller is in most cases irrelevant and all you need to do is connect the solar panel and battery with your load distribution connected to the battery, leaving the 'load' connection unused. This is what most people do.

What the 'load' connection does is to allow a timer controlled output from the controller and depending on the controller the ability to measure output (load) current. A typical example of this would be to automatically switch a light on and off. eg. at night time in a toilet at an unattended solar powered site. Not particularly useful in an automotive situation but could be used for example in a campervan to automatically switch the fridge off/on at night if the compressor noise was a problem whilst trying to sleep. In some controllers load current can be displayed giving the user an 'all in one' monitoring device without the need of additional meter(s). In this scenario the solar reg is left in its (usually default) mode of 'always on 24/7'. The downside of this is if the electronics fail in the timer/current measuring circuitry then you've got no power to the load ie. fridge and your beers hot and SWMBO's ****ed cos the foods gone off.

IMO best left unused.

Deano :)

I had an auto sparky install the solar setups in the van and the 79 series and the MPPT controllers in these have the "Load" connection unused, I will do the same[thumbsupbig]