Upgraded from PWM to MPPT solar charge controller for C/V.

[c_lee]

After about 4 years using a PWM solar charge controller with our 80W solar panel on our caravan I have just upgraded to a MPPT solar charge controller.

We have an 85 AH leisure battery in our van, LED internal lights throughout, and a motor mover ( fitted within about the last 12 months and before the MPPT controller ).

In use, the PWM controller has served us well during the past 4 years and we have often spent over 2 weeks ( sometimes 4 ) away on site without EHU during the warmer months and usually without any power shortage at all.

We watch, quite often, about 3 hrs of TV per night late evening/early morning.
Our caravan TV is LED back-lit and 24 inch.

Within the past month, and during one trip, we attended two THS sites over 6 nights without EHU and during the first 3 days the sky was almost permanently cloudy.
This caused power shortage problems after about 2 days.
During the second 3 day period at another location the problem wasn't so bad as it was not as cloudy.

The leisure battery was fully charged before we set off and is charged during driving time.

The power shortage during the first 3 days in cloudy weather and with a low sun angle at this time of year prompted me to buy the MPPT controller.

Low power, true MPPT controllers are not commonly advertised on the net.
PWM controllers masquerading as MPPT controllers are there at MPPT prices and I was aware of that.

This is what I bought:

http://www.ebay.co.uk/itm/3221347291...%3AMEBIDX%3AIT it is true MPPT not fake.

It arrived today and I am currently testing it off the van.

The price difference between PWM and MPPT controllers is quite substantial ( about 300% ).

My original 4 year old PWM controller was about £25.

I will report findings once testing is complete.

Colin

[Christerart]

Any figures yet?

[c_lee]

We have not been away in the caravan on solar since I received the MPPT controller so have been testing it more at home off the van.
This was about 3 weeks ago.

For testing I was using an 85AH battery, either no load or a 5 amp load on occasions, a DC clamp ammeter in various positions, and a Fluke DC voltmeter.

The first testing was done using my 80W ( 20 Voc, 15.7 Vmpp ) panel on days with long cloudy and clear intervals and the panel in a fixed inclined position on my shed roof.
In that position the panel never looked directly at the sun even during the clear intervals because of the low angle of the sun and obstructions - it just looked at the clear sky.

During this time the panel did give some charge ( ~ 200mA cloudy and ~ 600mA clear ) but the panel output voltage was below the 15.0V MPPT threshold switching voltage for the controller and in that situation the controller reverts back to PWM mode.
Had the input voltage fallen much lower then there would have been negligible charging.

This MPPT controller is capable of handling PV input voltages of up to 50V and has an MPPT input operating range of 15 - 37V.

In my mind I could see that in unfavorable conditions a major limiting factor for MPPT operation is the PV output voltage of the solar array.

I have only the one panel that I had used for testing but arranged for the loan from a friend ( for testing ) of an 80W dual 12V ( nominal ) folding panel, the type that are usually used with each panel connected in parallel.
( There was no on board charge controller for the dual panels ).

But I would be connecting them in series to help ensure that the total PV output voltage was above the 15.0 V MPPT threshold of the charge controller.

Testing was done on a similar day as previously.

I can't remember the exact figure now but I monitored the V mppt ( x 2 ) for the array ( 2 panels ) and the charge controller tended to keep the PV input voltage near to that figure so the controller was always operating in MPPT mode and never PWM mode even when cloudy.

The PV input voltage did vary a little around the array's V mmpt value but I can understand the need for that in a system that is constantly monitoring and then adjusting for best efficiency.

During the testing periods loads were applied to the battery at different stages to ensure I wasn't always trying to charge an already fully charged battery.

What is more relevant is the fact that at times when the input current from the PV array was around 1.5 - 2 amps ( bright but not in direct sunlight ), the battery charge current was more like ~4 amps and sometimes substantially more.
At one time 6 amps.

So, in conclusion I realize that my single PV panel ( Voc 20V, Vmppt 15.7V ) is not ideal as the output voltage in less than ideal conditions is too close ( and usually below at this time of year ) the MPPT switching threshold for the charge controller.

But in the case of dual PV panels connected in series then I think the difference is very noticeable in the charge current for the battery even at this time of year.

Overall I think that a pair of series connected PV panels would be much better and still allow reasonable charging even in less than ideal conditions.

I might give it a season used in the caravan before upgrading to dual PV panels and see how it goes.

I think during the summer months the caravan battery would be charged much sooner even with a single PV panel.

Don't know when the next time we will be away on just solar so not likely to update this much before springtime.

Colin

[Tannaton]

Thanks for posting this - it's educated me a bit.

This is a good article also:

https://www.victronenergy.com/blog/2...r-pwm-or-mppt/

[c_lee]

After our first, non EHU, spell away last week using the new MPPT charge controller with our new 2 x 50 watt roof mounted solar panels connected in series I can report that there are definite advantages using a true MPPT charge controller with high input voltage solar from the 2 panels ( about 42 Voc - 30 Vmppt ).

Advantages that definitely would not have been achieved had a single 100 watt panel been used with an open circuit solar voltage of about 21v and Vmppt 14.7V ( in ideal conditions ).

We were sited on a THS just South of Bridlington for 4 nights.

I noticed on the first morning following arrival the day before that the battery charge current was just short of 5 amps at about 9am - and the sky was partially cloudy and it was misty.

We had no power shortage whatsoever during the trip.

I was using 2 x 85AH leisure batteries for storage.

We had watched about 4 hrs TV from about 9 pm the previous night.
All internal lights are LED.
My Mrs uses a 600W mains hairdrier each morning for about 5 minutes powered from our on board invertor ( this is a big >50 amp hit ).

This situation would not have happened had we been using our older 80 watt solar panel with the old PWM charge controller - we'd have been short of power as happened on a THS later last year.

Each day away was similar with no power shortage.

In my mind it's the high solar voltage and the MPPT charge controller that made a big difference as I had hoped.

The system is able to partially compensate for part shade and/or cloudy situations on the solar panels.

I'm well pleased.

Colin