Solar controller recommendations

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Re: Solar controller recommendations

Post by sarran1955 »


Good morning mister sunshine... 8)

Well it is a solar thread.... :)

OK, my 2€ cents worth... :roll:

My setup:

3 years ago I fitted my flexy solar panel, nominally 200 watts, covering the rear roof of the van, from zeroinstore on ebay

Same source for my PWM module, 20 amps 2 entries.

The panel charges the starter battery first, then the smart relay charges the leisure battery 120 AH gel type.

The biggest amp consumers are the 18 l portable compressor fridge, 3 amps peak about 15 mins per hour and
the Chinese 2 kw diesel heater, 15 amps on startup and 3 amps when running.

I do not use an inverter, instead a 19.6 volt 90 watt plug in adapter, 40€, to run my HP stream travel computer.
The dashboard is powered by the leisure system with clock and radio a constant draw.
The leisure battery is protected by a low voltage cut off, draining 20 milli amps.
The heater is 'hot' wired to the leisure battery via a relay. The heater has its own low voltage sensor.
A 10 watt ventilator fan is usually running all day..
All the other accessories are 12 volt.

The result:

I have had no problems with the system, particularly as it does not use the vehicle chassis for 'earth', so phantom
drain is not an issue...
The little PWR controller fits with other stuff on a plate below/behind the front seat, so I can look down through the
side window and just see my 3 leds..(battery full)..

The next bit:

Due to Covid, I have been further upgrading my van with a pop top roof, so in preparation I got another flexy solar panel,(100 watts)
and a MPPT controller..
I was a bit shocked at the size of the thing ,compared to the PWM.

So I consulted with my EDF electrical engineer friend, the EDF are promoting domestic solar PV panels and he sent his friend round
to check and explain.

My second panel will only be used when parked up, with a flexy cord going to the existing outside 'solar in 12 volts out' twin socket.
Effectively 2 panels in series..

So the thing to understand here is the peak wattage of the system. This is tested with an induction amp meter, using a load that
exceeds the max solar output...NOT a battery (internal resistance)..more a series of 12 volt bulbs..

The results were a bit of an eye opener...
The EDF base their calculation on a maximum solar potential of 800 watts per sq metre.
The most efficient house polycrystalline panels are about 24% efficient, however the flexy monocrystalline panels on my van
are from 15 to 18% efficient.
If you allow 5 hours of effective sunshine, with an angle of incidence greater than 30 degrees

so: 800 x 0.18 x 5 = 720 watt/hours for 1 square metre.

so a nominal system (mine) of 300 watts will give 1500 watt hours per day in good conditions

However, there are 2 more main factors to take into account:
1 the type and internal resistance of your leisure battery
2 the efficiency of your controller PWM or MPPT.

The real killer here is the battery resistance, pretty much pushing against the charge you are trying to put in. Gets a bit complex..
The controller choice is based on system size and peak wattage.

In the worst case scenario a PWM is 30% less efficient than MPPT, so:

with PWM I get 1050 watt hours.

Now looking back to the system, 1050 wh @ 5 hrs is 210 wh per hour.
Nominal system voltage 18 volts , so a peak load of about 11.6 amperes....

However...we do the test on my van, and the induction amp meter only shows 5.3 amperes to the battery, but nearly 9 amperes
when connected directly to the load..this loss is due to the battery internal resistance and a little bit of electronic inefficiency.

A partial solution would be to use a better, eg Lithium battery, but with a BMS we are looking at 800€... :!:

So the conclusion we reached...
Because the leisure system efficiency is determined by the battery, the real amperage load below 6 amperes with nominally 300 watts
and the size/fitting problem. I am staying with the PWM as the money would be better used elswhere...

The MPPT will not be wasted, as somewhere on the list I have a solar charger project for my tractor... :)

Lunch on the terrace.... 8)



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