my boat has rubbish solar power

ltcom

ltcom

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My little boat has a tiny flexible solar panel connected via a rats nest of wires to a battery.
I'd like to do a proper job.
I have read about PWM and MPPT controllers
http://www.morningstarcorp.com/wp-content/uploads/2014/02/8.-Why-PWM1.pdf

https://www.solar-electric.com/mppt-solar-charge-controllers.html

I didn't understand much about what one offers over the other. I can do basic electrical stuff.

What do the PWM and MPPT offer over a simple lm317 set up to give 14.4 volts?

Panel gives out 20 V open circuit, I make a lm317 to give constant 14.4volts and all is ok or not? Does a battery at 14.4volts stop accepting amps from a solar panel that directs electricity through a £2 lm317 that should only allow 14.4 volts through. Won't the battery just stop accepting amps?

Very PBO I know and this is cheap, but I wouldn't learn much from fitting it
https://www.sunstore.co.uk/12v-Solar-Charge-Controllers/

Thanks in advance
 
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The PWM and MPPT controllers are varieties of switch mode regulators whereas the LM317 is a linear regulator. The difference lies in their efficiencies. Switch mode regulators, if it were possible to make them from ideal components, would deliver 100% of the electrical energy from their inputs to their output sides. In practise they commonly work to around 90% efficiency. A linear regulator works differently in that it delivers 100% of the current from its input to its output, but is more inefficient because to do that it has to drop the voltage. In your example above with 20V input to the LM317 and delivering 14.4V output would have an energy efficiency of just 72%. Nearly one third of your solar power would be lost.
The MPPT and PWM regulators despite having similar efficiencies give different amounts of power delivery to the battery. The MPPT adjusts the current drawn from the solar panel in such a way as to maximise the power extracted from the panel.
 
ltcom said:
My little boat has a tiny flexible solar panel connected via a rats nest of wires to a battery.

Panel gives out 20 V open circuit, I make a lm317 to give constant 14.4volts and all is ok or not? Does a battery at 14.4volts stop accepting amps from a solar panel that directs electricity through a £2 lm317 that should only allow 14.4 volts through. Won't the battery just stop accepting amps?
Click to expand...

Simple answer is yes. If your LM317 is set to produce 14.4V and you also are able to get the battery up to 14.4V there would be no current going into the battery. This illustrates one of the reasons battery charging gets very slow when the battery is close to fully charged.
 
ltcom said:
Many thanks.
Is pwm better than mppt?
Is this cheap product any good for charging an 80ahour wet cell deep cycle battery using a 20W solar panel?
Or should I look at something else.
thanks

https://www.sunstore.co.uk/EP-Solar-Landstar-5A-12V-Solar-Charge-Controller-60w.html
Click to expand...

mppt is better than pwm because it adjusts to the changes of sunlight to always get the most power out of the solar panel. That translates to a bit more charging current most of the time. But the practical difference may not be all that great ( I don't have the practical experience in comparing them) and mppt controllers are more expensive.

The product you link to appears to be suitable for your size of panel and type of battery. The 5A rating is more than enough for your 20W panel (which is unlikely to exceed 2A).
 
ltcom said:
Is pwm better than mppt?
Click to expand...

PWM controllers are very cheap and are often good enough. MPPT controlers help you squeeze more power out of the solar cell at a higher price.

Given where you are with a 20W panel, investing a few quid in a bigger (additional) panel might be the way to go. They are far cheaper than they were five years ago.

It really depends though on what you're hoping to get from your solar panels. e.g. living on board at anchor is more demanding than just a trickle charger at a mooring when you're not on board.
 
I have 3 solid mono panels. Cheap and higher performance that flexible but you do need a frame, ideally where it won't get any shade at all. Because I had three x 120x and I didn't want to run a huge cable back to the batteries I rigged them in series giving 60v open circuit system into a Victron MPPT. This does its thing and converts it back to 14v approx and into the batteries at the most optimal performance.

Video:


Benefit of series and MPPT is high efficiency and smaller cables due to low amps. Down side is shading one affects the whole array, albeit less than everyone makes you think. I got 330w from my 360w array the other day! I regularly make over 1kw per day and monitor it via an App in my phone with the Victron MPPT controller.

Panels wise.... I have one very expensive German panel £(600) and two cheap eBay panels (£60) and there is no differences at all. Literally none. I coasted the terminals of all in silicone grease and they have all be fine.
 
Many thanks.
Great stuff.
For my 22 footer on a swinging mooring the cheapest set up will suffice to power the little equipment onboard. Alot learned for future years though.
thanks
 
macd said:
That's meaningless, northcave: just an instantaneous value. Do you mean 1kWh (kilowatt-hour) per day? (Which is about 80Ah at 12V.)
Glad to see you're pleased with you new system. May the sun always shine on your array ;)
Click to expand...

Pretty sure he meant 1kwh per day, which would compare with my figures for my slightly smaller setup.
 
In the process of installing x2 flexible 100w panels on my saloon roof....I am just a little concerned about the size of the cables attached to the panels...they seem very thin...I have cut the ends off to attach my own MC4 connectors to wire in to my system....the wires themselves only seem about 1.5mm ....is it possible to open the junction box on the panels and replace the wiring with something beefier or is this not necessary...
 
If the junction box is potted, as it often is with flexi panels, you can take them apart (and make good) only with difficulty. (Although with some it's easy: just wait a few years and they fall to bits autonomously ;))

1.5mm cable is adequate for the job in terms of ampacity, but would certainly give an unacceptable volt drop if used over the entire circuit. But in a shortish tail, it won't make a lot of difference. Bear in mind, too, that it's dealing with significantly more than 12V, which also helps. If the two panels are connected in series, for a nominal 40V or so, you get similar compensation.
 
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geem said:
Victron who make MPPT and PWM regulators say that MPPT has little benefit until you get to 300/400w of solar power. Taking in to account cost of the MPPT I would go for a PWM in your case
Click to expand...

MPPT converters are widely used down to 1 watt solar cells.
The less solar power you have, the more valuable efficiency is. A lot of people with 400W on a boat will frequently be generating more power than they can use, so MPPT adds less for them.
Whether it's cost effective is another question....
 
Re OP question re using an LM317 yes this would work however...
Solar panels are made with enough cells to give around 20v open circuit in full sun. This means that in lower light/cloudy conditions you still get enough voltage to push current into a 12v Lead acid battery. So end effect is that we end up often with too much voltage in good conditions to get enough in poorer conditions. Excess voltage is not a problem in that it is lost in the internal resistance of the panel. Now if you use an LM317 I think you will end up losing a min of about 1.5 volts maybe more. This will reduce effectiveness in lower light conditions.
So a PWM controller uses Field Effect Transistors to minimise series volt drop and then cut off charge when battery shows fully charged. Or proceeds to turn off and on to limit charge total current.
An MPPT controller actually converts by switch mode power supply technology the 20 v down to our desired 14v so giving some advantage of less volts more current but with disadvantage of inefficiencies in converter. They can use cunning circuitry to control the switch mode converter to only take power from the panels as the optimum voltage (power point) for the conditions at the time. So ultimately you might get 10 or 15% advantage with MPPT for a lot more cost.
If OP does not want to buy a controller a very simple shunt regulator will start to shunt current from the solar panel (also the battery) if voltage exceeds 14v. My guessing is that in UK and given some regular use of the battery a direct panel to battery (no regulator) might be OK. If you are able to monitor fluid level in the battery you can check that battery is not being over charged to a point of boiling the battery. However at max 1 amp from your panel this may not be such a concern. Wisdom here suggest no more than 10% of battery rated AH or 10w max for panel. But I would be a bit less cautious.
Have a look at Ebay from China for cheap PWM controller. In some cases will switch on and off an anchor light or switch off a load when voltage falls too low with load control. good luck olewill
 
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