Basic Solar Charging Questions?

Dougal

Dougal

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Couple of Solar Charge Questions

Having extremely limited space for solar panels, we just have the one panel, allegedly rated at 100w. Our current 12v battery setup is one 95ah engine start battery, and two 105ah domestic batteries. All three are flooded lead, although the single engine battery is a so called 'maintenance free' item. The regulator is a generic PWM, dual output, 20amp item.

Basic question after a little Internet studying of PWM vs MPPT regulators...?

With only having the one panel, would switching to MPPT be worthwhile? From my limited understanding, the possible gains with such a small setup, would be minimal at best. Or have I misunderstood?

Anyone with a similar setup made the change to MPPT? And was it worth it?

Also, I'm a little concerned that our battery voltage maybe too high. Surely, the regulator should eventually pull down the volts to a float of about 13.7 volts, but unless the panel gets very little sun, we read 14.7 volts at the batteries.

These figures are working from a baseline of all being in good condition and fully charged, after several days of being hooked up to the 40amp 4 stage mains charger.
 
I get maybe 20% gain from a victron bluesolar MPPT - they're great and the logging is really handy to see what you've actually been getting.

If you just have a cheap PWM regulator then it very likely won't be multi stage so no float, just a set voltage which it won't go over so another plus from getting something like the victron.
 
100W of panel plus mains charging has the possibility of significant overcharging.
So you either want to get a good regulated solar charger, or avoid leaving the panels permanently connected.
Having two complex multi-stage chargers connected to the same battery bank can be a bad idea anyway.

A lot of the non-MPPT chargers are not really PWM anyway, they just stop charging when the battery reaches a set point. They are inefficient compared to a proper PWM converter. The cheap Victron units are in this category. Not because they're a bad product, but because they're designed for a particular application and that isn't a boat.

Whatever regulator you fit, when the sun first hits the panel, it will go to full charging voltage regardless of whether the batteries are fully charged. Most will only set back to float after an hour or more of 'absorption'. So if you get sun-shade-sun-shade.... throughout the day, or intermittently load the bank (a lot of regulators will come out of float every time the fridge cycles!) , you can get several hours of overcharging. Paying more for an MPPT regulator may just overcharge it more efficiently. But that is a problem most people would be happy to swap for.

If you can adjust your 14.7V down a bit to a less aggressive 14.4 or so, you might not have a problem at all.

If you want best efficiency when there's less sun and no mains, then look at MPPT controllers.
 
lw395 said:
100W of panel plus mains charging has the possibility of significant overcharging.
So you either want to get a good regulated solar charger, or avoid leaving the panels permanently connected.
Having two complex multi-stage chargers connected to the same battery bank can be a bad idea anyway.
Click to expand...

You can quite safely leave the solar controller on and the mains charger, assuming neither is a pile of junk, which would want changing anyway. The mains charger output will usually cause the solar controller to shut down, as it senses not only the output voltage from the mains charger, but the fact the batteries are likely to be charged anyway.

During the Winter, my panels don't keep up with consumption, so i switch the mains charger on. There are obviously times when the solar panels could be charging, but there is never a problem.

Again, if the solar controller is cheap and nasty junk, things could be different. I'd fit a Victron MPPT controller if i was the OP.
 
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massive thanks for replies. especially our resident professional, Paul Rainbow. How the hell do u ever get time for your proper job when looking after us;))) I don't think the sellers of all this kit like to tell us how it REALLY works:)
I'll duck as I write this bit rho Paul, I plan to be keeping my 1,2,both switch lol
 
Dougal said:
massive thanks for replies. especially our resident professional, Paul Rainbow. How the hell do u ever get time for your proper job when looking after us;))) I don't think the sellers of all this kit like to tell us how it REALLY works:)
I'll duck as I write this bit rho Paul, I plan to be keeping my 1,2,both switch lol
Click to expand...

To be honest, i'd rather spend an hour on here than be watching rubbish on the TV :encouragement:

As for your 1-2-B switch :disgust:
 
Dougal said:
Where are the Victron dual battery mppt controllers:(
Click to expand...

They don't exist.

Connect the controller to the domestic bank. If you are worried that your engine battery can't take care of itself between your visits, fit a VSR. In fact, fit the VSR anyway, it means you don't have to fiddle around with that lovely 1-2-B switch to keep your batteries all charged up :)
 
And what, typically, would the 'load' terminals be connected to on those Victron MPPT controllers? Will they simply supply whatever 12v current the panel can supply any given time, or will it supply battery ve?
 
Dougal said:
And what, typically, would the 'load' terminals be connected to on those Victron MPPT controllers? Will they simply supply whatever 12v current the panel can supply any given time, or will it supply battery ve?
Click to expand...

From the manual "The load output will disconnect the load when the battery has been discharged
to a pre-set voltage". So generally forget the load terminals, just connect the panels to the PV terminals and batteries to the battery terminals. Although you could, for instance connect the fridge to the loadd terminals, but i wouldn't want to connect everything to them.
 
Also, i would get the Smart Solar controller as it has built in bluetooth, so you can monitor what's going on and configure the controller.
 
OK, so if there's no such thing as a dual output MPPT controller, and my boat gets left in the water, all on its lonesome all winter, then MAYBE lol, I finally have to think about the 'possibility' of removing the 1,2,B switch?

1. Why no dual output regulators? The cynic says its so they can then sell you even more stuff such VSR kits? mmmmm...
2. If I do junk the much loved:-) 1,2,B switch, and fit yet more electrickery to go wrong (said VSR), then when left for 6 months with only solar power, will the VSR do the same as when engine alternator running; as in, can it switch the solar charge to starter battery when house bank full, or vice versa?
 
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Dougal said:
OK, so if there's no such thing as a dual output MPPT controller, and my boat gets left in the water, all on its lonesome all winter, then MAYBE lol, I finally have to think about the 'possibility' of removing the 1,2,B switch?

1. Why no dual output regulators? The cynic says its so they can then sell you even more stuff such VSR kits? mmmmm...
2. If I do junk the much loved:-) 1,2,B switch, and fit yet more electrickery to go wrong (said VSR), then when left for 6 months with only solar power, will the VSR do the same as when engine alternator running; as in, can it switch the solar charge to starter battery when house bank full, or vice versa?
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Yes.

If you want to keep the lovely 1-2-B switch you can still fit a VSR. It will charge all batteries from the alternator, or from the solar controller, so less need to fiddle with the switch to make sure they all get charged. Separate switches are of course better. Your worry about adding more stuff to go wrong is unfounded. Separate switches actually give you a backup. If the VSR stopped working you only revert to where you are now, the World won't end :)

Why no dual output MPPT controller ? MPPT relies on battery monitoring, if the two banks differ greatly in SOC it wouldn't work well. Better to monitor and charge the domestics and allow the VSR to take care of the engine battery.
 
Dougal said:
OK, so if there's no such thing as a dual output MPPT controller, and my boat gets left in the water, all on its lonesome all winter, then MAYBE lol, I finally have to think about the 'possibility' of removing the 1,2,B switch?

1. Why no dual output regulators? The cynic says its so they can then sell you even more stuff such VSR kits? mmmmm...
2. If I do junk the much loved:-) 1,2,B switch, and fit yet more electrickery to go wrong (said VSR), then when left for 6 months with only solar power, will the VSR do the same as when engine alternator running; as in, can it switch the solar charge to starter battery when house bank full, or vice versa?
Click to expand...

Yes there are.

Goggle will find them
 
http://www.photonicuniverse.com/en/...MIpJKAgIzR3QIVzLDtCh3mVw9mEAQYAyABEgK_k_D_BwE

I’d normally dig my heals in and always demand a Victron Bluetooth MPPT is fitted when I put panels on as they’re just nice and simple and I haven’t personally had an out the box failure of an MPPT from them yet.

Although the above link shows what appears to be a quality product and the company does have a good solar reputation. That MPPT allows domestic supply to be charged on the main output then a smaller limited output to trickle charge your engine batteries.

I’d not normally say to bother with engine battery as provided the battery is good and there is no leaching of power by something, the battery should sit for months on end with no issues.
 
PaulRainbow said:
Yes.

If you want to keep the lovely 1-2-B switch you can still fit a VSR. It will charge all batteries from the alternator, or from the solar controller, so less need to fiddle with the switch to make sure they all get charged. Separate switches are of course better. Your worry about adding more stuff to go wrong is unfounded. Separate switches actually give you a backup. If the VSR stopped working you only revert to where you are now, the World won't end :)

Why no dual output MPPT controller ? MPPT relies on battery monitoring, if the two banks differ greatly in SOC it wouldn't work well. Better to monitor and charge the domestics and allow the VSR to take care of the engine battery.
Click to expand...

Thanks Paul. Both for your info AND your patience lol.
Back in the 80s, no doubt pre reliable VSR and it's like, we were talked into having our 1-2-B switches removed and some form or split relay system fitted to the TSDY we then lived on. It was a disaster from day 1. Afraid I've been sceptical of electronic alternatives ever since.
I'll catch up eventually,:)
 
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