Solar Panel Controllers

[mark1882]

I am in the process of buying a couple of solar panels to fit onto a arch/gantry and would welcome any advice/experience that forum members have of using MPPT or PWM controllers. The MPPT controllers seem to cost quite a bit more and I am not sure if I need them or could have the cheaper PWM controllers. I am planning to have 2 x 85w solar panels, Do I need two controllers ie one controller for each panel or one controller for both panels.
Thanks
Mark

 

[vyv_cox]

I use a PWM controller. With two or more panels wired in parallel you need one basic controller for one battery bank. I have a more sophisticated controller that charges two battery banks, switching from one to the other when the first is deemed fully charged, or when the engine is charging.

There have been many, many threads on the subject so it worth searching. MPPT may be capable of supplying a little more power to the batteries when panels are wired in series but it suffers more from shadows in an installation with two or more panels.

 

[chuckr]

we have 400w and had a bluesky 2512 and just upgraded to a 3024i bluesky.

 

[Kelpie]

I use a relatively cheap (eBay) PWM controller to charge two banks from one panel. I believe I can add additional panels in parallel to the same setup.
The basic controller cost about £30, and another £25 for a remote monitor, which was optional.

 

[V1701]

I think the concensus used to be that the extra cost of an MPPT controller wasn't justified given the extra charge (over PWM) that they're able to provide but they can now be had for not much more than PWM ones (at least on ebay, assuming that the inexpensive ebay controllers are actually what they're described as). I've had both types of inexpensive controller & I can see with the MPPT one that at times it is working in MPPT charging mode. I've had no problems with either but can't say whether I get more from the MPPT than the PWM. You probably know already but make sure the current rating of whatever controller you buy is adequate, a 15amp controller for 170 watts of solar would suffice...

 

[charles_reed]

I am in the process of buying a couple of solar panels to fit onto a arch/gantry and would welcome any advice/experience that forum members have of using MPPT or PWM controllers. The MPPT controllers seem to cost quite a bit more and I am not sure if I need them or could have the cheaper PWM controllers. I am planning to have 2 x 85w solar panels, Do I need two controllers ie one controller for each panel or one controller for both panels.
Thanks
Mark

Wire the two in series and use an MPPT controller - that's what I did for 3 pairs of panels totalling 328 watts.
Alternative is to wire in parallel and use one PWM controller - people will have you believe you'll lose about 10-15% of the output, but I'd guess the loss would be lower @ 5-8%.
With the PWM controller you'll probably not fully recharge the batteries, just reduce the drain on them, with the MPPT you'll have a chance of recharging but will need rather more than 170w of panel.
So if you intend to increase your PV bank, go down the MPPT route, if you just intend to ameloirate your discharge stick with PWM.

 

[tri39]

You could of course not bother with a controller and spend the money on increasing the battery bank. The fridge/autopilot/windlass/startermotor during the day, and fridge/electronics/DVD/lights etc at night will use all the power your two panels will produce while you're on board. You do have to disconnect them when you leave the boat for any long period though'!!!!!

 

[Kelpie]

I think it would be a false economy not to install at least a basic £20 PWM controller.

 

[V1701]

You could of course not bother with a controller and spend the money on increasing the battery bank. The fridge/autopilot/windlass/startermotor during the day, and fridge/electronics/DVD/lights etc at night will use all the power your two panels will produce while you're on board. You do have to disconnect them when you leave the boat for any long period though'!!!!!

And be worrying about making sure you aren't overcharging the batteries all the time? There'd also be nothing to charge them while you're away, sorry it wouldn't make any sense doing it that way to me...

 

[vyv_cox]

You could of course not bother with a controller and spend the money on increasing the battery bank. The fridge/autopilot/windlass/startermotor during the day, and fridge/electronics/DVD/lights etc at night will use all the power your two panels will produce while you're on board. You do have to disconnect them when you leave the boat for any long period though'!!!!!

Not my experience. With 125 watts of panel, 3 x 110 Ah batteries, the controller shuts down charging at about midday in midsummer and always when the engine is running. Putting 8 amps into the batteries when they want none seems a recipe for problems. Even with a very effective controller we were topping up our wet cell batteries monthly.

 

[tri39]

It certainly does depend how much motoring you do. The panels confuse the alternator too, I could do with a flick switch to disconnect the panels when the engine's on. Yet some skippers are only too happy to get into a marina for a mains charge weekly or fortnightly, something we never need. And much advice is given on how to over-ride the controller!! I agree the batts need regular topping up. Last year I had 150watts charging 430Ah. Fridge running all day, but not all night! I know it's too KISS for most. I'm also an enthusiastic user of the windlass and HF radio!

 

[Mistroma]

Not my experience. With 125 watts of panel, 3 x 110 Ah batteries, the controller shuts down charging at about midday in midsummer and always when the engine is running. Putting 8 amps into the batteries when they want none seems a recipe for problems. Even with a very effective controller we were topping up our wet cell batteries monthly.

Our controller behaves in a similar fashion and stops charging quite early. However, I know that the batteries aren't fully charged (Smartguage + temp. corrected SG). It's pretty inefficient and it is annoying to watch Amps from panel and virtually nothing going to batteries.

It's a Marlec PWM unit and I liked the combined wind gen & solar panel control with readout for Amps coming in and going out (instant or running Ah total with hours). I worked around the problem by tweaking the default settings when at anchor (i.e. most of the summer). I think that the default max. V per cell is 2.4V (14.6V total) and I increase it to around 2.48 (14.9V). This usually results in around 14.75V at the batteries (despite having largest cable the regulator will take).

It performs much better with these settings but is very close to the high voltage alarm on my main panel and so I can't tweak the voltage up to 14.8V. However, it seems to be a reasonable workaround and I can easily reset to default if spending time in a marina. The improvement is significant as battery charging was very slow at 80% with the regulator "just throwing away" most of the available solar energy after that point.

I probably wouldn't have spotted this if the regulator did not show Amps In/Out and simply assumed that I was getting as much as I could from the panels.

N.B. I have Trojan T105s and the manufacturers say that the "daily charge" setting should be 14.8V.