mppt's

[whirlybird]

Greetings friends.

I have a small problem and I  wonder if someone on here may be able to answer it for me or at least put me on the right track.

I have 6 180watt solar panels and I am looking for an MPPT device for same ,But the only reasonable unit I can find is 30 amps ,That is not enough as you can imagine the panels can produce more than that under good conditions.

My dilemma is I would like to use two 30 amp units on 2 banks of 3 panels and the combine the output to the battery's, I have been told it may work and others say it wont.

Any thoughts on the matter would be most appreciated.

Best regards to all.

Bob.

[boB]

The current depends on your battery voltage.

You have 1080 Watts of modules.   At 100% efficiency,

that means you would need at least...

90. Amps for a 12V battery
    
43. Amps for a 24V battery
    
22. Amps for a 48V battery
    
    

Just divide PV Watts by battery voltage to get the ball-park Amps needed.

boB

[southpaw]

Hi Whirlybird

I have taken the liberty of ignoring efficiencies and rounding off for simplicity

so + or - this is my experience with mppt.

The beauty of mppt is the efficiency of converting watts to amps. A standard charge

controller would take the 30 amp output of three of your panels and if your batteries

were at 13v give you 30a X 13v = 390 watts.

 An mppt gives you 30a X 18v = 540 watts and 540w /13v = 41.5a too much for a 30 amp controller.

You should seriously consider a 24v system to reduce wire losses from panel to

batteries to inverter.

Something you might want to check out is Blue Sky's 6024H mppt controller or similar

with a unit similar to this you would be able to series 3 panels and 3 panels and then

parallel them giving you an output of about 54V at 10 amps times 2 which this controller would convert to about 45 amps at 24v.

 I have used this arrangement with 3 200 watt panels in a 12v system and it worked

very well giving me lower voltage drop from panels to controller and being able to use

 smaller wire on my 120 ft run.

 The savings in wire and the fact that this setup produces as much power as a standard

 controller on a 4 panel array would, paid for my controller.

[whirlybird]

I feel that the original post  did not give you enough information

the system is 24v

4. x24v panels connected in paralell
   
2. more cells (panels to be added this week)
   
5. x24v fork lift batts at about 3600amph capacity each.
   
   

i can get mppt's at a very cheap price (sorry but loads cheaper than you paid).

the limitation at this stage is they can only handle 30 amps hence my original question

thanks for the replys

good sun and clear winds,Rgards.

Bob.

[Ungrounded Lightning Rod]

Sounds like you could use three 30A 24V MPPT controllers, each connecting two paralleled 24V panels to the common set of batteries.

If the controllers are just MPPT charging and perhaps voltage limiting, rather than something that does smart charging to cycle the batteries, you can just parallel the outputs of all the controllers at the batteries.  (If they do fancy charging cycles they can't be paralleled because they'd have to be synchronized.)

[DamonHD]

I've been blithely paralleling smaller solar contrallers' outputs (from different input panel sets) and don't yet seem to have ruined anything, though one (panel set and controller) is much larger than the other which may help.

Rgds

Damon

[rossw]

Just because you haven't (yet) "ruined anything" doesn't automatically make this practice good or right.

Scenario:  two identical arrays, two identical controllers (MPPT or otherwise) with identical settings of float voltage etc. You'd THINK that would be fine. But what happens when one of them gets "out of whack" with the other in terms of ITS perception of what day of the month it is. One thinks today is the 26th, the other thinks it's the 8th (because you unplugged it last week while you were doing some maintenance). One is going to try to do it's equalisation charge in a couple of days (say), while the other "identical" one will do it (again) in 20 more days.

Nett result: you're doing TWO eq cycles per month. (Or three, or four, depending on how many controllers you have).

If the controllers have different configurations for charge voltage or absorb/boost/float times, then they're going to all be fighting against each other. It all becomes very "messy" if you have differnt hours of illumination (clouds, birds sitting on the panels, shaddows), and compounded with MPPT (different cell characteristics).

Sure, you MAY not notice anything, but there WILL be a gotchya. Who it gets, when it gets them, and how hard it bites is up to luck.

[DamonHD]

Luckily for the example you cite, which would be nasty I agree, my battery is sealed, the controllers are both set for that (no EQ), and they are both very very dumb.

Dumber even than me, thankfully.

But I don't dispute the core of your argument.

So when I said "blithely" I really meant "after thinking for a bit on how they might conflict in their 'smart' charging programmes".  %-P

Rgds

Damon