can solar regulators cancel each other out?

Hi v8 troopie

thanks for your reply.

just out of interest, if one of the regulators were outputting 14v, wouldnt the voltage at the terminals be 14v or close to? and wouldnt the other regulator be infact seeing the 14v at the terminals therefore thinking the battery was indeed 14v?

i am not doubting that your setup works, but it just got me thinking about it last night. when i put a multimeter on the battery yesterday with only one solar panel attached the voltage was 13.5v as it was charging (battery had been run down overnight and was 12.2v before connecting a panel), i just assumed when i then connected the second panel the regulator would see the 13.5v and not the 12.2v that the actual battery voltage is.
i hope thats not confusing and i do appreciate your responses.

doey

hi steve

thanks for clarifying the juta modes of charge.

im just not sure how the second regulator can determine the batteries SOC when charge voltage is being fed from another source.

maybe the regulators are smarter than i thought.

thanks for your reply.

Doey

well, theres 3 votes for - its fine!

i shall stop thinking about it- lol

the wiring is 6mm from all panels and the regs are close to the batt. i think i will upgrade to a 30A soon but for now its seems to be less critical.

thanks all for their feedback.

Doey

I have done a bit of net searching and it seems to me that there is not that much difference between the price of a MPPT regulator and a DC to DC battery charger with a solar input capability. Do they do the same job, because if so the DC to DC charger would seem to be better value is it provides for input from an additional source.

Kevin

(I'd really like the ability to EDIT my own posts as I think it'd be great to go and change or add things without having to make an entirely NEW post - Admin, can we have Edit please?)



Right, I should add to the above to say that a battery is charged NOT by the amount of VOLTS being put in to it, or by the amount of WATTS being put in to it but by the amount of AMPS.

So FOR EXAMPLE (and to those couch experts - please NOTE the FOR EXAMPLE because I'm trying to make it easier to understand) if you put 2 AMPS in to a battery for 24 hours you might charge it to being fully charged. But if you put in 4 AMPS it will only take 12 hours to charge the same battery, and if you put in 8 AMPS it will likewise be 4 hours to charge the battery.

Now bearing this EXAMPLE in mind (and of course their is an exact formula and reasoning to this but I'm not smart enough to understand it all perfectly or explain it for that matter), if you have 2 Regulators on 80W panels that are capable of 5 to 6 AMPS each (and my 80W is, so I'm taking the guess on that being the same), and ONE regulator cancels out the other than you are only getting 6 AMPS max charge all day.. BUT if you have a regulator capable of handling more panels then you might get 12 or even 18 AMPS out of 2 to 3 panels.. and 12 AMPS will charge a 100Ah deep cycle in a matter of about 6 hours to being fairly well charged (not necessarily full though).

Anyway, it's something to think about right?
I am expecting the arm-chair experts to flame the hell out of me, but you NEED a devils advocate right? Otherwise you wander in to some situation without the possible full story, and bearing in mind that ALL of my external lights at my place are SOLAR POWERED, and that I spent 2 full months with my fridge being ONLY solar powered with NO 240v power available, and being that I'm expanding my solar system to power ALL of my lights at my home, perhaps, just perhaps, I might know a little about it?????

(oh yeah, my entire drain on 240 volts town power supply at present comes from TV, 2 x lights, and my fridge/phone charger (both on the same 12c inverter power supply).. and I'm planning on reducing that to JUST TV, or TV and Fridge within the month if I can get my act in to gear).

I dunno, you can decide for yourself. But get another opinion from say your local electronics expert or something.

Good luck with however you decide to go.

Simon

There is one little thing you seem to miss Simon: The battery terminal voltage.

It does NOT instantly rise to whatever output you get from any regulator connected to the terminals. Especially true as you mentioned a "uncharged battery". You will NOT see the 14V of your example above at the battery terminals.

In this case the output from each regulator is related to what's available at their inputs. If, and only if the battery gets near fully charged its terminal voltage will rise to the point the regulators are throttling back and going from bulk to absorption and, eventually, to float charge.
Its exactly what they are designed to do. And its exactly how you want the battery charged.

Simon,

Without starting a fight, there are a few points worth making:

"someone who's got a degree in the field of electronics stuff" - there are a few of us here with such qualifications and a career's experience in electronic stuff!

"the regulator from one panel says 'oh an uncharged battery' and pumps in 14v" - NO - the regulator sees the battery voltage as being below fully charged and continues to allow available charge current into the battery. The regulator does NOT "pump out 14V"; it can't because the battery is holding it down and would draw more than the current available from the panels if it could. A compromise is reached where the available current goes into the battery whose terminal voltage consequently rises over time. It is always the battery terminal voltage that is in control of the action. This is one reason that it's better that the controller be close to the battery, not close to the panels.

One difficulty with using 2 controllers is that their end points may be different, so that one may cut out earlier than the other, so you don't gain the output of that panel.

"So, the advice given to me was to have ONE external regulator and run BOTH of the panels to the regulator (By-passing their built-in regulators) and then let one regulator control the two (or more) panels." Yes, agree totally. That's what I was indicating above. In the case of the original post though, his present controller wouldn't have the capacity to handle his additional panel.

Cheers

John

From John's post - "One difficulty with using 2 controllers is that their end points may be different, so that one may cut out earlier than the other, so you don't gain the output of that panel. "

I see that being of little consequence. When one regulator goes into float mode it means that the other is capable of supplying all the current the battery will absorb.

This will apply to any number of multi stage chargers connected to the battery. It does not matter if they are solar, 12 battery boosters or mains driven. Simply connect them all in parallel. The ones with lower set points will be the ones that will switch down first. When the lower voltage ones switch down to absorption or float it means the other(s) will be capable of supplying what the battery needs.

Yes Peter. I agree it's of little consequence since by that time, in a stable situation, the battery is close to 100% charged anyway. When though you are trying to squeeze the last drop out of the panels having one turned off prematurely doesn't help.

In real life, we don't have a stable situation anyway because the fridge is cutting in and out, and I'd expect a multistage regulator or MPPT controller to get pretty confused!

Cheers

John

See, this is exactly what I was talking about, we've got some spirited conversation going on now.. and lots more info coming out... which wasn't happening before.

Never fear guys, I love having differing points of view, and on top of that different opinions are a very valuable resource.




V8 Troopie - you might just be right there, it was one thing I missed, the terminal voltage (but surely if the clips from the solar panels are on top of each other they could interfere couldn't they? But, it's definitely something I'm going to look in to when I get around to it...

John - never fear, no argument is going to develop, it's a rational discourse (discussion), it's interesting, and I get to learn new stuff as well ;)