How many solar inputs can one put into the one battery

Woody n Sue · Guru

How many solar inputs can one put into the one battery

Peter_n_Margaret · Guru

Short answer is YES.
They need to have the same voltage output though.

Cheers,
Peter
OKA196 Motorhome

aussie_paul · Guru

Peter_n_Margaret wrote:
Short answer is YES.
They need to have the same voltage output though.

Cheers,
Peter
OKA196 Motorhome

As in 12 or 24 volts Peter?

Aussie Paul.

Plendo · Guru

Woody N Sue, as everyone has indicated yes you can have multiple sources charging the same battery.

There is however one small caution, if your existing charger is an older MPPT charger it may get confused if you add another MPPT charger. This happens as the charger sets its output voltage just above the battery voltage (typically 0.4 to 0.5v above), if you have multiple chargers doing this they tend to walk the voltage up (each one going just above the other). This is not a disaster, it just means you are not charging at the optimum voltage.

Depending how much solar you already have, it may make sense to replace your existing charger with a larger one, and hook all your solar to a single charger.

Reed · Senior Member

Consider putting the panels in series so that there is one higher voltage through cabling to MPPT. This results in lower amperage and thus smaller cables/less power loss. Your MPPT should handle this and drop voltage to 12 V or 24 V depending on your battery suite. The voltage from our panels is 90 V to MPPT. We have had in excess of 1400 W to MPPT. This would have been 140 amps at 12 V but is only 15 amps at 90 V. Our system is two series of 3 x 235 W panels (30 V each) which are then parallel at box to the MPPT. Our battery suite is 48 V nominal (8.6 kW-hr of LFP)
Reed and Elaine

A day without sun is like, you know, night!

-- Edited by Reed on Tuesday 4th of August 2015 11:26:27 AM

Peter_n_Margaret · Guru

As in 12 or 24 volts Peter?
Aussie Paul.

No, as in if one source is programmed to charge at 14.6V, the others should be roughly about the same otherwise one will tend to dominate the other.

If they are similar, you can get the full value of each, at the same time.

Yes, as Plendo says, some controllers can get confused with second charge sources and a bigger regulator may be the best option.

Then again, we can have 30A coming from the solar and also get 70A from the alternator at the same time, if the batteries are low.

Cheers,

Peter

Mark Bolton · Veteran Member

@ Reed : I was under the impression the Amperage rating on the controller refered to it's output not the input. I was never told / read that. I just assumed it. I started off with a 24 volt system so as I could buy a lower amperage MPPT. When I reconfigured it to 12volts because I couldnt get a tidy 12 volt split system going I went and got a 60 Amp MPPT.

@ All ; Also Am I hearing you guys right that instead of my 60A controller I could get two x 30 A similar MPPT units and parallel them onto the 12 volt bus? Split the panel input in two. Apart from a minor niggle about slightly different charge currents that would do the trick? 2 x 30 amp units @ 20 $buck VS x 60 @ $90? Am I also right in thinking if you had one panel /MPPT in the shade and the other in the sun you would get the full benifit on the one and the dark one would just be cut out of the circuit? Sounds like a better way to do it - albiet a bit messy and complicated.

-- Edited by Mark Bolton on Wednesday 5th of August 2015 02:24:14 AM

Reed · Senior Member

Mark

There is a good writeup on MPPT (maximum power point tracking) on the Northern Arizona Wind and Sun site. This is a commercial site.There is also a Northern Arizona Wind and Sun site that is one of the better solar and wind discussion sites.

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

A couple of excerpts are below

"...A MPPT, or maximum power point tracker is an electronic DC to DC converter that optimizes the match between the solar array (PV panels), and the battery bank or utility grid. To put it simply, they convert a higher voltage DC output from solar panels (and a few wind generators) down to the lower voltage needed to charge batteries.."

"...Maximum Power Point Tracking is electronic tracking - usually digital. The charge controller looks at the output of the panels, and compares it to the battery voltage. It then figures out what is the best power that the panel can put out to charge the battery. It takes this and converts it to best voltage to get maximum AMPS into the battery. (Remember, it is Amps into the battery that counts). Most modern MPPT's are around 93-97% efficient in the conversion. You typically get a 20 to 45% power gain in winter and 10-15% in summer (over standard controllers). Actual gain can vary widely depending weather, temperature, battery state of charge, and other factors..."

As written above, our energy goes from roof at 90 V to TriStar MPPT-45. We have received up to 1400 W so this is only 15 amps. However, it then goes to battery suite at around 50 V (48 V nominal) so it is 28 amps from MPPT to battery suite. If it came from roof at 12 V, the amperage would be 118 amps.

A Morningstar (TriStar) MPPT-45 costs $368 US while a MORNINGSTAR TS-45 TRISTAR THREE-FUNCTION SOLAR CONTROLLER costs $156 US. The MPPTs are expensive but far more versatile and efficient than a standard solar controller.

There are energy losses at MPPT and at inverter both.
Reed and Elaine

Jaahn · Guru

Hi,
I would like to add a bit to the discussion on the MPPT units. Reed and Elaine has covered it well but left off one point.
The T stands for tracking. and the MPPT units continually move the input settings up and down by small amounts to see if the power available goes up and down too. If it goes up one way then it goes to that setting and uses it as a start point. Then it starts again the same procedure. Better ones do it faster so they can follow small changes in the solar power. More important under some conditions than others but it is always trying while the battery voltage is below the set point.

Now you might appreciate the difficulties if you have two units trying to do the same thing on to one battery. They might get into a "bidding war" and fight with each other, as Plendo said. Or not perhaps, who knows ??

The other point to make is, if you have two or more different panels feeding into a MPPT controller they can have different maximum power points on each panel so the controller may "hunt" between the different points to try and find the best. Who knows what this means but probably not optimum output compared to matched panels.
Jaahn

Woody n Sue · Guru

Geeees just when I thought I had a bit of a handle on this I am now a little confused so will have to talk in person to a bloke in town at the auto elects
Thanks everyone for your input at least I now have some questions for him
Hell I might even sound like I know something about solar

PeterD · Guru

Reed wrote:
Consider putting the panels in series so that there is one higher voltage through cabling to MPPT. This results in lower amperage and thus smaller cables/less power loss. Your MPPT should handle this and drop voltage to 12 V or 24 V depending on your battery suite.

Which controllers are you referring to. Some MPPT controllers will only handle 12 V panels, others will only handle slightly higher voltage panels. The ones that handle higher input voltages are generally the ones designed for grid connect purposes. Consult the controllers specifications. There are several reports of forum members (particularly on other forums) who have blown the guts out of the Ctek D250S MPPT controllers after hearing advice like this.

Reed · Senior Member

Checked further on this and doing such is apparently not at all efficient.

Grego · Member

I have the following feeding into 2 /120 amp batteries wired in unison as 12 volt output.

2 x 180 watt solar panels each on a 20 amp 6 stage MPPT controllers set.3 or so amps apart
1 x 5000 watt integrated auto inverter feeding all power points. When plugged in to 240 volt it then activates a 6 stage 80 amp charger as required.
240 watt mobile panel on it's own MPPT controller direct to batteries.
1x Matson 20 amp DC to DC battery charger from vehicle

I find these all work in unison with each other no problem and all work to charge the batteries . However when the 80 amp charger cranks up on the inverter when on 240 volt it will take everything else over telling the other products the batteries are full or close to full but at 80 amps I don't need anything else feeding the batteries when this occurs anyway :)

I could have used 1 /20 amp MPPT charger but doing it this way it gives me a back up when free camping incase one fails.