Kyocera KC120-1 change panel from 12V to 24V?

JoanTheSpark

Hi there,

been looking all over the net to find any information about it, but no luck so far.
Maybe someone here has seen the inner workings of the KC120-1 panel and can help me.

My situation:
- 3 KC120-1 panels in parallel (3p configuration)
- all panels deliver about 6.xx amps in sunny condition (so still 'good')
- 4x Supreme CR-225 6V 215Ah in 2p2s configuration
- PL40 solar charger/controller

My goal is to reconfigure the system to 24V while still having all panels running.
Neither the batteries nor the charger are problematic.
The controller can be set to 24V and the batteries be reconfigured to 4s.

Now the panels.. I've seen the junction box on the back of them and inside you can see 4 screw posts.
From my understanding the cells in the panel are configured as 2p18s (18 cells in series and 2 of those strings parallel).
How:
As there are 4 posts, with 2 of them each holding the bypass diodes, these posts must be the 'ends' of the strings (red/blue connections).
The panel has got 21.5V without any bridges visible, so the strings must be configured parallel already (purple/turquoise connections).
It also looks like the junction box was 'designed' to be able to access a panel differently, it just wasn't employed with this.

My question now is:
Does anyone know if there is a possibility to get rid of the purple/turquoise connections?

Cheers,
Joan

mikeo

Re: Kyocera KC120-1 change panel from 12V to 24V?

Does anyone know if there is a possibility to get rid of the purple/turquoise connections?

I have some of the older KC-120 and KC-125 panels and you will find that each half is around 8 volts under load. So the two sides are in series, not parallel to get the 16 volts nominal. So you need one more panel and have two strings of 2 in parallel to get a 24 volt system. You can use an equivalent panels as long as the Vmp and Imp are within 10% of each other with out too much loss.

Windsun

Re: Kyocera KC120-1 change panel from 12V to 24V?

Those panels cannot be configured for 24 volts. They are basically 2 6-volt strings in series.

JoanTheSpark

Re: Kyocera KC120-1 change panel from 12V to 24V?

Oh, damn. Thanks guys.
I actually didn't measure the modules yet, as it's a remote location with scientific gear.. even had to grab the picture from the net (or this forum via google) as I never had the junction box open.

And yeah, I somehow forgot that each cell only produces 0.5V at the MPP.

Thanks for your help.

BB.

Re: Kyocera KC120-1 change panel from 12V to 24V?

The "usual" solution would be to put the three panels in series and then use a "higher voltage" MPPT charge controller to efficiently down convert to the local battery voltage/current.

Is a very nice solution, but MPPT charge controllers are not cheap. The smallest unit that will probably meet your existing needs is the:

Morningstar TriStar 45 amp MPPT solar charge controller
Price: $419.00

-Bill

JoanTheSpark

Re: Kyocera KC120-1 change panel from 12V to 24V?

Yes, I know. Already got the Morningstar 45A MPPT for another station which will have 6x 190W panels (ET solar), but there is no upgrade planned or feasible for the station in the original post. Just need it at 24V.

As for adding another panel.. not possible, as the mounting frame only has space for the 3 Kyoceras.

Anyhow.. not a total deal breaker. It just means that I'll have to disconnect one of the panels and get backup energy from 50m away to the system, which is feasible. So it's ok, would had just liked to keep all panels putting in.

PS: I think the Steca Solarix MPPT 20A would be probably cheaper and work also, but misses remote monitoring (serial RS-232).

BB.

Re: Kyocera KC120-1 change panel from 12V to 24V?

If you only need a little 24 volts, you can use a voltage doubler from 12 volts. You can then keep the existing setup.



12/24 Volt DC/DC 20 Amp DC-DC Converter
$225.90







-Bill

Windsun

Re: Kyocera KC120-1 change panel from 12V to 24V?

The easy way is to just wire up two of the panels in series, and drop the 3rd one from the configuration completely. Your total power will be reduced by 1/3, but if the two panels will supply enough current to keep the batteries charged that should not be an issue.

JoanTheSpark

Re: Kyocera KC120-1 change panel from 12V to 24V?

Thanks for the idea Bill.

@Windsun, yep. As I said.. there is backup 50m away and has to be made anyway, so I'll drop one panel.