CTEK DS250sa Max Solar Voltage

[JordanCrosby]

I've got a CTEK DS250sa fitted to my van but I'm searching around for the highest watt solar panels. I've been told that the CTEK has a 23v limit any suggestions on what panel to use?

[littleharbor]

There are 200 watt 12 volt panels being made these days but their Voc. is a tad over 23 volts. Look in the 175-180 watt range.

[soulcamper]

Hello.
I have the same, it is up to 300 watts on the manual.
Thanks

[inetdog]

Hello.
I have the same, it is up to 300 watts on the manual.
Thanks

Remember that if 23V is an absolute limit on the CTEK, you need to calculate the worst case cold weather Voc of the panels you use. If you do not have good actual temperature data and temperature coefficient of the panel, estimating at 125% of Voc at standard temperature is a conservative figure.

[soulcamper]

Woww.. Thanks for that . You might have just saved my ctek. Totally forgot about the volt situation! I have not wired anything yet. Ended up buying 2 solar panels both 100w. Voc s are 22.54 and 22.33 . Do you think I could wire them in paralel ? Ps. One has a 3 core cable and one 2 . It is so complicated. On the other hand ctek recommends 30 amp fuse for the solar does that mean i would have to keep changing the fuse all the time. Or perhaps I could just add an isolator and switch it off when it is cold or hot..
sorry for the mess .. any advice would be highly appreciated...
Thanks

[inetdog]

Woww.. Thanks for that . You might have just saved my ctek. Totally forgot about the volt situation! I have not wired anything yet. Ended up buying 2 solar panels both 100w. Voc s are 22.54 and 22.33 . Do you think I could wire them in paralel ? Ps. One has a 3 core cable and one 2 . It is so complicated. On the other hand ctek recommends 30 amp fuse for the solar does that mean i would have to keep changing the fuse all the time. Or perhaps I could just add an isolator and switch it off when it is cold or hot..
sorry for the mess .. any advice would be highly appreciated...
Thanks

I am not sure why you think you will be blowing the fuse. You have about 5A from each panel. If the voltage goes too high you are much more likely to blow up transistors than to blow a fuse.

The rule of thumb for combining is that all other things being equal you can parallel two panels whose voltage rating (either Voc or Vmp, since they track together for similar material panels) are within 5% can be paralleled with less than 1% loss compared to the individual panel wattages.
To lower the voltage you can do one of two things:
1. :Put one or more forward biased diodes in series to drop the voltage to the CTEK. This will cost you some power.
2. Put a zener diode or other voltage limiter in parallel with the panels to pull the voltage down from Voc toward Vmp even when the inverter is not loading down the epanels. This is the solution I would use. It does not take much current to drop the voltage from Voc a few volts, but you would need to have a pretty high powered zener diode anyway. Once the inverter pulls the voltage down toward Vmp the diode will stop conducting and so will not cost you any power.

[soulcamper]

Thank you I will study this and hopefully manage to get it done ...

[soulcamper]

Hi all ,
it has been some time ..Just wanted to give a little heads up... A good friend gave me a little gift. A solar mppt controller, after a little reading I found out that this mppt can handle my 2 solar panels. The power can go to ctek through this mppt. So the positive and the negative comes from the solar panels to the mppt, then the mppt connects to the ctek (through the mppt battery terminals) . And I will not wire the mppt load terminals as the power will come directly from the batteries through the control panel. Hope it is not too complicated...
thanks