Solar panel voltage?

ROnEM

Well-Known Member
Mar 13, 2012
650
356
63
Macedon Ranges, Vic
I am looking at using the CTEK D250S in the soon to arrive 17.56-2 OB to manage charging the dual 100AH batteries.

The solar input voltage on the CTEK is 22volts maximum.

The van is pre-wired for solar and in selecting a solar panel I have seen a 130 watt unit.

There are two voltage figures on the specs:
- Open Circut (Voc) - 22.4v
- Maximum Power Voltage - 18v

I am assuming the Max Power Voltage figure is the one I should use.

All assistance appreciated.

Ro
 

Tailor

Member
Jun 2, 2012
87
7
8
Newport Qld
Hi,

The Maximum Power Voltage is what it says, when connected to an appliance, or battery without a voltage regulator. Normally the output is regulated by a built in one, or an external regulator which limits output to around 14VDC, in order to avoid cooking the battery.

Just a note on this. The D250S provides the voltage regulator for the solar panel. Make sure your panel does not have a built in regulator and you should be fine.
 
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ElectricGuru

Member
Sep 5, 2011
189
22
18
SE Brisbane
Hey Ro

Good choice going with the D250S Dual.

If you have any load on the panel, then the voltage should never get towards the max 22.4 Vdc output. It is only during open circuit conditions with nothing connected that you would see the full OC Volts. However to ensure that there are no problems with the D250S, try to get a panel with an OC voltage of not more than 21 Vdc, most are 20-21 Vdc.

The panel has a rating at 130 Wp where Wp is peak watts. That is at a voltage of 18 Vdc, the current out is 7.22 A that is the maximum power (18 V x 7.22 A = 130 Wp) of the panel at 25 degC tested under nominal conditions. An example Voltage/Current curve is shown below for an 80W panel and note that the 25 degC curve has a knee point around the 17 Vdc mark that equates to the max voltage/current point...

Solar Panel Curve.jpg

This is taken from the Alternative Technology Association website - Solar panel buyers guide (Some other good solar panel info there as well...)

When they talk about Maximum Power Point Tracking (MPPT), what the regulator will do is keep the panel working at its maximum power voltage/current (knee point on the curve) to ensure it is working to maximum possible capacity during low light conditions.

Tailor is right on that the D250S has an inbuilt MPPT solar regulator and the best thing is that is will accept power from both the alternator and solar inputs and match the output to maximise the battery charging. Very smart box since you can have the car charging the battery with assistance from the panel whilst driving.

Hope this helps.

Cheers
 
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ROnEM

Well-Known Member
Mar 13, 2012
650
356
63
Macedon Ranges, Vic
Thanks Tailor & ElectricGuru.

Have found another 130 Watt panel for $235 with the following specs that should be a better panel (without a regulator) for the CTEK D250S:

Maximum Power: 130W
Open Circuit (Voc): 21.94V
Short Circuit (lsc): 7.85A
Maximum Power Voltage: 17.71V
Maximum Power current(lmp): 7.34A
Working Temperature: -40C to +85C
Tolerance: +-5%
Dimensions: 1485mm x 668mm x 35mm
Connection type: MC4
Tempered Glass: 3.2mm

Thanks,

Ro
 

Tailor

Member
Jun 2, 2012
87
7
8
Newport Qld
Hi ROnEM,

130 watts for $235 looks good with those specs although I'd be interested to hear ElectricGuru on those specs at that price.

Cheers

John
 

ElectricGuru

Member
Sep 5, 2011
189
22
18
SE Brisbane
130 watts for $235 looks good with those specs although I'd be interested to hear ElectricGuru on those specs at that price.

Hey John

Specs look ok and the fact there is a shop that Ro can go to, even better.

Main thing is that the panel is compatible with the D250S. Any troubles, just contact the seller that you are buying the D250S from and ensure that all is good.

Last note that I forgot to add previously is that the D250S MPPT regulator at best light conditions will give you almost full panel output (130 W) to the battery whereas other types will give reduced power depending on voltage reduction methods.

For this setup with a 130 W panel at maximum power, the D250S should deliver about 8.75 A to the battery at 14.4 Vdc. This is due to the power being almost completely transferred to the battery with minimal losses.

Main thing with any setup is to ensure that you are not wasting power by installing energy efficient lighting / appliances and only using what you need.

Reduce the load, reduce the system capacity and requirement of charging... ;)

Cheers.