Do you plan around Short-Circuit Current rating vs Fuse rating?

[tedsc]

I am looking to buy a charge controller that will handle 4 panels, each panel with the following specs:
Open-Circuit Voltage (Voc): 24.3V
Short-Circuit Current (Isc): 5.21A
Maximum Series Fuse Rating: 15A

There is obviously a big difference between a charge controller rated for a ~500 Watts and one rated at ~1500 Watts.

What amp rating spec should I be designing around?

Thanks,

Ted

 

[time2roll]

Are the panels in series or parallel or both? If series an MPPT controller with 150 volt input is probably needed. 500w rating should be plenty. Proper amp rating will depend on battery voltage.

Isc of 5.21 or 20.84 total amps would need a 25+ amp PWM controller if going that way.

Series fuse rating is for parallel strings requiring a fuse on each string when the total exceeds 15 amps. However for the listed system I would skip this due to low voltage and modest amp ratings in total. Could still be required to meet code on a home connected system.

 

[Hedges]

I am looking to buy a charge controller that will handle 4 panels, each panel with the following specs:
Open-Circuit Voltage (Voc): 24.3V
Short-Circuit Current (Isc): 5.21A
Maximum Series Fuse Rating: 15A

There is obviously a big difference between a charge controller rated for a ~500 Watts and one rated at ~1500 Watts.

What amp rating spec should I be designing around?

Voc of PV array, adjusted for cold temperature, must not exceed charge controller spec. Voc from panel label x 1.16 is a conservative estimate; otherwise data sheet has temperature coefficient.

Charge controller may have a spec for maximum array short-circuit current.

You haven't given panel wattage, Vmp, or Imp. Those would be power under STC; NOCT may be 85% or 75% of that. To avoid "clipping", charge control can be sized large enough so its output current times battery voltage doesn't exceed its capability. Or, most good charge controllers, you can "over panel" with extra wattage.

If 4 panels wired 2s2p fits voltage and current limits, you can orient one 2s string South East and the other string South West. This would reduce peak current to about 0.7x as much and extend hours of production.


Oversize charge controller would leave capacity for adding panels, also runs cooler, more reliable.

 

[tedsc]

I was going to do them all in parallel as I want to use a 12 volt battery and inverter I already own. Having said that, is it possible to get a MPPT charge controller that has 24 volt input and 12 volt output so I can put panels in series?

 

[time2roll]

I was going to do them all in parallel as I want to use a 12 volt battery and inverter I already own. Having said that, is it possible to get a MPPT charge controller that has 24 volt input and 12 volt output so I can put panels in series?

Yes. However all in series is close to 100 volts and may need 150v rated MPPT. Fairly common.

If two in series two parallel is close to 50 volts with 100 volt MPPT is also common.

Never exceed the controller input voltage. The specification of Voc will increase in cold temperatures.

 

[Hedges]

An MPPT charger won't (usually) have a 24V input. More like 50V, 100V, 150V, etc.
Some automotive PV/alternator MPPT chargers do have about 24V limit.

Depending on the MPPT SCC you select, you'll be able to connect panels in some series/parallel configuration.

Before you buy anything, plan everything. Some models play nicer together, and especially for PV panels and SCC you want array electrical specs to fit SCC capability across temperature range.

 

[mikefitz]

The MPPT controller is a power converter, taking in the panel power, watts, and converting to a suitable charge voltage for the battery.

MPPT solar controllers are specified for the maximum output current, with units for your power level, 400 watts and a 12v battery, you need a 400/12 = 33 amp unit. ( the actual charge voltage will be in the 13 to 14 volt range so the 33 amps is a maximum)
The controller will have limits on the maximum input voltage and current it can accept. The minimum input voltage from the panels must be higher than battery voltage by around 5 volts for the controller to start.

You have the option of connecting 4 panels in series, or in parallel, or a mix of series and parallel, ( two in series connected in parallel with two in series). The maximum voltage at normal temperatures would be 97.2v, 23.4v, 48.6v respectively. Since at low temperatures the panel volts increase an allowance must be made for that.
Thus is using the 4 panels in series a controller with 150 volt input specification is needed, the parallel and series/parallel options would end a 100 volt controller.
Popular solar controllers are from the Epever range and the Victron range of MPPT controllers.

You have stated a 15 amp fuse, with the panel array options, this series fuse is only needed where the 4 panels are connected in parallel.

a typical setup with 4 panels and a 100 volt input 30 amp solar controller. \this would be the preferred setup for the 4 panel array.



Mike

 

[tedsc]

The MPPT controller is a power converter, taking in the panel power, watts, and converting to a suitable charge voltage for the battery.

MPPT solar controllers are specified for the maximum output current, with units for your power level, 400 watts and a 12v battery, you need a 400/12 = 33 amp unit. ( the actual charge voltage will be in the 13 to 14 volt range so the 33 amps is a maximum)
The controller will have limits on the maximum input voltage and current it can accept. The minimum input voltage from the panels must be higher than battery voltage by around 5 volts for the controller to start.

You have the option of connecting 4 panels in series, or in parallel, or a mix of series and parallel, ( two in series connected in parallel with two in series). The maximum voltage at normal temperatures would be 97.2v, 23.4v, 48.6v respectively. Since at low temperatures the panel volts increase an allowance must be made for that.
Thus is using the 4 panels in series a controller with 150 volt input specification is needed, the parallel and series/parallel options would end a 100 volt controller.
Popular solar controllers are from the Epever range and the Victron range of MPPT controllers.

You have stated a 15 amp fuse, with the panel array options, this series fuse is only needed where the 4 panels are connected in parallel.

a typical setup with 4 panels and a 100 volt input 30 amp solar controller. \this would be the preferred setup for the 4 panel array.
View attachment 101150


Mike

That is very helpful. Thank you.