Voltage step-down from 48 to 24V DC...

[greg273]

I'm considering doubling my solar array, and while the existing wires will take the amperage, I'm wanting to make the system as efficient as possible by raising the voltage from the array to the charge controller, from 24 to 48volts.
The charge controller, inverter and battery bank is set up for 24 volts DC.
Without purchasing a new MPPT controller, what options are there in some sort of step-down transformer? Are there considerable energy losses involved in the step-down process?

thanks!

greg

[WisJim]

A transformer wouldn't work on DC, so a DC-to-DC converter would be required. Haven't seen any that would handle variable voltage high current DC. Even though you say you don't want to do it, why not check into something like an MX60 MPPT charge control? That would do exactly what you want.

[idahodave]

DC to DC voltage conversions will always have some loss. Might be only a few percent, but that's probably what you would save by going to 48 volts.

Looks like about a break even proposition, I'd leave the array at 24 volts.

[Jim-mi]

Will your current charge controller handle the additional currant . . ??

Might be better off in the long run just to make another run of wire to the pannel addition.

I would not put my faith in a dc\dc converter for the very long haul of what your application would be.

The likes of a MX60 MPPT would be a very good way to go.

Bite the bullet and do it right . . .

[WisJim]

I have a 24 volt battery system, and my newest array of PVs is about 250 away. I wired the panels as 48 volt and use an MX60. I could then use a smaller wire size for the same power loss, and save a couple of hundred dollars on wire because of the MX 60. In addition, I get 10% to 20% additional power because of the MPPT feature of teh MX60 charge controller. It was well worth going to a higher voltage and using the MX60.

[Allan Mistler]

I couldn't justify the expense of the MX60 at almost $500 where I would require two of them anyway since my arrays exceed 60 amperes combined. I opted for the BZ Products MPPT500 instead at $190. They too are MPPT controllers with a five year warranty and I've had great response (immediate replacement) from the factory when the display panel on one of them died.
Greg, perhaps you can justify that low a price to achieve your goals. I know they work since I have my arrays wired for 35 volts output (Each panel in an array of four produces Max output of 7.39 amperes at 17.6 volts series/parallel wired as 14 amperes at 35 volts) yet my battery bank is configured for 12 volts. The controller is switch selectable for input up to 100 volts and output to 12, 24 or 48 volts.