Jul 31, 2006 12:50 pm
Re: BZ Products MPPT500 step down voltage
Jonny,
Thanks for the reply - and I almost grabbed the phone to talk this over, but instead decided to write this for the forum. This would also be something best pasted into a email for BZ Products, if you have contact information for the company. I would really like to hear their comments.
After making the initial post, I decided to go back out and re-wire one of the PV arrays into a 12 volt, rather than a 24 volt source. I did this after thinking about getting 11.5 amperes battery current from my two panels in series, giving 6 amps to the controller. Duh, I can get 12 amps in the parallel wire scheme - and I do.
I verified that the MPPT500 performs as one would expect charging a 12 volt battery from a 12 volt PV source. So, I don't believe that the unit I have is defective. If there isn't a functional difference between the MPPT500 and the "HV" variant, other than standing up to a 60 volt source, there is no point in persuing a exchange.
Based on my experiments, I have decided that I'm better off wiring the PV's as 12 volts. I have to place an order to get another 50-foot #10 awg cable with the whacko MC connectors the Evergreen panels use, and I have another order already in effect for #10awg marine twin-conductor cable from another source for the other panels. It isn't as elegant as using a 24-volt source, but it is (in my opinion) necessary for the MPPT500.
Final judgement on my part for the MPPT500: While it is "autoranging" and indeed capable of operating with a 24-volt PV array, it is not able to autorange out of early morning sunrise and shadows. Once it "determines" that it has a 12-volt array because of weak light, it won't relax the current draw enough to find a higher source voltage from the PV.
The MPPT500 is "capable" of 24-to-12 volt conversion, but it is not suitable for this application.
While it has DIP switches inside to determine the battery voltage (12 volt in my application) and type of battery (AGM for me), it has no user programming for the PV array voltage. It needs it.
For the specifics of my setup:
I have two Evergreen EC-110 panels as one array. Not six of them, as you had thought. I measured 38 volts open-circuited from these, when wired in series.
I also have another array of four Solarex 48-watt panels that I found used locally. As an aside, I can tell the MPPT500 "likes" the power curve on the Solarex better than the Evergreen from an efficiency point.
Each of these arrays are wired independently as parallel sources to the MPPT500's input. The total package is about 400 watts, capable of 23 amperes when wired for 12 volts.
The battery bank is four 12-volt 100AH AGM batteries in parallel. Inverter is a Xantrex (Trace) DR1512, which hums along happily through this whole ordeal.
Again, I am very curious to see what BZ Products has to say, once they read this thread. I selected a MPPT type charger with the capability of using an array of greater voltage than the battery as a primary consideration. The multi-point power tracking is a secondary consideration, which is why I have no qualms about using a mixed-panel array that may have a weird optimum curve with double-humps.
I believe there is a market for a specific 24-to-12 charger, for minimizing PV wiring losses. MPPT500 isn't it. This would be great for a manufacturer to step up to the plate and answer to.
-Victor