MPPT Controller

[henjulfox]

I recently purchased a BZ Products MPPT charge controller. I got the "magic smoke"

on hooking it up but they replaced it quickly, no questions asked. Good customer

service.

My PV setup is 8 X 75 watt panels wired as 2 banks of 4, 24 volt. Each bank has it's

own 25' 12 gauge line to the controller. For fun I left one bank on the Trace C-40

controller and hooked the other to the MPPT. Watching over the last 2 weekends, the

MPPT always showed 10-20% more amps going to the battery, just like they advertise.

Today I tried testing the accuracy of the built-in meters. I unhooked the output of

the C-40 and ran it through another amp meter to the batteries. The C-40 read 5

amps, the other meter read 5 amps. Seems correct. However when I ran the MPPT

through the same meter the MPPT read 5.9 amps, the other meter read 5 amps. Same

test an hour later gave the same results - The built-in meter on the C-40 reads the

same as my other meter and the built in meter on the MPPT reads 10-20% higher than

the C-40 or the other meter.

Perhaps feeding the output through another meter is messing with the MPPT

functionality? Perhaps the obvious conclusion is correct?

-Henry

[ghurd]

Not sure how correct this is, but the 2nd meter should be between the MPPT and the battery. On a MPPT, the amps from the panel will not equal the amps to the battery.

Was the extra amp meter between the battery and controllers, or the panels and controller?

Very interesting either way.

G-

[henjulfox]

Yes, between the controller and the batteries.

My knee-jerk is that that would be the correct place to measure. But as I think about it, the amps gotta come from somewhere so wouldn't I get the same reading, less controller loss, from either location? I may give it a try next weekend.

I wanted so much for the advertised claims to be true!

-Henry

[wpowokal]

Henry, while amps is amps the purpose of a MPPT is to maximise the watts (amps x volts). As ghurd posted metre after MPPT. But you already knew that.

allan down under

[henjulfox]

The extra amps gotta come from somewhere - and where they come from is the volts. Got it. Thank-you

-Henry

[pyrocasto]

I'm thinking of buying one soon. Do you know if it really needs 100watts(68for the 250) minimum to charge?

[Tom in NH]

It has a relay that turns on as the sun brightens. I imagine that is why they specify a minimum wattage. I suggest you talk to Frank at BZ. He'll give good advice. I've had one of these units for the past couple months. The first unit they sent me charged the batteries very nicely, but the digital readout was wildly innacurate. It looked like it produced random numbers on the display. The second unit they shipped has a much more believable digital readout. I haven't tried reading the current to the batteries using a separate meter but battery voltage is a little on the high side (about .05v higher than my meter). I'll have to try a current measurement and see how it reads.

I have a long (150 foot) run between my panels and the batteries so I got the MPPT to allow me to wire my panels for 48 volts and charge at 12 volts. I can tell you that when I used the C40 I never saw much more than 25 amps going into the batteries. Now at midday it's not uncommon to see in excess of 35 amps, if you can believe the digital readout. Since I got my initial problem solved I'm very happy with the controller. It does a good job charging my batteries and it has a five year warranty which impressed me. --tom

[pyrocasto]

That's good to hear. I'll have to contact him with those questions. I'm mainly just wiring my cells in series to see what type of voltage I can get. I should end up with 60-80 volts a 3A, unless I decied to do 30-40 volts at 6A. Still deciding on where the batteries are going and how far from the house.

[ruddycrazy]

Hiya Guy's,

           I've got an AERL800 MPPT on my solar array and when the sune is shining the input volts is showing around 128 volts and 6 amps and the output is 26.9@ 12 to 14 amps. I've seent the output go higher but I only wish I got the software to log it but at $400 for the software they can go jump

Cheers Ruddy Crazy

[elvin1949]

Morning Henry

 Just a thought but did you compare the two in low light condition's IE early morning or late afternoon.My understanding of MPPT is that is when they realy make the biggest difference.

 Then again i may be what all my friend's call me .

LOCO

later

elvin

[henjulfox]

Kind of...

I was getting better than 22 amps from the whole array in july, 11+ from each bank. At 9 amps I know they were not opperating at peak but it was fairly sunny and around noon.

Now that I'm over my initial dissapointment I'm thinking of a better test set-up to gather more data over different conditions.

-Henry

[Tom in NH]

Here is a follow-up. This morning I took some readings in the indirect sun when I could safely use my meter without overloading it. It is hard to read the current, either from the PVs or to the batteries, because the MPPT500 switches it about 5 times per second. Maybe if I had an analog meter it would be easier to read, but alas, I do not.

Anyway, on my unit I was reading a PV current of about 1.0 to 1.3 amps @ 48 volts. At the same time, the MPPT 500 was registering a PV current of 1.2 to 1.4 amps. My meter said the 12 volt current going to the batteries was about 0.1 amp less than what the MPPT500 indicated. Likewise, my meter was about 0.3 volts less when measuring the battery voltage.

Using just the MPPT500 digital readout, I noted an input current of 1.5 amps at 48 volts nominal and an output current of 6.8 amps at 12 volts nominal. Thats 72 watts in and 81.6 watts out, or about a 14 percent boost. These readings also suggest that you can operate the MPPT500 on less than 100 watts. --tom

[Ungrounded Lightning Rod]

In particular:

The panel amps, running down the voltage difference between the MPPT controller's input and output, provide power to "pump" additional amps up from the ground and push them into the output.

A MPPT controller is a switching regulator.  This means the output current is varying with some oddball waveform at the switching rate.  You need an average-reading ammeter to read the output amps correctly.

[henjulfox]

The meters built into both controllers are digital. The additional meter I've been using is analog. The needle was steady reading the output from the C-40 but would move a little while measuring the output from the MPPT, maybe 2-5%. Do you think the analog meter was successfully reading the average? A pair of cumulative amp/hr meters would probably be best but I hate to throw that kinda $ at it, unless someone knows of an affordable way to accomplish.

-Henry

[Ungrounded Lightning Rod]

Yes, your analog ammeter should give you a good average reading.

The common faraday-effect analog DC ammeters (direct and shunted) read the average of any waveform that's cycling fast enough that the needle is not flapping around too much to get a good reading.

Analog THERMOammeters read RMS.  (These use a low-value resistor - like a shunt but NOT connected to the meter's coil - with a thermocouple attached.  The thermocouple uses the shunt's heating to generate the power to drive a sensitive faraday-effect meter.)