BZ 250W/25A Solar MPPT Charge Controller

harley4jcs

I was reading a 2Y/o thread stating this controller is a pile...2 / 3 years later is this still the case ??? Has BZ done no improvements ?? Is it the same unit ?? There were several post stating it was a great product BUT the NEG out weighed the POS 4 or 5 to 1 !!!!! THANKS FOR ANY INPUT.. They are being sold by a S/W Co. at $109.00

BB.

Re: BZ 250W/25A Solar MPPT Charge Controller

I have not heard anything has changed since the original threads.

It is hard using the forum search tools to find "BZ" (string appears to be too short)-- but, if you go to Google and use this search string, you will find a bunch of threads:

bz site:wind-sun.com

It has been purchased by several people here and found to be wanting. One user here who designs MPPT type solar controllers tested and reviewed the construction and was not impressed at all with the construction (i.e., stay away from them).

-Bill

icarus

Re: BZ 250W/25A Solar MPPT Charge Controller

Still a POS as far as anyone has reported. The fact that some "reputable" sellers still sell them is astounding. Some folks just don't know any better.

The bigger question is with the Morningstar, Rouge or Bluesky Mppt controllers that have a way better rep out there for similar money why would someone who know about BZ consider it?

Tony

harley4jcs

Re: BZ 250W/25A Solar MPPT Charge Controller

icarus wrote: »

Still a POS as far as anyone has reported. The fact that some "reputable" sellers still sell them is astounding. Some folks just don't know any better.

The bigger question is with the Morningstar, Rouge or Bluesky Mppt controllers that have a way better rep out there for similar money why would someone who know about BZ consider it?

Tony

Thanks,, What I figured but wanted to check.. The best deal on bluesky found was $230 something...... I'm pretty tight to call it a comp to $109.00.. This is the last piece I'm looking for SO I'll check the names listed...Thanks Again Harley

BB.

Re: BZ 250W/25A Solar MPPT Charge Controller

You also need to look at where the system will be installed (hot/cold weather?) and the size of the system...

A simple PWM controller setup with a "12 volt panel" connected to a 12 volt battery bank (or 24v panel to 24v battery bank, etc.)--may be better off taking that $100-$400 savings by getting a "cheap but good" PWM controller and spending the savings on extra solar panels.

At best, a MPPT controller may collect ~15%+/- more power over a season (more in winter, less in summer)... It may be "easy" to offset that small gain with a MPPT controller vs getting more solar panels.

Also, one of the reasons a MPPT controller can be a nice solution is if you have a long run from the solar panels to the battery shed. You can use "high voltage" on the solar panel run (~100 volts max) to a 12 volt battery bank and use much less copper (money) on the run from the panels to the battery bank...

No black or white answers--but working out the system on paper first can save you a bunch of money and/or give you a system that better meets your needs.

-Bill

icarus

Re: BZ 250W/25A Solar MPPT Charge Controller

An addition to what Bill says,

Some MPPT controllers WON'T support higher voltage arrays. The Bluesky series of 25 amp controllers will only allow input and output of 12vt nominal voltages.

I agree that a PWM controller is a good cost effective choice for a small system. My harvest can be as much as 30% greater, but only when the PV temps are low and my battery is low as well. In normal service, I might get 5-10% better yield at best when the battery/array voltage is above ~13vdc.

Tony

James

Re: BZ 250W/25A Solar MPPT Charge Controller

The BZ unit I purchased several years ago is still sitting in a bottom junk drawer...as a testiment to poor choices!
I don't know why I don't just pitch it....

PhilS

Re: BZ 250W/25A Solar MPPT Charge Controller

James wrote: »

The BZ unit I purchased several years ago is still sitting in a bottom junk drawer...as a testiment to poor choices!
I don't know why I don't just pitch it....

Prob'ly the same reason I haven't pitched my one (of three) remaining BZ controller.... someday I may need a metal box of about those dimensions or a cool red LED or some other part from it. (the other two were sent to members here for confirmation that they are pieces of c**p if that fact wasn't noticed in the referenced threads).

I have a detached garage for junk a long ways from the house and the BZ seems to belong there.

Phil

harley4jcs

Re: BZ 250W/25A Solar MPPT Charge Controller

Thanks Again Guys...I'm playing with a small sys.. (4) 90 w Panels, (4 to 6) 110 Ah Marine Batts, 3Kw pure sine wave. The panels are stationary @ 20 Degrees, 25' to 40' from batts.. The panels are rated @5 amps SO I was thinking a Cheep MPPT ($109.00) digital controller was the way to go.. 25 to 30 Amp capacity + 15 % to 30% net gain on the array sounded cool !! Was thinking of keeping it 12v in & 12v out.. ANY SUGESSITIONS ????

BB.

Re: BZ 250W/25A Solar MPPT Charge Controller

At this point, there is NO CHEAP MPPT CHARGE CONTROLLER THAT WORKS at this time... The BZ product usually does not perform as well as a cheap PWM controller either.

The Xantrex "C" series is an old but proven design.

And Morning Star has several PWM lines (and the Tri-Star line has a different PWM mode--that is slow on/off switching to try and reduce telecom noise).

In any case, ideally you should look for controllers that have a remote battery temperature sensor option (battery charging voltage changes with battery temperature).

Unfortunately, there are really no good "cheap" charge controllers. Our host sells products that they stand behind at their Northern Arizona Wind and Sun webstore. You are welcome to look at their products/prices and purchase there or elsewhere... None of us (other than the Admin Windsun) have any business connections with NAWS.

The Rogue MPPT looks like an interesting MPPT controller (you can even get the schematics and kit form if you want to assemble your own)... At least one person here has tested the unit and found it to work well. And the owner/designer of the company posts here too.

In general, if you can run at higher voltages (panel or panel+battery bank) -- you will be better off (less voltage drop).

However, there is a neat 12 volt / 300 watt True Sine Wave inverter (MorningStar) that, for low power systems, is a good argument for a 12 volt battery bank.

-Bill

icarus

Re: BZ 250W/25A Solar MPPT Charge Controller

Hey Phil,

I still have the one you sent me, gathering dust on my bench!

T

Solar Guppy

Re: BZ 250W/25A Solar MPPT Charge Controller

My two went to the recyclers, wasn't even worth keeping on the parts rack

Panamapat

Re: BZ 250W/25A Solar MPPT Charge Controller

harley4jcs wrote: »

Thanks Again Guys...I'm playing with a small sys.. (4) 90 w Panels, (4 to 6) 110 Ah Marine Batts, 3Kw pure sine wave. The panels are stationary @ 20 Degrees, 25' to 40' from batts.. The panels are rated @5 amps SO I was thinking a Cheep MPPT ($109.00) digital controller was the way to go.. 25 to 30 Amp capacity + 15 % to 30% net gain on the array sounded cool !! Was thinking of keeping it 12v in & 12v out.. ANY SUGESSITIONS ????

I've got a similar setup in terms of solar and batteries and concluded that an MPPT controller of 30 amps or so would be ideal. I ended up purchasing a Rogue and shared my prelinary results in the following thread:

http://forum.solar-electric.com/showthread.php?t=6070&page=3

While not noted in prior comments, I've grown to like the LCD display that supplies a small screen full of data of current performance as well as historical data for review. This is a nice addition to a product in this price range.

dwh

Re: BZ 250W/25A Solar MPPT Charge Controller

harley4jcs wrote: »

Thanks Again Guys...I'm playing with a small sys.. (4) 90 w Panels, (4 to 6) 110 Ah Marine Batts, 3Kw pure sine wave. The panels are stationary @ 20 Degrees, 25' to 40' from batts.. The panels are rated @5 amps SO I was thinking a Cheep MPPT ($109.00) digital controller was the way to go.. 25 to 30 Amp capacity + 15 % to 30% net gain on the array sounded cool !! Was thinking of keeping it 12v in & 12v out.. ANY SUGESSITIONS ????

3kw is probably too much inverter if you plan on loading it up - it'll drain 4 or 6 batteries pretty quickly.



P.S. Tony...Bill....it's Rogue NOT Rouge. (The second is used to catch the first.)

icarus

Re: BZ 250W/25A Solar MPPT Charge Controller

Yea well, not only do I do lousy math, my spelling sucks as well! lol

T

BB.

Re: BZ 250W/25A Solar MPPT Charge Controller

Oh oh... The gorilla is going rouge... Or is that the guerrilla is going rogue. Just Words...

-Bill

harley4jcs

Re: BZ 250W/25A Solar MPPT Charge Controller

dwh wrote: »

3kw is probably too much inverter if you plan on loading it up - it'll drain 4 or 6 batteries pretty quickly.



P.S. Tony...Bill....it's Rogue NOT Rouge. (The second is used to catch the first.)

No plans to load it up but possible spike ..Can & will add batts as ness, so purposely over bought inverter. Thanks for seeing that..Still looking for charge controller ...

icarus

Re: BZ 250W/25A Solar MPPT Charge Controller

You want to know how bad this controller REALLY is? I was messing around with couple of new panels this morning and I plugged into the controller and then then into a starting battery, with a 100 watt load on the battery. Now the panels were showing 5.6 amps into 12.2 volts. Cool panels, cool morning. Now the panel showed 5.6 amps, about right given the slight haze in the morning. The on board ammeter showed that the amps INTO the battery was a 5.1 amps. So it appears that the Mppt advantage was a whopping ~10% NEGATIVE!

So the controller's own on board display is telling you that this is a POS!

Tony

harley4jcs

Re: BZ 250W/25A Solar MPPT Charge Controller

BB. wrote: »

In general, if you can run at higher voltages (panel or panel+battery bank) -- you will be better off (less voltage drop).



-Bill

Bill: This is a area I don't really understand...I get that series increases volts & parallel increases amps on the Batt bank or Pv Array. I'm using 12v Batts & will keep the Batt bank @ 12v.(lights,fans & water pump in a RV), only occasional inverter use. With only (4) 90w panels @ 5amps ea ( & what 17v-20v or so ??) DON'T I WANT TO WIRE THE PANNELS IN PARALLEL TO PUT UP TO 20AMPs AVAILABLE TO CHARGE THE BATTS ??? WHAT GOOD IS IT TO increase VOLTS ?? I'M TRYING TO REPLACE THE AMP hr'S THAT WOULD HAVE BEEN USED OVERNIGHT CORRECT ??? In the shop my charger uses 120v but it's the # of amps it puts out that determines how long it takes to recharge the Batts.The smaller wire is no issue in my system..Thanks

BB.

Re: BZ 250W/25A Solar MPPT Charge Controller

Harley,

If I understand your questions correctly...

First, some basic electrical equations:

V=I*R (voltage = current * resistance)
P=V*I (power = voltage * current)
P=V^2 / R (power = voltage squared, divided by resistance)
P=I^2 * R (power = current squared, times resistance)

So--first of all... Power is power. Say you want 1,200 watts of power from your battery bank... It could be satisfied by either a 12 volt or 24 volt setup:

P=I*V= 100 amps * 12 volts = 1,200 watts
P=I*V= 50 amps * 24 volts = 1,200 watts

So--there is no difference between a 12 volt system vs a 24 system in power available (assuming solar panel wattage and battery storage in Watt*Hours is identical between both setups).

Now, we look at usable voltage... Most devices call a battery "dead" at 10.5 volts DC for a 12 volt lead acid storage battery. For a 24v system, 2x10.5v=21volts "dead battery" level.

12 volts - 10.5 volts = 1.5 volts maximum wiring drop
24 volts - 21 volts = 3 volts maximum wiring drop

So, you now have 2x the allowable voltage drop--you can run longer wires, or smaller gauge wires (depending on your needs).

Next, look at the current from the above power equations... One used 100 amps @ 12 volts, the other used 50 amps at 24 volts.

V=I*R

So, if Resistance is the same between a 12 volt vs 24 volt system (same wire awg)--the voltage drop in a 24 volt system will be 1/2 that of a 12 volt system...

So, now a 1.5 volt maximum drop in your 12 volt system becomes 0.75 volt drop in a 24v system with the same output load (1,200 watts). Plus, you now have 3 volts of "drop" available--more head room for surges.

Next, look at efficiency of wiring...

P=I^2 * R (heating losses in wiring--also called I squared R losses)

Because the losses go up with the square of the current, that means a 12 volt system (with otherwise the same wiring and load requirements) will waste 4x as much power due to the 100 amp # 12v vs 50 amp @ 24v system.

So, in a nutshell, that is the choice between a 12 volt vs 24 volt (or 48 volt) battery bank choice.

Now, regarding Charge Controllers... They (the more expensive models) are (typically) rated on maximum output current (i.e., 60 amps maximum). So, remembering:

P=I*V

If we change from 12 volts to 24 volts--the power transmitted by the charge controller will double (and you can put 2x the wattage of solar panels on one controller)... Go to 48v battery bank, 4x the number of solar panels with still the one lone charge controller.

For PWM Controller (voltage does not matter):

Imp solar panels = Ibatt (current from solar array goes into battery bank)

Note: for PWM ("simple") type solar charge controllers, the Vmp of the solar panels needs to match the Vbatt voltage... With PWM, current out from the solar panels equals current into the battery bank.

Next, there is the issue of using a MPPT type solar charge controller... Basically, these are (typically) switch mode power supplies that can "transform" high voltage/low current from the solar panels to low voltage/high current at the battery bank.

Example for MPPT Charge Controller:

P=I*V=20amps * 15volts = 300 Watts into the battery bank
P=I*V=3amps * 100volts = 300 Watts from the Vmp=100v solar array

Notice that for the panel array, you only have to deal with 3 amps... You can have longer runs and/or smaller gauge wire between the solar panels and the battery shed.

The 20 amps only needs the heavy wire for the short distance from the charge controller to the battery bank.

The MPPT charge controller can behave like a variable AC transformer that efficiently down-converts (or transforms) high voltage/low current DC into low voltage/high current DC.

Does what I typed make sense?

-Bill

PS: We can go into more detail with Amp*Hours and 120 VAC--but I wanted to make sure I was clear on this part first.

dwh

Re: BZ 250W/25A Solar MPPT Charge Controller

harley4jcs wrote: »

I'M TRYING TO REPLACE THE AMP hr'S THAT WOULD HAVE BEEN USED OVERNIGHT CORRECT ???

Nope.

What you are trying to replace, is the watts that were consumed. Say you ran 3 20w lights for 6 hours. Then you consumed 360wh (watt*hours).

Series or parallel on your PV array, the math works out the same: 90w PV x 4 = 360w. If you take power from that array for one hour, then you have taken 360wh (watt*hours) from it.


The trick is to get that 360wh you took from the array, and stuff it back into the battery to replace the 360wh you used last night.


The way you get those watts into the battery is by pushing the power to the battery with "a voltage higher than the battery's voltage". It's like they are butting heads - the battery is trying to push juice out, and the charger is trying to push juice in. The charger has to push harder or juice won't flow into the battery. Voltage is the pushing force or "pressure".

So, if you wire your PV in parallel and use a PWM charge controller, then the charge controller will simply connect the 17v from the panels directly to the battery and let the juice push in at 17v. That's certainly high enough to overcome the 12.5v or 13.9v or whatever voltage the battery happens to be at. Power will flow into the battery.


But that's not the most efficient way, because at 17v that 360w only works out to 21.17a (360 / 17 = 21.17). Which means that in perfect sunlight, you can recharge your batteries with a maximum of 21.17a per hour, or 21 amp*hours or 21ah.


Now, what the MPPT will do, is track the voltage of the battery, and then reduce the charge voltage to "just over the battery voltage". This still allows the juice to flow into the battery, since the charger is winning the push battle, but by lowering the voltage, it changes the equation.

Let's say the MPPT sees the battery is at say...13.6v. The MPPT decides that 14v is what the charge voltage should be. Now the math is (360 / 14 = 25.71). The watts are still the same, but by lowering the voltage, the amps go up. Now your same 360w PV array can charge the batteries at 25.71a per hour or 25.71ah because it's pushing the power at 14v instead of at 17v.

Watts / Volts = Amps

That's the advantage of the MPPT, and what MPPT means is that the charge controller tracks the battery voltage, and decides what is the best voltage to use when pushing power into that battery. That "best voltage to use" is the Maximum Power Point.


Now, most MPPT controllers can handle a decently high input voltage. So, if you were to wire your PV in series, then the array would be putting out 17v x 4 = 68v.

Again, the math is the same - 360w / 68v = 5.29a

So while it is "less amps", it's also a higher voltage, so it still works out to the same 360w.


Only now, you don't need to use wire that can handle 30a (next size up from 20a), you can use wire that can handle 10A (next up from 5a). For any long run of wire, that can save you a noticeable amount of money.

The other advantage is that at a higher voltage, there will be less current drop along the run of wire - which means more watts available out of that 360 for the charge controller to work with. The PV might be putting out 360w, but after losing some over the wire there might only be 340w actually getting into the charge controller.


Either way, the MPPT will still take whatever the input current is - 5.29a@68v or 21.17@17v - and convert it to 25.71a@14v output. (More or less...the actual numbers will be continually updated by the MPPT based on the battery's actual voltage.)



If you were using a PWM charge controller, then you definitely would NOT wire your PV array in series, since 68v would be way too much voltage to dump directly into a 12v battery.

stephendv

Re: BZ 250W/25A Solar MPPT Charge Controller

dwh wrote: »

That's the advantage of the MPPT, and what MPPT means is that the charge controller tracks the battery voltage, and decides what is the best voltage to use when pushing power into that battery. That "best voltage to use" is the Maximum Power Point.

An MPPT charge controller tracks the maximum power point of the solar array not the battery! The voltages used to charge the battery are preset within the controller - both MPPT and PWM controllers can have these preset values at which to charge the batts for each of the charging phases.

dwh

Re: BZ 250W/25A Solar MPPT Charge Controller

stephendv wrote: »

An MPPT charge controller tracks the maximum power point of the solar array not the battery! The voltages used to charge the battery are preset within the controller - both MPPT and PWM controllers can have these preset values at which to charge the batts for each of the charging phases.

http://www.solar-electric.com/charge_controls/mppt.htm

"Maximum Power Point Tracking - this is electronic tracking, and has nothing to do with moving the panels. Instead, the controller looks at the output of the panels, and compares it to the battery voltage. It then figures out what is the best power that the panel can put out to charge the battery. It takes this and converts it to best voltage to get maximum AMPS into the battery."


So...you're saying I read it backwards?

BB.

Re: BZ 250W/25A Solar MPPT Charge Controller

Well--technically, the MPPT controller also "tracks" the battery voltage too (as I understand the MPPT CC funcition--and it is possible I am wrong)... When near dead and/or heavy loads, the battery voltage may below 12 volts DC. When equalizing, the battery may be near 14.5-15 volts--and in any of those cases the MPPT still follows the Pmax=Ibatt*Vbatt=Imp*Vmp of array (less conversion losses). It is a small nit--but still important as there would be significant losses if the controller did not do the level conversion efficiently.

But, remember, if the battery voltage reaches the set-point of the MPPT charge controller (say 14.3 volts at 50 amps)--the battery will probably be near 80-90% charge and will transition from Bulk Charging (Pmax from panels and Pmax into battery) to Absorb Charging where the controller will hold 14.3 volts and start cutting back on the amperage to the next value (say 2 amps). Then transition to Float Stage where it may hold around 13.x volts.

Once an MPPT charge controller drops out of Bulk Charging mode, it will begin to behave like any other PWM controller and only draw enough current/voltage/power from the solar panels to meet the balance of the charging cycle as programmed for that battery bank.

The MPPT controller in Absorb and Float modes no longer has any need for Maximum Power Point tracking as it needs less power than the panels are currently producing.

-Bill

stephendv

Re: BZ 250W/25A Solar MPPT Charge Controller

BB. wrote: »

Once an MPPT charge controller drops out of Bulk Charging mode, it will begin to behave like any other PWM controller and only draw enough current/voltage/power from the solar panels to meet the balance of the charging cycle as programmed for that battery bank.

The MPPT controller in Absorb and Float modes no longer has any need for Maximum Power Point tracking as it needs less power than the panels are currently producing.

That's interesting, I always assumed that the MPPT function was independent of the charging function. i.e that the charger would always be finding the panels maximum power point irrespective of what was going on with the battery. Wonder if this is true for all MPPT chargers?

Back to the bit about tracking the battery voltage, I don't think I understand it clearly, so taking a hypothetical example:

Battery is at 12V.
Charger is preset to end bulk charging at 14V.
The maximum power that can be drawn from the array can be found at 50V (for argument's sake).

So the MPPT charger figures out this 50V value and then connects to the array at this voltage.

Now what voltage does the charge controller apply to the battery? 12V? a bit more than 12V? or 14V?

stephendv

Re: BZ 250W/25A Solar MPPT Charge Controller

Dwh, I think you answered my question in your original post:

dwh wrote: »

Now, what the MPPT will do, is track the voltage of the battery, and then reduce the charge voltage to "just over the battery voltage". This still allows the juice to flow into the battery, since the charger is winning the push battle, but by lowering the voltage, it changes the equation.

Ok, I think the confusing bit is using the term "MPPT" to describe what the charge controller does to the battery. Re-reading, I see that you used "MPPT" to mean "the MPPT charge controller device" and not "the MPPT algorithm within the charge controller".

It sounded to me as if you were saying that the charge controller has 2 MPPT trackers in it, one to track the array and one to track the battery.

icarus

Re: BZ 250W/25A Solar MPPT Charge Controller

This is making my head spin. In the name of KISS I'll toss my opine in.

MPPT takes panel voltage ABOVE battery voltage, converts this "extra" voltage to current. (amperage) 12 volt panel might have operating voltage Vmp of ~17 volts. Since the Pv will only put current into the battery (sans mppt controller) at the Voltage that the battery is, the difference between battery voltage and Pv voltage is essentially wasted. (Panels need to be able to put a higher voltage than the battery in order to "push"power into the battery. So lets say you have a 50 watt panel rated at 17 vdc. 50 watts at 17 vdc would be ~2.94 amps. If the battery is only at 12.3 volts say, the same 2.49 amps would only yield 30.67 watts. What MPPT does is convert the excess voltage and turn it to current. So you might see 12.3 volts at say 3.2 amps, an increase of ~.7 amps or a 28% increase. (39 watts) (Made up numbers mind you!) Only rarely can you get anywhere near 100% of rated out of Pv, for normal calculations, 80% into a battery would be pretty darn good. (50 watts X 80%= 40 watts).

So you can see that the lower the battery voltage is relative to the array voltage the greater advantage. So a 24 volt (or 48/96) down converted to charge a 12 volt battery you can get somewhat greater efficiency.

Hope this is clear as mud.

Tony

BB.

Re: BZ 250W/25A Solar MPPT Charge Controller

From the Xantrex XW MPPT Charge Controller manual (PDF):

Maximum Power Point Tracking allows the XW SCC to harvest the maximum energy available from the PV array and deliver it to the batteries.

The MPPT algorithm continuously adjusts the operating points in an attempt to find the maximum power point of the array. The algorithm can then determine if it is harvesting more or less power than the previous operating points.

The XW SCC applies a variable load on the array—shown by the power curve (solid line) in Figure 1-2—until it finds the maximum wattage (the point at which both operating voltage and current can be maximized at the same time), as indicated by “MPP” in Figure 1-2. The XW SCC then holds the array at this point for as long as the array continues to produce the maximum power possible. As panel shading, cloud cover, and sunlight angle shift, the XW SCC finds the new maximum power point without interrupting its output power flow.

The battery is a "dump" load for the MPPT harvesting function. Once the battery is accepting less power than the panel array is capable of producing, the controller will use less current (less than Imp) and the panel voltage will rise (Voltage is higher than Vmp).

I would guess that the overall "dance" is more complex (as clouds/evening progresses, even in lower power absorb/float modes, the controller will transition back to MPPT mode as the total panel power available drops below that needed to "absorb/float" the battery bank).

The controller is a power converter so it is always working under the Pin=Pout (+ losses). Where P=I*V...

At various points of operation, the controller output may look like it is power limited (Xantrex calls it a constant current mode--but, to me it appears that it should be a constant power mode--or a maximum power transfer from panel to battery mode). I would assume that the controller output follows this sort of equation (assuming 500 watts are available from the solar array and Iout is less than the 60 amp controller rating):

Pbatt=Ibatt*Vbatt=500w=11v*45.5a=14.4v*34.6a

Then the controller goes into voltage regulated mode where the controller puts whatever current into the battery is required to maintain 14.4 volts for the balance of the absorb time:

During the absorption stage, the XW SCC continues to deliver its maximum available current output until the battery voltage reaches the absorption voltage setting. The XW SCC then operates in constant voltage mode, holding the battery voltage at the absorption voltage setting for a pre-set time limit (the default time limit is three hours). During this time, current falls gradually as the battery capacity is reached. The XW SCC transitions to the float stage if any one of three criteria are met:

1. The charge current allowed by the batteries falls below the exit current threshold, which is equal to 2% of battery capacity (for a 500 amp-hour battery bank, this would be 10 amps), for one minute.
2. The battery voltage has been at or above the float voltage (which it reached during the bulk stage) for eight hours.
3. The battery voltage has been at the bulk/absorption voltage setting for a pre-set time limit (the Max Absorb Time).

-Bill

BB.

Re: BZ 250W/25A Solar MPPT Charge Controller

MPPT has several different assumed meanings for Solar RE equipment...

1. There is a switch mode power supply inside the controller that is capable of efficiently down converting from high voltage/low current to low current/high voltage--sort of the DC equivalent of the AC transformer.
2. There is an Maximum Power Point Tracking function/micro processor which is able to adjust the switch mode power supply such that the supply maximizes the Vmp/Imp/Pmp of the solar array energy transfer into the battery bank (only during Bulk Mode or when energy charging capacity required by the battery is greater than that available by the panel.

The MPPT Grid Tied Inverter is similar in the sense that the AC Inverter that tracks the utility power is controlled by the MPPT algorithm / control electronics to pull just enough solar panel current to keep the array at Pmp=Imp*Vmp of the solar array (the GT Inverter is sort of the equivalent of trying to charge the near infinitely large Utility Grid like an AC Battery).

The typical Computer Power Supply has #1 (buck mode power converter) to down convert the 120 VAC which has been rectified into high voltage DC down to the 5v/12v/etc. required by the computer's electronics.

What the computer power supply does not have is a method of maximizing 120 VAC 15 amps into the poor unsuspecting DC logic gates.

-Bill

PS: There are other types of voltage/current converters besides Buck Mode--I do not know what is any particular Solar RE Charge Controller--but the overall functions will be similar.

lorelec

Re: BZ 250W/25A Solar MPPT Charge Controller

An MPPT controller is simply a switching power supply. As much as the manufacturers of such devices :-) would like you to think that there's magic involved in the process, in most cases you're just looking at a buck converter possibly (depending on design) followed by a simple PWM stage for regulating charge to the battery in absorb and float stages. The MPPT controller regulates the INPUT (PV side) of the switcher at a duty cycle that corresponds to the difference in the Vmp of the array and the battery voltage. So if you have a 50v Vmp and a 24v battery, then the controller is operating at a 48% duty cycle (square wave that is "on" nearly half the time). The controller doesn't "do" anything as far as the battery voltage is concerned (until it leaves the bulk/MPPT charging phase) -- it's only interested in the ratio Vmp/Vb, where Vb is essentially fixed owing to the stiff voltage afforded by the battery, and Vmp is being tracked by the MPPT algorithm.

Contrast this to most other switching power supplies, and the only major difference is that most of them regulate only their outputs (in the case of a computer supply, for example, you might have 5v, 12v, 3.3v, and lower with many of the newer processors). But it's still the Vin/Vout ratio that matters.

Marc

Windsun

Re: BZ 250W/25A Solar MPPT Charge Controller

lorelec wrote: »

An MPPT controller is simply a switching power supply. As much as the manufacturers of such devices :-) would like you to think that there's magic involved in the process, in most cases you're just looking at a buck converter possibly (depending on design) followed by a simple PWM stage for regulating charge to the battery in absorb and float stages.
Marc

There is a bit more to it than just that. A buck converter is pretty easy to design, as you are working with voltages within a certain known and usually fairly steady range.

It took over 20 years to develop really decent MPPT charge controllers, and the now fairly common 97%+ efficiencies were not achieved until the past 5 years or so, when the digital algorithms were finally figured out. Analog types, such as pump LCB's and some older design MPPT controllers such as the Blue Sky have been around for quite a while, but they all had (and have) their problems and typical efficiencies usually fall about halfway between a standard controller, such as the Xantrex C-60, and a digital controller such as the Xantrex-SCC.