The BRAT Beta Program

[brad.midnite]

Speaking of winking, my BRAT's Orange LED is winking right now. Been in absorb the last half hour or so. Since the Sun is hiding behind the clouds lately my 48V battery is standing in. 12V deep cycle is on the other side and sitting at 14.7V during absorb. Manual says it should be closer to 14.4?

What position is BATTERY1/BATTERY2 in?

Also, did you measure at the terminal block or at the battery?

-Thanks
-Brad

[onanparts]

I wondered if anybody actually looked at attachments. 

Absolutely! 

[onanparts]

Speaking of winking, my BRAT's Orange LED is winking right now. Been in absorb the last half hour or so. Since the Sun is hiding behind the clouds lately my 48V battery is standing in. 12V deep cycle is on the other side and sitting at 14.7V during absorb. Manual says it should be closer to 14.4?

What position is BATTERY1/BATTERY2 in?

Also, did you measure at the terminal block or at the battery?

-Thanks
-Brad

Flooded profile #1, S1-4 On, S1-5 Off.  Voltage at terminal block and battery are the same. Fluctuates from 14.68-14.74 on both Flukes, a 179 and an 87.

About 3' of 10 AWG between the BRAT and 12V Battery. Input side at 50.9V

Zero experience here with PWM controllers. The audible Morse code it's sending is interesting...I assume it keeps saying, "I'm a BRAT" "I'm a BRAT" "I'm a BRAT".......

[brad.midnite]

Oh good you have quality DMMs. Perhaps it's the temperature compensation? With a 12 volt battery it should be -30mV/degree C. It wasn't 15C/59F was it?

Also no difference between the battery and terminal block? Pretty low current?

-Thanks
-Brad

[onanparts]

Oh good you have quality DMMs. Perhaps it's the temperature compensation? With a 12 volt battery it should be -30mV/degree C. It wasn't 15C/59F was it?

Also no difference between the battery and terminal block? Pretty low current?

-Thanks
-Brad

I forgot about about the ambient temp comp. It's around 48F-50F in the shop, no heat on today.

Now in float at 13.5V green LED solid. Going to start a manual EQ shortly. The 12V battery is not a "real" deep cycle batt. It's a wanna be RV/Marine type but fairly heavy. Two years old and never done an EQ to it. Mr. HydraVolt showed good SG's last week but several cells were off so I'll check the SG first before doing the EQ.

Current was low. 12V battery was on a cheap Battery Tender Plus charger about 2 weeks ago, resting voltage at 12.7 before wiring it up to the BRAT today.

Oh, and one of Midnites 600 Watt clipper resistors is between the 48V battery and the BRAT's PV input. Not sure if that's needed on a BRAT but I use it when feeding my KID with the big battery...

[brad.midnite]

Interesting. I'm not sure the resistance of the clipper resistor you're using, but I'm thinking it's probably a .8-.9 Ohm resistor. With a 48V input and a 12V output that's 40 Amps peak, double what the charger is intended for if you're using the load circuit. This does mean The Brat will run hotter in general, but it should protect itself through active-derating and thermal shutdown.

I misunderstood what you were trying to say before but this also I believe explains the somewhat oscillatory voltage readings you were getting.

It's interesting hearing the talk of the singing Brat. Ryan has also commented to me about this. I cannot hear it, damaged my hearing in my teenage years with 2-strokes (engines), concerts, and mill work. PWM chargers run at a lower frequency than MPPT, and in most cases, both operate at a fixed frequency.

In The Brat's case, the unit switches at 250Hz, which is a convenient number based on the clock frequency it operates at (integer division). Since 250Hz is at the upper-end of what people would consider 'bass', you're obviously hearing some harmonic of 250Hz. Maybe 750Hz, 1kHz etc. Does it seem to make more noise when it's sunny, or is it constant?

The resistor was indeed a good idea. PWM chargers are NOT like MPPT chargers. An MPPT charger like the Classic/Kid does buck conversion. In buck conversion current is switched through an inductor at a controlled duty-cycle to produce an output voltage (or maximize input power, e.g. BulkMppt/FloatMppt). Of course, The Classic/Kid are a lot more advanced than a basic buck converter, but the core concept is approximately the same.

This inductor provides somewhat of a buffer for current between the input and output, though with an infinitely large source you could destroy anything, no-matter the protection scheme.

In PWM, the charger connects the input to the output with varying duty-cycles many times a second. There's less reactance to limit the peak currents once the switch has turned fully on. PWM chargers are basically solid-state switches that connect and disconnect the solar panel to the battery rapidly to regulate its voltage.

Therefore, your peak currents are higher than they should be, probably doubly-so based on what you've told me. If you didn't have the source resistance on the PV side, you would probably trip the short-circuit protection.
Anyways, happy beta'ing.

-Brad

[dgd]

Brad,

Nice basic explanation 

Judging by the postings of some Classic users, who seem to drive their Classic at maximum ratings with over paneling, and now this trend towards recommending input voltage near battery voltage, I was wondering if a simple brute force PWM controller might be a feasible Midnite option.
Maybe similar to or surpassing the current rating of the 90's vintage Heliotrope 120A PWM controller       (Pity the company just faded away even though they had a winning controller)

MPPT was great when PVs were expensive and extracting every watt was paramount, but now PVs are so cheap maybe just a damm big PWM controller would be more useful.

dgd

[Westbranch]

MPPT was great when PVs were expensive and extracting every watt was paramount, but now PVs are so cheap maybe just a damn big PWM controller would be more useful.

I see only one drawback with that statement,  Those 'cheap ' panels are probably GT type with  higher voltages, which a lot of times are not high enough to charge a 24 V bank, and if you are at 12V you 'lose' a lot of the potential power in the buck down to 12V...  one would have to do some figuring to see just how many watts could be recovered from a GT panel and then divide the price by that lower # of watts for a more realistic price per Watt, WHEN using a PWM charge controller..  Up to normal output with MPPT 

Same concept for 24V bank , but worse economy,  you would need a second panel to get about 5 more volts so a greater %  of that extra panel is wasted with PWM...

[onanparts]

Brad,

MPPT was great when PVs were expensive and extracting every watt was paramount, but now PVs are so cheap maybe just a damm big PWM controller would be more useful.

dgd

Even if the panels were free, consider the advantage of MPPT in situations where real estate is at a premium. Boats/RV applications etc. Even permanent installs on land may not always have optimum placement and or the space for a large array. This is where MPPT "shines"  Pun intended! 

And now back to the BRAT's!  An affordable alternative to MPPT CC's.

[onanparts]

Interesting. I'm not sure the resistance of the clipper resistor you're using, but I'm thinking it's probably a .8-.9 Ohm resistor. With a 48V input and a 12V output that's 40 Amps peak, double what the charger is intended for if you're using the load circuit. This does mean The Brat will run hotter in general, but it should protect itself through active-derating and thermal shutdown.

Not planning to use the load circuit while testing it on the 48V battery.  .8 Ohm resistor. BRAT running very cool temp wise so far.



It's interesting hearing the talk of the singing Brat. Ryan has also commented to me about this. I cannot hear it, damaged my hearing in my teenage years with 2-strokes (engines), concerts, and mill work. PWM chargers run at a lower frequency than MPPT, and in most cases, both operate at a fixed frequency.

In The Brat's case, the unit switches at 250Hz, which is a convenient number based on the clock frequency it operates at (integer division). Since 250Hz is at the upper-end of what people would consider 'bass', you're obviously hearing some harmonic of 250Hz. Maybe 750Hz, 1kHz etc. Does it seem to make more noise when it's sunny, or is it constant?

Intended use for the BRAT is in my RV. It's in storage and under cover for the winter. At the moment my Radian's 48V battery is standing in for the sun. Has to be a harmonic...I just sent boB an audio file of it this morning. Dit Dit Dash Dit Dit Dash Dash etc. like morse code. You have to be within a few feet of the BRAT to hear it, even then it's not noticeable unless very quiet in the area.

Bulk, Absorb and EQ it's there. Barely while in float.

.

Therefore, your peak currents are higher than they should be, probably doubly-so based on what you've told me. If you didn't have the source resistance on the PV side, you would probably trip the short-circuit protection.
Anyways, happy beta'ing.

-Brad

[dgd]

Even if the panels were free, consider the advantage of MPPT in situations where real estate is at a premium. Boats/RV applications etc. Even permanent installs on land may not always have optimum placement and or the space for a large array. This is where MPPT "shines"  Pun intended! 

Ok, there will probably always be plenty of such situations were mppt is best.
But where such restrictions don't apply - space for decent size array, close to battery bank etc, then a brute PWM controller would work.
Dgd

[dgd]

MPPT was great when PVs were expensive and extracting every watt was paramount, but now PVs are so cheap maybe just a damn big PWM controller would be more useful.

I see only one drawback with that statement,  Those 'cheap ' panels are probably GT type with  higher voltages

AFAIK the standard 36 cell and 72 cell PVs are just as cheap per watt as the 60 cell GT type panels.
And just as available. At least in this godzone 
Dgd

[Free Energy Freak]

Ok, there will probably always be plenty of such situations were mppt is best.
But where such restrictions don't apply - space for decent size array, close to battery bank etc, then a brute PWM controller would work.
Dgd

Like Cambodia. 11° to 13° North Latitude.

[Westbranch]

AFAIK the standard 36 cell and 72 cell PVs are just as cheap per watt as the 60 cell GT type panels

OK I agree if pricing is approx equivalent , so I checked NAWS site and using Kyocera panels,
a 185W 12V panel is $1.15 US per Watt,
a 255W GT is selling for $0.94/W . 
Using 17 V for charging there is 13V,~ 44%  that will be lost off the top..now only ~ 143W, so the price just rose to ~$1.68 /W

http://www.solar-electric.com/solar-panels-mounts-kits-accessories/solarpanels/hiposopa.html

[onanparts]

Unless I missed it someplace, starting a manual EQ is spelled out but manually stopping it is not. Push and hold the button on the corner of the board to start but no mention of stopping the EQ if you need or want it to go for less than the timed 2 hours it will do on it's own.

Only took a few seconds to try the obvious.....push and hold the button while in EQ mode to stop it.  Might want to add that on page 8?