Diy mppt?
 

I've been looking into how I can get more PV watts into my 10 Ohm hot-water heater.

I've been looking at this pump controller.
http://www.voltscommissar.net/minimax/schemati.gif
Here: Build this simple Mini Maximiser

And thinking about the 'Knee' point (sweet spot) of a PV array.

http://users.tpg.com.au/users/robkemp/Power/Mpp.gif
This particular PV array seems to have a (1300w) sweet spot around 152 volts..
As you can see, the Open voltage (no load) is up around 200v.

Anyways, if you made a voltage divider similar to the Mini-Max (above),
fed the voltage to the comparator & FET, with your reference
pot pre-set to trigger the FET into conduction right at 152 volts (or higher)..

It seems like the load would only see 152v (or higher).
Once the RC time constant ran down a tad, the FET would turn off, and
the PV would take a little time to recharge the input cap, before the PV
voltage was high enough to trigger the FET again.

In weak sun, the off-on rate would slow down, as the PV struggled to keep up, charging up the input cap more slowly.

But, in bright sun, the off-on rate would zoom up and try to keep a continuous 152 volts on the load..

But, either way, while the FET was on, the load would see the highest voltage : power available from the PV.
Thus, making the fixed load, dissipate a maximum amount of watts.

Each time the FET turns on, it can hit the load with about 1300 watts.
If only for a short time.. But, the Flywheel Effect might help here.

By allowing only higher voltages to pass power on the feed lines,
allows for less line loss. (Especially with the small wire I'm using).


If I could use this type of circuit on my 10-Ohm hot-water heater,
zapping the load with full power hits, I'm sure it would put more heat into the water..


~~
Today, my 500w array shows 65.1v under load & 78.9v open (no load).
At the load, (after 75 feet of wire) the voltage is 63.3 (lost 1.8v ~ 11.4w).

63.3 volts (6.33 Amps) on the 10 ohm load dissipates about 401 watts.
With the line loss, 412 watts isn't too bad, but this is a peak reading.

The passing clouds allow the 10 ohm load to pull down the PV voltage,
making the line losses increase and the fixed load, seeing lower voltage,
can't draw as many amps.


I can't help but wonder if I could get closer to 500 watts, if the PV was
running at around 67-71 volts..?.

I have not worked with FETs for years, I hear they have some real good ones now.
What do you guys think? Good DIY, or start shopping for a pre-made? ;)

Cheers,
Rich

I looked into diy mppt a while back. Someone posted a link here to a chip that does it. It is over my head on how to use it, but I remember it wasn't cheap just to buy that chip. If I recall correctly the chip was ~$25. I think the cheapest MPPT controllers I've seen are at least $70 though.

What about using a PIC or other microcontroller? Use a voltage divider to measure the voltage and hardware PWM to control the MOSFET.

I wondered if there was a MPPT chip. Like the specialized PWM chips used in power supplies.

Using a micro controller adds a layer of complexity that I would like to avoid.

I kinda like that little pump controller (above), since it's very effective
and doesn't really cost a lot, in parts or time.

What would be the draw-backs to using that kind of circuit?

Or, maybe I could design a little 'watt meter' on the output, that would feed-back
an analog signal to the input, that would change the comparator reference voltage
to a setting where the most watts were present on the output.?.
Real-time active feed-back to keep the panels producing the
maximum amount of power under various lighting conditions.?.

Might make a more interesting project.. :D

I found a little dump-load / charge controller on Ebay.
UNIVERSAL RELAY DIVERSION CHARGE CONTROLLER REGULATOR - eBay (item 130409810996 end time Jul-20-10 04:14:47 PDT)

It seems to be made to monitor a 12V battery (tied to PV or wind) and if the battery
gets up to the 14.3v 'Charged' state, User Settable Dump/Diversion/On-Off Voltage Set-point (13.1 to 15.1 Volts)
It will turn on a load relay or SSR to discharge the battery a little.

See Solar hookup diagram here:
http://www.windandsunpower.com/Downl...RDC_Manual.pdf

Anyways, I was brainstorming ;) and came up with the idea that I could
put four or five 12V batteries in Series. To be fed by my 65-70 volt PV..
70v of PV / 5 batts = 14volts each..

AND, the little Ebay board could monitor just one of those series batteries!
But, when it switched on a fat SSR, it would be connecting not just 12v,
but the whole series string of batteries to the load!

The board could be adjusted to trigger at 13.5 (67.5v of PV w/ 5 batteries),
which should be near the sweet spot and maybe give a quick 455w jolt to the 10 ohm load.

And then, I snapped out of it and said, 'I can't afford 5 batteries right now'! :(


Then, I started thinking about 5 big capacitors in series!!
If they were matched, wouldn't they act like a voltage divider-battery string??

Then, I said.. Do I really need 5 caps? Wouldn't one big cap work?
If I put a pot across it? With the output tap set to 13.5v, when the cap
was at 67.5v?

I'm liking this idea, because caps will charge up Faster than batts..
And, the SSR will be cycling faster, delivering the jolts of watts/BTUs,
as fast as the PV can supply them. (Depending on the clouds).. :cool:

So, what do you guys think of my crazy ideas?

Cheers,
Rich

You could use a comparator as a MPPT controller. Find the voltage at which you get maximum power output and have a comparator switch the MOSFET based on hysteresis. Main disadvantage is that you'll have to retune the circuit for temperature and aging.

Maybe the IRFP150N driven by an LM339N ?

I was just looking at the pump circuit,
http://www.voltscommissar.net/minimax/schemati.gif

And, I wonder if you added an LDR (photocell) across that top left resistor (3k3),
Then exposed it to bright sun (beside the PV) while setting the set-point
trim-pot for maximum power to the load (with good sun).
(The 3k3 resistors might need to be changed to other vaules, to compensate for the parallel LDR).



My theory is, when some clouds appear, the resistance of the LDR would
increase, which would lower the set-point voltage and keep the circuit pulsing..
(Otherwise, those clouds could turn the gizmo off)..

Heck with some careful tweaking, this could be a close approximation of actual MPPT!! :eek:

Comments please:

Thanks,
Rich

I'm thinking maybe 300 uF on the input to get a faster charge.. Like 2 150uf caps..

2 X 150uF 450V Radial Electrolytic Capacitor 22*41 - eBay (item 330447531609 end time Jul-30-10 05:51:15 PDT)
2 X 150uF 450V Radial Electrolytic Capacitor

Also thinking about these..
IRFP150N, 100V, 42A, N-Channel, Power MOSFET, Qty 10 - eBay (item 390206596636 end time Aug-07-10 11:27:09 PDT)
IRFP150N, 100V, 42A, N-Channel, Power MOSFET

And these too!
10 x LM339N LM339 IC LOW POWER QUAD VOLTAGE COMPARATORS - eBay (item 320521805666 end time Jul-22-10 00:15:53 PDT)


Of course, I've got to build this thing to work with 40 to 80 volts from the PV.
I'm thinking the logic parts should have their own little regulated power supply.

~~~

Maybe the pulsed output of the pump circuit would be suitable to drive
a Buck circuit, to boost the voltage up a bit higher.

http://i220.photobucket.com/albums/d...ck_circuit.gif

A higher voltage (without much loss in power), could really help with the line loss.
And, higher voltage into the 10 ohm load, means it's going to work better..
Since it will draw more current and get hotter.. :)

What would happen if you placed your panels in series, get an old 500 watt computer power supply, hack it to remove the AC input section and fed the high voltage DC from your panels into the inverter high voltage DC input. The 12 volt DC output would be fairly constant into a fixed load for varying panel voltages. The psu has all the switching components. may be easy to replace (re-wind) the output windings from the low voltage outputs to something more suitable.

Cheers
Mike

The panels are already in series. Almost 80 volts w/o a load. About 63 volts with a load.
I've got a fixed 10 ohm load (water heater) and I would like to hit it with as much voltage as possible (within reason).
And, the least amount of conversions done, is likely to be better.

IIRC, the voltage coming off the full-wave bridge of a PC PS is pretty high,
in 230 mode, they turn off the voltage doubling of the bridge.

Here you go.. Found it again.
200W ATX PC POWER SUPPLY
"C5 and C6 together for about 300V"

They had a very similar PS in the NEC 5500 series printers.
I was pointing out the unsafe location of the live terminals
to the printer engineer, telling him that the off-on switch
wasn't in the AC primary, leaving the exposed terminals hot,
when he reached in, and said "these aren't hot" and took hold of 300vdc.

That was a shocking experience, to say the least.. :eek:

As we say here in NZ, Yeah right, he's a bloody idiot, anyone who has worked on switching power supplies should have a healthy respect for high voltage electro's, engineer indeed.

I may have a simple cct for what you require, will dig it out, if I can locate the magazine article.

Mike

I found it, too old not using Fets, see Silicon Chip mag Nov 1991

This microchip note has some good info on MPPT AN1211 - Maximum Power Solar Converter - Application Notes - Details

Also see Google Image Result for http://www.intusoft.com/nlpics/78/MPPT.gif

for some info.

Mike

Thanks Mike,
The AN1211 looks very interesting and it might be fun to write the program to control it.
But, since I'm getting old and simple, I'm going to try to keep this project simple too. :D


I did get a hit on another 'pump' controller page. Power point Trackers

Chris has a crude drawing of three MPP curves and he has an interesting take
on what is 'good' enough to get the job done..

"Looking at figure 2 it may be noticed that the PV maximum power
voltage is only within a couple of percent for differing isolation levels .

This means that if a unit could be built, that would maintain the cells output
voltage at a fixed value, "say - at the most predominate isolation
and cell temperature", the PV cell would operate at close or near it's
maximum efficiency for all isolation levels. "

In other words, the very simple pump controller (see up top) can do a very
good job, without the micro-management of a micro controller.
All it has to do is be within range to get pretty good performance..

~~~

I'm not against adding some amount of complexity, if it's easy to do (and un-do).

If the idea of using a Photocell to lower the set-point voltage for cloudy days,
could actually work, then maybe a thermistor (NTC) across the
lower 3k3 (below the trim-pot) could bring up the set-point
voltage a tad, on those very cool days.?. (When PV works best).

If the thermistor idea worked, I wonder if just reading the air temp in
the shade, would be as good as reading the temp right on the bottom a PV panel?

I was wrong..
 

When I looked at this circuit, I assumed it wasn't a voltage step-down. But a voltage booster.
http://i220.photobucket.com/albums/d...ck_circuit.gif

Assuming the Supply is the PV panels, the switch a MOSFET and the load is just a big non-reactive 10 Ohm resistor,
it seems to me there would be AC type voltage applied to the load when the FET is turned off..
So, the circuit is a step down for DC, but maybe it can make a little AC.?.


FET On:
66vdc applied to load, via inductor. Magnetic field builds up, until the load is
drawing about 6.6A. 66v x 6.6a = 435.6watts.

FET OFF:
Magnetic field quickly collapses inwards, generating a pulse of high voltage.
Since the field is moving in the opposite direction, the polarity is reversed.
The diode feeds the negative voltage-current pulse into the bottom of the load.
And the +plus side is fed into the top of the load.
Since the reverse-polarity pulse voltage is much higher than +66v,
it's power is absorbed almost instantly into the 10 Ohm load.

So, my argument is, repeated jolts of reverse-polarity of HV during
the FET-Off time, will heat up the load more, because that voltage
is not limited to 66v (into 10 ohms).
So, on average, over time, the voltage seen by the load is going to be higher than 66v.
(The resistor load doesn't know + from -).

Higher voltage into a load, means it's going to dissipate more power..

Or, maybe at FET On, the XL of the coil is going to slow down the current enough
to mathematically cancel out the large pulse of HV when the field comes down.?.
Making the average voltage even out..?.

Maybe it's time get out the books again.. :o

That article at Power point Trackers
is very informative.

In the situation where you have your panels in series and supplying a purely resistive load, logically you want a circuit that supplies the max current through your load at all times. So a series current sense or a voltage sense across the load needs to be the feedback mechanism to the voltage switch circuit.

If the load voltage is switched somewhat lower than the panel voltage (thus higher current) then this would give the control circuit some latitude for feedback variation.

Perhaps the simple switch circuit you found above could be modified. I have never heard of that chip LM78S40, is it still available ?

Cheers
Mike

NATIONAL SEMICONDUCTOR | LM78S40CN/NOPB | LM78S40 Series MDIP-16 Pin Universal Switching Regulator Subsystem - Future Electronics

Yeah it still around for 76 cents.. And there are some good app-notes on the page too.

The more I look at those Pump drivers from 'Down Under', the more I like them.

The MiniMax http://www.voltscommissar.net/minimax/schemati.gif
needs no feed back, it just delivers the max wattage available.
The pulse action will kick in when the clouds roll in.

The pulse rate will depend on the rise time of the panels and the size of the input capacitor.

When the sun gets really dim, I think a photocell mod might be a neat way to get those last few watts delivered..

14:27 edit:
Really over-cast out right now. Less than 30w of power. 17volts coming in.
But, when I open the cut-off switch, the open voltage jumps right up to 78 volts.
I'll bet the PV could charge up some caps pretty fast, even in this light.
This looks like the perfect app for a comparator controlled MOSFET..


20:32 edit:
The max power voltage for these panels (as marked on the labels) is 17.4 volts.
Times 4 panels is 69.6v. If the 10 ohm load saw 69.6v, that's 6.96 amps
that's 484 watts. Which would make me very happy.


Typically, it's running low, about 62.6v.. Into 10 ohms, that's only about 392 watts of power.
Being 7 volts low, (and 92w short of the dream wattage of 484) might be curable with a Pump controller..

Night shopping online
 

Checked my mail this morning, and it seems that late last night,
I got real groggy and somehow ordered (10) LM339N quad comparators,
(1) Capacitor 4700uf 100V and (10) IRFP150 / IRFP150N MOSFET 40A, 100V.

I guess some items are cheaper by the 10 pack? ;)


I think that 100v MOSFET should be suitable for this app. I plan to find
a small heat sink to use with it. If they don't require too much gate drive,
maybe I can use two in parallel. Just to be safe.

7/22/2010 8:30am edit:
Morning Email said "You won"! My lowball $2 bid (+3.05 shipping) for (20) LM311 comparators (8 pin dips),
means I now have a lifetime supply of comparators! ;)

Haha, sounds like a fun project. It'll be interesting to see how this works out.

MPPT (Manual Power Point Tracking) :)
 

I've decided to try using the pump circuit, almost exactly.

Here's the real deal,
http://www.voltscommissar.net/minimax/schemati.gif

and here's my (unbuilt) hack of the same rig.

http://i46.photobucket.com/albums/f1...ar/pump2-1.jpg


Comments?

I've been collecting parts for this project. Most of them are on the bench now.
All I have to do is get moving!

After seeing the way this cool weather has boosted the PV output. (70v at 7.2a today)!
I'm thinking how nice it would be if the array output was set to 70v all the time.. :)

Can you please tell me exactly what i should change to increase the current rating to at least 12amp for the mini max? Or can you redraw the circuit so that it can handle more current at the output
(at least 12amp).
Also on your unbuilt hack of the same rig where you have 80V max PV input voltage. Can the circuit still operate off a lower voltage say for example a 12V panel and still have the capability to operate up to 80V if a bigger size panel is used?
__________________

I think it should work!
 

If you Google up irfp150n datasheet, you will find it can do about 100A if you can keep it at room temperature.
http://www.irf.com/product-info/data...a/irfp150n.pdf
And about 30A at 100 deg C. :)

So, if you only run it at 12A, you shouldn't need to attach a heat sink.
The reason I put 80v max on my diagram (unbuilt project),
is because I figured that was the limit my panels could do.
Now that it's cold, I see them at 85v every time the sun comes out.. :o

The irfp150n is designed to run at 100v max (V(BR)DSS Drain-to-Source Breakdown Voltage).

So, I would stay away from any PV source that went too close to 100V.
Cloud-Edge voltage power jumps could put you over the limit..
My best guess right now (untested) is that 85v is gonna be okay.

Will it work at a lower PV voltage.?.
My little 10W 12V panels are actually able to make 20 to 23 volts. With peak power at 17 to 18 volts.
http://i46.photobucket.com/albums/f1...lar/r031-1.jpg

I think it should work as drawn. If you PV voltage is lower, there might be a problem with the Zener diodes.
I picked 12 & 15 volt Zener, because I have some.
Actually those could both be changed to 10v Zeners.
And perhaps the 5v Zener could be changed to something lower? Like 3V maybe.

The important thing to remember is the gate input protection Zener should
be about 10V. I picked 12V, because I have them.. (I think the MAX limit is +or- 20v).

The second thing to remember is the series resistor's wattage.
R1, R2 & R3 are voltage dividers, and should be large enough
for your high voltage PV.

Let's say you had an 50v PV. The total resistance of R2 & R3 is 32k.
50V / 32,000 is 0.00156 amp.
34.37v across R1 and 15.6v across the pot. (V=RxA or E=RI in school).

The power dissipated by a resistor is equal to the VxA (P=IE)
So, 0.00156A x R3@15.6v=0.024 watts. So, a 1/8w resistor would be fine.
At 100v, you could use a 1/4w..

R1 is a 10k with the PV voltage across it, minus the 15 volts of the Zener.
A 50V PV means R1 gets 35v. 35 / 10,000 = 3.5ma (or 0.0035A)
P=IE (or P=IsqR) gives us 35x0.0035= 0.1225w (~1/8 watt),
so it would be best to use a 1/4w resistor there.. For 50v PV..
And 1/2W for 100v.. :eek:

I guess this means that I can still remember a little of Ohms law.. :cool:
But, this circuit, using these parts has not been tested yet.
So, there might be a few bugs to iron out.. Seems like there always is..
I might be using resistors at overly high values.?. Maybe I need to
scale them down and increase the wattage of them.?. Not sure yet.


Here's a handy chart..

http://www.rmcybernetics.com/images/...-watts_law.jpg

Xringer, check out this...it may help :)

fieldlines dot com/board/index.php/topic,144675.msg978354.html#new

so basically you are saying i can connect my 30amp 12V solar array to this circuit without making any modifications because the mosfet can handle it?

I think it can.
The BUK455 used in the Mini-Max pump board is rated for 60A.
The IRFP150N that I will be using are rated pretty close to that.
These transistors can be used in pulsed mode for a lot higher current.

If you can build the circuit and run it at 10 or 15 Amps,
while watching the MOSFET temperature, you can decide if
you are going to need a heat sink or not..

30 Amps is a lot of current. You will need to keep the current carrying
lines of your circuit, short and fat.

This circuit might cause RFI/EMI signals that will interfere with radio signals.
You might want to consider adding some by-pass caps to the lines.

Cheers,
Rich

That kinda looks like simulation software. A lot to learn.. :eek:
It might be faster for me to just build what I need and see if it works..?.

when you say bypass caps or you talking electroyltic caps or the ceramic looking caps that can connect either way and when you say to add them to the lines do you mean to both the input and the output lines?

At work, I've used a lot (non-polarized) ceramic disc caps to bypass DC lines going in and out of project boxes.
The only lines not bypassed are optical fibers.. :p

It's basically adding caps from noisy lines to ground. High frequency
voltages (Spikes) will see those caps as a low impedance and short to ground.
I've used .001, .01 & .1 uF disc caps with some degree of success.

Just adding them across the + & - lines can cut transistor switching noise too.
But also connecting caps to each side (of + & -) to a good ground is important.

when you stated in a much earlier posts that "These transistors can be used in pulsed mode for a lot higher current" does the mini maximizer circuit operates on pulses of currents at all times? and if yes does that mean that the fet should be on a suitable heatsink just incase i get very large peak current going to to the fet. I am correct?

Nope, not if the load is well matched to the PV, where the PV is voltage is at it's sweet spot.
It's maximum power point. (About 17.6v on the little 10w panel shown above).
That transistor will stay turned fully ON all the time..
But, when the clouds come over (and the panel can't deliver continuous full power to the load) , the pulses will start back up.




The spec shows the IRFP150N has 0.036 ohms (Max) when it's fully turned on.

If you were running 30 amps, there would be (30 x 0.036) about 1 volt
across the transistor. Ouch! That's 30 watts of heat! Yeah, a good heat sink
is going to be needed. Think 30 watt soldering iron!

I'm glad my PV never puts out more than 8A.. (8A x 0,036=0.288w).
I don't need no stinking heat sink.. :D

Cheers,
Rich

i have been studying the circuit and i was looking at the diode (SF52 superfast diode) that is across the output going to each of the motor rail and i was wondering if that diode would have to change if i was going to operate the circuit at a higher current say for example the 30A that i mention earlier?

That diode is there to protect the transistor from spikes that originate from the motor.

Anytime you apply power to an inductor, (like a motor coil), it creates a electromagnetic field.
If the power is switched off, the EM field is no longer supported (no current flow).
It collapses backwards, right into the coil. It was stored energy.

Since it's now moving through the coil windings in the opposite direction,
(back in, instead of out) it generates a sharp power pulse (or spike),
in the opposite polarity..

The spike voltage is the reverse of the applied voltage, that's why the diode is in the circuit backwards.
It's not used, until the backwards spike appears.

So, the rating of the diode you pick, depends on the size of the coils in your motor.
A big honkin motor might need a higher amperage diode.

The diode needs to be fast (a fast switching speed), so it can intercept
that spike (turn it into heat), before it can harm the MOSFET..

If your load isn't a motor or other inductor, you might not even need
a special diode. Just a plain old 1A silicon general purpose switching diode might work fine.
Since you only need it for the weak spike that comes from the EMF around the power wires to the load.

Most designers include protection diodes for the collapsing EMF..

http://www.kpsec.freeuk.com/images/diopro.gif

so like how i am planning to use a battery at the load instead of a motor then i can always option for the 1amp diode right?

Yeah, the battery and the output capacitor is going to help keep the inductive effects
of the long lines to a minimum. The 1A should work okay.
One of those 0.1uf disc caps across the line will help too.

SO! You are building a battery charger! That's interesting, since there are tons of
pretty good Solar battery chargers on the market for cheap money..
However, those with full MPPT are a good deal more expensive.
I own three little 12V 8A chargers (PWM type I think) that I use on my 3 little 10w PVs.
They work real well, since the loads on the batts are pretty low.
The old Honda CRV batt is only used once in a while on my Ham Radio receiver/scanner.



Using the pump-control circuit should work out pretty well. It's going to zap pulses
of sweet spot power into battery, kinda like a PWM charger.

But, you need to be careful not to overcharge your battery.

http://www.rectifier.co.za/images/Mo...orningstar.gif
As you can see, by adjusting the pot so the transistor fires at the 17V MPP,
you are going to get a fast, high current charge on your batteries.

But, once they are charged up, they need to be in 'float' mode and
that voltage is typically much lower than 17v..

I skipped any over-charge problems by using these..
http://www.ramsond.com/solarpanel/ra...rollerpic2.jpg
They shut off when the battery is fully charged.

http://www.ramsond.com/solarpanel/ra...specs2.jpg.jpg
Cut-off is at 14.2 volts..

yes thanks for the info. I really appreciate your help in explaining the whole schematics to me. I know a little about electronics and i am kinda have it as a hobby. I am going to run the output of the mini maximizer to my diversion charge controller which in turn is connected to my battery and whenever the battery reaches 14.8v the charge controller will send over the input current to damp load. What is the prefer setting of the mini maximizer to let the PV operate at its peak value? My PV panel VOC is 21V and rated voltage is 16.8V. What setting do you recommend that i set the mini maximizer to operate?

Okay, if your pulsed output going right into a DCC, you should set the pump-controller pot to fire the MOSFET
at about 17.6v or what every your panels have listed for 'Voltage at Pmax'..
AKA the Sweet Spot.. :)

You might be able to adjust it using an amp meter, during a slightly overcast overcast day,
when your batteries are not already at full charge..

Please keep us posted on your results.

I would really like to work on my MPPT stuff, but I'm up to my neck
in all kinds of stuff this winter.. :)

Cheers,
Rich

ok thanks. Also currently I have a large capacitor 12000uf 63V connecting to the output of my PV and going to my charge controller which has improve my charging system greatly so far. Should I remove it if I am going to connect the mini maximizer to the PV? what are the disadvantages/advantages of letting it remain to the input of the mini maximizer?

You can try it both ways. If you leave it on the PV, it should be near the the mini-max board.
Because, with a cap that large, there will be some serious current pulled out, when the transistor fires.

If you have the cap out on the panels and mini-max indoors, the pulse will cause a big EMF surge all down the line.
Put them close together, and the EMF field will be much smaller.:cool:

My guess is, AM radio and shortwave reception will be affected,
if the input PV lines are seeing big current spikes..

If the cap is indoors, next to the mini-max, it will pull power out of cap
at a good rate, and the PV will replenish the cap at more even rate,
(slower rise time), depending on sunlight conditions.
The cap will probably act as a big noise filter. :)

in regards to what you stated If I put the cap out on the panels and mini-max indoors, the pulse will cause a big EMF surge all down the lines. What exactly is this? Is this a voltage spike or voltage & current spike? And is this good or bad for the mini maximizer/or the battery?

Yeah, voltage and current. It's a power spike. A charged cap can supply
current almost instantaneously to the mini-max.
The cap is a quick-dump device. It there is a sudden sharp jump
in current flow, the inductance* of the line will make the line look
like a high resistance for an instant. And then, as the current flows,
the magnetic field will rapidly expand outwards..
When that field hits a nearby AM radio, it's going to jam the tunes with a burst of noise.
Noise that repeats with every new pulse.


*note:
XL or inductive reactance is normally a factor in AC circuits,
but it also affects DC switching circuits..
Here's a tutorial. Inductive Reactance

As you can see, XL is measured in ohms, like a resistor.
And if F (frequency) is increased, XL will go up..

You aren't using AC, but a square-wave with a real fast rise time,
is kinda like using a very high frequency AC..

So, there will be an instant resistance to current flow in the long lines.
It will impede sooth operation of your rig. Slowing it down a bit.
Since the panels will likely have a bit slower rise time (recovery time),
they shouldn't pulse the line so hard.(Like a loaded cap).

So, put cap indoors, right next to the mini-max.. :D