Over Amperage to Charge Controller - MPPT-60

[littleharbor]

Are your panels series wired? If so then you likely have a MPPT controller. If you are parallel maybe not. If parallel then try series wiring them as they should be on an MPPT controller. The thing is when series wired you'll only see current equal or less than a single panel, but at higher voltage coming into your controller. The controller does the step down and current boost. If you have a bogus MPPT controller the current output will stay equal to or less than a single panel, no boost.

[Seano]

Are your panels series wired? If so then you likely have a MPPT controller. If you are parallel maybe not. If parallel then try series wiring them as they should be on an MPPT controller. The thing is when series wired you'll only see current equal or less than a single panel, but at higher voltage coming into your controller. The controller does the step down and current boost. If you have a bogus MPPT controller the current output will stay equal to or less than a single panel, no boost.

Thanks for this new information, mate. I am really quite a novice at this solar business, and am really lucky to have found this forum and some people who know a whole lot more about my situation than I have been able to fathom in the past six or seven weeks.

Well, the User Manual for the MP-3735 states that only a single array maybe connected to the panel, so what I have done has been to hook both the 150W roof-top panels and the Anderson connector for the 120W portable panel into the MP-3735 all in parallel. I figured that it would not be able to tell the difference if wired in parallel because three panels on a cloudy day are no different to one panel on a sunny day.

I cannot really go with series entirely because the portable panel is only hooked in when I am camped somewhere in the shade and am looking to boost the solar with the portable in the sunlight, with around 10m of lead to get out from under the trees. I could run the two rooftop panels in series, but I am not sure of what reason this would be for. Currently I can pop any one of the three fuses for LHF, RHF, or portable, and read the individual amps of what is left, (or the differrence between the two values before and after to calculate the amps of the disconnected panel).

The volts on the portable are most always 20.5VDC and the volts on the roof-top panels are usually 16.5VDC. I have not yet gotten around to testing the roof-top panels in the sun, so they might also manage a higher voltage then, if I think of the panel as the opposite of a battery, and how the battery voltage discharges slowly overnight. On the other hand, I notice that sun or cloud changes the amps quite dramatically, and not so much the volts. The rooftop panels just might prefer 16.5V. I will have to find some data on the web to check their standard. ***

If I was to connect the two roof-top panels in series, but then piggy-back the portable onto the +ve & -ve in parallel, then that might be workable, although I do wonder about the result of a 20V portable hooked in || with a 32-40V fixed roof-top. That should try to equalise the result to somewhere around halfway between the two inputs, with preference to the higher current, which is likely to be the portable when it is connected, by around 3:1. (due to shade over van roof and fixed roof-top panels).

I would likely achieve a voltage increase from 16V to 32V for the fixed roof-top panels alone, in changing from parallel to series. When the portable panel is connected in parallel though, the difference would likely be something like 18V in parallel to maybe 24V in series, parked in the shade, and 28V when parked in the sun, (which is not when the portable would nornally be used anyway).

The main advantage I can see in connecting in series where possible (on the rooftop fixed panels), is that the current is reduced by series connection, and the voltage increased, so that the length of the cables will cause less impedance, therby increasing the wattage delivered to the controller. I will definitely connect the two rear panels in series now that you have assured me that it is okay to run a high voltage such as 60-80VDC into the MPPT controller.
Thanks again, Little Harbor.



*** Open Circuit Voltage 22.4V - Short Circuit Current 8.66A - Voltage at Power Max 18.1V
I take it that 18.1V is what I could expect from the fixed panels in the sunshine, or 36.2V in series together.

[littleharbor]

The difference you're seeing is likely the Vmp. of the roof top panels and the Voc. of the un connected freestanding panel.

The point I'm trying to make regarding your controller being an MPPT controller, or not, is when you series wire your roof top panels you should see possibly higher current to your batteries. If your current is cut in half when wired in series you can be sure that you have a bogus MPPT controller.

The difference between the two types of controllers is this; PWM, current in = current out., MPPT, watts in = watts out.

Leave the freestanding panel out of the equation for now. The spec I saw for your controller for max voltage is 65 volts. That in itself doesn't guarantee an MPPT controller, all it means is that is the max voltage that controller can handle.

[Seano]

The point I'm trying to make regarding your controller being an MPPT controller, or not, is when you series wire your roof top panels you should see possibly higher current to your batteries. If your current is cut in half when wired in series you can be sure that you have a bogus MPPT controller.

The difference between the two types of controllers is this; PWM, current in = current out., MPPT, watts in = watts out.

Thank you for that rule which I have emboldened above, and most of all, sorry for being such a frustrating newbie about all this.

I see now that A purpose of rewiring the fixed panels from parallel to series is to test the controller; to determine whether it be MPPT or a pretender. Yes that makes sense, more sense than I was givng it before, because I have already run all the rooftop wiring and terminated all ends, right to the fuse block inside the van. To change from parallel to series now means an awful lot of back-and-forth for the circuit, because all +ve & -ve points are now inside here, not even 300mm from the top right of this browser window.

Before I was thinking that running in series would reduce the resistance in the wiring - higher voltage, lower current. Still that doesn't make much sense if what were 1m, 2m, 3m & 5m cable runs for LHF, LHR, RHF & RHR panels respectivelty is turned into four different 11m runs. On the next project, I'll wire them in series from the beginning. On this project, I can undo the wires from the panel and twitch them together in series to test the response from the controllerl.

As you mentioned that this Powertech MP-3735 'MPPT' controller cab handle up to 65V, I wonder if it would be suicidal to try to wire 4 x 18.1V panels into it in series. It might be best to try the test with just the two panels I currently have up on the roof and not try the two more I am still to collect from the shop next week.

I shall login and write up the results of the change from parallel to series early next week if not before. Right now I am hoping to make the best of the sunshine over the weekend to charge a rather depleted pair of 100AH SLA batteries. Thank you for putting up with me, for your patience, Little Harbor.

[inetdog]

Seano,
It is our pleasure to help newcomers to solar, as long as they, like you, are willing to listen to explanations and learn from them!

[littleharbor]

Thank you for that rule which I have emboldened above, and most of all, sorry for being such a frustrating newbie about all this.

I see now that A purpose of rewiring the fixed panels from parallel to series is to test the controller; to determine whether it be MPPT or a pretender. Yes that makes sense, more sense than I was givng it before, because I have already run all the rooftop wiring and terminated all ends, right to the fuse block inside the van. To change from parallel to series now means an awful lot of back-and-forth for the circuit, because all +ve & -ve points are now inside here, not even 300mm from the top right of this browser window.

Before I was thinking that running in series would reduce the resistance in the wiring - higher voltage, lower current. Still that doesn't make much sense if what were 1m, 2m, 3m & 5m cable runs for LHF, LHR, RHF & RHR panels respectivelty is turned into four different 11m runs. On the next project, I'll wire them in series from the beginning. On this project, I can undo the wires from the panel and twitch them together in series to test the response from the controllerl.

As you mentioned that this Powertech MP-3735 'MPPT' controller cab handle up to 65V, I wonder if it would be suicidal to try to wire 4 x 18.1V panels into it in series. It might be best to try the test with just the two panels I currently have up on the roof and not try the two more I am still to collect from the shop next week.

I shall login and write up the results of the change from parallel to series early next week if not before. Right now I am hoping to make the best of the sunshine over the weekend to charge a rather depleted pair of 100AH SLA batteries. Thank you for putting up with me, for your patience, Little Harbor.

You're quite welcome. You have a good attitude and seem willing to learn. One recommendation I have is study the Sticky subjects at the top of the appropriate off grid discussions page, here's one to start with.

https://www.solarpaneltalk.com/forum/off-grid-solar/12v-solar-for-rv-or-camping-etc/21436-12-volt-design-and-safety-considerations

If your controller turns out to be a true MPPT controller you should be able to wire 4 panels in 2s2p configuration. 2 series pairs, then parallel the two series pairs output, resulting in double the voltage and double the current of a single panel. Safe voltage for your controller this way

[Seano]

https://www.solarpaneltalk.com/forum...considerations

If your controller turns out to be a true MPPT controller you should be able to wire 4 panels in 2s2p configuration. 2 series pairs, then parallel the two series pairs output, resulting in double the voltage and double the current of a single panel. Safe voltage for your controller this way

Thank you again for that link about safety and design considerations, good sir. Some of it still eludes me but what would life be without the occasional challenge to justify all the carbon emissions that us animals pump up into the sky as part of our inherent nature, eh?

Most importantly, I believe that I am now taking this thread somewhat off-topic, and it occurs to me that I should begin a new thread. However all of our correspondence so far has been here, and the thread has not grown through the weekend, so I suppose it might be more convenient to more of us if I persevere here until told otherwise. Please let me know if a new thread would be a better choice and I will think something up to summarise what is already written if I can.

Now, I just got back from a new solar panel shop, borrowed the ladder from the caravan park owners, climbed up on the roof and reconnected the two 150W roof-top panels in series. After thinking about it for a few days, it was much easier than I had first imagined. Rather than unwire and rearrange all the +ve and -ve endings down here in the van, I just popped the fuses for both panels, to disconnect the +ves, and then unhooked the -ve MC4 connector on one panel and the +ve MC4 connector on the other panel, and joined them together. Viola! Series!
There appears to be more than one way to skin an electric cat indeed.

Chris Sadler from the *new solar panel shop where I just bought the first of a pair of 200W panels for the roof warned me that it could be unwise to connect a pair of 150W 18.1V panels in series and then connect them to a pair of 60W 20.1V portable panels in parallel, and it appears that this is true after initial trials.

At one point this morning I was getting over 16A from the twin roof-top panels and the 120W portable (60W x 2 in ||), all in parallel. When I got back from town, the Sun was still shining, and after reconnecting the rooftop panels in series (almost 40VDC), and then connecting them to the portable in parallel (which puts out 20VDC), the MPPT controller seemed to get quite confused. At first I was getting 7 or 8A, but it kept reducing bit-by-bit until the amperage was down to around 2 or 3A.

I don't think that this was the controller getting confused, in fact. I think it was the panels themselves, having a hard time mixing such a variance in their respective collective voltages. It is probably too early for me to draw any reliable conclusions.

I thought I might see if I could rewire the two 60W panels on the portable into series too, so that it would put out around 40VDC, like the roof-top panels in series Then maybe they would all be happy with each other in series, living in perfect harmony once more. The only drama is that it would be a oneway street because I would have to split a length of twinax wire to run the +ve into one panel and the -ve into the other, There is also a diode in the positive line on both panels, and my electrical knowledge thinks twice before mucking around with any circuit which has a diode in it. I don't quite know what might happen, although I guess that the diode is there to stop battery current from flowing back into the panel/s, and it would not cause any problems if rewired in series.

Here are a couple of photos of the backside of the portable panel to paint another thousand words.






Does anyone know whether I might stuff things up completely if I was to simply run one -ve cable across into the +ve of the other panel (with the diode), and then split the twinax with the Anderson connector on the end and run the red and black sides to their respective sides, creating a 40.2VDC series circuit?

I would also like to know what the advantage of running a 2s2p (or actually 2s3p if we include the portable/s) circuit when the 100% parallel circuit seems to be working quite well, and I expect that the additional 400W of front panels will see the amperes up around the 30A or maybe 25% over the MPPT maximum at the most. If this makes the MPPT controller start to melt and smell bad, then all I need to do is switch out one panel, (and leave the portable in behind th seat besides.).

I read it in the link that series was preferable to parallel, but I still can't understand why, and whether that would apply to a solar system on my scale of 820W rated maximum, which will never likely happen based on the amps I've been reading through the MPPT controller's LCD screen.

* When I went to Jaycar to pay for and collect the second pair of 150W panels which Troy had written a quote for me for the four panels at $165 AUD each, Barry the bastard told me that the price for the two panels had risen from $330 for the pair to $448, which was more than I had to my name anyway. I think he was just trying to capitalise on the fact that I had already built the roof-rack to perfectly fit those exact 670mm wide panels, and he has always struck me as a dirty scummy bastard since I first had the displeasure of meeting him anyway. His loss, not mine. I walked out and spent my money across the road at their competition.

So now I am dealing with a more reputable and trustworthy establishment than the bastards at Jaycar Bunbury, and have already purchased the first of two 200W panels for $410 AUD pr., and the only concern is that these bigger panels are 100mm longer (no worries), and also 138mm wider, so I will have to spend the rest of this week removing the entire roof-rack I have been building for the last two months and resizing the front panel sections to fit the larger panels. It will cost me a fair bit more than Jaycar wanted to rob me of last Saturday, but it's the principle of the whole thing, y'unnerstand?

You don't break a promise halfway through a transaction and you don't renegg on a written quotation and you don't mess around with Seano. (... or spit into the wind.)

[littleharbor]

A very likely reason the current into your batteries was so low is they were likely fully , or nearly fully, charged and not accepting any more current.

I don't recall your battery bank size, if you already included it but you need to have a proper ratio between amp hour size and charging amps.

After you add the other 2 150 watt panels you might want to leave the smaller panels out of the equation.

[Mike90250]

That appears to be an odd way to wire a diode into a system. It looks like it's in series for full time "blocking" and not a bypass diode. That means you loose nearly a whole volt across it, and it's going to be running quite warm all the time.

[Seano]

A very likely reason the current into your batteries was so low is they were likely fully , or nearly fully, charged and not accepting any more current.

Oh how I wish. It's doubtful to my limited understanding of these new deep-cycle batteries because it was only a couple of days ago that I woke up to greet the bright red LED screen of my 'house battery' voltmeter reading 5.8V after going to sleep with 12.1V the night before. I have recently been running the diesel for one hour at a time, last night twice between 16:45 and 17:45, then 18:30 to 19:30 just to try and charge the batteries as fully as possible before bedtime. They have been quite disappointing recently, reducing by around 0.3V / hr after switching off the diesel after sunset. For the past seven(7) months I've been following a 30 minute diesel policy. That was before installing any solar power at all, and meant running the diesel for 30 minutes around every three(3) hours between 06:00 and 19.30. I would still usually wake up with less than 7V at the times when I checked with a multimeter. That was before I bought the invaluable little $15 red LED voltmeter that shines all night at the foot of the bed. RIght now it is telling me 13.5V which is far better than I was getting before going solar.

I think that the batteries have been getting depleted over the stationary days because the deep-cycle batteries need more than 30 minutes for a reasonable charge in between 2.5hr discharge cycles. I am guessing here.

Another guess is that the most likely reason for a low current was some light cloud cover, and in the course of my test of running the twin 150W roof-top panels in series to make 39.9V, and those in parallel with the portable panel, (60W x 2 in parallel = 20.1V (or 20.5?)), the two different voltages may have confused either the panels themselves somehow, or the controller. My understanding of electrical engineering has been that if two different voltages are combined, then the resulting voltage will be somewhere between the two, depending on the input currents. How a 20.1V solar panel handles 39.9V being shunted through it is a question of which the answer is entirely beyond my understanding though. Or was it the controller?

I am not sure which, but after reconnecting the 150W roof-top panels back in parallel again, the controller was once more reading more normally at around 9A +or- 3A. If I am going to run the roof-top panels in 2s2p circuits, then I should take the giant leap and rewire my trusty little 120W portable in series too.

What I am still not quite sure about is why series would be preferable to parallel. If my total amps are not exceeding the 30A maximum and all the voltages are somewhere between 16 & 20V, then what would series wiring improve? I think the current system might suffice for now, but I would be grateful to know what benefits there are in the series wiring system over the parallel system I am using now. We are not yet exceeding 30A although we did enjoy a lovely 18.6A record in the sunshine around two minutes ago. The voltmeter has also reached a record 14.1V just now. This is purely on solar in the morning with the Sun shining on the van roof from the east. On the diesel I am lucky to ever see 13.9V by the way.

I don't recall your battery bank size, if you already included it but you need to have a proper ratio between amp hour size and charging amps.

After you add the other 2 150 watt panels you might want to leave the smaller panels out of the equation.

The 'house' batteries are 2 x 100AH Dia-Mec Chinese deep-cycle SLAs. I believe that they are also known as AGM because they have some glass matting inside the cells or something I I am only theoretically aware of. From what I have read of the specs, these batteries like to charge and discharge at 10AH, so the most current I need to charge the batteries at their preferred rate is 20A, I calculate.

The Ford Transit alternator is rated at 110A but I am not sure if that is achieved whilst idling at 750rpm. In any case I believe that it is more than the pair of 100AH deep-cycle batteries can use because even when idling, the diesel and alternator should produce more than 20A by far.

HOUSEHOLD APPLIANCES.

I have one Waeco Dometic 14l 'cooler', not a true fridge like an Engel, but just an insulated box with a fan that blows the hot air our the top or something like that. It needs 4A when running but only runs around a quarter of the time if one leaves the lid closed most of the time. That is the #1 appliance because it runs 24 hours a day and keeps my veges, eggs & cheese, and beer cold so it is highly vital. Especially the latter if all else goes, "kaput".

The #2 appliance is this Toshiba laptop which pulls 95W when all four of the CPUs are hard at work. There is a very noticable difference in the system voltage between sitting here typing text and the high drain on the batteries when watching a movie at night. That is when Toshi the laptop is likely drawing around 8A, and at times in the past it has set the warning piezo buzzer of an inverter sounding. Pause the movie and the buzzer shuts up again. Yes, the laptop computer probably draws around four times the power that the Waeco cooler does, I would estimate. Let's say 3A average, because I don't usually watch movies except just the one after 18:00 at night.

Let Appliance #3 refer to everything else on the 240VAC inverters. There is a 1000W which I am using exclusively now, and also a small 300W item which I was previously using for the laptop computer, the USB laptop speakers, USB phone charger, USB mobile-broadband modem and music keyboard. Previously I only used the 1000W inverter for charging the electric bicycle battery, (4A), the 240VAC vaccumn cleaner, cordless drill battery charging, jigsaw & angle-grinder. These are the heavy duty 240VAC electricals. Power tools in the van, man!

Because I noticed the little 300W inverter was getting quite hot when in use, and heat is wasted power in the summertime, I am now running all the 240V electrics off the 1000W inverter. If I need to use the vaccumn cleaner or angle-grinder, I will plug all the computer and USB back through the 300W inverter temporarily so as to not cause too much disruption to sensitive gadgets with power tools which can cause significant voltage changes, but usually I use the 1000W inverter for everything in the hot weather because it runs far cooler. In winter I will likely revert to the 300W for the small gadgets because the extra heat it puts out will be of higher value in keeping the operator warm in the cold weather.

Oh, and the music keyboard is now running straight off the battery because it happens to be 12VDC so it no longer needs the transformer. Lucky. This would be Appliance #4, in conjunction with a 6" 12V pedestal desk fan, a 4-way 12V NiMH AA-cell battery charger to charge the digital camera batteries, and a bedside reading lamp which is 12V LED so probably draws quite low current.

In total,
Appliance #1 - Cooler is 1A average,
Appliance #2 - Laptop is 3A average,
Appliance #3 - Everything else on 240VAC inverters probably around 2A average for modem, speakers, phone chargers, occasional power tool or vaccumn.
Appliance #4 - Keyboard, fan, NiMH charger, bedside lamp. Around 1A average over a 24hr day if yer lucky.

There are around 7A being used on average throughout the day from 06:00 to 20:00, which reduce to around 1A just for the cooler overnight, Charging the pair of 100AH house batteries wants 20A optimally, so somewhere between 25 & 30A from the MPPT is probably about the ideal for sustaining my current electrical living arrangement with optimal house battery charging capacity.

The only three additions I can see in the coming year if I am fortunate will be a proper Engel fridge, (which also uses 1A like the current cooler), and then I have two 12V bilge pumps packed away in the hardware box which I hope to use to pump cold water from a future under-floor tank up to sink height, shower height, and to the roof to the hot water tank, and then a couple of 700W kettle elements or somesuch to heat the water in the early morning so as I can take a shower before sunrise. It is hard to calculate the power for things which I have never tested, but the Engel fridge will use the same as what I am using now, apparently, and the water pumps and kettle elements for hot water will be used for only a small part fo the daily routine. The HWS will be a major drain of power, but I am not yet cluey about it except that it will only be for around 15 minutes in the early mornings, when I am too much of a sooky baby to take my cold shower like a man.

I think that 30A is probably just sufficient for the current and proposed future needs. There is always the diesel to fall back on when the skies are cloudy.

TO BE CONTINUED (exceeded 11,000 chars).

[Seano]

VIRTUES of MY PORTABLE PANEL.

It is a necessary part of the system, the portable, because whenever possible I try to park the van under as many trees as I can to reduce the heat inside here. Parking in the sun sheds light on the roof, and that radiates through my home-made insulation and roof-lining into the van, and sometimes makes me a bit dizzy when it is only 37*C outside but 47*C in here. When all the roof-top panels are fitted across the entire roof, this will reduce the heat inside the van, but not completely. This is why I try to park in the shade wherever possible to keep cool in the hot weather, and use the portable on its 3pc 12m of lead to gain the most of the current through the system. In the mornings when the Sun is near the van's incoming Anderson connector, only 3m of lead is needed, and then in the afternoons the whole 12m must be connected to put the panel down the hill past the trees on the west side.

As the weather cools down here approaching winter, then parking in the Sun will be a better idea, to warm the interior of my Transit van, and with a little luck, the portable will not be needed so much. Shorter days, more clouds and more acute angles to the Sun from the Southern Hemisphere might see the portable required to add what little it can to the whole power system though. In this 'summer parking' habit, it is the 120W portable that produces around two or three times the current of the 300W total on the roof, because I keep moving it around so it is pointing straight at the Sun, while the roof-top panels are often under the shade of trees, and fixed in position facing directly up.

In winter if I can revert to parking in sunny places, the portable will produce closer to its rated wattage compared to the 700W on the roof, although the capacity to angle the portable facing the Sun, while the roof-top panels will always face straight up, might see the portable put out more than its specified ratio. Hopefully the roof-tops will be enough most days, because moving the portable panel around is both a strain and an imposition on my time, albeit minor in both cases. It is also a security risk though, because I cannot leave the vicinity of the van when the portable panel is operating, due to its value and the ease of which someone could unplug it and walk off with it if they wanted to.

In conclusion, it would be nice to be able to do without the portable panel for convenience and security reasons, but right now it is producing the bulk of my power, and I can envisage that in winter, when I park in the sun to add power through the roof-top panels, the total solar power will be less than in summer, and until I can be sure otherwise, the portable might seem to be quite a necessity for all seasons.

Thank you for reading this epic monologue. I hope that clarifies some of the details I have neglected to mention before. The good news is that right now the Sun is shining and the little LED voltmeter is now reading 14.2V which is only 0.2V below my theoretical 100% target of 14.4V.

[Seano]

That appears to be an odd way to wire a diode into a system. It looks like it's in series for full time "blocking" and not a bypass diode. That means you loose nearly a whole volt across it, and it's going to be running quite warm all the time.

Thanks Mike. Your understanding of diodes far exceeds mine and is most welcome. I have figured that the two diodes are there to stop current flowing in a reverse direction somehow. If for instance it is night and the battery voltage is 12V but the solar panels are producing 0V. I am not sure if this is any kind of a wise notion though. My understanding of electrical systems is rather more automotive than electronic, and diodes, capacitors, resistors, FETs and stuff falls into the 'electronics' category of which I know very little.

Series and parallel are about the most complicated aspects of electronics that I can say I am somewhat understanding of.

Therefore assuming that someone can explain to me why it is that wiring 2 x 60W + 2 x 150W + 2 x 200W panels together in a 2s3p configuration, (series, series, series, then hook the three pairs together in parallel to average 40V rather than 20V if my shorthand is misleading), would I be reckless to attempt the following:

1. Disconnect the black half (-ve) of the twinax cable joining the two 60W panels in parallel.
2. Move the red terminal on the joining cable from the +ve to the -ve of one of the two terminal boxes, let's use the RHS one.
We have now rewired the two 60W panels from parallel to series.
3. Split the twinax output cable with the Anderson connector on the end from the other end, so that the two +ve & -ve ring (eye) terminals are spread apart.
4. Connect the black -ve of the output cable to the -ve of the LHS terminal box and the red +ve of said cable to the +ve of the RHS box.

This should theoretically combine the two 60W halves of the 120W portable panel from 20.1V parallel to 40.2V series, and cause the total voltage to coincide more closely with the 39.9V totals of the 150W x 2 and assumedly the 200W x 2 panels which I will also rewire in series instead of parallel.

Would you support my guess that the two diodes will not affect nor be affected by such a change in configuration because they look big and hefty enough to handle the doubling of voltage if they have to.

This is my concern with rewiring the portable to a series configuration. Would it blow up the diodes, rendering my $299 portable panel useless ever after?
,

[Mike90250]

Those are weenie little diodes, might pass a 15A surge, but only about 3 watts dissipation. Can you read the part number off them ? Could start with 1N _ _ _ _ _


If you have drained a 12V bank down to 6 or 7 volts several times, be prepared to kiss the batteries goodbye, they are toast, so freshly dead they don't know it.

Back feeding battery voltage into panels is not very efficient, and can only account for a couple watts of loss. Backfeed protection is included in modern controllers. Flip the breaker to the panels / controller and shut them off at night.

......from the *new solar panel shop where I just bought the first of a pair of 200W panels for the roof warned me that it could be unwise to connect a pair of 150W 18.1V panels in series and then connect them to a pair of 60W 20.1V portable panels in parallel, and it appears that this is true after initial trials.

At one point this morning I was getting over 16A from the twin roof-top panels and the 120W portable (60W x 2 in ||), all in parallel. When I got back from town, the Sun was still shining, and after reconnecting the rooftop panels in series (almost 40VDC), and then connecting them to the portable in parallel (which puts out 20VDC), the MPPT controller seemed to get quite confused. At first I was getting 7 or 8A, but it kept reducing bit-by-bit until the amperage was down to around 2 or 3A.......

Can you plainly tell us the Vmp and Imp of the panels (and quantity of each)
60W
120W
150W
200W

You can series panels with the same amps
you can parallel panels with the same volts

But we have to know the specs of each panel.

[Seano]

Those are weenie little diodes, might pass a 15A surge, but only about 3 watts dissipation. Can you read the part number off them ? Could start with 1N _ _ _ _ _

If you have drained a 12V bank down to 6 or 7 volts several times, be prepared to kiss the batteries goodbye, they are toast, so freshly dead they don't know it.
Back feeding battery voltage into panels is not very efficient, and can only account for a couple watts of loss. Backfeed protection is included in modern controllers. Flip the breaker to the panels / controller and shut them off at night.


Can you plainly tell us the Vmp and Imp of the panels (and quantity of each)
60W
120W
150W
200W

You can series panels with the same amps
you can parallel panels with the same volts

But we have to know the specs of each panel.

Thank you for such a prompt reply in what I presume to be the wee small hours in the New World, if that is where you are, Mike.

I have looked inside a terminal box on one of the portable 60W panels and the diode was soldered in and quite inflexible, but what I was able to read were the letters '6AIC' and then underneath were the letters 'MIC'. (Apostrophes added).

The reason I sometimes refer to 300W roof-top and sometimes 700W roof-top is because the 2 x 150W panels are currently installed and operational, and there are 2 x 200W panels to come, one of which is sitting across the front seats of the van, and the other in the shop still until I can collect it. Today there are 300W upstairs. Tomorrow there will be 500W and next Friday afternoon hopefully a full 700W. Add the portable 120 to get 820W total in ideal conditions.

I have read what I can on the decals on the back of the 2 x 60W portables, and the 200W fixed panel in the front cab, and taken the data for the 2 x 150W panels from the Jaycar website. At least they are still good for something.

Let me try and list the specifications in some kind of organised and readable order and forgive me if I should err, because Voc, Vmp and Imp are still brand new terms for me, only having read them in your previous post. So, E&OE:

Portable Panel/s - 60W x 2 = 120W
Voc = 21.6V
Vmp = 17.6V
Imp = 6.8A
Isc = 7.08A
MaxV= 1000V
Diode Id: 6AIC / MIC

Roof-top Panels (rear) - 150W x 2 = 300W
Voc = 22.4V
Vmp = 18.1V (voltage Max on website specs)
Imp = 8.31A (current Max on website specs)
Isc = 8.66A (short circuit on website)
MaxV= ????
Bypass diode included = YES

Roof-top Panels (front) - 200W x 2 = 400W
Voc = 22.32V
Vmp = 18.00V
Imp = 11.11A
ISC = 12.00A
MaxV= 1000V
Max Overcurrent = 15A

I apologise if this 3 x 2 combination causes you some frustrating arithmetic, and thank you for your efforts in helping me work this out before I make some fatal mistake and waste all my time and money or worse.

Lastly, in reply to your warning about draining Sealed Lead Acid batteries down to 5V. It has happened almost every other night since I bought the first one in July last year, and around every third night since I bought the second one in January this year. I have been hoping that they might recover if I give them the right duration of TLC from the diesel, and keep on trying. Two(2) hours of total diesel charging with the 110A Ford alternator every night around sunset.

As it happens, last night I switched off everthing except the Waeco food cooler, including the inverters but NOT the MPPT controller which was still connected to the roof-top panels because I have not yet wired in the four switches but only the fuses so I can only remove the fuses to cut the circuit and have hoped that the controller is smart enough to not require so much fiddling around on my part.

It worked because this morning before sunrise when I woke up we were still getting 12.1V purely from the pair of 100AH SLA batteries. Only the cooler was running. I think I may have been lucky as my batteries have proven to be able between them to hold a 12V charge overnight. I am trying very hard to maintain these two Chinese cheapie batteries at above 10V and hopefully above 12V for the rest of their lives, even if it costs me more diesel and upsets the Sky God from the fumes. With a bit of luck, when the additional 400W of front solar panels are wired in, then the daily charge will be enough to restore a good portion of those original 200AH, although I can accept that neither one would still be in its youth anymore, and 100Ah is just a faded memory for the two of them.

PS: Now the third 200W panel is installed on the RHF corner of the roof and connected to the MPPT controller. Testing the amperage with that panel alone I recorded 0.6A which is much the same as the other two 150s at the rear because the van is entirely parked in the shade now at this time of the afternoon, and shall be so until tomorrow morning. There are 8.2A currently going into the controller, mostly from the portable which is out in the Sun.

Tonight I shall remove all the 20A fuses to guard against any unexpected surprises in the morning, and then carefully insert one fuse at a time when the roof of the van is in (hopefully) good morning sunlight. If 300W + the 120W portable could only reach just over 18A this morning, then I estimate that the additional 200W on the front should see the total amperage not exceed 25A when all the fuses are inserted. It will be an interesting 75% milestone in the morning and boyo is this old fellow really looking forward to it.

Of course, if the sky is clear and the sun is shining when the full 700W contingent is all operational, then there will be no need to use the portable at that time, so hopefully, with some careful usage, it will be hopefully unlikely to exceed the 30A of the MPPT controller. If it does, I can remove fuses. When this prototype is all working as well as possible, all the wires will be carefully run in all the right places using cable ties and I'll finally be able to hook up the 4-way switch panel which is installed in the masonite board but not yet wired in. Then the fuses will be able to rest in peace.

Okay, it's four o'clock in the afternoon here in a few minutes. Time for a beer. See you tomorrow, or in around twelve hours. Thank you.

[Mike90250]

So distilling this down - the panel voltages are pretty close to each other. The amps are very different

I'd series each "like panel" the 2 60's, and so on.

Portable Panel/s - 60W x 2
Vmp = 17.6V
Imp = 6.8A

Roof-top Panels (rear) - 150W x 2
Vmp = 18.1V (voltage Max on website specs)
Imp = 8.31A (current Max on website specs)


Roof-top Panels (front) - 200W x 2
Vmp = 18.00V
Imp = 11.11A


After they are series'd, then you parallel them, each series string gets it's own fuse. the 60's get a 8A, the 150's get a 9A and the 200's get a 12A

You should get 35v at about 25A, and when you're all said & done, about 14V @ 50A with a good MPPT