Need Help Please.

[ICT]

When you parallel panels, their voltages do NOT add. If you put your 3 panels in parallel, they stay 46.2Voc. Their CURRENT adds, so your Imp would be 3X 8.48A (about 25A INTO the charge controller).

Essentially, if you parallel them, the only thing you have to worry about is the charging current. If you want the easy mode:

Outback FM-80
Victron 150/70

Yes, the Victron can only handle 70A, but you'll rarely produce more than that, so you're not giving up much. There's also a 150/85, but it may not be worth the extra $ for what little you'll get.

Will also lists other options here:

DIY Off Grid Solar Charge Controllers

Building a vehicle mounted solar power system? Let me help.

www.mobile-solarpower.com

So why couldn't I use 150/60 not the 80? I don't really care if I don't charge at the slightly higher rate.

 

[ICT]

Either series or parallel should work.

Shading? Whether panel has 2 diodes or 3, I think one section of a panel shaded would lose much/all of that panels production in parallel configuration (MPPT peak is voltage from other two panels.)
In series, MPPT finds voltage from sum of all non-shaded sections (less diode drop of the shaded one(s)

But there may be a greater inefficiency of switcher dropping voltage further, from 3 series to 12V battery instead of dropping from the voltage of single panel.

In the series configuration, the diodes had better be able to do their job, because current will be pushed through them.
In parallel, if the shaded one doesn't contribute, its diode doesn't have to carry current and dissipate heat.

This sure is complicated. So one of the reasons I am over paneling is when I first started reading the forum it became apparent that potential energy is rarely achieved no mater what. I might tilt panels in the future but based on my limited needs I am hoping that my over paneling will compensate for the inefficiencies. I try to live simply and not stress out. I will not move my rig every half hour to make sure I get a couple more amps charging. Hope this makes sense.

 

[chrisski]

Don't you mean a 12v to 24v converter? Using your vehicle's 12v system to charge your 24v system?

Victron might recommend having the charger be closer to one battery or the other but if not you could try making the 12v run shorter since the 24v side will have half the amps.

This is a fifth wheel trailer so no alternator to hook to for charging. If I make the solar batteries 24 volts, those will be charged by the sun, but I still want a way to keep the fifth wheel breakaway brake battery charged.

It gets the 12 volts from the battery, and the battery gets a little juice from the 7 pin trailer jack at 12 volts, but I don't see how a 12 volt trailer pin will keep a charge on the battery.

I want the 24 volt upgrade to keep the amp load on the wiring lower so I can run higher wattage devices off my Inverter.

This 24 Volt is a project I'm going to seriously look at and plan, but over the next couple of weeks, I'm "flipping the on switch" for the 12 volt build, so I got to get that down before I spend too much time on the 24 Volt upgrade/

 

[ICT]

This is a fifth wheel trailer so no alternator to hook to for charging. If I make the solar batteries 24 volts, those will be charged by the sun, but I still want a way to keep the fifth wheel breakaway brake battery charged.

It gets the 12 volts from the battery, and the battery gets a little juice from the 7 pin trailer jack at 12 volts, but I don't see how a 12 volt trailer pin will keep a charge on the battery.

I want the 24 volt upgrade to keep the amp load on the wiring lower so I can run higher wattage devices off my Inverter.

This 24 Volt is a project I'm going to seriously look at and plan, but over the next couple of weeks, I'm "flipping the on switch" for the 12 volt build, so I got to get that down before I spend too much time on the 24 Volt upgrade/

Sounds like a different thread should be started.

 

[DASH]

Not to make things even more complicated, but performance of most (lead type) batteries drops substantially in very cold conditions. Most battery manufacturers will have charts available showing the performance drop against the temperature of the battery.

Also, most Lead Acid Batteries can only take a charge at a fraction of the C rate. I think it's around .20C at room temperature. Something to keep in mind. I have heard that some of the Outback MPPT's are equipped where You can adjust the maximum current that will go into the battery regardless of how much current is being generated by the solar panels. Many MPPT's don't have that feature. It's a great feature as You can substantially over panel to cover low sunlight conditions, and not have to worry about damaging your batteries, of course You still need to stay in spec of the MPPT. Check with the Outback Representative, but I think the Outback MPPT's have a feature that takes into account the additional voltage that can occur on cold days. Personally, I would get an oversized EPEVER controller (less expensive) and not the Outback, so in the future I could add an additional panel of the same make and model of the other panels for additional power in the future.

The whole solar process isn't that complicated for a system like You wish to build. I built one similar and it's working like a charm.

 

[Deleted member 9967]

Not to make things even more complicated, but performance of most (lead type) batteries drops substantially in very cold conditions. Most battery manufacturers will have charts available showing the performance drop against the temperature of the battery.

Exactly. While not even close to what the OP is doing. My mobility scooter went from 20 km down to just less than 7 km on the lead acids once the temperature went down to about 9 Celsius.
Cold affects them dramatically.

EDIT: For reference they were 2 - 50 amps that were set up for 24 volts.

 

[ICT]

Not to make things even more complicated, but performance of most (lead type) batteries drops substantially in very cold conditions. Most battery manufacturers will have charts available showing the performance drop against the temperature of the battery.

Also, most Lead Acid Batteries can only take a charge at a fraction of the C rate. I think it's around .20C at room temperature. Something to keep in mind. I have heard that some of the Outback MPPT's are equipped where You can adjust the maximum current that will go into the battery regardless of how much current is being generated by the solar panels. Many MPPT's don't have that feature. It's a great feature as You can substantially over panel to cover low sunlight conditions, and not have to worry about damaging your batteries, of course You still need to stay in spec of the MPPT. Check with the Outback Representative, but I think the Outback MPPT's have a feature that takes into account the additional voltage that can occur on cold days. Personally, I would get an oversized EPEVER controller (less expensive) and not the Outback, so in the future I could add an additional panel of the same make and model of the other panels for additional power in the future.

The whole solar process isn't that complicated for a system like You wish to build. I built one similar and it's working like a charm.

Great comment on batteries. As a life long resident of the frigid North we learn this very early in life. Years ago we not only plugged cars in for engine block heaters some of us also had battery warmers that we plugged in. I doubt I will ever use this unit in cold weather other than driving it away from the cold. Many issues like frozen water tanks etc. Plan to get out of the cold before it hits. Also I really appreciate the SCC discussion on the Outback. That is the kind of information that is very helpful as I learn. Also will look at the EPEVER. What size would you suggest? I did not include this earlier but I do have a gas generator that I can run to charge batteries if weather conditions are such that solar can't keep up. It is small and sips fuel so good back up. First attempt at solar but understand it has limitations. Again thanks everyone for the replies.

 

[Hedges]

I have heard that some of the Outback MPPT's are equipped where You can adjust the maximum current that will go into the battery regardless of how much current is being generated by the solar panels. Many MPPT's don't have that feature. It's a great feature as You can substantially over panel to cover low sunlight conditions, and not have to worry about damaging your batteries, of course You still need to stay in spec of the MPPT.

You would want the charge controller to go ahead and deliver higher current if it is being drawn by inverter, not going into batteries. That could be accomplished either with a shunt or with datacom if the hardware was smart enough. I've read here that some brands will do that, where their charge controllers and inverters of same brand communicate.

My system accomplishes that because the battery <--> AC inverter/charger are one unit, and PV is AC coupled with separate GT inverters. It is also compatible with DC coupled charge controllers, but apparently only charge voltage is communicated, not current. If SCC and their PV were sized large enough to exceed 0.1C or 0.2C target, don't think it can reduce how much those deliver; it only has control over its own charging powered from the AC side. My PV is presently large enough to deliver about 0.6C but system limits that to 0.2C. I think I could add up to 0.2C of PV on DC coupled SCC if I wanted.

 

[ICT]

Either series or parallel should work.

Shading? Whether panel has 2 diodes or 3, I think one section of a panel shaded would lose much/all of that panels production in parallel configuration (MPPT peak is voltage from other two panels.)
In series, MPPT finds voltage from sum of all non-shaded sections (less diode drop of the shaded one(s)

But there may be a greater inefficiency of switcher dropping voltage further, from 3 series to 12V battery instead of dropping from the voltage of single panel.

In the series configuration, the diodes had better be able to do their job, because current will be pushed through them.
In parallel, if the shaded one doesn't contribute, its diode doesn't have to carry current and dissipate heat.

Lots of great discussions but I guess I am still looking for answers to my original question. Here it is------So I am FINALLY getting close to installing Solar on my camper build. I have three 315 watt panels that I will hook up in series. Vmp=37.2, Imp=8.48, Voc=46.2, Isc=9.01. I am using lead acid batteries as it gets well below zero where I live. What gauge wire and circuit breaker should I use from panels to MPPT and from MPPT to batteries? What size MPPT? Brand suggestions? Sounds like I need a 250v if hooked in series but how about paralleled? Another Idea is can two SCC be hooked to the same battery bank? I might start off with two panels this winter and add the third next summer. Time is running short and I need to head south.

 

[Hedges]

Lots of great discussions but I guess I am still looking for answers to my original question. Here it is------So I am FINALLY getting close to installing Solar on my camper build. I have three 315 watt panels that I will hook up in series. Vmp=37.2, Imp=8.48, Voc=46.2, Isc=9.01. I am using lead acid batteries as it gets well below zero where I live. What gauge wire and circuit breaker should I use from panels to MPPT and from MPPT to batteries? What size MPPT? Brand suggestions? Sounds like I need a 250v if hooked in series but how about paralleled? Another Idea is can two SCC be hooked to the same battery bank? I might start off with two panels this winter and add the third next summer. Time is running short and I need to head south.

It depends.
There are several things you can optimize, like getting all power on the best day, or minimizing cost, or maximizing battery life.

You need to make sure you never exceed max voltage into the SCC.
You should keep charge current low enough to not shorten battery life.

Three PV panels, total 945W STC? 12V system? On a cold day with full sun, could deliver 80A into a battery with low SoC.
To capture that, would need 80A or larger SCC.
What maximum charge rate is recommended for your battery? If 0.1C, then you need 800 Ah of battery. for instance four of the batteries in my system, 6V 405 Ah, connected 2S2P. That weighs 480 lbs. If 0.2C is OK on occasion, only half that much battery.

Another way to limit charge rate is 40A SCC. It will never capture max PV, but will stay flat at 40A for several hours. During times of partial sun less is available from the PV panels, but if they still make 500W you'll get 40A.

The manual for my battery said it could tolerate inrush up to 5C, and for frequent deep discharge should be given at least 0.2C, so I set my charge limit to that figure.

I would rather have an inverter/charge controller system which knows when inverter is using power (I do, with AC coupling), allows 900W from the PV panels but only 40A about 500W going to the battery. Some all-in-one may do that. I think someone said Victron inverters and charge controllers could talk with each other and do that.

The cheapest way will be to select your battery, then select SCC for the peak current you ever want the battery to receive. Since the sun comes up slowly and delivers less power at first, that may limit max charge rate most of the time.

 

[ICT]

It depends.
There are several things you can optimize, like getting all power on the best day, or minimizing cost, or maximizing battery life.

You need to make sure you never exceed max voltage into the SCC.
You should keep charge current low enough to not shorten battery life.

Three PV panels, total 945W STC? 12V system? On a cold day with full sun, could deliver 80A into a battery with low SoC.
To capture that, would need 80A or larger SCC.
What maximum charge rate is recommended for your battery? If 0.1C, then you need 800 Ah of battery. for instance four of the batteries in my system, 6V 405 Ah, connected 2S2P. That weighs 480 lbs. If 0.2C is OK on occasion, only half that much battery.

Another way to limit charge rate is 40A SCC. It will never capture max PV, but will stay flat at 40A for several hours. During times of partial sun less is available from the PV panels, but if they still make 500W you'll get 40A.

The manual for my battery said it could tolerate inrush up to 5C, and for frequent deep discharge should be given at least 0.2C, so I set my charge limit to that figure.

I would rather have an inverter/charge controller system which knows when inverter is using power (I do, with AC coupling), allows 900W from the PV panels but only 40A about 500W going to the battery. Some all-in-one may do that. I think someone said Victron inverters and charge controllers could talk with each other and do that.

The cheapest way will be to select your battery, then select SCC for the peak current you ever want the battery to receive. Since the sun comes up slowly and delivers less power at first, that may limit max charge rate most of the time.

Great reply and I understood some of it. Thank you!!! So I am NOT trying to ring out every last watt out of the system. I much rather have longer battery life. My theory with the panels I bought was very few hours of the day can you get max efficiency. I also would be charging when driving. I also have a small gas inverter generator when solar could not keep up although with my very limited usage of electricity I think it might most of the time. I did see a video months ago that showed a curve of an over paneled but limited out put system. The theory was you would lose some available power at peak sunlight time but you would get more power earlier and later in the day. I think this was one idea you were talking about and that is what I am trying to do. I really like the idea of longer battery life. I have no issue with maxing out at 40 amp charge. As you mentioned I am hoping to never to even hit that with solar. I went with a smart charger off shore power of 45 amps. With that said can you or anyone else recommend a SCC or two if I hook my system up in Parallel? Also wiring size and circuit breaker sizes. Thanks again for any and all suggestions!!!

 

[Hedges]

Yes, over paneled. Choose your battery and determine what charge current it should get.
Most MPPT SCC have a maximum output current that isn't adjustable. Either choose model for current or one that can be adjusted. Or, make final battery capacity selection to match.

 

[chrisski]

With that said can you or anyone else recommend a SCC or two if I hook my system up in Parallel? Also wiring size and circuit breaker sizes. Thanks again for any and all suggestions!!!

I really think you need to take some measurements yourself and do some math. I’m rather reluctant to make a recommendation for specifics because you’d doing somerging different than me. I don’t want you taking what I did and then one of your wires is a bit longer than mine, and then this starts a fire, which could happen with max inverter loads on a poor designed system.

People here will be more than happy to give you whether or not they think you did the math correct.

For specific wire size, there’s just too much that needs to be taken into account about. For example. I was told that 10 gauge wiring is fine for putting 6 panels in parallel. A couple things wrong with that is 10 gauge shouldn’t have more than 30 amps, which I would push up to 36 amps with that setup, and voltage loss is fairly significant.

I started With a DC online voltage loss calculator and aimed for between a 1% and 3% loss for each of my runs. https://www.calculator.net/voltage-drop-calculator.html

I then aimed to have the max amperage I expected going through the wire to be so that it was rated for 60 C on the NEC ampacity charts https://www.wireandcabletips.com/what-is-ampacity/.

I then had a good idea of the wires size I wanted, and then looked the wire manufactures specs to ensure this wire is rated for what I want to use. There’s a lot of different types of wires, and for example zip wire/speaker wire should not be used in most instances.

Finally for circuit breaker sizing for panels, I did short circuit amperage X 1.56, and then rounded up. I would recommed single POle 150 volt DC breakers or Dual Pole 300 volt breakers rated to the amperage yuo come up with. For my 2000 watt 12 volt inverter, although the wiring can handle it, I do not want to operate max power so instead of using the 350 and fuse my calculations came to, I toned it down to 200 amps. That 200 amp fuse is on the battery and is a ANL fuse rated for primary battery protection, not a cheaper ANL fuse for audio, and certainly not any of the higher amperage audio breakers having an easier installation that is much cheaper.

My opinion is you should have one charge controller for each panel, VICTRON 100 volt / XX amps which I’m sure not many would agree with. This is the same thing as setting up the system in parallel, but gets gives some redundancy if you ever lose a cvharge controller, keeps the wires a smaller gauge compared to paralleling, a few smaller rated charge controllers are not that much more compared to a single higher amperage charge controller, and makes it easier to add future upgrades for various reasons.

 

[ICT]

I really think you need to take some measurements yourself and do some math. I’m rather reluctant to make a recommendation for specifics because you’d doing somerging different than me. I don’t want you taking what I did and then one of your wires is a bit longer than mine, and then this starts a fire, which could happen with max inverter loads on a poor designed system.

People here will be more than happy to give you whether or not they think you did the math correct.

For specific wire size, there’s just too much that needs to be taken into account about. For example. I was told that 10 gauge wiring is fine for putting 6 panels in parallel. A couple things wrong with that is 10 gauge shouldn’t have more than 30 amps, which I would push up to 36 amps with that setup, and voltage loss is fairly significant.

I started With a DC online voltage loss calculator and aimed for between a 1% and 3% loss for each of my runs. https://www.calculator.net/voltage-drop-calculator.html

I then aimed to have the max amperage I expected going through the wire to be so that it was rated for 60 C on the NEC ampacity charts https://www.wireandcabletips.com/what-is-ampacity/.

I then had a good idea of the wires size I wanted, and then looked the wire manufactures specs to ensure this wire is rated for what I want to use. There’s a lot of different types of wires, and for example zip wire/speaker wire should not be used in most instances.

Finally for circuit breaker sizing for panels, I did short circuit amperage X 1.56, and then rounded up. I would recommed single POle 150 volt DC breakers or Dual Pole 300 volt breakers rated to the amperage yuo come up with. For my 2000 watt 12 volt inverter, although the wiring can handle it, I do not want to operate max power so instead of using the 350 and fuse my calculations came to, I toned it down to 200 amps. That 200 amp fuse is on the battery and is a ANL fuse rated for primary battery protection, not a cheaper ANL fuse for audio, and certainly not any of the higher amperage audio breakers having an easier installation that is much cheaper.

My opinion is you should have one charge controller for each panel, VICTRON 100 volt / XX amps which I’m sure not many would agree with. This is the same thing as setting up the system in parallel, but gets gives some redundancy if you ever lose a cvharge controller, keeps the wires a smaller gauge compared to paralleling, a few smaller rated charge controllers are not that much more compared to a single higher amperage charge controller, and makes it easier to add future upgrades for various reasons.

Again everyone thank you so much for the comments. I also went with a 200 amp fuse as my thinking was just like yours. I always try and err on the side of caution and not push limits. If calculations would say a 10 gauge wire I would probably go with 8 or even six. I think this is very cheap insurance. I went with a 2200 watt inverter with my biggest load being a 700 watt microwave. What is interesting that I have not brought up before is vehicle alternators. I have had vehicles with 90 or even 140 amp alternator. Cable were not even close to the size I am using. Even way back in the day it was not unusual to see 50 or 60 amp alternators with just normal size battery cables and even way smaller positive wire on the back of the alternator. I am sure I am missing something on that thought but is real life for decades and the worked.

 

[Hedges]

1) It takes time to heat up a copper wire. The small wire can take 140 amps for a while.
2) The alternator can't put out 140 amps, at least not for long. Recharging a lead-acid starting battery from cranking, it'll be OK. Jump starting with a dead lead-acid battery and then recharging from alternator, may kill it (alternator instructions say not to do this). Charging a lithium battery without current-limiting electronics will kill it.

 

[ICT]

1) It takes time to heat up a copper wire. The small wire can take 140 amps for a while.
2) The alternator can't put out 140 amps, at least not for long. Recharging a lead-acid starting battery from cranking, it'll be OK. Jump starting with a dead lead-acid battery and then recharging from alternator, may kill it (alternator instructions say not to do this). Charging a lithium battery without current-limiting electronics will kill it.

I agree mostly. Over the decades I have seen people either leave something on, have a draw on the system or a bad alternator that kills the battery as dead as can be. Many times the battery was just fine. Hard to say if it had a long term effect on the battery. I have also seen this in boats with deep cycle batteries. Had a buddy that didn't check and assume his kid turned the cabin lights on. Next weekend battery was dead as can be. Batteries were fine. I also reminded him that's why boats have battery switches that turn off everything but the bilge pumps.

 

[Hedges]

It's the alternator I meant could be killed. A 140A alternator can't deliver 140A for long. Not enough cooling, and the 3 diodes for positive have poorer heatsinks than the negative. Some abuse smokes the windings (as seen in a video of charging lithium), but diodes are what as died on mine. Maybe just with age, the ones on the positive side run hotter.

Lead acid batteries do recover to a great extent and go on to a fairly long life. I would expect it was shortened if left empty for a week. They keep doing their job with a fraction of original capacity and amperage output.

 

[ICT]

It's the alternator I meant could be killed. A 140A alternator can't deliver 140A for long. Not enough cooling, and the 3 diodes for positive have poorer heatsinks than the negative. Some abuse smokes the windings (as seen in a video of charging lithium), but diodes are what as died on mine. Maybe just with age, the ones on the positive side run hotter.

Lead acid batteries do recover to a great extent and go on to a fairly long life. I would expect it was shortened if left empty for a week. They keep doing their job with a fraction of original capacity and amperage output.

I want to sincerely that everyone who replied!!! I thought this would be a simple solution but I guess not. I continue to learn and I see a real need in the solar world for simple solutions. I am sure it will get there. I think the all in one is probably where it will end up but will see. I believe the average DIY person is happy to use solar when it makes sense but does not want to become an electrical engineer in order to do solar. Not trying to slam solar but every industry has the few that are extremely smart with that industry, the majority are just average folk and a few that have no clue. Again thank you SO MUCH for replies.

 

[Hedges]

I want to sincerely that everyone who replied!!! I thought this would be a simple solution but I guess not. I continue to learn and I see a real need in the solar world for simple solutions. I am sure it will get there. I think the all in one is probably where it will end up but will see. I believe the average DIY person is happy to use solar when it makes sense but does not want to become an electrical engineer in order to do solar. Not trying to slam solar but every industry has the few that are extremely smart with that industry, the majority are just average folk and a few that have no clue. Again thank you SO MUCH for replies.

There are some all-in-one units marketed to consumers which are plug-and-play. They are sized for what they do, and a consumer just needs to understand maximum load and how long it can power a load. They tend to be small.

"Simple" would mean pre-designed, fixed capacity. Either too small, or bigger and more expensive than necessary.

Anything with batteries installed in an RV or house pretty much has to be a custom design. Each application has different requirements and constraints. There may be some packages pre-sized by the RV dealer.

Grid-tie systems avoid most of that, just pick the size you want. But they still require some electrical knowledge to do correctly and safely.

A good dealer can design a system for you with charging from alternator, from PV, number and configuration of panels, size battery and inverter. In that case you can probably install it yourself. But you need a dealer who can actually design the complete system, not just someone selling several components without doing the complete design.

 

[ICT]

There are some all-in-one units marketed to consumers which are plug-and-play. They are sized for what they do, and a consumer just needs to understand maximum load and how long it can power a load. They tend to be small.

"Simple" would mean pre-designed, fixed capacity. Either too small, or bigger and more expensive than necessary.

Anything with batteries installed in an RV or house pretty much has to be a custom design. Each application has different requirements and constraints. There may be some packages pre-sized by the RV dealer.

Grid-tie systems avoid most of that, just pick the size you want. But they still require some electrical knowledge to do correctly and safely.

A good dealer can design a system for you with charging from alternator, from PV, number and configuration of panels, size battery and inverter. In that case you can probably install it yourself. But you need a dealer who can actually design the complete system, not just someone selling several components without doing the complete design.

I guess I am just naive about solar. Wait, there is no I guess it is an absolute fact. I also think that maybe I am different than most but maybe not. I am not trying to maximize anything. Just hopefully put some charge back in the battery and not start a fire. The whole solar world to me seems so inexact and it has to be. Specially for travelers. Is the sun going to shine, am I partially shaded for part of the day, where am I in the country, how much will I be driving this week versus next week and on and on. I have had people tell me I must know all the energy that I will use(an energy audit) and go from there. Again which week, which month, hot, mild, cold, humid or dry? It will always be changing and many people install solar and then make changes. Many are limited by roof space. Many then add panels on the ground. I think this is probably very normal as who really know how they will use it now and six months from now. Pretty easy to size a furnace for a house. What part of the country, how many square foot and how much insulation. Furnace runs more when it is bitter cold and less when mild. When someone takes solar mobile I think there are just so many variables. In my case I THINK I over paneled for my needs. Someday I will probably find out. My guess is that answer will change based on conditions. Rain for four days and I don't think it matters how much solar you have or how many batteries you will be short. Okay you could have a ton of batteries but most aren't going to do that. My solution for times like that is I pull out my little generator and charge back up. I think the subject is fascinating and pretty cool that you get energy from the sun.!! Not trying to rant but just thought it would not be this hard especially with my expectations. To me, from watching a ton of YouTube videos is tilting panels. That sure seems to make a big difference Anyway thanks again and my quest continues.