rv off grid solar charging system questions.

full time rver

Hello all. My name is mike and my wife and I have recently become full time rv'ers. I have had to learn alot recently and find myself having to learn alot more. I have a basic understanding of ohm's law and a little experience with electrical applications but not much. basically my questions are regarding solar battery charging. I am currently running on a 12v system with eight 6volt batteries wired in four sets in series then in parallel. the deep cycle batteries are rated at 230 AH each which I believe gives me somewhere around 900 Ah total of battery life. I've upgraded to LED lighting throughout the rv. such a small draw it's not even really a factor. however I am running a 10 w fan for my propane heater about an hour a day. a 90 w LED tv about 3 hours a day. a 90 w dvd player about 2 hours a day (average estimate). and two low wattage 200 w mini space heaters about 5 hours during the night and im charging phones and laptops for an average of 2 hours a day which is very low w maybe 10w total in a day. also a 600w hairdryer for maybe 10 min a day. a 90w hair straightener for 10 min. I don't run the microwave but I do run a toaster oven for about 5-10 min every morning. it is about 1250 w. if I did the math right that's about 223AH a day rounded up and that doesn't account for the power loss through the wires. I have a 2500w continuous with a 5000w surge power inverter.(not a pure sine wave unfortunately but it does the trick). so with all the details of my system and power usage estimates here are my questions:

1. what should my total solar panel wattage be to get a full charge on the batteries every day? (remember I am completely off grid)
2. would it be in my best interest to get 24v panels and wire them through an mppt controller to charge the 12v system? and would they still provide enough amperage to charge a 12v system and if so would It be better to run them in series to increase the voltage or would I not have enough current to charge the system if I wired 2 in series for 48v or 3 for 60v? basically will the mppt controller account for the amperage drop?
3. I saw some peal and stick flexible solar panels and im not sure about the quality of them. they would make the install much easier but are they as good quality as the standard glass panels?
4. for the controller and panels are there any manufacturers that are tried and true that anyone knows about for a reasonable price?

thank you in advance. and forgive me if some of what im saying doesn't make much sense. im just trying to understand this a little better.

Cariboocoot

Re: rv off grid solar charging system questions.

Welcome to the forum.

Well you've got a little problem there. Four parallel battery strings on a 12 Volt system is just asking for trouble. 920 Amp hours total, and that's going to need a lot of charging power too.

Under normal circumstances you'd want a peak charge current of 10% of that: 92 Amps. There's only one charge controller that will do that: the MidNite Classic. And even then it will need ~1434 Watts of panel.

You can use any Voltage array through an MPPT controller to charge a system providing it is above the minimum Vmp for a system. In the case of 12 Volts that's array Vmp of 17.5 or more. Usually the 'GT' panels work out to be cheapest per Watt, and as such even with an MPPT controller are the better bargain for systems larger than 400 Watt array. You do not want the array Vmp to be too much higher than system Voltage because it decreases controller efficiency. Usually 2X is as much as you'd want to go (i.e. 35 Vmp on a 12 Volt system).

Look at the specs on those peal-n-stick thin film panels carefully. Some of them have very odd characteristics which make working with them difficult. Not likely to be as long-lived as crystaline panels nor as efficient (Watts per square area). Usually RV's can benefit from monocrystaline panels because they offer the most power per area.

"Reasonable price" is a relative term. Having seen a lot of 'bargain' equipment go bad quickly (or indeed not work at all) I feel it is better to spend more money once on something of good quality than to buy cheap stuff over and over. Most all name-brand panels and controllers are a good investment. No-name stuff is a gamble.

I think you may want to get a Kill-A-Watt meter and do some actual measuring of the AC Watt hours of any and all loads you can. Your battery bank is quite substantial at a maximum usable 5.5 kW hours DC. You might want to be making some lifestyle choices to reduce the power need. Also I know that RV's usually have 12 Volt systems for convenience sake, but for full-time off-grid a 24 Volt system offers several advantages.

A couple of basic info threads:
System Voltages: http://forum.solar-electric.com/showthread.php?15989-Battery-System-Voltages-and-equivalent-power
Array configurations: http://forum.solar-electric.com/showthread.php?16241-Different-Panel-Configurations-on-an-MPPT-Controller

zoneblue

Re: rv off grid solar charging system questions.

That big bank might have its origins in one of two use cases:
1. previous user had access to grid charging periodically, and could absorb them say once a week, then off grid rest of the week.
2. The old way of thinking when pv was expensive and lead less so

For the latter that needs fixing, its a broken model. For the former if that still applies to you then with care, you may be able to make it work.

As Coot says roof space is often the limiting factor for RVs. I have seen large motorhomes with 2kWp on the roof, but they are very much the exception. Lucky to have uninterupted roof area in those cases. Mostly theres aircon, antennas, vents and such that make the common and cheap large grid tie panels difficult to fit never mind layout efficiently.
Im with coot stick with mC, do some drawings to see how you can best fit various size panels on the roof, then see how far the kWh they can produce will take you. If money is no object look for high efficiency panels, they are pushing nearer 20% now.

Once we know the PV Wp that will physically fit, we can talk about what kind of controller and batterys to suit.

full time rver

Re: rv off grid solar charging system questions.

thanks for the quick responses. OKAY.i have some more questions. also some updates. I do have access to shore power twice a week ive been charging my battery bank for about 36 hours from Monday afternoon to Tuesday night then from Thursday afternoon to Friday night and that seems to be doing the trick. I have a 50amp charger converter for the charging from shore power. however i'm trying to get away from that. I guess one of my questions is: is my battery bank too large? I noticed "cariboocoot" said i'm just asking for trouble with four strings in parallel. i'm a little worried now. what trouble should I be concerned about? please elaborate. as long as I keep the batteries charged that set up should provide me with extended power capabilities right?? another question is: what would be the benefit for me in my situation with going to a 24 volt system and what would that entail?? would I have to re wire the entire rv? or just change all the bulbs to 24 v bulbs and the 12v water pump to a 24 v pump etc..? also I took some measurements of the open space on the roof and I have 13ftx2.5ft (x2) 4.5ftx2.5ft(x1)2ftx3.5ft(x2) 3ftx6.5ft (x1) 4ftx2ft (x2) and 2ftx2.5ft(x1) for a total of about 130 sq ft. any idea what this translates to in panel wattage for a GT panel? thanks.

full time rver

Re: rv off grid solar charging system questions.

I just read the link you added to the first response you gave to my thread "system voltages" now I see that I need 92 amps to charge my battery bank. I only have a 50 amp charger/converter. does this mean I cannot fully charge my battery bank with the charger I currently have? or something else? what are the negatives to how it is currently set up? and how do I fix it? anyone??

Cariboocoot

Re: rv off grid solar charging system questions.

What you're looking at:

The multiple parallel battery strings increase the chance for unbalanced current sharing between the strings. So some batteries get used/charged more than others. That means you won't get full power capacity nor full lifespan from the batteries.

If you have 12 Volt loads you must keep, you can stay with 12 Volt but perhaps use different batteries so that you have the same Amp hours but not in four strings. Fewer connections = fewer problems.

If the 50 Amps from the charger are all going to the batteries (not supplying loads at the same time which reduces the actual charge rate) it would be just above the recommended minimum of 5%. Low charge rate increases the risk of shortened battery life too.

The first question to be addressed is whether or not you actually need that much battery bank.

animatt

Re: rv off grid solar charging system questions.

I have peel and stick panels. They are much bigger for the amount of power they provide. Also it heats rv up much more as effectively not it has a dark roof. Panels mounted off the roof with an air space would stay much cooler. For me there were other considerations, like stealth pv and to draw less attention.

I also had to move vents and do a bit of work to get panels to fit. Currently have 464watts of flexible panels on the roof and i have some more traditional panels lane out. I to have same amount of battery but wired as 24v 460ah.

Matthew

full time rver

Re: rv off grid solar charging system questions.

animatt wrote: »

I have peel and stick panels. They are much bigger for the amount of power they provide. Also it heats rv up much more as effectively not it has a dark roof. Panels mounted off the roof with an air space would stay much cooler. For me there were other considerations, like stealth pv and to draw less attention.

I also had to move vents and do a bit of work to get panels to fit. Currently have 464watts of flexible panels on the roof and i have some more traditional panels lane out. I to have same amount of battery but wired as 24v 460ah.

Matthew

thank you Mathew. did you do the conversion for your rv to 24v yourself? if so could you detail the process you went through for that? thanks....mike...

Chris

Re: rv off grid solar charging system questions.

This is a long read, but probably the best RV solar info I've come across......I've based alot of my spring wiring upgrades off him.....the only thing I disagree about is his opinion on MPPT.

http://handybobsolar.wordpress.com/the-rv-battery-charging-puzzle-2/

animatt

Re: rv off grid solar charging system questions.

I left rv system as is. I use a converter to take the 24vdc and supply 12vdc.to the fuse box. This requires a converter that can be adjusted to battery voltage. Or you could disconnect the main driving batteries from the power system and just directly to aconverter. Either way works but depends on the converter.

I to like handy bob except his views on mppt.

Just to be more clear. Driving batteries are 12v.

But RE batteries are 24v. Solar panels charge to 24v bank. The inverter is 24v and powers ac loads like microwave, etc. My 12v appliances and lites pull power from the drive batteries. The drive batteries have their charge replace but the converter. Basically drive batteries stay in float 24/7. This way is probably a bit more robust. I did originally have the 24v power a 12v converter to power loads directly. But that converter died as it was a cheap one. I had a backip on hand and that is how my system got to where it is

Matthew

Cariboocoot

Re: rv off grid solar charging system questions.

animatt wrote: »

I to like handy bob except his views on mppt.

Matthew

I read through that link to see what these controversial views on MPPT were and all I saw was that he had a bad experience with what was obviously a cheap controller, and like so many other doesn't understand what it's all about. Did I miss something?

Typically MPPT controllers don't offer much advantage in RV applications because there are no long wire runs from array to controller nor is the array likely to be very large (and thus accommodating of cheaper 'GT' style panels). But sometimes you do want to squeeze every Amp you can out of the panels, even at a premium price. As usual "it all depends".

vtmaps

Re: rv off grid solar charging system questions.

Cariboocoot wrote: »

The multiple parallel battery strings increase the chance for unbalanced current sharing between the strings. So some batteries get used/charged more than others. That means you won't get full power capacity nor full lifespan from the batteries.

For more details about this look here: http://forum.solar-electric.com/showthread.php?14674

If you must have four parallel batteries, the above discussion contains a link to the smartgauge site that shows how to wire a bank of 4 parallel batteries. I wish that rather than explain how to do it, the smartgauge site should explain the reasons not to have so many batteries in parallel.

The main reason not to parallel batteries is as Cariboocoot mentioned: unequal current sharing. That is a problem even if all the cells start out perfectly equal... but in fact the cells never are all equal. When cells are produced, inevitably about half are below average. A few cells are outliers, much weaker than the others. The more cells you have in a battery bank, the greater the chance you will have a weak cell, and that cell will pull down the whole bank (a battery bank is only as good as its weakest cell). When you put four batteries in parallel you have four times the chance of getting a weak cell. The best system has the fewest cells. Obviously, a 2 volt system is not practical... a good design compromise is to have a single string of cells at the lowest voltage that is practical for your power needs.

--vtMaps

full time rver

Re: rv off grid solar charging system questions.

ok great. this is all very helpful information and ive really learned a lot in the pst few days (ALOT of information to take in in such a short period of time. kinda feels like i'm back in college) I do have another question and it's kinda off topic a little for this particular thread but not for this forum. I currently don't have any fuses in any of my strings either parallel or series.I've learned that this is a huge no no and I plan on fusing them ASAP. my question is for my setup what size and type of fuse or circuit breakers should I use in each string? also is it necessary to fuse my series strings for safety in case a tool falls across the terminals? or is that unnecessary? 8x 6v batteries @ 230ah each in four parallel strings. also my inverter has a built in fuse and an emergency shutoff its a cobra 2500 continuous with 5000 w surge modified sine wave inverter.do I need to put another inline fuse from the batteries? and one more thing, ive read that not only should you fuse each string on the positive side with a comparable fuse but you can also fuse the main ground to the battery bank with an emergency fuse?? is that something I need to do also or should consider? thanks....mike

Cariboocoot

Re: rv off grid solar charging system questions.

You know what's a great thing to use for batteries? Blue Sea's terminal post fuses/holders. It keeps the protection very close to the source reducing the amount of unprotected circuit (against the dropped tool short you mention).

Sizing any over-current protection follows the same rules: wire has to be large enough to take the continuous current, fuse/breaker has to be large enough too. Your inverter should actually have specifications for this in the manual; you can't do better than what they recommend. A 12 Volt 2500 Watt inverter will probably have a 250 Amp fuse recommendation.

Best case scenario: each parallel battery string is fused against the full amount, and a single fuse of the same rating on the main lead to the inverter. That way if the total inverter current draw goes over the limit the main fuse will blow. If something goes wrong in the wiring nearer the battery the affected string fuse will blow. Possibly all will go in a 'cascade failure', but if only one gives out then the others can still provide power up to the limit.

Minimum scenario: the one fuse for the inverter, mounted as close to the battery bank as possible. Not recommended for more than two parallel battery strings.

full time rver

Re: rv off grid solar charging system questions.

I found the terminal post fuse blocks and those look great. thanks! I am running 4 awg wire to all the connections in my battery bank. I read somewhere that this wire is good up to 75 amps?? if i'm running 250 amp fuses do you think I would risk overheating the wire? they are very short runs. most under a foot and the longest about 3 ft. I used 4 gauge jumper cable for the wiring needs. however I am using a 2 awg for the main load to the coach and the ground as well is 2 awg. im going to use the blue seas terminal fuses for each leg in the string but I just want to be sure I get the right size fuses for the loads. thanks

mike

full time rver

Re: rv off grid solar charging system questions.

Cariboocoot wrote: »

You know what's a great thing to use for batteries? Blue Sea's terminal post fuses/holders. It keeps the protection very close to the source reducing the amount of unprotected circuit (against the dropped tool short you mention).

Sizing any over-current protection follows the same rules: wire has to be large enough to take the continuous current, fuse/breaker has to be large enough too. Your inverter should actually have specifications for this in the manual; you can't do better than what they recommend. A 12 Volt 2500 Watt inverter will probably have a 250 Amp fuse recommendation.

Best case scenario: each parallel battery string is fused against the full amount, and a single fuse of the same rating on the main lead to the inverter. That way if the total inverter current draw goes over the limit the main fuse will blow. If something goes wrong in the wiring nearer the battery the affected string fuse will blow. Possibly all will go in a 'cascade failure', but if only one gives out then the others can still provide power up to the limit.

Minimum scenario: the one fuse for the inverter, mounted as close to the battery bank as possible. Not recommended for more than two parallel battery strings.

just an update. I looked for the manual for the inverter and couldn't find it for the life of me so i emailed cobra with the question. they confirmed what you said a 250 amp fuse for one cable. there is a 2 cable option with this inverter and with that they recommended 2x 150 amp fuses. this is how I have mine set up with 2 positive leads going from the inverter to the battery bank and two negative going to ground. all wires are 4awg. so knowing this. would I use 150 amp fuses at the other legs of the parallel strings or 250 amp fuses. thanks for bearing with me I just want to get it right for the safest and most efficient possible outcome for my set up.

mike

BB.

Re: rv off grid solar charging system questions.

Worst case "code" calculations for an inverter usually look something like:

2,500 Watt AC power * 1/0.85 Inverter Eff * 1/10.5 volt batt cutoff * 1.25 NEC derate for Wire+Breaker+Fuse = 350 Amp minimum Branch Circuit

Nominal current may look more like:

2,500 Watts * 1/0.85 * 1/11.5 volt batt = 256 Amps "nominal" @ 2,500 watts

If you plan on using less wattage, you can back down on your fusing/wiring requirements.

-Bill

full time rver

Re: rv off grid solar charging system questions.

BB. wrote: »

Worst case "code" calculations for an inverter usually look something like:

2,500 Watt AC power * 1/0.85 Inverter Eff * 1/10.5 volt batt cutoff * 1.25 NEC derate for Wire+Breaker+Fuse = 350 Amp minimum Branch Circuit

Nominal current may look more like:

2,500 Watts * 1/0.85 * 1/11.5 volt batt = 256 Amps "nominal" @ 2,500 watts

If you plan on using less wattage, you can back down on your fusing/wiring requirements.

-Bill

funny I was in the middle of writing the last post and you were already answering the one right before it. ok so I think if I go with the formula ill be safest and most efficient without having to replace blown fuses all the time if I go with 300 amp fuses at the terminals and do 2 individual 150 amp fuses to the inverter. does that seem about right?

Cariboocoot

Re: rv off grid solar charging system questions.

You might want to increase that wire size if you run near the top power of the inverter.
Otherwise it should be fine, as the fuses are there to protect should the current be sustained over the maximum. 150 is actually a bit high for 4 AWG but you probably won't find anything in between that and 100 which would be too low.

full time rver

Re: rv off grid solar charging system questions.

I have extra 2awg wire and 2awg connectors. re wiring the inverter that would be relatively painless. im guessing I should rewire just the inverter with 2awg. that makes me wonder about the fuses on the parallel strings. if 150 is high for 4awg than would 300amps be too high on the strings with the 4awg connecting them? even know its not a direct draw through the strings from the inverter? now im wondering if I have to go to 2 awg for the strings too. please clarify this for me.. thanks

mike

Cariboocoot

Re: rv off grid solar charging system questions.

It's a difference of what you're protecting where.
So 4 AWG is good for about 100 Amps continuous and normally you'd want a fuse 20% over. This makes the fuse blow above the continuous current but below the peak which is about 135 Amps. Not every chart is going to agree on those current ratings, though. Confuses people no end.

At the battery bank you're looking at supplying both those lines with current, or 200 to 250 Amps. So any line off the battery would be protected according to that. Me, I'd use 250 Amps on each battery string and know the inverter would never be run at its maximum continuous current (full Watts output at minimum input Voltage).

The 2 AWG would be a better choice of wire to the inverter with 150 Amp fuses on each one.

This brings us to the whole question of how you are bringing the multiple battery strings together. With two strings you can do the diagonal wiring and even just count it as one big battery. With four your best bet is to run individual equal length wires from each string to a common connection point/bus bar. In that case the wires from the battery to the common connection should be fused according to the wire size, and if you use 2 AWG there that would mean 150 Amp fuse on each wire.

What you do not want is a 300 Amp fuse connected to a single 2 AWG wire as the wire will fry before the fuse blows. If you want full current capacity from each battery string to the common point you need to use 4/0 (0000) wire with the 300 Amp fuse per each.

full time rver

Re: rv off grid solar charging system questions.

wow. thank you. that was very informative and concise. thank you for dumbing it down for me. I wired my strings according to wiring diagram I found on this forum. but through a different discussion board. here is the link that I was sent to:

http://www.smartgauge.co.uk/batt_con.html

I used the suggested method at the bottom of that page called "method 4"

does that look like a good enough method or should I re wire it through a bus bar?

Cariboocoot

Re: rv off grid solar charging system questions.

full time rver wrote: »

wow. thank you. that was very informative and concise. thank you for dumbing it down for me. I wired my strings according to wiring diagram I found on this forum. but through a different discussion board. here is the link that I was sent to:

http://www.smartgauge.co.uk/batt_con.html

I used the suggested method at the bottom of that page called "method 4"

does that look like a good enough method or should I re wire it through a bus bar?

Smart Gauge's method #4 technically works, but can be confusing to someone not overly familiar with wiring. Again the fuse sizes used would depend on the wire size and current expected. In the case of that diagram you should be using 4/0 between the batteries if you want to potentially get the full current from each as it is creating common connection points at two of the battery posts. In essence two posts become the 'bus bars' and some very precise wire fitting evens out the resistance between batteries. It is usually much easier to cut all same-length wires and connect and utilize method #3 which is far easier to understand.

To be fair, you can decide to 'divide up the current' among the four batteries and so expect 75 Amps from each utilizing smaller wire (4 AWG) and fuses (100 Amp) but understand that if you do and one of the batteries is dropped for whatever reason you will have only the current potential of the remaining 3 available: 225 Amps instead of 300. Whereas otherwise you could drop one and just draw the current it was supplying from the three remaining.

Yes, a lot of it is choices and judgment based on how you are likely to utilize the system. The important thing is that the fuse on any piece of wire be rated for lower current than the maximum the wire can handle so that the fuse will blow first in any over-current condition.

zoneblue

Re: rv off grid solar charging system questions.

full time rver wrote: »

I have extra 2awg wire and 2awg connectors. re wiring the inverter that would be relatively painless. im guessing I should rewire just the inverter with 2awg. that makes me wonder about the fuses on the parallel strings. if 150 is high for 4awg than would 300amps be too high on the strings with the 4awg connecting them? even know its not a direct draw through the strings from the inverter? now im wondering if I have to go to 2 awg for the strings too. please clarify this for me.. thanks

mike

This is a bit more than a toy system, those batterys have the potential to burn, and explode if mishandled.
Hencegood quality components and attention to assembly is well justified. If you have room for a 10kWh bank you have room a proper MNDC disconnnect, and proper carling inverter breaker(s).

So you have 2 pairs of 4awg (40mm2 total) from bank to inverter? Ok at a squeak, but you have a big inverter (for 12v). It draws a lot of amps, and under surge youll need every tenth of a volt you can get out of the bank. Hence to my mind you need a minimum of 50mm2 (1/0 AWG), hard core guys would even go 70mm2. Even 1/0 at 6feet is going to drop a third of a volt. http://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=0.3224&voltage=12&phase=dc&noofconductor=1&distance=6&distanceunit=feet&amperes=250&x=57&y=16

With four strings youll then need a busbar, with exactly equal length subcables to the cells. While you might think those could be smaller, under fault conditions one string might take the entire load. So i wouldnt go much smaller. Check the ampacitys and temp ratings on the cables.

On the bank front, one solution to your 4 string predicament is getting a couple of those 500A battery switches, and charge and discharge them one at a time. Youd need to check if the bank can still keep up with the inverter. Getting a decent bit of amps into the cells helps keep stratification at bay.

If you are going to rewire it, that wire is relatively cheap in short lengths. Get a local auto sparky to do the crimps if you dont have a crimper.

Youve probably got a fair dose of reading ahead of you. Its a great hobby, enjoy. Stick around here for a few months and youll be an expert!

full time rver

Re: rv off grid solar charging system questions.

Cariboocoot wrote: »

Smart Gauge's method #4 technically works, but can be confusing to someone not overly familiar with wiring. Again the fuse sizes used would depend on the wire size and current expected. In the case of that diagram you should be using 4/0 between the batteries if you want to potentially get the full current from each as it is creating common connection points at two of the battery posts. In essence two posts become the 'bus bars' and some very precise wire fitting evens out the resistance between batteries. It is usually much easier to cut all same-length wires and connect and utilize method #3 which is far easier to understand.

To be fair, you can decide to 'divide up the current' among the four batteries and so expect 75 Amps from each utilizing smaller wire (4 AWG) and fuses (100 Amp) but understand that if you do and one of the batteries is dropped for whatever reason you will have only the current potential of the remaining 3 available: 225 Amps instead of 300. Whereas otherwise you could drop one and just draw the current it was supplying from the three remaining.

Yes, a lot of it is choices and judgment based on how you are likely to utilize the system. The important thing is that the fuse on any piece of wire be rated for lower current than the maximum the wire can handle so that the fuse will blow first in any over-current condition.

okay thanks. I guess i'll be rewiring it again. im going to use method 3 than. so is 4/0 AWG the best wire to use with 300 amp fuses per string at the busbar? also do I wire the negative sides to a busbar too? and do you have any manufacturer recommendations for a fused busbar, and cables? oh and since I have two cablesgoing to the inverteeer do I still need 4/0 AG for those or will 2 AWG be ok? thanks

mike

full time rver

Re: rv off grid solar charging system questions.

zoneblue wrote: »

This is a bit more than a toy system, those batterys have the potential to burn, and explode if mishandled.
Hencegood quality components and attention to assembly is well justified. If you have room for a 10kWh bank you have room a proper MNDC disconnnect, and proper carling inverter breaker(s).

So you have 2 pairs of 4awg (40mm2 total) from bank to inverter? Ok at a squeak, but you have a big inverter (for 12v). It draws a lot of amps, and under surge youll need every tenth of a volt you can get out of the bank. Hence to my mind you need a minimum of 50mm2 (1/0 AWG), hard core guys would even go 70mm2. Even 1/0 at 6feet is going to drop a third of a volt. http://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=0.3224&voltage=12&phase=dc&noofconductor=1&distance=6&distanceunit=feet&eres=250&x=57&y=16

With four strings youll then need a busbar, with exactly equal length subcables to the cells. While you might think those could be smaller, under fault conditions one string might take the entire load. So i wouldnt go much smaller. Check the ampacitys and temp ratings on the cables.

On the bank front, one solution to your 4 string predicament is getting a couple of those 500A battery switches, and charge and discharge them one at a time. Youd need to check if the bank can still keep up with the inverter. Getting a decent bit of amps into the cells helps keep stratification at bay.

If you are going to rewire it, that wire is relatively cheap in short lengths. Get a local auto sparky to do the crimps if you dont have a crimper.

Youve probably got a fair dose of reading ahead of you. Its a great hobby, enjoy. Stick around here for a few months and youll be an expert!

thank you for the help. I appreciate it. I responded to cariboocoots last post. if you have any insight into my questions there it would be appreciated.
mike

Cariboocoot

Re: rv off grid solar charging system questions.

full time rver wrote: »

okay thanks. I guess i'll be rewiring it again. im going to use method 3 than. so is 4/0 AWG the best wire to use with 300 amp fuses per string at the busbar? also do I wire the negative sides to a busbar too? and do you have any manufacturer recommendations for a fused busbar, and cables? oh and since I have two cablesgoing to the inverteeer do I still need 4/0 AG for those or will 2 AWG be ok? thanks

mike

With the bus bar method negative and positive are wired to common points through equal-length wires. The 'bus bars' don't actually have to be bars; the poor man's method is to use a single bolt in wood to pile all the wire lugs on.

4/0 will definitely handle 300 Amps. You can usually get the cables made to your sizes locally, rather than trying to buy pre-made lengths.

The wiring from the common points to the inverter can either be carried on single 4/0 as with the batteries or using the parallel 2 AWG (each with its own fuse).

full time rver

Re: rv off grid solar charging system questions.

Cariboocoot wrote: »

With the bus bar method negative and positive are wired to common points through equal-length wires. The 'bus bars' don't actually have to be bars; the poor man's method is to use a single bolt in wood to pile all the wire lugs on.

4/0 will definitely handle 300 Amps. You can usually get the cables made to your sizes locally, rather than trying to buy pre-made lengths.

The wiring from the common points to the inverter can either be carried on single 4/0 as with the batteries or using the parallel 2 AWG (each with its own fuse).

great thanks again. I guess I only have one more question regarding the batteries: should I use 4/0 AWG for the series connections also? or is there a better method?

Cariboocoot

Re: rv off grid solar charging system questions.

full time rver wrote: »

great thanks again. I guess I only have one more question regarding the batteries: should I use 4/0 AWG for the series connections also? or is there a better method?

The connections between batteries in series will be carrying the same current as the wires leading away from the batteries. So if you need 4/0 to handle the current from the battery to the inverter, you need it to handle the current between the batteries also. (Sometimes wire from the batteries is larger than necessary for the current in order to reduce the Voltage drop.)

westbranch

Re: rv off grid solar charging system questions.

I've forgotten if you stated the loads you want to run???

If you are not going to need your inverters full output you could wire it to handle the max expected loads and let the circuit breakers handle the odd overload... ie say 1500W rather than 2500 .
Know that electronics do NOT like to be run full out all the time, better all round to be at ~ 80% of rating

zoneblue

Re: rv off grid solar charging system questions.

full time rver wrote: »

and do you have any manufacturer recommendations for a fused busbar

These are inexpensive:
http://www.bluesea.com/products/category/PowerPost_Connectors/Dual_PowerPost

They also carry bat post fusing and battery switches.